LC-MS (Liquid chromatography mass spectrometry) with ESI (electrospray) ion source (LC-ESI-MS) enjoys ever increasing popularity as a powerful and versatile analytical tool. It has become the number one technique for a large number of different analytical tasks, ranging form pesticide determination in fruit and vegetables to drug residues in sewage sludge. A major drawback of this technique is the so-called matrix effect – ionization suppression or enhancement of the analyte of interest by other compounds present in the sample and co-eluting with the analyte. The matrix effect, if present, can cause large uncertainties in quantification using the LC-ESI-MS technique.

In principle, every effort should be made to reduce (or preferably eliminate) the matrix effect or to take it into account. However this can be extremely work-intensive – not least because of the high variability of matrix effects – and thus impractical at a routine laboratory. However, if the matrix effect exists and cannot be eliminated then it should be taken into account as an uncertainty source in the measurement uncertainty estimate of the result. Although this situation has been well recognized quite some time ago, interestingly, for a long time there was no understanding among the LC-MS practitioners as of how to estimate the uncertainty due to the matrix effect.

Recently Anneli Kruve from University of Tartu developed an approach for evaluating the uncertainty in LC-ESI-MS due to matrix effect. Her approach is based on evaluating the matrix effects for the same analyte in different matrixes and presenting the data in the form of a matrix effect graph. From this graph it is then possible to calculate the uncertainty contribution of matrix effect to the analyte content in the sample. This work has been published in the Journal of AOAC International 2010, 93, 306-314.

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