Dielectric barrier discharge-induced chemical vapor generation for highly sensitive analysis of iodine in seawater by ICP-MS

BACKGROUND

The accurate determination of iodine in seawater is essential to understanding its impact on the environment and human health. Inductively coupled plasma mass spectrometry (ICP-MS) is a widely used technique for elemental analysis due to its high sensitivity, speed, and low limit of detection (LOD). However, its capability in the detection of iodine in complex matrix samples is still limited by the low sample introduction efficiency of pneumatic nebulization and the high ionization energy of iodine. Dielectric barrier discharge microplasma-induced vapor generation (DBD-μPIVG) is a sample introduction technique that has been widely coupled with atomic spectrometry due to its high vapor generation efficiency, rapid reaction speed, high anti-interference capability, and environmental friendliness.

RESULTS

A new method was developed for the rapid and sensitive determination of iodine using DBD-μPIVG coupled with ICP-MS. The DBD-μPIVG sample introduction technique can convert both iodide and iodate to their volatiles with a vapor generation efficiency of 70 %. The experimental conditions were optimized in detail, and the LOD for iodine was 0.04 μg L-1, which was lower compared to pneumatic nebulization and comparable to that after the extraction treatment. The relative standard deviation (RSD) obtained after 11 replicate determinations was 2.4%. Furthermore, the potential mechanism and anti-interference performance of the proposed method were also carefully investigated.

SIGNIFICANCE

Compared to other analytical methods for iodine analysis, this approach is environmentally friendly, exhibits high anti-interference capability and enables accurate determination of iodine in complex matrix samples. The high vapor generation efficiency of DBD-μPIVG improves the sensitivity for iodine detection and expands the applicable elemental range of DBD-μPIVG. Finally, the proposed method was successfully applied to analyze the iodine content in seawater samples obtained from the Chinese coastal waters and retains great potential for assessing the distribution of iodine in different sea areas.

Ultraviolet assisted liquid spray dielectric barrier discharge plasma-induced vapor generation for sensitive determination of arsenic by atomic fluorescence spectrometry

In this study, a novel sensitive method for As determination by atomic fluorescence spectrometry was developed based on UV-assisted liquid spray dielectric barrier discharge (UV-LSDBD) plasma-induced vapor generation. It was found that prior-UV irradiation greatly facilitates As vapor generation in LSDBD likely because of the increased generation of active substances and the formation of As intermediates with UV irradiation. The experimental conditions affecting the UV and LSDBD processes (such as formic acid concentration, irradiation time, the flow rates of sample, argon and hydrogen) were optimized in detail. Under the optimum conditions, As signal measured by LSDBD can be enhanced by about 16 times with UV irradiation. Furthermore, UV-LSDBD also offers much better tolerance to coexisting ions. The limit of detection was calculated to be 0.13 μg L^-1 for As, and the relative standard deviation of the repeated measurements was 3.2% (n = 7). The accuracy and effectiveness of this new method were further verified by the analysis of simulated natural water reference sample and real water samples. In this work, UV irradiation was utilized for the first time as an enhancement strategy for PIVG, which opens a new approach for developing green and efficient vapor generation methods.

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.

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.

Indirect determination of mercury(II) by using magnetic nanoparticles, CdS quantum dots and mercury(II)-binding aptamers, and quantitation of released CdS by graphite furnace AAS

This work describes an aptamer based method for highly sensitive determination of Hg(II). A Hg(II)-binding ssDNA aptamer was linked to silica-coated magnetic nanoparticles (magNPs). Then, a conjugate composed of graphene and CdS quantum dots (Gr-CdS) was linked to the complementary ssDNA. On mixing the two components, a duplex of type magNP-dsNNA-Gr/CdS is generated. If Hg(II) is added, it wills capturing the aptamer, and this leads to the release of Gr/CdS because of the formation of a stable thymine-Hg²⁺-thymine link. External magnetic force is used to remove the remaining complex. The released graphene-CdS is decomposed by HNO₃ and injected into a graphite furnace AAS. The detectable amount of Cd is proportional to the concentration of Hg(II) in the sample. Under the optimal conditions, the method has a linear response in the 2.50 aM to 0.25 nM Hg(II) concentration range, and the detection limit is as low as 7.6 aM (at S/N = 3). It has high selectivity for Hg(II) over other metal ions. Graphical abstract.

Switchable electrochemiluminescence aptasensor coupled with resonance energy transfer for selective attomolar detection of Hg2+ via CdTe@CdS/dendrimer probe and Au nanoparticle quencher

In the present study, an ultrasensitive electrochemiluminescence (ECL) aptasensing assay for selective detection of Hg²⁺ was designed. In this electrochemiluminescence resonance energy transfer (ECL-RET) approach, Fe₃O₄@SiO₂/dendrimers/QDs exhibited amplified ECL emissions (switch "on" state) and with the hybridization between T-rich ssDNA(S₁) immobilized on the Fe₃O₄@SiO₂/dendrimers/QDs and AuNPs modified with complementary aptamer (AuNPs-S₂), the ECL of QDs nanocomposites was efficiently quenched (switch "off" state). In the presence of Hg²⁺ ions, formation of strong and stable T-Hg²⁺-T complex led to the release of the AuNPs-S₂ from double-stranded DNA(dsDNA) and the recovery of the ECL signal of QDs (second signal switch "on" state). Under optimal conditions, Hg²⁺ can be detected in a wide linear range from 20aM to 2µM with a very low detection limit of 2aM. The proposed ECL aptasensor showed high selectivity for Hg²⁺ determination compared to other environmentally relevant metal ions at concentration ratio more than 1000 times. The aptasensor was used for detection Hg²⁺ ions from samples of tap waters, carp and saltwater fishes with satisfactory results. The aptasensor exhibited high sensitivity, wide linear response (11 orders of magnitude), excellent reproducibility and stability. The proposed aptasensor will be a promising candidate for facile and rapid determination of Hg^2＋in environmental and fishery samples.

Atomization of Bismuthane in a Dielectric Barrier Discharge: A Mechanistic Study

Atomization of bismuthane in a planar dielectric barrier discharge (DBD) atomizer was investigated using a variety of probes, including atomic absorption spectrometry (AAS) to monitor distribution of free atoms along the optical path and direct analysis in real time (DART) coupled to an Orbitrap mass spectrometer to identify the structure of the species arising from the hydride generator as well as the atomizer. Results obtained with the DBD were compared to those from a conventional externally heated quartz tube atomizer (QTA). Free Bi atoms were essentially absent outside the central part of the DBD atomizer, suggesting their high reactivity. The gas phase analyte fraction transported beyond the confines of the DBD or QTA atomizers, quantified by inductively coupled plasma mass spectrometry (ICP-MS), was less than 10%. The amount of Bi found in acidic leachates of the interiors of both atomizers, representing the fraction retained on their surfaces, was ca. 90%. These complementary experiments comprising the determination of recovered Bi in the nitric acid leachates from deposition in the atomizer on the one hand and quantification of the Bi fraction transportable outside the atomizer on the other, were in excellent agreement, providing 100% mass balance of detected analyte. The high fraction of Bi deposited in the atomizers indicates significant reactivity of free Bi atoms, which is in accord with the fact that almost no free Bi atoms exist beyond the physical boundaries of the DBD. The extent of interference from other hydride forming elements (As, Sb, Se) on Bi response by AAS using DBD and QTA atomizers was investigated, with the former atomizer providing superior performance. Compared to QTA, DBD provided 2 orders of magnitude and 1 order of magnitude, respectively, better resistance to interference from Se and Sb.

Ultrasensitive quantum dot fluorescence quenching assay for selective detection of mercury ions in drinking water

Mercury is one of the most acutely toxic substances at trace level to human health and living thing. Developing a rapid, cheap and water soluble metal sensor for detecting mercury ions at ppb level remains a challenge. Herein, a metal sensor consisting of MPA coated Mn doped ZnSe/ZnS colloidal nanoparticles was utilized to ultrasensitively and selectively detect Hg(2+) ions with a low detection limit (0.1 nM) over a dynamic range from 0 to 20 nM. According to strong interaction between thiol(s) and mercury ions, mercaptopropionic acid (MPA) was used as a highly unique acceptor for mercury ions in the as-obtained ultrasensitive sensor. In the presence of mercury ions, colloidal nanoparticles rapidly agglomerated due to changes of surface chemical properties, which results in severe quenching of fluorescent intensity. Meanwhile, we find that the original ligands are separated from the surface of colloidal nanoparticles involving strongly chelation between mercury ion and thiol(s) proved by controlled IR analysis. The result shows that the QD-based metal ions sensor possesses satisfactory precision, high sensitivity and selectivity, and could be applied for the quantification analysis of real samples.

Direct determination of mercury in cosmetic samples by isotope dilution inductively coupled plasma mass spectrometry after dissolution with formic acid

A new method was proposed for the accurate determination of mercury in cosmetic samples based on isotopic dilution (ID)-photochemical vapor generation (PVG)-inductively coupled plasma mass spectrometry (ICP MS) measurement. Cosmetic samples were directly dissolved in formic acid solution and subsequently subjected to PVG for the reduction of mercury into vapor species following by ICP MS detection. Therefore, the risks of analyte contamination and loss were avoided. Highly enriched (201)Hg isotopic spike is added to cosmetics and the isotope ratios of (201)Hg/(202)Hg were measured for the quantitation of mercury. With ID calibration, the influences originating from sample matrixes for the determination of mercury in cosmetic samples have been efficiently eliminated. The effects of several experimental parameters, such as the concentration of the formic acid, and the flow rates of carrier gas and sample were investigated. The method provided good reproducibility and the detection limits were found to be 0.6 pg mL(-1). Finally, the developed method was successfully applied for the determination of mercury in six cosmetic samples and a spike test was performed to verify the accuracy of the method.