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GB/T 223.31-2026Iron, steel and alloy - Determination of arsenic content - spectrophotometric method and iodimetric method (English PDF)

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Issued by

State Administration for Market Regulation

Level / Type

National · Recommended

Issue date

February 27, 2026

Implementation date

September 1, 2026

Scope

GB/T 223.31-2026 (Iron, steel and alloy - Determination of arsenic content - spectrophotometric method and iodimetric method) is available as an English-translated PDF.

GB/T 223.31-2026 — This Document specifies methods for the determination of arsenic content in iron, steel, and alloys using spectrophotometry and iodometry. The application ranges for the methods in this Document are as follows.

Method I (distillation separation - molybdenum blue spectrophotometry) is applicable to the determination of arsenic content with mass fraction in the range of 0.0005% ~ 0.10% in iron, steel, and alloys; Method II (sodium hypophosphite reduction - iodometry) is applicable to the determination of arsenic content with mass fraction in the range of 0.010% ~ 0.65% in pig iron, carbon steel, and alloy steel.

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Document preview — GB/T 223.31-2026

National Standard of the People's Republic of China

ICS: 77.080.01

Issued by: State Administration for Market Regulation

Foreword...3
Introduction...6
1 Scope...7
2 Normative References...7
3 Terms and Definitions...8
4 Method I (Distillation Separation - Molybdenum Blue Spectrophotometry)...8
5 Method II (Sodium Hypophosphite Reduction-Iodometry)...15
6 Test Report...22
Appendix A (Informative) Parts of GB/T 223...23

Foreword

This Document was drafted as per the rules specified in GB/T 1.1-2020 Directives for

Standardization – Part 1.Rules for the Structure and Drafting of Standardizing Documents.

This Document is Part 31 of GB/T 223; the published parts of GB/T 223 are shown in Appendix

This Document replaced GB/T 223.31-2008 Iron, Steel and Alloy - Determination of Arsenic

Content - Distillation-Molybdenum Blue Spectrophotometric Method, and GB/T 223.32-1994

Methods for Chemical Analysis of Iron, Steel and Alloy - The Hypophosphite Reduction-

Iodometric Method for the Determination of Arsenic Content. Compared with GB/T 223.31-

2008 and GB/T 223.32-1994, the major technical changes of this Document are as follows

besides the structural adjustments and editorial modifications.

--- Change the determination range for Method II (sodium hypophosphite reduction-

iodometry) from "0.010% ~ 3.00%" to "0.010% ~ 0.65%" (see Clause 1 of this Document;

Clause 1 of GB/T 223.32-1994);

--- Add requirements for laboratory water for Method II (sodium hypophosphite reduction-

iodometry) (see 5.2 of this Document);

--- Add requirements for instruments and equipment for Method II (sodium hypophosphite

reduction-iodometry) (see 5.3 of this Document);

--- Add requirements for sample collection and preparation for Method II (sodium

hypophosphite reduction-iodometry) (see 5.4 of this Document);

--- Delete the "arsenic content range of 1.00% ~ 3.00% and the corresponding sample mass"

from Method II (sodium hypophosphite reduction-iodometry) (see 5.5.1 of this

Document; 4.1 of GB/T 223.32-1994);

--- Change the arsenic content range corresponding to a sample mass of 0.50 g in Method II

(sodium hypophosphite reduction-iodometry) from " >0.50 ~ 1.0" to " >0.50" (see 5.5.1

of this Document; 4.1 of GB/T 223.32-1994).

This Document modified and adopted ISO 17058.2004 Steel and Iron – Determination of

Arsenic Content – Spectrophotometric Method.

Compared with ISO 17058.2004, this Document made more structural adjustments. The

comparison list on the change in clause numbers between the two documents are shown in

Appendix B.

The technical differences and causes between this Document and ISO 17058.2004 are as

follows.

Iron, Steel and Alloy – Determination of Arsenic Content –

Spectrophotometric Method and Iodometric Method

WARNING. Users of this Document shall have practical experience working in standard

laboratory. This Document does not address all possible safety issues. It is the

responsibility of the user to adopt appropriate safety and health measures.

1 Scope

This Document specifies methods for the determination of arsenic content in iron, steel, and

alloys using spectrophotometry and iodometry.

The application ranges for the methods in this Document are as follows. Method I (distillation

separation - molybdenum blue spectrophotometry) is applicable to the determination of arsenic

content with mass fraction in the range of 0.0005% ~ 0.10% in iron, steel, and alloys; Method

II (sodium hypophosphite reduction - iodometry) is applicable to the determination of arsenic

content with mass fraction in the range of 0.010% ~ 0.65% in pig iron, carbon steel, and alloy

steel.

2 Normative References

The provisions in following documents become the essential provisions of this Document

through reference in this Document. For the dated documents, only the versions with the dates

indicated are applicable to this Document; for the undated documents, only the latest version

(including all the amendments) is applicable to this Document.

GB/T 6379.1 Accuracy (trueness and precision) of measurement methods and results - Part

1 General principles and definitions (GB/T 6379.1-2004, ISO 5725-1.1994, IDT)

GB/T 6379.2 Accuracy (trueness and precision) of measurement methods and results - Part

2 Basic method for the determination of repeatability and reproducibility of a standard

measurement method (GB/T 6379.2-2004, ISO 5725-2.1994, IDT)

GB/T 6379.3 Accuracy (trueness and precision) of measurement methods and results - Part

3 Intermediate measures of the precision of a standard measurement method (GB/T

6379.3-2012, ISO 5725-3.1994, IDT)

GB/T 6682 Water for analytical laboratory use - Specification and test methods (GB/T

6682-2008, ISO 3696.1987, MOD)

GB/T 12805 Laboratory glassware – Burettes (GB/T 12805-2011, ISO 385.2005, NEQ)

GB/T 12806 Laboratory glassware - One-mark volumetric flasks (GB/T 12806-2011, ISO

1042.1998, NEQ)

GB/T 12808 Laboratory glassware - One-mark pipettes

GB/T 20066 Steel and iron - Sampling and preparation of samples for the determination

of chemical composition (ISO 14284.1996, IDT)

3 Terms and Definitions

For the purposes of this Document, there are no terms and definitions required to be defined.

4 Method I (Distillation Separation - Molybdenum Blue

Spectrophotometry)

4.1 Principle

Dissolve the test materials in a mixture of hydrochloric acid and nitric acid; add sulfuric acid;

and continue heating until white fumes of sulfuric acid appear. In a medium of sulfuric and

hydrochloric acids, add hydrazine sulfate and potassium bromide to reduce the arsenic; and

separate it by distillation in the form of arsenic trichloride. Absorb the distillate in nitric acid;

simultaneously oxidizing As (III) to As (V). Using hydrazine sulfate as the reducing agent, form

a molybdenum blue complex from the arsenic and ammonium molybdate. Perform

spectrophotometric measurement at a wavelength of 840 nm; and calculate the mass fraction of

arsenic based on a pre-established calibration curve.

4.2 Reagents

Unless otherwise specified, only recognized analytically pure reagents and Grade 3 water as

specified in GB/T 6682 shall be used for the analysis.

4.2.1 Hydrochloric acid

Density (rho) is approximately 1.19 g/mL.

4.2.2 Nitric acid

Density (rho) is approximately 1.40 g/mL.

4.2.3 Nitric acid (3+1) solution

Add 3 volumes of nitric acid (4.2.2) to 1 volume of water.

4.2.4 Mixed acid (1+4) solution

Add 1 volume of nitric acid (4.2.2) to 4 volumes of hydrochloric acid (4.2.1).

4.2.5 Sulfuric acid

Density (rho) is approximately 1.84 g/mL.

4.2.6 Sulfuric acid (1+1) solution

Add 1 volume of sulfuric acid (4.2.5) to 1 volume of water in several portions, while cooling

in water and stirring continuously.

4.2.7 Sulfuric acid (1+6) solution

Add 1 volume of sulfuric acid (4.2.5) to 6 volumes of water in several portions, while cooling

in water and stirring continuously.

4.2.8 Reducing agent powder mixture

Weigh 2.5 g of hydrazine sulfate and 10 g of potassium bromide; place them in a mortar; grind

finely with a pestle; mix thoroughly; and set aside for later use.

4.2.9 Ammonium molybdate tetrahydrate solution, 10 g/L

4.2.10 Hydrazine sulfate solution, 0.6 g/L

4.2.11 Arsenic standard solution, 200 µg/mL

Weigh 0.1320 g of arsenic trioxide, accurate to 0.001 g; and place it in a 100 mL beaker. Slowly

add 10 mL of nitric acid (4.2.2); cover with a watch glass; and heat gently until completely

dissolved. Add 2 mL of sulfuric acid (4.2.6); heat slowly to expel nitrogen oxides; and continue

evaporation until copious white fumes appear. Remove from heat and allow to cool slightly;

rinse the watch glass and the inner walls of the beaker with a small amount of water; then heat

and evaporate again until copious white fumes appear. Remove from heat and allow to cool;

add approximately 10 mL of water and warm gently until the salts dissolve and the solution

becomes clear. Cool to room temperature; quantitatively transfer the solution to a 500 mL one-

mark volumetric flask; dilute to the mark with water; and mix well.

1 mL of this standard solution contains 200 µg of arsenic.

4.2.12 Arsenic standard solution, 10 µg/mL

Pipette 25.00 mL of the arsenic standard solution (4.2.11) into a 500 mL one-mark volumetric

flask; dilute to the mark with water; and mix well. Prepare fresh before use.

1 mL of this standard solution contains 10 µg of arsenic.

place the absorbent beaker into a cooling beaker containing cold water. Assemble the distillation

apparatus; and heat the distillation flask on a low-temperature electric heater; stop heating when

the temperature reaches 125 °C, ensuring the entire distillation process takes 6 min ~ 10 min.

Open the valve to prevent the solution from back-flowing from the absorbent beaker. Remove

the distillation flask; rinse the lower end of the gas outlet tube with a small amount of water;

and combine the washings with the solution in the absorbent beaker. Add 3.5 mL of sulfuric

acid (4.2.7); and mix well.

Cover with a watch glass leaving a small opening for fumes to escape; and evaporate until

copious white sulfuric acid fumes appear. No foaming shall occur during this process. Remove

from heat; allow to cool; and rinse the watch glass and beaker walls with water; evaporate again

until white fumes appear to expel nitrogen oxides. Remove from heat; allow to cool; rinse the

watch glass with water; and quantitatively transfer the solution into a 50 mL one-mark

volumetric flask.

4.5.3.3 Formation of the colored complex

Add 2.5 mL of ammonium molybdate tetrahydrate solution (4.2.9) and 2.5 mL of hydrazine

sulfate solution (4.2.10) to the volumetric flask; dilute to the mark with water; and mix well.

Heat in a boiling water bath for 10 min; then remove and allow to cool to room temperature.

4.5.3.4 Spectrophotometric determination

Set the spectrophotometer absorbance to zero using water as the reference. Perform

spectrophotometric measurement on the color-developed solution at a wavelength of

approximately 840 nm using a 4 cm (or 1 cm) absorption vessel.

4.5.4 Establishment of the calibration curve

4.5.4.1 Preparation of calibration solutions

For arsenic contents (mass fraction) of 0.0005% ~ 0.030% and 0.030% ~ 0.100%, add the

corresponding volumes of arsenic standard solution (4.2.13, 4.2.12) into a series of 50 mL one-

mark volumetric flasks, respectively, in accordance with Tables 2 and 3.Add 2.5 mL of sulfuric

acid (4.2.7) to each volumetric flask. Proceed as described in 4.5.3.3.

4.5.4.2 Spectrophotometric measurement

Set the spectrophotometer absorbance to zero using water as the reference. Perform

spectrophotometric measurements on the range of calibration solutions at a wavelength of

approximately 840 nm using 4 cm (or 1 cm) absorption vessel.

4.5.4.3 Plotting the calibration curve

Calculate the net absorbance by determining the difference between the calibration solution and

the calibration blank solution.

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This preview omits tables, figures, formulas and parts of the technical clauses. The complete document — 23 pages — is available in the English PDF.

Referenced standards

Normative references

GB/T 6379.1

Cited by

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