Human auditory thresholds during deep, saturation helium-oxygen dives.

A method is described for the enrichment of very long chain unsaturated fatty acids from total fatty acids of Ximenia oil and their identification as picolinyl esters by means of liquid chromatography-mass spectrometry with atmospheric pressure chemical ionization (LC-MS/APCI). The method is based on the use of preparative reversed phase HPLC and their subsequent identification by microbore LC-MS/APCI. The combination of these two techniques was used to identify unusual unsaturated VLCFAs up to tetracontenoic acid. All four positional isomers of tetratriacontenoic acid were also synthesized to unambiguously confirm their structure.

Atmospheric Pressure↗

PubMed2007

Determination of selenosugars in crude human urine using high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry.

The narrow gap between essentiality and toxicity of selenium requires detailed investigations on selenium metabolism in order to find suitable indicators for the selenium status in the human body. Current methods for quantitative selenium speciation in human urine are based on separation by high-performance liquid chromatography (HPLC) coupled online with elemental mass spectrometry (MS), and the potential of molecular MS detection techniques for the reliable identification and quantification of selenosugars in crude human urine has not been utilized. Now we report the development of an HPLC tandem mass spectrometric (MS/MS) method for the reliable determination in crude human urine of three significant selenium urinary metabolites, collectively termed selenosugars, namely methyl 2-acetamido-2-deoxy-1-seleno-beta-D-galactopyranoside (SeGalNAc), methyl 2-acetamido-2-deoxy-1-seleno-beta-D-glucopyranoside (SeGluNAc) and methyl 2-amino-2-deoxy-1-seleno-beta-D-galactopyranoside (SeGalNH2). Reversed-phase HPLC, with and without cation-exchange guard columns, was applied for the separation of the selenosugars, and atmospheric pressure chemical ionization (APCI) and selected reaction monitoring (SRM) were used for selective and sensitive detection. The collision-induced dissociation behaviour of the selenosugars was studied in detail using APCI triple quadrupole MS/MS and electrospray ion trap MS. The developed method was applied to urine samples collected prior to and after selenium supplementation for the quantification of SeGalNAc using both external calibration and the method of standard additions. Additionally, SeGalNH2 was detected in urine samples after Se supplementation. Finally, neutral loss scanning was explored as a possible method for the detection of unknown methyl-selenosugars.

Atmospheric Pressure↗

PubMed2007

New mass-spectrometry-based strategies for lipids.

In the past dozen years, many new strategies for mass-spectrometry-based analyses of lipids have been developed. Lipidomics has emerged as a comprehensive approach to analysis of lipids from biological systems, and the most-utilized lipidomics methodologies involve electrospray ionization (ESI) sources and triple quadrupole analyzers. While mass spectral techniques for lipid profiling have advanced, challenges in developing uniform data acquisition methods and in handling, storing, and analyzing mass spectral data remain. Investigation of other ionization methods, including matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure chemical ionization (APCI), has demonstrated that these are useful in specific applications. APCI is particularly amenable to analysis of less polar lipids, and MALDI provides a rapid technology with application for tissue imaging. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is particularly suited for imaging of tissues and cells.

Atmospheric Pressure↗