Dual Column Analysis of Organochlorine Pesticides Using SLB-5ms and SPB-608

By: Katherine Stenerson, Reporter EU Volume 22

Katherine Stenerson Senior Applications Chemist

Introduction

The analysis of low levels of organochlorine pesticides by US EPA Method 8081 demands the use of an electron capture detector (ECD), which is highly sensitive, and capable of detecting analytes at picogram levels. The highly sensitive nature of an ECD, in combination with the low detection limit requirements of Method 8081, make it necessary to use GC columns with low bleed for this application. In addition, the susceptibility of several analytes to degradation and adsorption make inertness another extremely important characteristic when choosing an analytical column.

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Dual Column Analysis

Method 8081 requires two analytical columns for the analysis of samples. The first, often referred to as the “primary” column, is used to determine, by retention time comparison with a standard, if any of the target analytes could be present in the sample. If peaks are found within an analyte’s retention time window on the primary column, the presence of the analyte must be “confirmed” on a secondary or “confirmation” column of different selectivity in order to be considered positive.

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Primary Column SLB-5ms

The SLB-5ms, developed for use in applications using a mass selective detector (MSD), is an excellent choice as a primary column for US EPA Method 8081. Its extremely low bleed character makes it compatible for use in low-level detection with an ECD. The proprietary surface deactivation of the SLB-5ms provides the inertness necessary for the analysis of compounds susceptible to degradation and adsorption, such as organochlorine pesticides. Figure 1 illustrates the analysis of twenty Method 8081 pesticides plus two surrogate compounds. Minimal baseline rise was detected, and the last analyte, decachlorobiphenyl, could be eluted in less than 20 minutes. These run conditions were chosen to reduce the analysis time, and a slower oven ramp rate can be used if increased resolution between endosulfan I and α-chlordane is desired. Endrin and 4,4’-DDT are susceptible to degradation, and must be monitored per Method 8081. On the SLB-5ms, these compounds exhibited good response.

Figure 1. Organochlorine Pesticides on SLB-5ms


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Confirmation Column SPB-608

The SPB™-608 is an excellent choice as a confirmation column for this method. This column was developed, and is tested, specifically for the analysis of organochlorine pesticides. Figure 2 illustrates the analysis of the same analytes in Figure 1, and under the same run conditions. Using these run conditions, between both columns all 22 analytes were resolved making this a suitable column set for this application.

Figure 2. Organochlorine Pesticides on the SPB-608


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Conclusion

The characteristics of the SLB-5ms, while making it compatible with MSD applications, also make it useful for applications requiring the use of other highly sensitive detectors, such as an ECD. For the dual column analysis of organochlorine pesticides, the SLB-5ms can be used in combination with the SPB-608 to provide separation and confirmation in the low level detection of these analytes.

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