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Background: Mass spectrometry (MS) is being introduced into a large number of clinical laboratories. It provides specificity because of its ability to monitor selected mass ions, sensitivity because of the enhanced signal-to-noise ratio, and speed because it can help avoid the need for intensive sample cleanup and long analysis times. However, MS is not without problems related to interference, especially through ion suppression effects. Ion suppression results from the presence of less volatile compounds that can change the efficiency of droplet formation or droplet evaporation, which in turn affects the amount of charged ion in the gas phase that ultimately reaches the detector.
Content: This review discusses materials shown to cause ion suppression, including salts, ion-pairing agents, endogenous compounds, drugs, metabolites, and proteins. Experimental protocols for examining ion suppression, which should include, at a minimum, signal recovery studies using specimen extracts with added analyte, are also discussed, and a more comprehensive approach is presented that uses postcolumn infusion of the analyte to evaluate protracted ionization effects. Finally, this review presents options for minimizing or correcting ion suppression, which include enhanced specimen cleanup, Chromatographie changes, reagent modifications, and effective internal standardization.
Summary: Whenever mass spectrometric assays are developed, ion suppression studies should be performed using expected physiologic concentrations of the analyte under investigation.
Mass spectrometry (MS)1 is a powerful qualitative and quantitative analytical technique that has been introduced into many clinical and research laboratories during the last 5 years. The cost of MS analyzers has dropped to a range that is affordable for a majority of laboratories. Compared with a decade ago, instruments are more robust, computer-interfaced, user-friendly, and easier to maintain. There is a greater awareness by manufacturers of the laboratory applications of MS in the clinical laboratory, so that technical support and assay development are high priorities with these companies. In the clinical laboratory, mass spectrometers are used to measure a wide range of clinically relevant analytes. When applied to biological samples, the power of MS lies in its selectivity toward the identification and quantification of compounds. The combination of gas chromatography or HPLC with MS yields a particularly powerful tool. This is especially so for HPLC-MS or HPLC-tandem MS, which is the reason that this combination is being used by many clinical...