An Experimental Investigation of the Liquid Flow Induced by a Pulsed Electrical Discharge Plasma

In this work, particle image velocimetry has been used to visualize and quantify plasma-induced flow fields in liquid water. Experiments were performed in a rod-plane plasma reactor with a thin wire electrode suspended above the surface of the liquid in argon gas and a grounded plate immersed in the liquid. The velocity field has been quantified for two types of solutions: (1) aqueous NaCl solutions of varying solution conductivities and discharge frequencies and (2) aqueous NaCl solutions containing varying concentrations of the following four organic compounds: rhodamine B dye, caffeine, fluoxetine, and perfluorooctanoic acid. Results show that in neat water and aqueous caffeine solutions, the liquid is “pulled” along by the interaction of the gas molecules with the liquid molecules at the free surface and thus the direction of the liquid flow is in the direction of the gas phase flow (i.e., away from the discharge location). However, the flow was reversed (i.e., towards the discharge) for those solutions with strong surfactants such as perfluorooctanoic acid. The magnitude of the reversal depended on the initial concentration of the compound and for some compounds as time progressed the reversed flow pattern weakened and then reverted to a normal flow pattern. To determine the most likely cause of these flow reversals, a simple numerical model of the velocity field was developed to estimate relative contributions of various flow inducing mechanisms. The model indicates that in the presence of surfactants, Marangoni stresses are responsible for inducing the flow in the liquid.     

A gas calorimeter for use at 10.6 μm

An SF₆ gas calorimeter has been developed and used operationally in a large aperture, multijoule, short-pulse, CO₂ laser system. Pressure rises rather than temperature rises are measured in the absorbing cell. Measured pressure sensitivities of 20 pascal/joule are in good agreement with the calculated values.     

Kinetically distinct triplets in the photorearrangement of 2-phenylcyclohexanone to cis- and trans-6-phenyl-5-hexenals

A reinvestigation of the photochemistry of 2-phenylcyclohexanone reveals that the two aldehyde products, cis- and trans-6-phenyl-5-hexanal, come from triplets of different lifetimes. That the two distinct triplets are not simply the two conformers with phenyl axial and equatorial is demonstrated by the similar behavior of cis-4-t-butyl-2-phenylcyclohexanone. The trans isomer of this ketone is photostable. It is concluded that trans-enal arises by an almost concerted out-of-plane cleavage which forms a 1,6-biradical in the perfect geometry for disproportionation to trans-enal.The precursor to cis-enal may be a minor rotamer of 1 which is forced by nonbonded interactions into a cleavage mode which twists the biradical into a geometry suitable for at least partial formation of cis-enal. In both cases biradicals must be very short-lived and not rotationally equilibrated.     

Gasanalyse

Ohne Zusammenfassung     

Gasanalyse

Analytical and Bioanalytical Chemistry -     

Measurement of 3-hydroxyisovaleric acid in urine from marginally biotin-deficient humans by UPLC-MS/MS

Measurement of 3-hydroxyisovaleric acid (3HIA) in human urine has been shown to be a useful indicator of biotin status for a variety of clinical situations, including pregnancy. The work described herein presents a novel UPLC-MS/MS method for accurate and precise quantitation of urinary 3HIA. This method utilizes sample preparation prior to quantitation that has been simplified compared to the previous GC-MS method. To demonstrate the suitability of the UPLC-MS/MS method for human bio-monitoring, this method was used to measure 3-HIA in 64 human urine samples from eight healthy adults in whom marginal biotin deficiency had been induced experimentally by egg white feeding. 3HIA was detected in all specimens; the mean concentration [±standard deviation (SD)] was 80.6 ± 51 μM prior to inducing biotin deficiency. Mean excretion rate for 3HIA (expressed per mol urinary creatinine) before beginning the biotin-deficient diet was 8.5 ± 3.2 mmol 3HIA per mol creatinine and the mean increased threefold with deficiency. These specimens had been previously analyzed by GC-MS; the two data sets showed strong linear relationship with a correlation coefficient of 0.97. These results provide evidence that this method is suitable for bio-monitoring of biotin status in larger populations.     

Micellar high-performance liquid chromatographic determination of folylpolyglutamate hydrolase activity

A rapid and sensitive method for the quantitative determination of folylpolyglutamate hydrolase activity in crude tissue extracts was developed. The procedure is based on high-performance liquid chromatographic separation of folate analogue mono- and polyglutamates on a reversed-phase column using sodium dodecyl sulfate in water as the mobile phase. Interfering substances in tissue extracts were removed by gel filtration on centrifugally-eluted mini-columns of Sephadex G-25 prior to incubation of polyglutamate substrate with tissue extract hydrolase. Reactions were terminated by denaturation of the enzyme in sodium dodecyl sulfate, which subsequently served as the micellar solvent system for chromatographic separation of substrate from reaction products.