Explanation #

The presence of target compounds at trace levels (mg/kg or mg/L) in an extract containing different chemical groups such as proteins, carbohydrates, lipids, and other miscellaneous compounds may reveal the dimension of food sample complexity (Kaufmann, 2014). The presence of coextractives influences the analyte signals, which can be either suppressed or enhanced when compared to the response in pure solvent (Trufelli, Palma, Famiglini, & Cappiello, 2011).

Matrix Effects in LC-based Methods #

Ion suppression is the most common matrix effect in LC-based methods, especially when MS operated with electrospray (ESI) positive polarity mode, which is the most used for pesticide analysis (Kittlaus, Schimanke, Kempe, & Speer, 2011). As described by Gómez-Ramos, Rajski, Lozano, and Fernández-Alba (2016) various causes are related with the ion suppression effect in ESI such as:
(1) competition between matrix components and analytes for available charges and access to the droplet surface and
(2) change in the viscosity and surface tension of the LC effluent that, consequently, influences the droplet formation and the evaporation process, affecting the number of charged ions.
Furthermore, nonvolatile components can form solid analyte inclusion particles, and matrix components may act as ion-pairing reagents with already ionized analytes (Trufelli et al., 2011).
However, the most discussed explanation is related to the competition for access to the droplet surface along with the competition for the surface excess charges (Gómez-Ramos et al., 2016).

Matrix Effects in GC-based Methods #

As explained by Erney, Gillespie, Gilvydis, and Poole (1993) and Gillespie, Daly, Gilvydis, Schneider, and Walters (1995), for GC methods, the matrix induced response enhancement can be explained based on the competition between coextractives and the pesticides to access the active sites present in the inlet and chromatographic column. The coextractives protect the target analytes from decomposition in the hot injector.

Otherwise, nonvolatile coextractives accumulated into the GC system promote the response diminishment because of the generation of new active sites (Gómez-Ramos et al., 2016).

Impact #

The matrix effect impact is related to different factors such as matrix type, applied sample preparation method (Kittlaus et al., 2011), mobile phase composition (Gosetti et al., 2010), and also the geometry/design of the ionization source (Stahnke, Kittlaus, Kempe, Hemmerling, & Alder, 2012). Matrix coextractives can affect each commodity differently and can be observed in different parts of the chromatogram.

Resolution #

Many matrix compounds often have similar masses to target compounds, and in the case of coelution of matrix compounds with analytes, the instrument might not be capable of fully resolving these two slightly different masses. Resolving power is an important factor in the correct identification of these compounds, especially in complex matrices. TOF instruments usually provide resolutions of up to 15,000 full width at half maximum (FWHM).

Reference #

p134, Applications in High Resolution Mass Spectrometrey Food Safety and Pesticide Residue Analysis, edited by Roberto Romero-González, ©2017 ELSEVIER.