Richard Titus

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.

Environmental Analysis by ab Initio Quantum Mechanical Computation and Gas Chromatography/Fourier Transform Infrared Spectrometry.

Computational chemistry, in conjunction with gas chromatography/mass spectrometry/Fourier transform infrared spectrometry (GC/MS/FT-IR), was used to tentatively identify seven tetrachlorobutadiene (TCBD) isomers detected in an environmental sample. Computation of the TCBD infrared spectra was performed with the Gaussian quantum chemistry software. The Hartree-Fock/6-31G* level of theory was employed, with IR frequencies scaled by a standard factor of 0.89. This approach shows great promise as a means of characterizing or confirming environmental analyte identifications when standard spectra, or pure standards required to measure standard spectra, are unavailable.

Hazardous Waste Analysis By Direct-Linked Fused Silica Capillary Column Gas Chromatography/Fourier Transform Infrared/Mass Spectrometry

A capillary gas chromatography/Fourier transform infrared (GC/FT-IR) spectrometer has been linked to a Mass Selective Detector (MSD). A 10:1 effluent splitter was used to divert 90% of the GC effluent to the FT-IR cell and 10% tO the MSD. This system has been used to characterize the GC-volatile portion of dye and herbicide manufacturing wastes, sediments, sludge extracts, and the extract of a freshwater turtle. Use of a 2300 member FT-IR spectral data base, in conjunction with the NBS mass spectral (MS) data base, greatly increases the number of on-line MS confirmations obtainable by this direct-linked system over that of the conventional EPA GC retention time method. Chromatographic separation on a single capillary GC column allows a direct one-to-one correlation of peaks in the FT-IR and MSD chromatograms. Although this MS detector is 10 to 100 times more sensitive than the FT-IR detector used, and although the MS search library is over 15 times larger than the FT-IR search library, for the samples analyzed it was determined that each detector provided approximately the same amount of useful structural data.