John C. Fjeldsted

Conformational ordering of biomolecules in the gas phase: nitrogen collision cross sections measured on a prototype high resolution drift tube ion mobility-mass spectrometer.

Ion mobility-mass spectrometry measurements which describe the gas-phase scaling of molecular size and mass are of both fundamental and pragmatic utility. Fundamentally, such measurements expand our understanding of intrinsic intramolecular folding forces in the absence of solvent. Practically, reproducible transport properties, such as gas-phase collision cross-section (CCS), are analytically useful metrics for identification and characterization purposes. Here, we report 594 CCS values obtained in nitrogen drift gas on an electrostatic drift tube ion mobility-mass spectrometry (IM-MS) instrument. The instrument platform is a newly developed prototype incorporating a uniform-field drift tube bracketed by electrodynamic ion funnels and coupled to a high resolution quadrupole time-of-flight mass spectrometer. The CCS values reported here are of high experimental precision (±0.5% or better) and represent four chemically distinct classes of molecules (quaternary ammonium salts, lipids, peptides, and carbohydrates), which enables structural comparisons to be made between molecules of different chemical compositions for the rapid “omni-omic” characterization of complex biological samples. Comparisons made between helium and nitrogen-derived CCS measurements demonstrate that nitrogen CCS values are systematically larger than helium values; however, general separation trends between chemical classes are retained regardless of the drift gas. These results underscore that, for the highest CCS accuracy, care must be exercised when utilizing helium-derived CCS values to calibrate measurements obtained in nitrogen, as is the common practice in the field.

Capillary supercritical-fluid chromatography with conventional flame detectors

Abstract Coupling of a supercritical-fluid chromatograph to flame-ionization and nitrogen-thermionic detectors is described. A fused-silica capillary restrictor was used to maintain pressure in the analytical column and to expand the effluent into the detector flame jet. Selected applications demonstrate the usefulness of these gas chromatographic detectors in supercritical-fluid chromatography.

Direct fluid injection interface for capillary supercritical fluid chromatography-mass spectrometry☆

Abstract A new interface for capillary column supercritical fluid chromatography-mass spectrometry (SFC-MS) is described and initial results are presented. The advantages of SFC include the ability to separate high-molecular-weight, non-volatile and thermally unstable compounds not amenable to gas chromatography. Capillary column SFC-MS has potential advantages aver high-performance liquid chromatography-MS owing to the higher possible chromatographic efficiency, mobile phase volatility and the simplicity of the interface design. The direct fluid injection interface provides for transfer of the total capillary SFC effluent into a chemical ionization source. Initial results are presented to illustrate the separation and analysis of simple mixtures of aromatic hydrocarbons and styrene oligomers using n -pentane as the mobile phase.

Scanning fluorescence detection in capillary supercritical fluid chromatography

Abstract The design and performance of a scanning fluorescence detector for capillary supercritical fluid chromatography are presented. On-the-fly spectra are obtained and stored using a microcomputer. A novel fiber optic-aided detector design eliminates most background noise, and quantities as low as 1 ng give rise to full spectra. Detector dead volume is also minimized when this configuration is used.

An Interlaboratory Evaluation of Drift Tube Ion Mobility–Mass Spectrometry Collision Cross Section Measurements

Collision cross section (CCS) measurements resulting from ion mobility-mass spectrometry (IM-MS) experiments provide a promising orthogonal dimension of structural information in MS-based analytical separations. As with any molecular identifier, interlaboratory standardization must precede broad range integration into analytical workflows. In this study, we present a reference drift tube ion mobility mass spectrometer (DTIM-MS) where improvements on the measurement accuracy of experimental parameters influencing IM separations provide standardized drift tube, nitrogen CCS values (DTCCSN2) for over 120 unique ion species with the lowest measurement uncertainty to date. The reproducibility of these DTCCSN2 values are evaluated across three additional laboratories on a commercially available DTIM-MS instrument. The traditional stepped field CCS method performs with a relative standard deviation (RSD) of 0.29% for all ion species across the three additional laboratories. The calibrated single field CCS method, which is compatible with a wide range of chromatographic inlet systems, performs with an average, absolute bias of 0.54% to the standardized stepped field DTCCSN2 values on the reference system. The low RSD and biases observed in this interlaboratory study illustrate the potential of DTIM-MS for providing a molecular identifier for a broad range of discovery based analyses.

Supercritical fluid chromatography - mass spectrometry

Abstract A new interface for capillary column supercritical fluid chromatographymass spectrometry (SFC-MS) is described and initial results are presented. The advantages of SFC include the ability to separate high molecular weight, nonvolatile, and thermally unstable compounds not amenable to GC. A capillary column SFC-MS interface can replace HPLC-MS in most applications and has advantages due to the higher possible chromatographic efficiency, mobile phase volatility, and the simplicity of the interface design. Pressure programming during the chromatographic separation also allows precise control over the solvating power of the supercritical fluid mobile phase. The direct fluid injection interface provides for transfer of the total SFC effluent into a chemical ionization source. Results are presented to illustrate the separation analysis of mixtures of aromatic hydrocarbons and styrene oligomers using n -pentane and carbon dioxide as the mobile phase.