Glow Discharge Plasma Ionization Mass Spectrometry for Direct Detection of Oxygenated Organic Compounds in the Gas-phase.

This study describes a direct analysis of oxygenated organic compounds, such as ketones, esters and ethers, rapidly and easily using a soft plasma ionization (SPI) source combined with a Q-mass spectrometer. A related molecular ion, [2M+H]+, in which a sample molecule (M) can undergo protonation via water clusters, such as [(H2O)n+H]+ and [N2(H2O)n+H]+, in an ambient air glow discharge plasma, can be dominantly detected as a base peak with little or no fragmentation at a pressure of several kPa. Oxygenated organic compounds with high proton affinity were found to generate their dimers through the hydrogen bonding interaction at higher pressures. A deuterated solvent was used to examine whether or not the adduct ion of analyte was derived from the solvent. The formation of [2M+H]+ strongly depended on the time. A two-dimensional spectrometer was used to obtain the distribution of several excited species and then to confirm the ionization reactions of the analyte in the SPI source. The sample molecule would be readily ionized through Penning-type collisions with excited N2, which causes fragmentation for oxygenated compounds due to the lower pressures (approx. 1.0 kPa) while it is ionized by an attachment with protons from water clusters at higher pressures (several kPa). The SPI source can be a new and powerful tool for soft ionization in direct analysis of volatile organic compounds (VOCs).

Direct analysis of saturated hydrocarbons using glow discharge plasma ionization source for mass spectrometry.

The ionization source based on glow discharge plasma using ambient air is driven by a pulsed direct-current voltage for soft plasma ionization (SPI). The novelty of this work is that molecular ions [M+13]+ related to the analyte species (M), which may be formed by numerous oxidation, can be dominantly detected as a base peak with little or no fragmentation of them in an air plasma at a pressure of several kPa. The unique ion [M+13]+ was assigned to the oxidation product, [M+O-3H]+, which was confirmed as a deuterated ion [M+O-3D]+ ([M+10]+) by using a deuterated solvent. The ionization reactions were suggested that the product ion [M+O-3H]+ may arise from hydride abstraction reaction of M with O2+•, dehydrogenation reaction of [M-H]+• and subsequently oxidation reaction of [M-3H]+ with O3. n-Alkane mixtures was also measured to evaluate the intermolecular interaction in this system. The limits of detection (LOD) were in the range of 0.126-1.68 ppmv and the relative standard deviation (RSD) for repeatability was approximately 10.0% at the lowest concentration. To our knowledge, this is the first report demonstrating that the spectrum pattern of saturated hydrocarbons could be directly determined without any complicated fragmentation.

Determination of fatty acids in human sweat during fasting using GC/MS.

Fatty acids (FAs) are biological molecules that are used as major metabolic fuels, and are concerned in important metabolic processes. We have performed a non-invasive and technically rapid and simple method for collecting sweat from humans, followed by GC/MS determination. The sweat was collected from each volunteer (the middle finger) by spraying 70% ethanol aqueous solution (no harmful solvent) into a 1.5-cm(3) plastic vial. Analysis of FAs in sweat showed that the sweat solution contains lauric acid (C12:0), myristic acid (C14:0), palmitic acid (C16:0), oleic acid (C18:1), and stearic acid (C18:0). Here, it is demonstrated that FA concentrations for 4 young subjects correlated positively with percent of body fat (r = 0.78) and that the total FA levels for them increased progressively with increasing fasting time when a subject fasted throughout the experiment.

Redox potentials and HPLC behavior of cobalt and iron complexes with pyridylazo compounds.

The redox potentials of cobalt and iron complexes with ten pyridylazo compounds, E(0)(ML2) (ML(2)(+/0); M: Co(III/II), Fe(III/II); L(-): pyridylazo compounds), have been determined in order to explore the difference in their reversed-phase HPLC behavior. The redox potentials of Co complexes were in the range of -0.62 - 0.03 V, while those of Fe complexes were -0.06 - 0.59 V relative to 0.20 V for ferricinium/ferrocene. The redox potentials of both the Co and Fe complexes were linearly correlated to the basicities of the ligands. The correlation was quantitatively explained by a difference in dependence of the stabilities of M(III) and M(II) complexes on the ligand basicities. The complex of [Co(III)L(2)](+) or [Fe(II)L(2)] with any compound injected in the reversed-phase HPLC system was detected without any change in the composition. When [Co(II)L(2)] was injected, only those complexes having the highest potentials of E(0)(CoL2) congruent with 0.0 V were detected as [Co(II)L(2)], while other complexes having lower potentials gave a peak of [Co(III)L(2)](+). When [Fe(III)L(2)](+) was injected, only complexes having the lowest potentials of E(0)(FeL2) congruent with 0.0 V were detected as [Fe(III)L(2)](+), while others having higher potentials gave a peak of [Fe(II)L(2)].

Identification of gas emanated from human skin: methane, ethylene, and ethane.

We investigated whether methane, ethylene and ethane gas can be detected in gas emanating from human skin, which is called skin gas. Skin gas was collected with a homemade stainless-steel trap system, which was cooled with liquid nitrogen, and analyzed with a gas chromatograph fitted with a flame ionization detector (FID). Skin-gas samples were obtained by covering a hand for 30 min with a polyfluorovinyl bag in which pure helium gas was introduced. The bag, the trap system and GC were set up online to avoid any contamination by air. Methane, ethylene and ethane in skin gas were successfully collected at an average amount emanated for 30 min (from ten subjects) of 150 +/- 63, 20 +/- 11 and 17 +/- 8 [mean +/- SD] pg/cm2, respectively.