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Flame atmospheric pressure chemical ionization (FAPCI) combined with negative electrospray ionization (ESI) mass spectrometry was developed to detect the ion/molecule reactions (IMRs) products between nitric acid (HNO) and negatively charged amino acid, angiotensin I (AI) and angiotensin II (AII), and insulin ions. Nitrate and HNO-nitrate ions were detected in the oxyacetylene flame, suggesting that a large quantity of nitric acid (HNO) was produced in the flame. The HNO and negatively charged analyte ions produced by a negative ESI source were delivered into each arm of a Y-shaped stainless steel tube where they merged and reacted. The products were subsequently characterized with an ion trap mass analyzer attached to the exit of the Y-tube. HNO showed the strongest affinity to histidine and formed (M-H+HNO) complex ions, whereas some amino acids did not react with HNO at all. Reactions between HNO and histidine residues in AI and AII resulted in the formation of dominant [M-H+(HNO)] and [M-H+(HNO)] ions. Results from analyses of AAs and insulin indicated that HNO could not only react with basic amino acid residues, but also with disulfide bonds to form [M-3H+(HNO)] complex ions. This approach is useful for obtaining information about the number of basic amino acid residues and disulfide bonds in peptides and proteins. Graphical Abstract ᅟ.

Rationale Solid‐phase microextraction coupled with thermal desorption electrospray ionization tandem mass spectrometry (SPME‐TD‐ESI‐MS/MS) is proposed as a novel method for the rapid quantification of acetaminophen in plasma samples from a pharmacokinetics (PK) study. Methods Traces of acetaminophen were concentrated on commercial fused‐silica fibers coated with a polar polyacrylate (PA) polymer using direct immersion SPME. No agitation, heating, addition of salt, or adjustment of the pH of the sample solution was applied during the extraction. Any acetaminophen absorbed on the SPME fibers was subsequently desorbed and detected by TD‐ESI‐MS/MS. Results Parameters of the absorption, sensitivity, reproducibility, and linearity for the SPME‐TD‐ESI‐MS/MS method were evaluated. The time required to complete a TD‐ESI‐MS/MS analysis was less than 30 seconds. Matrix‐matching calibration was performed to calculate the concentration of acetaminophen in the sample. A linear calibration curve with a concentration range of 100–10,000 ng/mL was constructed to calculate the quantity of acetaminophen. The SPME‐TD‐ESI‐MS quantification results for acetaminophen in plasma were in good agreement with those obtained by the conventional LC/MS/MS method. Conclusions With the proposed method, a 10‐min SPME time was enough to achieve the lower limit of quantitation (i.e. 100 ng/mL) and for a complete PK profiling of acetaminophen. A shorter extraction time could be achieved by applying agitation, heating, adding salt, or adjusting the pH of the sample solution to enhance analyte absorption efficiency. The time required to detect acetaminophen on the SPME fiber was less than 30 s, allowing the rapid quantification of acetaminophen in plasma with good accuracy.

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Flame-induced atmospheric pressure chemical ionization (FAPCI) has been used to directly characterize chemical compounds on a glass rod and drug tablet surfaces. In this study, FAPCI was further applied to interface thin layer chromatography (TLC) and mass spectrometry (MS) for mixture analysis.Methods: A micro-sized oxyacetylene flame was generated using a small concentric tube system. Hot gas flow and primary reactive species from the micro-flame were directed toward a developed TLC gel plate to thermally desorb and ionize analytes on the gel surface. The resulting analyte ions subsequently entered the MS inlet for detection.Results: A 1-1.5-mm-wide light-brown line was observed on the TLC plate after the desorption FAPCI/MS (DFAPCI/MS) analysis, revealing that the gel surface withstood a high temperature from the impact of the micro-flame. Volatile and semivolatile chemical compounds, including amine and amide standards, drugs, and aromatherapy oils, were successfully desorbed, ionized, and detected using this TLC/DFAPCI/MS. The limit of detection of TLC-DFAPCI/MS was determined to be 5 ng/spot for dibenzylamine and ethenzamide.Conclusions: TLC/DFAPCI/MS is one of the simplest TLC-MS interfaces showing the advantages such as low costs and an easy set up. The technique is useful for characterizing thermally stable volatile and semi-volatile compounds in a mixture.