An electrothermal vaporization (ETV) system was used to introduce aqueous samples into a helium microwave-induced plasma (He-MIP). The plasma was operated at 2.45 GHz and 500 W. The sample introduction system consisted of a carbon-cup-type electrothermal vaporizer in a glass chamber. A vapor restriction device was used to enhance the efficiency of sample transport to the plasma. For obtaining the best detection limits, matrix modifiers were used for the nonmetals. Lead nitrate as a matrix modifier was found to be particularly efficacious for the determination of bromide and chloride. Detection limits with the ETV-He-MIP with 15-ML samples were: Cd, 10 pg (0.6 ppb) at 228.8 nm; Cu, 30 pg (2 ppb) at 327.4 nm; Br, 300 pg (20 ppb) at 470.5 nm; and Cl, 120 pg (8 ppb) at 479.5 nm. Although the detection limits for the two metals studied are greater than those that have been obtained by ETV-ICP-AES, the detection limits for Br and Cl are the best that have been obtained by an ETV-AES technique to date in the UV-VIS spectral region. Linear responses of analytes were obtained for each element. Matrix effects of selected metals and nonmetals on chloride were investigated and found to be insignificant.
Abstract. Supercritical fluid extraction (SFE) can greatly reduce the sample preparation time of analytes in solid matrices. The on-line coupling of SFE with high-speed gas chromatography (GC) can further reduce the total analysis time. SFE has been coupled to GC with a thermal desorption modulator (TDM) interface. A thermal energy analyzer (TEA), a chemiluminescence detector which is specific for nitro and nitroso compounds, has been coupled to the system to analyze explosives in soil samples.The use of organic modifiers to increase the solvation power of carbon dioxide was necessary for the extraction of various explosives, and did not adversely affect the performance of the system. Thermally labile compounds, however, such as the nitrate esters, were shown to decompose in the modulator before the chromatographic separation.This method allows for the rapid analysis of relatively volatile and thermally stable nitro compounds from solid matrices. The system can be used for screening small samples in short periods of time. Total analysis can be completed in less than 10 minutes and requires only 200 mg of soil. The minimum detectable quantity for the analysis of 2,4-DNT was found to be 2.6 ppb in an actual soil sample.
A kilowatt-plus microwave-induced plasma (KiP-MIP) system was modified for better analytical performance. Modifications included the use of a redesigned plasma torch and a new plasma resonator cavity. The use of the redesigned plasma torch improved the detection of aqueous chloride by 2 orders of magnitude. With the redesigned plasma torch, the performance of the KiP-MIP utilizing the original 3-cm-depth and 2-cm-depth resonator cavities were studied. Results indicated that the KiP-MIP with the 2-cm-depth resonator cavity exhibited better characteristics in terms of plasma energy coupling, excitation characteristics, and determination of aqueous chloride.
A helium r.f. plasma was characterized for the selective detection of nitrogen in gas chromatographic eluents by atomic emission spectrometry. Nitrogen emission was detected at 868 nm. The principle sources of background emission at that wavelength were identified. The largest single source was back-diff usion from the discharge exit. There were also significant contributions from impurities in the high-grade make-up and reagent gases. An avalanche photodiode was evaluated as a photodetector and found to be superior to a photomultiplier tube for this application. End-on and side-on optical collection geometries were modelled by a computer. The detection limit for nitrogen in the discharge was 57 pg s-I.
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