First Commission Directive 79/796/EEC of 26 July 1979 laying down Community methods of analysis for testing certain sugars intended for human consumption
79/796/EEC • 31979L0796
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22.9.1979
EN
Official Journal of the European Communities
L 239/24
FIRST COMMISSION DIRECTIVE
of 26 July 1979
Laying down Community methods of analysis for testing certain sugars intended for human consumption
(79/786/EEC)
THE COMMISSION OF THE EUROPEAN COMMUNITIES,
Having regard to the Treaty establishing the European Economic Community,
Having regard to Council Directive 73/437/EEC of 11 December 1973 on the approximation of the laws of the Member States concerning certain sugars intended for human consumption (1), and in particular Article 11 thereof,
Whereas Article 11 of that Directive lays down that the composition of certain sugars shall be verified by Community methods of analysis;
Whereas it is desirable to adopt an initial series of methods in respect of which studies have been completed;
Whereas the method of determining the colour type for sugar or white sugar and for extra-white sugar, the method of measuring the conductivity ash in extra-white sugar, in sugar solution, in invert sugar solution and in invert sugar syrup, and the method of determining the colour in solution of extra-white sugar and sugar solution are laid down in the Annex to Directive 73/437/EEC;
Whereas, on the other hand, pending the formulation of further Community methods for the determination of reducing sugars, it would be advisable to allow the Member States the option of continuing to authorize the use of the Lane and Eynon method (methods 7 and 8 in Annex II, III.3 and III.4) instead of the Luff-Schoorl method (method 6 in Annex 11, III.3 and III.4);
Whereas the methods of analysis provided for in this Directive are in accordance with the opinion of the Standing Committee on Foodstuffs,
HAS ADOPTED THIS DIRECTIVE:
Article 1
1. Member States shall require that the analyses necessary for verification of the criteria set out in Annex I be performed according to the methods described in Annex II to this Directive.
2. Without prejudice to the second subparagraph, the Luff-Schoorl method (Annex II, method 6) shall be used to determine the reducing sugars in the following sugars:
—
sugar solution,
—
white sugar solution,
—
invert sugar solution,
—
white invert sugar solution,
—
invert sugar syrup,
—
glucose syrup,
—
dried glucose syrup,
—
dextrose monohydrate,
—
dextrose anhydrous.
Member States may, however, require the use in their territory of the Lane and Eynon method (Annex II, methods 7 and/or 8 as appropriate) to determine the reducing sugars in one or more of the sugars listed above.
3. If a Member State makes use of the option provided for in the second subparagraph of paragraph 2, it shall forthwith inform the Commission and the other Member States thereof.
Article 2
Loading citations...Member States shall bring into force the laws, regulations or administrative provisions necessary to comply with this Directive not later than 18 months following its notification. They shall forthwith inform the Commission thereof.
Article 3
This Directive is addressed to the Member States.
Done at Brussels, 26 July 1979.
For the Commission
Étienne DAVIGNON
Member of the Commission
(1) OJ No L 356, 27. 12. 1973, p. 71.
ANNEX I
SCOPE OF TOE COMMUNITY METHODS OF ANALYSIS FOR CERTAIN SUGARS INTENDED FOR HUMAN CONSUMPTION
I.
Determination of the loss of mass on drying in:
—
semi-white sugar
—
sugar or white sugar
—
extra-white sugar
(using method 1, Annex II)
II.
Dry matter determination in:
II. 1.
—
glucose syrup
—
dried glucose syrup
—
dextrose monohydrate
—
dextrose anhydrous
(using method 2, Annex II)
II.2.
—
sugar solution or white sugar solution
—
invert sugar solution or white invert sugar solution
—
invert sugar syrup or white invert sugar syrup
(using method 3, Annex II)
III.
Measurement of reducing sugars in:
III. 1.
—
semi-white sugar
(using method 4, Annex II)
III.2.
—
sugar or white sugar
—
extra-white sugar
(using method 5, Annex II)
III.3.
—
sugar solution
—
white sugar solution
—
invert sugar solution
—
white invert sugar solution
—
invert sugar syrup
—
white invert sugar syrup
(using method 6 or 7, Annex II)
III.4.
—
glucose syrup
—
dried glucose syrup
—
dextrose monohydrate
—
dextrose anhydrous
(using method 6 or 8, Annex II)
IV.
Sulphated ash determination in:
—
glucose syrup
—
dried glucose syrup
—
dextrose monohydrate
—
dextrose anhydrous
(using method 9, Annex II)
V.
Determination of polarization in:
—
semi-white sugar
—
sugar or white sugar
—
extra-white sugar
(using method 10, Annex II)
ANNEX II
METHODS OF ANALYSIS TO VERIFY THE COMPOSITION OF CERTAIN SUGARS INTENDED FOR HUMAN CONSUMPTION
INTRODUCTION
1. Preparation of the sample for analysis
Thoroughly mix the sample received at the laboratory.
Remove a sub-sample of at least 200 g and transfer immediately to a clean, dry, moisture-tight vessel fitted with an airtight closure.
2. Reagents and apparatus
In the description of the apparatus, reference is made only to special instruments and apparatus or to those calling for special standards.
Wherever mention is made of water, this means distilled water or demineralized water of at least equivalent purity.
All reagents shall be of analytical reagent quality unless otherwise specified.
Wherever reference is made to a reagent solution without further qualification, an aqueous solution is meant.
3. Expression of results
The result referred to in the official analysis report shall be the mean value of at least two satisfactory replicate determinations.
Unless otherwise stated the results shall be expressed as a percentage by mass of the original sample as received at the laboratory.
The number of significant figures in the result so expressed shall be governed by the precision of the method.
METHOD 1
DETERMINATION OF THE LOSS OF MASS ON DRYING
1. Scope and field of application
The method determines the loss of mass on drying in:
—
semi-white sugar,
—
sugar or white sugar,
—
extra-white sugar.
2. Definition
‘Loss of mass on drying’: the value of the loss of mass on drying as determined by the method specified.
3. Principle
The loss of mass on drying is determined by drying at a temperature of 103 ± 2 oC.
4. Apparatus
4.1.
Analytical balance, accurate to within 0.1 mg.
4.2.
Oven, suitably ventilated, thermostatically controlled, and capable of being maintained at 103 ± 2 oC.
4.3.
Metal weighing dish, flat-bottomed, resistant to attack by the samples and the conditions of test, diameter at least 100 mm, depth at least 30 mm.
4.4.
Desiccator, containing freshly activated silica gel or an equivalent desiccant, with a water content indicator.
5. Procedure
N.B.: The operations described in sections 5.3 to 5.7 must be performed immediately after opening the sample container.
5.1.
Dry the dish (4.3) to constant weight in the oven (4.2) at 103 ± 2 oC.
5.2.
Allow the dish to cool in the desiccator (4.4) for at least 30 to 35 minutes and then weigh to the nearest 0.l mg.
5.3.
Weigh accurately, to the nearest 0.1 mg, approximately 20 to 30 g of the sample into the dish.
5.4.
Place the dish in the oven (4.2) at 103 ± 2 oC for three hours.
5.5.
Allow the dish to cool in a desiccator (4.4) and weigh to the nearest 0.1 mg.
5.6.
Replace the dish in the oven at 103 ± 2 oC for 30 minutes.
Allow to cool in the desiccator (4.4) and weigh to the nearest 01 mg. Repeat this operation if the difference between two weighings is more than 1 mg. Should an increase in mass occur, the lowest recorded reading will be used in the calculation.
5.7.
Do not exceed four hours total drying time.
6. Expression of results
6.1. Formula and method of calculation
The loss of mass on drying, as a percentage by mass of the sample, is given by the following formula:
where:
m0
is the initial mass, in grams, of the test portion,
m1
is the mass, in grams, of the test portion after drying.
6.2. Repeatability
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0·02 g per 100 g of sample.
METHOD 2
DETERMINATION OF DRY MATTER
Vacuum oven method
1. Scope and field of application
The method determines the dry matter content in:
—
glucose syrup,
—
dried glucose syrup,
—
dextrose monohydrate,
—
dextrose anhydrous.
2. Definition
‘The dry matter content’: the content of dry matter as determined by the method specified.
3. Principle
The dry matter is determined at a temperature of 70 ± 1 oC using a vacuum oven at a pressure not exceeding 3·3 kPa (34 mbar). The test portions in the case of glucose syrup or dried glucose syrups, are prepared by mixing with water and kieselguhr before drying.
4. Reagents
4.1.
Kieselguhr: place in a Buchner funnel and purify by repeated washings with dilute hydrochloric acid (1 ml of concentrated acid, density at 20 oC = 1·19 g/ml per litre of water). The treatment is complete when the washings remain definitely acid. Wash with water until the pH value of the filtered water is greater than 4. Dry in an oven at 103 ± 2 oC and store in an airtight container.
5. Apparatus
5.1.
Vacuum drying oven, leak tight, thermostatically controlled and equipped with a thermometer and a vacuum manometer. The oven design must be such that the heat is rapidly transferred to the weighing dishes placed on the shelves.
5.2.
Air-drying train consisting of a glass tower filled with freshly activated dry silica gel or an equivalent desiccant containing a water content indicator. This tower is mounted in series with a gas scrubber containing concentrated sulphuric acid connected to the air intake of the oven.
5.3.
Vaccum pump capable of maintaining the presure in the oven at 3·3 kPa (34 mbar) or less.
5.4.
Metal weighing dish, flat-bottomed, resistant to attack by the samples and the conditions of test, diameter at least 100 mm, depth at least 300 mm.
5.5.
Glass rod of a length such that it cannot completely fall into the container.
5.6.
Desiccator containing freshly activated dry silica gel, or an equivalent desiccant, with a water content indicator.
5.7.
Analytical balance accurate to within 0.1 mg.
6. Procedure
6.1.
Pour approximately 30 g of kieselguhr (4.1) into the weighing dish (5.4) equipped with a glass rod (5.5). Place the whole in the oven (5.1) at 70 ± 1 oC and reduce the pressure to 3·3 kPa (34 mbar) or less.
Dry for at least five hours, drawing a slow stream of air into the oven through the drying train. Check the pressure from time to time and correct it if necessary.
6.2.
Restore atmospheric pressure in the oven by cautiously increasing the intake of dry air. Immediately place the dish together with the glass rod in the desiccator (5.6). Allow to cool and then weigh.
63.
Accurately weigh to the nearest 1 mg approximately 10 g of the sample to be analyzed into a 100 ml beaker.
6.4.
Dilute the test portion with 10 ml of warm water and transfer the solution quantitatively into the weighing dish, using the glass rod (5.5).
6.5.
Place the dish containing the test portion and the glass rod in the oven and reduce the pressure to 3.3 kPa (34 mbar) or less. Dry at 70 ± 1 oC, allowing a slow stream of dry air to pass through the oven.
The drying operation should proceed for 20 hours; the bulk of the loss should occur towards the end of the first day. It will be necessary to keep the vacuum pump working at a preset pressure and allow a slow stream of dry air to enter the oven so as to maintain a pressure of approximately 3·3 kPa (34 mbar) or less during the night.
6.6.
Restore atmospheric pressure in the oven by cautiously increasing the intake of dry air. Immediately place the weighing dish and contents in the desiccator. Allow to cool and then weigh to the nearest 1 mg.
6.7.
Continue operation (6.5) for a further four hours. Restore atmospheric pressure in the oven and immediately place the dish in the desiccator. Allow to cool and then weigh. Ascertain whether constant mass has been reached. It is considered that constant mass has been satisfactorily attained if the difference between the two weighings of the same dish does not exceed 2 mg. If the difference is greater, repeat operation 6.7.
6.8.
For the determination of the dry matter in dextrose anhydrous or dextrose monohydrate samples the use of kieselguhr and water is not required.
7. Expression of results
7.1. Formula and method of calculation
The dry matter content, expressed as a percentage by mass of the sample is given by:
where:
m0
=
the initial mass, in grams, of the test portion,
m1
=
the mass, in grams, of the weighing dish plus the kieselguhr, the glass rod and the residue of the test portion after drying,
m2
=
the mass, in grams, of the weighing dish plus the kieselguhr and the glass rod.
7.2. Repeatability
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0·12 g per 100 g of sample.
METHOD 3
DETERMINATION OF TOTAL DRY MATTER
(Refractometric method)
1. Scope and field of application
The method determines the dry-matter content in:
—
sugar solution,
—
white sugar solution,
—
invert sugar solution,
—
white invert sugar solution,
—
invert sugar syrup,
—
white invert sugar syrup.
2. Definition
‘Dry matter content’: the content of dry matter as determined by the method specified.
3. Principle
The refractive index of a test portion is determined at 20 oC and converted into dry matter content by reference to tables showing the concentration as a function of the refractive index.
4. Apparatus
4.1.
Refractometer, accurate to four decimal places, provided with a thermometer and a water-circulation pump connected to a water-bath thermostatically controlled at 20 ± 0·5 oC.
4.2.
Light source consisting of a sodium vapour lamp.
5. Procedure
5.1.
If any crystals are present in the sample, redissolve them by diluting the sample in the ratio 1 : 1 (m/m).
5.2.
Measure the refractive index of the sample at 20 oC in the refractometer (4.1).
6. Expression and calculation of results
6.1.
Calculate the dry matter content from the refractive indices for sucrose solutions at 20 oC in the table given and correct for the presence of invert sugars by adding to the result obtained from the tables, 0.022 for every 1 % of invert sugar present in the sample as analyzed.
6.2.
If the sample was diluted to 1: 1 (m/m) with water, the calculated dry matter content must be multiplied by two.
6.3.
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0·2 g dry matter per 100 g of sample.
REFERENCE TABLES
Refractive indices (n) of sucrose solutions at 20 oC (1)
n
(20 oC)
Sucrose
(%)
1·3330
0·009
1·3331
0·078
1·3332
0·149
1·3333
0·218
1·3334
0·288
1·3335
0·358
1·3336
0·428
1·3337
0·498
1·3338
0·567
1·3339
0·637
1·3340
0·707
1·3341
0·776
1·3342
0·846
1·3343
0·915
1·3344
0·985
1·3345
1·054
1·3346
1·124
1·3347
1·193
1·3348
1·263
1·3349
1·332
1·3350
1·401
1·3351
1·470
1·3352
1·540
1·3353
1·609
1·3354
1·678
1·3355
1·747
1·3356
1·816
1·3357
1·885
1·3358
1·954
1·3359
2·023
1·3360
2·092
1·3361
2·161
1·3362
2·230
1·3363
2·299
1·3364
2·367
1·3365
2·436
1·3366
2·505
1·3367
2·574
1·3368
2·642
1·3369
2·711
1·3370
2·779
1·3371
2·848
1·3372
2·917
1·3373
2·985
1·3374
3·053
1·3375
3·122
1·3376
3·190
1·3377
3·259
1·3378
3·327
1·3379
3·395
1·3380
3·463
1·3381
3·532
1·3382
3·600
1·3383
3·668
1·3384
3·736
1·3385
3·804
1·3386
3·872
1·3387
3·940
1·3388
4·008
1·3389
4·076
1·3390
4·144
1·3391
4·212
1·3392
4·279
1·3393
4·347
1·3394
4·415
1·3395
4·483
1·3396
4·550
1·3397
4·618
1·3398
4·686
1·3399
4·753
1·3400
4·821
1·3401
4·888
1·3402
4·956
1·3403
5·023
1·3404
5·091
1·3405
5·158
1·3406
5·225
1·3407
5·293
1·3408
5·360
1·3409
5·427
1·3410
5·494
1·3411
5·562
1·3412
5·629
1·3413
5·696
1·3414
5·763
1·3415
5·830
1·3416
5·897
1·3417
5·964
1·3418
6·031
1·3419
6·098
1·3420
6·165
1·3421
6·231
1·3422
6·298
1·3423
6·365
1·3424
6·432
1·3425
6·498
1·3426
6·565
1·3427
6·632
1·3428
6·698
1·3429
6·765
1·3430
6·831
1·3431
6·898
1·3432
6·964
1·3433
7·031
1·3434
7·097
1·3435
7·1642
1·3436
7·230
1·3437
7·296
1·3438
7·362
1·3439
7·429
1·3440
7·495
1·3441
7·561
1·3442
7·627
1·3443
7·693
1·3444
7·759
1·3445
7·825
1·3446
7·891
1·3447
7·957
1·3448
8·023
1·3449
8·089
1·3450
8·155
1·3451
8·221
1·3452
8·287
1·3453
8·352
1·3454
8·418
1·3455
8·484
1·3456
8·550
1·3457
8·615
1·3458
8·681
1·3459
8·746
1·3460
8·812
1·3461
8·878
1·3462
8·943
1·3463
9·008
1·3464
9·074
1·3465
9·139
1·3466
9·205
1·3467
9·270
1·3468
9·335
1·3469
9·400
1·3470
9·466
1·3471
9·531
1·3472
9·596
1·3473
9·661
1·3474
9·726
1·3475
9·791
1·3476
9·856
1·3477
9·921
1·3478
9·986
1·3479
10·051
1·3480
10·116
1·3481
10·181
1·3482
10·246
1·3483
10·311
1·3484
10·375
1·3485
10·440
1·3486
10·505
1·3487
10·570
1·3488
10·634
1·3489
10·699
1·3490
10·763
1·3491
10·828
1·3492
10·892
1·3493
10·957
1·3494
11·021
1·3495
11·086
1·3496
11·150
1·3497
11·215
1·3498
11·279
1·3499
11·343
1·3500
11·407
1·3501
11·472
1·3502
11·536
1·3503
11·600
1·3504
11·664
1·3505
11·728
1·3506
11·792
1·3507
11·856
1·3508
11·920
1·3509
11·984
1·3510
12·048
1·3511
12·112
1·3512
12·176
1·3513
12·240
1·3514
12·304
1·3515
12·368
1·3516
12·431
1·3517
12·495
1·3518
12·559
1·3519
12·623
1·3520
12·686
1·3521
12·750
1·3522
12·813
1·3523
12·877
1·3524
12·940
1·3525
13·004
1·3526
13·067
1·3527
13·131
1·3528
13·194
1·3529
13·258
1·3530
13·321
1·3531
13·384
1·3532
13·448
1·3533
13·511
1·3534
13·574
1·3535
13·637
1·3536
13·700
1·3537
13·763
1·3538
13·826
1·3539
13·890
1·3540
13·953
1·3541
14·016
1·3542
14·079
1·3543
14·141
1·3544
14·204
1·3545
14·267
1·3546
14·330
1·3547
14·393
1·3548
14·456
1·3549
14·518
1·3550
14·581
1·3551
14·644
1·3552
14·707
1·3553
14·769
1·3554
14·832
1·3555
14·894
1·3556
14·957
1·3557
15·019
1·3558
15·082
1·3559
15·144
1·3560
15·207
1·3561
15·269
1·3562
15·332
1·3563
15·394
1·3564
15·456
1·3565
15·518
1·3566
15·581
1·3567
15·643
1·3568
15·705
1·3569
15·767
1·3570
15·829
1·3571
15·891
1·3572
15·953
1·3573
16016
1·3574
16·078
1·3575
16·140
1·3576
16·201
1·3577
16·263
1·3578
16·325
1·3579
16·387
1·3580
16·449
1·3581
16·511
1·3582
16·573
1·3583
16·634
1·3584
16·696
1·3585
16·758
1·3586
16·819
1·3587
16·881
1·3588
16·943
1·3589
17·004
1·3590
17·066
1·3591
17·127
1·3592
17·189
1·3593
17·250
1·3594
17·311
1·3595
17·373
1·3596
17·434
1·3597
17·496
1·3598
17·557
1·3599
17·618
1·3600
17·679
1·3601
17·741
1·3602
17·802
1·3603
17·863
1·3604
17·924
1·3605
17·985
1·3606
18·046
1·3607
18·107
1·3608
18·168
1·3609
18·229
1·3610
18·290
1·3611
18·351
1·3612
18·412
1·3613
18·473
1·3614
18·534
1·3615
18·595
1·3616
18·655
1·3617
18·716
1·3618
18·777
1·3619
18·837
1·3620
18·898
1·3621
18·959
1·3622
19·019
1·3623
19·080
1·3624
19·141
1·3625
19·201
1·3626
19·262
1·3627
19·322
1·3628
19·382
1·3629
19·443
1·3630
19·503
1·3631
19·564
1·3632
19·624
1·3633
19·684
1·3634
19·745
1·3635
19·805
1·3636
19·865
1·3637
19·925
1·3638
19·985
1·3639
20·045
1·3640
20·106
1·3641
20·166
1·3642
20·226
1·3643
20·286
1·3644
20·346
1·3645
20·406
1·3646
20·466
1·3647
20·525
1·3648
20·585
1·3649
20·645
1·3650
20·705
1·3651
20·765
1·3652
20·825
1·3653
20·884
1·3654
20·944
1·3655
21·004
1·3656
21·063
1·3657
21·123
1·3658
21·183
1·3659
21·242
1·3660
21·302
1·3661
21·361
1·3662
21·421
1·3663
21·480
1·3664
21·540
1·3665
21·599
1·3666
21·658
1·3667
21·718
1·3668
21·777
1·3669
21·836
1·3670
21·896
1·3671
21·955
1·3672
22·014
1·3673
22·073
1·3674
22·132
1·3675
22·192
1·3676
22·251
1·3677
22·310
1·3678
22·369
1·3679
22·428
1·3680
22·487
1·3681
22·546
1·3682
22·605
1·3683
22·664
1·3684
22·723
1·3685
22·781
1·3686
22·840
1·3687
22·899
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1·4422
60·144
1·4423
60·188
1·4424
60·232
1·4425
60·276
1·4426
60·320
1·4427
60·364
1·4428
60·408
1·4429
60·452
1·4430
60·496
1·4431
60·540
1·4432
60·584
1·4433
60·628
1·4434
60·672
1·4435
60·716
1·4436
60·759
1·4437
60·803
1·4438
60·847
1·4439
60·891
1·4440
60·935
1·4441
60·979
1·4442
61·023
1·4443
61·066
1·4444
61·110
1·4445
61·154
1·4446
61·198
1·4447
61·241
1·4448
61·285
1·4449
61·329
1·4450
61·372
1·4451
61·416
1·4452
61·460
1·4453
61·503
1·4454
61·547
1·4455
61·591
1·4456
61·634
1·4457
61·678
1·4458
61·721
1·4459
61·765
1·4460
61·809
1·4461
61·852
1·4462
61·896
1·4463
61·939
1·4464
61·983
1·4465
62·026
1·4466
62·070
1·4467
62·113
1·4468
62·156
1·4469
62·200
1·4470
62·243
1·4471
62·287
1·4472
62·330
1·4473
62·373
1·4474
62·417
1·4475
62·460
1·4476
62·503
1·4477
62·547
1·4478
62·590
1·4479
62·633
1·4480
62·677
1·4481
62·720
1·4482
62·763
1·4483
62·806
1·4484
62·849
1·4485
62·893
1·4486
62·936
1·4487
62·979
1·4488
63·022
1·4489
63·065
1·4490
63·108
1·4491
63·152
1·4492
63·195
1·4493
63·238
1·4494
63·281
1·4495
63·324
1·4496
63·367
1·4497
63·410
1·4498
63·453
1·4499
63·496
1·4500
63·539
1·4501
63·582
1·4502
63·625
1·4503
63·668
1·4504
63·711
1·4505
63·754
1·4506
63·797
1·4507
63·840
1·4508
63·882
1·4509
63·925
1·4510
63·968
1·4511
64·011
1·4512
64·054
1·4513
64·097
1·4514
64·139
1·4515
64·182
1·4516
64·225
1·4517
64·268
1·4518
64·311
1·4519
64·353
1·4520
64·396
1·4521
64·439
1·4522
64·481
1·4523
64·524
1·4524
64·567
1·4525
64·609
1·4526
64·652
1·4527
64·695
1·4528
64·737
1·4529
64·780
1·4530
64·823
1·4531
64·865
1·4532
64·908
1·4533
64·950
1·4534
64·993
1·4535
65·035
1·4536
65·078
1·4537
65·120
1·4538
65·163
1·4539
65·205
1·4540
65·248
1·4541
65·290
1·4542
65·333
1·4543
65·375
1·4544
65·417
1·4545
65·460
1·4546
65·502
1·4547
65·544
1·4548
65·587
1·4549
65·629
1·4550
65·672
1·4551
65·714
1·4552
65·756
1·4553
65·798
1·4554
65·841
1·4555
65·883
1·4556
65·925
1·4557
65·967
1·4558
66·010
1·4559
66·052
1·4560
66·094
1·4561
66·136
1·4562
66·178
1·4563
66·221
1·4564
66·263
1·4565
66·305
1·4566
66·347
1·4567
66·389
1·4568
66·431
1·4569
66·473
1·4570
66·515
1·4571
66·557
1·4572
66·599
1·4573
66·641
1·4574
66·683
1·4575
66·725
1·4576
66·767
1·4577
66·809
1·4578
66·851
1·4579
66·893
1·4580
66·935
1·4581
66·977
1·4582
67·019
1·4583
67·061
1·4584
67·103
1·4585
67·145
1·4586
67·186
1·4587
67·228
1·4588
67·270
1·4589
67·312
1·4590
67·354
1·4591
67·396
1·4592
67·437
1·4593
67·479
1·4594
67·521
1·4595
67·563
1·4596
67·604
1·4597
67·646
1·4598
67·688
1·4599
67·729
1·4600
67·771
1·4601
67·813
1·4602
67·854
1·4603
67·896
1·4604
67·938
1·4605
67·979
1·4606
68·021
1·4607
68·063
1·4608
68·104
1·4609
68·146
1·4610
68·187
1·4611
68·229
1·4612
68·270
1·4613
68·312
1·4614
68·353
1·4615
68·395
1·4616
68·436
1·4617
68·478
1·4618
68·519
1·4619
68·561
1·4620
68·602
1·4621
68·643
1·4622
68·685
1·4623
68·726
1·4624
68·768
1·4625
68·809
1·4626
68·850
1·4627
68·892
1·4628
68·933
1·4629
68·974
1·4630
69·016
1·4631
69·057
1·4632
69·098
1·4633
69·139
1·4634
69·181
1·4635
69·222
1·4636
69·263
1·4637
69·304
1·4638
69·346
1·4639
69·387
1·4640
69·428
1·4641
69·469
1·4642
69·510
1·4643
69·551
1·4644
69·593
1·4645
69·634
1·4646
69·675
1·4647
69·716
1·4648
69·757
1·4649
69·798
1·4650
69·839
1·4651
69·880
1·4652
69·921
1·4653
69·962
1·4654
70·003
1·4655
70·044
1·4656
70·085
1·4657
70·126
1·4658
70·167
1·4659
70·208
1·4660
70·249
1·4661
70·290
1·4662
70·331
1·4663
70·372
1·4664
70·413
1·4665
70·453
1·4666
70·494
1·4667
70·535
1·4668
70·576
1·4669
70·617
1·4670
70·658
1·4671
70·698
1·4672
70·739
1·4673
70·780
1·4674
70·821
1·4675
70·861
1·4676
70·902
1·4677
70·943
1·4678
70·984
1·4679
71·024
1·4680
71·065
1·4681
71·106
1·4682
71·146
1·4683
71·187
1·4684
71·228
1·4685
71·268
1·4686
71·309
1·4687
71·349
1·4688
71·390
1·4689
71·431
1·4690
71·471
1·4691
71·512
1·4692
71·552
1·4693
71·593
1·4694
71·633
1·4695
71·674
1·4696
71·714
1·4697
71·755
1·4698
71·795
1·4699
71·836
1·4700
71·876
1·4701
71·917
1·4702
71·957
1·4703
71·998
1·4704
72·038
1·4705
72·078
1·4706
72·119
1·4707
72·159
1·4708
72·199
1·4709
72·240
1·4710
72·280
1·4711
72·320
1·4712
72·361
1·4713
72·401
1·4714
72·441
1·4715
72·482
1·4716
72·522
1·4717
72·562
1·4718
72·602
1·4719
72·643
1·4720
72·683
1·4721
72·723
1·4722
72·763
1·4723
72·803
1·4724
72·843
1·4725
72·884
1·4726
72·924
1·4727
72·964
1·4728
73·004
1·4729
73·044
1·4730
73·084
1·4731
73·124
1·4732
73·164
1·4733
73·204
1·4734
73·244
1·4735
73·285
1·4736
73·325
1·4737
73·365
1·4738
73·405
1·4739
73·445
1·4740
73·485
1·4741
73·524
1·4742
73·564
1·4743
73·604
1·4744
73·644
1·4745
73·684
1·4746
73·724
1·4747
73·764
1·4748
73·804
1·4749
73·844
1·4750
73·884
1·4751
73·924
1·4752
73·963
1·4753
74·003
1·4754
74·043
1·4755
74·083
1·4756
74·123
1·4757
74·162
1·4758
74·202
1·4759
74·242
1·4760
74·282
1·4761
74·321
1·4762
74·361
1·4763
74·401
1·4764
74·441
1·4765
74·480
1·4766
74·520
1·4767
74·560
1·4768
74·599
1·4769
74·639
1·4770
74·678
1·4771
74·718
1·4772
74·758
1·4773
74·797
1·4774
74·837
1·4775
74·876
1·4776
74·916
1·4777
74·956
1·4778
74·995
1·4779
75·035
1·4780
75·074
1·4781
75·114
1·4782
75·153
1·4783
75·193
1·4784
75·232
1·4785
75·272
1·4786
75·311
1·4787
75·350
1·4788
75·390
1·4789
75429
1·4790
75469
1·4791
75·508
1·4792
75·547
1·4793
75·587
1·4794
75·626
1·4795
75·666
1·4796
75·705
1·4797
75·744
1·4798
75·784
1·4799
75·823
1·4800
75·862
1·4801
75·901
1·4802
75·941
1·4803
75·980
1·4804
76·019
1·4805
76·058
1·4806
76·098
1·4807
76·137
1·4808
76·176
1·4809
76·215
1·4810
76·254
1·4811
76·294
1·4812
76·333
1·4813
76·372
1·4814
76·411
1·4815
76·450
1·4816
76·489
1·4817
76·528
1·4818
76·567
1·4819
76·607
1·4820
76·646
1·4821
76·685
1·4822
76·724
1·4823
76·763
1·4824
76·802
1·4825
76·841
1·4826
76·880
1·4827
76·919
1·4828
76·958
1·4829
76·997
1·4830
77·036
1·4831
77·075
1·4832
77·113
1·4833
77·152
1·4834
77·191
1·4835
77·230
1·4836
77·269
1·4837
77·308
1·4838
77·347
1·4839
77·386
1·4840
77·425
1·4841
77·463
1·4842
77·502
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77·541
1·4844
77·580
1·4845
77·619
1·4846
77·657
1·4847
77·696
1·4848
77·735
1·4849
77·774
1·4850
77·812
1·4851
77·851
1·4852
77·890
1·4853
77·928
1·4854
77·967
1·4855
78·006
1·4856
78·045
1·4857
78·083
1·4858
78·122
1·4859
78·160
1·4860
78·199
1·4861
78·238
1·4862
78·276
1·4863
78·315
1·4864
78·353
1·4865
78·392
1·4866
78·431
1·4867
78·469
1·4868
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1·4869
78·546
1·4870
78·585
1·4871
78·623
1·4872
78·662
1·4873
78·700
1·4874
78·739
1·4875
78·777
1·4876
78·816
1·4877
78·854
1·4878
78·892
1·4879
78·931
1·4880
78·969
1·4881
79·008
1·4882
79·046
1·4883
79·084
1·4884
79·123
1·4885
79·161
1·4886
79·199
1·4887
79·238
1·4888
79·276
1·4889
79·314
1·4890
79·353
1·4891
79·391
1·4892
79·429
1·4893
79·468
1·4894
79·506
1·4895
79·544
1·4896
79·582
1·4897
79·620
1·4898
79·659
1·4899
79·697
1·4900
79·735
1·4901
79·773
1·4902
79·811
1·4903
79·850
1·4904
79·888
1·4905
79·926
1·4906
79·964
1·4907
80·002
1·4908
80·040
1·4909
80·078
1·4910
80·116
1·4911
80·154
1·4912
80·192
1·4913
80·231
1·4914
80·269
1·4915
80·307
1·4916
80·345
1·4917
80·383
1·4918
80·421
1·4919
80·459
1·4920
80·497
1·4921
80·534
1·4922
80·572
1·4923
80·610
1·4924
80·648
1·4925
80·686
1·4926
80·724
1·4927
80·762
1·4928
80·800
1·4929
80·838
1·4930
80·876
1·4931
80·913
1·4932
80·951
1·4933
80·989
1·4934
81·027
1·4935
81·065
1·4936
81·103
1·4937
81·140
1·4938
81·178
1·4939
81·216
1·4940
81·254
1·4941
81·291
1·4942
81·329
1·4943
81·367
1·4944
81·405
1·4945
81·442
1·4946
81·480
1·4947
81·518
1·4948
81·555
1·4949
81·593
1·4950
81·631
1·4951
81·668
1·4952
81·706
1·5953
81·744
1·4954
81·781
1·4955
81·819
1·4956
81·856
1·4957
81·894
1·4958
81·932
1·4959
81·969
1·4960
82·007
1·4961
82·044
1·4962
82·082
1·4963
82·119
1·4964
82·157
1·4965
82·194
1·4966
82·232
1·4967
82·269
1·4968
82·307
1·4969
82·344
1·4970
82·381
1·4971
82·419
1·4972
82·456
1·4973
82·494
1·4974
82·531
1·4975
82·569
1·4976
82·606
1·4977
82·643
1·4978
82·681
1·4979
82·718
1·4980
82·755
1·4981
82·793
1·4982
82·830
1·4983
82·867
1·4984
82·905
1·4985
82·942
1·4986
82·979
1·4987
83·016
1·4988
83·054
1·4989
83·091
1·4990
83·128
1·4991
83·165
1·4992
83·202
1·4993
83·240
1·4994
83·277
1·4995
83·314
1·4996
83·351
1·4997
83·388
1·4998
83·425
1·4999
83·463
1·5000
83·500
1·5001
83·537
1·5002
83·574
1·5003
83·611
1·5004
83·648
1·5005
83·685
1·5006
83·722
1·5007
83·759
1·5008
83·796
1·5009
83·833
1·5010
83·870
1·5011
83·907
1·5012
83·944
1·5013
83·981
1·5014
84·018
1·5015
84·055
1·5016
84·092
1·5017
84·129
1·5018
84·166
1·5019
84·203
1·5020
84·240
1·5021
84·277
1·5022
84·314
1·5023
84·351
1·5024
84·388
1·5025
84·424
1·5026
84·461
1·5027
84·498
1·5028
84·535
1·5029
84·572
1·5030
84·609
1·5031
84·645
1·5032
84·682
1·5033
84·719
1·5034
84·756
1·5035
84·792
1·5036
84·829
1·5037
84·866
1·5038
84·903
1·5039
84·939
1·5040
84·976
1·5041
85·013
1·5042
85·049
1·5043
85·086
1·5044
85·123
1·5045
85·159
1·5046
85·196
1·5047
85·233
1·5048
85·269
1·5049
85·306
1·5050
85·343
1·5051
85·379
1·5052
85·416
1·5053
85·452
1·5054
85·489
1·5055
85·525
1·5056
85·562
1·5057
85·598
1·5058
85·635
1·5059
85·672
1·5060
85·708
1·5061
85·744
1·5062
85·781
1·5063
85·817
1·5064
85·854
1·5065
85·890
1·5066
85·927
1·5067
85·963
1·5068
86·000
1·5069
86·036
1·5070
86·072
1·5071
86·109
1·5072
86·145
1·5073
86·182
1·5074
86·218
1·5075
86·254
1·5076
86·291
1·5077
86·327
1·5078
86·363
1·5079
86·399
METHOD 4
MEASUREMENT OF REDUCING SUGARS EXPRESSED AS INVERT SUGARS
(Berlin Institute method)
Scope and field of application
1.
The method determines the reducing sugar content expressed as invert sugar in semi-white sugar.
2. Definitions
‘Reducing sugars expressed as invert sugar’: the content of reducing sugars as determined by the method specified.
3. Principle
The sample solution containing reducing sugars is used to reduce a solution of copper II complex. The copper I oxide formed is then oxidized with standard iodine solution, the excess of which is determined by back-titration with standardized sodium thiosulphate solution.
4. Reagents
4.1.
Copper II solution (Muller's solution)
4.1.1.
Dissolve 35 g of copper II sulphate, pentahydrate (CuSO4.5H2O) in 400 ml of boiling water. Allow to cool.
4.1.2.
Dissolve 173 g of sodium potassium tartrate tetrahydrate (Rochelle salt or Seignette salt; KNaC4H4O64H2O) and 68 g of anhydrous sodium carbonate in 500 ml of boiling water. Allow to cool.
4.1.3.
Transfer both solutions (4.1.1 and 4.1.2) to a one litre volumetric flask and make up to one litre with water. Add 2 g of activated carbon, shake, allow to stand for several hours and filter through thick filter paper or a membrane filter.
If small amounts of copper I oxide appear during storage, the solution should be re-filtered.
4.2.
Acetic acid solution 5 mol/litre.
4.3.
I odine solution 0·01665 mol/litre (i.e. 0·0333 N, 4·2258 g/litre).
4.4.
Sodium thiosulphate solution 0·0333 mol/litre.
4.5.
Starch solution: to one litre of boiling water add a mixture of 5 g of soluble starch slurried in 30 ml of water. Boil for three minutes, allow to cool and add, if required, 10 mg of mercury II iodide as a preservative.
5. Apparatus
5.1.
Conical flask, 300 ml; precision burettes and pipettes.
5.2.
Water-bath, boiling.
6. Procedure
6.1.
Weigh a portion of the sample (10 g or less) containing not more than 30 mg of invert sugar in a 300 ml conical flask and dissolve in about 100 ml of water.
Pipette 10 ml of the copper II solution (4.1), into the flask containing the sample solution. Mix the contents of the flask by swirling and place it in the boiling water-bath (5.2) for exactly 10 minutes.
The level of the solution in the conical flask should be at least 20 mm below the level of the water in the water-bath. Cool the flask rapidly in a stream of cold running water. During this operation the solution should not be stirred otherwise atmospheric oxygen will reoxidize some precipitated copper I oxide.
Add 5 ml of 5 mol/litre acetic acid (4.2) by pipette without shaking and immediately add an excess (between 20 and 40 ml) of the iodine solution 0.01665 mol/litre (4.3) from a burette.
Stir to dissolve the copper precipitate. Titrate the excess iodine against the sodium thiosulphate solution 0·0333 mol/litre (4.4) using the starch solution (4.5) as indicator. The indicator is added towards the end of the titration.
6.2.
Carry out a blank test with water. This is to be carried out with each new copper II solution (4.4). The titration shall not exceed 0·1 ml.
6.3.
Carry out a control test under cold conditions with the sugar solution. Allow to stand at room temperature for 10 minutes to permit any reducing agents such as sulphur dioxide which may by present to react.
7. Expression of results.
7.1. Formula and method of calculation
Volume of iodine consumed = ml 0·01665 mol/litre iodine added in excess minus ml 0·0333 mol/litre sodium thiosulphate used in titration.
The volume (in ml) of 0·01665 ml/litre iodine consumed is corrected by subtracting:
7.1.1.
The number of ml consumed in the blank test carried out with water (6.2).
7.1.2.
The number of ml consumed in the cold test with the sugar solution (6.3).
7.1.3.
A value of 2·0 ml for every 10 g of sucrose present in the aliquot used, or a proportionate quantity where the sample contains less than 10 g sucrose (correction for sucrose).
After these corrections are made each ml of iodine solution (4.3) which has reacted corresponds to 1 mg of of invert sugar.
The invert sugar contents, as a percentage of the sample, is given by the formula:
where:
V1
=
the number of ml of iodine solution (4.3) after correction,
mo
=
the mass, in grams, of the sample used.
7.2. Repeatability
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 0·02 g per 100 g of sample.
METHOD 5
MEASUREMENT OF REDUCING SUGARS EXPRESSED AS INVERT SUGAR
(Knight and Allen method)
1. Scope and field of application
The method determines the reducing sugar content expressed as invert sugar in:
—
sugar or white sugar,
—
extra white sugar.
2. Definition
‘Reducing sugars expressed as invert sugar’: the content of reducing sugars as determined by the method specified.
3. Principle
Copper II reagent is added in excess to the sample solution, reduced and the unreduced portion is back-titrated with EDTA solution.
4. Reagents
4.1.
Ethylene diamine tetra-acetic acid solution (disodium salt) (EDTA) 0·0025 mol/litre: dissolve 0·930 g of EDTA in water and make up to one litre with water.
4.2.
Murexide indicator solution: add 0·25 g of murexide to 50 ml of water and mix with 20 ml of a 0·2 g /100 ml aqueous solution of methylene blue.
4.3.
Alkaline copper reagent: dissolve 25 g of anhydrous sodium carbonate and 25 g of potassium sodium tartrate tetrahydrate in about 600 ml of water containing 40 ml of 1.0 mol/litre sodium hydroxide. Dissolve 6·0 g of copper II sulphate pentahydrate (CuSO4.5H2O) in about 100 ml of water, and add to the tartrate solution. Dilute to one litre with water.
N.B.: the solution has a limited life (one week).
4.4.
Standard invert sugar solution: dissolve 23·750 g of pure sucrose (4.5) in about 120 ml of water in a 250 ml graduated flask, add 9 ml of hydrochloric acid (ζ = 1·16) and allow to stand for eight days at room temperature. Make the solution up to 250 ml and check for completion of hydrolysis by a polarimeter or saccharimeter reading in a 200 mm tube. This should be - 11·80o ± 0·05 oS (see Note 8). Pipette 200 ml of this solution into a 2 000 ml graduated flask. Dilute with water and while shaking (to avoid excessive local alkalinity) add 71·4 ml of sodium hydroxide solution (1 mol/litre) in which 4 g of benzoic acid has been dissolved. Make up to 2 000 ml to give a 1 g/100 ml solution of invert sugar. This solution should be approximately pH 3.
This stable stock solution should only be diluted immediately before use.
4.5.
Pure sucrose: sample of pure sucrose with an invert sugar content not greater than 0·001 g/100 g.
5. Apparatus
5.1.
Test tubes, 150 x 20 mm.
5.2.
5.3.
Analytical balance, accurate to within 0·1 mg.
6. Procedure
6.1.
Dissolve 5 g of sugar sample in 5 ml of cold water in the test tube (5.1). Add 2·0 ml of the copper reagent (4.3) and mix. Immerse the tube in a boiling water bath for five minutes and then cool in cold water.
6.2.
Transfer quantitatively the solution in the test tube to the white porcelain dish (5.2) using as little water as possible, add three drops of indicator (4.2) and titrate with EDTA solution (4.1). Vo is the number of ml of EDTA used in the titration.
Just before the end-point the colour of the solution changes from green through grey to purple at the end-point. The purple colour will disappear slowly because of oxidation of copper I oxide to copper II oxide at a rate dependent on the concentration of reduced copper present. The end-point of the titration shall therefore be approached fairly rapidly.
6.3.
Construct a calibration graph by adding known amounts of invert sugar (as solution 4.4 appropriately diluted) to 5 g of pure sucrose (4.5) and add sufficient cold water so that a total of 5 ml of solution is added. Plot the titration volumes (in ml) against the percentage of invert sugar added to the 5 g of sucrose: the resultant graph is a straight line over the range 0·001 to 0·019 g/100 g invert sugar/100 g sample.
7. Expression of results
7.1.
Read on the calibration curve the percentage of invert sugar corresponding to the value Vo ml of EDTA determined when analyzing the sample.
7.2.
When a concentration greater than 0·017 g invert sugar/100 g sample is expected in the sample to be analyzed, the sample size taken in Procedure (6.1) must be appropriately reduced but the analysis sample made up to 5 g with pure sucrose (4.5).
7.3.
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same, analyst, under the same conditions, shall not exceed 0·005 g per 100 g of sample.
8. Note
Divide by 2·889 to convert oS to polarmetric degrees of arc (precision tubes of 200 mm; light source consisting of a sodium vapour lamp; the instrument must be installed in a room where the temperature may be maintained close to 20 oC).
METHOD 6
DETERMINATION OF REDUCING SUGARS EXPRESSED AS INVERT SUGAR OR DEXTROSE EQUIVALENT
(Luff-Schoorl method)
1. Scope and field of application
The method determines:
1.1.
The reducing sugars content expressed as invert sugar in:
—
sugar solution,
—
white sugar solution,
—
invert sugar solution,
—
white invert sugar solution,
—
invert sugar syrup,
—
white invert sugar syrup.
1.2.
The reducing sugar content, expressed and calculated (on the dry matter) as the dextrose equivalent in:
—
glucose syrup,
—
dried glucose syrup
1.3.
The reducing sugar content expressed as D-glucose in:
—
dextrose monohydrate,
—
dextrose anhydrous
2. Definition
‘Reducing sugars expressed as invert sugars, D-glucose or dextrose equivalent’: the content of reducing sugars expressed or calculated as invert sugar, D-glucose or dextrose equivalent as determined by the method specified.
3. Principle
The reducing sugars in the sample (clarified if necessary) are heated to boiling point under standardized conditions with a copper II solution, which is partially reduced to copper I. The excess copper II is subsequently determined iodometrically.
4. Reagents
4.1.
Carrez solution I: dissolve 21·95 g of zinc acetate dihydrate (Zn(CH3COO)2.2H2O) (or 24 g of zinc acetate trihydrate (Zn(CH3COO)2.3H2O) and 3 ml of glacial acetic acid in water and make up to 100 ml with water.
4.2.
Carrez solution II: dissolve 10·6 g of potassium hexacyanoferrate IT trihydrate K4 [Fe(CN)6]. 3H2O in water and make up to 100 ml with water.
4.3.
Luff-Schoorl reagent: prepare the following solutions:
4.3.1.
Copper II sulphate solution: dissolve 25 g of iron-free copper II sulphate pentahydrate (CuSO4.5H2O) in 100 ml water.
4.3.2.
Citric acid solution: dissolve 50 g of citric acid monohydrate (C6H8O7.H2O) in 50 ml of water.
4.3.3.
Sodium carbonate solution: dissolve 143.8 g of anhydrous sodium carbonate in about 300 ml of warm water and allow to cool.
4.3.4.
Add the citric acid solution (4.3.2) to the sodium carbonate solution (4.3.3) in a one litre volumetric flask with gentle swirling. Swirl until effervescence ceases and then add the copper II sulphate solution (4.3.1) and make up to 1 000 ml with water. Allow the solution to stand overnight and then filter if necessary. Check the molarity of the reagent thus obtained by the method described in 6.1 (Cu 0·1 mol/litre; Na2CO3 1 mol/litre).
4.4.
Sodium thiosulphate solution, 0·1 mol/litre.
4.5.
Starch solution: to one litre of boiling water add a mixture of 5 g of soluble starch slurried in 30 ml of water. Boil for three minutes, allow to cool and add, if required, 10 mg of mercury II iodide as a preservative.
4.6.
Sulphuric acid, 3 mol/litre.
4.7.
Potassium iodide solution, 30% (m/v).
4.8.
Pumice chips, boiled in hydrochloric acid, washed free of acid with water and then dried.
4.9.
4.10.
Sodium hydroxide, 0·1 mol/litre.
4.11.
Hydrochlorie acid, 0·1 mol/litre.
4.12.
Phenolphthalein solution, 1% (m/v) in ethanol.
5. Apparatus
5.1.
Conical flask, 300 ml, fitted with a reflux condenser.
5.2.
6. Procedure
6.1.
Standardization of the Luff-Schoorl reagent (4.3)
6.1.1.
To 25 ml of Luff-Schoorl reagent (4.3) add 3 g of potassium iodide and 25 ml of 3 mol/litre sulphuric acid (4.6).
Titrate with 0·1 mol/litre sodium thiosulphate (4.4) using starch solution (4.5) as indicator added towards the end of the titration. If the volume of 0·1 mol/litre sodium thiosulphate used is not 25 ml the reagent must be made up afresh.
6.1.2.
Pipette 10 ml of the reagent into a 100 ml volumetric flask and dilute to volume with water.
Pipette 10 ml of the diluted reagent into 25 ml of 0·1 mol/litre hydrochloric acid (4.11) in a conical flask and heat for one hour in a boiling water-bath. Cool, make up to the original volume with freshly boiled water and titrate with 0·1 mol/litre sodium hydroxide (4.10) using phenolphthalein (4.12) as indicator.
The volume of 0·1 mol/litre sodium hydroxide (4.10) used must be between 5·5 and 6·5 ml.
6.1.3.
Titrate 10 ml of the diluted reagent (6.1.2) with 0·1 mol/litre hydrochloric acid (4.11) using phenolphthalein (4.12) as indicator. The end-point is characterized by the disappearance of the violet colour.
The volume of 0·1 mol/litre hydrochloric acid (4.11) used must be between 6·0 and 7·5 ml.
6.1.4.
The pH of the Luff-Schoorl reagent must be between 9·3 and 9·4 at 20 oC.
6.2.
6.2.1.
Accurately weigh, to the nearest 1 mg, 5 g of the sample and transfer quantitatively to a 250 ml volumetric flask, with 200 ml water. Clarify, if necessary, by adding 5 ml of Carrez solution I (4.1) followed by 5 ml of Carrez solution II (4.2). Mix after each addition. Make up to 250 ml with water. Mix well. Filter if necessary.
6.2.2.
Dilute the solution (6.2.1) so that 25 ml of the solution contains not less than 15 mg and not more than 60 mg of reducing sugars expressed as glucose.
6.3.
Pipette 25 ml of Luff-Schoorl reagent (4.3) into a 300 ml conical flask (5.1). Pipette 25 ml of the sugar solution (6.2.2) into the conical flask and introduce two pumice chips (4.8). Fit a reflux condenser to the conical flask (5.1) and immediately place the apparatus on an asbestos wire gauze over a Bunsen flame. The gauze shall have a hole cut in the asbestos part of the same diameter as the base of the flask. Heat the liquid to boiling point over a period of about two minutes and simmer gently for exactly 10 minutes. Cool immediately in cold water and after five minutes titrate as follows:
Add 10 ml of potassium iodide solution (4.7) then immediately add with caution (because of effervescence) 25 ml of 3 mol/litre sulphuric acid (4.6). Titrate with 01 mol/litre sodium thiosulphate solution (4.4) until the solution is almost colourless, then add a few ml of starch solution (4.5) as indicator and continue titrating until the blue colour disappears.
Carry out a control test, using 25 ml of water in place of the 25 ml of sugar solution (6.2.2).
7. Expression of results
7.1. Formula and method of calculation
From the table below, find (interpolating if necessary) the weight of glucose or of invert sugar in mg corresponding to the difference between the two titration readings, expressed in ml of 0·1 mol/litre sodium thiosulphate.
Express the result in terms of invert sugar or D-glucose as percentage (m/m) of the dry matter.
7.2. Repeatability
The difference between the results of two titrations when carried out simultaneously or in rapid succession on the same sample by the same analyst, under the same conditions, shall not exceed 0·2 ml.
8. Note
A small volume of isopentanol (4·9) may be added before acidifying with sulphuric acid to reduce foaming.
Table of values according to Luff-Schoorl reagent
0·1 mol/litre Na2S2O3
Glucose, fructose, invert sugars C6H12O6
ml
mg
difference
1
2·4
2
4·8
2·4
3
7·2
2·4
4
9·7
2·5
5
12·2
2·5
6
14·7
2·5
7
17·2
2·5
8
19·8
2·6
9
22·4
2·6
10
25·0
2·6
11
27·6
2·6
12
30·3
2·7
13
33·0
2·7
14
35·7
2·7
15
38·5
2·8
16
41·3
2·8
17
44·2
2·9
18
47·1
2·9
19
50·0
2·9
20
53·0
3·0
21
56·0
3·0
22
59·1
3·1
23
62·2
3·1
METHOD 7
MEASUREMENT OF REDUCING SUGARS EXPRESSED AS INVERT SUGAR
(Lane and Eynon constant volume modification)
1. Scope and field of application
The method determines the reducing sugars, expressed as invert sugar, in:
—
sugar solution,
—
white sugar solution,
—
invert sugar solution,
—
white invert sugar solution,
—
invert sugar syrup,
—
white invert sugar syrup.
2. Definition
‘Reducing sugars expressed as invert sugar’: the content of reducing sugars as determined by the method specified.
3. Principle
The sample solution is titrated at the boiling point against a specified volume of Fehling's solution, using methylene blue as internal indicator.
4. Reagents
4.1.
4.1.1.
Solution A:
Dissolve 69·3 g of copper II sulphate pentahydrate (CuSO4.5H2O) in water and make up to 1 000 ml.
4.1.2.
Solution B:
Dissolve 346·0 g of double sodium potassium tartrate tetrahydrate (KNaC4H4O6.4H2O) with 100·0 g of sodium hydroxide in water and make up to 1 000 ml. The clear solution should be decanted from a sediment that may form from time to time.
Note:
These two solutions should be stored in brown or amber bottles.
4.2.
Sodium hydroxide solution, 1 mol/litre.
4.3.
Standard invert sugar solution: dissolve 23·750 g of pure sucrose in about 120 ml of water in a 250 ml graduated flask, add 9 ml of hydrochloric acid (ζ = 1·16) and allow to stand for eight days at room temperature. Make the solution up to 250 ml and check for completion of hydrolysis by a polarimeter or saccharimeter reading in a 200 mm tube. This should be - 11·80o ± 0·05 oS (see note 8). Pipette 200 ml of this solution into a 2 000 ml graduated flask. Dilute with water and while shaking (to avoid excessive local alkalinity) add 71·4 ml of sodium hydroxide solution (1 mol/litre) (4.2) in which 4 g of benzoic acid has been dissolved. Make up to 2 000 ml to give a 1 g/100 ml solution of invert sugar. This solution should be a pH of approximately 3.
This stable stock solution should only be diluted immediately before use.
To make up the 0·25 g/100 ml invert sugar solution, fill a 250 ml graduated flask to the mark with the stock 1 g/100 ml invert solution at 20 oC. Wash the contents of this flask into a 1 000 ml graduated flask and dilute to the mark with water again at 20 oC.
4.4.
Methylene blue solution, 1 g/100 ml.
5. Apparatus
5.1.
Narrow-necked laboratory boiling flasks, 500 ml.
5.2.
Burette, 50 ml, with tap and offset tip, graduated to 0·05 ml.
5.3.
Pipettes graduated at 20, 25 and 50 ml.
5.4.
One mark volumetric flasks, 250, 1 000 and 2 000 ml.
5.5.
A heating device, suitable for maintaining boiling according to the conditions described in 6.1, permitting the observation of the end-point colour change without the necessity of removing the boiling flask (5.1) from the source of heat.
5.6.
Stop-watch, indicating to within at least one second.
6. Procedure
6.1. Standardization of Fehling's solution
6.1.1.
Pipette 50 ml of solution B (4.1.2) and then 50 ml of solution A (4.1.1) into a clean dry beaker and mix well.
6.1.2.
Rinse and fill the burette with 0·25 % (0·25 g/100 ml) standard invert sugar solution (4.3).
6.1.3.
Pipette a 20 ml aliquot of the mixed solutions A and B (6.1.1) into a 500 ml boiling flask (5.1). Add 15 ml of water to the flask. Run in, from the burette, 39 ml of the invert sugar solution, add a small quantity of anti-bumping granules and mix the contents of the flask by gentle swirling.
6.1.4.
Heat the flask and contents till boiling and allow to boil for exactly two minutes; the flask must not be removed from the heat source during the course of the rest of the procedure, or allowed to cease boiling.
Add three or four drops of methylene blue solution (4.4) at the end of the two-minute boiling period: the solution should be a definite blue colour.
6.1.5.
Continue the standardization by adding, from the burette, the standard invert sugar solution in small increments, initially of 0·2 ml; then 0·1 ml and finally in single drops until the end-point is reached. This is indicated by the disappearance of the blue colour imparted by the methylene blue. The solution has then assumed the reddish colour associated with a suspension of copper I oxide.
6.1.6.
The end-point should be reached at the end of three minutes from when the solution started to boil. The final titre, Vo, shall be between 39·0 and 41·0 ml. If Vo lies outside these limits, adjust the copper concentration of Fehling's solution A (4.1.1) and repeat the standardization process.
6.2. Preparation of sample solutions
The concentration of the sample test solution should be such that it contains between 250 and 400 mg invert sugar per 100 ml.
6.3. Preliminary test
6.3.1.
A preliminary test must be carried out to ensure that the quantity of water to be added to the 20 ml of mixed solutions A and B is sufficient to ensure that a final volume after titration of 75 ml is obtained.
The same procedure as described in 6.1.4 is carried out except that the sample solution is used instead of the standard invert sugar solution, i.e. 25 ml of the sample solution is run into the flask from the burette. 15 ml of water is added, and the solution is allowed to boil for two minutes and then titrated until the end-point is reached as described in 6.1.5.
6.3.2.
If, after the addition of the methylene blue solution, the reddish colour persists, the sample solution used is too concentrated. In this case, the test is discarded but repeated using a less concentrated sample solution.
If more than 50 ml of sample solution are required to obtain the reddish colour, a more concentrated solution of the sample must be used.
Calculate the quantity of water to be added by subtracting the volumes of mixed Fehling's solution (20 ml) and of the sample solution from 75 ml.
6.4. Final analysis of sample solution
6.4.1.
Pipette into the boiling flask 20 ml of mixed Fehling's solution and the quantity of water determined as in 6.3.
6.4.2.
Add, from the burette, the observed titre of the sample solution (as determined in 63) less 1 ml. Add some anti-bumping granules, mix the contents of the flask by swirling, boil the flask and contents and titrate as previously (6.3). The end-point should be reached one minute from the time of addition of the methylene blue solution. Final titre = V1.
7. Expression of results
7.1. Formula and method of calculation
The reducing sugars content of the sample calculation as invert sugar, is given by:
% reducing sugars (as invert sugar =
where:
C
=
the concentration of the sample test solution in g per 100 ml.
Vo
=
the volume in ml of the standard invert solution used in the standardization titration,
V1
=
the volume in ml of the sample test solution used in the accurate analysis in 6.4.2,
f
=
the correction factor to take account of the sucrose concentration in the sample test solution. Values are shown in the table below:
Sucrose (g in boiling mixture)
Correction factor f
0
1·000
0·5
0·982
1·0
0·971
1·5
0·962
2·0
0·954
2·5
0·946
3·0
0·939
3·5
0·932
4·0
0·926
4·5
0·920
5·0
0·915
5·5
0·910
6·0
0·904
6·5
0·898
7·0
0·893
7·5
0·888
8·0
0·883
8·5
0·878
9·0
0·874
9·5
0·869
10·0
0· 64
Corrections for varying sucrose contents of the sample test solution may be calculated from the table by interpolation.
Note:
The approximate sucrose concentration may be found by subtraction of the dissolved solids concentration due to the invert sugar (estimated for the purposes of this calculation f as 1.0), from the total dissolved solids concentration, expressed as sucrose, obtained from the refractive index of the solution using method three of this document.
7.2. Repeatability
The difference between the results of two determinations, carried out simultaneously or in rapid succession on the same sample by the same analyst under the same conditions, shall not exceed 1·0 % of their arithmetic mean.
8. Note
Divide by 2·889 to convert oS to polarmetric degrees of arc (precision tubes of 200 mm; light source consisting of a sodium vapour lamp; the instrument must be installed in a room where the temperature may be maintained close to 20 oC).
METHOD 8
DETERMINATION OF DEXTROSE EQUIVALENT
(Lane and Eynon constant)
1. Scope and field of application
This method determines the dextrose equivalent of:
—
glucose syrup,
—
dried glucose syrup,
—
dextrose monohydrate,
—
dextrose anhydrous.
2. Definition
2.1.
‘Reducing power’: the reducing sugar content, determined by the method specified, expressed in terms of anhydrous dextrose (D-glucose) and calculated as a percentage by mass of the sample.
2.2.
‘Dextrose equivalent’: the reducing power, calculated as a percentage by mass of the dry matter in the sample.
3. Principle
The test solution is titrated at the boiling point against a specified volume of mixed Fehling's solution, under strictly specified conditions, using methylene blue as an internal indicator.
4. Reagents
4.1. Fehling's solution:
4.1.1.
Solution A:
Dissolve 69·3 g of copper II sulphate pentahydrate (CuSO4.5H2O) in water and make up to volume in a 1 000 ml volumetric f ask.
4.1.2.
Solution B:
Dissolve 346·0 g of sodium potassium tartrate tetrahydrate (KNaC4H4O6.4H2O) and 100 g of sodium hydroxide in water. Make up to volume in a 1 000 ml volumetric flask. Decant the clear solution from any sediment that may from time to time form.
Note:
These two solutions (4.1.1 and 4.1.2) should be stored in brown or amber bottles.
4.1.3.
Preparation of the mixed Fehling's solution
Pipette 50 ml of solution B (4.1.2) and then 50 ml of solution A (4.1.1) into a clean dry beaker and mix well.
Note:
Mixed Fehling's solution shall not be stored but made up afresh every day and standardized (6.1).
4.2. Anhydrous dextrose (D-glucose) (C6H12O6)
This material shall be dried before use for four hours in a vacuum oven at 100 ± 1 oC or less, and an internal pressure of approximately 10 kPa (103 mbar).
4.3. Standard dextrose solution, 0·600 g/100 ml
Weigh, to the nearest 0·1 mg, 0·6 g of anhydrous dextrose (4.2), dissolve it in water, transfer the solution quantitatively into a 100 ml volumetric flask (5.4), dilute to the mark and mix.
This solution shall be freshly prepared on each day of use.
4.4. Methylene blue solution, 0·1 g/100 ml
Dissolve 0·1 g of methylene blue in 100 ml water.
5. Apparatus
5.1.
Narrow necked laboratory boiling flasks, 250 ml.
5.2.
Burette, 50 ml, with tap and offset tip, graduated to 0·05 ml.
5.3.
One mark pipettes, 25 ml and 50 ml.
5.4.
One mark volumetric flasks, 100 and 500 ml.
5.5.
A heating device, suitable for maintaining boiling according to the conditions described in 6·1, permitting the observation of the end-point colour change without the necessity of removing the boiling flask (5.1) from the source of heat (see 6.1, note 3).
5.6.
A stop-watch, indicating to at least the nearest second.
6. Procedure
6.1. Standardization of the Fehling's solution
6.1.1.
Pipette 25 ml of Fehling's solution (4.1.3) into a clean, dry boiling flask (5.1).
6.1.2.
Fill the burette (5.2) with standard dextrose solution (4.3) and adjust the meniscus to the zero mark.
6.1.3.
Run into the boiling flask (5.1) from the burette 18 ml of standard dextrose solution (4.3). Swirl the flask to mix contents.
6.1.4.
Place the boiling flask on the heating device (5.5), previously adjusted so that boiling commences in 120 ± 15 seconds.
The heating device shall not be further adjusted during the whole of the titration (see note 1).
6.1.5.
When boiling commences, start the stop-watch from zero.
6.1.6.
Boil the contents of the flask for 120 seconds, as timed by the stop-watch.
Add 1 ml of methylene blue solution (4.4) towards the end of this period.
6.1.7.
After boiling has continued for 120 seconds (by the stop-watch) start adding standard dextrose solution to the boiling flask (5.1) from the burette (6.1.2) in 0·5 ml increments until the colour of the methylene blue is discharged (see notes 2 and 3).
Note the total volume of standard dextrose solution added up to and including the penultimate 0·5 ml increment (X ml).
6.1.8.
Repeat 6.1.1 and 6.1.2.
6.1.9.
Run into the boiling flask (5.1) from the burette a volume of standard dextrose solution equal to (X-0·3) ml.
6.1.10
Repeat 6.1.4, 6.1.5 and 6.1.6.
6.1.11.
After boiling has continued for 120 seconds (by the stop-watch), start adding standard dextrose solution to the boiling flask (5.1) from the burette, initially in 0·2 ml increments and finally dropwise, until the colour of the methylene blue is just discharged.
Towards the end of this action the time between successive additions of standard dextrose solution shall be 10 to 15 seconds.
These additions shall be completed within 60 seconds, making the total time to boiling no longer than 180 seconds.
A third titration with a slightly larger, appropriately adjusted, initial addition of standard dextrose solution (6.1.9) may be necessary to achieve this.
6.1.12.
Note the volume (Vo ml) of standard dextrose solution used up to the end-point of the final titration (see note 4).
6.1.13.
Vo shall be between 19·0 and 21·0 ml standard dextrose solution (4.3).
If Vo lies outside these limits, adjust the concentration of the Fehling's solution A (4.1.1) appropriately and repeat the standardization process.
6.1.14.
For the day-to-day standardization of the mixed Fehling's solution, as Vo is known with accuracy, a single titration only is necessary, using an initial addition of (Vo — 0·5) ml standard dextrose solution.
Note 1:
This ensures that once boiling has commenced the evolution of steam is brisk and continuous throughout the whole of the titration process, thus preventing to the maximum possible extent the entrance of air into the titration flask with consquent re-oxidation of its contents.
Note 2:
The disappearance of the colour of the methylene blue is best seen by looking at the upper layers and the meniscus of the contents of the titration flask, as these will be relatively free from the precipiated, red copper I oxide. The colour disappearance is more easily seen when indirect lighting is used. A white screen behind the titration flask is helpful.
Note 3:
The burette should be isolated as much as possible from the source of heat during the determination.
Note 4:
As there is always a personal factor involved, each operator shall carry out his own standardization titration and use his own value of Vo in the calculation (7.1).
6.2. Preliminary examination of the prepared sample
6.2.1.
Unless the reducing power (2.1) of the prepared sample is known approximately, it is necessary to carry out a preliminary examination in order to obtain an approximate figure for it so that the mass of the test portion (6.3) can be calculated.
This examination is carried out as follows:
6.2.2.
Prepare a 2% m/v solution of the sample ‘Z’, having an estimated value.
6.2.3.
As 6.1.2, using the sample solution (6.2.2) in place of the standard dextrose solution.
6.2.4.
As 6.1.1.
6.2.5.
As 6.1.3, using 10·0 ml sample solution instead of 18·0 ml standard dextrose solution.
6.2.6.
As 6.1.4.
6.2.7.
Heat the contents of the flask to boiling. Add 1 ml methylene blue solution (4.4).
6.2.8.
Immediately boiling has started, start the stop-watch (5.6) from zero and commence adding sample solution to the flask from the burette in 1·0 ml increments at intervals of approximately 10 seconds until the blue colour of the methylene blue is discharged.
Note the total volume of sample solution added up to and including the penultimate increment (Y ml).
6.2.9.
‘Y’ must not exceed 50 ml. If it does, increase the concentration of the sample solution and repeat the titration.
6.2.10.
The approximate reducing power of the prepared sample in percent by mass is given by:
6.3. Test portion
Weigh out, to the nearest 0·1 mg, a mass of the prepared sample (mg) which contains between 2·85 and 3·15 g reducing sugars, expressed as anhydrous dextrose (D-glucose) using in the calculation either known approximate figure for the reducing power (2.1) or the approximate figure obtained in 6.2.10.
6.4. Test solution
Dissolve the test portion in water and make up to 500 ml in a volumetric flask.
6.5. Determination
6.5.1.
As 6.1.1.
6.5.2.
Fill the burette (5.2) with test solution (6.4) and adjust the meniscus to the zero mark.
6.5.3.
Run into the boiling flask from the burette 18·5 ml test solution. Swirl the flask to mix the contents.
6.5.4.
As 6.1.4.
6.5.5.
As 6.1.5.
6.5.6.
As 6.1.6.
6.5.7.
As 6.1.7, using test solution in place of standard dextrose solution.
6.5.8.
As 6.1.8.
6.5.9.
As 6.1.9, using test solution in place of standard dextrose solution.
6.5.10.
As 6.1.10.
6.5.11.
As 6.1.11, using test solution in place of standard dextrose solution.
6.5.12.
Note the volume (V1) of test solution used up to the end-point of the final titration.
6.5.13.
V1 shall be between 19·0 and 21·0 ml test solution.
If V1 lies outside these limits, adjust the concentration of the test solution appropriately and repeat 6.5.1 to 6.5.12.
6.5.14.
Carry out two determinations on the same test solution.
6.6. Dry matter content
Determine the dry matter content of the prepared sample by method 2.
7. Expression of results
7.1. Formulae and method of calculation
7.1.1.
Reducing power
The reducing power, calculated as a percentage by mass of the prepared sample, is given by:
where:
V0
=
the volume, in ml, of the standard dextrose solution (4.3) used in the standardization titration (6.1),
V1
=
the volume, in ml, of the test solution (6.4) used in the determination titration (6.5),
M
=
the mass, in grams, of the test portion (6.3) used to make 500 ml test solution.
7.1.2.
Dextrose equivalent
The dextrose equivalent, calculated as a percentage by mass of the dry matter in the prepared sample, is given by:
where:
RP
=
the reducing power, calculated as a percent by mass of the prepared sample (7.1.1),
D
=
the dry matter content of the prepared sample in percent by mass.
7.1.3.
Take as the result the arithmetic mean of the two determinations provided that the requirement concerning repeatability (7.2) is satisfied.
7.2. Repeatability
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 10 % of their arithmetic mean.
METHOD 9
DETERMINATION OF SULPHATED ASH
1. Scope and field of application
The method determines the sulphated ash content in:
—
glucose syrup,
—
dried glucose syrup,
—
dextrose monohydrate,
—
dextrose anhydrous.
2. Definition
‘Sulphated ash content’: the content of sulphated ash as determined by the method specified.
3. Principle
The residual mass of a test portion is determined after incineration in an oxidizing atmosphere at 525 oC in the presence of sulphuric acid and calculated as a percentage by mass of the sample.
4. Reagents
4.1.
Sulphuric acid, dilute solution: slowly and cautiously add 100 ml of concentrated sulphuric acid (density at 20 oC = 1·84 g/ml; 96 % m/m) to 300 ml water with stirring and cooling.
5. Apparatus
5.1.
Electric muffle furnace, equipped with a pyrometer and capable of operating at a temperature of 525 ± 25 oC.
5.2.
Analytical balance, accurate to 0·1 mg.
5.3.
Ashing crucibles, platinum or quartz, of suitable capacity.
5.4.
Desiccator, containing freshly activated silica gel or an equivalent desiccant with a water content indicator.
6. Procedure
Heat a crucible (5.3) to the ashing temperature, cool in a desiccator and weigh. Accurately weigh, to the nearest 01 mg, 5 g of glucose syrup or dried glucose syrup, or about 10 g of dextrose monohydrate or dextrose anhydrous into the crucible.
Add 5 ml of sulphuric acid solution (4.1) (see note 8.1) and carefully heat the sample in the crucible over a flame or on a hotplate until it is completely carbonized. This carbonization process, during which vapours are burnt off from the sample (see note 8.2), should be carried out in a fume cupboard.
Place the crucible (5.3) in the muffle furnace (5.1) heated to 525 ± 25o C until a white ash is obtained. This normally takes two hours (see note 8.3).
Allow the sample to cool for about 30 minutes in a desiccator (5.4) and then weigh.
7. Expression
7.1. Formula and method of calculation
The sulphated ash content expressed as a percentage by mass of the sample to be analyzed is given by:
where:
m1
=
the mass, in grams, of the ash,
m0
=
the mass, in grams, of the test portion.
7.2. Repeatability
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, shall not exceed 2% of their arithmetic mean.
8. Notes
8.1.
The sulphuric acid is added in small quantities to prevent excessive foaming.
8.2.
Every relevant precaution must be taken during the first carbonization to prevent losses of sample or of ash through excessive swelling of the sample.
8.3.
If the sample is difficult to ash completely (i.e. black particles remain) the crucible should be removed from the muffle furnace and the residue moistened, after cooling, with a few drops of water before being returned to the furnace.
METHOD 10
DETERMINATION OF POLARIZATION
1. Scope and field of application
The method determines the polarization in:
—
semi-white sugar,
—
sugar or white sugar,
—
extra-white sugar.
2. Definition
The polarization is the rotation of the polarized light plane by a sugar solution with 26 g of sugar per 100 ml contained in a tube of 200 mm in length.
3. Principle
The polarization is determined by using a saccharimeter or a polarimeter according to the conditions described in the following method.
4. Reagents
4.1.
Clarification agent: basic lead acetate solution.
Add 560 g of dry basic lead acetate to about 1 000 ml of freshly boiled water. Boil the mixture for 30 minutes and then leave it to stand overnight.
Decant the supernatant liquid and dilute with freshly boiled water to obtain a solution of density of 1·25 g/ml, at 20 oC.
Protect this solution from contact with air.
4.2.
5. Apparatus
5.1.
This instrument must be installed in a room where the temperature may be maintained close to 20 oC. Calibrate the instrument against standard quartz plates.
5.2.
Light source, consisting of a sodium vapour lamp.
5.3.
Precision polarimeter tubes, length 200 mm, error not exceeding ± 0·02 mm.
5.4.
Analytical balance, accurate to within 0·1 mg,
5.5.
Individually calibrated 100 ml volumetric flasks stoppered. Flasks with a real capacity in the range 100·00 ± 0·01 ml may be used without correction. Flasks with a capacity outside those limits must be used with an appropriate correction to adjust the capacity to 100 ml.
5.6.
Water-bath, controlled thermostatically at 20 ± 0·1 oC.
6. Procedure
6.1. Preparation of the solution
Weigh as quickly as possible 26 ± 0·002 g of the sample and transfer it quantitatively into a 100 ml volumetric flask (5.5) with approximately 60 ml of water.
Dissolve by swirling but without heating.
Where clarification is necessary, add 0·5 ml of lead acetate reagent (4.1).
Mix the solution by rotating the flask and wash the flask walls, until the volume is such that the meniscus is about 10 mm below the calibration mark.
Place the flask in the water-bath controlled (5.6) at 20 ± 0·1 oC until the temperature of the sugar solution is constant.
Eliminate any bubbles formed at the surface of the liquid with a drop of diethyl ether (4.2).
Make up to volume with water.
Stopper and mix thoroughly by inverting the flask at least three times.
Allow to stand for five minutes.
6.2. Polarization
Maintain the temperature at 20 ± 1 oC for all subsequent operations.
6.2.1.
Obtain the zero correction of the apparatus.
6.2.2.
Filter the sample through a filter paper. Discard the first 10 ml of the filtrate. Collect the next 50 ml of the filtrate.
6.2.3.
Wash the polarimeter tube by rinsing twice with the sample solution to be examined (6.2.2).
6.2.4.
Fill the tube carefully at 20 ± 0·1 oC with the sample solution to be examined.
Remove all air bubbles when sliding the end-plate into position. Place the filled tube in the cradle of the instrument.
6.2.5.
Read the rotation to within 0·05 oS or 0·02 angular degrees. Repeat a further four times. Take the mean of the five readings.
7. Expression of results
7.1. Formula and method of calculation
The results are expressed in degrees S to the nearest 0·1 oS. To convert the angular degrees into degrees S, the following formula is used:
oS = degree of arc × 2·889
7.2. Repeatability
The difference between the results of two determinations when carried out simultaneously or in rapid succession on the same sample, by the same analyst, under the same conditions, and each representing the mean of five readings, must not exceed 0·1 oS.
(1) n values in these tables are calculated from the equation developed by K. Rosenhauer for ICUMSA, programed and computed by Frank G. Carpenter of UDSA, and published in Sugar J. 33, 15-22 (June 1970). Refractive index was measured at 20 oC with 0 line of Na. Brix (% sucrose by weight) was obtained by weighing at 20 oC in air at 760 Torr (mm Hg) pressure and 50% relative humidity. It replaces the previous table, 47.012, 11th edition, taken from Intern. Sugar J. 39, 22s (1937).