Analysis of steroid derivatives by LC-MS/MS methods: Selective sample preparation procedures by using mixed-mode solid phase extraction and pH control
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2017, Wessling International Research and Educational Centre Nonprofit Beneficial Ltd. All rights reserved. The analysis of veterinary drug residues and banned crop yield boosters in foods of animal origin is one of the largest and most important areas of food analysis. A prerequisite for effective tests is the development of accurate methods that satisfy the requirements of todays analysis for selectivity, low limits of detection and accuracy. The high sensitivity and selectivity of liquid chromatographic triple quadrupole tandem mass spectrometric (LC-MS/MS) methods allows for the detection of trace amounts of the organic target compounds even in complex samples. However, the reliability of LC-MS/MS methods depends greatly on the sample preparation preceding the analysis, the objective of which is to decrease the concentrations of matrix components coeluting with the target compounds, thus minimizing the matrix effect in the ion source of the instrument. During sample preparation, low performance liquid chromatographic clean-up, the so-called solid phase extraction (SPE) is often used. The pH of the eluent is one of the most important parameters in liquid chromatography, and so the proper selection of pH during extraction can have a a critical influence on sample preparation and, consequently, the accuracy of the analysis. This statement holds especially true when matrix compounds with functional groups susceptible to protonation have to be removed from the analytical sample. The objective of this paper is to present mixedmode SPE sample preparation methods that demonstrate clearly the necessity for pH control during the extraction. Examples include the determination of both neutral and basic target compounds using mixed-mode strong ion exchange SPE columns.
