Development of a stir-bar-sorptive extraction–liquid desorption–large-volume injection capillary gas chromatographic–mass spectrometric method for pyrethroid pesticides in water samples

Abstract

Stir-bar-sorptive extraction followed by liquid desorption and large-volume injection capillary gas chromatography with mass spectrometric detection (SBSE-LD-LVI-GC-MS), had been applied for the determination of ultra-traces of eight pyrethroid pesticides (acrinathrin, cypermethrin, deltamethrin, esfenvalerate, fenpropathrin, fenvalerate, and permethrin cis and trans isomers) in water samples. Instrumental calibration for selected-ion monitoring acquisition and conditions that could affect the SBSE-LD efficiency are fully discussed. By performing systematic assays on 30-mL water samples spiked at the 0.10 microg L(-1) level it was established that stir-bars coated with 47 microL polydimethylsiloxane, an equilibrium time of 60 min (750 rpm), 5% methanol as organic modifier, and acetonitrile as back-extraction solvent, provided the best analytical performance to monitor pyrethroid pesticides in water matrices. Good accuracy (81.8-105.0%) and remarkable reproducibility (<11.7%) were obtained, and the experimental recovery data were in good agreement with the theoretical equilibrium described by octanol-water partition coefficients (log K(O/W)), with the exception of acrinathrin for which lower yields were measured. Excellent linear dynamic ranges between 25 and 400 ng L(-1) (r2>0.994), low quantification (3.0-7.5 ng L(-1)) and detection (1.0-2.5 ng L(-1)) limits were also achieved for the eight pyrethroid pesticides studied. The method was successfully used for analysis of tap-water and groundwater matrices spiked at the 0.10 microg L(-1), revealing the suitability of the method for determination of pyrethroid pesticides in real samples. The method was shown be reliable and sensitive and a small volume of sample was required to monitor pyrethroids at ultra-trace levels, in compliance with international regulatory directives on water quality.

Optimisation of stir bar sorptive extraction and liquid desorption combined with large volume injection-gas chromatography–quadrupole mass spectrometry for the determination of volatile compounds in wines

“…1a). No longer times were evaluated, since several authors had point out that for periods higher than 60 min, no advantages were observed for volatile enrichment purposes [8,9]. Therefore, the extraction time of 60 min was set for further experiments.…”

“…In a preliminary study, different desorption solvents were tested for the back-extraction process, including MeOH and ACN, since they are the most used for LD of the semi-volatile compounds analysed by SBSE [6][7][8][9]. Nevertheless, this analytical approach needs a solvent switch step, i.e.…”

“…Thereby, by using this approach, it is also important to avoid fronting peaks and guarantee precision, excluding ACN as a suitable solvent for LVI in solvent-vent mode. In the first step, He flow rate at 150 mL min −1 was used, based on the experimental conditions reported for the analysis of semi-volatile compounds [6][7][8][9]. However, this condition was not considered acceptable since from the 10 compounds under study, only five, i.e.…”

“…In addition, TD does not offer the opportunity of reanalysis, which is an important issue in many studies for validation purposes. Alternatively, SBSE with liquid desorption (LD) has shown very interesting features to overcome these limitations and, besides being cost-effective, it has been successfully applied to the analysis of several classes of semi-volatile compounds in many types of matrices prior to GC-MS analysis [6][7][8][9]. Meanwhile, SBSE combined with LD as far as we know was never proposed for the enrichment of volatile compounds, which can be easily performed by trapping the analytes followed by removal through back-extraction with a small volume (typically microliters) of a convenient organic solvent.…”

“…0.5-2 L, of this extract is injected in the gas chromatograph for analysis. Although this approach works quite successfully, the sensitivity can be highly enhanced through the combination of LD with large volume injection (LVI) [6][7][8][9].…”