The distributable speciation analysis of arsenic in red tangerine peel

Wang Mengge, Qiao Fengxia, Yan Hongyuan, Tian Baojuan, Kang Yongsheng
(Department of Chemistry, Baoding Teacher's College, Baoding 071000, China)

Received Nov. 1, 2005.

Abstract Lipidic compounds and flavone compounds of red tangerine peel were extracted and separated by Soxhlet extraction method with petroleum aether and methanol as the extractive solvent. The element As in petroleum aether extract, methanol extract and residue's fibrin compounds was determined by HG-AFS. The result showed that the major arsenic species in red tangerine peel was lipidic compounds, fibrin compounds was the second. The content of As has not been detected in flavone compounds. The proposed method has a detection limit of 0.030mg·L^-1, while the sample detection limit was 0.039mg·g^-1.
Keywords Arsenic; speciation analysis; Red tangerine peel

1 INTRODUCTION
The red tangerine peel has the effect of removing sputum, resisting canker, strengthening immunity etc ^[1] . Arsenic is one of potential elements to human, animal and plants. The toxicity of arsenic varies widely, ranging from highly hazardous inorganic species to relatively harmless organic species. With the increasing concern on health, people pay much attention to the content and species of toxicity elements in Chinese herbs. Zhao et al. had given a review of the research progress of trace elements in traditional Chinese medicine ^[2]. Wang had determined eight elements in the flowers of Hylocereus Undatus by FAAS^[3]. Furthermore, in order to improve the sensitivity, some sensitization agents was used for the determination of trace toxic elements determination in Chinese herbs. Ascorbic acid and thiourea were employed for the determination of As Sb Se Hg in Chinese herbs of Qingzang tableland by AFS^[4]. L-cysteine was used as the prereductant for the determination of As and Sb species in Chinese herbs ^[5]. And thiourea citric acid was selected as a sensitization agent for the speciation analysis of mercury^[6]. At present, the toxic element's speciation analysis was a meaningful and potential work, it would help people reduce the poison to the lowest and the artifactitious products process will be more and more reasonable.
    The aim of this work was to analyze the distributable speciation of arsenic in red tangerine peel by HG-AFS. This would help to improve the level of artifactitious technics and detection of arsenic in red tangerine peel.

2 EXPERIMENTAL
2.1 Apparatus
A model AFS-610A atomic fluorescence spectrometer(Beijing Ruili Analytical Instrument Co., Beijing, China) equipped with As hollow cathode lamps was used for all the determinations. The operating parameters are given in Table1.

Table 1 The parameters of instrument working conditions

2.2 Reagents
All the reagents were of the highest available purity, and of at least analytical grade. Super-purity water was used thorough the work.
    The As(III) standard stock solution , 1.000 g·L^-1[GBW(E) 080283] was provided by China Central Office of Standard Substance. The KBH₄ solutions were prepared daily by dissolving the reagent in 0.5% (w/v) sodium hydroxide solution. The tartaric acid solution（200 g·L^{- 1}）and hydrochloric hydroxylamine100g·L^{- 1}）were prepared by dissolving the reagent in water.
2.3 Samples
Red tangerine peel was bought from the market.
2.4 Procedure
2.4.1 Sample pretreatment
Approximately 1.000g of dried red tangerine peel was accurately weighed and wrapped by filter paper, then at the temperature 60-90ºC,extracted by 90mL petroleum aether in Soxhlet extractor for 2-3 hours. The petroleum aether extracted solution was concentrated to about 10.0ml for the further work. The residue was extracted by 80ml methanol in Soxhlet extractor, until the extracted liquid was colorless. This methanol extracted liquid was dried in a blast desiccator at room temperature, and was transferred in 100 mL volumetric flask with 200g·L^-1 tartaric acid. The residue of methanol extracted and aether extracted solution were digested by HNO₃ and HCl(HNO₃ : HCl = 1:3) at lower temperature and transferred in 25mL volumetric flask with 200 g·L^{- 1} tartaric acid, and 1.0 mL 100g·L^{- 1} hydrochloric hydroxylamine was added, diluted to 25.0ml with tartaric acid. After over 10 minutes, the solution was directly used for the determination of As. At the same time, a sample blank determination of As was employed.
2.4.2 Working standard curve
Using 1.00mg·mL^-1 As standard solution with different amounts of 1.0, 0.10, 0.20, 0.30, 0.40, 0.60, 0.80, 1.00 ml was added in 10.0 ml volumetric flask respectively, and 1.0ml hydrochloric hydroxylamine （100g·L^{- 1}）added, diluted to 10.0ml with tartaric acid (200 g·L^-1 ), after over 10 min. These solutions were directly used for the working curve making.

3 RESULTS AND DISCUSSION
3.1 The parameters chosen for the instrument
The parameters of instrument such as lamp current, High voltage of PMT, carrier gas rate , were main factors which affect As fluorescence sensitivity greatly. The test data showed that at 60mA of lamps current, 300V of high voltage of PMT and 600 mL·min^-1 of carrier gas rate could get more stable and sensitive signal of As.
3.2 Effect of KBH₄ concentration
KBH₄ was used as both a reducer and a hydrogen supplier, which was necessary to sustain the argon-hydrogen flame. In this work, the effect of KBH₄ concentration was studied strictly, the test showed that the using of KBH₄ concentration of < 1.8%(w/v) has resulted in a more arsenic lower signal. When the use of the KBH₄ was >3%(w/v) , it may result in a vigorous production of arsines as well as the production of large quantities of hydrogen gas, which both can cause large signal instability and sensitivity decreasing. If it was in the range of 1.8 % to 3% (w/v), the signal was more stable and higher, so 2.0% KBH₄ was employed in this work.
3.3 Effect of the reacting acidity
In tartaric acid medium it can get a more sensitive, stable As signal by HG-AFS ^[7].
   With a 1.5% w/v KBH₄ as a reducer and a 1.0ml hydrochloric hydroxylamine (100g·L^-1)as the pre-reductant). The influence of the HCl concentration in the carrier liquid on fluorescence signal was investigated. In the range of 1.0-3.0 mol·L^-1HCl concentration, the signals increased with the HCl concentration increasing. While the HCl concentration was above 3.5 mol·L^-1, the signals showed a decreasing trend. So 3.0 mol·L^-1 HCl was employed in this work
3.4 Interference
In this work, the influences of common interferents on the fluorescence signals were investigated.1000-fold Al³⁺ ,V³⁺, Fe³⁺, Cu²⁺, Mn²⁺ and Co²⁺, 500-fold Ag⁺ ,Ni²⁺, Pb²⁺, Hg²⁺ Cd²⁺ have no obvious influence for the determinations of 10mg· L^-1 As .
3.5 Linearity and detection limits.
On the optimized conditions, the linearity can extend up to 60mg·L^-1, linear regression equation: Y = -7.04348 +15.50495X (Y: The relative fluorescence intensity; X concentration of As,unit:mg·L^-1) The detection limit(3s·k^-1 ，k: slope of linear equation)was 0.030mg·L^-1(r:>0.9996). The detection limit for As in red tangerine peel was 0.039mg·g^-1 .
3.6 The extraction optimization
70, 80, 90,100,110 mL petroleum aether was used as the extractive solvent for 1.000g dried red tangerine peel respectively. At the temperature 70℃, they were extracted in Soxhlet extractor for 3.0 hours. Then petroleum aether extracted solution was concentrated to about 10.0 mL, which was digested as the procedure 2.4.1 and the concentration As of them was anlyzed. The results were shown in Table2, which suggusted that when the volume of petroleum aether was up to 80mL,the content of As was stable. This indicated that the extraction was thoroughly. 90mL petroleum aether was applied in this work.
    After 1.0000 g samples was thoroughly getting rid of lipidic compounds ,it was extracted further by 70,80,90,100,110 mL methanol respectively as the procedure 2.4.1. The tolal flavone compounds content was determined for each methanol extracted solution by photometric method^[8]. The results were shown in Table2. It could be seen that the volume of 70 mL methanol had lower extracted ratio, other quantity of the other volume gave a similar extracted ratio. 80 mL methanol was used in this work.
    Extraction temperature and time was also investigated. When the temperature was up to 90ºC or the time delayed 1 hours, both As content and total flavone compounds extracted ratio were changed little. 70ºC was proposed for this work, and 3.0 hours and 6.0 hours were applied for petroleum aether and methanol extraction respectively.

Table2 The As content of petroleum aether extracted solution and total flavone compounds content of methanol extracted solution in red tangerine peel.

3.7 The speciation and distribution of As in red tangerine peel
The results of As species in red tangerine peel were listed in Table2.

Table 2 The analysis results of As species in red tangerine peel

It is known about that the petroleum aether is one of lipophilic reagents, so the content of As in petroleum aether represented the concentration of As in lipidic compounds of red tangerine peel. When the red tangerine peel was extracted by petroleum aether and methanol, the residue was mainly fibrin compounds, whose level of As indicated the content of arsenic species of fibrin compounds. While the As concentration of the methanol extracted solution indicated the level of as content in flavone compounds, it is shown that the major arsenic species in red tangerine peel was lipidic compounds. The second arsenic species was fibrin compounds. However, the arsenic compound content of flavone compounds, tangerine peel glycoside compounds and organic amine compounds, which were got from methanol extraction liquid, were very low that can not be detected. So in the artifactitious progress of red tangerine peel we must get ride of the lipidic compounds.

REFERENCES              
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[8] The pharmacopoeia committee of PRC. Pharmacopoeia of the people's republic of China 2005, Part 1. Beijing: Chemical Industry Press, 2005. 23.

陈皮中砷的分布形态分析
王孟歌 乔凤霞 闫宏远 田宝娟 康永胜
（保定师范专科学校 保定 071000）
摘要   以石油醚和甲醇为萃取剂，用索氏抽提取法从陈皮中分离出了脂类化合物和黄酮类化合物。用HG-AFS法测定了分离出的产物和残渣中的纤维素类化合物中的As元素含量，结果表明：陈皮中的砷主要以脂类化合物的形式存在，纤维素类化合物中含量次之；黄酮类化合物中未检测到As的存在。本文的检出限为0.030mg·L^-1，样品的检出限为0.039mg·g^-1
关键词  砷， 形态分析，陈皮