Session: Advances in Mass Spectrometry:

Collision cross-section (CSS) measurements of prohibited steroids are of great interest to the competitive sporting world. The narrow mass to charge (m/z) window for most steroids provides a major challenge for the identification of steroids using traditional Mass Spec techniques as identical masses lead to the different steroids obscuring each other. Ion-mobility spectrometry provides an accurate measure of the molecules’ rotationally averaged collision cross-section (CCS) in the gas phase and is thus related to ionic shape. Ion Mobility in conjunction with Mass Spec provides a separation between isomers based on their physical dimensions when passed through a buffer gas. Our group has developed a class-specific calibration mix that reduces the relative standard deviation (RSD) when compared to the traditional Agilent tune mix.
The Mason-Schamp equation can be used to determine the CCS of ions through the drift tube. Many of the required parameters are measured directly in the instrument, but ion time inside the drift tube must be determined. Stepped field measurements vary the electrical field to determine a linear slope. Extrapolating the slope to the intercept provides a value for determining the time in the drift tube.
The time required for a stepped field cannot work on the chromatographic timescale so a calibration curve is required. To determine CCS in chromatographic time requires the creation of a calibration curve. Many IMMS calibration curves use the Agilent tune mix with repeatability of approximately 2% RSD.
Our group has performed stepped field and single field measurements for numerous prohibited steroids. We have developed a steroid specific steroid mix that reduces the RSD from 2% to 0.2%. Using this class-specific tune mix would greatly improve CCS measures of steroid molecules during single field measurements. The new calibration mix will improve the identification of steroids when using IMMS techniques.

shon neal

Florida Institute of Technology (FIT)

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