Determination of 23 Organochlorine Pesticides in Ambient Air by Wayeal Gas Chromatography

Organochlorine pesticides are a class of synthetic persistent organic pollutants that have been extensively used as broad-spectrum insecticides. These pesticides are extremely stable in chemical properties and difficult to degrade, and can persist in the environment for long periods. They can enter ambient air through atmospheric transport, dry and wet deposition, and other processes, posing a long-term threat to ecosystems and human health.

This article refers to the standard "Ambient Air — Determination of Organochlorine Pesticides — Gas Chromatography" (HJ 901-2017) and employs the Wayeal GC6100 gas chromatograph equipped with an ECD detector for the determination of 23 organochlorine pesticides in ambient air.

Keywords: Organochlorine pesticides; Gas chromatography; ECD detector; Ambient air.

1. Instrument Configuration

1.1 Instrument Configuration

Table 1 Configuration List of Gas Chromatograph

1.2 Experimental Materials and Auxiliary Equipment

23 organochlorine standard stock solution (1000μg/mL): commercially purchased certified standard solution, stored sealed and protected from light under refrigeration below 4 °C.

Surrogate standard stock solution (1000μg/mL): commercially purchased certified standard solution, containing a mixture of 2,4,5,6-tetrachloro-m-xylene (TCX) and decachlorobiphenyl (DCBP), stored sealed and protected from light under refrigeration below 4 °C.

Internal standard stock solution (5000μg/mL): commercially purchased certified standard solution, containing 1-bromo-2-nitrobenzene (BNB), stored sealed and protected from light under refrigeration below 4 °C.

n-Hexane: pesticide residue grade

Carrier gas: high-purity nitrogen.

1.3 Test Conditions

Chromatographic column: quartz capillary column, stationary phase of 14% cyanopropylphenyl–86% methylpolysiloxane, dimensions 30 m × 0.32mm × 0.25μm.

1.4 Solution Preparation

1.4.1 Internal Standard Intermediate Solution (100μg/mL):

Pipette 1.0mL of the internal standard stock solution (5000μg/mL) into a 50mL volumetric flask, dilute to volume with n-hexane, and mix thoroughly.

1.4.2 Internal Standard Working Solution (10μg/mL)

Pipette 1.0mL of the internal standard intermediate solution (100μg/mL) into a 10mL volumetric flask, dilute to volume with n-hexane, and mix thoroughly.

1.4.3 Surrogate Intermediate Solution (50μg/mL):

Pipette 0.5mL of the surrogate standard stock solution (1000μg/mL) into a 10mL volumetric flask, dilute to volume with n-hexane, and mix thoroughly.

1.4.4 Surrogate Working Solution (1μg/mL):

Pipette 1.0 mL of the surrogate intermediate solution (50 μg/mL) into a 50 mL volumetric flask, dilute to volume with n-hexane, and mix thoroughly.

1.4.5 23-Component Organochlorine Standard Intermediate Solution (40μg/mL):

Pipette 1.0mL of the 23-component organochlorine standard stock solution (1000μg/mL) into a 25mL volumetric flask, dilute to volume with n-hexane, and mix thoroughly.

1.4.6 23-Component Organochlorine Standard Working Solution (1μg/mL):

Pipette 250μL of the standard intermediate solution (40μg/mL) and 200μL of the surrogate intermediate solution (50μg/mL) into a 10mL volumetric flask, dilute to volume with n-hexane, and mix thoroughly.

1.4.7 Linear Calibration Standard Working Solutions

Pipette appropriate amounts of the 23-component organochlorine standard working solution (1μg/mL) and dilute with n-hexane to prepare a calibration standard series at concentrations of 20μg/L, 50μg/L, 100μg/L, 200μg/L, and 300μg/L. Quantification is performed by the internal standard method, with 10.0μL of the internal standard working solution (10μg/mL) added to every 1.0mL of standard solution.

2. Result and Discussion

2.1 Qualitative Test of Standard Samples

Fig 1 Chromatogram of the 23-organochlorine Pesticide Standard Solution (300μg/L)

(Elution order: 1: BNB (internal standard), 2: TCX (surrogate), 3: hexachlorobenzene, 4: α-HCH, 5: γ-HCH, 6: heptachlor, 7: aldrin, 8: β-HCH, 9: δ-HCH, 10: heptachlor epoxide, 11: endosulfan I, 12: γ-chlordane, 13: α-chlordane, 14: 4,4'-DDE, 15: dieldrin, 16: endrin, 17: 2,4'-DDT, 18: 2,4'-DDD, 19: endosulfan II, 20: 4,4'-DDT, 21: endrin aldehyde, 22: mirex, 23: methoxychlor, 24: endosulfan sulfate, 25: endrin ketone, 26: decachlorobiphenyl (surrogate).)

Table 2 Chromatographic Parameters of the 23-Organochlorine Pesticide Standard Solution (300μg/L)

Note: As can be seen from the above chromatogram, the resolution between the chromatographic peaks of all substances in the standard solution is greater than 1.0, which meets the requirements of experimental analysis.

2.2 Linearity

Fig 2 Calibration Curves and Correlation Coefficients of the 23 Organochlorine Pesticides

Note: The linearity of each component in the 23-organochlorine pesticide standard solution is good, with linear correlation coefficients > 0.999, which is higher than the standard requirement (linear correlation coefficient≥0.995) and meets the requirements of experimental analysis.

2.3 Precision

Fig 3 Chromatogram of the 23-organochlorine Pesticide Standard Solution (low concentration, 20μg/L)

Fig 4 Chromatogram of the 23-organochlorine Pesticide Standard Solution (medium concentration, 100μg/L)

Fig 5 Chromatogram of the 23-organochlorine Pesticide Standard Solution (high concentration, 300μg/L)

Table 3 Chromatographic Parameters for Precision

Note: The 23-organochlorine pesticide standard solutions at the lowest, middle, and highest concentration points of the calibration curve were each determined in 5 replicate measurements. Their relative standard deviations (RSDs) were 0.8–2.2%, 0.7–1.6%, and 0.4–1.6%, respectively. The RSDs of the chromatographic peaks for all substances meet the standard requirements.

2.4 Limit of Detection

Fig 6 Chromatogram of the Detection Limit Solution (10μg/L)

Table 4 Method Detection Limits and Lower Limits of Determination for Each Component of the 23 Organochlorine Pesticides

The 23-organochlorine pesticide standard solution (10μg/L) was determined in 8 replicate measurements. Calculations showed that, with a sampling volume of 350m³ and a concentration volume of 1.0mL, the method detection limits for the 23 organochlorine pesticides were in the range of 0.0003ng/m³ to 0.0025ng/m³, and the lower limits of determination were in the range of 0.0012ng/m³ to 0.010ng/m³, which comply with the standard requirements.

3. Conclusion

This method uses the Wayee GC6100 gas chromatograph equipped with an ECD detector for the determination of 23 organochlorine pesticides in ambient air. The experimental results show that the resolution between the chromatographic peaks of all organochlorine pesticides is greater than 1.0, which meets the requirements of experimental analysis. The linearity of each component in the 23-organochlorine pesticide standard solution is good, with linear correlation coefficients > 0.999, which is higher than the standard requirement (linear correlation coefficient ≥ 0.995). The precision test results, as well as the method detection limits and lower limits of determination, all meet the standard requirements. Therefore, this method can be adopted for the determination of 23 organochlorine pesticides in ambient air.