Abstract: A linear time-of-flight (TOF) mass spectrometer equipped with a quadrupole ion trap for ion storage was developed for mass analysis of ions generated by electrospray ionization (ESI). With this technique, the continuous ion beam from the ESI source is collimated by a set of focusing lenses into the ion trap where the ions are accumulated for a predetermined period of time. Extraction of the ions into the flight tube of the TOF mass spectrometer is achieved by applying a short duration voltage pulse to the exit endcap of the ion trap. The extraction frequency is variable, but is typically set at 10 Hz. It was shown that with a linear TOF mass spectrometer, mass resolution in the range of 600-950 can be routinely obtained. It was also demonstrated that a complete mass spectrum of bradykinin can be obtained with a direct injection of 75 fmol, or 0.5 µL of 150 nM of sample solution. Buffer gas pressure and the energy of the ions entering the ion trap, were found to be the key parameters in obtaining this sensitivity and resolution. In addition, the ESI ion trap/TOF system was developed and applied for microcolumn liquid chromatography detection of a simple protein mixture.

Abstract: A 1-m silica tube (75 µm i.d., 363 µm o.d.) is inserted into a stainless steel tube (6.35 mm i.d., 1.27 cm o.d.) and extends to the probe tip (5 mm long, 5 mm o.d., 1 mm i.d.) made from Vespel; the top section (~ 7.62 cm) of the silica is coated with Vespel as insulation, and a stainless steel frit is fitted into the end of the tip. The probe is inserted via a solid-probe lock into a time-of-flight mass spectrometer, in which ions are detected by using a multi-channel plate detector. A solution of peptide or protein in aqueous 0.1% trifluoroacetic acid is mixed (1:1:1:1) with methanol, ethanediol and 3-nitrobenzyl alcohol and is introduced continuously (1 to 5 µL min-1) by a micro-syringe pump onto the tip of the flow probe; a flow injection variant is also described. A Nd:YAG laser operating at 266 nm and repetition rate 10 Hz is used to effect desorption ionization; the conditions used for MS are given. The mass spectra of myoglobin obtained by this technique and with a solid probe are similar, but the flow system can provide a stable signal for extended periods; however, the signal in the dynamic mode is less intense by a factor of 5 to 10. Use of the flow injection variant with bacitracin affords reproducible signals with an acceptable degree of peak tailing and no memory effect. Mass resolution is ~10 for the compounds examined but is higher for molecules of mol. wt. 1000.

Abstract: Sample molecules carried by a liquid carrier (e.g., methanol at 0.5 mL min-1) were vaporized by passage through a heated capillary tube to form aerosol droplets which were entrained in the sample vaporizer of a high-temp. pulsed nozzle. The vapor was injected into the time-of-flight mass spectrometer at a repetition rate determined by the ionization source. The interface described was used to detect both volatile and non-volatile compounds, including those of environmental and biological significance. The average coefficient of variation was 4 to 8%. There were no memory effects or severe peak tailing, and cluster formation during supersonic jet expansion was not a problem. The detection limits for aniline, tryptamine and indole-3-acetic acid were 3, 4 and 140 ng, respectively. The calibration graphs were rectilinear over two-orders of magnitude of analytical range. A pulsed sample introduction (PSI) interface is developed to combine flow injection analysis with a time-of-flight mass spectrometer. In PSI, sample molecules carried by a liquid carrier such as methanol at a flow rate of 0.5 mL/min are vaporized by passing through a heated capillary tube and then through a sample vaporizer of a high-temp. pulsed nozzle. The resulting sample vapors are introduced into the mass spectrometer in a pulsed form and ionized by laser-induced multiphoton ionization. The applicability of this interface for the detection of volatile and nonvolatile compounds is studied. It is found that a variety of chemicals including molecules with environmental or biological significance can be studied by this method. Preliminary studies of the performance of this interface are reported. It is shown that reproducible results from repeated injection of the same concentration. of samples can be readily obtained. The average relative standard deviation is in the range of 4-8%. No memory effects and severe peak tailing are found with this PSI interface. The detection limits of the present technique are compound dependent. For aniline, tryptamine, and indole-3-acetic acid, the detection limits are found to be 3, 140, and 4 ng, respectively. Excellent linearity over two orders of magnitude of analytical range can be obtained for quantitation. It is also shown that cluster formation during the supersonic expansion is not a major problem in this technique.