Abstract
A single-use optical chemical sensing film based on immobilized disodium-1-nitroso-2-naphthol-3,6-disulfonate or nitroso-R salt (NRS) in a modified chitosan film was developed for the determination of Co(II) in aqueous solution. In the presence of Co(II), the color of the sensing film changed from yellow-green to reddish orange as a result of complex formation between Co(II) and NRS. The absorbance measurement of the complex was made at 525nm because the background of the sensing membrane was minimal. An optimum response of the sensing film to Co(II) was obtained in a solution with a pH of 5. Two sample sizes were studied: 3mL with a Co(II) concentration range of 1–60ppm and 300mL with a Co(II) concentration range of 35–400ppb. Linear calibration curves were obtained from both sample sizes with limits of detection of 0.82ppm and 12ppb, respectively. The relative standard deviation for five separate films in 10ppm Co(II) solution was 1.7% and that for the other five individual films in 40ppm Co(II) solution was 0.41%. The sensing films exhibited good stability for 2 months and were applied for determination of Co(II) in water samples with satisfactory results.
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