Colorimetric Concurrent Determination of Ultra-Trace Amounts of Pilocarpine and Timolol as anti-Glaucoma Drugs in Binary Mixtures Using a Multivariate Calibration Approach Based on the Aggregation of Gold Nanoparticles

Background To study the ultra-trace simultaneous determination of drugs, the colorimetric method in combination with chemometrics can be used. Objective In this study, a simple, rapid, and sensitive UV-Vis spectrophotometric method using gold nanoparticles (AuNPs) was introduced for the simultaneous determination of ultra-trace amounts of Pilocarpine (PIL) and Timolol (TIM) in binary mixtures and biological sample. Methods AuNPs interacted with components and the aggregation mode of NPs occurred and finally, the color change of the solution (red to gray) was observed with the naked eye without the most modern and expensive instruments. The characterization of AuNPs was evaluated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Results The validation of the colorimetric way was studied in the concentration range of 100–800 and 100–600 μg/L with good linearity equal to 0.9772 and 0.9891 for PIL and TIM, respectively. The limit of detection (LOD) was found to be 165.00 and 92.40 μg/L, where the limit of quantitation (LOQ) was 500.00 and 280.00 μg/L for PIL and TIM, respectively. The effect of some factors such as interaction time, the concentration of components, and the volume of buffer on absorbance was investigated. Partial least squares (PLS) as an efficient multivariate calibration method was combined with colorimetry for the simultaneous determination of PIL and TIM in binary mixtures. The optimum number of latent variables was selected by k-fold cross-validation based on minimum mean square error prediction (MSEP) and the number of components equal to 1 with MSEP of 1.085 and 0.763 was considered for PIL and TIM, respectively. The mean recovery was obtained at 100.20% and 101.55% for PIL and TIM, respectively. Conclusion The colorimetric method can be introduced as a proper option for the simultaneous determination of components in pharmaceutical formulations and other samples. Highlights A colorimetric method using AuNPs was proposed. PLS method was coupled with a colorimetric method for the ultra-trace simultaneous estimation of PIL and TIM in binary mixtures. Ultra-trace amounts of PIL and TIM were also determined in biological sample. The proposed method is simple, fast and less expensive than chromatography methods.