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: 5.64). 04/2011; 83(9):3365-70. DOI: 10.1021/ac2004899
Source: PubMed


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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Available from: Ehsanul Hoque, Jan 13, 2014
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    • "All the samples were analyzed within 24 h after prepa- ration. Due to their similar porous structures, agarose gel has been widely used as a medium to mimic animal tissue in investigations of diffusion mechanism [29] [30] [31] [32]. Research found that the agarose gel showed no binding effect toward organic compounds [32]. "
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    ABSTRACT: Solid phase microextraction (SPME) has become a useful tool for in vivo monitoring the behavior of environmental organic pollutants in biological species due to its simplicity, relatively non-invasive, and cost-effective manner. However, the complex matrices in biological samples could significantly influence the extraction kinetic, and bias the quantification result. In this study, we investigated the effect of complex matrix on the extraction kinetic of SPME for biological sample analysis. Two sample matrices, phosphate-buffered saline (PBS) with bovine serum albumin (BSA) and agarose gel with BSA were used to simulate the biological fluid and tissue. Results showed that the addition of BSA significantly enhanced the mass transfer of organic compounds onto SPME fiber in both PBS buffer and gel sample. Enhancement factors ranging from 1.3 to 27, and 2.0 to 80 were found for all selected polyaromatic hydrocarbons (PAHs) in PBS buffer and agarose gel with BSA concentration of 0.1-5%, respectively. Then, an improved theoretical model was applied to quantify the observed enhancement effect, and the result showed that the predicted sampling time constant agreed well with the experimental one in complex matrix. Furthermore, a simplified equation was proposed for the real biological sample analysis. Copyright © 2015 Elsevier B.V. All rights reserved.
    Full-text · Article · Aug 2015 · Journal of Chromatography A
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    • "In recent years, C18 functionalized SPME fibers were used to determine polycyclic aromatic hydrocarbons (PAHs) and pesticides in water samples [27] [28]. Biocompatible C18 composite probes were also designed for in vivo or in vitro study of biological samples [29] [30]. Organochlorine pesticides (OCPs), which are known to instigate disruptions in endocrine system [31], were widely used to kill the insects in the planting of farm crops in the past years. "
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    ABSTRACT: In this work, a C18 composite solid-phase microextraction (SPME) fiber was prepared with a new method and applied to the analysis of organochlorine pesticides (OCPs) in water sample. A stainless steel wire (o.d. 127μm) was used as the substrate, and a mixture of the C18 particle (3.5μm) and the 184 silicone was used as the coating material. During the process of fiber preparation, a section of capillary column was used to fix the mixture onto the stainless steel wire and to ensure the constant of coating thickness. The prepared fiber showed excellent thermal stability and solvent resistance. By coupling with gas chromatography-mass spectrometry (GC-MS), the fiber exhibited wide linearity (2-500ngL(-1)) and good sensitivity for the determination of six OCPs in water samples, the OCPs tested included hexachlorobezene, trans-chlordane, cis-chlordane, o,p-DDT, p,p-DDT and mirex. Not only the extraction performance of the newly prepared fiber was more than seven times higher than those of commercial fibers, the limits of detections (LODs) (0.059-0.151ngL(-1)) for OCPs achieved under optimized conditions were also lower than those of reported SPME methods. The fiber was successfully applied to the determination of OCPs in real water samples by using developed SPME-GC-MS method. Copyright © 2015 Elsevier B.V. All rights reserved.
    Full-text · Article · Mar 2015 · Analytica Chimica Acta
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    ABSTRACT: Solid-phase microextraction (SPME) coupled to liquid chromatography with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) has been widely used to analyze biological fluids, tissues, and environmental matrixes for a variety of organic compounds including pharmaceuticals. However, effects of the sample matrix coextracted by SPME on tandem mass spectrometry analysis have not been systematically investigated. In this study, we characterized the complexity of matrix effects (ME) by analyzing SPME extracts of fish muscle and brain tissue, blood, and bile, as well as tap water, surface water, and the influent and effluent from a wastewater treatment plant. Significant enhancement or suppression of ionization (>15%) was observed with all biological and environmental samples. Intrasample ME variability was assessed through comparison of multiple samples from the same sample matrix, while intersample variability between different experimental subjects or varying sample treatment, storage, and sampling conditions were evaluated. To correct for ME, an isotopic internal standard (IIS) method was developed, with the strengths and limitations of the approach discussed. This study provides a framework for applying SPME within complex sample systems where the influences of ME are inevitable, thus ensuring more accurate quantitation of analytes during biological and environmental analysis.
    No preview · Article · Aug 2011 · Analytical Chemistry
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