Arthur P. D'Silva

A new He discharge-afterglow and its application as a gas chromatographic detector

Abstract A description is given for a low frequency, high voltage, electrodeless discharge-afterglow sustained in helium at atmospheric pressure. When this discharge-afterglow was used as an element-selective, multi-element detector for gas chromatography, absolute limits of detection in the picogram range were obtained for F, Cl, Br, I, C, P, S, Si, Hg and As. Because GC effluents were introduced directly into the afterglow region of the discharge, extinguishment and contamination of the primary discharge were completely eliminated.

Aerosol Mass Measurement and Solution Standard Additions for Quantitation in Laser Ablation-Inductively Coupled Plasma Atomic Emission Spectrometry

A new approach for quantitation in laser ablation-inductively coupled plasma atomic emission spectrometry (LA-ICPAES) is presented. A portion of the laser-ablated sample aerosol is diverted to an aerosol mass monitor to measure variations in the amount of sample ablated and transported to the ICP torch. This provides a normalization for variations in laser ablation efficiency due to changes in laser power and focus at the sample and variations in material transport out of the ablation cell and into the ICP torch. During the laser ablation sampling process, solution standards are nebulized and the aerosol is added to the laser-ablated aerosol to generate a standard addition curve for the analyte being determined. The standard addition procedure corrects for potential plasma-related matrix effects in the ICP emission signal resulting from the ablated sample. The precision of this method, for triplicate analyses for the determination of 16 elements in four glass samples, and the accuracy of this method relative to the nominal glass compositions are both approximately 10%. 19 refs., 4 figs., 4 tabs.

Atmospheric Pressure Active Nitrogen (APAN)—A New Source for Analytical Spectroscopy

An atmospheric pressure “active nitrogen” (APAN) afterglow was generated in pure flowing nitrogen (<10 ppm O2) excited in an electrodeless ozonizer discharge. The afterglow, which contains several metastable species, has been observed to be an efficient source for the excitation of atomic emission, through energy transfer. The application of the APAN afterglow for the detection and determination of ultratrace levels of Hg and the volatile hydride forming elements, As, Bi, Ge, Pb, Sb, Se, Sn, and Te is documented.

In situ determination of uranium in soil by laser ablation-inductively coupled plasma atomic emission spectrometry

The concentration of uranium in soil has been determined for 80 sites in an area suspected to have uranium contamination by in situ laser ablation - inductively coupled plasma atomic emission spectrometry (LA-ICPAES), utilizing a field-deployable mobile analytical laboratory. For 15 of the 80 sites analyzed, soil samples are collected so that the field LA-ICPAES results could be compared to laboratory-determined values. Uranium concentrations determined in the field by LA-ICPAES for these 15 sites range from <20 parts per million (ppm) by weight to 285 ppm. The uncertainty in the values determined, however, is large relative to the uranium concentrations encountered at this site. The 95% confidence interval (CI) values are approximately 85 ppm. The uranium concentrations determined by laboratory LA-ICPAES analysis range from <20 to 102 ppm (95% CI of approximately 50 ppm); microwave dissolution and subsequent standard addition determination of uranium by solution nebulization ICPAES using an ultrasonic nebulizer yields 19-124 ppm uranium (95% CI of approximately 10 ppm). For 11 of the 15 samples, the field- and laboratory-determined uranium concentrations agree, within the uncertainty of the determined values. 19 refs., 5 figs., 3 tabs.

Detection of Benzo[a]Pyrene Metabolites by Laser-Excited Shpol'skii Spectrometry

Chemical carcinogenesis studies mandate isomer-selective detection at ultratrace levels of the metabolites of polycyclic aromatic compounds (PACs). The formation of hydroxy PACs is a key step in the metabolic process, particularly detoxification, for PACs in mammals. The infamous carcinogen benzo[a]pyrene (B[a]P) and its metabolites are often used as marker compounds to assess human exposure to total PACs and to study the development of cancer. In this work, isomers related to two alternative metabolic pathways for B[a]P have been selectively detected from urine and blood sera samples by laser-excited Shpolskii spectrometry (LESS). The polar metabolites are derivatized and extracted into the n-alkane Shpolskii solvent for direct, trace-level, isomer-selective detection. An absolute detection limit for 9-methoxy B[a]P was 50 attomole for a 20-μL sample.

Destruction of Polycyclic Aromatic Hydrocarbons with Ultrasound

Abstract Dilute ethanol-water solutions of a few polycyclic aromatic hydrocarbons, a dioxin, and neat chlorinated solvents were sonicated and then characterized by UV-visible absorption spectrophotometry and laser excited Shpolskii spectrometry. The results indicate that all the compounds were destroyed on sonication leaving a carbonaceous residue.

Site-Selective Shpol'skii Spectrometry of Sulfur-, Oxygen-, and Nitrogen-Containing Aromatic Compounds in Complex Samples

Laser excited Shpolskii spectrometry (LESS) was utilized to directly determine nitrogen (N-), oxygen (O-), and sulfur (S-) heterocyclic compounds in solvent refined coal (SRC-II), petroleum crude oil, and carbon black. Characteristic quasilinear LESS excitation and emission spectra of the heterocyclic compounds are presented for the first time under site-selective conditions. Deuterated analogs of dibenzothiophene and dibenzofuran were utilized for quantitation. Site-selective fluorescence spectra of aminopyrene derivatives of polycyclic aromatic compounds (PAC) are also presented for the first time. The potential for utilizing the LESS technique in critical environment and biological studies for the direct determination of N-, O-, and S-heterocyclic compounds and substitutional derivatives of parent PAC has been demonstrated.

Analytically useful spectra excited in an atmospheric pressure active nitrogen afterglow

An atmospheric pressure active nitrogen (APAN) discharge has been utilized for producing characteristic molecular emissions from nonmetallic species introduced into the afterglow region of the discharge. The addition of inorganic S-, P-, B-, CI-, and Br-containing compounds into the afterglow has resulted in the formation of excited S2, PN, BO, NCI, and NBr species, respectively. Intense molecular Br2 emission and I2 emission, as well as atomic I emission, have also been observed. Preliminary analytical utilization of the molecular or atomic emissions observed revealed that the APAN afterglow may serve as a potentially useful detector for the aforementioned elements.

An atmospheric-pressure, argon-afterglow detector for gas chromatography

Abstract The development of an atmospheric-pressure argon-afterglow, produced from an ozonizer-type discharge tube, for element-selective, multielement detection in gas chromatography is described. Characteristic atomic emission is observed from chlorine, bromine, iodine, carbon, sulfur and phosphorus in organic compounds, with limits of detection ranging from 0.02 ng for phosphorus to 20 ng for bromine. Element-selective detection for several pesticides is demonstrated.

X-ray excited optical luminescence in the yttrium-gadolinum-terbium phosphate system

Abstract The X-ray excited optical luminescence of Tb in YPO 4 present at 0.01 mol Tb 2 O 3 /mol Y 2 O 3 was found to consist primarily of emission in the 3800–4500 A region arising from 5D 3 → 7F J transitions of Tb 3+ . This luminescence was in addition found to be sensitized by Gd. Preliminary tests on the radiographic properties of the Y 0.8 Gd 0.2 PO 4 : Tb 3+ composition show that this phosphor offers promise as an efficient radiographic screen phosphor.