A negative ion electrospray ionization tandem mass spectrometric technique was developed for the analysis of glycerophospholipids. Examination of the product ion mass spectrum of the deprotonated molecular ion provided sufficient information to identify both the class of glycerophospholipid and the molecular weights of the two fatty acid moieties. This technique was applied to the profiling of glycerophospholipids present in the chloroform/methanol extracts of four different bacterial species. The principal bacterial phospholipids detected by this technique were phosphatidylglycerols and diphosphatidylglycerols, accompanied by small amounts of phosphatidylethanolamines for two of the bacterial species examined. The fatty acid composition of the phosphatidylglycerols for each bacteria was determined by tandem mass spectrometry and presented graphically. Differences in the fatty acid composition for each bacterial species were readily apparent from a visual examination of the data sets.

In ion mobility spectrometry (IMS), reduced mobility values (K0) are used as a qualitative measure of gas phase ions, and are reported in the literature as absolute values. Unfortunately, these values do not always match those collected in the field. One reason for this discrepancy is that the buffer gas may be contaminated with moisture or other volatile compounds. In this study, the effect of moisture and organic contaminants in the buffer gas on the mobility of IMS standards and analytes was investigated for the first time using IMS directly coupled to mass spectrometry. 2,4-dimethylpyridine, 2,6-di-tert-butyl pyridine (DTBP), and tetrabutylammonium, tetrapropylammonium, tetraethylammonium, and tetramethylammonium chlorides were used as chemical standards. In general, the mobility of IMS standard product ions was not affected by small amounts of contamination while the mobilities of many analytes were affected. In the presence of contaminants in the buffer gas, the mobility of analyte ions is often decreased by forming ionmolecule clusters with the contaminant. To ensure the measurement of accurate reduced mobility values, two IMS standards are required: an instrument and a mobility standard. An instrument standard is not affected by contaminants in the buffer gas, and provides an accurate measurement of the instrumental parameters, such as voltage, drift length, pressure, and temperature. The mobility standard behaves like an analyte ion in that the compound's mobility is affected by low levels of contamination in the buffer gas. Prudent use of both of these standards can lead to improved measurement of accurate reduced mobility values.

No abstract

Ion mobility spectrometry (IMS) is widely used to characterize compounds of interest (COIs) based on their reduced mobility ( K) values. In an attempt to increase the accuracy and agreement of studies, the most recommended method has been to use a reference compound with a known K value to calibrate the instrument and calculate COI K values from normalized spectra. Researchers are limited by the accuracy of previous K value reference measurements on which to base their calibrations. Any inaccuracy in these reference K values, typically ±2%, will propagate through to the calculated K value of the COI. For this reason, there is a need to standardize reference K values with improved accuracy. Through improvement of the accuracy of reference measurements, a lower degree of error will propagate through new K value calculations. The K values of the ammonium reactant ion, the potential reference standard dimethyl methylphosphonate (DMMP), and three explosive COIs were characterized at multiple drift gas temperatures, drift gas water contents, and electric field strengths on an accurate ion mobility spectrometry instrument. K values reported here are known to ±0.1% as a result of reducing the error of all instrumental parameters.