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    Development of an Atmospheric Pressure Ion Mobility Spectrometer–Mass Spectrometer with an Orthogonal Acceleration Electrostatic Sector TOF Mass Analyzer

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    Recently developed ion mobility mass spectrometer is described. The instrument is based on a drift tube ion mobility spectrometer and an orthogonal acceleration electrostatic sector time-of-flight mass analyzer. Data collection is performed using a specially developed fast ADC-based recorder that allows real-time data integration in an interval between 3 and 100 s. Primary tests were done with positive ion electrospray. The tests have shown obtaining 100 ion mobility resolving power and 2000 mass resolving power. Obtained for 2,6-di-<i>tert</i>-butylpyridine in electrosprayed liquid samples during 100 s analysis and full IMS/MS data collection mode were 4 nM relative limits of detection and a 1 pg absolute limit of detection (S/N=3). Characteristic ion mobility/mass distributions were recorded for selected antibiotics, including amoxicillin, ampicillin, lomefloxacin, and ofloxacin. At studied conditions, lomefloxacin forms only a protonated molecule-producing reduced ion mobility peak at 1.082 cm<sup>2</sup>/(V s). Both amoxicillin and ampicillin produce [M + H]<sup>+</sup>, [M + CH<sub>3</sub>OH + H]<sup>+</sup>, and [M + CH<sub>3</sub>CN + H]<sup>+</sup>. Amoxicillin shows two peaks at 0.909 cm<sup>2</sup>/(V s) and 0.905 cm<sup>2</sup>/(V s). Ampicillin shows one peak at 0.945 cm<sup>2</sup>/(V s). Intensity of protonated methanol containing cluster for both ampicillin and amoxicillin has a clear tendency to rise with sample keeping time. Ofloxacin produces two peaks in the ion mobility distribution. A lower ion mobility peak at 1.051 cm<sup>2</sup>/(V s) is shown to be formed by [M + H]<sup>+</sup> ions. A higher ion mobility peak appearing for samples kept more than 48 h is shown to be formed by both [M + H]<sup>+</sup> ion and a component identified as the [M + 2H + M]<sup>+2</sup> cluster. The cluster probably partly dissociates in the interface producing the [M + H]<sup>+</sup> ion
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