Potential passive empore C18 disk extraction for analysis of water samples containing fine particulates

Although the conventional methodology works well for extracting and concentrating organic chemicals from clean water, actual water samples taken in the field are often more difficult to filter because they contain fine particulates that clog the pores in the filter disk. A possible way to reduce the time necessary for extraction of these types of samples would be to passively extract the sample by shaking the water and disk together rather than filtering the water through the disk. If satisfactory recovery results can be obtained, then the problem of having the disks clogged with the fine particulates can be avoided. This approach has been tried by Reagan and Vo (1994) using a 90 mm Empore Disk and EPA Method 608 pesticides. They emphasized that process variables for their procedure had not been optimized, but average recoveries were within 75-80% of recoveries using liquid-liquid extraction procedures. Since our laboratory commonly encounters water samples that are difficult to filter, we investigated using Empore disks to passively extract nine pesticides from water. We particularly wanted to investigate the effect on extraction efficiency of different shaking speeds, different shaking times, and different disk areas and the relative importance of these variables.