Cleanup methods,pesticide recovery

Sample Cleanup. The recoveries from a quick cleanup method for waste solvents based on sample filtration through a Elorisd and sodium sulfate column are given in Table 2 (40). This method offers an alternative for analysts who need to confirm the presence or absence of pesticides or PCBs. 

TABLE 7.1 PERCENT PESTICIDE RECOVERY WITH VARIOUS CLEANUP METHODS 1 (9)... 

The analysis of pesticides in samples of high color content needs the optimization of cleanup parameters. Carrots, spinach, and apple extracts were extracted with acetone, partitioned into methylene chloride, and finally purified on a mixed adsorbent column (Table 1). The loadability of the TLC plates and the effectiveness of this cleanup method were tested not only by GLC but by TLC as well (23). TLC can be used as a detection method, as a test of the cleanup (see above), and furthermore can be applied as a cleanup procedure (16). In MCPA (4-chloro-2-methylphenoxyacetic acid) analysis the recovery data showed that TLC cleanup was as effective as H20-toluene partitioning. 

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

A variety of methods have been developed for sampling pesticides in air. Suitable procedures must deal with difficulties posed by the uncertainty regarding the physical state (aerosols, solid particles, vapors) of airborne residues, their relatively low concentrations (less than 1 mg/m, ca 80 ppb), fluctuations in pesticide concentrations and the levels of potential interferences with time, potential reactivity during the sampling process, and limited availability of sampling devices. These are in addition to the problems of cleanup, recovery, quantitation, and confirmation which are common to trace analytical processes once the sample has been collected and brought to the laboratory for determination. 

However, it was decided to keep the method simple and not to introduce any pH-adjustment in the extraction/partitioning step, since the base-sensitive pesticides tested gave acceptable recoveries when extrachon and injechon were performed fast, and since the recoveries of the basic peshcides were shown to be completely unaffected by pH. As to the protechon of base-sensitive peshcides following PSA cleanup, the addition of acehc acid to the hnal extracts was suggested in the original procedure. 

---