Photochemical Vapor Generation of Tellurium: Synergistic Effect from

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Photochemical Vapor Generation of Tellurium: Synergistic Effect from Ferric Ion and Nano-TiO2 Hongyan He, Xiuhong Peng, Ying Yu, Zeming Shi, Mo Xu, Shijun Ni, and Ying Gao Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 03 Apr 2018 Downloaded from http://pubs.acs.org on April 3, 2018

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Analytical Chemistry

Photochemical Vapor Generation of Tellurium: Synergistic Effect from Ferric Ion and Nano-TiO2

Hongyan He a,b, Xiuhong Peng* b, Ying Yu b, Zeming Shi b, Mo Xu a, Shijun Ni b and Ying Gao* a,b a: State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China b: College of Earth Sciences, Chengdu University of Technology Chengdu, Sichuan 610059, China.

*Corresponding authors: Y Gao ([email protected]); X Peng ([email protected])

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Analytical Chemistry 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

ABSTRACT Photochemical vapor generation (PVG) is emerging as a promising analytical tools for Te determination, thanks to its efficient matrix separation, and simple and green procedure. However, the low PVG generation efficiency of Te is the bottleneck for its wide application in environmental samples containing trace Te. Herein, we reported a high efficient PVG for Te determination by synergistic effect of ferric ion and nano-TiO2. The analytical sensitivity was enhanced approximately 15-fold for Te(IV) in the presence of both ferric ions and nano-TiO2, comparing to conventional PVG. Besides, the use of nano-TiO2 can provide Te(VI) and Te(IV) an equal and high PVG efficiency in the presence of ferric ions, owned to the high photocatalytic performance of TiO2 under short-wavelength UV irradiation (254 and 185 nm). Under the optimized experimental conditions, a detection limit of 1.0 ng L-1 was obtained. The precision of replicate measurements was 2.3% (RSD, n=7) at 0.5 µg L-1 for Te(IV). The methodology was validated by successful determination of Te in surface waters and two standard reference sediment samples. To our best knowledge, this is the first report of the synergistic enhancement of transitional metal ions and nano-TiO2 in PVG, which possesses potential for highly sensitive determination of vapor-forming elements.

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INTRODUCTION Tellurium (Te) is regarded as a toxic element for humans, which can affect various organs1-3. Te receives great attention due to its optoelectronic and thermal properties, which has been widely used in industrial applications, new materials development and fluorescent probes production4. Thus the potential risks of humans exposing to tellurium is increasing. Due to unique feature of Te to form volatile species, photochemical vapor generation (PVG) is emerging as a promising analytical tools for its determination5-7. PVG utilizes free radicals as reductants, which is generated by photodecomposition of low molecular weight organic compounds (LMWOCs)5,8. PVG can efficiently separate analyte from troublesome sample matrix, and provide a very simple and green procedure for chemical vapor generation9-17. However, the low PVG generation efficiency of Te often limits its wide application in environmental samples with trace Te levels7,18. Recently, we found PVG generation efficiency can be significantly enhanced by transition metal ions. In the presence of Co2+ and Ni2+, an obvious efficiency improvement was found for Pb PVG19, which has been successfully applied in sensitive determination of Pb in environmental certified reference materials with a detection limit of 0.005 ng g-1. A quite similar phenomena was also discovered for As determination in the presence of Fe3+ by Wang et al20. Besides, the species-depended PVG generation was found for As measurement, as only As(III) PVG reduction could be enhanced by ferric ions20. The prereduciton of As(V) was a prerequisite for total As determination, which increases the possibility of analyte loss and contamination making the analysis process more complicated. On the other hand, nano-TiO2, an efficient photocatalyst for organic pollutants and heavy metals removal21,22, was applied in PVG for Se analysis to enhance the vapor generation efficiency of Se(VI)23. The generated electrons of nano-TiO2 (conduction band) can 3



reduce Se(VI) and convert it to volatile species under UV irradiation5. The decoration of TiO2 with noble metal or noble metal nanoparticles can notably improve the PVG efficiencies of Se and As including their high valence species24,25. Alternatively, the use of TiO2 under short-wavelength (254 nm and 185 nm) UV irradiation can greatly improve the catalytic performance of TiO2 and enhanced the photodegradation efficiencies of volatile organic compounds 26. Herein, enlightened by the above-mentioned phenomena, a highly sensitive Te PVG assay was developed after the synergistic enhancement of transitional metal ions and nano-TiO2. The PVG was carried out under short-wavelength UV irradiation (254 nm and 185 nm), in the presence of ferric ion and photocatalytic nano-TiO2. The ferric ion enhances the signal intensity of Te(IV), while nano-TiO2 can further enhance the signal intensity and photo-reduce Te(VI) to Te(IV) in the presence of ferric ion. The risks of analyte loss and sample contamination during the traditional pre-reduction procedure are eliminated for Te determination. The main parameters potentially influencing PVG of Te and its transport efficiency to ICPMS were optimized, including the concentration of ferric species, nano-TiO2 and LMWOCs, irradiation time and Ar carrier gas flow rate. The accuracy of the proposed method is validated by the analysis of three surface waters and two sediment samples. To our best knowledge, this is the first report of synergistic enhancement of transitional metal ions and nano-TiO2 in PVG, which possesses potential for highly sensitive determination of vapor-forming elements.

EXPERIMENTAL SECTION Instrumentation An ICPMS (ELAN DRC-e, Perkin Elmer) affiliated with a quartz torch and an alumina sample

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injector tube was employed. A PVG-system was constructed to replace the nebulizer and spray chamber for tellurium determination. For the sample introduction for PVG system, a model IFIS-D injection pump (Xi’an Remex Analysis Instrument Co. Ltd., Xi’an, China) was used. A schematic of the PVG photo-reactor is shown in Figure 127. A 19 W flow-through UV lamp was used to construct the PVG (Beijing Titan Instruments Co.), which provides 185 nm and 254 nm irradiation. It was covered by aluminum foil to protect operators from the UV light irradiation. The carrier gas (argon) was flowed through a T-shaped tube and two gas-liquid separators (GLSs), maintained at 0 oC in an ice bath to avoid liquid droplets. The system parameters of ICPMS were performed as recommended by the manufacture. The experimental parameters for PVG system were optimized independently, as summarized in Table 1.

Figure 1. Schematic diagram of PVG-ICPMS system for the determination of Te. GLSs: gas liquid separators.

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Table 1. The experimental parameters of ICPMS instrument. Instrument settings

ICPMS

RF generator power

1175 w

Plasma gas flow

15 L min-1

Auxiliary argon gas flow

1.2 Lmin-1

Scanning mode

Peak hopping

Isotope monitored

130

Resolution

0.7 amu

Dwell time

30 ms

Dead time

50 ns

PVG Sample flow

4.0 mL min-1

PVG Ar carrier gas flow

0.95 L min-1

Te

Reagents All reagents were of at least analytical reagent grade. Deionized water (DIW) was used in all experiments. Formic acid and acetic acid of ACS grade were purchased from Aladdin Industrial Corporation (Shanghai, China). Stock solution of Te purchased from Environmental Express Corporation (South Carolina, USA) was used for sample analysis. The impact of Te species on PVG was investigated using solution of Te (IV) and Te(VI) . The 1000 µg L-1 Te (IV) and Te(VI) stock solutions were obtained by dissolving sodium tellurite (Aladdin Industrial Corporation, Shanghai, China) and sodium tellurate dehydrate (Sinopharm Chemical Reagent Corporation, Shanghai, China) in DIW respectively. The nano-TiO2 obtained from Aladdin Industrial Corporation (Shanghai, China) is anatase crystal and its particle size is about 10-25 nm. River water, tap water, and lake water were sampled from Chengdu, and stored in 0.2% (v/v) hydrochloric acid. Oxalic acid with a concentration of 2% (m/v), serving as the elution reagent, was prepared by dissolving solid oxalic acid in DIW.

Sample preparation A two-step oven vessel digestion method reported by Chen et. al. was used for the preparation of sediments samples GBW07303a and GBW07305a28. Briefly, 0.15 g subsamples of three replicates 6


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of each sediment were weighed into perfluoroalkoxy (PFA) vessels. Then 2.5 mL HNO3 and 1.0 mL HClO4 was added to each vessel, and the sample was digested for 90 min at 200 ℃ with the lid loosely capped. Subsequently, 1.5 mL of HF was added and the sample was digested for an additional 2 h at 200 ℃ with the lid tightly closed. After cooling, the digests were evaporated to near dryness at 200 ℃ to eliminate excess HF with the lid open. At the end, the digest was leached back and filled up to 10.0 mL with DIW. A 5-fold dilution of digests was prepared prior to nano-TiO2 based separation. The final pH of the diluted digests was 1.6. Three sample blanks were processed along with samples.

Implementation of Nano-TiO2 The separation of sample matrix by nano-TiO2 was carried out based on previous report29. Briefly, 10.0 mL sample solution was added to a 10 mL centrifuge tube and followed by 50 mg TiO2. The suspension was stirred for 10 min to completely adsorb Te on the surface of nano-TiO2. The mixture was centrifuged at 4000 rpm for 10 min to efficiently deposit the TiO2 onto the bottom of the tube. Then the supernatant was discarded. Subsequently, the mixture solution of 20% (v/v) acetic acid, 2% (v/v) formic acid and 20.0 mg L-1 Fe2+ was added to the precipitated TiO2 to mark for the followed PVG. The nano-TiO2 slurry solution was dispersed uniformly by ultrasonic irradiation prior to analysis.

Analysis Procedure The sample solutions were subjected to PVG-ICPMS detection system as described before19. Briefly, the samples were delivered to the PVG reactor quickly with a sample flow of 4.0 mL min-1, and remained in the photo reactor for 50 s by stopping the pump to reduce Te into volatile species. Subsequently, the irradiated sample was transferred to the GLSs at the same sample flow rate for

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analyzing by ICPMS. For next analysis, a solution of 2% (m/v) oxalic acid followed by DIW was applied to clean the system efficiently to avoid any carry over. The peak area of the 130Te isotope was used to construct an external calibration curve for samples.

RESULTS AND DISCUSSION Metal Ion and Nano-TiO2 Synergistic Assisted PVG Transition metal ions assisted PVG strategy was reported in our recent paper

19

. A significant

improvement in PVG efficiency of Pb is achieved in the presence of transition metal ions (Co2+ and Ni2+). Enlightened by this phenomena, a preliminary screening of transitional metal ions (Co2+, Ni2+, Fe2+, and Fe3+) was performed in our laboratory to enhance PVG efficiency of Te(IV), among which iron ions (both Fe2+ and Fe3+) provide the best results. The effects of Fe2+ and Fe3+ as enhancement reagents to the Te PVG efficiency were thus studied in detail. As shown in Figure 2a, a relatively weak response was obtained without iron ions, which was no more than one fifth of the highest signal response. With the increasing of the Fe2+/Fe3+ concentration from 0 to 15.0 mg L-1, the PVG efficiencies increased quickly, and then leveled off above 20.0 mg L-1. When ferric ions was added, the UV absorption intensity of PVG solution (below 250 nm) was obviously higher than that of the mixed acetic acid and formic acid, which may partly account for the increase in PVG yields of analytes5,20. The similar enhancement effects of Fe2+ and Fe3+ on photochemical reduction of Te may due to the co-reduction of volatile Fe and Te. Both Fe2+ and Fe3+ can be efficiently transferred to volatile iron species under UV irradiation in the presence of high concentration of formic acid30. However, volatile iron species were also generated in the mixture of 20% (v/v) AA and 2% (v/v) FA. The signal response of iron increased linearly with increasing concentration of ferric ion, but the PVG efficiency was rather low compared to the system using high concentration of formic acid. 8


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Interestingly, a serious interference from trace Te(IV) was reported for the PVG30 of Fe3+ , resulting in the largely decrease of signal response for Fe. The depression of Fe signal response was also observed when As3+ was added to the PVG system of Fe30, in contrast the addition of ferric species into PVG solution of As can greatly enhance the generation efficiency 20 of As3+. It is speculated that the intermediate products of photochemical reduction of iron can facilitate the PVG reaction of Te and enhance charge transfer reactions of photochemical reduction of Te. In this work, a 20.0 mg L−1 Fe2+ solution was chosen to assist Te PVG for subsequent experiments.

Figure 2. The enhancement effect of transitional metal ions and nano-TiO2. a, the effect of the concentrations of Fe2+ and Fe3+ on PVG-ICPMS response from 2.0 µg L−1 standard solutions of Te(IV); Experimental conditions: 50 s irradiation time, and 20% (v/v) acetic acid and 2% (v/v) formic acid. b, the effect of nano-TiO2 concentration on 9



PVG-ICP MS response from 2.0 µg L−1 standard solutions of Te(IV) and Te(VI). Experimental conditions: 20.0 mg L-1 Fe2+, 50 s irradiation time, and 20% (v/v) acetic acid and 2% (v/v) formic acid.

Te mainly exists as Te(IV) and Te(VI) in geological samples and natural waters 4. To determine total Te, prereduction of Te(VI) to Te(IV) is often used, which increases the possibilities of analyte contamination and loss. The comparison of responses from Te(IV) and Te(VI) by PVG-ICPMS system in the presence of Fe2+ was investigated in our preliminary study. The response of Te(VI) was less than 15% of that from photochemical reduction of Te(IV) under the same conditions. It is reported that the use of nano-TiO2 can enhance the PVG efficiency of Se(VI)23,25. Therefore, the influences of nano-TiO2 on the reduction of Te(VI) to Te(IV)were investigated in the presence of 20.0 mg L-1 of Fe2+ in our lab. As shown in Figure 2b, PVG efficiency of Te(VI) was initially sharply enhanced as nano-TiO2 content increased from 0 to 5.0 g L-1, thereafter, the improvement was minimal. The signal response of Te(IV) also greatly increased with increasing nano-TiO2 concentration from 0 to 5.0 g L-1. The analytical sensitivity was enhanced approximately 15-fold for Te(IV) in the presence of 5.0 g L-1 nano-TiO2 and 20.0 mg L−1 Fe2+, comparing to conventional PVG. While for Te(VI), the signal was increased from very low sensitivity (5% of Te(IV)) to equal to Te(IV). The PVG of Te may follow a mechanism similar to that of Se as proposed by Sturgeon and Grinberg5,31. A redox of Te(IV) by hydrated electron (derived from the photodecomposition of formic/acetic acid) or the electron at the conduction band of nano-TiO2 produced (e-cb) under UV irradiation may occur. The reduced intermediate of Te was subsequently attacked by photochemically generated radicals, accounting for the PVG of Te(IV)5,25,31. For the PVG of Te(VI), the reduction of Te(VI) with e-cb into Te(IV) may occur firstly5,31.The vacuum UV irradiation can largely enhance the photocatalytic activity of nano-TiO2 and produce abundant photo-generated electrons/ reducing radicals for the photochemical reduction of Te(VI) and Te(IV)26,32. Besides, the addition of ferric ions 10


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can largely eliminate the serious interference form trace Cu2+, which was discussed in detail later. Thus the 5.0 g L-1 nano-TiO2 and 20.0 mg L−1 Fe2+ solution was selected to assist Te PVG.

Optimization of Experimental Conditions PVG efficiencies of elements highly depend on the concentration and type of organic acids of low molecular weight (LMWOAs )7,33,34. Acetic acid and formic acid are the most widely used LMWOAs in PVG system for photochemical reduction of inorganic elements. The effects of acetic acid and formic acid concentrations on the responses of Te were investigated, respectively. As shown in Figure 3a, the PVG of volatile Te was more efficient in acetic acid system. Signal response initially increased sharply with the acetic acid concentration increased from 0% (v/v) to 10% (v/v). Thereafter, the further improvement was minimal. The efficient reduction of Te(IV) in the absence of ferric ions were found to occur at highly acidic condition with acetic acid greater than 40% (v/v), which further confirm the enhancement effect of Fe2+ for the photochemical reduction of Te(IV). Therefore, 20% (v/v) of acetic acid was selected for subsequent studies.

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Figure 3. The optimization of experimental conditions for Te determination in the presence of 20 mg L-1 Fe2+ and 5 g L-1 TiO2: a, the concentrations of acetic acid and formic acid; b, the concentrations of formic acid in mixed acids; c, the irradiation time; d, the carrier argon flow rate.

PVG efficiency of arsenic was reported to be efficiently enhanced by using a mixture of LMWOAs

6,8

. The effect formic acid and acetic acid mixture on the Te PVG efficiency was studied.

As shown in Figure 3b, by choosing acetic acid at 20% (v/v), approximate 40% improvement was obtained when formic acid was added between 2%-5% (v/v). The improvement is likely attributed to that more reactive radical species are available from photodecomposition of formic acid as well as the interaction between formic acid and ferric ions under UV irradiation6,30. Thus, a mixture of 20% (v/v) acetic acid with 2% (v/v) formic acid was selected for subsequent experiments. The irradiation time is another crucial parameter impacting the PVG efficiency of elements. The influence of UV irradiation time of 10-80 s was investigated using 2 µg L-1 Te standard solution. As 12


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shown in Figure 3c, responses initially increased significantly by the increase of UV irradiation time from 10 s to 50 s, thereafter the signal improvement was minimal. Slight decrease was observed beyond 70 s probably because of the decomposition of the produced volatile species. Thus, the 50 s irradiation time was selected for the following studies. The carrier argon flow determines the GLS efficiency of volatile Te as well as the ICP sampling depth. As shown in Figure 3d, its influence on signal intensity of 2 µg L-1 Te in mixed acid medium was optimized from 0.85 to 1.10 L min-1. The optimum carrier argon gas flow was found to be 0.95 L min-1. Lower gas flow causes low transfer efficiency of volatile Te species, and higher gas flow results in the volatile species dilution. Thus, an argon gas flow of 0.95 mL min-1 was selected for subsequent studies.

Interference Study The potential interferences were studied using 0.5 µg L−1 Te in this work. As shown in Table 2, the influence from 1.0 mg L-1 K+, Ca2+, Na+, Mg2+ and Zn2+ standard solutions was negligible. And there were no significant interferences from 0.5 mg L-1 Ni2+, Co2+ and Mn2+. Anion ions including 50.0 mg L-1 NO3-, Cl-, PO43- and SO42- had no obvious effect on the determination of Te. However, 0.5 mg L-1 Cu2+ caused severe interference for the measurement of Te in the present of ferric ions. To investigate the possible mechanism effects of Cu2+ on the determination of Te, a study was performed to measure Te response after PVG using high concentration of copper (0.5 mg L-1) without ferric ions. The recovery was only 28%, showing no obvious difference between the recoveries with or without iron ions. However, the interference caused by trace Cu (0.020 mg L-1) was found to be serious without adding iron ions, which was also found in HG for Te determination28,35-37. The recovery of Te(IV) in the presence of 0.020 mg L-1 Cu2+ without ferric ions 13



was only 50% in the PVG system, while it was 105% when 20.0 mg L-1 Fe2+ was added. The formation of a charge neutral tellurium copper colloidal compound during the PVG procedure may occur as in the case of HG28,37. Probably similar to HG of Te, a preferential reduction of iron may happen before reduction of copper ions in the presence of ferric ions in PVG system36, resulting in the elimination of the serious interference from trace Cu2+. As reported before, Cu2+ don’t caused significant interference for the photochemical reduction of Fe30. In addition, the interferences from the hydride forming elements for Te measurement were investigated. The addition of 0.5 mg L-1As standard solutions didn’t cause obvious influence for Te determination. In the presence of 0.5 mg L-1 of Se, Bi and Sb, slight interferences were observed. But 0.5 mg L-1 Hg2+ caused a sharp decrease in the peak area signal of Te in this PVG system. According to previous report, nano-TiO2 can be used as the absorbent for separating Se and Te from aqueous solution38. Quantitative sorption (at least 97% ) of Te from aqueous solution by nano-TiO2 was reported38. To eliminate the interferences from coexisting metal ions, nano-TiO2 based separation was carried out before analysis. As a result, the interferences from Cu2+ as well as other potential coexisting ions in sample matrix were greatly alleviated as shown in Table 2. Thiourea was found to be the best masking reagent in HG for Te determination28. But when Cu2+ concentration is more than 2000 times of that for Te, the masking capacity dropped remarkably (with 65% recovery), even with increased concentration of thiourea28. In this work, 90% recovery of Te was obtained after TiO2 separation when 5.0 mg L-1 Cu2+ was added (up to 10000 times concentration of Te), showing the possibility of the developed method for the analysis of complicated samples.

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Table 2. The effect of coexisting substances. Interfering

Concentration/

Ions Na

[Interferent]/[Te]

Recovery/%

-1

（ n=3））

mg L

+

1.0

2000

109±2

+

1.0

2000

103±2

Ca2+

1.0

2000

97±1

Mg2+

K

1.0

2000

109±2

2+

Zn

1.0

2000

110±1

Ni2+

0.5

1000

92±2

2+

0.5

1000

97±1

Mn

0.5

1000

90±3

Cu2+

0.1, 0.5, 5.0

200, 1000,10000

85±2, 39±3, 90±2a

Se

0.1, 0.5

200, 1000

104±2, 87±2

Bi

0.1, 0.5

200, 1000

90±2, 82±1, 94±2 b

As

0.1, 0.5

200, 1000

99±2, 95±3

Sb

0.1, 0.5

200, 1000

111±3, 126±2, 100±1 c, 111±2 d

0.1, 0.5

200, 1000

84±1, 53±3, 90±2 e

50.0

100000

90±1

Co

2+

Hg2+ NO3 Cl

-

-

50.0

100000

98±2

2-

50.0

100000

101±1

PO43-

50.0

100000

SO4 a

−1

2+

b

98±2 −1

Te recovery with 5 mg L of Cu after nano-TiO2 separation; Te recovery with 0.5 mg L of Bi after nano-TiO2 separation; c Te recovery

with 0.1 mg L−1 of Sb after nano-TiO2 separation; dTe recovery with 0.5 mg L−1 of Sb after nano-TiO2 separation; e Te recovery with 0.5 mg L−1 of Hg2+ after nano-TiO2 separation.

Analytical Figures of Merit and Sample Analysis The analytical figures of merit were evaluated under optimum experimental parameters. A 15-fold sensitivity enhancement was acquired by the proposed metal ion and nano-TiO2 synergistic assisted PVG. The vapor generation efficiency was found to be 91±2% by comparing the signal intensities of Te solutions before and after PVG from slurry sampling and HG-AFS detection. A relatively good precisions of 2.3% and 2.9% relative standard deviations (RSD) were obtained from 7 replicate measurements of 0.5 µg L-1 Te(IV) standard solution and 0.5 µg L-1 Te(℃) standard solution respectively (Figure 4). By measuring a series of standard solutions of Te(IV) and Te(VI) (0.02 µg L-1 to 5.0 µg L-1), the calibration curves were established. The linear regression coefficients 15



(R2) were 0.997 and 0.996, respectively. As shown in Figure 5, no obvious differences in sensitivity for Te(IV) and Te(VI) were realized, making direct determination of total Te feasible. A method limit of detection (LOD) of 1.0 ng L-1 for Te was obtained (3σ). The LOD of the proposed method is significantly improved, comparing with previous reports of Te vapor generation. As shown in Table 3, the current assay is among the most sensitive Te analysis techniques, due to the high efficiency of the synergistic assisted PVG system and powerful elemental sensitivity of ICPMS.

Figure 4. Repeat measurements of a 0.5 µg L-1 Te standard solution in 20% (v/v) acetic acid, 2% (v/v) formic acid and containing 20.0 mg L-1 Fe2+ and 5.0 g L-1 nano-TiO2 .

Figure 5. Calibration curves established by using the proposed method for Te(IV) and Te(VI).

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Three environmental water samples were analyzed to validate the proposed method. To eliminate the interference from Cu2+, nano-TiO2 based separation was carried out before analysis. External calibration method was applied and the result was shown in Table 4. To validate this method, a spike recovery test was carried out by adding 0.02 µg L-1 Te to the water samples. The spiked recoveries were from 95% to 110%. Furthermore, the proposed method was applied for the analysis of Te in two standard reference materials after nano-TiO2 based separation as shown in Table 5. There was no significant difference between the analytical results obtained from external calibration method and the reference values, demonstrating the feasibility of this method for the ultratrace Te determination in real samples. Table 3. Comparison of LODs. Method

Samples

Pre-concentration

LOD ng L-1

Reference

PVG-ICPMS

Water

-

1.0

This work

PVG-ICPMS

Alcoholic beverages

-

121

18

PVG-AFS

Water

-

80

7

EC-HG-AFS

Soldering tin

-

2200

39

HG-AAS

Geological standard reference

tungsten coil trapping

80

35

Dispersive liquid phase

0.56

40

materials ETV-ICPMS

Water

microextraction GF-AAS

Water

Co- precipitation

7

41

ET-AAS

Water

Hollow fiber liquid phase

4

42

microextraction

Table 4. The analytical results and recoveries of surface water samples. Sample

Measured µg L-1 a

Lake water

0.012±0.001 -1

Tap water

< 1 ng L

River water

0.010±0.001

a

Added µg L-1

Found µg L-1 a

Recovery %

0.020

0.031±0.003

95

0.020

0.020±0.002

100

0.020

0.032±0.002

110

Mean value ± standard deviation (n = 3).

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Table 5. The analytical results of sediment certified reference materials. Sample

Measured µg g-1 a

Reference value µg g-1

GBW07303a

0.083 ± 0.003

0.09

GBW07305a

0.28± 0.01

0.3

a

Mean value ± standard deviation (n = 3).

CONCLUSION A sensitive method was developed for the determination of total Te by PVG-ICPMS detection in a mixed acid medium. The addition of iron ions and nano-TiO2 can synergistically and efficiently improve the PVG efficiency of Te(IV) and Te(VI), making the direct measurement of the total Te feasible. Compared to conventional HG method, this technique is simple and largely decreases the risk of sample contamination and loss. This metal ion and nano-TiO2 synergistic assisted PVG method may have promising potential for the sensitive determination of other trace PVG elements.

ACKNOWLEDGMENT National Natural Science Foundation of China (No. 21205007), Sichuan Youth Science and Technology

Foundation

(No.2017JQ0043),

China

Postdoctoral

Science

Foundation

(No.2016M590870), 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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For TOC only

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Photochemical Vapor Generation of Tellurium: Synergistic Effect from

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