Solution Cathode Glow Discharge Research Articles

Solution Cathode Glow Discharge – Atomic Emission Spectrometry (SCGD-AES) With an Interference Filter for Spectral Discrimination for the Determination of Thallium in Surface Water

Solution cathode glow discharge atomic emission spectrometry (SCGD-AES) using wide-bandpass (10-nm) interference filters (IF) as a spectral discrimination device was used for the determination of thallium (Tl) in surface water. The use of wide-bandpass interference filters greatly reduces the cost of traditional detection instruments. The influence of solution flow rate, discharge current and pH on the detection limit was characterized. Moreover, matrix effect experiments were performed to study the effect of different concentrations of Na+, K+, Ca2+, and Mg2+ on the Tl signal intensity. Using a solution flow rate of 2.8 mL/min, a discharge current of 50 mA, and pH of 1.0 with HNO3 as the supporting electrolyte, SCGD coupled with an interference filter provided a detection limit of 7.76 μg/L for Tl in water samples, comparable to traditional SCGD-AES. Furthermore, the spiked recovery rate of Tl is quantitative in real water samples and comparable to the performance of inductive coupled plasma – optical emission spectrometry (ICP-OES).

Rapid Determination of Calcium, Iron, and Zinc in Gluconate Oral Solutions by Solution Cathode Glow Discharge – Atomic Emission Spectroscopy (SCGD-AES)

A novel solution cathode glow discharge atomic emission spectroscopy (SCGD-AES) system coupled with simplified sample preparation was developed for determining Ca, Fe, and Zn in gluconate oral solution. The preparation of the oral solution only involves diluting 1 g of the sample 100-fold and acidification with HNO3 to a concentration of 0.1 mol L−1. The preparation of each solution requires less than 5 min. Five oral solutions containing Ca, Fe, and Zn were analyzed. The results indicate that the optimal parameters are HNO3 of pH 1.0 as the electrolyte, a sample flow rate of 2.05 mL min−1, and a discharge current of 65 mA. The detection limits (DLs) of Ca, Fe, and Zn were 58.64, 64.29, and 15.92 µg L−1. The analyses by SCGD-AES for Ca, Fe, and Zn using direct dilution are in agreement with the values by ICP-OES and SCGD-AES with digestion. A t-test was conducted on the oral liquid samples, revealing that the majority of the obtained p-values exceeded .05. In addition, SCGD-AES reduces the time, energy, and quantity of concentrated HNO3 compared with previous studies, and the measurement time of each oral liquid sample was less than 2 min. These findings demonstrate the use of SCGD-AES as an expedited and dependable method for the determination of trace elements in health food products.

Solution cathode glow discharge coupled to atmospheric pressure chemical ionization for elemental detection of S and P in organic compounds

We report a post-plasma chemical ionization approach to evaluate solution cathode glow discharge (SCGD) for S and P elemental analysis. Here, the SCGD serves as a reactor to produce chemical vapors for S and P from organic compounds containing these elements, while a corona discharge operated in negative mode is used to ionize the products. The approach creates long-lived ions in atmospheric pressure, enabling direct investigation of chemical vapor products via mass spectrometric and ion mobility separations. The investigations indicate that SCGD converts S and P to H2SO4 and H3PO4, respectively. These species are then ionized as HSO4HNO3− and H3PO4NO3HNO3− via reactions with NO3HNO3− produced by corona discharge. The response factors for P among several small molecules varies within 10% of the average response from the compounds, suggesting a reasonable species-independent characteristic. The response factors for S show larger variations among compounds, indicating a higher dependence of chemical vapor generation efficiency on analytes' chemical structures. Detection limits of 15 and 29 ng/mL are achieved for P and S detection, respectively. These figures are limited by background equivalent concentrations and low ion flux in the utilized ion mobility-time of flight mass spectrometer, indicating potential for significant improvements. In particular, the specificity of clustering for S and P-containing ions produced in this approach suggest facile analysis of S and P using quadrupole-based mass spectrometers for improved analytical performance.

Sensitive and rapid determination of the iodine/calcium ratio in carbonate rock samples by ICP-MS based on solution cathode glow discharge sampling

A solution cathode glow discharge (SCGD) sampling technique coupled with ICP-MS for highly sensitive and accurate determination of I/Ca in low-iodine carbonate samples.

Construction and Application of a New Experimental Device for Determination of Alkaline Metal Elements by Plasma Atomic Emission Spectrometry Based on Solution Cathode Glow Discharge: An Alternative Approach for Fundamental Teaching Experiments in Emission Spectroscopy

Construction and Application of a New Experimental Device for Determination of Alkaline Metal Elements by Plasma Atomic Emission Spectrometry Based on Solution Cathode Glow Discharge: An Alternative Approach for Fundamental Teaching Experiments in Emission Spectroscopy

Concomitant ion matrix effects in SCGD-OES enhanced with formic acid

SCGD-OES is an attractive approach for on-line and in situ elemental analysis. This communication deals with concomitant ion matrix effects, especially if formic acid is added to improve sensitivity, and including a brief mechanistic discussion.

Comprehensive evaluation of matrix effect in the detection of Zn, Cd, Ni, Cu, Cr and Pb by solution cathode glow discharge optical emission spectrometry

Herein, the effect of different salt matrices on the signals of Zn, Cd, Ni, Cu, Cr, and Pb using solution cathode glow discharge optical emission spectrometry (SCGD-OES), was discussed at length. The cation interference test covered sodium, potassium, magnesium and calcium ions, while the anion interference test covered chloride and sulfate ions. Overall, the order of interference levels for the four cations was: Na+≈K+>Mg2+≈Ca2+. The emission of most elements was inhibited at Na+/K+/Mg2+/Ca2+ concentration exceeding 200 mg L-1. The impact of the two anions is not measurably different and almost no interference occurred when anion content reaching 200 mg L-1. The spectral interference caused by Na+ and K+ was also much greater than that of Mg2+ and Ca2+, which was reflected in the diminution of spectral bands of the two main molecules (OH and N2). The role of formic acid (HCOOH) has been reassessed at a salinity of 200 mg L-1 Na+. HCOOH was found to play a positive role on volatile species forming metals such as Pb, regardless of the presence of sodium salts. For elements (Cr) that are hard to evaporate and stimulate, HCOOH exhibited a strong inhibitory effect, possibly due to exacerbating the deterioration of the excitation state. For other transition metal elements in the fourth period, e.g., Zn, HCOOH demonstrated minor effects.

Solution-cathode glow discharge under high NaCl concentration: Impact on excitation conditions and analyte transfer processes

The Solution-Cathode Glow Discharge (SCGD) is a useful plasma source for elemental analysis, gathering atomization/excitation/ionization capabilities for aqueous solutions with simplicity and low consumption. When combined with Optical Emission Spectrometry (OES), ng/mL limits of detection can be achieved for multiple elements. Additionally, this plasma source presents certain robustness against the presence of dissolved non-analyte ions. Nevertheless, the mechanisms by which the SCGD can transfer the dissolved analytes from the solution into the plasma, and the mechanisms of how concomitant ions in the sample solution affect the performance of the analysis, are still not fully understood. Therefore, fundamental plasma diagnostics of the SCGD are performed in this work, including electrical measurements, electron densities and rotational and excitation temperatures. In particular, these measurements are performed introducing solutions with NaCl concentrations up to 3.5 g/L in order to understand how they affect the atomization/excitation efficiency and the analyte solution-to-plasma transfer processes of the source. The information is correlated with the signal produced by three analytes (Cd, Zn and Cu).

Determination of Metals by Portable Millisecond Pulsed Solution Cathode Glow Discharge (SCGD) Atomic Emission Spectroscopy (AES)

In order to determine metal ions in aqueous solution, a millisecond pulsed solution cathode glow discharge (SCGD) source coupled with a portable spectrometer was developed for atomic emission spectrometry (AES). The millisecond pulsed SCGD source was operated with two high-voltage DC power supplies and a high-voltage pulse switch, specifically boosting the analyte excitation and sustain the glow discharge. The method to excite the plasma discharge contrasts with traditional approaches that employ a single power source. The influence of operating parameters, including pulsed voltage, pulsed frequency, duty ratio, and sample flow rate, were optimized to construct a system having good stability and improved excitation of metal ions. The optimum detection limits for Na, K, Li, Mg, Ag, Cs, Rb, and Sr were 0.17, 0.32, 0.38, 0.50, 2.65, 1.30, 0.22, and 74.02 µg·L−1, respectively. Furthermore, mountain spring, Yangtze River, and reservoir water were spiked with Ag, Rb, and Cs; the recoveries ranged from 105% to 106%, 106% to 107%, and 107% to 108% indicating that the developed system has favorable analytical performance.

Determination of Metals in Environmental Waters by Solution Cathode Glow Discharge -Atomic Emission Spectroscopy (SCGD-AES) with a Syringe Pump for Sample Introduction

This study reports a syringe injection pump for sample introduction for solution cathode glow discharge (SCGD) atomic emission spectroscopy (AES). The experimental conditions are optimized at 60 mA discharge current, 2.5 mm gap spacing, 2.0 mm distance from the glass capillary to cathode, 1.60 mL/min flow rate, and pH 1.0 based on the detection limits (DLs) obtained for Li, Cd, Cu, Ag, Mn, Pb, Cr, and Zn. The detection limits for Li, Cd, Cu, Ag, Mn, Pb, Cr, and Zn were 0.24, 12.26, 12.08, 1.09, 46.42, 25.81, 183.05, and 29.01 µg/L, respectively, significantly lower than using the traditional peristaltic pump. The detection limits decreased by 1.4, 1.8, 2.2, 5.0, 1.4, 1.4, 1.4, 1.6, and 2.2-fold for these elements. The flow rate and the solution consumed per unit time were significantly reduced using this design. The spectral detection revealed stable and practical operation of the system with relative standard deviations <0.85%. Water samples from Yangtze River, Baixi River, and Baiyun Reservoir are analyzed using the modified SCGD system and its evaluation is based upon comparison to inductively coupled plasma—optical emission spectroscopy (ICP-OES). The modified device operates at atmospheric pressure without inert gas and integrates a syringe injection pump and a compact spectrometer to optimize solution utility, analytical performance, and operation size for industrial and environmental monitoring applications.

Solution-Based Glow Discharges for Atomic Emission Spectroscopy Come of Age

The solution-cathode glow discharge (SCGD) is a low-power, atmospheric-pressure, ambient-atmosphere microplasma that is proving to be a proficient excitation source for atomic emission spectroscopy (AES). The analytical figures of merit of SCGD-AES experiments often compete with established, conventional approaches despite the fact that it is a simple, small, low-cost instrument. The operating principles of the SCGD are reviewed here, including experimental operating parameters, plasma conditions, analytical performance, matrix interferences, and application examples.

Multi-element Simultaneous sensitization of solution cathode glow discharge atomic emission spectrometry by using portable semiconductor anode refrigeration

In this study, a modified solution cathode glow discharge atomic emission spectrometry (SCGD-AES) was used to detect metal elements in electroplating sewage. The SCGD-AES device was equipped with a portable semiconductor anode refrigeration unit, which was built independently. The red-heat effect of tungsten electrode was alleviated by adding the portable refrigeration unit, thus improving thermal stability with the withstand voltage from 1040 V to 1140 V. Compared with the devices without semiconductor refrigeration, the chromium was excited more favorable when the discharge voltage increased, and the limit of detection (LOD) decreased by 8.5 times. Furthermore, the LODs of Zn, Cd, Ni, Cu and Pb decreased by 1.8–3.2 times, respectively, which realized the detection of elements in electroplating sewage and showed high performance in the field of trace elements analysis. Furthermore, the accuracy of the method was verified by stream sediment reference material (GBW07312), and the results were consistent with the certified values. The recoveries of elements added to industrial sewage and seawater range were from 90.5 to 98.7%, demonstrating good accuracy of the proposed method.

Elemental Analysis of Environmental Waters by Solution Cathode Glow Discharge—Atomic Emission Spectrometry (SCGD-AES) with a Multifunctional Injection System

A multifunction sample injection system combined with solution cathode glow discharge—atomic emission spectrometry (SCGD-AES) was developed based on several simple devices (six-way valve, peristaltic pump and medical injector). The equipment enables two analytical modes (continuous flow and flow injection), selected according to the sample. Moreover, the equipment can be operated at atmospheric pressure without any inert gas. Under the optimal experimental conditions (1150 V discharge voltage, 2.5 mm discharge gap, 2.32 mL min−1 flow rate and solution pH 1.0), ten elements (Na, K, Mg, Cu, Rb, Ag, Tl, Cd, Zn, and Mn) were determined using SCGD-AES in the continuous flow and flow injection modes. The detection limits for metals were from 0.1 to 264 µg L−1 (continuous flow mode) and 0.9 to 282 µg L−1 (flow injection mode). The relative standard deviations of the spectral intensities were below 2%. The instrumentation was successfully applied to the Yangtze River and reservoir water samples. The accuracy and viability were confirmed by comparison with inductively coupled plasma—atomic emission spectrometry (ICP-AES) measurements.

A novel solution cathode glow discharge geometry for improved coupling to optical emission spectrometry

The Solution-Cathode Glow-Discharge (SCGD) is an atmospheric pressure glow discharge used for atomic emission spectrometry that is sustained between a metallic pin-anode and a liquid cathode, which is also the sample solution.

Multi-Element Simultaneous Sensitization of Solution Cathode Glow Discharge Atomic Emission Spectrometry by Using Portable Semiconductor Anode Refrigeration

Multi-Element Simultaneous Sensitization of Solution Cathode Glow Discharge Atomic Emission Spectrometry by Using Portable Semiconductor Anode Refrigeration

Development of milli-second pulsed atmospheric pressure solution cathode glow discharge optical emission spectroscopy for detecting metal elements in aqueous solution

A novel atmospheric-pressure plasma source has been developed to determine metal ions in an aqueous solution by means of optical emission spectroscopy.

Critical evaluation of SCGD-OES analytical performance in the presence of NaCl

The present study deals with the influence of sodium chloride (NaCl) on the analytical response and performance of solution-cathode glow discharge coupled to optical emission spectroscopy (SCGD-OES).

Direct and Sensitive Determination of Antimony in Water by Hydrogen-Doped Solution Anode Glow Discharge-Optical Emission Spectrometry Without Hydride Generation.

In the present work, a novel, simple, and sensitive method for the direct determination of trace Sb in water samples was developed based on hydrogen-doped solution anode glow discharge-optical emission spectrometry (SAGD-OES). It was found that the vapor generation and excitation of Sb occurred simultaneously in the SAGD, contributing to the significant improvement in the sensitivity of Sb as compared with normal pure He-operated SAGD or solution cathode glow discharge. Besides, the proposed hydrogen-doped SAGD-OES could be operated even at pH = 14, which could reduce the interference of coexisting ions as many metal ions could be precipitated and removed. Our results demonstrated that the proposed method offered good tolerance to the interferences of Li, Na, Ca, Mg, Fe, Ni, Mn, and Zn ions even at a concentration of 50 mg L-1. Under optimized conditions, the limit of detection of Sb was 0.85 μg L-1, which was comparable to that of microplasma sources coupled with conventional hydride generation. The linearity of the Sb calibration curve reached R2 > 0.999 in the 5-5000 μg L-1 range. Finally, the accuracy of the proposed method was validated by the determination of certified reference materials [GSB 07-1376-2001 (1) and (2))] and real water samples. The proposed low-power (6 W), green, sensitive, rapid, and robust method provides a promising approach for on-site trace Sb analysis and may also be extended to other elements.

Ultrasensitive determination of mercury by ICP-OES coupled with a vapor generation approach based on solution cathode glow discharge

We herein proposed a sample introduction technique based on solution cathode glow discharge (SCGD) of a portable design for inductively coupled plasma-optical emission spectrometry (ICP-OES) and its application in sensitive determination of mercury. The products from SCGD containing mercury vapor, were transported by an Ar flow to ICP spectrometer for detection. A gas liquid separator (GLS) and a dryer were used to condense and remove most of the accompanying moisture, which greatly improved both the stability and sensitivity of the signal. The detection limit (DL) acquired by this developed method was 0.22 µg/L (194.1 nm), which was nearly 82 times lower than that obtained by pneumatic nebulization (PN). The relative standard deviation (RSD) was 1.4% (n = 14) for a 50 µg/L standard. Blank solution (HNO3, pH 1) can effectively elute mercury residue. Its accuracy and practicality were also demonstrated by the determination of GBW10029 (fish) certified reference material, shrimp, crawfish, soil and human hair samples. The results showed good consistency with the certified values and the values obtained using inductively coupled plasma−mass spectrometry.

Improved solution cathode glow discharge micro-plasma source with a geometrically optimized stainless steel auxiliary cathode for optical emission spectrometry of metal elements

An improved micro-plasma source for the quantitative analysis of heavy metal elements by solution cathode glow discharge-optical emission spectrometry (SCGD-OES) was developed. The glow-discharge plasma source was fabricated using a geometrically optimized stainless steel auxiliary cathode solution and a tungsten anode. Optimum discharge could be attained at reduced solution flow rates under the following operating conditions: pH 1.0 (HNO3); a discharge current of 80 mA; a solution flow rate of 1.65 mL/min; and a discharge gap of 2.5 mm. The detection limits (DLs) of the improved micro-plasma source for K, Na, Ni, Cd, Co and Hg were 0.17, 0.06, 18, 10, 25 and 66 μg/L, respectively. The recoveries of metal elements from spiked samples of spring river, Yangtze River and reservoir water measured by SCGD-OES showed good agreement with those obtained using ICP-OES. The results from this study may provide a new direction for the design of glow discharge sources for the in situ determination of metal elements in complex water samples.