Atmospheric pressure photoionization for ionization of both polar and nonpolar compounds in reversed-phase LC/MS

Atmospheric pressure photoionization can provide high ionization efficiency simultaneously to both polar and nonpolar compounds delivered in reversed-phase solvent. The method to achieve this utilizes toluene as a dopant and simply requires that the solvent flow be limited so that reactions between toluene photoions and the organic component of the solvent are not driven to completion. Under these conditions, toluene photoions remain in the source for ionizing nonpolar compounds via charge exchange (electron transfer), while protonated solvent ions are available for proton-transfer reactions with polar molecules. The reagent ion mixture is then suitable for ionizing a wide range of both polar and nonpolar compounds. The critical effect of solvent flow rate is demonstrated here with results for a test analyte, 9-methylanthracene, which may be ionized by either charge exchange or proton transfer. For a solvent of 50:50 methanol/water (v/v), lowering the flow from 200 to 50 microL min-1 results in a 10x increase in charge exchange ionization efficiency--further flow reductions provide even greater enhancements. This method is compatible with sample delivery by direct infusion and micro- and narrow-bore LC, as well as conventional LC using a flow splitter.     

Effects of aerobic and anaerobic conditions on P, N, Fe, Mn, and Hg accumulation in waters overlaying profundal sediments of an oligo-mesotrophic lake

Concentrations of key nutrients and metals in water overlaying profundal sediments were evaluated in replicate experimental chambers containing undisturbed sediment-water interface samples from Deer Lake, an oligo-mesotrophic lake in eastern Washington. Chambers were incubated under three sequential phases: aerobic (21d), anaerobic (27d), and second aerobic (14d). In general, nutrients and metals in chamber water were lower under aerobic versus anaerobic conditions. However, in some cases compounds anticipated to appear only under anaerobic conditions, including ammonia, phosphate, and manganese, were observed during aerobic conditions. Correlation analysis elucidated a number of interactions between compounds. Phosphate correlated significantly (p<0.05) with iron during all incubation phases, suggesting that phosphorus cycling was controlled by iron. Cycling of nitrate and ammonia was tightly and significantly coupled under aerobic conditions. During both aerobic phases, nitrate increased while ammonia decreased, likely as a result of biological nitrification. Finally, mercury appeared during mildly reducing conditions and showed a significant correlation with manganese during the anaerobic phase, suggesting that Mn oxide reduction was the source of Hg in chamber water.