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Applications

Determination of 666 and DDT in drinking water

(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

 

Serial number Name Quantity Technical requirement Accessory
1 gas chromatography 1 Instrument model: Agilent 7890B Electron capture detector

(ECD)

2 chromatographic column 1 DB-1701 Quartz Capillary Column (30m

×0.25mm×0.25μm)

 
3 high purity nitrogen 1 >99.999%  

 

4.1.2 Pre-treatment equipment

Serial number Name Quantity Technical requirement Accessory
1 Rotary evaporator/RE-2000B 1 Speed: 0-200rpm; Temperature: Room

Temperature~99 ℃

Equipped with a standard port collection

Bottle (500ml)

2 Vacuum pump/SHZ-iii 1 Maximum vacuum degree 0.09Mpa  
3 Low-temperature thermostat/YRDC 1 Temperature range -5 to 100 ℃ Pump flow rate 8L/min
4 analytical balance 1 Sensitivity: 0.0001g  

4.2 Reagents

4.2.1 Reagents

 

Serial number Name Quantity Technical requirement Accessory
1 cyclohexane 1 HPLC  
2 Anhydrous sodium sulfate 1 analytical grade  

 

4.2.2 Preparation of reagents

 

Serial number Name Preparation method Remarks
1

 

4.3 Standard products

4.3.1 Stock solution

 

Number Serial number Name Technical requirement Remarks
1 YJLHH(L)20200617-1 ~2 666, DDT standard solution 100μg/mL  
   

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

Injector temperature 260℃
Split flow mode Split flow, split ratio 10:1
Injection volume 1μL
Column oven Maintain 210 ℃ for 30 minutes
Detector temperature 260℃
Column flow 1mL/min
Makeup airflow 40 mL/min
Carrier gas High purity nitrogen

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

Test items Serial number 1 2 3 4 5 6 7
 

α-666

Spike concentration (μg/L) 25
Actual value (μg/L) 24.8 25.4 25.2 25.1 26.0 25.6 25.5
RSD(%) 1.19
 

γ-666

Spike concentration (μg/L) 25
Actual value (μg/L) 26.0 26.1 26.0 26.1 26.2 26.8 26.0
RSD(%) 1.1
 

β-666

Spike concentration (μg/L) 25
Actual value (μg/L) 25.5 24.5 27.2 27.4 27.9 27.8 28.0
RSD(%) 5.54
 

δ-666

Spike concentration (μg/L) 25
Actual value (μg/L) 25.5 25.2 26.5 27.1 26.9 25.0 25.0
RSD(%) 4.26
 

p.p’- DDE

Spike concentration (μg/L) 50
Actual value (μg/L) 46.3 48.0 46.0 46.0 45.8 45.0 46.1
RSD(%) 1.95
 

o.p’-DDT

Spike concentration (μg/L) 50
Actual value (μg/L) 46.2 48.0 44.8 48.3 48.1 48.0 49.0
RSD(%) 3.11
 

p.p’- DDD

Spike concentration (μg/L) 50
Actual value (μg/L) 45.5 46.8 45.3 45.6 46.0 46.2 49.1
RSD(%) 2.86
 

p.p’-DDT

Spike concentration (μg/L) 50
Actual value (μg/L) 47.0 47.6 45.7 47.2 47.4 46.5 46.5
RSD(%) 1.38

 

 

 

6.3 Accuracy

Testing items Added concentration (mg/L) Added concentration (mg/L) Average recovery rate

(%)

 

α-666

0.05 100.2 97.8 100.3 99.4
0.1 91.5 93.3 89.5 91.4
0.5 91.3 90.7 88.4 90.1
 

γ-666

0.05 99.95 97.9 101.7 99.85
0.1 92.3 93.7 90.2 92.1
0.5 93.6 93.6 90.7 92.6
 

β-666

0.05 102.4 100.9 105.8 103.0
0.1 93.0 95.0 91.5 93.2
0.5 95.3 95.5 93.2 94.7
 

δ-666

0.05 97.0 96.1 99.0 97.4
0.1 92.0 91.1 92.4 91.8
0.5 94.5 94.9 91.6 93.7
 

p.p’- DDE

0.05 100.8 98.7 102.9 100.8
0.1 92.3 93.7 91.7 92.6
0.5 95.0 95.5 92.5 94.3
 

o.p’-DDT

0.05 96.1 95.9 100.3 97.4
0.1 89.7 92.2 89.2 90.4
0.5 94.8 95.9 93.0 95.6
 

p.p’- DDD

0.05 100.2 100.3 104.2 101.6
0.1 91.3 94.4 91.0 92.2
0.5 94.6 95.7 92.8 94.4
 

p.p’-DDT

0.05 98.3 94.4 99.7 97.5
0.1 92.8 92.6 90.3 91.9
0.5 96.2 96.2 93.3 95.2

6.4 Linear range

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

6.5 Other

 

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