Topics in Solid-Phase Extraction. Part 1. Ion Suppression in LC/MS Analysis: A Review. Strategies for its elimination by well-designed, multidimensional solid-phase extraction [SPE] protocols and methods for its quantitative assessment.

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Uwe D. Neue and Patrick D. McDonald
Waters Whitepaper
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Oasis MCX Oasis MAX
Propranolol; Ciprofloxacin; Enrofloxacin
plasma; beef kidney extract

Ion suppression - a common phenomenon in the LC/MS analysis of complex samples - can be effectively eliminated by good solid-phase extraction methods. Today, with tools such as SPE, coupled with the availability of methods for the quantitative assessment of ion suppression, significant errors in LC/MS analysis due to ion suppression are avoidable and inexcusable.

Over the last decade, the combination of high-performance liquid chromatography and mass spectrometry has become the most important tool in many fields, especially when a determination of specific analytes in a complex matrix needs to be performed. Examples are the analysis of drugs and their metabolites in biological fluids, especially blood and urine, and the measurement of residual contaminants in food matrices or in the environment.

The reason for this widespread acceptance is the high selectivity and high sensitivity of MS techniques that permit the detection of very low levels of target analytes in the presence of a complex matrix background. However, experience has taught that, while detection is no longer an obstacle, quantitative determination of the species of interest may be problematic. If a significant background is present, the signals for the analytes of interest are often suppressed. The magnitude of this suppression may vary from sample to sample1. Thus, one cannot rely upon the results of an analysis with a high level of ion suppression. Steps must be taken prior to analysis to minimize or eliminate ion suppression effects via sample clean-up techniques.

The detailed causes of ion-suppression are not clear and, apparently, can be manifold. Even commonly used mobile phase components such as trifluoroacetic acid cause ion suppression. Of course, the presence of a complex matrix amplifies the problem. This is not only true for plasma1 or urine samples, but also in the analysis of food samples such as cattle or fish tissues, fruits and vegetables, or environmental water. In all these cases, the investigator needs to be concerned about the inaccuracy of the analytical results caused by matrix interferences. Procedures have been established to quantitate matrix effects, and the authors of this study have strongly advocated the measurement and elimination of such effects. Only then can one avoid significant errors in the analytical results.

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