Development of Colorimetric Method for Trace Determination of Dextromethorphan and Pseudoephedrine Components Separately in Urine Matrix Based on Plasmonic Response of Gold Nanoparticles: Optimization Study

In this study, colorimetry as a convenient, rapid, and sensitive method was introduced to determine trace amounts of dextromethorphan (DM) and pseudoephedrine (PSE) individually in urine samples based on Localized Surface Plasmon Resonance (LSPR) feature of synthesized gold nanoparticles (AuNPs). The AuNPs can reveal color changes (red to grey) in the presence of µg/L levels of DM and PSE, which can be observed with the naked eye and monitoring is possible through a UV-vis spectrophotometer. The characterization of AuNPs and AuNPs in combination with the drug was performed using Transmission Electron Microscopy (TEM). Dynamic Light Scattering (DLS) was used to estimate the size distribution of AuNPs and AuNPs along with the drug, which was obtained around 10 and 100 nm, respectively. The influence of the experimental factors on the absorbance was investigated. The pH of 4.33 for DM and 4.5 for PSE, phosphate buffer for DM and formate buffer for PSE, 200 µL of buffer for DM and 150 µL for PSE, 4.5 mM of AuNPs concentration for both drugs, interaction time of 8 min for DM and 12 min for PSE, electrolyte concentration of 2 µg/L for DM and 1 µg/L for PSE were selected as the best conditions. The absorbance was linearly correlated to the concentration of DM and PSE over the ranges of 60-100 and 50-130 μg/L, respectively. The Limit of Detection (LOD) was 5.61 and 17.00 µg/L, while the Limit of Quantification (LOQ) was 9.51 and 28.82 µg/L for DM and PSE, respectively. The colorimetric assay was successfully used to determine DM and PSE in spiked urine samples with Relative Standard Deviation (RSD) < 0.4% and 0.6% for DM and PSE, respectively. This approach demonstrated good precision and accuracy with simplicity and high speed in the analysis of the drugs without the need for complicated and high-cost devices.