Comparison of two CE-ICP-MS interfaces and quantitative measurements of carboplatin in plasma samples using an internal standard

Two commercially available CE-ICP-MS interfaces were investigated with respect to precision, limits of detection and ease-of-use. Our results demonstrate that the CEI-100 interface was more suited for the detection of carboplatin in our experimental set-up. A relative detection limit of 21 mu g Pt L-1 corresponding to an absolute detection limit of 0.1 fg Pt was found for the CEI-100 interface. The quantitative aspects of CE-ICP-MS were addressed and a method was developed using sodium diatrizoate as an internal standard added to the samples to correct for changes in sensitivity between runs. A significant improvement on the repeatability was obtained. The method was applied for the determination of free carboplatin in plasma incubations. The percentage of free carboplatin was calculated both based on the calibration curve and based on the fraction of free carboplatin relative to the total platinum area. Significantly different results were obtained using the two methods, probably due to adsorption of the plasma proteins to the incubation vial or to the capillary or due to formation of carboplatin adducts in concentrations below the limit of detection. This indicates a need for critical evaluation of the quantitative CE-ICP-MS measurements used for kinetic profiling.