Matrix Effects in Mass Spectrometry Analysis

Accurate determinations of the concentrations of analytes in complex matrix samples, such as agricultural, environmental, and biological, still present analytical challenges because of the complexity of the samples, which makes the analytical procedures complicated. The analytical technique of mass spectrometry (MS) combined with chromatography is a powerful tool for the analysis of such samples because the improvements in the sensitivity and selectivity have readily been achieved. However, the “matrix effects” arising from endogenous matrix components may interfere with accurate and precise quantifications of analytes in a MS analysis.1,2 Electron ionization (EI)-MS in conjunction with gas chromatography (GC) has been generally applied to the analysis of relatively volatile and low-polarity compounds, such as alkylmercury in wastewater,3 alkaloids in tobacco product,4 and semi-volatile organic compounds in indoor air.5 The matrix effects encountered in GC-EI-MS are found in response enhancements of the analytes in complex matrix samples compared to a standard sample. This is because the adsorption and/or degradation of analytes on the active sites, which mainly involves the silanol group in the inlet liner, column, and El ion source, is often observed in the standard sample analysis. In contrast, the analytes in a matrix sample are not interacted with the active sites, resulting in the response enhancement and in an inaccurate quantification of the analytes. On the other hand, it is known that the response suppression by the matrix effects is mainly observed in liquid chromatography (LC) equipped with electrospray ionization (ESI)-MS. This effect should be attributed to ionization competition between the analytes and co-eluting matrix components of LC, and it often causes inaccurate quantification results of the target analytes. Nevertheless, the analytical performance of the LC-ESI-MS method may be superior to other detection methods, and it has been utilized for the analysis of many compounds, as follows. Ando et al. employed nano-flow LC-MS for the sensitive quantification of eicosanoids in biological samples.6 Matsumoto et al. reported an LC-MS determination method for urinary tetrahydrogluco- corticoid glucuronides, which might be helpful for the diagnosis of diseases caused by abnormal cortisol secretion, with derivatization using an ESI-enhancing reagent.7 Ohno et al. also introduced a derivatization method for the LC-MS analysis of testosterone and dihydrotestosterone, and successfully applied it to a saliva sample analysis.8 Chun et al. presented a simultaneous analysis of catecholamines in mice brain samples by separation through cation-exchange/reversed phase (mixed-mode) LC, followed by ESI-MS detection.9 Furthermore, Gowda et al. performed a lipidomics study with ultra-high-performance LC-MS to obtain a comprehensive profile of circulating plasma lipids using high-fat diet-induced rat samples.10 To eliminate the matrix effects from the MS analysis, various approaches are employed.11 Among them, a dilution approach, a matrix-matched calibration, and standard addition methods have often been utilized. Besides, using the stable isotope-labeled internal standard method12 is another useful technique to compensate for the MS responses induced by matrix effects. The sample clean-up preparation and/or adequate chromatographic separation may also be effective for removing endogenous components that cause matrix effects. In many cases, these approaches are essential for accurate and precise MS analysis of the target analytes. 2020 © The Japan Society for Analytical Chemistry