Standard Overview and Scope of Application
GB/T 22105.1-2008 is an authoritative method standard for the determination of total arsenic in soil quality testing, using atomic fluorescence spectrometry for quantitative analysis. This standard is applicable to the determination of arsenic content in various soil samples, with low detection limit and high sensitivity, and is a common method for environmental monitoring and agricultural geological surveys.
The standard is divided into three parts, and this part is specifically for the determination of total arsenic. Compared with traditional spectrophotometry, atomic fluorescence spectrometry has a lower detection limit and fewer interferences, making it suitable for rapid analysis of large batches of soil samples.
Method Principle
After soil samples are digested with aqua regia, the arsenic in them is converted to pentavalent arsenic. In an acidic medium, thiourea-ascorbic acid is added to reduce pentavalent arsenic to trivalent arsenic, which then reacts with potassium borohydride to generate arsine gas.
The arsine is carried by the carrier gas into the atomizer, where ground-state arsenic atoms are formed in an argon-hydrogen flame. Excited by an arsenic hollow cathode lamp, the arsenic atoms produce atomic fluorescence, and the fluorescence intensity is proportional to the arsenic content, based on which quantitative determination is performed.
Reagents and Instruments
Main Reagents
- Aqua regia: a mixture of hydrochloric acid and nitric acid in a 3:1 ratio
- Thiourea-ascorbic acid mixed solution: reducing agent, prepared fresh before use
- Potassium borohydride solution: reducing agent, must be prepared fresh
- Arsenic standard solution: used for preparing the calibration curve
Instruments and Equipment
- Atomic fluorescence spectrometer: equipped with an arsenic hollow cathode lamp
- Electric hot plate or microwave digestion instrument: used for sample digestion
- Analytical balance: precision 0.0001 g
Analysis Procedure
- Sample digestion: Weigh 0.2-0.5 g of air-dried soil sample, add aqua regia, heat and digest to near dryness, cool, and then make up to volume.
- Reduction treatment: Take an appropriate amount of the digestion solution, add thiourea-ascorbic acid mixed solution, and let stand at room temperature for 30 minutes.
- Calibration curve preparation: Prepare a series of arsenic standard solutions and measure the fluorescence intensity under the same conditions.
- Sample determination: Introduce the treated sample solution into the atomic fluorescence spectrometer and record the fluorescence intensity.
- Result calculation: Calculate the arsenic content according to the calibration curve, expressed in mg/kg.
Key Parameters and Conditions
| Parameter | Recommended Condition |
|---|---|
| Negative high voltage | 300-350 V |
| Lamp current | 60-80 mA |
| Carrier gas flow rate | 300-400 mL/min |
| Atomizer temperature | 200-300°C |
| Potassium borohydride concentration | 1.0-2.0% |
Interferences and Elimination
Common metal ions in soil may interfere with the determination of arsenic. The addition of thiourea-ascorbic acid can effectively eliminate interference from elements such as copper and nickel. For high-content samples, appropriate dilution is required before determination.
Note: During the digestion process, avoid excessively high temperatures that may cause volatilization loss of arsenic; it is recommended to control the temperature below 150°C. At the same time, the potassium borohydride solution must be prepared fresh before use to avoid failure.
Result Calculation and Quality Control
The arsenic content is calculated according to the formula: ω(As) = (ρ × V) / (m × 1000), where ρ is the concentration obtained from the calibration curve (μg/L), V is the final volume (mL), and m is the sample mass (g).
For each batch of samples, blank tests and spike recoveries should be performed, with recovery rates controlled between 90% and 110%. The correlation coefficient of the calibration curve should be ≥ 0.999.
Precautions
- All glassware must be soaked in nitric acid overnight to avoid contamination
- Digestion should be carried out in a fume hood to prevent acid mist hazards
- The arsenic standard solution must be stored refrigerated to avoid concentration changes
- The instrument must be preheated and stabilized before measurement
This standard provides a standardized operating procedure for the determination of total arsenic in soil. Engineering technicians and procurement personnel can select suitable instruments and reagents according to this standard to ensure the accuracy and reliability of test results.