GB/T 17134-1997 Soil Quality Determination of Total Arsenic Silver Diethyldithiocarbamate Spectrophotometric Method
GB/T 17134-1997 is an important Chinese national standard method for the determination of total arsenic in soil quality, employing the silver diethyldithiocarbamate spectrophotometric method. This method is applicable to the determination of total arsenic content in various types of soil, featuring high sensitivity, simple operation, and low cost, and is widely used in environmental monitoring, agricultural soil surveys, and scientific research fields.
Method Principle
After soil samples are digested, 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 then reacts with zinc granules to generate arsine (AsH₃) gas. Arsine is absorbed by a solution of silver diethyldithiocarbamate (Ag-DDC) in triethanolamine-chloroform, forming a red complex, and the absorbance is measured at a wavelength of 530 nm to quantify arsenic content.
Reagents and Materials
- Nitric acid (guaranteed reagent grade)
- Sulfuric acid (guaranteed reagent grade)
- Perchloric acid (guaranteed reagent grade)
- Potassium iodide solution (15%)
- Stannous chloride solution (40%)
- Arsenic-free zinc granules (particle size 1-3 mm)
- Silver diethyldithiocarbamate-triethanolamine-chloroform absorption solution
- Arsenic standard solution (1.0 μg/mL)
- Lead acetate cotton
Instruments and Equipment
- Spectrophotometer (wavelength 530 nm)
- Arsine generation apparatus (including reaction flask, gas guide tube, absorption tube)
- Electric heating plate or digestion instrument
- Analytical balance (sensitivity 0.0001 g)
Analysis Procedure
- Sample digestion: Weigh 0.5 g (accurate to 0.0001 g) of air-dried soil sample into a digestion tube, add nitric acid-sulfuric acid-perchloric acid mixed acid, heat and digest until the solution is clear, remove acid, and make up to volume.
- Reduction reaction: Take an appropriate amount of digestion solution into an arsine generation flask, add potassium iodide solution and stannous chloride solution, shake well, and let stand for 15 minutes.
- Arsine generation and absorption: Add zinc granules, quickly connect the gas guide tube (containing lead acetate cotton) and absorption tube (containing 5 mL absorption solution), and react for 40 minutes.
- Photometric determination: Using reagent blank as reference, measure the absorbance of the absorption solution at 530 nm wavelength.
- Standard curve: Take 0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 μg of arsenic standard solution respectively, operate in the same way, and plot 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 × w_dm)
- m₁: arsenic amount of sample found from the standard curve (μg)
- m₀: blank arsenic amount (μg)
- V₁: constant volume of digestion solution (mL)
- V₂: volume taken for determination (mL)
- m: sample mass (g)
- w_dm: soil dry matter content (%)
Method Performance Parameters
| Parameter | Indicator |
|---|---|
| Detection limit | 0.5 mg/kg |
| Measurement range | 0.5～20 mg/kg |
| Precision (RSD) | ≤10% |
| Spike recovery | 90%～105% |
Precautions
- Arsenic-free zinc granules should be selected with uniform particle size and smooth surface to ensure consistent reaction rate.
- Lead acetate cotton should be replaced promptly to prevent interfering gases such as hydrogen sulfide from entering the absorption tube.
- Temperature should be strictly controlled during digestion to avoid arsenic volatilization loss.
- The absorption solution should be prepared fresh before use and stored away from light.
- Blank tests and spike recoveries should be performed simultaneously for each batch of samples to ensure accurate and reliable data.
Following the GB/T 17134-1997 standard method can effectively determine total arsenic content in soil, providing a scientific basis for soil environmental quality assessment and pollution control.