Coupling stir bar sorptive extraction-dispersive liquid-liquid microextraction for preconcentration of triazole pesticides from aqueous samples followed by GC-FID and GC-MS determinations

Stir bar sorptive extraction (SBSE) combined with dispersive liquid liquid microextraction (DLLME) has been developed as a new approach for the extraction of six triazole pesticides (penconazole, hexaconazole, diniconazole, tebuconazole, triticonazole and difenconazole) in aqueous samples prior to GC-flame ionization detection (GC-FID). A series of parameters that affect the performance of both steps were thoroughly investigated. Under optimized conditions, aqueous sample was stirred using a stir bar coated with octadecylsilane (ODS) and then target compounds on the sorbent (stir bar) were desorbed with methanol. The extract was mixed with 25 mu L of 1,1,2,2-tetrachloroethane and the mixture was rapidly injected into sodium chloride solution 30% w/v. After centrifugation, an aliquot of the settled organic phase was analyzed by GC-FID. The methodology showed broad linear ranges for the six triazole pesticides studied, with correlation coefficients higher than 0.993, lower LODs and LOQs between 0.53-24.0 and 1.08-80.0 ng/mL, respectively, and suitable precision (RSD < 5.2%). Moreover, the developed methodology was applied for the determination of target analytes in several samples, including tap, river and well waters, wastewater (before and after purification), and grape and apple juices. Also, the presented SBSE-DLLME procedure followed by GC-MS determination was performed on purified wastewater. Penconazole, hexaconazole and diniconazole were detected in the purified wastewater that confirmed the obtained results by GC-FID determination. In short, by coupling SBSE with DLLME, advantages of two methods are combined to enhance the selectivity and sensitivity of the method. This method showed higher enrichment factors (282-1792) when compared with conventional methods of sample preparation to screen pesticides in aqueous samples.