Ultrasensitive Determination of Selenium and Arsenic by Modified Helium Atmospheric Pressure Glow Discharge Optical Emission Spectrometry Coupled with Hydride Generation

Electrothermal desolvation-enhanced microplasma optical emission spectrometry for sensitive determination of Cd, Zn Pb and Mn in environmental water samples

Herein, a novel electrothermal desolvation (ED) introduction approach is developed to enhance the analytical sensitivity of the point discharge (PD)-based microplasma-optical emission spectrometric (PD-MIP-OES) system for detecting trace Cd, Zn, Pb and Mn in environmental water samples. Liquid samples are converted into aerosols through a miniature ultrasonic nebulizer, and subsequently desolvated by electric heating at 350 °C. The analytes obtained after condensation (referring to the smaller apertures aerosols and volatile analytes after ED and condensation) are excited and detected by PD-MIP-OES. For a 160 μL liquid sample, analysis is completed within 10 s, achieving a desolvation efficiency of 93 %. Under the optimized conditions, the detection limits for Cd, Zn, Pb and Mn are 1.3, 1.2, 2.4 and 2.1 μg L-1, respectively. Compared to traditional direct ultrasonic nebulization introduction, sensitivity increases by 17, 12, 10 and 14 times, respectively. The accuracy and practicality of the proposed method are verified by measuring certified reference material and several real water samples. The ED-enhanced PD-MIP-OES device presented is compact, easy to operate, and capable of rapid analysis, which provides a convenient and reliable tool for the field analysis of Cd, Zn, Pb and Mn in environmental water samples.

Real-Time Monitoring of Metal Ions during the Molten Salt Electrolysis Process by Optical Emission Spectrometry Based on Microplasma

Molten salt electrolysis has been widely used in the production and separation of metals, but it still lacks in situ real-time analysis methods to monitor the electrolysis process. In this work, a microplasma spectroscopic real-time analysis (MIPECA) system is developed based on noncontact direct current (DC) glow discharge. With the MIPECA system, the atomic emission spectroscopy of Li and K could be obtained in situ in LiCl-KCl molten salt, and the impact of different operating conditions on spectral signals was investigated. Then, the characteristic spectra of ten representative elements, including alkali metals (Na, Cs), alkaline earth metals (Mg, Ca, Sr, Ba), transition metals (Ag, Cu, Ni), and lanthanide metals (Ce), were all successfully excited for qualitative analysis. Under the optimal operating conditions, quantitative analysis of Ag, Cs, and Sr was achieved with high sensitivity and low limits of detection (LOD) of about 0.063, 0.021, and 0.073 wt %, respectively. Finally, the electrolysis process of Ag+ in LiCl-KCl molten salt was real-time monitored by using this MIPECA system, showing its application potential in molten salt electrolysis.

3D printed microplasma optical emission spectrometry coupled with ZIF-8 based dispersive solid-phase extraction for field analysis of waterborne arsenic

BACKGROUND

Arsenic contamination of drinking water has become a public health challenge over the world, particularly in Bangladesh, India, and China. Compared to the most used field test kits of waterborne arsenic, miniature microplasma atomic spectrometry retains advantages of accuracy, elemental specificity, and less matrix interference. Despite increased interest in arsenic detection by using miniature microplasma spectrometry, the improvements of its analytical performance, manufacturing cost and consistency still remain significant challenges.

RESULTS

Herein, a miniature, battery-operated, and integrated hydride generation point discharge optical emission spectrometer (HG-μPD-OES, 116 mm length × 92 mm width × 104 mm height) was printed with a simple 3D printer and used for the highly sensitive and element-specific determination of arsenic by coupling to a dispersive solid-phase extraction (d-SPE) using zeolitic imidazolate framework-8 as adsorbent. The d-SPE simplifies sample treatment, significantly alleviates the interference arising from transition metal ions and improves sensitivity. A LOD of 0.07 μg L-1 for arsenic was obtained with relative standard deviations (RSDs, n = 11) better than 3.8 %.

SIGNIFICANCE

The 3D printing technique significantly improves the manufacturing cost and fabricating consistency of HG-μPD-OES. LOD were remarkably improved 27-fold compared to those obtained by conventional HG-μPD-OES, providing a promising method for the reliable, sensitive, and convenient field analysis of waterborne arsenic even its concentration as low as 0.2 μg L-1. The practicability and accuracy of the proposed method have been successfully verified via the field analysis of waterborne arsenic in a Certified Reference Material (GBW(E)080390) and a series of river and lake water samples.

A Portable Microplasma Optical Emission Spectrometric Device with Online Digestion Function for Field and Sensitive Determination of Lead in Biological Samples

Accurate detection and screening of Pb in biological samples is helpful to assess the risk associated with lead pollution to human health. However, conventional atomic spectroscopic instruments are bulky and cumbersome, requiring additional sample pretreatment equipment, and difficult to perform field analysis with. Herein, a portable point discharge (PD) microplasma-optical emission spectrometric (OES) device with online digestion function is designed for field and sensitive determination of lead in biological samples. With rice as a model, online digestion of a batch of six 50 mg samples can be achieved in the HNO3 and H2O2 system within 25 min by a temperature control and timing module. Compared to the conventional microwave digestion, the digestion efficiency of this device reaches 97%. Pb in digestion solution is converted into volatile species by hydride generation (HG) and directly introduced into PD-OES for excitation and detection by a self-designed rotatable and telescopic cutoff gas sampling column. Six samples can be successively detected in 2 min, and argon consumption of the whole process is only <800 mL. Under the optimized conditions, the detection limit of Pb is 0.018 mg kg-1 (0.9 μg L-1) and precision is 3.6%. The accuracy and practicability of the present device are verified by measuring several certified reference materials and real biological samples. By virtue of small size (23.5 × 17 × 8.5 cm3), lightweight (2.5 kg), and low energy consumption (24.3 W), the present device provides a convenient tool for field analysis of toxic elements in biological samples.

Quantification of lithium in molten chlorides by optical emission spectrometry using a novel molten-salt-electrode microplasma source

A new molten-salt-electrode microplasma (MSEMP) source for optical emission spectrometry (OES) was constructed, equipped with a molten salt electrode and a metal hollow tube (fed with helium) counter electrode. The use of the MSEMP-OES for constituent analysis of molten salt was primarily evaluated. The acquirement of characteristic spectral lines of some elements in several molten chloride samples verified the good qualitative ability of the proposed MSEMP-OES. Solid copper was dissolved via charge transfer and excited in glow discharge, indicating its potential application in solid sample analysis. The temperature and composition of molten salt were found to have no influence on the lithium response and the accurate quantification of lithium in molten salt was achieved. This work provides new insights for promoting the application of microplasma technology in the in-situ analysis of elements, even in special samples.

Selenium-based metabolic oligosaccharide engineering strategy for quantitative glycan detection

Metabolic oligosaccharide engineering (MOE) is a classical chemical approach to perturb, profile and perceive glycans in physiological systems, but probes upon bioorthogonal reaction require accessibility and the background signal readout makes it challenging to achieve glycan quantification. Here we develop SeMOE, a selenium-based metabolic oligosaccharide engineering strategy that concisely combines elemental analysis and MOE,enabling the mass spectrometric imaging of glycome. We also demonstrate that the new-to-nature SeMOE probes allow for detection, quantitative measurement and visualization of glycans in diverse biological contexts. We also show that chemical reporters on conventional MOE can be integrated into a bifunctional SeMOE probe to provide multimodality signal readouts. SeMOE thus provides a convenient and simplified method to explore the glyco-world.

Nozzle Electrode Point Discharge-Enhanced Oxidation and Portable Gas Phase Molecular Fluorescence Spectrometry for Sensitive Field Detection of Sulfide

It is still a challenge to accurately determine dissolved sulfide due to its susceptibility to contamination and loss during transportation, storage, and analysis in the laboratory, thus highlighting the necessity for its sensitive field analysis. Herein, a robust nozzle electrode point discharge (NEPD) enhanced oxidation coupling with chemical vapor generation (CVG) is described for the highly efficient and flameless conversion of sulfide (S^2-) to SO₂. Subsequently, a portable and low-power consumption gas phase molecular fluorescence spectrometry (GP-MFS) was constructed for the highly selective and sensitive determination of the generated SO₂ via detecting its molecular fluorescence excited by a zinc hollow cathode lamp. Under optimal conditions, a limit of detection (LOD) of 0.1 μM was obtained for dissolved sulfide with a relative standard deviation (RSD, n = 11) of 2.6%. The accuracy and practicability of the proposed method were validated by the analyses of two certified reference materials (CRMs) and several river and lake water samples with satisfactory recoveries of 99%-107%. This work confirms that NEPD enhanced oxidation is a low energy consumption yet highly efficient method for the flameless oxidation of hydrogen sulfide and thus is suitable for the easy field detection of dissolved sulfide in environmental water by CVG-GP-MFS.

Rapid detection of ultratrace urinary arsenic by direct sampling microplasma vaporization based on silicon nitride

At present, immediate monitoring urinary arsenic is still a challenge for treating arsenic poisoning patients. Thus, a fast, reliable and accurate analytical approach is indispensable to monitor ultratrace arsenic in urine sample for health warning. In this work, a silicon nitride (SN) rod was first integrally utilized as a sample carrier for ≤50 μL urinary aliquot, an electric heater for removing water and ashing sample as well as a high voltage electrode for dielectric barrier discharge vaporization (DBDV). The direct analytical method of arsenic in urine without sample digestion was thus developed using atomic fluorescence spectrometer (AFS) as a model detector. After 4 V electrically heating the SN rod for 60 s, urine sample was dehydrated and ashed outside; then, DBD was exerted under 0.8 A with 0.8 L/min H₂ + Ar (1:9, v:v) for 20 s to vaporize arsenic analyte from the SN rod. After optimization, 0.014 μg/L arsenic detection limit (LOD) was reached with favorable analytical precision (RSD <5%) and accuracy (91-110% recoveries) for real sample analysis. As a result, the whole analysis process only consumes <3 min to exclude complicated sample preparation; furthermore, the designed DBDV system only occupies 25 W and <2 kg, which renders a miniature sampling component to hyphenate with a miniature detector to detect arsenic. Thus, this direct sampling DBDV method extremely fulfills the fast, sensitive and precise detection of ultratrace arsenic in urine sample.

Array Point Discharge as Enhanced Tandem Excitation Source for Miniaturized Optical Emission Spectrometer

A new compact tandem excitation source was designed and constructed by using an array point discharge (ArrPD) microplasma for a miniaturized optical emission spectrometer through coupling a hydride generation (HG) unit as a sample introduction device. Three pairs of point discharges were arranged in sequence in a narrow discharge chamber to construct the ArrPD microplasma, for improved excitation capability owing to the serial excitation. Besides, the discharge plasma region was greatly enlarged, therefore, more gaseous analytes could be intercepted to enter into the microplasma for sufficient excitation, for improved excitation efficiency and OES signal. To better understand the effectiveness of the proposed ArrPD source, a new instrument for simultaneous detection of atomic emission and absorption spectral responses was also proposed, designed, and constructed to reveal the excitation and enhancement process in the discharge chamber. Under the optimized conditions, the limits of detection (LODs) of As, Ge, Hg, Pb, Sb, Se, and Sn were 0.7, 0.4, 0.05, 0.7, 0.3, 2, and 0.08 μg L^-1, respectively, and the relative standard deviations (RSDs) were all less than 4%. Compared with a commonly used single point discharge microplasma source, the analytical sensitivities of these seven elements were improved by 3-6-fold. Certified Reference Materials (CRMs) were successfully analyzed with this miniaturized spectrometer, which features low power, compactness, portability, and high detectability, and is thereby a great prospect in the field of elemental analytical chemistry.

Fabrication and Characterizations of Axial View Liquid Electrode Plasma Atomic Emission Spectrometry for the Sensitive Determination of Trace Zinc, Cadmium, and Lead

Axial view liquid electrode plasma-atomic emission spectrometry (axial view LEP-AES) was proposed and fabricated successfully in this work. The emission spectra from Zn, Cd, Pb, Ca, and K were applied for characterization and optimization. Comparing with conventional radial view LEP-AES devices, the newly designed axial view-LEP provided better sensing ability toward trace heavy metals. Moreover, pulsed voltage discharge was found to be advantageous over continuous discharge under the same discharge time for detection. The optimized parameters facilitate the limit of detection to achieve 0.24, 0.051, and 0.85 μg L^-1 for Zn, Cd, and Pb, respectively. Furthermore, the axial view LEP-AES possessed excellent reproducibility and good durability. The real sample tests using two different certified reference water samples revealed the great potential of the axial view LEP-AES as a novel practical elemental analysis tool.

Microdischarge in Flame as a Source-in-Source for Boosted Excitation of Optical Emission of Chromium

A compact tandem excitation source-in-source was designed by arranging a point discharge (PD) ignited in argon/hydrogen (Ar/H₂) flame and utilized for boosted excitation for the optical emission of chromium. Through a tungsten coil (W-coil) electrothermal vaporizer (ETV) located right under the tandem source without any interface for sample introduction, a miniaturized optical emission spectrometer was realized. Because the discharge gaseous atmosphere of PD was activated in the flame, the energy consumption of PD for breaking down discharge gas and maintenance of plasma was greatly saved. In addition, the flame could partially atomize or keep the atomized state of analyte atoms through its reducing environment. Therefore, the excitation capability of the tandem source was greatly improved, owing to the synergistic effect of PD microplasma and Ar/H₂ flame. In addition, part of the analyte was atomized/excited on the W-coil, and thereby, dry, pure, and activated analyte species were released from the W-coil and swept into the tandem source for atomization/excitation. Through the collective effect of W-coil ETV, Ar/H₂ flame, and PD microplasma, analytical sensitivity for Cr was greatly enhanced. Under the optimized conditions, with 10 μL sample solution, a limit of detection of 1.5 μg L^-1 and a relative standard deviation of 3.6% (20 μg L^-1, n = 5) were achieved. Its accuracy was demonstrated by successful analysis of several certified reference materials. Owing to the advantages including high sensitivity, compactness, and cost effectiveness, it is promising to facilitate the miniaturized spectrometer for more elements and potential field analytical chemistry.

MoS2-Covalent Organic Framework Composite as a Bifunctional Supporter for the Determination of Trace Nickel by Photochemical Vapor Generation-Microplasma Optical Emission Spectrometry

A microplasma-based optical emission spectrometry (OES) system has emerged as a potential tool for field analysis of heavy metal pollution due to its features of portability and low energy consumption, while the development of an efficient sample introduction approach against matrix interference is crucial to meet the requirements of complex sample analysis. Herein, a MoS₂-covalent organic framework (COF) composite serves as a bifunctional supporter for efficient sample separation/enrichment and photochemical vapor generation (PVG) enhancement, thereby achieving highly selective and sensitive detection of heavy metals in environmental water by dielectric barrier discharge (DBD) microplasma-OES. With trace nickel analysis as a model, the MoS₂-COF composite with a large specific surface area and a porous structure can not only efficiently separate and enrich nickel ions from a sample matrix through electrostatic interaction and coordination to reduce the interference of coexisting ions but also significantly improve the subsequent PVG efficiency due to the formed heterojunction and more negative reduction potential. Under optimized conditions, a linear range of 0.1-10 μg L^-1 along with a detection limit of 0.03 μg L^-1 is obtained for nickel. Compared with direct PVG, the tolerance to coexisting ions is greatly enhanced, and the detection limit is also improved by 43-fold. The accuracy and practicability of the present PVG-DBD-OES system are verified by measuring several certified reference materials and real water samples. MoS₂-COF as a bifunctional supporter promotes the performance of the PVG-DBD-OES system in terms of anti-interference ability and detection sensitivity, especially for robust and efficient on-site analysis of complex samples.

Rapid detection and classification of hongmu by atmospheric pressure ionization mass spectrometry

A schematic diagram of atmospheric pressure glow discharge mass spectrometry (APGD-MS) for hongmu detection.

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.

Novel Dielectric Barrier Discharge Trap for Arsenic Introduced by Electrothermal Vaporization: Possible Mechanism and Its Application

In this work, a novel integrated dielectric barrier discharge (IDBD) reactor coupled to an electrothermal vaporizer (ETV) was established for arsenic determination. It is for the first time gas-phase enrichment (GPE) was fulfilled based on the hyphenation of ETV and DBD. The mechanisms of evolution of arsenic atomic and molecular species during vaporization, transportation, trapping, and release processes were investigated via X-ray photoelectron spectroscopy (XPS) and other approaches. Tentative mechanisms were deduced as follows: the newly designed DBD atomizer (DBDA) tube upstream to the air inlet fulfills the atomization of arsenic nanoparticles in vaporized aerosol, leading to free arsenic atoms that are indispensable for forming arsenic oxides; the DBD trap (DBDT) tube traps arsenic oxides under an O₂-domininating atmosphere and then releases arsenic atoms under H₂-dominating atmospheres. In essence, this process is a physical-chemical process rather than an electrostatic particle deposition. Such a trap and release sequence separates matrix interference and enhances analytical sensitivity. Under the optimized conditions, the method detection limit (LOD) was 0.04 mg/kg and the relative standard deviations (RSDs) were within 6% for As standard solution and real seafood samples, indicating adequate analytical sensitivity and precision. The mean spiked recoveries for laver, kelp, and Undaria pinnatifida samples were 95-110%, and the results of the certified reference materials (CRMs) were consistent with certified values. This ETV-DBD preconcentration scheme is easy and green and has low cost for As analysis in seafood samples. DBD was proved a novel ETV transportation enhancement and preconcentration technique for arsenic, revealing its potential in rapid arsenic analysis based on direct solid sampling ETV instrumentation.

Direct Ultratrace Detection of Lead in a Single Hair Using Portable Electromagnetic Heating Vaporization-Atmospheric Pressure Glow Discharge-Atomic Emission Spectrometry

In this paper, the first demonstration of direct ultratrace determination of lead in a single human hair by direct current-atmospheric pressure glow discharge-atomic emission spectrometry (DC-APGD-AES) coupled with electromagnetic heating vaporization (EMV) was described. Only the ultramicro mass of a human hair sample (about 0.15 mg, often a single human hair) was required during the analysis, and fast detection was implemented without tedious pretreatment processes, such as grinding and digestion. A limit of detection (LOD) of 30.8 μg kg^-1 (4.8 pg) for Pb was obtained under optimized conditions, which was even equivalent to that of conventional LA-ICP-MS/ETV-ICP-MS/GFAAS. EMV-APGD-AES, meanwhile, can facilitate miniaturization and portability with low power and small size. The accuracy and practicality of the method were verified by the analysis of certified reference materials (CRMs) GBW09101b (human hair) and human hair samples from three volunteers. A simple, efficient, and low-cost method for detecting Pb in human hair has been developed.

Methanol-Enhanced Liquid Electrode Discharge Microplasma-Induced Vapor Generation of Hg, Cd, and Zn: The Possible Mechanism and Its Application

Despite increased interest in microplasma-induced vapor generation (μPIVG) over the past several years, applications in real sample analyses remain limited due to their relatively low vapor generation efficiency and ambiguous mechanism. In this work, a novel method using methanol for significantly enhancing the liquid electrode discharge μPIVG efficiency was developed for the simultaneous and sensitive determination of Hg, Cd, and Zn by atomic fluorescence spectrometry (AFS). It is worth noting that the possible enhancement mechanism was investigated via the characterizations of volatile products by AFS, microplasma optical emission spectrometry, online gas chromatography, and gas chromatography-mass spectrometry, which involved the reductive species such as electrons, hydrogen radicals (·H), methyl radicals (·CH₃), and other intermediates in the argon plasma adding methanol. Under the optimized conditions, the limits of detection of 0.007, 0.05, and 0.5 μg L^-1 were obtained for Hg, Cd, and Zn, respectively, with relative standard deviations of 3.1, 3.7, and 5.2% for these elements, respectively. Vapor generation efficiencies of 90, 83, and 55% were achieved for Hg, Cd, and Zn, respectively, and improved 2.7-, 4.8-, and 7.9-fold, respectively, compared to those obtained in the absence of methanol. The accuracy and practicability of the proposed method were validated by the determination of Hg, Cd, and Zn in a certified reference material (CRM, Lobster hepatopancreas, TORT-3) and crayfish samples collected from three different provinces of China.

Highly sensitive determination of cadmium and lead in whole blood by electrothermal vaporization-atmospheric pressure glow discharge atomic emission spectrometry

In this study, a fast and simple method for highly sensitive detection of Cd and Pb elements based on atmospheric pressure glow discharge atomic emission spectrometry (APGD-AES) coupling with tungsten coil electrothermal vaporization (ETV) was proposed. A small amount of sample (10 μL) was dropped onto the tungsten coil, followed by drying, pyrolysis and vaporization procedures, and then the vaporized analyte was transported to APGD for excitation. The whole procedure took approximately 3 min. Multi-step heating of the ETV unit can separate matrices and solvents from the analyte, providing an advantage in detecting samples with complex matrix. Under the optimal experimental conditions, limits of detection of 0.4 μg L^-1 (4 pg) for cadmium and 1.2 μg L^-1 (12 pg) for lead were obtained, with relative standard deviations of 20 μg L^-1 Cd and 100 μg L^-1 Pb both being <5%. The accuracy of the ETV-APGD-AES system was verified by the determination of heavy metals in whole blood standard sample (GBW(E)090,251) and the practicability of the ETV-APGD-AES system were demonstrated by the determination of heavy metals in human whole blood. The results obtained by this instrument agree well with the standard values and those obtained by ICP-MS.

Headspace Solid-Phase Microextraction Following Chemical Vapor Generation for Ultrasensitive, Matrix Effect-Free Detection of Nitrite by Microplasma Optical Emission Spectrometry

A new chemical vapor generation method coupled with headspace solid-phase microextraction miniaturized point discharge optical emission spectrometry (HS-SPME-μPD-OES) for the sensitive and matrix effect-free detection of nitrite in complex samples is described. In an acidic medium, the volatile cyclohexene was generated from cyclamate in the presence of nitrite, which was volatilized to the headspace of the container, efficiently separated, and preconcentrated by HS-SPME. Consequently, the SPME fiber was transferred to a laboratory-constructed thermal desorption chamber wherein the cyclohexene was thermally desorbed and swept into μPD-OES for its sensitive quantification via monitoring the carbon atomic emission line at 193.0 nm. As a result, the quantification of nitrite was accomplished through the determination of cyclohexene. The application of HS-SPME as a sampling technique not only simplifies the experimental setup of μPD-OES but it also preconcentrates and separates cyclohexene from N₂ and sample matrices, thus eliminating the interference from water vapor and N₂ and significantly improving the analytical performance on the determination of nitrite. Under the optimum experimental conditions, a limit of detection of 0.1 μg L^-1 was obtained, which is much better than that obtained by conventional methods. The precision, expressed as relative standard deviation, was better than 3.0% at a concentration of 10 μg L^-1. The proposed method provides several advantages of portability, simplicity, high sensitivity, and low energy consumption and eliminates expensive instruments and matrix interference, thus retaining a promising potential for the rapid, sensitive, and field analysis of nitrite in various samples.

"Insert-and-Go" Activated Carbon Electrode Tip for Heavy Metal Capture and In Situ Analysis by Microplasma Optical Emission Spectrometry

The miniaturized optical emission spectrometry (OES) devices based on various microplasma excitation sources provide reliable tools for on-site analysis of heavy metal pollution, while the development of convenient and efficient sample introduction approaches is essential to improve their performances for field analysis. Herein, a small activated carbon electrode tip is employed as solid support to preconcentrate heavy metals in water and subsequently served as an inner electrode of the coaxial dielectric barrier discharge (DBD) to generate microplasma. In this case, heavy metal analytes in water are first adsorbed on the surface of the activated carbon electrode tip via a simple liquid-solid phase transformation during the sample loading process, and then, fast released to produce OES during the DBD microplasma excitation process. The corresponding OES signals are synchronously recorded by a charge-coupled device (CCD) spectrometer for quantitative analysis. This activated carbon electrode tip provides a new tool for sample introduction into the DBD microplasma and facilitates "insert-and-go" in subsequent DBD-OES analysis. With a multiplexed activated carbon electrode tip array, a batch of water samples (50 mL) can be loaded in parallel within 5 min. After drying the activated carbon electrode tips for 5 min, the DBD-OES analysis is maintained at a rate of 6 s per sample. Under the optimized conditions, the detection limits of 0.03 and 0.6 μg L^-1 are obtained for Cd and Pb, respectively. The accuracy and practicability of the present DBD-OES system have been verified by measuring several certified reference materials and real water samples. This analytical strategy not only simplifies the sample pretreatment steps but also significantly improves the sensitivity of the DBD-OES system for heavy metal detection. By virtue of the advantages of high sensitivity, fast analysis speed, simple operation, low cost, and favorable portability, the upgraded DBD-OES system provides a more powerful tool for on-site analysis of heavy metal pollution.

A miniaturized UV-LED array chip-based photochemical vapor generator coupled with a point discharge optical emission spectrometer for the determination of trace selenium

Ultraviolet light emitting diode array chip-based photochemical vapor generation was combined with hollow electrode point discharge to establish a miniaturized optical emission spectrometer for efficient vapor generation and excitation of selenium.

Atmospheric pressure glow discharge optical emission spectrometry coupled with laser ablation for direct solid quantitative determination of Zn, Pb, and Cd in soils

A device utilizing atmospheric pressure glow discharge as the second excitation source coupled with laser ablation (LA) for direct solid sampling was developed, with few operating costs and low gas consumption. This new device was first utilized for the highly sensitive determination of Zn, Pb, and Cd elements in complex matrix soil samples. It also provided a new method for monitoring these three trace elements in soil samples. Good linearity was observed in the quantitative results for Zn, Pb, and Cd detection, and the respective linear correlation coefficients (R²) were 0.9953, 0.9897, and 0.9961. Moreover, the limit of detection (LOD) of 0.68, 2.71, and 0.31 mg kg^-1 were achieved for Zn, Pb, and Cd, respectively; the LOD of Zn reduced by more than one order of magnitude compared to that observed in laser-induced breakdown spectroscopy results. In addition, the quantitative analysis results showed good agreement with the certified values and those obtained of ICP optical emission spectrometry, proving the detection accuracy and practicability of the developed device.

On the coupling of hydride generation (HG) with flowing liquid anode atmospheric pressure glow discharge (FLA-APGD) for determination of traces of As, Bi, Hg, Sb and Se by optical emission spectrometry (OES)

A novel atmospheric pressure glow discharge (APGD) microplasma system, sustained between a miniaturized flowing liquid anode (FLA) and a He jet nozzle cathode, was combined with a hydride generation (HG) technique to improve the determination performance of As, Bi, Hg, Sb, and Se with the aid of optical emission spectrometry (OES). The discharge current, the He flow rate, and the concentrations of HCl and NaBH₄ were considered to affect both the HG reaction and the excitation conditions in the discharge, thus they were thoroughly studied. Under the optimized conditions, the detections limits (LODs), assessed on the basis of the 3σ criterion, reached 1.7, 0.85, 0.04, 0.51, and 2.9 μg L^-1 for As, Bi, Hg, Sb, and Se, respectively. The HG and transport efficiency for these elements was evaluated to be 88-100%, which is notably better, as compared to their transport efficiency in the conventional FLA-APGD system, without the HG technique. This yielded an improvement of the LODs achievable in this system and, simultaneously, enabled to determine As, Sb, and Se at a level, which is unobtainable with the use of the FLA-APGD system alone. The proposed methodology was then successfully applied for a quantitative determination of the examined elements in wastewater (ERM-CA713) and spiked water samples. The recoveries of the elements added to these waters (at the maximum acceptable levels in drinking water set by the U.S. Environmental Protection Agency) ranged between 81 and 104%, confirming the excellent accuracy, usefulness, and reliability of the developed HG-FLA-APGD technique.