Spectrophotometric determination of some pesticides in water samples after preconcentration with Saccharomyces cerevisiae immobilized on sepiolite.

A sensitive and selective method for the preconcentration and determination of carbaryl, chlorpyrifos, linuron, and thiram was developed. The column sorption method was used for the preconcentration studies. Several parameters, such as amount of sorbent, pH, flow rate, volume of elution solution, and interferences, that can influence the retention of pesticides on Saccharomyces cerevisiae immobilized on sepiolite were investigated. Results showed that it was possible to achieve quantitative analysis when the sample pH was in the range 4-6 for carbaryl and thiram, 4-8 for linuron and 6 for chlorpyrifos using 100 mL of sample solution containing 20 microg of pesticide and 5 mL of eluent. Recoveries of carbaryl, chlorpyrifos, linuron, and thiram were 93.2 +/- 0.4%, 97.1 -/+ 0.3%, 98.5 +/- 0.4%, and 96.1 +/- 0.2%, respectively, at 95% confidence level under optimum conditions. The capacity of the sorbent was found to be 41, 28, 35, and 46 mg g(-1) for carbaryl, chlorpyrifos, linuron, and thiram, respectively. Saccharomyces cerevisiae immobilized on sepiolite is suitable for repeated use without loss of capacity up to twenty five cycles. The pesticides studied have been determined in river water with high precision and accuracy.