In-line sequential injection-based hollow-fiber sorptive microextraction as a front-end to gas chromatography-mass spectrometry: A novel fully automatic sample processing technique for residue analysis

摘要

A novel and affordable analytical setup is herein reported for automatic flow-through sorptive microextraction of organic contaminants, exploiting polydimethylsiloxane (PDMS) as a front-end to gas chromatography-ion trap-tandem mass spectrometry. The analytical procedure involves a short single-strand PDMS hollow fiber integrated in a sequential injection (SI) network for automatic fluidic handling by programmable flow. The target species are in-line extracted from 10 mL of sample containing 20 % (v/v) methanol followed by elution with a metered volume of organic solvent, which is whereupon quantitatively transferred into the programmed temperature vaporization (PTV) injector of the GC. Diffusional resistance to mass transfer was overcome by effecting the overall concentration and stripping steps at a single PDMS tubing interface. The proof of concept of the novel hyphenated system was demonstrated for extraction and determination of organochlorine pesticides (OCPs), namely, heptachlor, dieldrin, endrin, endosulfan, p,p′-dichlorodiphenyldichloroethane, p,p′-dichlorodiphenyltrichloroethane, dichlorodiphenyldichloroethylene, and endrin ketone, taken as model analytes, in environmental and industrial waters. Four organic solvents with a broad spectrum of polarity were investigated as eluents in the SI-based assembly, namely, ethyl acetate, methyl tert-butyl ether, hexane, and chloroform. Chloroform was proven the most suitable solvent for expedient elution and fast evaporation in the PTV injector. Under the selected experimental variables, limits of detection (signal-to-noise ratio (S/N) = 3) within the range of 0.3-1.1 ng L~(-1), limits of quantification (S/N = 10) of 1.0-3.6 ng L~(-1), and method repeatabilities spanning from 1.7 to 4.7 % were obtained for the suite of OCPs. The hyphenated flow analyzer was harnessed to the analysis of samples of varying matrix complexity with good relative recoveries (86-112 %) in drinking water, surface water, and influent and effluent wastewaters, with quantification limits far below those endorsed by WHO and EU drinking water directives setting maximum allowed concentrations at ≤100 ng L~(-1) OCPs.