Pre-equilibrium solid-phase microextraction of free analyte in complex samples: correction for mass transfer variation from protein binding and matrix tortuosity.

Department of Biology, University of Waterloo, Ontario, Canada.
Analytical Chemistry (Impact Factor: 5.82). 04/2011; 83(9):3365-70. DOI: 10.1021/ac2004899
Source: PubMed

ABSTRACT The accurate measurement of free analyte concentrations within complex sample matrixes by pre-equilibrium solid-phase microextraction (SPME) has proven challenging due to variations in mass uptake kinetics. For the first time, the effects of the sample binding matrix and tortuosity on the kinetics of analyte extraction (from the sample to the SPME fiber) are demonstrated to be quantitatively symmetrical with those of the desorption of preloaded deuterated standards (from the fiber to the sample matrix). Consequently, kinetic calibration methods can be employed to correct for variation in SPME sampling kinetics, facilitating the application of pre-equilibrium SPME within complex sample systems. This approach was applied ex vivo to measure pharmaceuticals in fish muscle tissues, with results consistent with those obtained from equilibrium SPME and microdialysis. The developed method has the inherent advantages of being more accurate, precise, and reproducible, thus providing the framework for applications where rapid measurement of free analyte concentrations (within complicated sample matrixes such as biological tissues, sediment, and surface water) are required.

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    ABSTRACT: Solid-phase microextraction (SPME) is a biomimetic tool ideally suited for measuring bioavailability of hydrophobic organic compounds (HOCs) in sediment and soil matrices. However, conventional SPME sampling requires the attainment of equilibrium between the fiber and sample matrix, which may take weeks or months, greatly limiting its applicability. In this study, we explored the preloading of polydimethylsiloxane fiber with stable isotope labeled analogs (SI-SPME) to circumvent the need for long sampling time, and evaluated the performance of SI-SPME against the conventional equilibrium SPME (Eq-SPME) using a range of sediments and conditions. Desorption of stable isotope-labeled analogs and absorption of PCB-52, PCB-153, bifenthrin and cis-permethrin were isotropic, validating the assumption for SI-SPME. Highly reproducible preloading was achieved using acetone-water (1:4, v/v) as the carrier. Compared to Eq-SPME that required weeks or even months, the fiber concentrations (Cf) under equilibrium could be reliably estimated by SI-SPME in 1 d under agitated conditions or 20 d under static conditions in spiked sediments. The Cf values predicted by SI-SPME were statistically identical to those determined by Eq-SPME. The SI-SPME method was further applied successfully to field sediments contaminated with PCB 52, PCB 153, and bifenthrin. The increasing availability of stable isotope labeled standards and mass spectrometry nowadays makes SI-SPME highly feasible, allowing the use of SPME under non-equilibrium conditions with much shorter or flexible sampling time.
    Environmental Science & Technology 08/2013; · 5.48 Impact Factor


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May 22, 2014