Current advances of chemical vapor generation in non-tetrahydroborate media for analytical atomic spectrometry

Sensitive and Spectral Interference-Free Determination of Rhodium by Photochemical Vapor Generation Inductively Coupled Plasma Mass Spectrometry

A sensitive method for Rh determination was developed by coupling photochemical vapor generation (PVG) for sample introduction to inductively coupled plasma mass spectrometry (ICPMS). PVG was conducted in a thin-film flow-through photoreactor operated in a flow injection mode from a photochemical medium comprising 10 M HCOOH. PVG efficiency was substantially enhanced by the addition of 10 mg L-1 Cu2+ and 5 mg L-1 Co2+ as mediators as well as 50 mM NaNO3. The volatile product (likely Rh(CO)4H) was found to be less stable when in prolonged contact with the liquid medium at the output from the photoreactor. Hence, further enhancement was achieved by introducing an Ar carrier gas near the exit of the photoreactor to minimize the interaction of volatile species with the liquid medium. Despite PVG efficiency reaching only 15%, measurement at the ultratrace level (20 ng L-1) was characterized by very good repeatability of peak area response (2.9%) and outstanding limits of detection (13 pg L-1, 6.5 fg absolute) using He in the collision cell. Interferences from potential coexisting metals, inorganic acids, and their anions were investigated. Accuracy was verified by analysis of OREAS 684 (Platinum Group Element Ore) and SRM 2556 (Used Auto Catalyst) following peroxide fusion for sample preparation. Application to the direct analysis of real river and lake water samples and reference materials AQUA-1 and SLRS-6 demonstrated excellent selectivity of the PVG-ICPMS methodology over conventional pneumatic nebulization-ICP(MS)/MS, the results of which were seriously biased by polyatomic interferences, especially from Sr and Cu, despite the use of various reaction/collision cell modes.

A miniaturized flow batch chemical vapor generation system for Hg determination in fish by ICP-MS

A new flow batch (FB) system for chemical vapor generation (CVG) is proposed for mercury (Hg) determination in fish. An inductively coupled plasma mass spectrometer was used as a detector. Low-cost peristaltic mini pumps were used to propel the solutions and different configurations of FB systems (reactor/gas/liquid separator) were studied. The proposed configuration of the FB-CVG system allows good sensitivity, low limit of detection (LOD) and low consumption of reagents and sample solutions. In summary, only 1 mL of reductant, 1 mL of acid and 0.16 mL of sample are needed. The proposed method has good linearity, precision (better than 5 %), LOD of 0.008 μg g-1 and LOQ of 0.012 μg g-1, and high sample throughput, allowing 90 measurements/h. The accuracy of the method was evaluated through the analysis of a certified reference material (DOLT-4 Dogfish Liver), whose result is in good agreement with certified value (t-test with 95 % confidence level) and the quantification limit meets current legislations, of 1.0 μg g-1 (Brazil) and 0.3 μg g-1 (EU). In addition, analyte recovery test was done, where Hg recovery was better than 95 %, demonstrating the good analytical performance of the method. To demonstrate the applicability of the method, five samples of fish tissue (muscle) were analyzed. The proposed FB-CVG system, in addition to being low cost, is robust and requires only the volume of reagents necessary for Hg vapor generation, producing a very low amount of waste. It can be concluded that the proposed system can be used for routine analysis for Hg determination in fish tissue. It is worth noting that with the appropriate adjustments, the system can be coupled to different Hg detectors.

Pb-based metal organic framework as substrate: Chemical vapor generation-visual/smartphone colorimetric analytical system for sensitive and selective detection of sulfide ion in water and beers

A visual/smartphone colorimetric system was developed for the sensitive and selective detection of sulfide ion (S2-) using chemical vapor generation (CVG) as a gaseous sampling technique. S2- in samples were converted into H2S after the addition of H2SO4, which separated from the solution during CVG process, ensuring high efficiency of vapor generation (sensitivity) and eliminated interferences (selectivity). The H2S was subsequently reacted with Pb-BTC and PbS was thus formed, causing the test paper turned to black. It was utilized for the detection of S2- by visual/smartphone colorimetric system. Detectable limits of 0.05 μg/mL and 0.2 μg/mL were obtained under smartphone mode and visual mode, respectively. Furthermore, this colorimetric system was successfully used for the analysis of S2- in several beer samples and water samples, with recoveries ranging 97 %-111 %. This system represents a potential miniaturized, easy used and high-effective method for rapid and on-site detection of S2-.

High sensitivity atomic fluorescence spectroscopy for the detection of AsIII by selective electrolysis of arsenic on nanoflowers-like Fe/NFE

Modified electrosynthetic sample introduction technique is a reliable means of solving the problem of high sensitivity analysis of trace arsenite. This article attempts to achieve selective electroreduction of AsIII through the construction of electrode surfaces with different structures and materials from the perspective of interface reactions. Among the four transition metal modifiers, the iron modified nickel foam electrode with nano-flower structure documented higher efficiency in inducing arsenic reduction and better species selectivity. Systematic electrochemical and spectroscopic tests suggest that strong adsorption effect between Fe and AsIII, appropriate hydrogen evolution potential, and catalytic activity jointly promote efficient electroreduction of AsIII. Optimization based on electrode materials and electrolysis conditions, with high sensitivity, wide linear range (0.1-50 μg L-1), and excellent species selectivity, this paper offers an efficient and economic sample introduction method for trace AsIII/V selective atomic spectroscopy direct determination.

A portable/miniaturized analytical kit for on-site analysis: Chemical vapor generation-visual colorimetric and smartphone RGB dual-mode for detection of sulfide ion in water and food additives

Chemical vapor generation (CVG) was used as a gaseous sample introduction technique for the visual/smartphone RGB readout colorimetric system, with the advantages of efficient matrix elimination and high vapor generation efficiency, this analytical system exhibits a good selectivity and sensitivity. Sulfide ion (S2-) in solution was transformed to its volatile form (H2S), the generated H2S reacted with a silver-containing metal organic framework (Ag-BTC) selectively, Ag2S was thus generated. Ag-BTC (fabricated on paper sheet) changed from white to dark brown, the color variance was identified by smartphone and naked-eye simultaneously. Under the optimized conditions, a limit of detection of 0.02 μg/mL was obtained by naked-eye. Several water samples and commercial food additives were analyzed for confirming its accuracy and potential application for on-site detection, recoveries ranging 94-110 % were obtained. To meet the demand of on-site analysis of S2-, this colorimetric system was integrated in a portable/miniaturized analytical kit. It is an easy-used, affordable and portable analytical kit for S2- detection in field.

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.

Determination of trace tellurium by photochemical vapor generation-atomic fluorescence spectrometry using bifunctional Co-MOF-74 for preconcentration and sensitization

The determination of trace tellurium in real samples with complicated matrix can be rather challenging due to the low abundance and interferences. Herein, we report a new method for the highly sensitive detection of Te(IV) by photochemical vapor generation-atomic fluorescence spectrometry (PVG-AFS), utilizing Co-MOF-74 as an adsorbent and a precursor of Co²⁺ ion sensitizer for preconcentration and enhanced PVG efficiency. The synthesized Co-MOF-74 can completely adsorb Te(IV) within 10 min in a wide pH range. Following filtration and re-suspension in a dilute solution of formic and acetic acid, the adsorbed Te(IV) was converted to volatile compounds under the UV irradiation and swept to AFS for detection. A limit of detection of 0.08 ng/mL for Te(IV) was obtained after a 50-fold preconcentration. The proposed method was used for analysis of various natural water samples for trace Te(IV), with satisfactory spike recoveries achieved.

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.