Smart Colorimetric Determination of Ionic Surfactants with Bromothymol Blue at the Presence of Nonionic Surfactant Triton X-100

The application of digital colorimetry for the determination of ionic surfactants, moderately hydrophobic medicinal substances of ionic nature in the system with bromothymol blue (BTB) in aqueous solutions using a smartphone has been shown. The influence of the solution nonionic surfactant Triton X-100 (TX-100) on the parameters of the colorimetric determination of bromothymol blue has been studied. It was established that the addition of TX-100 improves the linearity of the graduation dependence of the colorimetric signal of bromothymol blue (r ˃ 0.99) and reduces the detection limit of the dye by 15 %. The optimal conditions for the colorimetric determination of the cationic surface-active substance cetylpyridinium chloride (CPC), reagent concentration, and pH were established (LOD = 2.5·10-6 mol L-1, Sr ˂ 2 %). The spike recovery method checked the trueness of the results obtained in the model solutions analysis. The procedure for determining CPC in the drug "Septolete Total" was verified by the addition technique. The ability of a nonionic surface-active substance to stabilize the colloidal chemical state of solutions of hydrophobic counterions associates was used for the colorimetric determination of the anionic surfactant sodium dodecyl sulfate (r = 0.99; LOD = 7.5·10-7 mol L-1) and the less hydrophobic indomethacin (LOD = 6.6·10-6 mol L-1) with the BTB-TX-100-CPC reagent system.