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RationaleFemtoamp and picoamp electrospray ionization (ESI) characteristics of a nonpolar solvent were explored. The direct ESI mass spectrometry analysis of chloroform extract solution enabled rapid analysis of perfluorinated sulfonic acid analytes in drinking water. MethodsNeat chloroform solvent and extracts were directly used in a typical wire‐in ESI setup using micrometer emitter tips. Ionization currents were measured with femtoamp sensitivity while ramping the spray voltage from 0 to −5000 V. Methanol was used as a comparison to illustrate the characteristics of electrospraying chloroform. The effects of spray voltage and inlet temperature were studied. A liquid–liquid extraction workflow was developed to analyze perfluorooctanoate sulfonate (PFOS) in drinking water using an ion‐trap mass spectrometer. ResultsThe ionization onset of chloroform solution was 41 ± 17 fA at 300 V. The ionization current gradually increased with voltage while remaining below 100 pA when using voltages up to −5000 V. The ion signal of PFOS was significantly enhanced to improve the limit of detection (LoD) to 25 ppt in chloroform. Coupled with a liquid–liquid extraction workflow, LoD of 0.38–5.1 ppt and a quantitation range of 5–400 ppt were achieved for perfluorinated sulfonic compounds in 1‐ml water samples. ConclusionsFemtoamp and picoamp modes expand the solvent compatibility range of ESI and can enable quantitative analysis in parts per trillion (ppt) concentrations.
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Enhancement in MS‐based peptide detection by microfluidic free‐flow zone electrophoresis
Abstract Matrix components are known to significantly alter the ionization of a target analyte in ESI‐based measurements particularly when working with complex biological samples. This issue however may be alleviated by extracting the analyte of interest from the original sample into a relatively simple matrix compatible with ESI mass‐spectrometric analysis. In this article, we report a microfluidic device that enables such extraction of small peptide molecules into an ESI‐compatible solvent stream significantly improving both the sensitivity and reproducibility of the measurements. The reported device realizes this analyte extraction capability based on the free‐flow zone electrophoretic fractionation process using a set of internal electrodes placed across the width of the analysis channel. Employing lateral electric fields and separation distances of 75 V/cm and 600 µm, respectively, efficient extraction of the model peptide human angiotensin II was demonstrated allowing a reduction in its detection limit by one to three orders of magnitude using the ESI‐MS method. The noted result was obtained in our experiments both for a relatively simple specimen comprising DNA strands and angiotensin II as well as for human serum samples spiked with the same model peptide.
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- Award ID(s):
- 1808507
- PAR ID:
- 10457451
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ELECTROPHORESIS
- Volume:
- 41
- Issue:
- 7-8
- ISSN:
- 0173-0835
- Format(s):
- Medium: X Size: p. 545-553
- Size(s):
- p. 545-553
- Sponsoring Org:
- National Science Foundation
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