Joseph R. Donnelly

Correlation of structure with retention index for chlorinated dibenzo-p-dioxins

The method presented here allows calculation of the retention indices for the chlorinated dibenzo-p-dioxins under a specific set of experimental conditions, using a limited data set. This technique provides a simple way to obtain retention index data for those isomer standards not readily available. Thus, the technique can aid in structure assignment of specific congeners whether obtained from synthesis or found in environmental monitoring efforts. These calculations have proved highly successful in checking gas chromatographic retention data for internal consistency.

Capillary electrophoresis and capillary electrochromatography of organic pollutants

Capillary electrophoresis (CE) has a unique capability for separation of analytes of environmental concern, particularly those that are more polar and ionic, based on the complementary separation principle of electrophoresis. In the past few years, CE has been selectively used to analyze various classes of compounds having current or potential environmental relevance. This review outlines the current status of CE for the determination of environmental pollutants, based predominantly on research results published from the beginning of 1997 to early 1999. Covered are environmental pollutants of all types except pesticides and inorganics. Certain naturally produced toxins are also covered because of their significant impacts upon human health and the environment. CE methods, as with all methods, must be judged on their ability to provide approaches that are reliable, sensitive, selective, and rapid, while meeting “green chemistry” initiatives for pollution prevention. We also compare CE methods to benchmark environmental techniques involving gas chromatography‐mass spectrometry (GC‐MS), liquid chromatography‐mass spectrometry (LC‐MS), and high performance liquid chromatography (HPLC).

Correlation of structure with linear retention index for bromo- and bromochlorodibenzo-p-dioxins and bromodibenzofurans

Abstract A model-correlating structure with gas chromatographic retention index was developed to assist in making positional isomer assignments for dioxins halogenated by bromine and/or chlorine using commercially available standards and synthetic mixtures. Bromodibenzofuran assignments were made using pyrolysate mixtures, assuming the elution order was the same as for chlorinated dibenzofurans. These strategies can be used, on an interim basis, for isomer assignments in environmental monitoring efforts.

Identification of pollutants in a municipal well using high resolution mass spectrometry.

An elevated incidence of childhood cancer was observed near a contaminated site. Trace amounts of several isomeric compounds were detected by gas chromatography/mass spectrometry (GC/MS) in a concentrated extract of municipal well water. No matching library mass spectra were found and Fourier transform IR and NMR analyses were not feasible due to the low concentration of the compounds. Mass peak profiling from selected-ion-recording data (MPPSIRD) provided the sensitivity and scan speed necessary to acquire mass peak profiles at mass resolutions of 10,000 to 20,000 for the molecular ion (M+) and 10 fragment ions as capillary GC peaks eluted. Using a profile generation model (PGM), the elemental composition of the molecular ion was determined from the exact masses and abundances of the M, M + 1 and M + 2 profiles. Fragment ion compositions were determined from their exact masses based on the elements in the molecular ion. Exact mass differences between the molecular and fragment ions corresponded to unique combinations of atoms for the neutral losses. Consequent reduction of the number of possible structures for the fragment ions simplified mass spectral interpretation. After inspecting library mass spectra for smaller molecules, isomeric structures were hypothesized with cyano and alkylcyano groups attached to tetralin. A literature search found such isomers produced by an industrial polymer synthesis. Three isomers in a standard form polymerization of styrene and acrylonitrile provided the same mass spectra and GC retention times as isomers in the extract.

Software-based mass spectral enhancement to remove interferences from spectra of unknowns.

Gas chromatography-mass spectrometry data from the analysis of complex environmental samples were converted into ASCII text and imported into a personal computer spreadsheet. A macro was written to perform mass spectral enhancement by statistical and mathematical procedures to separate the spectra of compounds of interest from interfering mass spectral responses, such as those of broadly eluting hydrocarbons. The extracted mass spectra were compared to reference spectra, with the result that usually 80–90% of the ions common to those in the reference spectra were successfully extracted by using this method. This procedure improved mass spectral quality and the ability of the data system to perform successful library searches. The fitted quality parameters showed systematic improvements after the data were subjected to the spectral enhancement procedures. These procedures could help to identify unknowns by separating their spectra from other signals, such as those of background aliphatic hydrocarbons.

Gas chromatographic elution patterns of chlorinated dioxins versus column polarity

Abstract A model has been developed which successfully predicts the order of elution and relative retentions of tetra-, penta- and hexachloro-dibenzo-p-dioxins for gas chromatography (GC) columns of different polarity. These congeners include the most toxic 2,3,7,8-substituted isomers, and contain numerous difficult-to-separate isomers. This model allows the correlation of GC retention time to dioxin substitution pattern. The model also allows the prediction of dioxin elution order and relative retention time spacing for GC columns of different polariy.