Overview of GB/T 14550-93 Standard
GB/T 14550-93 is a Chinese national standard that specifies the gas chromatographic method for the determination of BHC and DDT residues in soil. This standard is applicable to agricultural soil, environmental monitoring, and scientific research, providing a technical basis for the assessment of organochlorine pesticide contamination.
The standard employs gas chromatography, which features high separation efficiency, good sensitivity, and accurate qualitative and quantitative analysis. Engineering technicians and procurement personnel can select instruments, reagents, and standardize operations based on this standard.
Method Principle
After organic solvent extraction and cleanup, BHC and DDT in soil samples are detected using a gas chromatograph equipped with an electron capture detector (ECD). Qualitative analysis is based on retention time, and quantification is performed using the external standard method with peak area or peak height.
The electron capture detector exhibits extremely high response to halogenated compounds, making it suitable for trace analysis of organochlorine pesticides. The minimum detection limit of this method can reach the ng/g level.
Reagents and Materials
Main Reagents
- Acetone: analytical grade, redistilled.
- n-Hexane: analytical grade, redistilled.
- Petroleum ether: analytical grade, redistilled.
- Concentrated sulfuric acid: guaranteed reagent grade.
- Anhydrous sodium sulfate: analytical grade, ignited at 300°C for 4 hours before use.
- BHC and DDT standard solution: commercially available or self-prepared.
Instruments and Equipment
- Gas chromatograph: equipped with an electron capture detector (ECD).
- Chromatographic column: glass column packed with diatomaceous earth coated with a mixed stationary phase of OV-17 and QF-1.
- Rotary evaporator, shaker, centrifuge, etc.
Analysis Procedure
Sample Extraction
- Weigh 20 g of air-dried soil sample (passed through a 60-mesh sieve) and place it into a stoppered Erlenmeyer flask.
- Add 80 mL of petroleum ether-acetone (1:1) mixed solvent and extract by shaking for 30 minutes.
- Allow to stand for layer separation, and filter the supernatant through an anhydrous sodium sulfate funnel into a rotary evaporation flask.
- Extract the residue again with 40 mL of the mixed solvent, and combine the extracts.
- Rotary evaporate to near dryness in a 40°C water bath, and dilute to 5 mL with n-hexane.
Cleanup
- Transfer the extract to a 10 mL centrifuge tube, add 1 mL of concentrated sulfuric acid, and shake thoroughly for 1 minute.
- Centrifuge for 5 minutes (3000 r/min) and take the supernatant.
- Repeat the sulfuric acid cleanup once until the sulfuric acid layer is colorless.
- Wash the supernatant twice with 2% sodium sulfate solution, and dehydrate the organic phase with anhydrous sodium sulfate.
- Concentrate to 1 mL under nitrogen blowdown for analysis.
Gas Chromatographic Conditions
| Parameter | Setting |
|---|---|
| Chromatographic column | Glass column (2 m × 3 mm), stationary phase OV-17 + QF-1 |
| Column temperature | 180°C |
| Inlet temperature | 220°C |
| Detector temperature | 250°C |
| Carrier gas | High-purity nitrogen, flow rate 60 mL/min |
| Injection volume | 1 μL |
Determination
- After the instrument baseline is stable, inject the standard solution and sample solution sequentially.
- Record the retention times and peak areas of BHC (α, β, γ, δ isomers) and DDT (p,p'-DDE, p,p'-DDD, o,p'-DDT, p,p'-DDT).
- Calculate the concentration of each component in the sample based on the standard curve.
Result Calculation
The residue of BHC or DDT in soil is calculated according to the following formula:
W = (C × V) / (m × f)
- W: pesticide residue in the sample, mg/kg.
- C: concentration obtained from the standard curve, μg/mL.
- V: final volume, mL.
- m: mass of soil sample, g.
- f: recovery correction factor.
Precautions
- All organic solvents must be redistilled to avoid interfering peaks.
- During concentrated sulfuric acid cleanup, thorough shaking is required to prevent emulsification.
- The chromatographic column must be aged before use to ensure baseline stability.
- Standard solutions and samples should be determined on the same day to reduce errors.
- Operators must wear protective equipment to avoid contact with toxic reagents.
Download the Full Standard
To view the complete standard text, you may download the following PDF file: