Solution Cathode Glow Discharge Research Articles

Ultratrace Determination of Tin, Germanium, and Selenium by Hydride Generation Coupled with a Novel Solution-Cathode Glow Discharge-Atomic Emission Spectrometry Method.

We herein describe a novel method of hydride generation (HG) coupled to a newly designed atmospheric pressure solution-cathode glow discharge (SCGD) spectrometric technique for the ultratrace determination of tin, germanium, and selenium. In this novel SCGD process, gas introduction was permitted using a hollow titanium tube as both the anode and sampling port. In these experiments, the analytes were converted into volatile hydrides upon passing through the hydride generator, and were introduced into the near-anode region of the SCGD system, where they were detected directly by atomic emission spectrometry (AES). A significant improvement in both selectivity and sensitivity was achieved, which was reflected in an improvement in the detection limits (DLs) by 3 orders of magnitude, in addition to successful valence analysis of Se without the requirement for chromatographic separation. In the absence of a strict sample pretreatment process and with a reduction in electrolyte consumption, the detection limits of Sn, Ge, and Se were determined to be 0.8, 0.5, and 0.2 μg·L-1. Moreover, our HG-SCGD-AES system demonstrated excellent repeatability (<3% peak height relative standard deviation) and more than 2 orders of linear dynamic range. The optimal operating conditions are outlined herein, and the analytical performance of the system is evaluated as described. Furthermore, our method was applied for the analysis of Sn, Ge, and Se in both environmental and biological samples, and the obtained results were in good agreement with reference values.

Elemental Analysis of Mineral Water by Solution-Cathode Glow Discharge–Atomic Emission Spectrometry

ABSTRACTA solution-cathode glow discharge was used for atomic emission spectrometry. The acidic reagent, discharge current, and flow rate were optimized. The detection limits for sodium, potassium, calcium, and magnesium were 1.51, 4.13, 131, and 54.9 µg L−1, respectively. The relative standard deviation for five replicates was from 0.52 to 3.00%. Sodium, potassium, calcium, and magnesium were determined in mineral water by solution-cathode glow discharge–atomic emission spectrometry. The results demonstrate that the protocol is suitable for the elemental analysis of mineral water.

Spatially resolved measurements to improve analytical performance of solution-cathode glow discharge optical-emission spectrometry

Past studies of the solution-cathode glow discharge (SCGD) revealed that elemental and molecular emission are not spatially homogenous throughout the source, but rather conform to specific zones within the discharge. Exploiting this inhomogeneity can lead to improved analytical performance if emission is collected only from regions of the discharge where analyte species emit strongly and background emission (from continuum, elemental and/or molecular sources) is lower. Effects of this form of spatial discrimination on the analytical performance of SCGD optical emission spectrometry (OES) have been investigated with an imaging spectrograph for fourteen atomic lines, with emphasis on detection limits and precision. Vertical profiles of the emission intensity, signal-to-background ratio, and signal-to-noise ratio were collected and used to determine the optimal region to view the SCGD on a per-element basis. With optimized spatial filtering, detection limits ranged from 0.09–360ppb, a 1.4–13.6 fold improvement over those obtained when emission is collected from the full vertical profile (1.1–840ppb), with a 4.2-fold average improvement. Precision was found to be unaffected by spatial filtering, ranging from 0.5–2.6% relative standard deviation (RSD) for all elements investigated, closely comparable to the 0.4–2.4% RSD observed when no spatial filtering is used. Spatial profiles also appear useful for identifying optimal line pairs for internal standardization and for flagging the presence of matrix interferences in SCGD-OES.

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.

Atmospheric-pressure ionization and fragmentation of peptides by solution-cathode glow discharge.

Modern "-omics" (e.g., proteomics, glycomics, metabolomics, etc.) analyses rely heavily on electrospray ionization and tandem mass spectrometry to determine the structural identity of target species. Unfortunately, these methods are limited to specialized mass spectrometry instrumentation. Here, a novel approach is described that enables ionization and controlled, tunable fragmentation of peptides at atmospheric pressure. In the new source, a direct-current plasma is sustained between a tapered metal rod and a flowing sample-containing solution. As the liquid stream contacts the electrical discharge, peptides from the solution are volatilized, ionized, and fragmented. At high discharge currents (e.g., 70 mA), electrospray-like spectra are observed, dominated by singly and doubly protonated molecular ions. At lower currents (35 mA), many peptides exhibit extensive fragmentation, with a-, b-, c-, x-, and y-type ion series present as well as complex fragments, such as d-type ions, not previously observed with atmospheric-pressure dissociation. Though the mechanism of fragmentation is currently unclear, observations indicate it could result from the interaction of peptides with gas-phase radicals or ultraviolet radiation generated within the plasma.

Measurement of sample and plasma properties in solution-cathode glow discharge and effects of organic additives on these properties

Effects of organic additives on spectroscopic and electrical properties of a solution-cathode glow discharge are measured. Effects of the discharge on sample solutions with and without additives are measured.

Evaluation of interference filters for spectral discrimination in solution-cathode glow discharge optical emission spectrometry

Solution-cathode glow discharge optical emission performance is evaluated with interference filters and critically compared to a traditional spectrometer.

Online mercury determination by laser-induced breakdown spectroscopy with the assistance of solution cathode glow discharge

The trace mercury in an aqueous solution was determined by laser-induced breakdown spectroscopy (LIBS) with the assistance of a solution cathode glow discharge (SCGD) system.

Automatable on-line generation of calibration curves and standard additions in solution-cathode glow discharge optical emission spectrometry

Two methods are described that enable on-line generation of calibration standards and standard additions in solution-cathode glow discharge optical emission spectrometry (SCGD-OES). The first method employs a gradient high-performance liquid chromatography pump to perform on-line mixing and delivery of a stock standard, sample solution, and diluent to achieve a desired solution composition. The second method makes use of a simpler system of three peristaltic pumps to perform the same function of on-line solution mixing. Both methods can be computer-controlled and automated, and thereby enable both simple and standard-addition calibrations to be rapidly performed on-line. Performance of the on-line approaches is shown to be comparable to that of traditional methods of sample preparation, in terms of calibration curves, signal stability, accuracy, and limits of detection. Potential drawbacks to the on-line procedures include signal lag between changes in solution composition and pump-induced multiplicative noise. Though the new on-line methods were applied here to SCGD-OES to improve sample throughput, they are not limited in application to only SCGD-OES—any instrument that samples from flowing solution streams (flame atomic absorption spectrometry, ICP-OES, ICP-mass spectrometry, etc.) could benefit from them.

Determination of Hg2+ by on-line separation and pre-concentration with atmospheric-pressure solution-cathode glow discharge atomic emission spectrometry

A simple and sensitive method to determine Hg2+ was developed by combining solution-cathode glow discharge atomic emission spectrometry (SCGD-AES) with flow injection (FI) based on on-line solid-phase extraction (SPE). We synthesized l-cysteine-modified mesoporous silica and packed it in an SPE microcolumn, which was experimentally determined to possess a good mercury adsorption capacity. An enrichment factor of 42 was achieved under optimized Hg2+ elution conditions, namely, an FI flow rate of 2.0mLmin−1 and an eluent comprised of 10% thiourea in 0.2molL−1 HNO3. The detection limit of FI–SCGD-AES was determined to be 0.75μgL−1, and the precision of the 11 replicate Hg2+ measurements was 0.86% at a concentration of 100μgL−1. The proposed method was validated by determining Hg2+ in certified reference materials such as human hair (GBW09101b) and stream sediment (GBW07310).

Signal enhancement in solution-cathode glow discharge — optical emission spectrometry via low molecular weight organic compounds

HCOOH, CH3COOH, and CH3CH2OH were used as chemical modifiers in a solution-cathode glow discharge. Emission was measured directly from the discharge, without a gas–liquid separator or a secondary excitation source. Emission from Ag, Se, Pb, and Hg was strongly enhanced, and the detection limits (DL) for these elements were improved by up to an order of magnitude using a combination of HCOOH and HNO3 compared to using HNO3 alone. The DL was measured for Mg (1μg/L), Fe (10μg/L), Ni (6μg/L), Cu (6μg/L), Pb (1μg/L), Ag (0.1μg/L), Se (300μg/L), and Hg (2μg/L). Coefficients of determination (R2) were between 0.9986 and 0.9999. A voltage of 1kV was used, which produced a current of approximately 70mA.

Solution–cathode glow discharge – optical emission spectrometry of a new design and using a compact spectrograph

A solution–cathode glow discharge is coupled to a compact spectrograph. Such a coupling results in a small, potentially portable instrument that can simultaneously detect a range of metals by optical emission spectrometry. Detection limits were calculated for Ag (1 ppb), Cd (2 ppb), Cu (8 ppb), Fe (40 ppb), Hg (20 ppb), Mg (3 ppb), Ni (12 ppb), Pb (10 ppb) and Se (3 ppm). These values are similar to those for an earlier, monochromator-based solution–cathode glow discharge system. All calibration curves showed good linearity (R2 ≥ 0.9994). Short-term precision ranged from 0.6–7%.

Determination of trace sodium, lithium, magnesium, and potassium impurities in colloidal silica by slurry introduction into an atmospheric-pressure solution-cathode glow discharge and atomic emission spectrometry

Trace impurities of sodium, lithium, magnesium, and potassium in colloidal silica were determined by slurry introduction into an atmospheric-pressure solution-cathode glow discharge (SCGD). The applied voltage, solution flow rate, and distance between the metal anode and surface of the solution were optimized. Emission from K (766.5 nm), Na (589.0 nm), Mg (285.2 nm) and Li (670.8 nm) demonstrated a linear range of nearly 4 orders of magnitude (R2 ≥ 0.998) and steady-state sample introduction yielded limits of detection of 0.7, 0.4, 0.5 and 0.2 ng mL−1, respectively. For an integration time of 0.3 s, relative standard deviations (RSDs) from 1000 ng mL−1 standard solutions introduced continuously were found to be better than 3% for all four elements. Transient sample introduction into the SCGD was also optimized and provided limits of detection for K, Na, Mg and Li of 3, 2, 2 and 0.8 ng mL−1, respectively, and RSDs for 1000 ng mL−1 standard solutions of better than 3%. Determined concentrations of trace impurities in colloidal silica agreed satisfactorily (accuracy from 1.3 to 7.7% and precision from 4 to 14%) with those obtained from inductively coupled plasma atomic emission spectrometry.

On line vapor generation of osmium based on solution cathode glow discharge for the determination by ICP-OES

A novel plasma induced vapor generation method is proposed to determine osmium in solutions. Without any chemical oxidizing agents, osmium ion can be readily converted to volatile osmium tetraoxide vapor in the solution cathode glow discharge (SCGD) system. The generated osmium vapor is then transported to inductively coupled plasma for determination by optical emission spectrometry. The influences of background electrolyte, carrier gas flow rate, sample flow rate, ICP power and discharge current were investigated. The analytical performances of this proposed technique were evaluated under optimized conditions. The detection limit of Os was calculated to be 0.51ngmL−1. The reproducibility, expressed as the relative standard deviation (n=11) of a 2.0μgmL−1 standard solution, was 1.9%. This SCGD induced vapor generation is sensitive and simple, oxidation reagents free, providing an alternative analytical method for measuring Os in geological or environmental water samples.

Universal Anion Detection by Replacement-Ion Chromatography with an Atmospheric-Pressure Solution-Cathode Glow Discharge Photometric Detector

A new method of detection for ion chromatography (IC) is described that couples replacement-ion chromatography (RIC) with an atmospheric-pressure solution-cathode glow discharge (SCGD). In the new instrument, a conventional suppressed IC arrangement is followed by a "replacement column" that consists of a cation-exchange micromembrane suppressor continuously regenerated with Li(2)SO(4). In this arrangement analytes are stoichiometrically converted to Li salts when they pass through the replacement column and are introduced into the SCGD, where they are detected indirectly by atomic emission spectrometry. Though found to be unsuitable for cation determinations, the SCGD-RIC instrument shows good repeatability (<3.5% peak area relative standard deviation), approximately 4 orders of linear dynamic range, universal calibration (similar molar sensitivity for anions of the same charge), and detection limits between 0.08 and 0.64 μg·mL(-1) (25-μL injection) for several mono- and divalent anions. Deviations from the universal calibration were also observed and are critically evaluated. Optimal operating conditions are described, analytical figures of merit are presented, and background sources present in the system are characterized and explained.

Visual observations of an atmospheric-pressure solution-cathode glow discharge

The solution-cathode glow discharge (SCGD) is an optical emission source for atomic spectrometry comprised of a moderate-power atmospheric-pressure DC glow discharge sustained directly upon the surface of an electrically conductive solution. The SCGD boasts a simple, inexpensive design and has demonstrated detection limits similar to those of more conventional excitation sources used in atomic spectrometry. Although the analytical performance of the SCGD as an optical emission source is well characterized, the mechanism through which the discharge atomizes and excites analyte from the sample solution remains a point of debate. The current paper presents visual observations of the SCGD from a variety of imaging techniques. The implications of the images regarding the mechanism of analyte solution-to-plasma transport and excitation in the SCGD are discussed.

Solution cathode glow discharge induced vapor generation of mercury and its application to mercury speciation by high performance liquid chromatography–atomic fluorescence spectrometry

A novel solution cathode glow discharge (SCGD) induced vapor generation was developed as interface to on-line couple high-performance liquid chromatography (HPLC) with atomic fluorescence spectrometry (AFS) for the speciation of inorganic mercury (Hg 2+), methyl-mercury (MeHg) and ethyl-mercury (EtHg). The decomposition of organic mercury species and the reduction of Hg 2+ could be completed in one step with this proposed SCGD induced vapor generation system. The vapor generation is extremely rapid and therefore is easy to couple with flow injection (FI) and HPLC. Compared with the conventional HPLC–CV-AFS hyphenated systems, the proposed HPLC–SCGD-AFS system is very simple in operation and eliminates auxiliary redox reagents. Parameters influencing mercury determination were optimized, such as concentration of formic acid, discharge current and argon flow rate. The method detection limits for HPLC–SCGD-AFS system were 0.67 μg L −1 for Hg 2+, 0.55 μg L −1 for MeHg and 1.19 μg L −1 for EtHg, respectively. The developed method was validated by determination of certified reference material (GBW 10029, tuna fish) and was further applied for the determination of mercury in biological samples.

Solution cathode glow discharge induced vapor generation of iodine for determination by inductively coupled plasma optical emission spectrometry

A novel vapor-generation technique is described for iodine determination in aqueous solutions. The iodide and iodate in the solution are converted to volatile iodine vapor through solution cathode glow discharge induced advanced redox processes. It is achieved by in situ produced highly reactive chemical species in the discharge, thereby eliminating the need for externally supplied sources of any redox reagents. Iodine vapor is readily generated from a background electrolyte containing 0.01 mol L−1 HNO3. The generated iodine vapor is then transported to inductively coupled plasma for determination by optical emission spectrometry. The influences of the background electrolyte, pH, discharge voltage, carrier gas flow rate and ICP power were examined. The detection limits of plasma induced vapor generation for KI and KIO3 were 0.30 and 0.43 μg L−1, respectively. The repeatability, expressed as the relative standard deviation (n = 11) of a 0.05 mg L−1 standard, was 1.2% for KI and 1.9% for KIO3. Compared with conventional vapor generation technology, it offers several advantages. First, it eliminates the need for redox regents, and thus minimizes a source of contamination as well as hazards. Second, it is applicable to both iodide and iodate determination. In addition to iodide, iodate could also be directly converted to volatile iodine vapor without prior reduction. The method is sensitive and simple in operation, and requires no auxiliary reagents, served as a useful alternative to conventional vapor generation for trace iodine determination.

Use of a Solution Cathode Glow Discharge for Cold Vapor Generation of Mercury with Determination by ICP-Atomic Emission Spectrometry

A novel vapor-generation technique is described for mercury determination in aqueous solutions. Without need for a chemical reducing agent, dissolved mercury species are converted to volatile Hg vapor in a solution cathode glow discharge. The generated Hg vapor is then transported to an inductively coupled plasma for determination by atomic emission spectrometry. Mercury vapor is readily generated from a background electrolyte containing 0.1 M HNO 3. Vapor generation efficiency was found to be higher by a factor of 2-3 in the presence of low molecular weight organic acids (formic or acetic acids) or alcohols (ethanol). Optimal conditions for discharge-induced vapor generation and reduced interference from concomitant inorganic ions were also identified. However, the presence of chloride ion reduces the efficiency of Hg-vapor generation. In the continuous sample introduction mode, the detection limit was found to be 0.7 microg L (-1), and repeatability was 1.2% RSD ( n = 11) for a 20 microg L (-1) standard. In comparison with other vapor generation methods, it offers several advantages: First, it is applicable to both inorganic and organic Hg determination; organic mercury (thiomersal) can be directly transformed into volatile Hg species without the need for prior oxidation. Second, the vapor-generation efficiency is high; the efficiency (with formic acid as a promoter) is superior to that of conventional SnCl 2-HCl reduction. Third, the vapor generation is extremely rapid and therefore is easy to couple with flow injection. The method is sensitive and simple in operation, requires no auxiliary reagents, and serves as a useful alternative to conventional vapor generation for ultratrace Hg determination.

High-Throughput Elemental Analysis of Small Aqueous Samples by Emission Spectrometry with a Compact, Atmospheric-Pressure Solution-Cathode Glow Discharge

A miniaturized version of an atmospheric-pressure glow discharge using a solution as the cathode was recently evaluated for elemental analysis of continuously sampled aqueous solutions. Although continuous sampling is useful, transient analysis is required for certain applications, including chromatographic or similar separations, small-volume sampling, high-throughput sampling, and on-line preconcentration. The miniaturized solution-cathode glow discharge seems particularly well suited to transient analysis by virtue of its low dead volume and high sensitivity. Two benefits of transient analysis were exploited here: high throughput and small sample volume. Sampling 25-microL volumes at 1000 samples/h, the discharge achieved detection limits ranging from 5 pg (0.2 ppb) for Li to 6 ng (270 ppb) for Hg.