No abstract

The atmospheric pressure sampling nozzle (orifice, heated capillary, or inlet) of a high mass accuracy time-of-flight mass spectrometer (TOF-MS) was modified by replacing its single nozzle with multiple atmospheric pressure nozzles. This allowed multiple streams of liquids to be introduced into the MS in parallel (an electrosprayer for each nozzle), with minimum analyte interactions between the streams. The chemical contents of all liquid streams were analyzed concurrently using a single mass spectrometer. To obtain a higher mass accuracy by providing internal reference on each scan (acquisition) and to evaluate the suitability of TOF-MS for molecular-formula confirmation, a dual-ESI-sprayer, dual-nozzle version of this design was used. The accurate masses of tens of organic compounds in the mass range of 200-3000 Da were measured, and the results were compared with those obtained using dual-sprayer, single-nozzle TOF-MS. A significant improvement in mass accuracy was observed when the former technique was used. Comparison between the mass accuracy using dual-ESI-sprayer, dual-nozzle TOF-MS and that obtained using a double-focusing mass spectrometer operating under chemical ionization (CI) and fast atom bombardment (FAB) shows the suitability of the technique for elemental-composition confirmation. Approximately 85% of samples analyzed had mass errors of less than 5 ppm, and the other 15% had mass errors less than 8 ppm. Using a high-performance liquid chromatography (HPLC) as a device for introduction of one liquid stream (sample) and a syringe pump as a device for introduction of the second liquid stream (reference standard), the accurate mass of a tryptic digest of cytochrome c was measured. The range of mass errors was from -6.1 ppm to +3.6 ppm, a significant improvement over our previously reported mass accuracy for this digest using single-nozzle TOF-MS. The interactions between analytes in the liquid streams also were investigated using a variety of sample-introduction and nozzle-design combinations, including single-ESI-sprayer, single-nozzle; dual-ESI-sprayer, single-nozzle; dual-ESI-sprayer, Y-shaped inlet; and dual-ESI-sprayer, dual-inlet. The results demonstrated that the dual-ESI-sprayer, dual-inlet design provides reference peaks on every acquisition with minimum analyte-reference interaction and, therefore, higher consistent mass accuracy.

The chemical ionization mass spectra of cyclic glycols and mono-and di-saccharides using trimethyl borate as reagent gas have been studied. In the gas phase, the trimethyl borate ions react stereospecifically with molecules of &-cyclic glycols to form characteristic ions, from which the stereochemical isomers of l,&cyclopentanediols, 1,t-cyclohexanediols and mono-and di-saccharides can be definitely distinguished.

Ultramark 1621, a commercially available mixture of fluorinated phosphazines, was found to be a useful calibration compound for negative and positive ion fast-atom bombardment (FAB) high-resolution mass spectrometry. Ultramark 1621 worked very well with the most widely used matrices such as glycerol, nitrobenzyl alcohol, and triethanolamine. The negative and positive ion FAB mass spectra of Ultramark include a series of intense peaks extending from 700 to 1900 u.

Gated multi-inlet mass spectrometry is introduced for high-throughput chemical analysis. In this design, multiple high-pressure liquid chromatography (HPLC) columns or capillary electrophoresis (CE) capillaries are attached to multiple electrosprayers (one for each column or capillary) that spray toward a gated multi-inlet time-of-flight mass spectrometer (TOF-MS). Although all of the sprayers are spraying continuously, only one inlet is exposed at any given time for a specific duration set by the MS data system. The gated multi-sprayer, multi-inlet design significantly enhances the performance of the multi-ESI, multi-inlet TOF-MS with minimal cost and reduces analysis time. The gated multi-sprayer, multi-inlet design was applied to the investigation of column-to-column reproducibility of multiple HPLCs using a peptide mixture and to the simultaneous analysis of four protein digests. In addition, it was applied to the analysis of peptide mixtures using eight CE capillaries. The gated multi-inlet MS has several advantages compared to our previous non-gated multi-inlet MS. For example, because only one inlet is open at one time, the original manufacturer's inlet inner diameter and pumping system can be used, which enhances the sensitivity of detection for each inlet and minimizes the manufacturing cost. In addition, the number of inlets can be increased as desired. The maximum number of liquid streams that can be concurrently analyzed is limited by: (1) the number of inlets, (2) the chromatographic (electrophoretic) peak width, and (3) how fast the gate can move from one position to the next.