Cathode Glow Discharge-atomic Emission Research Articles

Evaluation of flow injection-solution cathode glow discharge-atomic emission spectrometry for the determination of major elements in brines

A new method for the determination of major metal elements in high salinity brines was developed by solution cathode glow discharge (SCGD) with flow injection analysis (FIA). The matrix interferences of major cations and anions in brines have been evaluated. It was found that high concentration of Na+ and K+ could interfere each other, K+ at a concentration of 400mgL−1 enhanced the signal intensity of Na+ more than 20%. The effect of the anions was observed and it was noted that the signal intensity of both Ca2+ and Mg2+ were suppressed significantly when the SO42− reached 100mgL−1. It was demonstrated that some low molecular weight organic substances such as formic acid, glycerol and ascorbic acid could eliminate interference of SO42− even with volume percentages of 0.5%. Under the optimized condition, the proposed FIA-SCGD can determine K, Na, Ca and Mg with the limits of detection of 0.49 (K), 0.14 (Na), 11 (Ca) and 5.5 (Mg) ngmL−1. The proposed method has been successfully applied to the analysis of 5 salt lake samples and compared with those obtained with inductively coupled plasma atomic emission spectrometry (ICP-AES). The advantages of small size, low energy consumption, good stability and repeatability indicated that the SCGD is promising for the determination of major ions in brine samples.

Determination of trace heavy metals in environmental and biological samples by solution cathode glow discharge-atomic emission spectrometry and addition of ionic surfactants for improved sensitivity

Solution cathode glow discharge-atomic emission spectrometry (SCGD-AES) was evaluated for its ability to determine toxic heavy metals, including cadmium (Cd), mercury (Hg), lead (Pb), and chromium (Cr), in environmental and biological samples. A significant enhancement in heavy metal signal was observed by addition of a small amount of cetyltrimethylammoniumchloride (CTAC, C16H33 (CH3)3NCl) to the samples. The net intensity of atomic emission lines of Cd, Hg, Pb, and Cr increased by 2.1-, 4.8-, 6.6-, and 2.6-fold, respectively, after addition of 0.15% CTAC to the test solutions. The effects of ionic surfactants (CTAC) compared with non-ionic surfactants, e.g., Triton x-45 and Triton x-100, on the sensitivity of Cd, Hg, Pb, and Cr were also investigated in the present study. The enhancement effect is in the order Triton x-45<Triton x-100<CTAC for Hg, Pb and Cr and Triton x-45<CTAC<Triton x-100 for Cd. Addition of CTAC to the electrolyte solutions decreased the background intensity and fluctuation of atomic emission lines of studied metals. It also changed the surface tension and the viscosity, and increased average discharge current of electrolyte solution. SCGD sensitivity to the heavy metals greatly improved by addition of the surfactant. The improved detection limits of Cd, Hg, Pb, and Cr were 1.0, 7.0, 2.0, and 42 ng mL(-1), respectively. The proposed method was validated by quantifying Cd, Hg, Pb, and Cr in certified reference materials, including human hair (GBW 09101b) and stream sediment (GBW 07310 and GBW07311). Measurement results obtained for the determination of Cd, Hg, Pb, and Cr in the reference materials agreed well with reference values. This study improves the application of SCGD-AES in quantifying very low levels of Cd, Hg, Pb, and Cr from biological and environmental materials.

Determination of mercury in hepatitis-B vaccine by electrolyte cathode glow discharge atomic emission spectrometry (ELCAD-AES)

A simple, rapid and sensitive method has been developed for the determination of mercury in Hepatitis-B vaccine samples using electrolyte cathode glow discharge atomic emission spectrometry (ELCAD-AES). This method obviates the need of any sample digestion, except simple dilution followed by analysis of the vaccine samples. Analytical performance of the ELCAD-AES for the inorganic as well as the organic mercury (methyl and thiomersal mercury) in the aqueous solutions is investigated. Biological certified reference materials, Tuna fish-IAEA-350 and Tuna fish-BCR-463 are examined for the applicability of ELCAD-AES to quantify the mercury. These results show an accuracy of between 0.6 to 2.1% with an analytical precision expressed as relative standard deviation (RSD%) of between 3 to 7% based on the multiple measurements on multiple sample loadings. In the absence of any CRM of the vaccine sample, the method has been validated by analyzing the same samples by Cold vapour-AAS and Electrothermal-AAS. Accuracy of the ELCAD results for vaccine samples is determined to be within 2 to 9% at various levels of mercury. Detection limit of the method is found to be 25 ng mL−1 and the analytical precision is between 2–5%.

Investigation of the role of hollow cathode (vaporization) temperature on the performance of particle beam-hollow cathode atomic emission spectrometry (PB-HC-AES)

An evaluation of the effect of cathode temperature on analyte emission responses for the particle beam-hollow cathode glow discharge atomic emission spectroscopy (PB-HC-AES) system is described. A series of Cu salts were introduced as both nebulized solutions and dry particulates to examine the effect of vaporization temperature on the resulting Cu I emission intensity. For the analysis of aqueous samples, a high-efficiency thermoconcentric nebulizer was used to generate a fine aerosol of the solution flowing at rates of 1.5 mL min−1. A momentum separator–particle beam interface was employed for desolvation and subsequent introduction of dry analyte particles into a heated hollow cathode glow discharge source for vaporization, atomization and excitation. In the case of dry particle analysis, the particle beam interface was modified to allow introduction of samples by vacuum action through a 1 mm id stainless-steel tube. The effects of both vaporization temperature and analyte particle size were investigated by monitoring Cu emission intensity as well as by examining collected particles by scanning electron microscopy. Results indicate an optimum vaporization temperature of 200–300 °C for this group of Cu salts, with increased analyte emission intensities obtained through the introduction of smaller-sized particles.

Optimization of hollow cathode diameter for particle beam/hollow cathode glow discharge atomic emission spectrometry

An evaluation of the effect of cathode diameter on analyte emission intensity for the particle beam/hollow cathode glow discharge atomic emission spectroscopy (PB–HC–AES) system is described. A high-efficiency thermoconcentric nebulizer is used to generate a fine aerosol of the aqueous solution flowing at rates of ∼1 ml/min. Desolvation and use of a momentum separator/particle beam interface serves to introduce analyte particles into a heated HC glow discharge source for subsequent vaporization, atomization and excitation. The effects of discharge gas (He) pressure and current on emission responses for sodium and copper are evaluated in flow injection mode using 200-μl injection volumes for a series of fixed-length (25 mm) cylindrical HC having inner diameters of 2, 3, 5 and 7 mm. Analytical response curves obtained with the 2-mm i.d. HC for sodium and copper yield detection limits of 0.6 and 1.3 ppb in elemental Na and Cu, respectively, with less than 10% relative standard deviation (R.S.D.) for triplicate injections over a concentration range of 0.5–20 ppm.

Mercury speciation by capillary gas chromatography with radiofrequency hollow cathode glow discharge atomic emission detection

Hollow cathode (HC) glow discharge (GD) atomic emission spectrometry (AES) with a radiofrequency (rf) source was investigated as a detector in gas chromatography (GC) for elemental speciation of methylmercury, ethylmercury and inorganic mercury following a Grignard derivatisation reaction (butylmagnesium chloride). The HC design and the transfer line between the source and the GC column are described; in addition, the parameters governing the discharge (pressure, He flow rate, rf power) on the emission of the analytes were optimised. The analytical performance characteristics of this hyphenated technique were evaluated and compared with those of other more common plasmas used as atomic detectors in GC. The absolute detection limits were found to be 0.2, 0.2 and 0.3 pg for methylmercury, ethylmercury and inorganic mercury, respectively, with the variability being lower than 8% RSD at the 10 pg level. Finally, the accuracy of the proposed methodology was successfully tested by analysing two certified reference materials from the National Research Council of Canada (DORM-2 and DOLT-2).

Analysis of amino acids and organometallic compounds by particle beam–hollow cathode glow discharge atomic emission spectrometry

An evaluation of the particle beam–hollow cathode glow discharge atomic emission spectroscopy (PB-HC-AES) system as an element-specific detector for liquid chromatography is described for aromatic amino acids and organomercury and organolead compounds. A high-efficiency thermoconcentric nebulizer is used to introduce analyte particles into a heated hollow cathode glow discharge source for subsequent vaporization, atomization and excitation. Emission responses for hydrogen and nitrogen of amino acids in flow injection mode using 200 µL injection volumes indicate detection limits of 0.13 and 3.6 ppm elemental H and N, respectively, with RSD <10% for triplicate injections over a concentration range of 10−3–10−2 M. Analysis of the response of hydrogen and nitrogen emission signal intensities to differences in amino acid stoichiometries indicates the potential of the PB-HC-AES system for the determination of empirical formulas based on HI/NI intensity ratios. Detection limits for metals and non-metals in organomercury compounds as determined through flow injection of 200 µL sample volumes fall in the sub-ppm range. Liquid chromatographic separations of both amino acids and organolead compounds demonstrate the feasibility of the PB-HC-AES system as a detector for liquid chromatography. Retention times for 20 µL injections of the selected component mixtures as determined by CI emission for amino acids and PbI emission for organolead compounds correlate well with the corresponding UV absorbance results.

Analysis of Organic Compounds by Particle Beam/Hollow Cathode Atomic Emission Spectroscopy: Determinations of Carbon and Hydrogen in Amino Acids

A detailed evaluation of the analytical characteristics of a particle beam/hollow cathode glow discharge atomic emission spectroscopy (PB/HC-AES) system is described for applications in the area of organic sample analysis. The optimization of sample introduction, nebulization parameters, and glow discharge conditions was performed for the elemental analysis (focusing on C and H) of a group of amino acids. By use of a high-efficiency thermoconcentric nebulizer, analyte particles are introduced into a heated hollow cathode glow discharge source, in either flow injection or continuous-flow mode, for subsequent vaporization/atomization and excitation. Nebulization temperature, solvent composition, and liquid flow rate were studied to elucidate their roles in the ultimate analyte emission characteristics for organic compound analysis. The hollow cathode operating discharge current and gas pressure were optimized, with the general responses found to be similar to those for the case of metal analysis. Background interferences from solvent and additive media on carbon and hydrogen determinations were studied and substantially reduced. The analytical response curves for carbon and hydrogen present in amino acids were obtained using 200 μL injection volumes, showing less than 10% RSD for replicate injections over a concentration range of 10-250 ppm, with detection limits of 3 and 1 ppm, respectively, for C (I) and H (I) emission. Subsequent studies of the response of carbon and hydrogen emission signal intensities to differences in amino acid stoichiometries suggest a capability of the PB/HC-AES system for the determination of empirical formulas based on H (I)/C (I) intensity ratios.

Determination of Silicate by Hollow Cathode Glow Discharge-Atomic Emission Spectrometry with Hydride Generation Technique

Abstract Hollow cathode glow discharge atomic emission spectrometry has been applied to the determination of silicon coupled with a novel gaseous hydride generation technique, involving drying of an aqueous solution of silicate (sample) and mixing with powdered LiAlH4. Sample introduction into the glow discharge chamber was performed via a pinhole at the center of the cathode which was connected to the hydride generator. The detection limit for silicon was 6μg at 288.1 nm and 30 μg at 251.6 nm. ∗ on leave from Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, 739, Japan

Nebulization and analysis characteristics of a particle beam–hollow cathode glow discharge atomic emission spectrometry system

A detailed evaluation of the nebulization characteristics of a particle beam/hollow cathode glow discharge atomic emission spectrometry system is described. The optimization of sample introduction and particle beam interface operation was further evaluated for applications in elemental analysis for a number of transition metals. A high efficiency thermoconcentric nebulizer, coupled to a particle beam LC–MS interface, was employed to introduce analyte particles into a heated hollow cathode glow discharge source in either flow injection or continuous flow mode. The measurement of pressure and temperature in the desolvation chamber, along with the addition of a helium supplement gas, provides an insight into the sample/particle transport mechanism. The effects of capillary size (inner diameter) and solvent composition (methanol–water volume ratio) at various liquid flow rates were studied to evaluate optimum sample introduction conditions. Calibration graphs of Cu, Pb, Fe and Mg in the range 50 ppb–10 ppm show promising linearity under optimized conditions. The variability of multiple injections at a single concentration is less than 15% RSD over this concentration range. The limits of detection for Cu, Pb, Fe and Mg are 12, 25, 20 and 15 ppb, respectively, for 200 µl injection volumes.