QUANTIFICATION OF SILVER NANOPARTICLES IN A PHARMACEUTICAL PRODUCT BY SPECTROPHOTOMETRY AND POTENTIOMETRY: A PROPOSAL FOR PRACTICAL CLASSES IN ANALYTICAL CHEMISTRY

Spectrophotometry and potentiometry techniques were used to quantify silver in an ophthalmic solution. A standard solution of silver nanoparticles was synthesized, from which an analytical method was developed to quantify silver in the sample. Potentiometric titrations of three samples were made, using an electrochemical cell containing an alternative metallic indicator electrode and an Ag|AgCl double junction reference electrode, connected to a potentiometer. A digital burette containing a standard solution 5.00 x 10-3 mol L-1 NaCl was used. Characterization of the ophthalmic solution by spectrophotometry showed that Ag in this medicine is in the form of nanoparticles. The sample preparation for potentiometric measurements was carried out using a mixture of 50 µL of the ophthalmic solution and 2.00 mL of nitric acid. The average concentrations of Ag obtained were 1.65 ± 0.03% (w/v) by spectrophotometry, and 1.73 ± 0.06% (w/v) by potentiometry. The relative standard deviations were 2% and 4%, respectively. The precision of the measurements obtained by the cited methods showed no significant differences (f test). It was also observed that average silver concentrations obtained by the two methods were not statistically different (t test). Both tests were made at a 95% confidence level.本研究采用分光光度法（Spectrophotometry）与电位分析法（Potentiometry）对眼用制剂中的银元素进行定量分析。首先合成银纳米颗粒标准溶液，并以此为基础建立适用于样品中银元素定量的分析方法。对三份样品开展电位滴定（Potentiometric titration）实验：采用连接至电位计（Potentiometer）的电化学池（Electrochemical cell），该池配备替代型金属指示电极（Indicator electrode）与Ag|AgCl双接界参比电极；同时使用装有5.00×10^-3 mol·L^-1氯化钠标准溶液的数字滴定管。通过分光光度法对该眼用制剂进行表征，结果显示药剂中的银元素以纳米颗粒形式存在。电位法测量的样品前处理步骤为：取50 μL眼用制剂与2.00 mL硝酸混合制备待测样品。分光光度法测得的银元素平均浓度为1.65 ± 0.03%（质量体积比，w/v），电位分析法测得的平均浓度为1.73 ± 0.06%（w/v）；两者的相对标准偏差分别为2%与4%。采用F检验（F test）分析两种方法的测量精密度，结果显示二者无显著性差异；同时通过t检验（t test）验证，两种方法得到的银元素平均浓度在统计学层面无显著差异。上述两项检验均设定95%的置信水平。