A portable and field optical emission spectrometry coupled with microplasma trap for high sensitivity analysis of arsenic and antimony simultaneously

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.

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.

Electrothermal Desolvation-Enhanced Dielectric Barrier Discharge Plasma-Induced Vapor Generation for Sensitive Determination of Antimony by Atomic Fluorescence Spectrometry

A novel simple electrothermal desolvation-enhanced dielectric barrier discharge plasma-induced vapor generation (ETD-DBD-PIVG) method has been developed for sensitive Sb determination by atomic fluorescence spectrometry (AFS). In our proposed ETD-DBD-PIVG, 20 μL sample solution was dried first; then, the resulting solution residue was directly converted into molecular volatile species efficiently through the interactions with hydrogen-doped DBD plasma; and finally, it was transported to AFS for detection. It was found that the desolvation process could greatly enhance Sb vapor generation, and the Sb fluorescence signal intensity is almost independent of its speciation, where comparable sensitivity is achieved for Sb(III) and Sb(V), enabling efficient total Sb detection without pre-reduction. Influencing parameters were evaluated in detail, including heating time, discharge gap, solution pH, and flow rates of argon and hydrogen, as well as coexisting ion interference. Under optimized conditions, the limit of detection was calculated as 0.86 μg L^-1 (17.2 pg) for Sb. The accuracy of the proposed method was validated by the analysis of certified reference materials of simulated natural water samples and several river water samples. Compared with conventional hydride generation, the new ETD-DBD-PIVG offers an alternative green vapor generation technique with several advantages: (1) it eliminates the use of a sample flow system (e.g., no use of any syringe or peristaltic pump); instead, 20 μL of a sample is directly pipetted onto the glass plate for analysis; (2) it greatly simplifies the sample pretreatment steps as no pre-reduction process is needed; (3) it is sensitive and suitable for volume-limited sample analysis: efficient Sb vapor generation without chemical reducing reagents in ETD-DBD-PIVG enables Sb detection with an absolute limit at the picogram level. All the results demonstrate that the proposed method provides a simple, green, and sensitive method for Sb determination and it can also be extended to other elements such as Cd and As.

Magnetic Ion Imprinted Polymers (MIIPs) for Selective Extraction and Preconcentration of Sb(III) from Environmental Matrices

Antimony(III) is a rare element whose chemical and toxicological properties bear a resemblance to those of arsenic. As a result, the presence of Sb(III) in water might have adverse effects on human health and aquatic life. However, Sb(III) exists at very ultra-trace levels which may be difficult for direct quantification. Therefore, there is a need to develop efficient and reliable selective extraction and preconcentration of Sb(III) in water systems. Herein, a selective extraction and preconcentration of trace Sb(III) from environmental samples was achieved using ultrasound assisted magnetic solid-phase extraction (UA-MSPE) based on magnetic Sb(III) ion imprinted polymer-Fe3O4@SiO2@CNFs nanocomposite as an adsorbent. The amount of antimony in samples was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The UA-MSPE conditions were investigated using fractional factorial design and response surface methodology based on central composite design. The Sb(III)-IIP sorbent displayed excellent selectivity towards Sb(III) as compared to NIIP adsorbent. Under optimised conditions, the enrichment factor, limit of detection (LOD) and limit of quantification (LOQ) of UA-MSPE/ICP-OES for Sb(III) were 71.3, 0.13 µg L-1 and 0.44 µg L-1, respectively. The intra-day and inter-day precision expressed as relative standard deviations (%RSDs, n = 10 and n = 5) were 2.4 and 4.7, respectively. The proposed analytical method was applied in the determination of trace Sb(III) in environmental samples. Furthermore, the accuracy of the method was evaluated using spiked recovery experiments and the percentage recoveries ranged from 95-98.3%.

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.

Trace arsenic analysis in edible seaweeds by miniature in situ dielectric barrier discharge microplasma optical emission spectrometry based on gas phase enrichment

In this work, a novel method using low-cost miniaturized hydride generation optical emission spectrometry equipment coupled with an in situ dielectric barrier discharge trap (HG-in situ DBD trap-OES) was established for the determination of As in edible seaweed samples. An improved peak volume algorithm, where the start time point and end time point of the spectrum at each concentration are determined according to the unified judgment criteria, was first proposed to extend the linear range from 1-100 μg L^-1 to 1-200 μg L^-1, and increase the sensitivity by about 30%. In addition, a modification was done on the DBD implementation, providing an enhancement of sensitivity by a factor of about 4 for As. All in all the detection limit (LOD) was improved from 0.5 μg L^-1 to 0.2 μg L^-1. By applying the method to seaweed samples, a method detection limit (MD) of 0.25 mg kg^-1 was achieved, with less than 3% relative standard deviations (RSDs). The calibration linearity reached R² > 0.990 in the 1.25-250 mg kg^-1 range. Results obtained by the proposed method showed good agreement with that of certified reference materials (CRMs), and spiked recoveries were 103% to 114%, indicating favorable accuracy. The proposed method is attractive in terms of instrumentation size (0.6 m × 0.5 m × 0.3 m), power consumption (<60 W), manufacturing cost, and gas consumption (300 measurements for 4 L compressed Ar/H₂ gas), and therefore more advantageous than conventional atomic spectrometric methods.