J. David Pinkston

New time-of-flight mass spectrometer for improved mass resolution, versatility, and mass spectrometry/mass spectrometry studies

Reported here is the design and experimental investigation of the performance characteristics of a new time‐of‐flight (TOF) mass spectrometer. The instrument combines the advantages of beam deflection for ion pulse formation with an electrostatic analyzer which reduces the energy spread of the ions admitted to the TOF region. The instrument is able to use ion sources which cannot be pulsed on a time scale suitable for conventional TOF analysis (e. g., chemical ionization sources). Improved mass resolution is demonstrated over a wide mass range such that all of the ions are in focus simultaneously. A resolution of 982 (full width at half‐maximum) is achieved for the molecular ion peak of perfluorotributylamine at m/z 614. A preliminary investigation of a proposed technique for collecting information typically obtained by tandem mass spectrometry (MS/MS) has also been conducted using this instrument. This new method, named time‐resolved ion kinetic energy spectrometry (TRIKES), combines time‐of‐flight (velo...

Industrial applications of supercritical-fluid chromatography—mass spectrometry involving oligometric materials of low volatility and thermally labile materials

Abstract Three recent applications of supercritical-fluid chromatography with flame ionization (SFC—FID) and with mass spectrometric (SFC—MS) detection are discussed. These applications involve thermally labile and/or relatively non-volatile materials. Specifically, they involve ethoxylated alcohols, inositol triphosphate and peroxides. Amonia chemical ionization (Cl) and methane Cl SFC—MS were used to deconvolute complex chromatograms and to confirm postulated identities. The SFC—MS “electron ionization like” spectrum of the trimethylsilyl (TMS) derivative of inositol triphosphate was shown to be very similar to the library electron ionization spectrum of TMS-inositol diphosphate. SFC—MS was shown to be particularly suitable for the anlaysis of thermally labile peroxides using ammonia CI SFC—MS. All three applications discussed here would have been difficult, if not impossible, by traditional gas or liquid chromatographic methods.

Development and application of packed-column supercritical fluid chromatography/ pneumatically assisted electrospray mass spectrometry

A pneumatically assisted electrospray liquid chromatography/mass spectrometry (LC/MS) interface has been modified for use with packed-column supercritical fluid chromatography (pcSFC). The modifications include the addition of a concentric sheath-flow liquid to the spray device. This allowed the addition of modifiers at the sprayer tip that promote ionization of neutral, pcSFC-separated components. Post-column chromatographic fidelity was preserved using a novel pressure-regulation scheme. Post-column pressure regulation was accomplished by adding a “pressure-regulating fluid” (supplied under pressure control) to the effluent just ahead of the sprayer. The modified interface has been used to characterize a variety of mixtures including emollients, modified polysiloxanes, and pharmaceutical agents. The spectra produced by using this pcSFC/MS interface are similar to electrospray LC/MS spectra.

Characterization of low molecular weight alkoxylated polymers using long column SFC/MS and an image analysis based quantitation approach

The utility of low viscosity mobile phases and long chromatographic columns for complex polymer analysis is demonstrated. We use long column supercritical fluid chromatography/ mass spectrometry (SFC/MS) with electrospray ionization (ESI) to characterize a variety of complex, low molecular weight polymers. When quantitative analysis is desired, the resulting three-dimensional (time, intensity, and mass-to-charge ratio [m/z]) data are converted to images. Custom image analysis software is used to detect and integrate peaks in arbitrarily defined regions of the time-m/z map. These integrated peak volumes can be used to quantitate distinct component classes of the polymer mixtures.

Evaluation of capillary supercritical fluid chromatography with mass spectrometric detection for the analysis of a drug (mebeverine) in a dog plasma matrix

Supercritical fluid chromatography with mass spectrometric detection was evaluated as a technique for the analysis of drugs in biological fluids. Dog plasma was spiked with a model drug, mebeverine, and with a deuterium-labeled analog of mebeverine. The spiked plasma was prepared for analysis by solid-phase extraction on octadecylsilane cartridges. Mebeverine levels in the spiked dog plasma samples were determined by interpolation from a standard curve. Accuracy and precision of the analysis were determined within and between days. In general, accuracy was found to be 100 +/- 15% for plasma samples spiked with 6 to 60 ng mebeverine/ml. The relative standard deviation for replicate sample analysis over this concentration range was between 5 and 12.5%.

Off-line supercritical fluid chromatography/plasma desorption mass spectrometry for simple mixture characterization

SummarySupercritical fluid chromatography/mass spectrometry (SFC/MS) is a powerful tool for the characterization of less volatile, complex mixtures. Unfortunately, on-line SFC/MS instrumentation is relatively expensive, and instrument time is limited. Here we describe an investigation of off-line SFC/plasma desorption mass spectrometry (PDMS) for the characterization of relatively simple mixtures. As an example of the potential of this approach, PD mass spectra of individual oligomers from a mixture of propoxylated dimethylpyrazoles are presented. The mixture was separated by capillary SFC with ultraviolet (UV) absorbance detection, individual peaks were collected on PDMS foils, and the foils were subjected to PDMS analysis. A variety of PDMS foils were compared, and NaI-pretreated, nitrocellulose-coated, aluminized-mylar foils provided the best results for the mixtures investigated in this work. Thirteen nanograms of an ethoxylated standard provided a signal-to-noise ratio of 3. The reproducibility of the overall method, as implemented here with manual collection, was relatively poor. The relative standard deviation of the PDMS response for an alkyl-phenol ethoxylate standard was 26%. Off-line PDMS characterization of a non-UV-absorbing compound, sucrose octamyristate, is also demonstrated. The retention time of the compound of interest is determined during an SFC separation using flame ionization detection. During a second separation, the detector flame is extinguished and the PDMS foil is held above the detector at the appropriate retention time. While limited in its ability to resolve closely eluting components, the off-line approach does provide greater flexibility and potentially greater mass range than conventional on-line SFC/MS. This approach also has the potential to provide the majority of SFC users, who do not have on-line SFC/MS capabilities, with a relatively straightforward method for obtaining mass spectral information on important peaks in an SFC separation.