Improving figures of merit and expanding applications for inductively coupled plasma mass spectrometry



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Although inductively coupled plasma mass spectrometry (ICP-MS) is generally considered a reliable analytical technique, increasing demands on its capabilities require continued research and improvements. ICP-MS is susceptible to both matrix effects and drift, leading to a decline in accuracy and precision. A number of techniques are routinely used to compensate for these issues. Internal standardization is one such solution that requires relatively simple sample preparation and yet offers the possibility of improving both accuracy and precision. In order to be effective, an optimal analyte/internal standard pair must be chosen. Traditionally, analyte/internal standard pairs are chosen based on similarities in mass and/or ionization potential. The present studies sought to develop a program that determined standards based on the minimization of analytical error. 102 masses were monitored over 27 perturbations, i.e., changes to sample matrix and operating parameters. The standard deviations of the analyte/internal standard ratios were then used as a measure of internal standard performance. A thorough statistical analysis was conducted to determine trends between a good analyte/internal standard pair and similarities in chemical property. Similarities in mass offered the strongest relationship to a good internal standard choice, although many exceptions existed. The program was then tested over time and multiple instrument optimizations as well as on a completely different ICP-MS instrument. Results of these tests suggest that the data originally collected for the prediction program is not instrument-specific and thus provided a broader base of useful applications.
Due to its unmatched sensitivity and multielement capabilities, ICP-MS is frequently utilized for biological samples. A more recent application, however, seeks to use ICPMS for the purpose of determining specific associations between metals and proteins. Such speciation requires a high resolution and reproducible separation prior to ICPMS analysis. Gel electrophoresis offers good separation and is well matched with the scanning properties of laser ablation sample introduction. The present study utilized native gel electrophoresis coupled with a uniquely modified electroblot system to improve sensitivity and to elucidate additional information. Chemically modified quartz fiber filters were successfully used as the transfer membrane to improve protein and metal capture efficiency.