GB/T 17134-1997 Determination of Total Arsenic by Spectrophotometry

GB/T 17134-1997 Standard Overview

GB/T 17134-1997 is an important Chinese national standard method for the determination of total arsenic in soil quality. This standard uses the silver diethyldithiocarbamate spectrophotometric method, applicable to the laboratory determination of total arsenic content in various types of soil. This method has the characteristics of high sensitivity, good selectivity, and relatively simple operation, and is a classic analytical method widely used in environmental monitoring and soil pollution investigations.

For engineering technicians and procurement personnel, understanding the core points of this standard helps to correctly select reagents and instruments, and ensure the accuracy and compliance of test data.

Method Principle

After acid digestion of soil samples, the arsenic therein is converted to pentavalent arsenic. Under acidic conditions, potassium iodide and stannous chloride are used to reduce pentavalent arsenic to trivalent arsenic, which is then reduced by zinc granules to generate arsine (AsH₃) gas.

Arsine is absorbed in a silver diethyldithiocarbamate-triethanolamine-chloroform absorption solution, and reacts with silver ions to form red colloidal silver. The absorbance is measured at a wavelength of 530 nm, and the total arsenic content is calculated according to the standard curve.

Reagents and Materials

Main Reagents

• Nitric acid (guaranteed reagent): used for sample digestion.
• Sulfuric acid (guaranteed reagent): provides an acidic reaction environment.
• Potassium iodide: reducing agent, reduces pentavalent arsenic to trivalent arsenic.
• Stannous chloride: auxiliary reduction and interference suppression.
• Zinc granules: arsenic-free zinc granules, used to generate arsine.
• Silver diethyldithiocarbamate (Ag-DDC): color developer.
• Triethanolamine: stabilizes colloidal silver.
• Chloroform: solvent.

Standard Solutions

• Arsenic standard stock solution: accurately weigh arsenic trioxide to prepare.
• Arsenic standard working solution: dilute to the required concentration before use.

Instruments and Equipment

• Spectrophotometer: wavelength range covers 530 nm.
• Arsine generation apparatus: including reaction bottle, gas guide tube, and absorption tube.
• Analytical balance: readability 0.0001 g.
• Hot plate or digestion instrument: used for sample digestion.
• Volumetric flasks, pipettes and other conventional glassware.

Operating Procedures

1. Sample Pretreatment

1. Air-dry, grind, and sieve the soil sample (usually through a 100-mesh nylon sieve).
2. Accurately weigh 0.5~1.0 g of sample into a digestion bottle.
3. Add aqua regia or nitric acid-sulfuric acid mixed acid, heat and digest until the solution is clear.
4. After cooling, make up to volume, filter or let stand to take the supernatant.

2. Preparation of Standard Curve

1. Pipette 0, 1.0, 2.0, 4.0, 6.0, 8.0, 10.0 mL of arsenic standard working solution into arsine generation bottles respectively.
2. Add deionized water to a total volume of 50 mL.
3. Add sulfuric acid, potassium iodide, and stannous chloride in sequence, shake well, and let stand for 15 min.
4. Add zinc granules, quickly connect the absorption tube, which has been pre-filled with 5.0 mL of absorption solution.
5. After reaction for 45 min, remove the absorption tube, and measure the absorbance at 530 nm using the reagent blank as reference.
6. Plot the standard curve with arsenic content as the abscissa and absorbance as the ordinate.

3. Sample Determination

1. Pipette an appropriate amount of sample digestion solution into an arsine generation bottle.
2. Operate in the same way as the standard curve steps.
3. Measure the absorbance and find the arsenic content from the standard curve.

Result Calculation

The total arsenic content in soil (mg/kg) is calculated according to the following formula:

ω(As) = (m₁ - m₀) × V₁ / (V₂ × m)

• m₁: mass of arsenic in the sample found from the standard curve (μg).
• m₀: mass of arsenic in the blank (μg).
• V₁: volume of digestion solution made up to (mL).
• V₂: volume taken for determination (mL).
• m: mass of soil sample weighed (g).

Precautions

• Interference elimination: elements such as antimony and bismuth may interfere with the determination, which can be eliminated by controlling acidity or adding masking agents.
• Zinc granule quality: arsenic-free zinc granules must be used, with uniform particle size, to ensure consistent arsine generation rate.
• Reaction time: strictly control the reaction time and temperature to avoid arsine loss or incomplete absorption.
• Stability of absorption solution: after color development, the determination should be completed within 1 hour to avoid a decrease in absorbance due to aggregation of colloidal silver.
• Safety protection: arsine is highly toxic, all operations should be carried out in a fume hood.

Method Characteristics and Applicability

For procurement personnel, it is recommended to select reagents and instruments that meet the requirements of GB/T 17134-1997 to ensure the comparability and legal validity of test results.