Steven M. Pyle

Environmental applications of gas chromatography/atomic emission detection.

A gas chromatograph/atomic emission detector (GC/AED) system has been evaluated for its applicability to environmental analysis. Detection limits, elemental response factors, and regression analysis data were determined for 58 semivolatile environmental contaminants. Detection limits for injected analytes ranged from 0.17 to 3.0 ng on the hydrogen 486-nm channel, from 1.0 to 5.0 ng on the nitrogen 174-nm channel, from 0.65 to 11.7 ng on the oxygen 777-nm channel, from 0.071 to 3.0 ng on the chlorine 479-nm channel, and from 0.023 to 0.038 ng on the sulfur 181-nm channel. Mean elemental response factors (ERFs) measured on these channels, relative to the carbon 496-nm channel, were hydrogen, 0.084 (mean %RSD = 6.6); nitrogen, 0.246 (mean %RSD = 19); oxygen, 0.459 (mean %RSD = 16); and chlorine, 0.417 (mean %RSD = 3.6). The higher precision obtained for hydrogen and chlorine, relative to that for nitrogen and oxygen, is attributed to the ability to scan these elemental channels in the same GC run as the carbon 496-nm channel (diode array wavelength range limitation of ∼40 nm/run). Mean ERFs of standard compounds were used to determine the molecular formulas of chlorinated hydrocarbons and chlorinated organosulfur compounds in a contaminated environmental soil sample. These formulas are in good agreement with the molecular weights and chlorine isotopic data obtained from low-resolution gas chromatography/mass spectrometry.

Qualitative and quantitative environmental analysis by capillary column gas chromatography/lightpipe Fourier-transform infrared spectrometry.

rn A new state-of-art commercial gas chromatography/ Fourier transform infrared (GC/FT-IR) lightpipe-containing system has been evaluated for its applicability to qualitative and quantitative environmental analysis of typical environmental contaminants. This system exhibited minimum identifiable quantities, for many compounds, in the 10-50-ng range. On a wide-bore capillary column, quantitation curves generated from chromatogram peak areas were linear over the 10-250-ng range. The mean correlation coefficient for 38 quantitation calibration curves on 24 standards was 0.976. The selectivity of the new system was evaluated with standards, soil, and stillbottom samples. It was demonstrated with 27 standards that no discernible loss in identification selectivity occurred when a narrow-band infrared detector (spectral cutoff 750 cm-l) was used in place of a midband detector (cutoff 700 cm-l). This allows the meaningful utilization of the extra sensitivity associated with narrower frequency range infrared detectors.

Supercritical fluid extraction of high sulfur soils, with use of a copper scavenger.

Supercritical fluid extraction (SFE) of sulfur-containing soils and sediments was hindered by deposition of elemental sulfur in the restrictor stopping the flow of carbon dioxide. It was found that a copper scavenger column placed after the sample cell removed the elemental sulfur, making SF extraction and quantification possible. Conditions are described for SFE and analysis of two standard reference materials (SRM), with use of a copper scavenger column. Quantification was performed by gas chromatography with mass spectrometric detection and the results were compared with the certified SRM values.

Volatile organic analysis by direct aqueous injection

Gas chromatographic environmental analysis by direct aqueous injection (DAI) was studied for 24 volatile organic analytes (VOAs). Internal standardization was used to determine the precision of analysing these compounds by DAI. Aqueous samples were directly introduced to a gas chromatograph using fused-silica, mega-bore capillary column separation with subsequent full-scan ion trap mass spectral detection. Triplicate injections at seven levels of VOA standard solutions over a 10(3) concentration range were performed using an autosampler set up for on-column injection of 0.2 microl. Comparison of single-ion response curves to triple-ion response curves showed that triple-ion quantitation was more sensitive and precise than single-ion quantitation. Of the 24 VOAs determined at the 20 parts per billion (ppb) level, 19 and 20 were detected by the single-ion calibration and triple-ion calibration, respectively. The weighted and non-weighted regression correlation coefficients, r(2), for the 24 responses curves by the two methods, ranged from 0.910 to 0.998, with 76 of 96 being greater than 0.990. Precision, as measured by per cent relative standard deviation, was shown to be best for later eluting compounds and for higher concentrations. Analysis of an environmental sample by DAI was accomplished in 12 min and indicated the presence of benzene at 80 ppb and chlorobenzene at 2 ppm. This demonstrated the feasibility of applying this technique for screening. Several chlorinated benzenes were also detected, establishing the potential for expanding the method to include higher boiling compounds.

Thiodiglycolic acid: a major metabolite of bis(2-chloroethyl)ether.

Abstract Male rats were given a single oral dose (40 mg/kg) of bis(2-chloroethyl)ether (BCEE). Less than 2% of the dose was recovered from the expired air as the unaltered parent compound during an 8-hr collection period. Urine samples representing 48 hr of collection were analyzed by gas chromatography-mass spectrometry. Methyl ester/trimethylsilyl ether derivatives of the isolated urinary acid fraction were prepared for gas-phase analysis. Two metabolites were identified in this fraction: thiodiglycolic acid (TDGA) and 2-chloroethyl β- d -glucosiduronic acid. Quantitative analysis for TDGA gave an average (seven rats) yield for 48 hr of 33 ± 11.8 mg (± SD) of TDGA/kg from a single dose of 40 mg/kg BCEE. The glucuronide of 2-chloroethanol was synthesized using rabbit liver microsomes in an incubation mixture. The matching mass spectrum of the glucuronide prepared in vitro to that identified in the urine of the rats verified 2-chloroethyl β- d -glucosiduronic acid as a metabolite of BCEE.

Analysis of volatiles and semivolatiles in drinking water by microextraction and thermal desorption.

A new technique to analyze aqueous samples for nanograms per liter levels of volatile and semivolatile compounds using microextraction and thermal desorption into a gas chromatograph/ion trap mass spectrometer (GC/MS) is described. This method is inherently sensitive (50 mL of aqueous sample is extracted prior to each desorption), uses no solvents, and detects volatiles and semivolatiles in the same analysis. Aqueous standards and environmental samples are pumped through a length of porous-layer open-tubular capillary column, which is then thermally desorbed onto a 30 m x 0.25 mm i.d. analytical column interfaced to an ion trap mass spectrometer for subsequent separation and detection. Sharp chromatographic peaks and reproducible retention times (RT) were observed. Replicate injections of surrogates (n=6) averaged 32.6% R.S.D. Analysis of domestic tap water detected 55 analytes, some at the low-nanograms per liter level, and detected 3 halogenated ethenes, not previously reported in drinking water. Analysis of an aqueous sample from a municipal ground water source detected the presence of numerous semivolatile compounds at trace-levels.

Analysis of Volatiles and Semivolatiles by Direct Aqueous Injection

Abstract Direct aqueous injection analysis (DAI) with gas chromatographic separation and ion trap mass spectral detection was used to analyze aqueous samples for μg/L levels of 54 volatile and semivolatile compounds, and problematic non-purgeables and non-extractables. The method reduces sample handling, increases sample throughput, and avoids the use of solvents ordinarily required for solvent exchange and analyte pre-concentration which would otherwise require disposal as hazardous waste. Aqueous standards containing volatile and semivolatile organic compounds were directly injected in 0.1-μL volumes into a 0.22-mm id capillary column interfaced to an ion trap mass spectrometer. Peak shape was adequate for quantification, and method detection limits for replicate injections (n=7) ranged from 3 to 20 000 μg/L, averaging 100 μg/L. Precision (%RSD) was calculated at each level for each compound and averaged 12% at the highest level. Analysis of domestic tap water readily revealed the presence of three trihalomethanes (chloroform, dichlorobromomethane, and chlorodibromomethane) at the low-μg/L level. Analysis of an aqueous sample from a hazardous waste site monitored the presence of various volatile and semivolatile compounds at mg/L levels.

Metabolism of bis(2-chloroethyl)ether and bis(2-chloroisopropyl)ether in the rat

Male rats were given single peroral doses of bis(1-14C-2-chloroethyl)ether ([1-14C]BCEE) (40 mg/kg) and of bis(1-14C-2-chloroisopropyl)ether ([1-14C]BCIE) (90 mg/kg). Excretion of14CO2 and urinary14C was followed for 48 hr. The time required to eliminate one half of the dose was 12 hr for [1-14C]BCEE and 19 hr for [1-14C]BCIE. In the case of [1-14C]BCEE, expired14CO2 accounted for 11.5 ± 5.6(SD) % of the dose, urinary14C accounted for 64.7 ± 14.8%, and 2.4 ± 1.3% was found in the feces. The figures for [1-14C]BCIE were 20.3 ± 9.4% expired as14CO2, 47.5 ± 8.1% as urinary14C, and 3.8 ± 0.3% as fecal14C. Thiodiglycolic acid (TDGA) accounted for roughly 75% of the total urinary14C collected after the [1-14C]BCEE dose. Lesser metabolites of BCEE were 2-chloroethoxyacetic acid (CEAA) (5%), and N-acetyl-S-[2-(2-chloroethoxy)ethyl]-L-cysteine (ACEEC) (7%). Metabolites of [1-14C]BCIE identified in rat urine were 2-(2-chloro-1-methylethoxy)propanoic acid (CMEPA), roughly 36% of the total urinary14C, and N-acetyl-S-(2-hydroxypropyl)-L-cysteine (AHPC) at 19%.

The nature of C10H2+ in mass spectra of polynuclear aromatic hydrocarbons☆

Abstract Ab initio and density functional theory (DFT) calculations have been performed to determine the heats of reaction for the process C 16 H 10 + → C 10 H 2 + that takes place in an ion trap mass spectrometer. Comparisons have been made with the experimental and derived data available for this process. The theoretical values at the DFT level verify the experimental heats of reaction within 0.4-0.8 eV. Furthermore, the structure of the product ion, C 10 H 2 + , has been investigated. Several structures have been proposed, and the ab initio and DFT geometry optimizations and frequency calculations have been performed to determine the most stable species. At the level of theory and the approximations that were used in this work, the linear form of C 10 H 2 + is the most stable species of three different geometries considered.