The determination and characteristics of trace arsenic(Ⅲ), total arsenic, antimony(III) and total antimony in water

Qiao Fengxia ^1,2, Sun Hanwen ¹, Yan Hongyuan^1,2 , Liang Shuxuan¹

( ¹Key Laboratory of Analytical Science and Technology of Heibei Province, College of Chemistry and Environmental Science, Hebei University, Baoding, 071002;  ²Department of Chemistry, Baoding Teacher's College, Baoding , 071051,China)

Received May 3, 2004; Supported by the Natural Science Foundation of Hebei Province for the project No.203110.

Abstract The determination and characteristics of trace arsenic(III), total arsenic, antimony(III) and total antimony in three kinds of water was investigated by a recommendatory method - simultaneous determination of trace Arsenic(III), total arsenic, antimony(III) and total antimony in water by interrupted injection-hydride generation atomic fluorescence spectrometry. The result showed that the ignored life wasted water had a potential harm to people.
Keywords Hydride generation; Atomic fluorescence spectrometry; Arsenic; Antimony; Characteristics

1 INTRODUCTION
The determination of trace arsenic and antimony, especially their species, has received increasing attention in environmental pollution studies. The toxicity of arsenic and antimony varies widely, ranging from highly hazardous inorganic species to relatively harmless organic species^[1]. As(III) is more toxic than As(V) , and Sb(III) is ten times more toxic than Sb(V). Therefore, from a toxicological point total concentration data are not sufficient and special studies have to be performed to assess the facing risk due to arsenic and antimony containing water.
    A simple, sensitive and accurate method was required for the determination of trace levels of arsenic and antimony in water, which directly affected the precision and accuracy. Recently some analytical methods had already been developed for arsenic and antimony analysis, such as DCP-AES^[2], ICP-MS^[3], HPLC-ICP-MS^[4], HG-AAS ^[5], HG-AFS^[6], of which the most popular and preferred one in terms of simplicity , sensitivity , precision , speed, and less expensive instrumentation is atomic spectral analysis ,especially HG-AFS. But the procedure of simultaneous determination of As and Sb determination was too complicate for application.
    We have proposed a new method for simultaneous determination of As and Sb by interrupted injection-hydride generation atomic fluorescence Spectrometry (HG –AFS), to study their dissolving capability and their assimilation at stomach and intestine acidity.^[7] Our aims of this work described here was to use this simple, sensitive, precise, speed and inexpensive technique for the simultaneous determination and characterization of arsenic and antimony species in water, which would help controlling and preventing from the pollution of As and Sb.

2 EXPERIMENTAL
2.1 Apparatus
A model AFS-230 double-channel nondispersive atomic fluorescence spectrometer (Beijing Haiguang Analytical Instrument Co., Beijing, China) equipped with As and Sb two hollow cathode lamps(general Research Institute of Non-Ferrous Metals, Beijing, China) was used for all the determinations. The operating parameters are given in Table 1.

Table 1 Instrument parameters and operating conditions

2.2 Reagents
All reagents used were of the highest available purity, and of at least analytical grade. Sub-boiling distilled water was used throughout this work.
    The As(III) standard stock solution , 1.000 g·L^-1.
    The Sb(III) standard stock solution, 1.000 g·L^-1.
    Working standard solutions of As(III), Sb(III) were prepared by stepwise dilution of the stock solutions just before use.
    The KBH₄ solutions were prepared daily by dissolving the reagent in 0.3% (m/v) sodium hydroxide solution. The L-cysteine solutions were prepared by dissolving the reagent in water.
2.3 Procedure
2.3.1 Sample pretreatment
The water sample was filtered through a 0.45μm membrane to get rid of solid substance. Adjusted acid concentration of hydrochloric acid was 0.02-0.06 mol·L^-1. They were kept at 4ºC before analysis.
2.3.2 Determination of arsenic and antimony species
An aliquot of the sample solution (1.0 mL), a 12.5 mL of L-cysteine solution, a 2.1 mL of hydrochloric acid (2.0 mol·L^-1) were mixed together, then diluted to 25.0 mL with water. This solution was set aside for 15 min at room temperature for the determination of total arsenic and total antimony by HGAFS
    A 1.0 mL of the sample solution was added into acetic acid-sodium acetate buffer solution to obtain a 25.0 mL sample solution (pH 5.0), then the concentration of As(III) and Sb(III) were determined directly by HG-AFS.

3 RESULTS AND DISCUSSION
3.1 Factors of As and Sb hydride generation
The affected hydride generation conditions such as reaction acidity, KBH4 concentration, prereductant of L-cysteine concentration and interferences was discussed in detail in the recommendatory method [7].
    1.5%(w/v) KBH₄ , 1.8%(w/v) L-cysteine, 0.17 mol·L^-1 sample acidity (HCl) and 0.35 mol·L^-1 carrier liquid acidity (HCl) were employed in this work, and pH5.0 was chosen for the selective determination of As(III) and Sb(III). A detection limit of 0.05mg·L^-1 ,0.02mg·L^-1 for As and Sb respectively.
3.2 Application to practical samples
The practical feasibility of the proposed system was tested on six water samples. Since standard reference materials with certified arsenic and antimony values were not available, the specificity and accuracy of the method were tested by standard spiking method: The recoveries were obtained by spiking the standard analyte solutions into the samples, so that the spiked concentrations of the analytes were similar to these in the original water. The recoveries were between 95.9% and 106% and RSD of 1.3-4.5%, which demonstrated the general reliability of the method. The results are listed in Table 2 and Table3.

Table 2. Determination of As(III) and Sb(III) in water samples

* Content in water sample; ND: not detected

Table 3 Determination of total As and total Sb in water samples

* Content in water sample; ND: not detected

    For the analysis of As and Sb, we divided the six kinds of water into three groups: drinking water(tap water, mineral water(1) and mineral water(2)), life-wasted water( Binhe water) and industry-wasted water (Chemical industry water and medical industry water)
    As Table 2 and 3 shown, this three groups of water have their own characteristics. For the life-wasted water, though the total content of As was not the highest, the percent of As³⁺ to total As was higher. For the element Sb, the total content of Sb was the highest in the three groups of water and the percent of Sb³⁺ to total Sb was much higher. This indicated that there is a potential harm still existing. We must pay much attention to the life-wasted water's treatment.
    For the industry-wasted water, the total content of As and Sb and the percentage of As³⁺ and Sb³⁺ were both higher. Though the total content of Sb³⁺ was lower than life wasted water, but its percentage was of the highest. Still the industry-wasted water required more effective controlled management.
    For drinking water, although in mineral (2) the percentage of As³⁺ was higher, from a whole point, both As and Sb and their species were listed in the lowest content.

4 CONCLUSIONS
In the past years, drinking water and industry water were more regarded by people with a series of protecting device. While life wasted water were neglected. It is an urgent task for us to take some effective measures for life-wasted water's treatment.

REFERENCES
[1] Zhang X, Cornelis R, Kimpe J D et al. Clin Chem, 1996, 42 (8):1231.
[2] Chen H W, Brindle I D, Le X C et al. Anal Chem, 1992, 64 (6): 667.
[3] Santosa S J, Mokudai H, Tanaka S. J Anal At Spectrom, 1997, 12 (4): 409
[4] Vanhaecke F, Moens L. Fresenius' Journal of Anal Chem, 1999, 364: 440.
[5] Ochsenkuhn-Petropulu M, Varsamis J, Parissakis G. Anal Chim Acta, 1997, 337: 323.
[6] Hou J, Gong Z B, Guo X M et al. Chinese Journal of Analysis Laboratory (Fen Xi Shi Yan Shi), 2000, 19 (6): 13.
[7] Sun H W, Qiao F X, Suo R et al. Analytica Chimica Acta, 2004, 505:255.

水体中的砷(Ⅲ)，总砷，锑(Ⅲ),总锑的测定及分布特征
乔凤霞^1,2 孙汉文¹ 闫宏远^1,2 梁淑轩¹
(1.河北省分析科学技术重点实验室, 河北大学化学与环境科学学院,保定 071002;  2.保定师范专科学校化学系，保定 071051)
摘要 采用断续流动进样-氢化物发生原子荧光光谱法同时测定痕量砷(Ⅲ)、总砷、锑(Ⅲ)、总锑的方法,研究了三类水样中砷(Ⅲ)、总砷、锑(Ⅲ)、总锑的含量及分布特征。结果表明：常被忽视的生活废水对人类存在着潜在的威胁。
关键词 氢化物发生；原子荧光光谱；砷；锑；特征