Color catcher sheet as an optical sensor for the determination of CTAB

A simple, low-cost competitive assay for the determination of hexadecyltrimethylammonium bromide (CTAB) has been developed. This assay employs a specific type of color catcher sheet which can adsorb the cationic dye crystal violet. Solutions containing various amounts of cationic surfactant and constant amount of crystal violet were prepared and the dye was subsequently extracted using color catcher sheet. Digital images of the sheets with the adsorbed crystal violet were taken with a mobile phone; the image analysis of the photos was performed using Color Picker application. The values of several color spaces were collected. Specific values from RGB, CMY, XYZ and LAB color spaces were either directly or indirectly proportional to the concentration of CTAB in the analyzed samples. The described inexpensive, simple and elution free assay enables analysis of cationic surfactant in various solutions.