Combining targeted and nontargeted data analysis for liquid chromatography/high-resolution mass spectrometric analyses.

Increasing importation of food and the diversity of potential contaminants have necessitated more analytical testing of these foods. Historically, mass spectrometric methods for testing foods were confined to monitoring selected ions (SIM or MRM), achieving sensitivity by focusing on targeted ion signals. A limiting factor in this approach is that any contaminants not included on the target list are not typically identified and retrospective data mining is limited. A potential solution is to utilize high-resolution MS to acquire accurate mass full-scan data. Based on the instrumental resolution, these data can be correlated to the actual mass of a contaminant, which would allow for identification of both target compounds and compounds that are not on a target list (nontargets). The focus of this research was to develop software algorithms to provide rapid and accurate data processing of LC/MS data to identify both targeted and nontargeted analytes. Software from a commercial vendor was developed to process LC/MS data and the results were compared to an alternate, vendor-supplied solution. The commercial software performed well and demonstrated the potential for a fully automated processing solution.

Online standard additions calibration of transient signals for inductively coupled plasma mass spectrometry.

An online standard additions calibration method for transient signals in ICPMS is demonstrated in which a small volume of standard is injected as a spike into the sample/carrier stream, overlaying the analyte peak. This technique provides the advantages of conventional standard additions but requires only a single sample run. The method corrects for matrix effects and is suitable for transient signals in which the severity of the matrix effect changes over the analyte peak. The method uses a peak-fitting program to determine the area of the underlying peak and is shown to be effective for the determination of trace metal concentrations in both a high ionic strength matrix and in a biological matrix (urine). Eight analytes with concentrations in the range of 0.82-233.2 mug L-1 in urine were simultaneously determined using a standard spiking solution of 75 mug L-1 injected through a 100-muL loop. The measured concentrations for analytes free of spectral interferences agreed with the certified values, and the precision achieved was comparable to that achieved by the certifying agency. Using a conventional cross-flow nebulizer and Scott-type spray chamber, the accuracy obtained for online standard additions calibration was within 2%, and the precision was within 5%.