分光光度法测定矿泉水中的铅含量

摘 要

本论文是应用分光光度法测定矿泉水中的铅含量。以二甲酚橙作为显色剂，柠檬酸三铵和硫脲为掩蔽剂，在pH值为6的醋酸-醋酸钠缓冲液中，铅离子与显色剂生成红色的络合物，在575nm处有最大吸收波长。在室温下，显色时间为30min，铅离子的浓度在0～4.0μg·mL-1范围内符合朗伯-比尔定律，铅离子的线性回归直线方程为：A=0.0757C+0.0017(C为铅离子浓度，单位为μg·mL-1),相关系数?=0.9998，摩尔吸光系数?=1.59×104L·cm-1·mol-1。实验对15种离子进行干扰考察，发现在测定允许范围内有7种离子对测定结果存在较大干扰，分别是Co2+，Cu2+，Al3+，Fe3+，Cd2+，Sb3+，Ni2+。加入硫脲和柠檬酸三铵作为掩蔽剂，可以消除Co2+，Cu2+，Al3+，Fe3+，Cd2+，Sb3+，Ni2+的干扰，其他离子对矿泉水中的铅离子测定都在允许值的范围内。

本实验表明用分光光度法测定矿泉水中的铅含量的操作简单，时间短，不需要萃取分离，试剂用量少，加标回收率为98.3%～100%，相对标准偏差小于5%，准确度和灵敏度较高。此方法也可以用于其他样品中的铅离子测定。

关键词：分光光度法，二甲酚橙，铅，矿泉水

I

Abstract

A method for determining in lead content in mineral water with spectrophotometry is proposed in this paper. Xylenol orange is selected as the chromomeric reagent,in a acidic solution of pH6,Pb(Ⅱ) reach with the above mentioned to form red complexes with the wavelength of maximum absorption at 575nm.In the room temperature ,color develop in the range of 0～4.0μg·mL-1 for lead ,it conforms lambert beer’s law. Curve linear regression equation is: A=0.0757C+0.0017(C：μg·mL-1),correlation coefficient is: γ=0.9996,molar absorption coefficient is：?=1.59×104 L·cm-1·mol-1.15 kind of ions are interference studied in the experiment. Within the allowable range of 7 kind of ions on the determination there is a big disturbance that in proper order are Co2+,Cu2+,Al3+,Fe3+,Cd2+,Sb3+,Ni2+. Adding thiourea and ammonium citrate a masking agent to eliminate the interference of Co2+,Cu2+,Al3+,Fe3+,Cd2+,Sb3+,Ni2+.The experiment shows that by spectrophotometer to measure the lead simple operation, mineral real reagent consumption, recovery rate is 98.3% ～100%.Satongfen relative standard deviation is less than 5%, high accuracy and sensitivity. This method can also be used for other samples of the determination of lead ions.

Keyword:spectrophotometry，Xylenol orange，lead，mineral water.

II

目录

1前言 .............................................................. 1 2实验部分 .......................................................... 2 2.1实验原理 ........................................................ 2 2.2仪器的结构原理 .................................................. 3 2.2.1 721B分光光度计的结构 .......................................... 3 2.2.2 721B型分光光度计外观示意图 .................................... 5 2.2.3 721B型分光光度计工作原理 .......................................... 6 2.2.4 721B型仪器的光学系统 .......................................... 7 2.3 仪器和试剂 ...................................................... 9 2.3.1 实验仪器 ...................................................... 9 2.3.2 试剂和标准样的配制 ............................................ 9 2.4 仪器的测试条件 .................................................. 10 3结果和讨论 ........................................................ 10 3.1 最佳条件的选择 .................................................. 10 3.1.1 测定波长的选择 ................................................ 11 3.1.2 显色剂用量的选择 .............................................. 12 3.1.3 显色时间的考察 ................................................ 13 3.1.4 缓冲溶液pH的考察 ............................................. 14 3.2 工作曲线的绘制 .................................................. 15 3.3干扰离子的考察 .................................................. 17

III

3.4干扰离子的掩蔽 .................................................. 24 3.5 样品分析试验 .................................................... 28 3.5.1 样品测定及精密度考察 .......................................... 28 3.5.2 准确度的考察 .................................................. 29 4结论 ............................................................................................................................. 31 参考文献 ........................................................................................................................ 32 致谢 ................................................................................................................................ 34

IV