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An analytical procedure using accelerated solvent extraction and capillary gas chromatography with electron capture and flame photometric detections was developed to simultaneously determine residues of different pesticides in fruits and vegetables. Single laboratory validation of the method was carried out for 28 compounds selected from eight pesticide classes, in blank and fortified samples of fresh pear, cantaloupe, white potato, and cabbage. The method had to meet specific established validation criteria for regulatory purposes applicable to our laboratory. At each of the two fortification levels studied, 24 of the 28 pesticides gave recoveries of more than 70% with a coefficient of variation of less than 10%. With respect to existing procedures, the method showed acceptable limits of detection (from 0.0019 to 0.14 microg/g depending on the pesticide and matrix) while minimizing environmental concerns, time, and labor.

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A charge reduction (CR) interface for electrospray ionization was characterized that permits simultaneous analysis of nanoparticle solutions by multiple detection methods. In the direct infusion configuration, a constant flow of analyte solution undergoes electrospray ionization (ESI). The charged aerosol is sampled directly into the atmospheric pressure inlet of a quadrupole time-of-flight mass spectrometer (QTOF) and to a CR device followed by a differential mobility analyzer (DMA) and condensation particle counter (CPC). In the plug injection configuration, analyte solution is injected into a liquid chromatograph. The effluent is split to an evaporative light scattering detector (ELSD) and the ESI interface. The charged aerosol is then sampled through the CR device directly into the CPC. Performance characteristics of the two configurations were studied with sucrose and protein solutions. When a liquid flow rate in the low µL/min range was used, the reconstructed droplet size distribution from the ESI interface had an average diameter of 184 nm with a geometric standard deviation of 1.4. For the first configuration, the linear working range was wider for ESI-MS than CR-DMA-CPC. For the second configuration, the detection efficiency, defined as the fraction of molecules flowing through the ESI interface that are ultimately detected by the CPC, was on the order of 10 −6 . Simultaneous measurements with ELSD and CPC were consistent with analyte molecular size and may provide a means of estimating the size of unknown particles.

A novel approach involving the use of reversed phase liquid chromatography-mass spectrometry (RPLC-MS), charge reduced electrospray (CRES), and condensation particle counting (CPC) for the absolute quantification of intact proteins in liquid solutions is introduced. Under analysis conditions optimized for the quantification of select proteins within their predetermined linear ranges, a set of at least five protein standards with molecular weights (MW) spanning the dynamic ranges of both a quadrupole time-of-flight (QTOF) MS and a suitably selected RPLC column is used to generate a calibration curve of CPC detection efficiency (DE) as a function of the square root of MW. Next, the sample of interest is analyzed, and from the MS-generated MW data, the DE of each target protein is determined from the calibration curve. On the basis of MW, DE, and number concentration (molecules/unit volume), absolute quantification is achieved for each protein of interest. Application of this approach to the absolute quantification of cytochrome C (as target compound) in a commercial protein mixture is demonstrated with a deviation of 8%, a coefficient of variation (CV) of 5%, and a quantification limit of 432 fmol. For nontarget components of the mixture (ribonuclease A, holotransferrin, and apomyoglobin), the percent deviation from the stated concentrations and the CV varied from 0.20 to 23 and from 4.1 to 18, respectively. Performance of the method was further assessed by analyzing a laboratory quality control mixture comprising 0.33 μM of cytochrome C. The calculated value was 0.34 (CV: 5.1%). Universal in essence, the new technique holds strong promise for the absolute quantification of select proteins in liquid samples under conditions of good peak resolution and stable baseline.