Magnetic Sector MS Research Articles

Real-time characterization of mammalian cell culture bioprocesses by magnetic sector MS.

Mammalian cell culture processes were characterized upon the analysis of the exhaust-gas composition achieved through the on-line integration of a magnetic sector MS analyser with benchtop bioreactors. The non-invasive configuration of the magnetic sector MS provided continuous evaluation of the bioreactor's exhaust gas filter integrity and facilitated the accurate quantification of O2 and CO2 levels in the off-gas stream which ensured preserved bioreactor sterility prior to cell inoculation and provided evidence of the ongoing cellular respiratory activity throughout the cultures. Real-time determination of process parameters such as the Respiratory Quotient (RQ) allowed for precise pin-pointing of the occurrence of shifts in cellular metabolism which were correlated to depletion of key nutrients in the growth medium, demonstrating the suitability of this technology for tracking cell culture process performance.

Quantifying Short-Chain Chlorinated Paraffin Congener Groups.

Accurate quantification of short-chain chlorinated paraffins (SCCPs) poses an exceptional challenge to analytical chemists. SCCPs are complex mixtures of chlorinated alkanes with variable chain length and chlorination level; congeners with a fixed chain length (n) and number of chlorines (m) are referred to as a "congener group" CnClm. Recently, we resolved individual CnClm by mathematically deconvolving soft ionization high-resolution mass spectra of SCCP mixtures. Here we extend the method to quantifying CnClm by introducing CnClm specific response factors (RFs) that are calculated from 17 SCCP chain-length standards with a single carbon chain length and variable chlorination level. The signal pattern of each standard is measured on APCI-QTOF-MS. RFs of each CnClm are obtained by pairwise optimization of the normal distribution's fit to the signal patterns of the 17 chain-length standards. The method was verified by quantifying SCCP technical mixtures and spiked environmental samples with accuracies of 82-123% and 76-109%, respectively. The absolute differences between calculated and manufacturer-reported chlorination degrees were -0.9 to 1.0%Cl for SCCP mixtures of 49-71%Cl. The quantification method has been replicated with ECNI magnetic sector MS and ECNI-Q-Orbitrap-MS. CnClm concentrations determined with the three instruments were highly correlated (R2 > 0.90) with each other.

Cryogenic zone compression for the measurement of dioxins in human serum by isotope dilution at the attogram level using modulated gas chromatography coupled to high resolution magnetic sector mass spectrometry

A liquid nitrogen jet-cooled thermal modulator dedicated to comprehensive two-dimensional gas chromatography has been mounted in a GC oven coupled to a high resolution magnetic sector mass spectrometry instrument. The data acquisition parameters of the slow double-focusing magnetic sector MS instrument have been optimized to accommodate the description of the narrow modulated GC peaks. Acquisition rates were increased to 20 Hz, while maintaining high mass resolution. Selected ion monitoring (SIM) descriptors, typically including several ions for both native and labeled analytes, were thus reduced to one or two to ensure enough MS cycle time. For maximization of the sensitivity enhancement due to cryogenic zone compression (CZC), the entire GC peak of interest was trapped and remobilized in one event. Optimization of the method resulted in the ability to detect low attogram (ag) amounts of 2,3,7,8-tetrachlorodibenzo- p-dioxin (2,3,7,8-TCDD) (313 ag gives a S/N of 400:1), a level that had not yet been attained using classical GC–HRMS. An isotope-dilution calibration curve was constructed using 13C 12-2,3,7,8-TCDD as the internal standard over the range of 500 ag/μL to 35,000 ag/μL ( R 2 = 0.9953). Analyses of a standard natural human reference serum-matrix NIST SRM 1589a containing 223 ag of 1,2,3,7,8-pentachlorodibenzo- p-dioxin (1,2,3,7,8-PeCDD) (70% recovery rate assumed) resulted in a peak with a S/N of 188:1 (4 sigma, m/ z = 355.8546). Measurement of 2,2-bis (4-chlorophenyl-1,1,1-trichloroethane) (DDE) and 2,2′,4,4′,5,5′-hexabromobiphenyl (BB-153) in human dried-blood spot (DBS) samples is also reported to illustrate the usefulness of such a sensitive technique. Finally, some of the challenges related to sample preparation, blank levels, and to the fact of measuring of such a limited number of molecules (less than 600,000 TCDD molecules) are discussed.

A GC – magnetic sector MS method for identification and quantification of fatty acids in ewe milk by different acquisition modes

A general method for qualitative and quantitative determination of fatty acids (FAs) using GC-MS was developed and tested on ewe milk. A total number of 38 poly unsaturated FAs, monounsaturated FAs and saturated FAs, from C6:0 to C24:1, were used in a comparative study of scan, reconstructed ion chromatogram and SIM. Fatty acid methyl esters in standard solutions as well as in milk from ewe were analyzed by these techniques, using a sector instrument. Instrument precision, linearity, LOD and LOQ, as well as calibration behavior and response factors were investigated for each approach. The quantitative results obtained by each technique were compared. All techniques had values for LOD and LOQ in the ng/mL region.

A microcapillary column switching HPLC-electrospray ionization MS system for the direct identification of peptides presented by major histocompatibility complex class I molecules.

A microcapillary column switching high-performance liquid chromatography (HPLC) system was developed for the separation of major histocompatibility complex (MHC) class I associated peptides. Combination of the column switching system with electrospray ionization mass spectrometry (ESIMS) enabled the detection and identification of the peptides at low-femtomole levels. Sample volumes of 30-50 microL were injected and concentrated onto a short, 100-micron-i.d. precolumn. The precolumn was coupled to a 100-micron-i.d. reversed-phase analytical HPLC column via a six-port valve. Peptides were separated on the analytical column using an ESI-compatible mobile phase at a flow rate of 0.5 microL/min. Peptides were eluted directly into the ESI source of either a magnetic sector MS or an ion trap MS. Peptides associated with human leukocyte antigen A*0201 molecules were determined in immunoaffinity-purified extracts from either measles virus infected cells or uninfected cells by microcapillary column switching HPLC-ESIMS. The approach toward detection of virus-specific peptides we used was based on the comparison of ion chromatograms obtained from the LC-MS analysis of extracts from virally infected cells and their uninfected counterparts. In this way, the molecular mass of peptides unique to virus infected cells was obtained. The utility of the system is demonstrated by the identification of a candidate epitope. Microcapillary column switching HPLC was used along with ESI ion trap tandem MS to identify the naturally processed viral peptide KLWESPQEI. This peptide was found to derive from the measles virus nonstructural protein C. The approach described here provides a versatile and sensitive method for the direct identification of viral peptides associated with MHC class I molecules.

Analytical Currents: Interfacing a magnetic sector MS to SFC

Analytical Currents: Interfacing a magnetic sector MS to SFC