Abstract

The present study investigated the chemical composition and optical properties of a commercial liquid detergent, Servin Quality Ultra, 1L, cherry aroma, using FT-IR spectroscopy, visible reflectance spectroscopy (400-700nm), colorimetric analysis and computational chemistry calculations. The detergent was analyzed in 3%w/w ethanol solution, as well as in 1% and 10% w/w aqueous solutions, all showing a stable pH of 6.9. FT-IR spectra revealed the presence of long-chain alkyl surfactants, ethoxylated non-ionic surfactants, and builder components such as phosphonates and silicates. In addition, determination of anionic-active matter by the standard two-phase titration method revealed no detectable anionic surfactants (0.0%w/w), confirming that the formulation was dominated by non-ionic alcohol ethoxylate surfactants. The results were discussed in the context of the different physicochemical characteristics of the non-ionic, anionic, cationic and amphoteric surfactant classes, commonly employed in commercial liquid detergents. The FT-IR analysis of the ethanolic soluble fraction of the liquid detergent Servin revealed characteristic absorption bands corresponding to aliphatic C-H stretching vibrations (~2921cm-1 and 2844cm-1), ether C-O-C stretching modes (1148cm-1-1037cm-1), carbonyl groups (~1739cm-1) and weak aromatic or carboxylate contributions (~1577cm-1) confirming thus the predominance of ethoxylated nonionic surfactants and minor oxygen-containing additives. Reflectance measurements indicated low overall reflectance 6%-8%, with absorption in the green region (500-560nm) and increased reflection in the yellow-orange region (560-600nm), producing a slightly reddish appearance. Reflectance data were further analyzed using the Kubelka-Munk transformation to estimate the optical band gap via Tauc plot methodology. The Kubelka-Munk transformation and Tauc analysis suggested an apparent optical transition energy of approximately 3.1eV, consistent with localized molecular HOMO-LUMO transitions rather than semiconductor-like band structures. The calculated band gap suggested predominantly insulating behavior with localized electronic transitions attributed to molecular chromophores. Colorimetric analysis confirmed this observation, with L*=30.84, a*=+5.56, and b*=-0.53, while ISO brightness which was 6.73% and CIE Whiteness which was 14.83whiteness units, indicated low optical brightness. The results suggested a weak reddish-blue coloration that the color of the detergent was primarily due to minor chromophoric additives rather than the surfactant components. The pH remained constant across concentrations, indicating chemical stability. The results indicated a weakly absorbing, semi-transparent colloidal system with moderate light scattering attributed to micellar structures. Density Functional Theory (DFT) and population analyses performed on a representative ethoxylated alcohol fragment (C6H14O2) demonstrated pronounced charge localization on oxygen atoms and sp3 hybridization along the hydrocarbon backbone, supporting the amphiphilic and insulating nature of the system. This integrated approach demonstrated how FT-IR, reflectance spectroscopy, colorimetry and computational analyses could provide complementary information for detergent characterization by understanding the detergent’s composition and its physicochemical behavior.

Keywords:Liquid detergent; FT-IR spectroscopy; Diffuse reflectance spectroscopy; Colorimetry; Kubelka- Munk analysis; Tauc plot; Surfactants; Nonionic surfactants; Anionic surfactants; Alcohol ethoxylates; Optical properties; CIE whiteness; pH stability; DFT; GAMESS