Advances in atmospheric pressure plasma-based optical emission spectrometry for the analysis of heavy metals

Over the past decade, miniaturized optical emission spectrometry (OES) systems utilizing atmospheric pressure plasmas (APPs) as radiation sources have exhibited impressive capabilities in trace heavy metal analysis. As the core of the analytical system, APPs sources possess unique properties such as compact size, light weight, low energy requirement, ease of fabrication, and relatively low manufacturing cost. This critical review focuses on recent progress of APP-based OES systems employed for the determination of heavy metals. Influences of technical details including the sample introduction manner, the sampling volume, the sample flow rate, the pH of the solutions on the plasma stability and the intensity of analytical signals are comprehensively discussed. Furthermore, the review emphasizes the analytical challenges faced by these techniques and highlights the opportunities for further development in the field of heavy metal detection.

A miniature chemiluminescence spectrometric system induced by atmosphere microplasma jet to avoid using hydrogen peroxide and catalyst

A miniature luminol chemiluminescence system based on atmosphere microplasma is proposed for detection without any catalysts. In our research, atmosphere microplasma jet is employed to oxidize luminol and produce chemiluminescence instead of H₂O₂. The transport of OH radicals to the plasma-liquid interface and induce the chemiluminescence. The weight of the system is only 3.6 kg (including a 1.2 kg laptop), and the power consumption of the microplasma is only 0.045 W. The mechanism of luminol chemiluminiscence induced by microplasma jet and generation of microplasma jet are investigated in this study. A 1 mL sample solution is sufficient for trace 3-NPA determination within an analysis time of 6 min. In the range of 0.03-10 mg L^-1, 3-NPA can be quantitatively analyzed along with a detection limit of 0.008 mg L^-1. In addition, the proposed system is employed for real-world samples detection, including water samples, brown sugar and tainted sugarcane, which demonstrates the reliability and practical feasibility of the detection method.

In Situ Detection of Trace Heavy Metal Cu in Water by Atomic Emission Spectrometry of Nebulized Discharge Plasma at Atmospheric Pressure

The in situ detection of trace heavy metal is very important for human health and environmental protection. In this paper, a novel and stable nebulized discharge excited by an alternating current (AC) power supply at atmospheric pressure is employed to detect the trace metal copper by atomic emission spectrometry. Different from the previous experiments in which a conductive object was wrapped around a pneumatic nebulizer directly as a discharge electrode. Plasma is generated near needle electrodes and aerosol is introduced from above the electrode gap by a pneumatic nebulizer, which avoid damage to the fragile device. The effects of applied voltage, gas flow rate, pH value of liquid, and concentration of organic addition agents on the emission intensity of Cu I (3d104p-3d104s, 324.75 nm) are investigated for the purpose of optimizing the experiment conditions. For studying the discharge characteristics and understanding the mechanisms of metal atomic excitation, the waveforms of applied voltage and discharge current are measured, and the vibrational and rotational temperature are calculated by the spectra of N2 (C3∏u-B3∏g, Δυ = −2). In addition, gas temperature evolution of nebulized discharge is acquired and it is found that the emission intensity of Cu I (3d104p-3d104s, 324.75 nm) can be affected by applied voltage, gas flow rate, pH value of liquid, and concentration of organic addition agents. An optimized experimental condition of nebulized discharge for Cu detection is 3.59 of the pH, 5.6 kV of applied voltage, 1.68 L/min of Ar flow rate, and 2% of the ethanol. Under this condition, the limit of detection (LOD) of Cu can reach up to 0.083 mg/L.

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.

Determination of Zn2+ and Cd2+ by glassy carbon electrode modified with Perilla frutescens activated carbon

A Perilla frutescens (L.) Britton activated carbon that had high specific surface area (HSAPFAC) was modified on the surface of the glassy carbon electrode (GCE) for preparing a HSAPFAC/GCE, and on this basis, a differential pulse voltammetry (DPV) method for the simultaneous determination of zinc and cadmium ions (Zn2+ and Cd2+) was developed by using HSAPFAC/GCE. The determination conditions such as the film thickness, deposition potential, deposition time, and electrolyte acidity were investigated. The amperometric determination was carried out in a NaAc–HAc buffer solution (0.1 mol L−1, pH 5.5) after enriching for 550 s at –1.3 V. The oxidation peaks appear at –1.160 V and –0.845 V for Zn2+ and Cd2+, respectively. The oxidation peak currents of Zn2+ and Cd2+ are proportional to their concentrations in the ranges of 0.5 ∼ 20 μg L−1 and 0.25 ∼ 10 μg L−1, with the detection limits of 0.15 μg L−1 and 0.01 μg L−1 (signal/noise (S/N) = 3). The proposed method was applied to the determination of Zn2+ and Cd2+ in tap water samples. The recoveries were 101.6%∼103.0% and 84.0%∼88.8%, respectively.

Alternating-Current-Driven Microplasma for Multielement Excitation and Determination by Optical-Emission Spectrometry

Microplasma optical-emission spectrometry (OES) is a promising technique for developing portable analytical instrumentations for real-time and on-site measurement of trace elemental species. However, its analytical performance is far from satisfactory for multielement analysis. Herein, a miniature OES system is developed for simultaneous multielement analysis with alternating-current-driven microplasma generated on the nozzle of a pneumatic micronebulizer as the excitation source. Because of the strong excitation capability of the microplasma and its sufficient contact with solution, a series of elements, including Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, and Zn, is directly excited in the spray with solution nebulization at a flow rate of 8 μL s^-1. The characteristic optical emissions are measured by a charge-coupled-device (CCD) spectrometer. In addition, hydride generation is compatible with the present system, which makes it feasible for the simultaneous excitation of hydrides of As, Ge, Hg, Sb, and Sn by reaction with 0.8% (m/v) NaBH₄. The microplasma-OES system exhibits a powerful capability for multielement analysis with favorable limits of detection for the mentioned elements.

A novel liquid chromatography detector based on a dielectric barrier discharge molecular emission spectrometer with online microwave-assisted hydrolysis for determination of dithiocarbamates

A novel detector for liquid chromatography (LC) for the determination of dithiocarbamate (DTC) fungicides is presented with a miniaturized dielectric barrier discharge–microplasma molecular emission spectrometer and an online microwave-assisted hydrolysis reactor.

Tri-pillar[5]arene-based multi-stimuli-responsive supramolecular polymers for fluorescence detection and separation of Hg2+

A novel tri-pillar[5]arene based supramolecular polymer (JP5G) shows multiple stimuli-response properties and could detect and remove Hg²⁺ from aqueous solution.