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）对眼用溶液中的银元素进行定量检测。首先合成银纳米颗粒标准溶液，并以此为基础建立了适用于样品中银元素定量的分析方法。针对三份样品开展电位滴定实验：采用连接至电位计的电化学池，该池包含替代型金属指示电极与Ag|AgCl双接界参比电极。实验使用装有浓度为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溶液进行表征，结果显示药物中的银元素以纳米颗粒形式存在。电位滴定检测的样品前处理流程为：取50 μL眼用溶液与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）比对两种方法的检测精密度，结果显示无显著性差异；通过t检验（t test）验证两种方法所得银元素平均浓度的统计学差异，结果显示二者无统计学显著性。两项检验均设定95%的置信水平。