Polychlorinated aromatic hydrocarbons in a soil sample measured using gas chromatography/multiphoton ionization/time-of-flight mass spectrometry.

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was applied to a soil sample to survey several groups of polychlorinated aromatic hydrocarbons (polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), polychlorinated diphenylethers (PCDEs), and polychlorinated terphenyls (PCTs)). The signal peaks in the two-dimensional display of GC/MS could be easily and accurately assigned from the intensity distribution of the isotope peaks, even in the presence of numerous interfering species. Using this technology, mutual interferences between organochlorine compounds can be readily recognized from the data of the two-dimensional display after a measurement, although the separation of these compounds is sometimes difficult using high-resolution magnetic-sector-type mass spectrometry. This approach, based on MPI, results in less fragmentation, and is useful for the identification of analytes. Thus, GC/MPI/TOF-MS allows for the simultaneous determination of PCDD/Fs and related compounds in real samples containing numerous interfering species.

Analysis of dioxins by gas chromatography/resonance-enhanced multiphoton ionization/mass spectrometry using nanosecond and picosecond lasers.

Dioxins in a soil sample were measured using gas chromatography/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry coupled with different types of laser sources. The fourth-harmonic emission (266 nm) of a nanosecond Nd:YAG laser (1 ns) provided low ionization efficiency, especially for highly chlorinated dioxins/dibenzofurans (CDDs/CDFs). The ionization efficiency was improved using the fourth-harmonic emission (266 nm) of a picosecond Nd:YAG laser (4 ps), due to shorter singlet excited-state lifetimes. It was, however, difficult to efficiently ionize hepta-CDD and octa-CDD/CDF, because of their shorter lifetimes, which were induced by stronger spin-orbit coupling that led to efficient relaxation of the excited molecule to triplet levels. The ionization efficiency was substantially improved using the fifth-harmonic emission (213 nm) of the picosecond Nd:YAG laser (4 ps), in which the analyte molecule that was relaxed to triplet levels was efficiently ionized using a photon with sufficient energy for ionization, although the pulse energy obtained at 213 nm was only one-third of the pulse energy obtained at 266 nm. The limits of detection achieved for 17 toxic polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs) were 0.41-45 pg. The analytical instrument developed in the present study performed sufficiently well for the practical trace analysis of dioxins in soil samples.

Gas chromatography/femtosecond multiphoton ionization/time-of-flight mass spectrometry of dioxins.

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was developed for trace analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The use of an ultraviolet femtosecond laser (266 nm) allowed the sensitive, as well as selective, determination of PCDD/Fs with short singlet-excited-state lifetimes; the detection limit was 19 fg for 1,3,6,8-tetraCDF. Performance of the analytical instrument was examined and was ascertained to be satisfactory for all the criteria (K0311) prescribed by the Japanese Industrial Standards (JIS). The relative ionization efficiencies of (12)C-native PCDD/Fs against (13)C-labeled PCDD/Fs were 1.002 +/- 0.012. This suggests that (13)C-labeled isotopes can be used as internal standards with no intensity calibration and that the concentrations of PCDD/Fs can be determined to within an error of ca. 1%. In addition, multiphoton ionization provides negligible levels of background interference for the real soil samples even with curtailed pretreatment. The toxicity equivalence (TEQ) of the real sample was determined using GC/MPI/TOF-MS for performance evaluation against high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). The results suggest equivalent or even superior performance for GC/MPI/TOF-MS, due to low background interference and to the ability to check the reliability of the assignment from the intensity distribution of the isotope peaks.

Enhancement of molecular ions in mass spectrometry using an ultrashort optical pulse in multiphoton ionization.

The spectral domain of an ultraviolet femtosecond laser was expanded by stimulated Raman scattering/four-wave Raman mixing, and the resulting laser pulse was compressed using a pair of gratings. The pulse width was then measured using an autocorrelator comprised of a Michelson interferometer equipped with a multiphoton ionization/mass spectrometer which was used as a two-photon detector. A gas chromatograph/mass spectrometer was employed to analyze triacetone triperoxide (TATP), and the molecular ion induced by multiphoton ionization was substantially enhanced by decreasing the laser pulse width.

Data processing technique in gas chromatography/time-of-flight mass spectrometry.

A complete mass spectrum was measured at an acquisition rate of 1 kHz using a femtosecond-multiphoton-ionization time-of-flight mass spectrometer for analyte eluting from a gas chromatograph. A contour-map display, i.e. a two-dimensional plot, of the data was first constructed for a simultaneous overview of the mass spectra and the mass chromatograms. The noise component in the signal was then reduced by digital filtering and reduced further by smoothing the data. The detection limit (S/N = 3) was improved from 240 to 76 fg for 2,3,4,6,7-pentachlorodibenzofuran, with no appreciable loss of resolution in the chromatogram. The achieved value was lower than the value (<100 fg) required by Japanese Industrial Standards for dioxin analysis. A new parameter, referred to as a 'reliability factor', was defined in this study to calculate the similarity between the intensity distribution of the isotope peaks observed in the mass spectrum and that calculated from the natural abundance ratio of the isotopes. This parameter was useful for evaluation of the purity of the chromatographic peak.

Near-ultraviolet femtosecond laser ionization of dioxins in gas chromatography/time-of-flight mass spectrometry.

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was applied to the trace analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). To determine the optimum wavelength for analysis of PCDD/Fs, the wavelength of the femtosecond laser utilized for multiphoton ionization was converted to near-ultraviolet status using stimulated Raman scattering. A femtosecond laser emitting at 300 nm completely eliminated the background signal arising from the bleeding compounds generated from a stationary phase of the capillary column in GC.

Measurement of volatile organic compounds (VOCs) in new residential buildings and VOCs behavior over time.

For the purpose of the investigation of characteristics of VOCs found indoors in recently constructed residential buildings, we measured the behavior of VOCs which were sampled at one-month intervals over a period of one year from the, initial occupancy date in both a detached house and an apartment in a multiple' dwelling. At the first passive sampling from the wooden detached residential building, n-hexane, n-undecane, toluene, ethylacetate, methylethylketone, alpha-pinene and (+)-limonene were present in relatively high concentrations of 10 ppb or higher in the living room. Then these VOCs showed a declining trend with time. p-Dichlorobenzene showed an extremely high concentration (approx. 320 ppb) in June, which subsequently declined with each passing month. There is a high possibility that the cause was the use of a pesticide containing p-dichlorobenzene during the period of changeover from winter to summer clothes in June. On the other hand, from the multiple dwelling, four VOCs showed values of 10 ppb or more (toluene, 1,2,4-trimethylbenzene, methylethylketone and alpha-pinene). Of these VOCs, methylethylketone concentration was in excess of 100 ppb, and then also showed a declining trend with time. Even for new residential buildings completed during the same time frame, it was shown that the types of VOC contaminants and their concentrations varied significantly.

Evolution of water chemistry in natural acidic environments in Yangmingshan, Taiwan.

In Yangmingshan National Park, located in the northern part of the Taiwan Island, there is a very rare area where fish (Channa asiatica) live in spite of acid environments. The origin of the acid in local acid ponds and rivers and the evolution of the water chemistry are discussed on the basis of sulfur stable isotope ratios and chemical equilibria. One of the sources of the acid is sulfuric acid, which is derived from the oxidation of hydrogen sulfide in volcanic gas gushing out from fumaroles around the area and from acid deposition supplied from Taipei City. It is also derived from the oxidation of pyrite: the sulfur stable isotope ratios of delta 34S of +1@1000 to +4@1000 (relative to CDT) of sulfate in acid pond waters (pH 3-4) could be related to those of hydrogen sulfide in volcanic gas, pyrite in local pond sediments and soils, and sulfate in rain water. One acid source is sulfuric and hydrochloric acids arising in springs from geothermal activity: the delta 34S values were characterised by +13@1000 to +17@1000 sulfate-S, which was provided by a disproportionation reaction of sulfur dioxide in the depths. Another acid source could be the oxidation of iron(II). Under acidic conditions, the water-rock reaction gives rise to high concentrations of aluminium and iron. While flowing down surface streams, iron(II) is oxidised to iron(III) and then hydrolysed to cause further acidification under oxic conditions. The concentrations of iron and aluminium are controlled by redox and dissolution equilibria.