Alachlor and atrazine show increasing percent recoveries in the first three extractions then in the last extraction, the recovery decreases. Perylene shows an increase in recovery between the first and second extraction followed by decreasing recoveries in the last two extractions. Trifluralin decreases slightly between the first and second extractions then jumps quite a bit in the third extraction. Because a constant pattern is not seen for all of the analytes, conclusions are difficult to make. It is possible that certain analytes are adhering better than other analytes resulting in an increase in recoveries for some analytes, but not for others.
More experimentation needs to be done before concrete conclusions can be made.
Problems were encountered when not all of the analytes were detected in the calibrations and when the internal standard was not detected in the samples. Because the calculations were based upon the ratio of internal standard to the analyte, percent recoveries could not be reported when the internal standard was not detected. In an attempt to remedy the situation, simple maintenance procedures were performed on the injection port into the GC such as changing the septum, cleaning the liner, and clipping off the top of the column. By the time the maintenance was complete and the samples were ready to be injected, the samples had partially evaporated which would result in higher percent recoveries due to the more concentrated sample. Thus, all samples were discarded.