Construction of an optical sensor for cobalt determination based on methyltrioctylammonium chloride immobilized on a polymer membrane

An optical sensor has been designed for the determination of cobalt by spectrophotometry. The sensing membrane is made by immobilizing methyltrioctylammonium chloride on a triacetylcellulose membrane. In the presence of Co( II) and thiocyanate ions, the colorless membrane changes to blue. The response time of the optode was about 7 min. The sensor can readily be regenerated with 0.02 mol L-1 sodium oxalate solution. This optode is stable and can be stored under water for more than a month without reagent leaching. The calibration curve was linear in the range of 8.5 x 10(26) 1.3 x 10(24) mol L-1 of Co( II) ion with a limit of detection 5.9x 10 26 mol L-1. The relative standard deviations for seven replicate measurements of 3.4 x 10(25) and 1 x 10(24) mol L-1 of Co( II) were 1.58 and 1.10%, respectively. The sensor was successfully applied to the determination of cobalt in food samples and vitamin B-12 ampoule.