Headspace versus Direct Immersion Solid Phase Microextraction in Complex Matrixes: Investigation of Analyte Behavior in Multicomponent Mixtures

Abstract

This work aims to investigate the behavior of analytes in complex mixtures and matrixes with the use of solid-phase microextraction (SPME). Various factors that influence analyte uptake such as coating chemistry, extraction mode, the physicochemical properties of analytes, and matrix complexity were considered. At first, an aqueous system containing analytes bearing different hydrophobicities, molecular weights, and chemical functionalities was investigated by using commercially available liquid and solid porous coatings. The differences in the mass transfer mechanisms resulted in a more pronounced occurrence of coating saturation in headspace mode. Contrariwise, direct immersion extraction minimizes the occurrence of artifacts related to coating saturation and provides enhanced extraction of polar compounds. In addition, matrix-compatible PDMS-modified solid coatings, characterized by a new morphology that avoids coating fouling, were compared to their nonmodified analogues. The obtained results indicate that PDMS-modified coatings reduce artifacts associated with coating saturation, even in headspace mode. This factor, coupled to their matrix compatibility, make the use of direct SPME very practical as a quantification approach and the best choice for metabolomics studies where wide coverage is intended. To further understand the influence on analyte uptake on a system where additional interactions occur due to matrix components, ex vivo and in vivo sampling conditions were simulated using a starch matrix model, with the aim of mimicking plant-derived materials. Our results corroborate the fact that matrix handling can affect analyte/matrix equilibria, with consequent release of high concentrations of previously bound hydrophobic compounds, potentially leading to coating saturation. Direct immersion SPME limited the occurrence of the artifacts, which confirms the suitability of SPME for in vivo applications. These findings shed light into the implementation of in vivo SPME strategies in quantitative metabolomics studies of complex plant-based systems.

Solid Phase Microextraction On-Fiber Derivatization Using a Stable, Portable, and Reusable Pentafluorophenyl Hydrazine Standard Gas Generating Vial

“…This is particularly important, as PDMS coatings are more robust, and have been applied to both ex vivo and in vivo samplings from tissues, 40 minimizing the occurrence of possible artifacts associated with the extraction process. 41 Due to the hydrophobic nature of the PDMS polymer, successful extraction of underivatized and short-chain aldehydes could prove to be difficult due to their polarity and relatively low concentrations. Consequently, the risk of losing important chemical information when sampling complex matrices with PDMS under underivatized conditions is high.…”

Calibrant Free Sampling and Enrichment with Solid-Phase Microextraction: Computational Simulation and Experimental Verification

“…This feature is also referred to as balanced coverage. 6 Since analytes with higher logP values tend to have both higher K and Ka values, the reduced uptake rate forbids them from saturating the fiber coating. Figure 7.…”

“…In some cases, long extraction times may also cause sufficient accumulation of substances on the coating so as to initiate competition between analytes and/or interferences, leading to saturation and displacement effects. [4][5][6] Diffusive sampling is a method in which analytes are collected by an extraction phase (or, extractant) at a rate controlled by molecular diffusion of analytes through the diffusion boundary layer formed around the extractant in the sample matrix. 7,8 It has been shown previously that by exposing a SPME fiber directly to a sample matrix for a short period of time, diffusive sampling can be obtained.…”

A critical review of the state of the art of solid-phase microextraction of complex matrices I. Environmental analysis

“…A direct consequence of coating 90 saturation is inter-analyte competitive adsorption. This phenomenon was first studied for a two-component system, and recently 91 deeply investigated to interpret analyte behavior in complex matrices [8,9]. 92 In summary, a mathematical description of the phenomenon can be given by the following equation for a two-analyte system at where K A and K B are the adsorption equilibrium constants for the analytes A and B, and 97 represents the maximum concentration of active sites on the coating.…”

“…99 Considering B as the analyte that induces coating saturation, it possible to notice that, when K B and are large enough to render the 100 term negligible, the amount of analyte A extracted at equilibrium will decrease when the concentration of saturating compound 101 B in the matrix is higher. Saturation of the coating, especially in complex mixtures, may eventually affect the HS-SPME mode more 102 than the DI-SPME mode [9]. This mainly relates to the mass-transfer resistance of the analytes at the interface of the HS/matrix and to 103 their Henry's law constants.…”