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

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 cm²/(V s). Both amoxicillin and ampicillin produce [M + H]⁺, [M + CH₃OH + H]⁺, and [M + CH₃CN + H]⁺. Amoxicillin shows two peaks at 0.909 cm²/(V s) and 0.905 cm²/(V s). Ampicillin shows one peak at 0.945 cm²/(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 cm²/(V s) is shown to be formed by [M + H]⁺ ions. A higher ion mobility peak appearing for samples kept more than 48 h is shown to be formed by both [M + H]⁺ ion and a component identified as the [M + 2H + M]⁺² cluster. The cluster probably partly dissociates in the interface producing the [M + H]⁺ ion