Applications

(GB/T 5750.9-2006 1 Standard inspection method for drinking water-Pesticide indicators- Gas Chromatography)

1 Overview of methods

Extract various isomers of DDT and BHC from water using cyclohexane, concentrate them, and separate and determine them using a gas chromatograph with an electron capture detector.

2 Scope of application

This method is suitable for the determination of various isomers of BHC and DDT (α-666, γ-666, β-666, δ-666, p.p’- DDE, o.p’-DDT, p.p’- DDD, p.p’-DDT) determination.

3 Reference basis

This method is based on the national standard GB/T 5750.9-2006 1 Standard Test Methods for Drinking Water – Pesticide Indicators – Gas Chromatography.

4 Instruments and reagents

4.1 Instruments and equipment

4.1.1 Testing instruments

4.1.2 Pre-treatment equipment

4.2 Reagents

4.2.1 Reagents

4.2.2 Preparation of reagents

4.3 Standard products

4.3.1 Stock solution

5 Operation process

5.1 Sample processing

5.1.1 Preparation of test solution

5.1.2 Preparation of standard solution

1. 666, DDT standard stock solution: 100μg/mL.
2. 666, DDT standard intermediate solution (10 μg/mL): Accurately draw 100 μL of standard stock solution in a 1mL volumetric flask, dilute to volume with cyclohexane and shake well. Prepare when needed.
3. 666, DDT standard working solution 1~5: accurately draw 5μL, 10μL, 20μL, 40μL, and 50μL in a 1mL volumetric flask, dilute with cyclohexane and make it to volume. The concentration of the standard working solutions becomes 0.05μg/mL, 0.1μg/mL, 0.2μg/mL, 0.4μg/mL, and 0.5μg/mL. These standard working solutions are prepared for temporary use.

5.2 Sample testing

1) Testing conditions

2) Sample testing

Take 500mL of water sample and place it in a 1000mL separating funnel. Add 70mL of cyclohexane or petroleum ether and extract it three times (30mL, 20mL, 20mL). Shake thoroughly for 3 minutes each time, let it stand for layering, combine the cyclohexane extraction solution, dehydrate it with anhydrous sodium sulfate, and concentrate it to 1mL for measurement.

5.3 Result Calculation

ρ(B)=                         (1)

In the formula:

ρ(B)—The mass concentration of each monomer DDT or various isomers of BHC in the water sample, in micrograms

per liter (ug/L);

ρ₁ —The mass concentration equivalent to the standard curve, in micrograms per milliliter (ug/mL);

—The total volume of the extraction solution, in milliliters (mL) ;

V —The volume of the water sample, in milliliters (mL).

6 Appendix (applicable to method validation, etc.)

6.1 Detection limit

This method has a detection limit of 0.02 μg/L for each isomer of DDT when the sampling volume of drinking water is 500 mL, and each isomer of 666 is 0.01μg/L.

6.2 Precision

6.3 Accuracy

6.4 Linear range

The linear range of this method is 0.05mg/L~0.5mg/L.

6.5 Other