Ralph J. May

Comprehensive, quantitative, congener-specific analyses of eight aroclors and complete PCB congener assignments on DB-1 capillary GC columns

Abstract We have determined complete polychlorinated biphenyl (PCB) congener assignments and weight percent distributions for all major (> 0.5 wt %) PCB components of Aroclors 1221, 1232, 1242, 1016, 1248, 1254, 1260, 1262 that are resolved by DB-1 (polydimethylsiloxane) capillary GC columns. Aroclor components present between 0.05 and 0.5 wt % were also identified but not quantified. Quantitation was done using a combination of GC-ELCD (Hall electrolytic conductivity detector) and GC-MS measurements. All 209 PCB congeners have been assigned to the 124 peaks that can be resolved on DB-1 columns. The data support use of these eight Aroclors individually or in customized standards for calibrating the comprehensive, quantitative, congener-specific PCB analyses that are necessary for accurate quantitation of the complex and often radically altered mixtures of PCBs typically found in the environment.

Aerobic degradation of polychlorinated biphenyls by Alcaligenes sp. JB1: metabolites and enzymes.

In contrast to the degradation of penta-and hexachlorobiphenyls in chemostat cultures, the metabolism of PCBs by Alcaligenes sp. JB1 was shown to be restricted to PCBs with up to four chlorine substituents in resting-cell assays. Among these, the PCB congeners containing ortho chlorine substituents on both phenyl rings were found to be least degraded. Monochloro-benzoates and dichlorobenzoates were detected as metabolites. Resting cell assays with chlorobenzoates showed that JB1 could metabolize all three monochlorobenzoates and dichlorobenzoates containing only meta and para chlorine substituents, but not dichlorobenzoates possessing an ortho chlorine substituent. In enzyme activity assays, meta cleaving 2,3-dihydroxybiphenyl 1,2-dioxygenase and catechol 2,3-dioxygenase activities were constitutive, whereas benzoate dioxygenase and ortho cleaving catechol 1,2-dioxygenase activities were induced by their substrates. No activity was found for pyrocatechase II, the enzyme that is specific for chlorocatechols. The data suggest that complete mineralization of PCBs with three or more chlorine substituents by Alcaligenes sp. JB1 is unlikely.

Isomer specific analysis of selected chlorodibenzofurans

Abstract Two-dimensional gas chromatography has been used to provide full chromatographic resolution of three chlorodibenzofuran isomers. The materials studied were: 2,3,7,8-tetrachlorodibenzofuran, 2,3,4,7,8-pentachlorodibenzofuran and 1,2,3,7,8,9-hexachlorodibenzofuran. The materials were detected using medium resolution mass spectrometry.

Target compound analysis by two-dimensional gas chromatography—mass spectrometry

Abstract The use of two-dimensional gas chromatography 1 for the analysis of specific target compounds in complex matrices in combination with mass spectrometry has been investigated. The combination of a high capacity, high polarity packed first gas chromatography column followed with a low capacity, low polarity, high resolution second column has been found useful. A component of interest is switched from the first column into a cold trap and then flash-evaporated into the second column. This combination allows part per billion analyses in complex mixtures such as soil extracts, crude oils, and biological extracts without any prior sample cleanup whatever. Two important advantages arise naturally therefore from this approach: a significant reduction in analysis time and a major improvement in the specificity of the analysis. The method offers a relatively inexpensive yet powerful alternative to mass spectrometry—mass spectrometry.

Dynamic high throughput screening of chemical libraries using acoustic-wave sensor system

We report a novel sensor-based high throughput screening (HTS) system for identification and quantitation of volatile substances in combinatorial chemical libraries. The measurement method employs a combination of a periodic introduction of a minute amount of a liquid sample into the HTS system, rapid evaporation of volatile components in the sample at room temperature, and dynamic measurement of a generated vapor pulse. These measurements are performed using an array of four 10 MHz acoustic-wave thickness-shear mode sensors coated with different chemically sensitive films. Developed HTS system is applied for screening of multiple samples such as those created in combinatorial chemical libraries of catalyst candidates in an industrially important arene oxidation process. The temporal modulation of the concentration of analyte vapors and measurement of both the temporal profile and the magnitude of the response improves sensor selectivity and makes possible robust identification and quantitation of arene oxidation components such as cresol and benzoquinone in multicomponent combinatorial mixtures with reduced number of sensors in the array. Different solvents such as water, acetonitrile, benzene, and toluene do not alter the response of sensors to analytes. Depending on the gas flow rate, quantitative measurements are performed 10–150 s after the sample introduction and provide significant throughput advantage over gas-chromatographic instruments. Determinations of mixtures of analytes in a variety of solvents are performed using multivariate locally weighted regression. This data analysis method provides the root mean squared error of prediction of less than 2 μg when measurements of cresol and benzoquinone amounts ranging from 0 to 50 μg are performed in 2 μL samples. This method of dynamic sensor-based measurements allows for instrument miniaturization and increases the usefulness of the instrument in space-limited applications. Upon operation of multiple sensors in parallel, effective analysis of dense combinatorial libraries of materials is possible.

Levels of bioactive PCDF congeners in PCB dielectric fluids from capacitors and transformers

Abstract The levels of three pharmacologically active PCDF congeners, namely the 2,3,7,8,-tetra-, 2,3,4,7,8-penta-, and 1,2,3,7,8,9-hexachlorodibenzofurans, were measured by a precise two-dimensional gas chromatographic mass spectrometric procedure in PCB dielectric fluids taken from both used and unused capacitors and transformers, as well as in Aroclor standards. It was found that the electrical uses did not cause increases in bioactive PCDF levels.

Recognition and quantitation of closely related chlorinated organic vapors with acoustic-wave chemical sensor arrays

An array of four acoustic wave chemical sensors has been developed and tested for recognition and quantitation of six closely related chlorinated organic vapors at low part-per- million concentrations. These vapors include PCE, TCE, VC, and DCE, cis-1,2-DCE, trans-1,2-DCE, and 1,1-DCE. The developed sensor array can detect as little as 0.2 ppm of PCE, 0.8 ppm of TCE, 1.4 ppm of cis-1,2-DCE, 1.4 ppm of trans-1,2-DCE, 3 ppm of 1,1-DCE, and 3.5 ppm of VC in air. Quantitation of TCE and cis-1,2-DCE vapor mixtures was achieved using multivariate calibration techniques. The locally weighted regression analysis provides more accurate results over the partial least squares regression.