Sample throughput limitations for organochlorine pesticides analysis can delay reporting and create bottlenecks in the lab. However, the method described here improves efficiency and productivity by using a two-pronged approach. CarboPrep Plus SPE was used for a more effective sample extract cleanup that reduced inlet contamination and allowed more samples to be run before maintenance was required. In addition, a dual column setup was used with a GC Accelerator oven insert kit in order to speed up overall run times and allow simultaneous confirmation and quantification.<\/p>\n\n\n\n
In many areas of the world, chlorinated (organochlorine) pesticide use has been banned due to human health and environmental concerns, but these compounds are still widely monitored because of their persistence in the environment. Both soil and wastewater samples are routinely tested to verify the presence or absence of organochlorine pesticides and to assess the risk of exposure from historical contamination.<\/p>\n\n\n\n
Organochlorine pesticides analysis can be accomplished by GC using an electron capture detector (ECD) or a mass spectrometer (MS). However, analysis can be challenging because some of the target compounds breakdown when exposed to active sites in the hot inlet. These active sites are typically caused by nonvolatile sample matrix interferences that are coextracted and then injected along with the target analytes. Once deposited in the inlet and on the head of the analytical column, they foul the system and cause QC failures that lead to downtime for maintenance. SPE cleanup can remove some matrix components from sample extracts, but the Florisil material that is often used is limited in its ability to remove the high molecular weight contaminants that typically cause the problems.<\/p>\n\n\n\n
Here, we demonstrate a more effective and efficient approach for organochlorine pesticides analysis. First, Resprep CarboPrep Plus SPE cartridges were used for sample extract cleanup because the graphitized carbon material removes more high molecular weight contaminants than Florisil SPE while still following the same procedure. Second, a GC Accelerator oven insert kit was used along with an Rtx-CLPesticides and Rtx-CLPesticides2 column set for fast, simultaneous confirmation and quantification. Using this approach, labs can increase sample throughput both by removing the nonvolatile matrix compounds that cause QC failures and by speeding up overall analysis times.<\/p>\n\n\n\n
To extract the samples, 10 g of soil was weighted into 50 mL centrifuge tubes containing 5 grams of anhydrous magnesium sulfate. Then, 20 mL of acetone:methylene chloride (50:50) was added, and the samples were centrifuged at 3000 g for five minutes.<\/p>\n\n\n\n
Prior to analysis, matrix interferences were removed from the sample extracts using SPE cleanup. For this work, two cleanup options were compared: Resprep Florisil normal phase SPE cartridges (6 mL\/1 gm;\u00a0cat.# 28993) and Resprep CarboPrep Plus graphitized carbon SPE cartridges (3 mL\/95 mg;\u00a0cat.# 25845).<\/p>\n\n\n\n
CarboPrep Plus SPE cartridges are designed to use the same solvents and volumes as a standard Florisil cleanup, so the same procedure was employed for both SPE cartridge types (Figure 1). First, one cartridge volume of hexane:acetone (90:10) was added and held for five minutes to condition and equilibrate the beds. Then, using a 1 mL Class A pipette, 1 mL of sample extract was dispensed into each cartridge. The sample extract was loaded until the level matched the upper frit, and the eluent was collected dropwise into a 10 mL volumetric flask. Once the sample was completely loaded, it was immediately followed by the addition of 1 mL of hexane:acetone (90:10), which was also drawn down to the level of the top frit. Then, an additional 8 mL of solvent was added to the cartridges and eluted dropwise into the flask.<\/p>\n\n\n