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
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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.
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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
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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
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