GB/T 35950-2018 PDF in English
GB/T 35950-2018 (GB/T35950-2018, GBT 35950-2018, GBT35950-2018)
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Determination of inorganic sulfites and bisulfites in cosmetics
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Standards related to (historical): GB/T 35950-2018
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GB/T 35950-2018: PDF in English (GBT 35950-2018) GB/T 35950-2018
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 71.100.70
Y 42
Determination of Inorganic Sulfites
and Bisulfites in Cosmetics
ISSUED ON: FEBRUARY 06, 2018
IMPLEMENTED ON: SEPTEMBER 01, 2018
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Titration ... 4
4 Ion chromatography ... 8
Appendix A (Informative) Calibration method of sodium sulfite standard
solution ... 13
Appendix B (Informative) Sulfite standard chromatogram ... 15
Determination of Inorganic Sulfites
and Bisulfites in Cosmetics
1 Scope
This Standard specifies the reagents and materials, instruments and
apparatuses, analysis steps, result calculation, recovery and precision,
allowable difference and the like of titration and ion chromatography of the
determination of sulfites and bisulfites in cosmetics.
Note: The user selects titration or ion chromatography according to the
configuration of the instrument. If the results are inconsistent, the ion
chromatography method will prevail.
This Standard applies to the determination of sulfites and bisulfites in cosmetics.
For the contents of sulfites and bisulfites, the quantitation-limit of titration in this
Standard is 50 mg/kg; the detection-limit of ion chromatography is 2 mg/kg, and
the quantitation-limit is 10 mg/kg.
2 Normative references
The following documents are indispensable for the application of this document.
For dated references, only the dated version applies to this document. For
undated references, the latest edition (including all amendments) applies to this
document.
GB/T 6682, Water for analytical laboratory use. Specification and test
methods
3 Titration
3.1 Principle
Under the heating condition, the free sulfur dioxide in the sample reacts
excessively with hydrogen peroxide to form sulfuric acid; then, use alkali
standard solution to titrate the resulting sulfuric acid. Thus, the content of free
sulfur dioxide in the sample can be obtained.
3.2 Reagents and materials
Unless otherwise specified, the used reagents are analytical reagents; the
water is that in accordance with 3.2.1.
3.4.3 Titration
Take down the pear-shaped flask; use a small amount of water to wash the
upper end and let it flow into the pear-shaped flask; use sodium hydroxide
standard solution (3.2.8) to titrate the solution in the pear-shaped flask to an
olive color; record the volume of the consumed sodium hydroxide standard
solution; at the same time, do a blank test.
3.4.4 Blank test
Except that the sample is not weighed, it is carried out according to the above
steps of distillation and titration.
3.4.5 Parallel test
The contents of sulfites and bisulfites in the sample shall be determined from
the average of two independent parallel test results.
3.5 Result calculation
The contents of inorganic sulfites and bisulfites in the sample (calculated as
sulfur dioxide) is calculated according to Formula (1):
Where:
X -- the content of inorganic sulfites and bisulfites in the sample (calculated as
sulfur dioxide), in milligrams per kilogram (mg/kg);
c -- the mass concentration of the sodium hydroxide standard solution, in moles
per liter (mol/L);
V -- the volume of sodium hydroxide standard solution that is consumed to
determine the sample, in milliliters (mL);
V0 -- the volume of sodium hydroxide standard solution that is consumed in the
blank test, in milliliters (mL);
32 -- the mass of sulfur dioxide that is equivalent to 1.00 mL of sodium hydroxide
standard solution [c(NaOH) = 1.00 mol/L], in milligrams.
m -- sampling amount, in grams (g);
The calculation result shall keep two significant figures.
3.6 Recovery and precision
4.2.8 Sodium sulfite grade-2 standard intermediate solution 5.00 mg/L (content
based on sulfur dioxide): accurately transfer 2.50 mL of sodium sulfite grade-1
standard intermediate solution (4.2.7) to a 10 mL volumetric flask; use water to
dilute to the mark; shake well. Store it at 0°C ~ 4°C out of the sun. Formulate
when needed.
4.2.9 Sodium sulfite standard working solution: accurately transfer 0.20 mL,
0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL and 4.00 mL of sodium sulfite grade-2
standard intermediate solution to a 10 mL volumetric flask respectively; use
water to dilute to the mark; shake well. The concentrations are 0.10 mg/L, 0.25
mg/L, 0.50 mg/L, 1.00 mg/L, 1.50 mg/L and 2.00 mg/L respectively (content
based on sulfur dioxide); prepare when needed.
4.3 Instruments and apparatuses
4.3.1 Ion chromatograph: equipped with a conductivity detector.
4.3.2 Analytical balance: sensitivity of 1 mg.
4.3.3 Analytical balance: sensitivity of 0.01 g.
4.3.4 Volumetric flasks: 10 mL and 100 mL.
4.3.5 Colorimetric tube with a stopper: 10 mL.
4.3.6 RP C18 ion chromatography solid-phase extraction column (1.0 mL), or a
pre-treatment column with equivalent performance to remove organic matters.
Use 5 mL of methanol (4.2.3) and 10 mL of water to activate before use; place
for 30 min before use, or carry out activation with reference to the extraction
column technical file.
4.3.7 Centrifuge: (speed ≥ 8 000 r/min).
4.3.8 Filter: pore size of 0.22 μm.
4.3.9 Vortex oscillator.
4.3.10 Pipette or pipettor: 200 μL, 1 mL, and 5 mL.
4.4 Analysis steps
4.4.1 Preparation of sample solution
Weigh 2 g (accurate to 0.01 g) of sample; place it in a 10 mL colorimetric tube
with a stopper; use acetonitrile (4.2.2) to dilute to the mark of 10 mL; vortex for
2 min; centrifuge at 8 000 r/min for 5 min.
Accurately transfer 0.50 mL of the supernatant to another 10 mL colorimetric
tube with a stopper; use water to dilute to the mark of 10 mL; mix well.
Determine the sample solution; obtain the concentration (mg/L) of sulfites and
bisulfites in the measurement solution from the standard curve.
4.4.6 Blank test
Except that the sample is not weighed, it is carried out according to the above
steps.
4.4.7 Parallel test
The contents of sulfites and bisulfites in the sample shall be determined from
the average of two independent parallel test results.
4.5 Result calculation
The contents of sulfites and bisulfites in the sample (calculated as sulfur dioxide)
is calculated according to Formula (2):
Where:
X -- the contents of sulfites and bisulfites in the sample (calculated as sulfur
dioxide), in milligrams per kilogram (mg/kg);
c -- the measured value of sodium sulfite in the sample solution (calculated as
sulfur dioxide), in milligrams per liter (mg/L);
c0 -- the measured value of sodium sulfite in the sample blank solution
(calculated as sulfur dioxide), in milligrams per liter (mg/L);
V1 -- the fix-volume of the sample when it is extracted with acetonitrile; in
milliliters (mL);
V3 -- the fix-volume of the extract when it is diluted with water; in milliliters (mL);
m -- sample mass, in grams (g).
V2 -- the fix-volume of the pipetted extract when it is diluted with water; in
milliliters (mL);
1 000 -- unit conversion coefficient.
The calculation result shall keep two significant figures.
4.6 Recovery and precision
For sulfites and bisulfites (calculated as sulfur dioxide) in the range of 10.0
Appendix A
(Informative)
Calibration method of sodium sulfite standard solution
A.1 Principle
In a weakly acidic solution, add an excess of iodine oxide sulfite. Take the starch
as the indicator; use the sodium thiosulfate solution to titrate the excess iodine.
A.2 Reagents and materials
Unless otherwise indicated, the reagents are all analytical reagent, and the
water is distilled water or water of comparable purity.
A.2.1 Iodine standard solution [c(1/2I2) = 0.1 mol/L].
A.2.2 Sodium thiosulfate standard titration solution [c(Na2S2O3) = 0.1 mol/L].
A.2.3 Glacial acetic acid (CH3COOH).
A.2.4 Starch indicator solution (10 g/L): weigh 1 g of soluble starch; use a little
water to mix and make it a paste; slowly pour in 100 mL of boiling water while
stirring; boil for 2 min; let cool for use; prepare when needed.
A.3 Instrument
A.3.1 Pipette.
A.3.2 Iodine flask.
A.3.3 Burette.
A.4 Analysis steps
Pipette 10 mL of sodium sulfite standard solution into a 250 mL iodine flask;
add 100 mL of water; accurately add 20 mL of 0.1mol/L iodine standard solution,
5 mL of glacial acetic acid; shake well; place in the dark; after 2 minutes, quickly
use the standard solution of sodium thiosulfate 0.1mol/L to titrate to pale yellow;
add 0.50 mL of starch indicator; continue to titrate until it is colorless; do a blank
test at the same time.
A.5 Result calculation
Calculate the concentration of sodium sulfite standard solution according to
formula (A.1):
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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