Photochemical Vapor Generation Research Articles

Cadmium-Assisted Photochemical Vapor Generation of Arsenic from Low Concentration of Formic Acid Media.

A highly sensitive method for the determination of total arsenic (As) has been developed using photochemical vapor generation (PVG) coupled with inductively coupled plasma mass spectrometry (ICP MS). The efficient PVG of As is reported for the first time in the presence of Cd(II) in diluted formic acid (FA) medium. The PVG efficiency of 93 ± 1% can be achieved in the system with 0.15% (v/v) FA and 40.0 mg L-1 Cd(II) under 100 s UV irradiation. The limit of detection (LOD, 3σ) for As was determined to be 0.2 ng L-1, which was enhanced about 43-fold over the traditional solution nebulization method. The anti-interference capability against sample matrices was enhanced compared to previous PVG systems that used diluted formic acid alone or a combination of sodium formate and sodium sulfite as the medium. The established method was applied for the analysis of natural waters and certified reference materials (CRMs) of rice with satisfactory results. The mechanism of the PVG system was investigated, and the generation of volatile As species as AsH3 was found in all investigated systems, including monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), As (III), and As(V). Additionally, volatile cadmium species were also generated simultaneously. The efficient reduction of As in diluted FA observed in this study is beneficial to understanding the interaction between As and Cd in the photochemical process.

Green and Low-Cost Method for Selenium Analysis in Beans by Photochemical Vapor Generation Coupled to Atomic Absorption Spectrometry (PVG-AAS)

Green and Low-Cost Method for Selenium Analysis in Beans by Photochemical Vapor Generation Coupled to Atomic Absorption Spectrometry (PVG-AAS)

Efficient Photochemical Vapor Generation from Low Concentration Formic Acid Media.

Herein, we report on surprisingly efficient photochemical vapor generation (PVG) of Ru, Re, and especially Ir, achieved from very dilute HCOOH media employing a thin-film flow-through photoreactor operated in flow injection mode. In the absence of added metal ion sensitizers, efficiencies near 20% for Ir and approximately 0.06% for Ru and Re occur in a narrow range of HCOOH concentrations (around 0.01 M), significantly higher than previously reported from conventionally optimized HCOOH concentrations (1-20 M). A substantial enhancement in efficiency, to around 9 and 1.5%, could be realized for Ru and Re, respectively, when 0.005 M HCOONa served as the PVG medium. The addition of metal ion sensitizers (particularly Cd2+ and Co2+) to 0.01 M HCOOH significantly enhanced PVG efficiencies to 17, 2.2, and 81% for Ru, Re, and Ir, respectively. Possible mechanistic aspects occurring in dilute HCOOH media are discussed, wherein this phenomenon is attributed to the action of 185 nm radiation available in the thin-film flow-through photoreactor. An extended study of PVG of Fe, Co, Ni, As, Se, Mo, Rh, Te, W, and Bi from both dilute HCOOH and CH3COOH was undertaken, and several elements for which a similar phenomenon appears were identified (i.e., Co, As, Se, Te, and Bi). Although use of dilute HCOOH media is attractive for practical analytical applications employing PVG, it is less tolerant toward dissolved gases and interferents in the liquid phase due to the likely lower concentrations of free radicals and aquated electrons required for analyte ion reduction and product synthesis.

Transition metal ion assisted photochemical vapor generation of niobium and tantalum

The photochemical vapor generation of Nb and Ta was reported for the first time. The addition of Cu2+ led to an enhancement of 76- and 91-fold for Nb and Ta, respectively.

A miniaturized microplasma excitation source coupled with photochemically induced volatile species generation as a cost-effective tool for in situ mercury pollution analyses

A portable, miniaturized atmospheric microplasma discharge system coupled with the photochemical vapour generation was developed for the sensitive Hg determination in water samples using OES.

INSIGHTS INTO THE ROLE OF TRANSITION AND NOBLE METALS MEDIATING PHOTOCHEMICAL VAPOR GENERATION

Abstract The recent expansion of the suite of elements amenable to photochemical vapor generation (PVG) is primarily linked to the addition of mg/L concentrations of selected transition metals (TMs) to...

Selenium in Photochemical Vapor Generation: Mechanism Study and Potential Nonchromatographic Speciation Analysis.

The mechanism of selenium in the UV photochemical vapor generation (PVG) process was investigated by the use of multiple analytical methods. It was found that the UV-induced photooxidation trapping of the generated volatile SeH2 should be responsible for the previous opinion of relative inertness of Se(VI) in PVG with formic acid. Furthermore, the formation of Se(IV) was found during the PVG process, and the comproportionation of Se(IV) with SeH2 and the photooxidation of Se(IV) into Se(VI) were investigated. Then, a preliminary model was proposed for the PVG process of Se(VI) and Se(IV) with low-molecular-weight organic acids. Then, a novel, simple, and green photocontrolled method without any photocatalyst was thus proposed for the nonchromatographic speciation analysis of Se(IV) and Se(VI), with a limit of detection of 0.2 and 5 ng/mL, respectively.

Sensitive Determination of Arsenic by Photochemical Vapor Generation with Inductively Coupled Plasma Mass Spectrometry: Synergistic Effect from Antimony and Cadmium.

A novel method for the determination of trace arsenic (As) by photochemical vapor generation (PVG) with inductively coupled plasma mass spectrometry measurement was developed in this study. The synergistic effect from antimony (Sb) and cadmium (Cd) was found for the photochemical reduction of As for the first time. Effective photochemical reduction of As was obtained in the system containing 10% (v/v) acetic acid, 5.0 mg L-1 Sb(III), and 20.0 mg L-1 Cd(II) with 100 s UV irradiation. Analytical sensitivity of As(III) was comparable with that of As(V) under the tested conditions, making direct determination of total As feasible. Compared to the pneumatic nebulization method, analytical sensitivity of the developed method was enhanced about 50 folds. The PVG efficiency was estimated up to be 99 ± 3%. The limit of detection (LOD) (3σ) was found to be 2.1 ng L-1 for As, which was improved about 30-fold compared to that using direct sample introduction solution nebulization. Considering the sample dilution prior to analysis (usually one-fold), the LOD was actually enhanced about 15 folds. The relative standard deviations of seven replicate measurements of 1.0 μg L-1 As(III) and As (V) standard solutions were 2.3 and 2.9% for As(III) and As(V), respectively. The proposed method was successfully applied for the detection of As in certified reference materials of sediments (GBW07303a and GBW07305a), as well as three water samples. The mechanism of the PVG system was investigated by using gas chromatography mass spectrometry, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. (CH3)3As along with (CH3)3Sb were synthesized under UV irradiation. Besides, volatile species of Cd were also found. The result obtained in this study is useful for developing efficient "sensitizers" in PVG and understanding the transformation of As in the presence of hydride/cold vapor forming elements in the photochemical process.

Determination of Trace Se and Te in Geological Samples by Photochemical Vapour Generation Combined with Inductively Coupled Plasma‐Mass Spectrometry

An analytical method to accurately determine trace levels of Se and Te is essential to meet the growing importance of these elements to Earth science research. Herein, an in‐house assembled photochemical vapour generation (PVG) unit, instead of normal sample nebulisation, with inductively coupled plasma‐mass spectrometry (ICP‐MS), was developed for the detection of Se and Te in geological samples. The major parameters that might potentially influence the PVG efficiencies of Se(IV) and Te(IV) were investigated. The unit could fully generate volatile species under 30 s of ultraviolet irradiation in the presence of 15% v/v formic acid, 15% v/v acetic acid and 50 mg l‐1 of Co2+. Under optimised conditions, the limit of detections (LODs, 3s, n = 11) of the proposed method were 0.5 ng l‐1 for Se and 0.6 ng l‐1 for Te. The RSDs of Se and Te were 2.0% and 2.3% (1 μg l‐1, n = 7), respectively. Interference experiments showed that Fe, Ti, V and Cu have certain negative effects, so the standard addition method was used for real sample analysis. Measurement results for eleven CRMs, including soils (GSS‐4, GSS‐7), sediments (GSD‐9, GSD‐10) and rocks (GSR‐1, GSR‐2, GSR‐3, GSR‐5, AGV‐2, GSP‐2 and W‐2a), were consistent with literature values, and showed better precision, indicating the feasibility of the proposed method for determination of trace Se and Te in geological samples.

Sensitive method for total selenium determination in garlic and nuts by UV–photochemical vapor generation coupled to atomic absorption spectrometry using mild conditions

Photochemical vapor generation (PVG) coupled on–line to atomic absorption spectrometry using a flow injection mode was investigated for the determination of total Se in garlic and nut samples. In the presence of low molecular weight organic acid solutions, Se(IV) is converted by UV irradiation to volatile species which are transported to the heated quartz tube atomizer. Formic and acetic acids were tested as photochemical reagents and a mixture of 1.5 % (v/v) formic and 5 % (v/v) acetic acid was the best alternative. Central composite design was employed for parameters optimization. The effect of potential interfering elements such as hydride–forming elements, transition metals and nitric acid was investigated to ascertain possible effects of the matrix on Se(IV) signal. Under optimized conditions a detection limit (LOD) of 33 ng g–1 (3σ) was reached. Samples of garlic and nuts purchased at a local market were analyzed and Se concentrations spanned the range 0.36–248 µg g–1. These results were compared with ICP–MS measurements utilizing an elliptical joint confidence region (EJCR) with bilinear least squares analysis, and good results were obtained.

Chemical vapor generation of tungsten for atomic spectrometric determination: Homogeneous sensitizer and mechanism study

BackgroundInductively coupled plasma-mass spectrometry (ICP-MS) is one of the most powerful instrumental techniques for the determination of tungsten for its low detection limit and wide linear range, while it remains challenging since the analytical performance can be affected by complicated sample matrix. Chemical vapor generation (CVG) harbors the potential to be an alternative to conventional solution nebulization for sample introduction to reduce matrix effect. However, the CVG of tungsten was low in efficiency. It is clear that green and homogeneous enhancement for CVG of tungsten is desired and the mechanism is worth in-depth investigation. ResultsTwo green and homogeneous enhancement systems for CVG of tungsten were studied, including photochemical vapor generation (PVG) and hydride generation (HG) with sensitizers, Fe3+ and DDTC, respectively. Under optimal conditions, the limits of detection (LODs) were 0.02 μg L−1 for the PVG and 0.003 μg L−1 for the HG, respectively. For PVG, the Fe3+/Fe2+ cycling, free radical species, gaseous product, and the chemical speciation evolution of W in the PVG process were studied in detail. Photo-Fenton effect, generated reductive radical ·CO2−, gaseous product Fe(CO)5, and the mixed valence of W5+/W6+ in the PVG process were found to be crucial for the enhancement. As for HG, the complexation between W(VI) and DDTC might be conducive to the enhanced HG efficiency. SignificanceThis work not only in-depth expands the element scope of CVG, but also investigates the enhancement mechanisms experimentally, which might render a deep insight into the CVG processes and foreshadow new guidelines for screening green and efficient homogeneous sensitizers for CVGs of more elements in the future.

Photochemical vapor generation of Zinc and Gallium

Photochemical vapor generation (PVG) of Zinc (Zn) and Gallium (Ga) was firstly reported in this study. The main parameters influencing PVG of Zn and Ga were investigated with inductively coupled plasma mass spectrometry (ICP-MS), such as the type and concentration of low molecular weight organic acids (LMWOAs), the concentration of transition metal ions and their synergistic effects, the wavelength and time of UV irradiation, and pH of sample solution. Formic acid (FA) and Cu2+ were required for the generation of volatile species of Zn and Ga. In addition, the effects of interfering ions on the PVG of Zn and Ga were investigated. Good precisions with 2.3% and 2.7% were obtained under the selected conditions for replicate measurement of 200 ng mL−1 Zn and Ga standard solution (n = 7), respectively. The limits of detection (LOD, 3σ, n = 11) were calculated to be 8.8 ng mL−1 and 0.77 ng mL−1 for Zn and Ga with PVG-ICP-MS measurement, respectively. Carbonyl compounds were speculated to be formed in this study. Moreover, nanoparticles containing Cu, Zn or Ga were found in liquid solution after UV irradiation, which may be useful for investigating the formation of natural nanoparticles in environment as well as the isotope fractionation of Zn and Ga in photochemical processes.

Photochemical Hydride Generation in Sulfite Medium: Sample Introduction into an Inductively Coupled Plasma Mass Spectrometer for the Determination of Ultratrace Inorganic Arsenic.

This Technical Note reports a new UV photochemical hydride generation (PHG) of As(III/V) in a sulfite medium. Combining PHG for sample introduction with sector field inductively coupled plasma mass spectrometry (SF-ICPMS) for detection, we established a novel and ultrasensitive approach for the determination of total inorganic As. Arsine was generated simply by exposing arsenic solutions containing 2 mM of sodium sulfite to UV irradiation for 10 s with 1 mM of sodium formate for sensitivity enhancement. An impressive limit of detection of 0.2 ng/L for As, suitable for the quantitation of inorganic arsenic at ultratrace levels, was readily achieved. Formation of hydrated electrons and hydrogen radicals was experimentally validated, and this may be responsible for the reduction of the high-valent arsenic species. The PHG may also provide a new and useful alternative to conventional hydride generation and photochemical vapor generation for the determination of other trace elements, such as Se(VI) and Te(VI), and by other atomic spectrometric techniques.

One-Pot Pretreatment Coupled to Microplasma Optical Emission Spectrometry for Field and Sensitive Determination of Inorganic Mercury and Methylmercury in Fish.

Field and sensitive analysis of mercury species in seafood is helpful to assess the risk of human exposure to mercury, but the cumbersome pretreatment process is time-consuming and laborious. Herein, a simple one-pot pretreatment system is designed for extraction, separation, and enrichment of inorganic mercury (Hg(II)) and methylmercury (MeHg) in fish, and coupled to dielectric barrier discharge (DBD) microplasma optical emission spectrometry (OES). Both Hg(II) and MeHg species in fish can be effectively extracted by tetramethylammonium hydroxide under ultrasound, then separated from the fish matrix by vapor generation and photochemical vapor generation, and finally enriched on the activated carbon electrode tips. Mercury trapped on the activated carbon electrode tips can be rapidly released to produce OES under the DBD microplasma excitation for quantitative analysis. The pretreatment and analysis of a batch of 12 samples are completed within 50 min, and the extraction efficiency of total mercury is up to 90% for 100 mg of freeze-dried fish or 86% for 1 g of fresh fish. Under the optimized conditions, the detection limits are 2 μg kg-1 for Hg(II) and 1.2 μg kg-1 for MeHg in freeze-dried fish, and precisions are 3.2% for Hg(II) and 3.9% for MeHg. The present method is applied to the analysis of the certified reference material and real marine fishes, giving rise to spiked recoveries of 95-103%. The present system hardly leads to MeHg and Hg(II) transforming into each other during extraction, providing a simple, convenient, and low-cost analytical tool to evaluate the risk of mercury species in fish.

Detection of trace antimony by vanadium (IV) ion assisted photochemical vapor generation with inductively coupled plasma mass spectrometry measurement

In this work, a method for sensitive detection of trace antimony (Sb) was developed by inductively coupled plasma mass spectrometry (ICP MS) coupled with photochemical vapor generation (PVG). V(IV) ions were used as new “sensitizers” for improving the PVG efficiency of Sb. Factors influenced the PVG and the detection of Sb by ICP MS were investigated, including the type and concentration of low molecular weight organic acids, the UV irradiation time, the concentration of V(IV) ions, the air-liquid interface, the flow rate of Ar carrier gas, and interferences from co-existing ions. It was found that efficient reduction of Sb was obtained in the medium of 10% (v/v) formic acid (FA), 10% (v/v) acetic acid (AA), and 80 mg L−1 of V(IV) with 100 s UV irradiation. Under the selected conditions, there was no significant difference in analytical sensitivity between Sb(III) and Sb(V). The limit of detection (LOD, 3σ) was 4.7 ng L−1 for Sb with ICP MS measurement. Compared to traditional direct solution nebulization, the analytical sensitivity obtained in this work was enhanced about 19-fold. Relative standard deviations (RSDs, n = 7) were 1.9% and 2.3% for replicate measurement of 0.5 μg L−1 Sb(III) and Sb(V) standard solutions, respectively. The proposed method was applied for the determination of trace Sb in water samples and two certified reference materials (CRMs) of sediments with satisfactory results. Moreover, the generated volatile species of Sb in this work was found to be (CH3)3Sb.

Highly Efficient Photochemical Vapor Generation for Sensitive Determination of Iridium by Inductively Coupled Plasma Mass Spectrometry.

Herein, we describe the highly efficient photochemical vapor generation (PVG) of a volatile species of Ir (presumably iridium tetracarbonyl hydride) for subsequent detection by inductively coupled plasma mass spectrometry (ICPMS). A thin-film flow-through photoreactor, operated in flow injection mode, provided high efficiency following optimization of identified key PVG parameters, notably, irradiation time, pH of the reaction medium, and the presence of metal sensitizers. For routine use and analytical application, PVG conditions comprising 4 M formic acid as the reaction medium, the presence of 10 mg L-1 Co2+ and 25 mg L-1 Cd2+ as added sensitizers, and an irradiation time of 29 s were chosen. An almost 90% overall PVG efficiency for both Ir3+ and Ir4+ oxidation states was accompanied by excellent repeatability of 1.0% (n = 15) of the peak area response from a 50 ng L-1 Ir standard. Limits of detection ranged from 3 to 6 pg L-1 (1.5-3 fg absolute), dependent on use of the ICPMS reaction/collision cell. Interferences from several transition metals and metalloids as well as inorganic acids and their anions were investigated, and outstanding tolerance toward chloride was found. Accuracy of the developed methodology was verified by analysis of NIST SRM 2556 (Used Auto Catalyst) following peroxide fusion for sample preparation. Practical application was further demonstrated by the direct analysis of spring water, river water, lake water, and two seawater samples with around 100% spike recovery and no sample preparation except the addition of formic acid and the sensitizers.

Modified MSIS chamber as a novel gas–liquid separator coupled with the photochemical vapor generation of trace mercury with MP-AES detection

A modified MSIS chamber operating with high sample flow rates was used as a novel gas–liquid separator in the MP-AES detection of trace mercury after photochemical vapor generation.

Learning from Headspace Sampling: a Versatile High-Throughput Reactor for Photochemical Vapor Generation.

Inspired by the headspace sampling (HS) device, a versatile high-throughput photochemical reactor with twenty vessels serving as both the photochemical vapor generator and the HS device was developed for the rapid and sensitive determination of mercury, nickel, and selenium by coupling photochemical vapor generation (PVG) to atomic fluorescence spectrometry (AFS) or point discharge optical emission spectrometry (μPD-OES). The photochemical reactor utilized a specially designed annular UV lamp around which the vessels containing sample solution were automatically rotated and irradiated to yield gaseous analyte species. Subsequently, the species escaped into the headspace of vessels prior to introduction to the atomic spectrometer. Compared with the conventional flow injection (FI) or continuous flow (CF) PVG, the developed PVG-HS method possesses several unique advantages including high throughput (260 pcs h-1), high sensitivity, and the elimination of matrix interference from transition metal ions and the memory effect associated with the quantification of mercury. Limits of detection (LODs) of 0.002, 0.007, and 0.01 μg L-1 were obtained for Hg (II), Ni (II), and Se (IV) by PVG-HS-AFS, respectively, and 0.02 and 0.2 μg L-1 were obtained for Hg (II) and Ni (II) by PVG-HS-μPD-OES, respectively. The practicality of the reactor was evaluated by the detection of Hg (II), Ni (II), and Se (IV) in five certified reference materials, including water (GBW08603, GBW08607, and GBW(E)080395), National Research Council Canada dogfish liver (DOLT-5), fish protein (DORM-4), and three river water samples with good recoveries (92-106%).

Quantum dots immobilized paper for specific and sensitive quantitation of Ni(II) by headspace photochemical vapor generation: Mechanism and application for RGB detection in tea fusion with a smartphone

To avoid the interferences of coexisting ions from sample matrixes during CdTe quantum dots (QDs) based fluorescence and colorimetric assay, an instrument-free paper-based analytical device immobilized CdTe QDs was developed for specific and sensitive quantitation of Ni(II) by headspace photochemical vapor generation (HS-PVG). In the PVG procedure, Ni(II) was converted to volatile Ni(CO)4 by reacting with formic acid under ultraviolet light irradiation, which can effectively quench the fluorescence of the CdTe QDs coated paper. The quenching mechanism was studied in depth via both experimental and theoretical investigations. The results of X-Ray diffraction, X-ray photoelectron spectroscopy, and density functional theory (DFT) show that the generated Ni(CO)4 was reacted with O2 to decompose into NiO at room temperature, which was deposited on the surface of CdTe QDs coated paper, causing its fluorescence quenching. Moreover, visual detection of Ni(II) was achieved with a smartphone by identifying the RGB value of QDs coated paper via HS-PVG procedure. A limit of detection (LOD) of 6.2 μg L−1 was required, which can match those obtained by other large-scale instruments. The concentration of Ni(II) in a series of tea infusions was accurately detected with different leaching experiments and soaking conditions.

Sensitive determination of Ag, Bi, Cd, Hg, Pb, Tl, and Zn by inductively coupled plasma optical emission spectrometry combined with the microplasma-assisted vapor generation

A technique of vapor generation assisted by a microplasma was used for sample introduction into inductively coupled plasma optical emission spectrometry (ICP OES). Replacing a pneumatic nebulizer with a novel microplasma device improved the sensitivities of analytical signals for Ag, Bi, Cd, Pb, Tl, and Zn (by 2–13 times), as well as a concomitant reduction in their detection limits (DLs). Moreover, an outstanding improvement (30-fold) was achieved for Hg. The factors contributing to the boosted signal intensities were higher analyte fluxes and less water vapor produced by the microplasma system. The DLs of Ag, Bi, Cd, Hg, Pb, Tl, and Zn in microplasma-ICP OES were 0.4, 4, 0.06, 0.2, 2, 5, and 0.2 μg L−1, respectively, and the measurement precision was within the range of 0.7–2.4% (it was significantly improved as compared to that achievable with pneumatic nebulization). The proposed microplasma-assisted vapor generation eliminates the use of toxic reductants, e.g., sodium tetrahydridoborate, and it is characterized by higher resistance to matrix effects from transition metal ions (as compared to chemical vapor generation (CVG) and photochemical vapor generation (PVG)). To validate the trueness of the SAGD-ICP OES method, certified reference materials of lobster hepatopancreas (TORT-2), cormorant tissue (MODAS-4) as well as spiked tap water and seawater samples were analyzed to determine levels Cd and Hg. The standard additions method was used for calibration in both cases. Recoveries of the analytes in the case of the analysis of TORT-2 and MODAS-4 samples as well as the spiked tap water and seawater was within the range of 98–113%, which indicated that the developed sample introduction system can be successfully used for very sensitive determinations of selected hazardous elements in environmental samples.