Photochemical Vapor Generation for Colorimetric Speciation of

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Photochemical Vapor Generation for Colorimetric Speciation of Inorganic Selenium Yonggang Ding, Yu Liu, Youliang Chen, Yi Huang, and Ying Gao Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b05117 • Publication Date (Web): 05 Feb 2019 Downloaded from http://pubs.acs.org on February 5, 2019

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Analytical Chemistry

Photochemical Vapor Generation for Colorimetric Speciation of Inorganic Selenium Yonggang Ding,† Yu Liu,† Youliang Chen,† Yi Huang,‡ Ying Gao*, †

†

State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, College of

Earth Sciences, Chengdu University of Technology, Sichuan 610059, China. ‡

Institute of Environment, Chengdu University of Technology, Chengdu, Sichuan 610059, China.

*Corresponding Author Email: [email protected]

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Abstract Gold nanoparticles (AuNPs) are widely used as optical probes in colorimetric detection, thanks to their high molar extinction coefficient. However, sample matrixes of high salinity or strong acidity/alkalinity often break the electrostatic repulsion of AuNPs suspension, or/and the surface functionality of AuNPs, causing strong and unfavorable interferences. Photochemical vapor generation (PVG) is an efficient technique for the sample matrix separation. Besides, it possesses distinct features of green reducing reagent, reduced interferences from concomitant elements, and direct speciation by the assistance of photocatalyst. Herein, we developed a photochemical vapor generation (PVG) method for the green, and direct speciation analysis of inorganic selenium (i.e., Se(IV) and Se(VI)), by colorimetric or visual monitoring of unmodified AuNPs. The generated Se species from PVG were directed into the AuNPs solution for a reaction to take place which produced a specific new absorption band at 600 nm for detection. The experimental parameters, including the concentration of organic acid, the sample flow rate, the concentration of AuNPs, and the flow rate of carries gas, were optimized in detail. Under optimized conditions, the limits of detection (LOD) for Se (IV) and Se (VI) were 0.007 μg mL-1 and 0.006 μg mL-1 by UV-vis detection, respectively. It’s worth mentioning that 0.08 µg mL-1 Se can induce an obvious color change, which can be directly observed with naked eyes. Relative standard deviations (RSD) of 4.5% and 4.3% were obtained from seven replicate measurements of 0.15 µg mL-1 Se (IV) and Se (VI) standard solution, respectively. The developed assay has been successfully applied for the speciation of Se in a dietary supplement sample and environmental water samples including lake water, seawater, simulated water reference


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materials, and tap water.

1. Introduction Gold nanoparticles (AuNPs) have been widely applied in colorimetric detection as optical probes in recent years,1,

2

thanks to their higher molar extinction coefficient in the

visible region and thus higher sensitivity compared to the conventional organic probes.3 Color change is even readily monitored by the naked eyes without using any advanced and expensive instruments. The aggregation of AuNPs is the main reason causing a change in surface plasmon resonance (SPR) during colorimetric analysis. Since the pioneering work by Mirkin et al.,4 AuNPs have served as optical probes for sensing metal elements,5, 6 anions,7 proteins,8 nucleic acids,9 microorganisms10 etc. The limit of detection (LOD) of AuNPs-based colorimetric assays ranges from nM to μM without any signal amplification procedure. However, for the complicated real sample analysis, matrixes of high salinity or strong acidity/alkalinity may break (i) the electrostatic repulsion of AuNPs suspension, or/and (ii) the surface functionality of AuNPs and consequently affect their aggregation state,11 resulting in strong and unfavorable interferences. Considering to eliminate these interferences, it is worth mentioning Wu et al. recently delicately designed a hydride generation-based AuNPs colorimetric assay for total inorganic selenium.12 The target analytes were first converted to its volatile hydrides and then transferred into AuNPs solution to induce color change, thus alleviate matrix effect to a great extent. Photochemical vapor generation (PVG) is the new member in the family of chemical vapor generation techniques (CVG) for atomic and mass spectrometry, contributing enhanced



analyte introduction efficiency and matrix separation.13 Photochemical reactions have wide applications in industry for many years, such as wastewater treatment and nanoparticle synthesis. Its analytical usability was not realized until Sturgeon et al. converted Se(IV) to volatile Se species for atomic absorption spectrometry sample introduction on 2003,14 by the exposure of a solution of Se(IV) to UV radiation in the presence of low molecular weight organic acids (LMWOAs). PVG is usually composed of a low cost UV lamp, a simple flow through system, LMWOAs, and a common gas-liquid phase separator. PVG has now been successfully applied to elements typically amenable to hydride generation (HG), such as Hg,15 As,16 Bi,17, 18 Sb,19 Sn,20 Se,21 Te,22 and Pb,23 as well as transition metals (Fe, Co, Ni, Cd, Mo and Os)24-27 and non-metals (I, S, Cl and Br).28-31 Comparing to conventional hydride generation (HG), it is interesting to highlight the following distinct and attractive properties: (i) Green chemistry-the use of expensive and unstable tetrahydroborate(III) is eliminated, conferring some degree of green chemistry;13 (ii) Reduced interferences from concomitant elements-up to 100-fold greater tolerable concentrations of Co(II), Cu(II) and Ni(II) was reported than typically tolerated with hydride generation;14 (iii) Direct speciation scenarios achievable by applying photocatalysts-the generated electrons of photocatalyst (i.e., nano-TiO2) was reported to reduce Se(VI)/ Se(IV) and convert them to volatile species under UV irradiation, while only Se(IV) converted to volatile species in the absence of nano-TiO2.32 Despite intriguing properties, it is surprising to recognize that PVG-based colorimetric analysis has not been reported till now. Herein, we developed a green, interference-free, and direct speciation colorimetric assay for inorganic selenium (i.e., Se(IV) and Se(VI)), utilizing a system combined PVG with unmodified AuNPs. Selenium was firstly transformed into


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H2Se under UV irradiation in the presence of a relatively green reducing reagent (i.e., formic acid). Sample matrixes such as high salinity, high acidity/alkalinity, and other coexisting metal elements were efficiently separated by a gas-liquid separator. Without photocatalyst (nano-TiO2), only the Se(IV) was reduced to H2Se thus detectable, while both Se(VI) and Se(IV) signals were recorded in the presence of nano-TiO2, realizing a facile speciation analysis. The interaction between volatile H2Se and the AuNPs suspension immediately affects the aggregation of AuNPs, and then the subsequent SPR change can be sensitively observed by both UV-vis spectrophotometer and naked eyes.

2. Experimental section 2.1. Chemical reagents and samples All reagents used in this work were at least of analytical grade. Deionized water (DIW) (18.2 MΩ cm) was used throughout. Formic acid and acetic acid of ACS grade were purchased from Aladdin Reagents Corporation (Shanghai, China). Nano-TiO2 (>99.5% purity, anatase crystal, 10-25 nm) was obtained from Aladdin Industrial Corporation (Shanghai, China). Stock solutions of Se(VI) and Se(IV) (1000 μg mL-1) was prepared from sodium selenate (Xiya Reagent Corporation) and sodium selenite (Xiya Reagent Corporation). Chloroauric acid (HAuCl4) was obtained from Aladdin Reagents Corporation (Shanghai, China). Hydrochloric acid, nitric acid, and trisodium citrate were purchased from Changzheng Chemical Reagent Co. Ltd. (Chengdu, China). The 1000 μg mL-1 of Cu2+, Fe3+, Sn4+, Bi3+, Cr3+, Mn2+, Pb2+, Co2+, Ni2+, Ag+, Hg2+, Cd2+, Zn2+ were obtained from Environmental Express Corporation (South Carolina, USA). Arsenious acid solution, sodium



tellurite and Sb2O3 were purchased from Aladdin Reagents Corporation (Shanghai, China). Calcium chloride, sodium chloride, aluminum chloride, potassium chloride, magnesium sulfate, sodium nitrate, sodium nitrite, and sodium iodate were all purchased from Kelong Chemical Reagents (Chengdu, China). The river water sample was collected from Dongfeng River near Chengdu University of Technology. The tap water and the lake water were collected from our laboratory and our campus, respectively. Two seawater samples were collected from Sanya (Hainan, China) and Chongmingdao (Shanghai, China), respectively. The collected water samples were filtered through a syringe filters of 0.45 µm pore size prior to analysis and stored in formic acid. A mineral water sample and a dietary supplement tablet were obtained from local market. The accuracy was also evaluated by analysis of a simulated nature water sample (GBW(E)080395) purchased from the National Research Center for Standard Materials (Beijing, China).

2.2. Instrumentation The PVG system was comprised of a low-pressure UV mercury lamp (19W, Beijing Titan Instruments Co., Beijing China) in tandem with a gas-liquid separator (GLS), as shown in Figure 1. The UV lamp, providing 185 nm and 254 nm UV irradiations, was covered by aluminum foil to protect operators from the UV light irradiation. A UV-vis spectrophotometer (TU-1810PC, Perrsee, China) was used to record absorption spectra and for the quantitation of Se using the developed procedure. A JEM-100CX transmission election microscope (TEM, JEOL Co., Japan) was used to observe gathered state of the


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AuNPs before and after reaction. A flow injection analysis processor was used for introducing samples into PVG system (FIA-3110, Beijing Titan Instruments Co., Beijing, China). A commercial two-channel atomic fluorescence spectrometry (AFS-930, Beijing Jitan Instrumental Co., Beijing China) was employed for the hydride generation confirmation measurements.

Figure 1. Schematic of the PVG-AuNPs-based colorimetric assay for inorganic Se species

2.3. Synthesis of AuNPs AuNPs were prepared by reducing chloroauric acid (HAuCl4) with trisodium citrate.8 Briefly, 1 mL HAuCl4 (1% m/v) was diluted to 100 mL with DIW in a 250 mL beaker and then heated to boil. Then 2 mL sodium citrate (1% m/v) was rapidly added to the HAuCl4 solution. The solution was boiled for an additional 20 min under stirring. The color of the solution changed from pale yellow to wine red during this time. Subsequently, the synthesized AuNPs solution was cooled to room temperature and stored in the refrigerator at 4 °C. The average diameter of AuNPs was about 13 nm. Before analysis, the AuNPs solution was dialyzed in DIW using a membrane bag with molecular weight cut off 1000 for 6 h to



remove the remnant sodium citrate in solution.

2.4. Preparation of samples The dietary supplement is in the form of tablet. The sample preparation procedure was carried out as previous report.33 Tablets were weighted and ground into fine powder before extraction. Then 0.3 mol L-1 NaOH and DIW were added for quantitative extraction of Se (IV) and Se(VI) with ultrasound irradiation for 30 min at 35 oC, respectively. After that, the sample solutions were filtered through syringe filter with 0.45 µm pore size. The filtered sample solutions were diluted 5 times with water prior to analysis. Sample blank was also processed along with the sample. For the analysis of seawater samples, five milliliter samples were added resulting in one fold dilution. HG coupled with AFS was used to verify the concentration of total Se and Se(IV) in water samples. Since Se(VI) could not be directly converted to volatile species in HG system, the pre-reduction of Se(VI) to Se(IV) in water samples with 6 mol L-1 HCl at a temperature between 90-95 °C for 10 min was carried out for the determination of total Se. The concentration of Se (VI) was obtained by total concentration of Se subtracting the concentration of Se (IV).

2.5 Analytical procedure Ten milliliter samples or standard solution of Se (IV) containing 10% (v/v) formic acid was introduced into PVG system by a pump of the flow injection analysis processor. Volatile compounds of Se were produced under ultraviolet light irradiation as a result of


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photochemical reduction of Se, and then were separated from the liquid by introducing 150 mL min-1 argon gas in a gas-liquid separator. Subsequently, volatile compounds were bubbled into a 2 mL disposable polypropylene tube containing 600 μL of 0.56 nM AuNPs with 10 mM Tris-HCl (pH=8.0 ） and incubated at ambient temperature for 15 min. The corresponding UV-visible spectra were recorded. The maximum absorbance wavelength of the AuNPs solution shifted from 520 to 600 nm when volatile Se species were introduced. And the ratio of absorbance at these two wavelengths increased with Se concentration. Therefore, A600/520 was selected as instrumental response. For analysis of total concentration of Se, sample solution or standard solution containing 1.4 g L-1 nano-TiO2 and 10% (v/v) formic acid were continuously introduced into the PVG reactor. The concentration of Se (VI) was obtained by the total concentration of Se subtracting the concentration of Se (IV). The schematic of the PVG-based colorimetric speciation was shown in Figure 1.

3. Results and discussion 3.1 Speciation of Se(IV) and Se(VI) by PVG -AuNPs-based colorimetric assay The PVG efficiency of Se relies on its existing oxidation state.14,

32, 34, 35

Volatile Se

species can be easily generated from Se (IV) under UV irradiation. However, Se (VI) is not amenable to PVG. The use of photocatalysts facilitates the PVG of Se (VI). In the presence of photocatalysts including TiO2, modified-TiO2, ZrO2, Cd2+, as well as metal organic



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frameworks (MOFs)21, 32, 35, 36, Se (VI) was easily transformed into volatile species, making the proposed assay feasible for inorganic Se speciation.

Figure 2. Effect of the concentration of nano-TiO2 on the signal responses from 0.15 µg mL-1 Se (IV) and Se (VI). Nano-TiO2, the most frequently used photocatalyst, is selected for the speciation of Se (IV) and Se (VI) by colorimetric assay. As shown in the Figure 2, the effect of nano-TiO2 concentration on Se response was investigated. The PVG efficiency of Se (VI) increased sharply when increasing nano-TiO2 content from 0 to 0.5 g L-1, thereafter, the enhancement was minimal. Se (VI) can be directly reduced to Se0 by electrons released from the conduction band of TiO2 under UV irradiation thermodynamically spontaneous, then attacked by photochemically generated radicals to yield the volatile products (mostly in the form of H2Se).13 Further increasing the concentration of TiO2 would lead to a slight decrease of signal due to the poor transmission of the UV flux through the sample.

Interestingly, the signal

response of Se (IV) also increased as the concentration of nano-TiO2 increased 1.0 to 1.4 g L-1. The use of nano-TiO2 may facilitate the generation of H2Se from formic acid solution13, 32.

The analytical sensitivity of Se (VI) almost equaled to that of Se (IV) in the presence of


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TiO2 ranging from 1.4 to 2.0 g L-1. In consequence, 1.4 g L-1 nano-TiO2 was added for the determination of total Se. While for the selective determination of Se (IV), nano-TiO2 was not involved. The concentration of Se (VI) was calculated from the difference between total Se and Se (IV). The working principle of the proposed colorimetric assay for the speciation of inorganic Se species is illustrated in Figure 1. The sample solution of containing formic acid (with or without photocatalysts) was continuously injecting into the PVG reactor, with Se volatile compounds generated. Then, the carrier gas (Ar) together with the gaseous selenium species were flushed into gas-liquid separator, isolated from matrix solution and introduced into AuNPs solution. Subsequently, selenium volatile compound (only H2Se) was converted to Se0 by the oxidation of dissolved oxygen in solution of AuNPs and adsorbed on the surface of AuNPs, leading to partial citrate separating.12 As a result, the color of AuNPs solution changed from red to blue because of destroying the electrostatic repulsion of the negatively charged citrate on the surfaces of AuNPs and inducing the aggregation of gold nanoparticles (Figure 3A). Simultaneously, the SPR band of AuNPs at 520 nm decreased and displayed a red-shift according to the UV-vis spectra as is evident in Figure 3B. In the TEM image (Figure 3D), the aggregation of AuNPs was confirmed and a membrane like substance was found coating on the aggregated AuNPs. The substance was presumed to be elemental Se (rather than SeO32-, Figure S1) as the consequence of oxidizing H2Se with dissolved oxygen in the solution.12 The XPS spectra of AuNPs (Figure S2) after reaction with volatile Se generated from PVG also showed formation of a new selenium species. The strong peak



appeared at 55.0 eV was identified as elemental selenium Se0 (3d).37 Peaks at 5eV, 59 eV and 61 eV for Se2-, Se4+ and Se6+ were not observed, respectively. To our knowledge, this is the first report for the speciation of Se using AuNPs based colorimetric assay after PVG. The influencing factors on the speciation of Se were investigated in details.

Figure 3. UV-vis spectrum and TEM images (C, D) of the AuNPs without or with H2Se generated from 2 µg mL-1 Se (IV).

3.2 Optimization of PVG-AuNPs based colorimetric system


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Figure 4. Optimiation of experimental conditions for 0.15 µg mL-1 Se (IV) determination: (A) Effect of the concentraiton of formic and acetic acids; (B) Effect of the sample flow rate; (C) Effect of the concentration of AuNPs solution; (D) Efffect of the purfication of AuNPs by centrifugation and dialysis. The influencing factors on the speciation of Se were investigated in details. The used type and the concentration of LMWOAs determine PVG efficiencies of elements.17, Formic acid and acetic acid are the most widely used reductants for PVG of Se.14,

32

38, 39

The

effects of formic acid and acetic acid concentrations from 1% to 20% (v/v) on the responses of Se (IV) were investigated, respectively. The signal response of Se (IV) was more sensitive in formic acid medium, which was enhanced with the formic acid concentration increasing from 0% to 10% (v/v) as shown in Figure 4A,. Further increasing the concentration of formic acid resulted in the decrease of signal response. Acetic acid was reported to be most efficient reaction medium for the photochemical generation of volatile Se. However, the response of Se (IV) from acetic acid was rather low, as dimethyl selenide [(CH3)2Se)] instead of H2Se is the main product by UV photolysis of Se (IV) in acetic acid solution.14 H2Se can be completely absorbed and easily decomposed in the alkaline AuNPs solution.12,


14

Whereas


dimethyl selenide is sufficiently stable to pass through the alkaline solution, leading to the rather low analytical sensitivity.14 In consideration of the analytical sensitivity, 10% (v/v) formic acid was chosen for the subsequent experiment. The irradiation time of the analytes and the analytical throughput of samples are depended on the transport pump flow rate. Fixing the sample introduction volume at 10 mL, the influence of sample delivery flow rate was investigated in the range of 1.0-4.0 mL min-1. As shown in Figure 4B, optimum response is obtained at 2.5-3.0 mL min-1 (with 16-20 s irradiation times). Higher sample flow rate leads to the short irradiation time of sample solution and inefficient reduction of analytes, whereas lower sample flow rate results in the part decomposition of generated volatile species with prolonging irradiation time. Considering the analytical sensitivity and the sample throughout, 3.0 mL min-1 (with 16 s irradiation time) sample flow rate was chosen for subsequent experiment. Shorter wavelength and stronger irradiation intensity promote the photochemical reduction of analytes40. The effect of UV irradiation wavelength and the intensity on the determination of Se(IV) in the presence of TiO2 was investigated. A PTFE tubing was wrapped around the 19 W flow-through UV lamp, 70% incident UV irradiation at 185 nm was thus absorbed.27, 41 The comparison of signal responses for Se(IV) in the presence of nano-TiO2 flowing within the PTFE tubing or through the UV lamp was carried out. There was no obvious difference in signal responses. Furthermore, a 15 W germicidal mercury UV lamp was used for the PVG of 0.15 µg mL-1 Se(IV). No significant difference was found between the signal responses using different PVG reactors (Figure S3). Therefore, vacuum UV irradiation is not necessary for the efficiently photochemical reduction of Se.


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The concentration of AuNPs plays an important role for sensitive determination of Se. The effect of the concentration of AuNPs from 0.28 to 1.1 nM on the determination of Se (IV) was evaluated. Evidently, low concentration of AuNPs is in favor of the interaction between H2Se and AuNPs, leading to the aggravated aggregation of AuNPs and subsequent more sensitive signal response. However, the sensitivity for naked eye determination largely decreased because of the light color of AuNPs solution at low concentration. Thus, 0.56 nM AuNPs was selected for the subsequent studies. Besides, it was found that the remnant sodium citrate in solution during AuNPs has counteractive effect for the colorimetric determination of As (III) because of the unavoidable binding effect, resulting in the low analytical sensitivity for analytes detection.42 Therefore, removing free citrate ions form AuNPs solution by dialysis and centrifugation was investigated in this work.42,

43

The

analytical results were shown in Figure 4D, large improvement of analytical sensitivity was observed after purification of AuNPs prior to analysis. The dialysis of AuNPs using a membrane bag with molecular weight cut off 1000 for 6 h showed slightly better performance than that using centrifugation of AuNPs at 12000 rpm for 20 min. Therefore, dialysis of AuNPs before analysis was selected for subsequent experiments. The GLS efficiency of volatile Se and the residence time of Se in alkaline AuNPs solution rely on the used carrier argon flow rate. Lower gas flow rate leads to low delivery efficiency of analytes, and higher gas flow causes short residence time between volatile Se spices and AuNPs solution. Its influence on Se signal response was optimized from 50 to 300 mL min-1. The optimum carrier argon gas flow was obtained in the range of 100 to 200 mL min-1. Thus, an argon gas flow of 150 mL min-1 was selected for subsequent experiments



(Figure S4). The effect of the reaction time between volatile Se and AuNPs on the determination of Se was investigated. The signal responses kept constant after introducing volatile Se into AuNPs solution for 12 min (Figure S5). Furthermore, the effect of AuNPs size on the detection of Se (IV) in the presence of nano-TiO2 was studied. As the particle diameter increased, the analytical sensitivity decreased which is likely due to the darker color of large size of AuNPs solution leading to the insensitivity of color change when introducing the same amount of volatile Se.

3.3 Selectivity and interferences of colorimetric assay Unmodified citrate-capped AuNPs is vulnerable to high salinity of sample matrix and tend to aggregate in sample solution. The influence of high salinity in sample matrix on the detection of Se by the proposed assay was investigated. As evident from Figure 5, even when the salt content of NaCl was up to 5% (m/v), no appreciable response change of the AuNPs or the interference on Se determination was observed. As reported in previous studies, the severe matrix inferences occurred for the analysis of Se in seawater samples using acetic acid as the photochemical reductant by atomic absorption spectrometry (AAS) determination.14 The investigation result suggests that reductive radicals generated from photodecomposition of formic acid not only involve in the production of H2Se, but also participate in the consuming potentially oxidative radicals arising from the sample matrix, greatly improved the salt resistance capability of the PVG system.16


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Figure 5. Effect of the sample matrix with high salinity. (A) 0.15 µg mL-1 Se(IV) and (B) 0.075 µg mL-1 Se (IV), 0.075 µg mL-1 Se (VI), and 1.4 g L-1 nano-TiO2. Experimental conditions: 10% (v/v) formic aicd, 5% (m/v) KCl, 5% (m/v) NaCl, 5% (m/v) CaCl2; 2% (m/v) MgSO4 and 2% (m/v) AlCl3. Furthermore, the selectivity of the proposed assay for the speciation of Se was tested. As shown in Figure S6 and Figure S7, transition metal ions, hydride forming elements and several anions including 5 µg mL-1 Fe3+, Sn4+, Sb3+, Bi3+, Cr3+, Mn2+, Co2+, Ni2+, Ag+, Hg2+, Cd2+ and Zn2+ did not show obvious SPR change as 0.15 µg mL-1 Se (IV) or total Se in the presence of TiO2 did. However, the similar colorimetric response was observed from Te (IV), but the analytical sensitivity was largely lower than that of Se under the selected experimental conditions. Furthermore, the interferences from those elements in the presence 0.15 µg mL-1 Se(IV) or total Se were also evaluated. It was found that 5 µg mL-1 As3+, Pb2+ and Cu2+ caused suppression for Se determination with the recoveries of 50%, 28% and 25%, respectively. The depression effect from As(III) and Pb(II) on Se determination was probably due to the liquid phase interference during their photochemical reduction.44 The formation of Cu0 from Cu2+ under UV irradiation caused serious liquid phase interference for Se either.45, 46

As Te and Se belong to the same group, the similar colorimetric response was observed for

Te (IV). The addition of 5 µg mL-1 Te(IV) lead to the positive effect for the determination of



Se with a recovery of 110% for Se(IV). The recovery was found to be 122% for total Se determination in the presence of TiO2. However, when 0.1 µg mL-1 Cu2+; 0.2 µg mL-1 Pb2+ and As3+ and 1.0 µg mL-1 Te4+ were added, no obvious inferences were observed for inorganic Se speciation. Furthermore, quantitative absorption of Se (VI) and Se (IV) from aqueous solution was accessible using TiO2 as the absorbent at pH value below 3.0. Thus, the separation of analytes from sample matrix using nano-TiO2 as the absorbent before analysis can be carried out to eliminate the interferences from coexisting metal ions47. As the consequence, interferences from 5 µg mL-1 of Cu2+, As3+ and Pb2+ can be greatly alleviated for total Se determination as shown Figure S7. However, interference from 5 µg mL-1 Te(IV) was obvious (with the recovery of 118%) even after using nano-TiO2 based separation. When 1.0 µg mL-1 was added, no obvious interference (with the recovery of 101%) was observed for the speciation of inorganic Se. Besides, the abundance of Te in typical samples is often significantly low.48 It should be notified that the elimination of sample matrix effect using TiO2 based adsorption was only suitable for quantification of total Se. For further improving the anti-interference capability of this proposed for Se speciation, simultaneous adsorption of Se(VI) and Se(VI) at the pH of 1.0-3.0 and selective elution of Se (VI) at alkaline condition ( pH=8.0) may be feasible based on the investigated result of the effect of pH on the adsorption of Se(IV) and Se(VI) on TiO2 (Figure S8).49 But it is beyond the scope of this work.

3.4 Analytical figures of merit


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Under the optimized conditions, AuNPs-based colorimetric assay with PVG for sample introduction was established for the speciation of Se (IV) and Se (VI). Good linear correlations between the A600/A520 values and the concentration of Se (IV) and Se (VI) from 0.01 to 0.4 µg mL-1 with the regression coefficients of 0.991 and 0.987 were obtained, respectively. The difference of analytical sensitivity between Se (IV) and Se (VI) in the presence of TiO2 was within 3%, and no obvious signal for Se(VI) was observed in the absence of TiO2 (Figure 6), showing the feasibility of direct speciation. The detection limits of Se (IV) and Se (VI) (in the presence of TiO2) were 0.007 μg mL-1 and 0.006 μg mL-1 with sample consumption of 10 mL by UV-vis detection, which was comparable with that determination by using HG for colorimetric assay of Se (IV).12 But the pre-reduction of Se (VI) by concentrated HCl in HG system and the possible conversion between Se (VI) and Se (IV) was avoided in the developed method.45 With the naked eye, 0.08 µg mL-1 Se can induce the visible color change, demonstrating the high sensitivity of the proposed assay. The analytical sensitivity could be further improved by increasing the sample consumption volumes. With the sample consumption of 60 mL, the detection limit of Se (IV) could be down to 0.0009 μg mL-1 in the absence of TiO2 by UV-vis detection. Also, more efficient photocatalysts such as modified nano-TiO2 nano-ZrO2, and C3N4 could be used to further enhance the analytical sensitivity of Se (IV) and Se (VI). The relative standard deviations (RSD) obtained from 7 replicate measurements of 0.15 µg mL-1 Se (IV) and Se (VI) standard solution were 4.5% and 4.3%, respectively. As shown in Table 1, the analytical sensitivity of the propose assay was comparable to AAS and ICP-OES based methods, but the proposed method is with low cost and offers the feasibility for direct speciation of Se species,



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eliminating the possible sample contamination and loss during the essential pre-reduction procedure in HG-based analytical strategies.45

Figure 6. Plots of absorbance ratio (A600/A520) of AuNPs versus the concentration of Se(IV) and Se(VI). Table 1. Comparison of analytical figures of merit. Method PVG-AuNPs-based colorimetric assay HPLC-HG-OES HPLC-HG-ICP MS

Samples

LOD

Water and dietary supplements

Se (VI): 0.006 μg mL-1 Se (IV): 0.007 μg mL-1 Se (IV ): 0.030 μg mL-1 Se (IV): 0.00016μg mL-1 Se (IV): 0.0029 μg mL-1 Se (VI): 0.0035 μg mL-1 Se (IV): 0.010 μg mL-1 Se (IV ): 0.010 μg mL-1

Urine

Ref. This work 50

HPLC-EVP-AFS

Water-soluble extracts of garlic shoots

HPLC-HG-AAS

Dietary supplements

HPLC-UV-HG-AFS

Urine

Se (IV): 0.001 μg mL-1

53

PVG-AFS

Table salts and water

Se(IV): 0.0001 μg mL-1 Se (VI): 0.0001μg mL-1

54

51 52

3.5 Application The proposed assay was applied for the speciation of selenium in a selenium supplement sample and environmental samples including lake water, seawater, simulated water reference materials and tap water with external calibration quantification (Table 2 and 3). As shown


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from Table 3, 0.98 mg L-1 Se(VI) and 25.8µg tablet-1 of Se(IV) were found in the simulated water reference material and the selenium supplement which are in good agreement with the certified value/ declared value. Besides, 13.7±2.7 μg L-1 Se(VI) were found in the mineral water sample. To validate this method, a spike recovery test was carried out by adding Se(IV) and Se(VI) to the water samples. The spiked recoveries varied from 80% to 115%, indicating the feasibility of this method for speciation of inorganic Se species in real samples (Table 2). Table 2. Analytical results for the detection of Se (IV) and Se (VI) in water samples. Added values (μg L-1) Sample

Se(IV)

Se (VI)

Detected values (n=3, μg L-1) Se (IV)

Se (VI)

Recovery (%) Se(IV)

Se (VI)

— — ˂ LODa ˂ LODb — — 50.0 50.0 52.3 ± 2.5 48.0 ± 1.6 104.6 96 a b — — ˂ LOD ˂ LOD — — 50.0 50.0 44.5 ± 2.5 52.3 ± 1.7 89.0 105 a b — — ˂ LOD ˂ LOD — — Tap water 50.0 50.0 43.8 ± 2.2 52.6 ± 1.2 87.6 105 — — ˂ LODa ˂ LODb — — Seawater 1 50.0 50.0 41.5 ± 4.1 57.6 ± 2.3 83.1 115 a b — — ˂ LOD ˂ LOD — — Seawater 2 50.0 50.0 ˂40.0 ± 4.0 48.2 ± 3.2 80.0 96 a LOD for Se(IV) with 10 mL sample consumption: 0.007 mg L-1; b LOD for Se(VI) with 10 mL sample consumption: 0.006 mg L-1. Dongfeng River water Campus lake water

Table 3. Analytical results for the detection of Se (IV) and Se (VI) in real sample matrices. Sample

Certified values L-1

Detected (n = 3) Se (IV) 0.98±0.1 mg L-1

Se (VI) ˂ LOD c

GBW(E)080395

1.0 mg

Dietary supplement

23.7 µg tablet-1

25.8±2.2 µg tablet-1

˂ LOD c

14.1±0.3 μg L-1a

˂ LOD b

13.7±2.7 μg L-1

Mineral water a

Detected by HG-AFS; b LOD for Se(IV) with 10 mL sample consumption: 0.007 mg L-1; c LOD for Se(VI) with 10 mL sample consumption: 0.006 mg L-1.



4. Conclusion A green, selective and direct speciation colorimetric assay for inorganic selenium [Se(IV) and Se(VI)] was developed, utilizing a system combining PVG with unmodified AuNPs. Sample matrixes such as high salinity, and other coexisting metal elements were successfully separated by a gas-liquid separator, resulting in an interference-free assay. Without photocatalyst (nano-TiO2), only Se(IV) was reduced to H2Se thus detectable, while both Se(VI) and Se(IV) signals were recorded in the presence of nano-TiO2, realizing a facile and direct speciation analysis. The proposed method was successfully applied for the sensitive determination of Se(IV) and Se(VI) in water samples and dietary supplement with external calibration quantification. Considering the versatility of nanoparticles synthesis and surface-functionalization, the proposed method is potentially applicable for the colorimetric assay of other PVG-forming elements.

Acknowledgment National Natural Science Foundation of China (No. 21205007), Sichuan Youth Science and Technology Foundation (No.2017JQ0043), China Postdoctoral Science Foundation (No. 2016M590870 and No. 2018T110952), State Key Laboratory of Geohazard Prevention and Geoenviroment Protection Independent Research Project (SKLGP2016Z006), and the Education Department of Sichuan Province (Grant No. 17ZA0040) are acknowledged for their financial support.


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Supporting Information Effect of adding Se(IV) and Se(VI) directly into AuNPs solution, XPS spectra of AuNPs, Effect of UV wavelength, Effect of the flow rate of Ar carrier gas, effect of the reaction time, Selectivity and influence of interferences against co-existing ions for Se (IV) detection, and selectivity and influence of interferences against co-existing ions for total Se detection without or with nano-TiO2 based separation prior to analysis, Effect of the pH value on adsorption of

Se(IV) and Se(VI) on nano-TiO2.

References 1. Chen, Y. P.; Xianyu, Y. L.; Jiang, X. Y., Surface modification of gold nanoparticles with small molecules for biochemical analysis. Accounts Chem. Res. 2017, 50, (2), 310-319. 2. Ong, Q.; Luo, Z.; Stellacci, F., Characterization of ligand shell for mixed-ligand coated gold nanoparticles. Accounts Chem. Res. 2017, 50, (8), 1911-1919. 3. Xu, J. X.; Siriwardana, K.; Zhou, Y. D.; Zou, S. L.; Zhang, D. M., Quantification of gold nanoparticle ultraviolet-visible extinction, absorption, and scattering cross-section spectra and scattering depolarization spectra: the effects of nanoparticle geometry, solvent composition, ligand functionalization, and nanoparticle aggregation. Anal. Chem. 2018, 90, (1), 785-793. 4. Elghanian, R.; Storhoff, J. J.; Mucic, R. C.; Letsinger, R. L.; Mirkin, C. A., Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles. Science 1997, 277, (5329), 1078-81. 5. Tan, Z. Q.; Liu, J. F.; Liu, R.; Yin, Y. G.; Jiang, G. B., Visual and colorimetric detection of Hg2+ by cloud point extraction with functionalized gold nanoparticles as a probe. Chem. Commun. 2009, (45), 7030-7032. 6. Tan, Z. Q.; Liu, J. F.; Yin, Y. G.; Shi, Q. T.; Jing, C. Y.; Jiang, G. B., Colorimetric Au nanoparticle probe for speciation test of arsenite and arsenate inspired by selective interaction between phosphonium ionic liquid and arsenite. ACS Appl. Mater. Interfaces 2014, 6, (22), 19833-19839. 7. Fang, C.; Dharmarajan, R.; Megharaj, M.; Naidu, R., Gold nanoparticle-based optical sensors for selected anionic contaminants. Trac-Trends Anal. Chem. 2017, 86, 143-154. 8. Liu, R.; Liu, X.; Tang, Y. R.; Wu, L.; Hou, X. D.; Lv, Y., Highly sensitive immunoassay based on immunogold-silver amplification and inductively coupled plasma mass spectrometric detection. Anal. Chem. 2011, 83, (6), 2330-2336. 9. Storhoff, J. J.; Lucas, A. D.; Garimella, V.; Bao, Y. P.; Muller, U. R., Homogeneous detection of unamplified genomic DNA sequences based on colorimetric scatter of gold nanoparticle probes. Nat. Biotechnol. 2004, 22, (7), 883-887. 10. Li, B. Y.; Li, X. Z.; Dong, Y. H.; Wang, B.; Li, D. Y.; Shi, Y. M.; Wu, Y. Y., Colorimetric



sensor array based on gold nanoparticles with diverse surface charges for microorganisms identification. Anal. Chem. 2017, 89, (20), 10639-10643. 11. Al-Johani, H.; Abou-Hamad, E.; Jedidi, A.; Widdifield, C. M.; Viger-Gravel, J.; Sangaru, S. S.; Gajan, D.; Anjum, D. H.; Ould-Chikh, S.; Hedhili, M. N.; Gurinov, A.; Kelly, M. J.; El Eter, M.; Cavallo, L.; Emsley, L.; Basset, J. M., The structure and binding mode of citrate in the stabilization of gold nanoparticles. Nat. Chem. 2017, 9, (9), 890-895. 12. Cao, G.; Xu, F.; Wang, S.; Xu, K.; Hou, X.; Wu, P., Gold nanoparticle-based colorimetric assay for selenium detection via hydride generation. Anal Chem 2017, 89, (8), 4695-4700. 13. Sturgeon, R. E., Photochemical vapor generation: a radical approach to analyte introduction for atomic spectrometry. J. Anal. At. Spectrom. 2017, 32, (12), 2319-2340. 14. Guo, X. M.; Sturgeon, R. E.; Mester, Z.; Gardner, G. J., UV vapor generation for determination of selenium by heated quartz tube atomic absorption spectrometry. Analytical Chemistry 2003, 75, (9), 2092-2099. 15. Mo, J.; Li, Q.; Guo, X.; Zhang, G.; Wang, Z., Flow injection photochemical vapor generation coupled with miniaturized solution-cathode glow discharge atomic emission spectrometry for determination and speciation analysis of mercury. Anal. Chem. 2017, 89, (19), 10353-10360. 16. Gao, Y.; Sturgeon, R. E.; Mester, Z.; Hou, X.; Yang, L., Multivariate optimization of photochemical vapor generation for direct determination of arsenic in seawater by inductively coupled plasma mass spectrometry. Anal. Chim. Acta 2015, 901, 34-40. 17. Zheng, C. B.; Ma, Q.; Wu, L.; Hou, X. D.; Sturgeon, R. E., UV photochemical vapor generation-atomic fluorescence spectrometric determination of conventional hydride generation elements. Microchem J. 2010, 95, (1), 32-37. 18. Yu, Y.; Jia, Y.; Shi, Z.; Chen, Y.; Ni, S.; Wang, R.; Tang, Y.; Gao, Y., Enhanced photochemical vapor generation for the determination of bismuth by inductively coupled plasma mass spectrometry. Anal. Chem. 2018. 2018, 90, 22, 13557-13563. 19. Gao, Y.; Sturgeon, R. E.; Mester, Z.; Hon, X. D.; Zheng, C. B.; Yang, L., Direct Determination of trace antimony in natural waters by photochemical vapor generation icpms: method optimization and comparison of quantitation strategies. Anal. Chem. 2015, 87, (15), 7996-8004. 20. Duan, H. L.; Gong, Z. B.; Yang, S. F., Online photochemical vapour generation of inorganic tin for inductively coupled plasma mass spectrometric detection. J. Anal. At. Spectrom. 2015, 30, (2), 410-416. 21. Xu, F.; Zou, Z.; He, J.; Li, M.; Xu, K.; Hou, X., In situ formation of nano-CdSe as a photocatalyst: cadmium ion-enhanced photochemical vapour generation directly from Se(vi). Chem. Commun. 2018, 54, (38), 4874-4877. 22. He, H.; Peng, X.; Yu, Y.; Shi, Z.; Xu, M.; Ni, S.; Gao, Y., Photochemical vapor generation of tellurium: synergistic effect from ferric ion and nano-TiO2. Anal. Chem. 2018, 90, (9), 5737-5743. 23. Gao, Y.; Xu, M.; Sturgeon, R. E.; Mester, Z.; Shi, Z. M.; Galea, R.; Saull, P.; Yang, L., Metal ion-assisted photochemical vapor generation for the determination of lead in environmental samples by Multicollector-ICPMS. Anal. Chem. 2015, 87, (8), 4495-4502. 24. Zheng, C.; Yang, L.; Sturgeon, R. E.; Hou, X., UV photochemical vapor generation sample introduction for determination of ni, fe, and se in biological tissue by isotope dilution ICPMS. Anal. Chem. 2010, 82, (9), 3899. 25. Nobrega, J. A.; Sturgeon, R. E.; Grinberg, P.; Gardner, G. J.; Brophy, C. S.; Garcia, E. E., UV photochemical generation of volatile cadmium species. J. Anal. At. Spectrom. 2011, 26, (12), 2519-2523.


Page 24 of 27

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


26. Zhu, Z. L.; He, D.; Huang, C. Y.; Zheng, H. T.; Zhang, S. C.; Hu, S. H., High-efficiency photooxidation vapor generation of osmium for determination by inductively coupled plasma-optical emission spectrometry. J. Anal. At. Spectrom. 2014, 29, (3), 506-511. 27. Šoukal, J.; Sturgeon, R. E.; Musil, S., Efficient photochemical vapor generation of molybdenum for ICPMS Detection. Anal. Chem. 2018, 90, (19), 11688-11695. 28. Hu, J.; Sturgeon, R. E.; Nadeau, K.; Hou, X. D.; Zheng, C. B.; Yang, L., Copper ion assisted photochemical vapor generation of chlorine for its sensitive determination by sector field inductively coupled plasma mass spectrometry. Anal. Chem. 2018, 90, (6), 4112-4118. 29. Sturgeon, R. E., Detection of bromine by ICP-oa-ToF-MS following photochemical vapor generation. Anal. Chem. 2015, 87, (5), 3072-3079. 30. Grinberg, P.; Sturgeon, R. E., Photochemical vapor generation of iodine for detection by ICP-MS. J. Anal. At. Spectrom. 2009, 24, (4), 508-514. 31. Yu, H. M.; Zheng, C. B.; Jiang, X. M.; Wu, X.; Hou, X. D., On-line chemical vapor generation for determination of total sulfur dioxide in wine samples using an atomic fluorescence spectrometer. J. Anal. At. Spectrom. 2018, 33, (2), 161-167. 32. Li, H. M.; Luo, Y. C.; Li, Z. X.; Yang, L. M.; Wang, Q. Q., Nanosemiconductor-based photocatalytic vapor generation systems for subsequent selenium determination and speciation with atomic fluorescence spectrometry and inductively coupled plasma mass spectrometry. Anal. Chem. 2012, 84, (6), 2974-2981. 33. Nováková, E.; Linhart, O.; Červený, V.; Rychlovský, P.; Hraníček, J., Flow injection determination of Se in dietary supplements using TiO2 mediated ultraviolet-photochemical volatile species generation. Spectrochim. Acta B 2017, 134, 98-104. 34. Shih, T. T.; Lin, C. H.; Hsu, I. H.; Chen, J. Y.; Sun, Y. C., Development of a titanium dioxide-coated microfluidic-based photocatalyst-assisted reduction device to couple high-performance liquid chromatography with inductively coupled plasma-mass spectrometry for determination of inorganic selenium species. Anal. Chem. 2013, 85, (21), 10091-10098. 35. Sun, Y. C.; Chang, Y. C.; Su, C. K., On-line HPLC-UV/nano-TiO2-ICPMS system for the determination of inorganic selenium species. Anal. Chem. 2006, 78, (8), 2640-2645. 36. Jia, J.; Long, Z.; Zheng, C.; Wu, X.; Hou, X., Metal organic frameworks CAU-1 as new photocatalyst for photochemical vapour generation for analytical atomic spectrometry. J. Anal. At. Spectrom. 2015, 30, (2), 339-342. 37. Gao, X. Y.; Zhang, J. S.; Zhang, L., Hollow sphere selenium nanoparticles: Their in-vitro anti hydroxyl radical effect. Adv. Mater. 2002, 14, (4), 290-293. 38. Zhang, S.; Luo, H.; Peng, M.; Tian, Y.; Hou, X.; Jiang, X.; Zheng, C., Determination of Hg, Fe, Ni, and Co by miniaturized optical emission spectrometry integrated with flow injection photochemical vapor generation and point discharge. Anal. Chem. 2015, 87, 21, 10712-10718 39. de Jesus, H. C.; Grinberg, P.; Sturgeon, R. E., System optimization for determination of cobalt in biological samples by ICP-OES using photochemical vapor generation. J. Anal. At. Spectrom. 2016, 31, (8), 1590-1604. 40. Zou, Z. R.; Tian, Y. F.; Zeng, W.; Hou, X. D.; Jiang, X. M., Effect of variable ultraviolet wavelength and intensity on photochemical vapor generation of trace selenium detected by atomic fluorescence spectrometry. Microchem. J. 2018, 140, 189-195. 41. Campanella, B.; Menciassi, A.; Onor, M.; Ferrari, C.; Bramanti, E.; D'Ulivo, A., Studies on photochemical vapor generation of selenium with germicidal low power ultraviolet mercury lamp.



Spectrochim. Acta B 2016, 126, 11-16. 42. Gong, L. L.; Du, B. B.; Pan, L.; Liu, Q. J.; Yang, K. H.; Wang, W.; Zhao, H.; Wu, L.; He, Y. J., Colorimetric aggregation assay for arsenic(III) using gold nanoparticles. Microchim. Acta 2017, 184, (4), 1185-1190. 43. Wang, X. K.; Wei, Y. Q.; Wang, S. S.; Chen, L. X., Red-to-blue colorimetric detection of chromium via Cr (III)-citrate chelating based on Tween 20-stabilized gold nanoparticles. Colloid Surf. A-Physicochem. Eng. Asp. 2015, 472, 57-62. 44. Novakova, E.; Rybinova, M.; Hranicek, J.; Rychlovsky, P.; Cerveny, V., Comparison of interference in chemical, electrochemical and UV-photochemical generation methods of volatile Se species. J. Anal. At. Spectrom. 2018, 33, (1), 118-126. 45. Rybinova, M.; Musil, S.; Cerveny, V.; Vobecky, M.; Rychlovsky, P., UV-photochemical vapor generation of selenium for atomic absorption spectrometry: Optimization and Se-75 radiotracer efficiency study. Spectrochim. Acta B 2016, 123, 134-142. 46. Gao, Y.; Sturgeon, R. E.; Mester, Z.; Pagliano, E.; Galea, R.; Saull, P.; Hou, X.; Yang, L., On-line UV photochemical generation of volatile copper species and its analytical application. Microchem. J. 2016, 124, 344-349. 47. Jiang, X.; Huang, K.; Deng, D.; Xia, H.; Hou, X.; Zheng, C., Nanomaterials in analytical atomic spectrometry. Trac-Trends Anal. Chem. 2012, 39, 38-59. 48. Belzile, N.; Chen, Y. W., Tellurium in the environment: A critical review focused on natural waters, soils, sediments and airborne particles. Appl. Geochem. 2015, 63, 83-92. 49. Huang, C. Z.; Hu, B.; He, M.; Duan, J., Organic and inorganic selenium speciation in environmental and biological samples by nanometer-sized materials packed dual-column separation/preconcentration on-line coupled with ICP-MS. J. Mass Spectrom. 2008, 43, (3), 336-345. 50. Lafuente, J. M. G.; Sanchez, M. L. F.; SanzMedel, A., Speciation of inorganic selenium and selenoaminoacids by on-line reversed-phase high-performance liquid chromatography focused microwave digestion hydride generation atomic detection. J. Anal. At. Spectrom. 1996, 11, (12), 1163-1169. 51. Liang, J.; Wang, Q. Q.; Huang, B. L., Electrochemical vapor generation of selenium species after online photolysis and reduction by UV-irradiation under nano TiO2 photocatalysis and its application to selenium speciation by HPLC coupled with atomic fluorescence spectrometry. Anal. Bioanal. Chem. 2005, 381, (2), 366-372. 52. Kozak, L.; Rudnicka, M.; Niedzielski, P., Determination of inorganic selenium species in dietary supplements by hyphenated analytical system HPLC-HG-AAS. Food Anal. Method. 2012, 5, (6), 1237-1243. 53. Liang, L.; Mo, S.; Zhang, P.; Cai, Y.; Mou, S.; Jiang, G.; Wen, M., Selenium speciation by high-performance anion-exchange chromatography-post-column UV irradiation coupled with atomic fluorescence spectrometry. J. Chromatogr. A 2006, 1118, (1), 139-143. 54. Zheng, C. B.; Wu, L.; Ma, Q.; Lv, Y.; Hou, X. D., Temperature and nano-TiO2 controlled photochemical vapor generation for inorganic selenium speciation analysis by AFS or ICP-MS without chromatographic separation. J. Anal. At. Spectrom. 2008, 23, (4), 514-520.


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For TOC only


Photochemical Vapor Generation for Colorimetric Speciation of

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