Development of flow-based analysis system for determination of selenium sulfide in cosmeceutical products

Abstract

Flow-based extraction system was developed for determination of selenium sulfide in cosmeceutical products. The method was based on iodometry, where selenium(IV) was reduced to selenium(0) by iodide ion producing iodine that was then on-line extracted into the organic solvent and detected by the fiber optic spectrophotometer at wavelength 521 nm. Several extraction units using polypropylene hollow fiber membrane as a phase separator were investigated. The tubular extraction unit with vertical setup provided the best performance. The extracting solvent was hexane that could be used in place of chloroform. The sample solution was first mixed with excess iodide and filled in the glass tube of the extraction unit while the hexane was pumped inside the membrane. The iodide concentration, extraction time, the length of the membrane, the cleaning system, reuse of membrane and matrix effect of sample were studied and optimized. All processes except washing were controlled by a microcontroller on a computer. The working range of 80 to 373 mg L⁻¹ selenium was obtained with 60 sec extraction time providing sample throughput of 20 samples hr-1 (included washing). The recovery for determination of selenium in the forms of selenium dioxide and selenium sulfide were 97-106% with 1-4%RSD and 95-105% with 1-3%RSD, respectively. This method was applied for determination of selenium sulfide in anti-dandruff shampoo and cosmeceutical samples obtained from Pan Rajthevee Group Public Company Limited. The results obtained from the developed method were similar to those labeled on the products with the relative error less than 2%; especially, it showed less error than the standard titration method.