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WS/T 572-2017Determination of iodine in serum - As3+ (English PDF)

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Issued by

National Health and Family Planning Commission of the People's Republic of China

Level / Type

National · Recommended

Issue date

August 16, 2017

Implementation date

February 1, 2018

Scope

WS/T 572-2017 (Determination of iodine in serum - As3+) is available as an English-translated PDF.

WS/T 572-2017 — This standard specifies the arsenic-cerium catalytic spectrophotometric method for the determination of iodine in serum. This standard applies to the determination of total iodine concentration in serum.

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Document preview — WS/T 572-2017

National Standard of the People's Republic of China

ICS: 11.020
Classification: C 61

Issued by: National Health and Family Planning Commission of the People's Republic of China

Foreword
1 Scope
2 Principle
3 Instruments
4 Reagent
5 Solution preparation
5.1 Sodium chlorate solution [c (NaClO3) = 2.0mol/L]
5.2 Sulfuric acid solution [c (H2SO4) = 2.5mol/L]
5.3 Arsenite solution [c (H3AsO3) = 0.025mol/L]
5.4 Cerium ammonium sulfate solution [c (Ce4) = 0.025mol/L]
5.5 Iodine standard stock solution [rho (I) = 100µg/mL]
5.6 Iodine standard intermediate solution [rho (I) = 10µg/mL]
5.7 Iodine standard use series solution [rho (I) = 0µg/L ~ 300µg/L]
6 Sample collection and storage
7 Analysis steps
8 Results calculation
9 Method characteristics
9.2 Detection limit and measurement range
9.3 Precision
9.4 Accuracy
10 Quality Assurance and Quality Control

Foreword

This standard was drafted in accordance with the rules given in GB/T 1.1-2009.

This standard was drafted. China Centers for Disease Control and Prevention, Endemic Disease Control Center, Xiamen City, Fujian Province Center for Disease Control and Prevention, Shanxi Provincial Institute of Endemic Disease Control.

1 Scope

This standard specifies the arsenic-cerium catalytic spectrophotometric method for the determination of iodine in serum.

This standard applies to the determination of total iodine concentration in serum.

2 Principle

Serum samples were digested with perchloric acid-sodium chlorate solution, and the catalytic effect of iodine on the oxidation-reduction reaction of arsenic and cerium.

H3AsO3 2Ce

H2O H3AsO4 2Ce

During the reaction, yellow Ce4 is reduced to colorless Ce3. The higher the iodine content, the faster the reaction speed, and the less Ce4 remaining;

The reaction temperature and time were determined, and the absorbance value of the remaining Ce4 in the system was measured colorimetrically to determine the iodine content.

3 Instruments

3.1 Digestion temperature control heating device. constant temperature digestion instrument (temperature control point accuracy 130 °C ± 2 °C, temperature difference between holes <=1 °C).

3.2 Constant temperature water bath. The temperature control accuracy is ± 0.3 °C.

3.3 Spectrophotometer, 1cm cuvette.

3.4 Glass test tube. 15mmx100mm or 15mmx120mm.

3.5 Quantitative pipettes. 100 µL, 1000 µL, 5000 µL;

Quantitative glass pipettes. 5 mL and 10 mL.

3.6 Stopwatch.

3.7 Constant temperature drying oven.

3.8 Centrifuge.

4 Reagent

4.1 Unless otherwise specified, the reagents used in this standard are analytical reagents, and the experimental water should meet the secondary water specifications in GB/T 6682.

4.2 Perchloric acid (HClO4, 70% ~ 72%), excellent grade pure.

4.3 Sodium chlorate (NaClO3, M = 106.4).

4.4 concentrated sulfuric acid (H2SO4, rho20 = 1.84g/mL), excellent grade pure.

4.5 Arsenic trioxide (As2O3, M = 197.8).

4.6 Sodium chloride (NaCl, M = 58.4), excellent grade pure.

4.7 Sodium hydroxide (NaOH, M = 40.0).

4.8 Ammonium cerium sulfate [Ce (NH4) 4 (SO4) 4 · 2H2O, M = 632.6] or ammonium cerium sulfate tetrahydrate [Ce (NH4) 4 (SO4) 4 · 4H2O, M = 668.6].

4.9 Potassium iodate (KIO3, M = 214.0), reference reagent or standard substance.

5 Solution preparation

5.1 Sodium chlorate solution [c (NaClO3) = 2.0mol/L]

After weighing 106.5g of sodium chlorate (4.3) and dissolving it in 400 mL of pure water, add pure water to 500mL, and store it in a refrigerator (4 °C) for 12 Months.

5.2 Sulfuric acid solution [c (H2SO4) = 2.5mol/L]

Take 140mL of concentrated sulfuric acid (4.4) and slowly add it to 700mL of pure water. Stir while adding. After cooling, dilute to 1000mL with pure water.

5.3 Arsenite solution [c (H3AsO3) = 0.025mol/L]

Weigh 2.5g of arsenic trioxide (4.5) and 3.0g of sodium hydroxide (4.7) into a 1L beaker, add about 30mL of pure water and stir until full Partially dissolve, add about 500mL of pure water to the beaker, and add 40.0g of sodium chloride (4.6), stir until completely dissolved, and then slowly add.200mL Sulfuric acid solution (5.2), make up to 1000 mL with pure water at room temperature, store in a brown bottle, and store at room temperature for 6 months.

5.4 Cerium ammonium sulfate solution [c (Ce4) = 0.025mol/L]

Weigh 15.8g of cerium ammonium sulfate (4.8) or 16.7g of cerium ammonium sulfate tetrahydrate [Ce (NH4) 4 (SO4) 4 · 4H2O] dissolved in 700mL sulfuric acid solution (5.2), make up to 1000 mL with pure water, store in a brown bottle, and store at room temperature for 6 months.

5.5 Iodine standard stock solution [rho (I) = 100µg/mL]

Accurately weigh 0.1686g of potassium iodate that has been dried to a constant weight at 105 °C ~ 110 °C in a volumetric flask, add pure water to dissolve, and make up to volume with pure water.

1000 mL. Store in tightly closed brown bottle, and store in refrigerator (4 °C) for 6 months.

5.6 Iodine standard intermediate solution [rho (I) = 10µg/mL]

Pipette 10.00 mL of iodine standard stock solution (5.5) into a 100 mL volumetric flask, and make up to volume with pure water. Store tightly the brown bottle can be stored in the refrigerator (4 °C) for 1 month.

5.7 Iodine standard use series solution [rho (I) = 0µg/L ~ 300µg/L]

Pipette iodine standard intermediate solution (5.6) 0 mL, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL, 2.50 mL, and 3.00 mL before use Place them in 100 mL volumetric flasks and make up to volume with pure water. The iodine concentrations of this standard series of solutions are 0 µg/L, 50 µg/L, 100 µg/L, 150 µg/L,.200 µg/L, 250 µg/L, and 300 µg/L.

6 Sample collection and storage

Use a disposable vacuum non-coagulation blood collection tube to collect not less than 2mL of blood, leave it at room temperature for 0.5h, and centrifuge at 3000r/min for 10min.

The separated serum was placed in a polyethylene plastic tube with a stopper and hermetically sealed to prevent evaporation. Can be stored for 7 days at room temperature (20 ° C) and at 4 ° C it can be stored for 1 month, and frozen (-20 ° C) for at least 3 months after being sealed.

7 Analysis steps

7.1 Take 0.10mL of iodine standard use series solution (5.7) and serum sample (if the iodine concentration of the serum sample exceeds the iodine concentration of the standard curve) Degree range, then dilute with pure water and sample) Put them in glass test tubes (3.4), add 0.5mL perchloric acid (4.2), 0.6mL chlorine to each tube the sodium solution (5.1) was mixed and placed in a 130 ° C digestion temperature control heating device, digested for 120 min, and removed and cooled to room temperature. Available at 15 °C ~ Under a stable temperature environment (room temperature or temperature control) between 30 °C, perform the following 7.2 ~ 7.4 analysis steps, and the temperature fluctuation is required to not exceed ± 0.3 °C.

7.2 Add 3.0mL of arsenite solution (5.3) to each tube, mix thoroughly and let stand for 15min to bring the temperature to equilibrium (note that the standard system the tubes are arranged in descending order of iodine concentration).

7.3 Stopwatch timing, add 0.60mL cerium ammonium sulfate solution (5.4) to each tube exactly in the same time interval (30s or 20s) in sequence, Mix immediately.

7.4 When the absorbance of the first tube (ie, the standard series plus 300g/L iodine concentration tube) reaches about 0.10 (the response corresponding to different temperatures) refer to Appendix A for the time reference value. In order, the interval between each tube is the same (in accordance with the interval time of 7.3) at a wavelength of 400nm, using a ratio of 1cm.

Color cup, using pure water as a reference, determine the absorbance value of each tube.

7.5 Standard curve drawing. Draw the standard curve with the iodine concentration as the abscissa and the logarithm of the absorbance value as the ordinate.

8 Results calculation

8.1 Regression equation method. The linear relationship between the mass concentration of iodine c (g/L) and the logarithm of the absorbance value A. see equation (1), and find it according to equation (1) Draw out the regression equation of the standard curve, substitute the absorbance of the sample tube into formula (1), find the mass concentration of iodine in the measured sample, and then use formula (2) Calculate the mass concentration of iodine in the serum.

c = a + b lgA (or c = a + b lnA) (1) in the formula.

C--Iodine standard uses the mass concentration of iodine in a series of solutions (or measured samples) in micrograms per liter (µg/L);

a--the intercept of the standard curve regression equation;

b--the slope of the standard curve regression equation;

A--The iodine standard uses a series of solutions (or measured samples) to determine the absorbance value.

8.2 Standard curve method. The iodine mass concentration of a series of solutions using the iodine standard is the abscissa and the absorbance value is the logarithmic ordinate, at the semi-logarithmic Draw a standard curve in the coordinate system. Use the absorbance value of the sample tube to check the iodine mass concentration of the measured sample on the standard curve.

Calculate the mass concentration of iodine in the serum.

8.3 The mass concentration of iodine in serum is calculated according to formula (2).

rho (I) = c × K (2)

In the formula.

rho (I)-mass concentration of iodine (I) in serum, the unit is micrograms per liter (µg/L);

c--The mass concentration of iodine in the sample measured by the standard curve or calculated by the standard curve regression equation, in micrograms per unit Liters (µg/L);

K--serum sample dilution.

9 Method characteristics

9.2 Detection limit and measurement range

The detection limit of this method is 6.9 µg/L (taking a serum sample volume of 0.10 mL), which can be directly sampled and digested to determine blood in the concentration range of 0 µg/L to 300 µg/L.

Clear iodine.

9.3 Precision

In the range of iodine concentration of 0µg/L ~ 300µg/L, 5 laboratories made 6 repeated determinations of serum samples containing low, medium and high iodine concentrations.

The relative standard deviation is 0.7% -3.8%, with an average of 1.7%.

9.4 Accuracy

In the range of 0µg/L ~ 300µg/L iodine concentration, 5 laboratories performed spike recovery of serum samples containing low, medium and high iodine concentrations, and added the iodine standard solution increased the concentration of the spiked recovered sample by 50 µg/L to 100 µg/L, and the recovery was 90.0% to 110.0%, with an average of 99.8%.

Under the conditions of this method, hemolysis and the following substances do not interfere with the determination. 11g/L NaCl, 1.5g/L HPO4 2-, 700mg/L KNO3,.200mg/L Ca 2, 365mg/L Mg2, 2mg/L F-, 2mg/L Fe2, 2mg/L Zn2, 2mg/L Cu2, 0.05mg/L Hg2, 2g/L glycine, 10g/L glucose, 3g/L urea, 30mg/L ascorbic acid, 100g/L protein.

10 Quality Assurance and Quality Control

10.1 The experimental environment, utensils and reagents shall be free from iodine contamination. Serum samples shall be avoided from iodine-containing substances during field collection, transportation and storage.

Product contact.

10.2 For the digestion of the sample, use a glass test tube with a length of 100 mm or 120 mm, which is matched with the pore size of the digestion pore of the thermostatic digester, so that the digestion effect is consistent, ensuring the accuracy and precision of the measurement.

10.3 A standard series must be set at the same time for each batch of sample digestion and determination.

10.4 If the room temperature is unstable or the room temperature is low, the analysis of steps 7.2 to 7.4 should be performed with a super-constant water bath.

Over ± 0.3 °C.

10.5 The absolute value of the correlation coefficient of the standard curve regression equation c = a blgA or c = a blnA should be >= 0.999.

10.6 The consistency of the blank absorbance of the cuvette should be checked before the measurement. The sample dish and the reference dish contain pure water at the measurement wavelength. The absorbance value is compared.

The difference does not exceed ± 0.002.

Appendix A

(Informative appendix) Reaction time for arsenic-cerium reaction at different temperatures for the determination of serum iodine in the range of 0 µg/L to 300 µg/L, analyze the first tube measured in step 7.4 (that is, in the standard series) at different temperatures.

Add a 300 µg/L iodine concentration tube) The reference value of the time required for the reaction of arsenic and cerium when the absorbance reaches about 0.10 is shown in Table A.1.

Table A.1 Response time of serum iodine at different temperatures in the range of 0 µg/L to 300 µg/L

Temperature/°C reaction time/min temperature/°C reaction time/min

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