My colleague Linx Waclaski blogged about a tale of two columns that started with the introduction of a pair of stationary phases specifically tuned for the resolution of the 20 legacy pesticides found in US EPA Method 8081(1). The story examined the gains in speed over the years as measured by the last eluting compound decachlorobiphenyl (DCB). When choosing the right columns, conditions, and assisting with oven ramp rates, DCB elutes in under 6 minutes (2,3,4,5).
These fast run times allow more samples in less time which can put additional demands on the analytical system (i.e. more samples more contamination). Unfortunately, its far more likely labs will receive highly contaminated extracts rather than those rare clean samples we commonly see when analyzing drinking water. A standard cleanup procedure uses Florisil which is comprised of synthetic magnesium silicate (US EPA Method 3620C) and is an excellent option for removing polar contamination. High molecular weight and non-polar contamination can make it through the Florisil cartridge and ultimately cause instruments to fail their calibration checks, requiring maintenance.
Restek’s CarboPrep Plus SPE cartridge can be used in place of Florisil for extract clean up, since this carbon removes more matrix interferences that cause instrument calibration failures. This new product has been specifically designed to directly replace Florisil, using the same glassware, solvents and even elution solvent volumes. Other carbon material has variability in cleanliness and reproducibility and has not been specifically tested to assure elution of the common 20 chlorinated pesticides including the planar pesticides; for example, hexachlorobenzenes (EPA 8081). Our initial experiments using off-the-shelf carbon produced clean extracts with high background interferences, and low recoveries of planar compounds. Restek’s carbon is manufactured and treated under controlled conditions in an isolated room and packed in foil to assure low background and long-shelf life.
Visually there is a difference in the final color of the extracts after passing through each of the materials. Jason Thomas, who helped with the development and testing of this new product took these photographs illustrating the differences in extract color following cleanup. Figure 1 is the extract before any cleanup is performed. Running the soil extract through the Florisil leaves a colored extract, which will cause active sites in the GC inlet and column (figure 2). The soil extract eluted through Carboprep Plus is clear, indicating more of the matrix interferences have been removed (figure 3). The same extracted soil sample was passed through Florisil and Carboprep Plus and the analytical results are shown in figure 4. This material has potential advantages in a variety of other applications which we will be exploring in the future.
Figure 1: Soil extract with no cleanup. Dark color is typical of contamination.
Figure 2: Soil extract after cleanup using Florisil cartridge.
Figure 3: Soil extract after cleanup using CarboPrep Plus cartridge.
Figure 4: Comparison of extracts cleaned using CarboPrep Plus and Florisil. Cleaner extracts result in less contamination reaching the inlet and analytical column keeping the instrument running longer (click to enlarge).
Florisil® is a registered trademark of U.S. Silica Company