荧光光度法测定水中硫化1

sulphides in water

Zhao Baowei, Jiang Bing, Dong Wenjuan, Zhu Kun (School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China) Abstract A novel spectrofluorimetric determination method of trace amounts of sulphides was described on the basis of Hg (II)-2-(2'-hydroxylphenyl) benzoimidazole (HPBI) fluorescence quenching system. The fluorescence intensity was linear with the concentration of sulphide in the range of 1.0×10-8 - 9.5×10-6 mol/L. The detection limit was down to 9.02×10-9 mol/L. Interferences was avoided by using standard distillation procedure. The main advantages, apart from the extremely high sensitivity of the method, were the high stability of the reacted sulphide system. The method was also applied to measure the trace amounts of sulphides in water sample with satisfactory results. Keywords 2-(2' -hydroxylphenyl)benzoimidazole, mercury (II), spectrofluorimetry, sulphide 1. INTRODUCTION The extreme toxicity of hydrogen sulphide is produced through the great ability of sulphide ion reacting with many metals in the human metabolism. Sulphides in water are oxygen demand substance, which consume the dissolved oxygen and can restrain the activity of aquatic creature [1]. The water containing sulphides causes the roots of plant to decay by irrigation. The increase in the concentration of this species in water is mainly attributed to the indiscriminate discharge of inadequate treated effluents of organic matter from industrial wastes as well as the bacterial reduction of sulphate results in the release of sulphide into wastewater. The toxic nature of H2S has claimed several lives, especially of those working in the sewerage systems[2,3]. Therefore, the facts mentioned above lead to a requirement for sensitive analytical methods for the determination of sulphides. The quantitative determination of sulphide in different types of samples has been reported by employing a range of analytical techniques which include iodometry, spectrophotometry, anodic stripping voltammetry, reciprocal oscillographic chronopotentiometry, ion chromatography, enthalpimetry, chemiluminescence, gravimetry, ion selective electrode and gas chromatography [4-18]. The samples analyzed in these experiments ranged from water, wastewater, food materials to inorganic compounds. Spectrofluorimetry is widely used to detect the trace amounts of substances due to its high sensitivity and selectivity. To our knowledge, rare studies on the fluorescent determination of sulphides were reported in recent years. It has been previously reported that the determination of mercury in wastewater based on the fluorescence quenching system of mercury (II)-2-(2'-hydroxylphenyl)benzoimidazole (HPBI). In the further study, mercury (II) sulphide was formed and equivalent amount of the fluorescent organic ligand was released if the sulphide ion was allowed to enter the system. Thus, the spectrofluorimetric system for the determination of sulphides was established.

2. EXPERIMENTAL 2.1 Apparatus Fluorescence measurements were performed on a RF-540 Spectrofluorimeter (Shimadzu, Japan) equipped with a xenon light source and quartz cells of 1 cm pathlength. The excitation and emission slits were both 10 nm. The pH values of the solutions used were measured with PHS-2 Acidity Meter (Shanghai, China). 2.2 Reagents Standard stock solution of mercury (II) (1.0×10-3 mol/L) was prepared by dissolving 0.2006 g of pure mercury with concentrated nitric acid, heating the solution to dry, adding 2 drops of concentrated nitric acid and diluting the solution to 1000 mL. This solution was standardized with EDTA. 2-(2' -hydroxylphenyl) benzoimidazole (HPBI) was synthesized according to literature [19]. Its purity was nearly 100% as measured by element analysis and NMR. Its solution (1.0×10-3 mol/L) was prepared by dissolving 0.0206 g of HPBI into 100 mL of ethanol. The standard stock solution of sodium sulphide (1.0×10-2 mol/L) was prepared by dissolving 0.2402 g of Na2S·9H2O into 50 mL of water, adding 1 mL of 4 mol/L NaOH and diluting to 100 mL of volume. Na2B4O7-NaOH buffer solution (pH = 9.5) was also prepared. All reagents were analytical grade and water used was twice distilled one. 2.3 Sampling and storage The samples were preserved by adding 0.2 mL (4 drops) of 2 mol/L zinc acetate and 0.05 mL (1 drop) of 6 mol/L sodium hydroxide to a 100-mL polyethylene bottle, which was completely filled with the sample and was stoppered. If the concentration of sulphide was greater than approximately 100 mg/L, the volume of both regeants added to each 100 mL sample was increased. 2.4 Procedures To a series of 100 mL flasks, 0.8 mL of mercury standard stock solution, 1.0 mL of HPBI solution and 5.0 mL of buffer solution were added and diluted to a volume of about 60 mL. Then appropriate amount of standard solution of sodium sulphide or the sample solution treated by the standard distillation procedure was added, and the solution was diluted to 100 mL and mixed well. The intensity of fluorescence of solution was measured at excitation wavelength of 320 nm and emission wavelength of 430 nm. 3. RESULTS AND DISCUSSION 3.1 Optimum conditions It is evident that the excitation and emission wavelength of the reagent HPBI is at 320nm and 430nm respectively. After the complex of HPBI with mercury (II) is formed, the excitation and emission wavelength of HPBI is not changed. However, its fluorescent intensity of emission largely decreases. The further study showed that not only the excitation and emission wavelength did not change, but also the intensity of emission at 430 nm quenched by mercury (II) was regained because mercury (II) sulphide was formed while sulphide ion was mixed into system. Therefore, 320 nm and 430 nm were chosen as the excitation and emission wavelength respectively, at which the fluorescent intensity of solutions was measured (Fig. 1).

Fig.1 Fluorescent spectra (a: excitation spectra; b: emission spectra)

Acidity plays an important role in this system. A change in pH value of solution causes a change in fluorescent intensity. Consequently the pH value of solution was controlled strictly by addition of Na2B4O7-NaOH buffer solution. It is found that the intensity maintains maximum and constant in the pH range from 9.6 to 10.5 (Fig. 2). When the optimum addition of the buffer solution was determined as 2.0 mL, a pH value of 10.0 was therefore adopted in the following procedure.

Fig.2 Effect of acidity on the fluorescent Intensity

The presence of surfactants could affect the intensity of system. Various kinds of surfactants were tested and it was found that the addition of surfactant resulted in a slighter decrease of intensity, perhaps because the stability of complex of mercury (II) with HPBI increased, which prevented mercury from reacting with sulphide ion. HPBI is slightly dissolvable in water. Its working solution was prepared in ethanol as mentioned previously. The addition of HPBI solution was controlled strictly since the presence of ethanol could greatly enhance the intensity of system. At the optimum conditions, the complexing reaction of mercury with HPBI occurred instantly and the fluorescent intensity of system was constant within 10 h after the addition of sulphide ion. The calibration graph for the determination of sulphide was constructed under the optimum conditions. Excellent linearity was obtained over the concentration range 1.0×10-8 - 9.5×10-6 mol/L of sulphides. The limit of detection was down to 9.02×10-9 mol/L. Corresponding regression results were obtained as: F（%）=5.5 + 8.5×106 C (mol/L), R=0.9978，SD=0.0075，N=11, where F is the fluorescent intensity of the system and C the concentration of sulfide ion. The effect of foreign ions on the fluorescent intensity of system was studied for 2.0×10-6 mol/L of sulphide ion. Given tolerance did not cause 5 % deviation. The results showed that the oxidizing ions, such as ClO3-, BrO3- and IO3-, interfered the fluorescence seriously. However, sulphide ion does not co-exist with these ions in

water body. Metal ions or heavy metal ions caused the fluorescent intensity to change, but their interferences can be avoided by the standard distillation. The anions, which can enter the alkaline absorption solution with hydrogen sulphide in the distillation procedure, were tested. The results are shown as follows: F-, Cl-, Br-, I- (500), C2O42-, HPO32-, HSO4- (100)，CN- (60)，SCN- (50). Here tolerance times are notified in brackets.

Table 1 Analysis results of wastewater samples (n=6) Values of Addition of Standard Values after addition of Recovery Samples Determination Sulphide Standard sulphide (%) (ng/mL) (ng/mL) (ng/mL) 1 0.875 3.20 4.01 98.1 2 0.417 6.40 6.72 98.5 3.2 Sample analysis and results By this method, two kinds of wastewater containing sulphides were detected. The results are shown in Table 1. If the presence of interfering substances is suspected or if the analysis has to be delayed, the sulphide is fixed by allowing it to react with zinc acetate. 4. CONCLUSIONS The studied method for the determination of sulphide in water has a high sensitivity and a high selectivity and takes less time. It can be utilized to determine trace amounts of sulphides in wastewater. Its application in environmental monitoring for atmospheres and anaerobic sediments will be continued. REFERENCES

[1] Borum J, Pedersen O, Greve T M et al. The Journal of Ecology, 2005, 93 (1): 148-158.

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[11] Rucklin R D, Johnson E L. Anal.Chem., 1983, 55 (1): 4-7. [12] Kiba N, Nishijma M, Furusawa M. Talanta, 1980, 27 (12): 1090-1092. [13] Burguera J L, Townshend A. Talanta, 1980, 27 (4): 309-314. [14] Teckentrup J, Klockow D. Talanta, 1981, 28 (9): 653-663. [15] Padma D K. Talanta, 1986, 33 (7): 550-552. [16] Hiti I K A, Moody G J, Thomas J D R. Analyst, 1983, 108(1282): 43-52. [17] Hara H, Okazai S. Analyst, 1984, 109 (10): 1317-1320.

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荧光光度法测定水中硫化物 赵融入,江兵,董文全,朱坤(学校环境和市政工程、兰州交通大学,兰州

730070,中国)

摘要：本文以Hg (II)- 2-(2'-羟基苯基)苯并咪唑荧光体系为基础, 建立了水样中痕量硫化物的荧光分析法. 荧光强度与硫化物浓度呈线性关系, 线性范围1.0×10-8 ~ 9.5×10-6 mol/L, 检测限为9.02×10-9 mol/L. 以蒸馏法消除共存物质干扰. 方法灵敏度高,反应体系稳定, 用于水样中痕量硫化物分析, 得到较好结果. 关键词 ：2-(2'-羟基苯基)苯并咪唑, 汞(II), 荧光光度法, 硫化物 1. 介绍

极端含毒性的硫化氢是通过伟大的能力产生硫化物的许多金属离子反应在人类新陈代谢。水中硫化物需氧量物质消耗溶解氧并能抑制活性的水生生物[1]。灌溉水含有硫化物导致植物的根衰变。该物种在水中浓度的增加主要归因于的随意排放废水有机物的处理不足从工业废物以及硫酸盐还原细菌导致释放硫化物的污水。因此,上面提到的事实导致要求用敏感分析方法测定硫化物。确定硫化物的定量在不同类型的示例已经报告过使用一系列的分析技术,包括次法、分光光度法、阳极溶出伏安法、示波计时电位法、离子色谱法、热函测量法、化学发光法、重力测量、离子选择性电极与气相色谱[4-18]。在这些实验样品分析范围从水、废水、食品材料到无机化合物。由于荧光具有高灵敏度和选择性，被广泛用于检测的微量物质,

据我们所知,荧光测定研究硫化物在最近几年被罕见的报道。它之前已经报道过,测定废水中汞的基于荧光淬系统的汞(II)。 在进一步的研究中,汞(II)硫化物形成了相当数量的荧光有机配体被释放如果硫化物离子被允许进入系统。因此, 建立了荧光系统测定硫化物。 2. 实验 2.1 仪器

荧光测量进行了RF - 540分光荧光计(日本岛津)万能试验机配备氙气灯源和石英细胞1厘米的路径。激发和发射的缝隙都只有10海里。这个解决方案使用的pH值的测量PHS-2酸度米(上海,中国)。 2.2试剂

标准水平的解决方案的汞(II)(1.0×摩尔/升)的方法制备了溶解0.2006克的纯水与硝酸,加热溶液干燥,添加2滴浓硝酸历年来的解决方案和稀释到1000毫升。这个解决方案是用EDTA标准化。 其纯度为近100%通过测量元素分析、核磁共振。它的解决方案(1.0×打出摩尔/升)的方法制备了0.0206 g的HPBI溶解到100毫升的乙醇。标准的股票的解决方案的钠硫化物(1.0×10 - 2摩尔/升)的方法制备了溶解0.2402 g的9水合硫化钠成50毫升的水,加1毫升的4摩尔/升氢氧化钠和稀释到100毫升的体积。硼酸钠-氢氧化钠缓冲溶液(pH = 9.5)也准备。 所有试剂是分析品位和水的使用是一次蒸馏。 2.3采样和存储

样品保存完好,通过增加0.2毫升(4滴)2摩尔/升醋酸锌和0.05毫升(1滴)6摩尔/升氢氧化钠以100毫升的聚乙烯瓶,完全是充满了示例,加塞。如果硫化物的浓度大于大约100毫克/升,两份试样的体积添加到每100毫升样品的量是增加的。 2.4 过程

一系列的100毫升烧瓶,0.8毫升的汞标准股票的解决方案,1.0毫升的HPBI解决方案和5.0毫升的缓冲溶液添加到卷和稀释大约60毫升。然后适量的钠硫

化物标准溶液或示例解决方案治疗标准的蒸馏过程添加,并且解决方案被稀释到100毫升,混合好。荧光强度的解决方案是在激发波长测量的320 nm和发射波长430纳米的。 3. 结果与讨论 3.1最优条件

显然,激发和发射波长的试剂HPBI在320 nm制程,分别为430纳米。复杂的HPBI后与汞(II)构成,激发和发射波长的HPBI并未改变。然而,其荧光强度在很大程度上减少排放。进一步研究表明,不仅激发和发射波长没有变化,但也排放强度在430 nm淬火汞(II)被收复因为水星(II)硫化物形成而硫化物离子被混合到系统。因此,320 nm和430nm被选为激发和发射波长,荧光强度测定的解决方案(图1)。

酸度起了重要作用，改变溶液的pH值对荧光强度变化有重要影响。因此, 严格的控制pH值的解决方案是通过添加Na2B4O7-NaOH缓冲溶液。这是发现强度保持最大而持续的pH值的范围从9.6到10.5(图2)。当最优增加缓冲溶液被确定为2.0毫升,pH值为10.0因此采用下列程序。

表面活性剂的存在可能影响系统的强度。各种表面活性剂进行了测试,发现表面活性剂的加入导致一个微弱的强度降低,也许是因为稳定的复杂的汞(II)与HPBI增加,从而避免了水星与硫化物离子的反应。

在最佳工艺条件下,络合反应的汞与HPBI立即发生和荧光强度是恒定的系统在10小时后添加硫化物的离子。

标定图测定硫化物建造在最佳工艺条件下。所得到的线性度好是浓度范围1.0×9.5×10 - 6票选-摩尔/升的硫化物。检测的极限降到了9.02×10 - 9摩尔/升。给出了相应的回归结果:F(%)= 5.5 + 8.5×106 C(摩尔/升),R = 0.9978,SD = 0.0075,N = 11,F是荧光强度的系统和C离子浓度的硫。

荧光强度的系统研究了2.0×10 - 6摩尔/升硫化物的离子在外围离子的影响。鉴于并未导致5%的偏差。结果表明,氧化的离子(例如ClO3 -,BrO3——和IO3 -,严重干扰了荧光。然而,离子不共存的硫化物这些离子水体中。金属离子或重金属离子荧光强度的变化引起的,但是他们的干扰情况是可以避免的,标准的蒸馏。这个阴离子,它可以进入碱性溶液吸收与硫化氢蒸馏过程,进行了测试。结果如下:F -,Cl -、Br -,I-(500),C2O42 -,HPO32 -,HSO4 -(100),CN -(60),SCN -(50)。 这里宽容时间包括在内。

表1分析结果的废水样本(n = 6) Values of Determination Samples (ng/mL) 1 2 0.875 0.417 Addition of Standard Sulphide (ng/mL) 3.20 6.40 Values after addition of Standard sulphide (ng/mL) 4.01 6.72 Recovery (%) 98.1 98.5 3.2样例分析和结果

通过这个方法,两种的废水被探测到。结果如表1所示。如果干扰物质的存在或者如果分析已被推迟,硫化物是固定的,允许其与醋酸锌反应。 4. 结论

研究测定方法中硫化物的水有高灵敏度和高选择性,而且花费更少的时间。它

可以用于确定痕量废水中硫化物。其将继续应用于环境监测大气和厌氧沉积物。