A Practical Method for Trace Level Analysis of Chlorinated Organic Pesticides by Gas Chromatography–Mass Spectrometry

Apr 01, 2012

This article discusses a practical and reliable gas chromatographic procedure that has been successfully developed for the direct measurement of trace levels of lindane, aldrin, heptachlor epoxide, dieldrin, o,p-DDD, and dichlorodiphenyltrichloroethane (DDT). With appropriate sample preparation, this analytical technique can be applied to matrices such as soil, consumer products, fruits, and vegetables.



Chlorinated organic pesticides are chemical substances that are widely used against household, garden, and plant pest diseases. The use of pesticides, however, demands great care and control as they can enter the environment and have a negative impact on human health. For instance, lindane is a persistent organic pollutant with a relatively long life in the environment, it is transported long distances by natural processes like global distillation, and can bioaccumulate in food chains. Dieldrin and aldrin are chemicals that were widely applied in agricultural areas throughout Canada and the world. Both chemicals are toxic and bioaccumulative. Aldrin does break down to dieldrin in living systems, but dieldrin is known to resist bacterial and chemical breakdown processes in the environment. Heptachlor epoxide is another commonly employed insecticide and is a well known persistent organic pollutant (POP). Dichlorodiphenyltrichloroethane (DDT) is one of the most well publicized synthetic insecticides, with a unique and controversial history especially with birds.

The topic of analyzing ultratrace levels of chlorinated pesticides has been reported by researchers with many references in the open literature (1–5). Developed techniques include the incorporation of sample enrichment devices such as headspace, purge-and-trap, solid-phase extraction (SPE), solid-phase microextraction (SPME), and stir-bar sorptive enrichment with selective detection like electron capture or electrolytic conductivity detection, as well as with the employment of mass spectrometry (MS) (5–10). One of the issues commonly reported by researchers is the decomposition and irreversible adsorption of the organopesticides in the solute path from inlet liner to the column used and even inside the detectors, especially with mass spectrometers (5–15). Recently, highly inert quartz wool–filled liners (14), column technologies, and mass spectrometers have been innovated and commercialized. Highly inert equipment has been incorporated in developing a practical and reliable gas chromatography–mass spectrometry (GC–MS) method for the characterization of trace levels of chlorinated organic pesticides, such as lindane (CAS-58-89-9), aldrin (CAS-309-00-2), heptachlor epoxide (CAS-1024-57-3), dieldrin (CAS60-57-1), o,p-DDD (CAS-53-19-10), and dichlorodiphenyltrichloroethane (DDT) (CAS-50-29-3). This article summarizes the results obtained.

Experimental

Two Agilent 7890 gas chromatographs (Agilent Technologies) were used for the development of this analytical technique:

The first gas chromatograph was equipped with an Agilent G-4513A autosampler and an Agilent G-4514A tray, as well as a multimode inlet, a split–splitless inlet, and a flame ionization detector. A 30 m × 0.25 mm, 0.25-μm d f DB-5ms Ultra-inert (Agilent Technologies) capillary column was used for all analyses. An Ultra-Inert split inlet liner from Agilent also was used.

The second gas chromatograph was equipped with an Agilent G-4512A autosampler, an Agilent split–splitless inlet, and an Agilent 5975B Inert mass selective detector. A 30 m × 0.25 mm, 0.25-μm d f DB-5ms Ultra-Inert (Agilent Technologies) capillary column was used for all analyses. An Ultra-Inert split inlet liner from Agilent also was used.


Table I: Gas chromatographic conditions for the analysis of chlorinated organic pesticides
Chromatographic data were collected using Agilent ChemStation B.03.01 Service Pack 1 and Agilent ChemStation G-1720A Mass Selective Detector software. Instrument operating conditions are reported in Table I.

Chemicals used for testing were all obtained from Polyscience Inc. Cyclohexane was obtained from JT Baker. The limit of detection for the solutes of interest was calculated based on a signal-to-noise ratio of 3:1.