Use of Gradient Dilution to Detect and Correct Matrix Interferences in Inductively Coupled Plasma–Time-of-Flight Mass Spectrometry (ICP-TOFMS)

Abstract

Our research group earlier used dispersion that occurs during flow injection to detect and reduce matrix interference in inductively coupled plasma–time-of-flight mass spectrometry (ICP-TOFMS). In the absence of a matrix interference, the ratio of signals from any two sample constituents should remain constant, independent of the dilution, over the course of a flow-injection transient. However, when an interferent is present, the signal ratio from different analytes will change with dilution, owing to the difference in severity of the interference on specific analytes. As a result, matrix interference can be recognized (flagged) by monitoring the signal ratios of two analytes over the course of a flow-injection transient; a ratio that changes over time indicates the presence of an interferent. The drawback of this earlier method was that dispersion, and therefore dilution, was somewhat element-specific, causing the ratios to wander even when no interference existed. Here, a gradient HPLC pump is used to overcome this drawback by creating a longer, better-controlled dilution. Under these conditions, variation in dispersion between elements is negligible and difficulties associated with it are reduced or eliminated. Further, when an interference exists, the optimal dilution factor to reduce the interference to an acceptable level can be found from the gradient-dilution curve as the point where the signal ratio between two elements becomes constant.