Gas chromatography-mass spectrometry selected ion monitoring and gas chromatography-tandem mass spectrometry selected reaction monitoring analyses of mono-, di- and tri-unsaturated C highly branched isoprenoid alkene biomarkers in sea ice and sediment samples: A comparative study.

Rationale: The efficiency of selected ion monitoring (SIM) and selected reaction monitoring (SRM) analyses for the quantification of three mono-, di- and tri-unsaturated highly branched isoprenoid (HBI) alkenes (IP , IPSO and HBI III, respectively), often used as proxies for the occurrence of Arctic and Antarctic sea ice or the adjacent open waters, was compared.

Methods: Gas chromatography (GC)-mass spectrometry (MS)/SIM and GC/MS/MS/SRM analyses were carried out on dilute solutions made from purified standards of these three HBIs, and then on hydrocarbon fractions of several sediment and sea ice sample extracts. More efficient and specific SRM transitions were selected after collision-induced dissociation of each precursor ion at different collision energies.

Singlet oxygen-induced alteration of bacteria associated with phytodetritus: Effect of irradiance.

Contrasting irradiation of senescent cells of the diatom Thalassiosira sp. in association with the bacterium Pseudomonas stutzeri showed the effect of intensity of irradiance on the transfer of singlet oxygen ( O ) to bacteria attached to phytoplanktonic cells. Under low irradiances, O is produced slowly, favors the oxidation of algal unsaturated lipids (photodynamic effect), and limits O transfer to attached bacteria.

Cellular Damage of Bacteria Attached to Senescent Phytoplankton Cells as a Result of the Transfer of Photochemically Produced Singlet Oxygen: A Review.

Several studies set out to explain the presence of high proportions of photooxidation products of cis-vaccenic acid (generally considered to be of bacterial origin) in marine environments. These studies show that these oxidation products result from the transfer of singlet oxygen from senescent phytoplankton cells to the bacteria attached to them in response to irradiation by sunlight. This paper summarizes and reviews the key findings of these studies, i.

Use of Trifluoro-Acetate Derivatives for GC-MS and GC-MS/MS Quantification of Trace Amounts of Stera-3β,5α,6β-Triols (Tracers of Δ-Sterol Autoxidation) in Environmental Samples.

Stera-3β,5α,6β-triols make useful tracers of the autoxidation of Δ-sterols. These compounds are generally analyzed using gas chromatography-mass spectrometry (GC-MS) after silylation. Unfortunately, the 5α hydroxyl groups of these compounds, which are not derivatized by conventional silylation reagents, substantially alter the chromatographic properties of these derivatives, thus ruling out firm quantification of trace amounts.