A versatile stable cobalt optical sensor based on pyrogallol red immobilization on cellulose acetate film

A new optical chemical sensor based on pyrogallol red immobilization on a cellulose acetate membrane is reported for the determination of trace amount of cobalt. The method is based on the spectrophotometric measurement of complex of pyrogallol red with Co(II) at 550 nm. The observed absorbance intensity increased with increasing Co(II) concentration from 1.7 × 10−6 M up to 1.52 × 10−4 M, with a limit of detection of 3.6 × 10−7 M Co(II). The time for the membrane sensor to reach the output signal of 98% of the steady-state response was 120 s. The relative standard deviations (R.S.D.%) for eight determinations of 12.0 μM, 84.0 μM and 140.0 μM Co(II) solutions were ±2.1%, ±1.3% and ±0.8%, respectively. The sensor can be regenerated by placing the film onto a 0.01 M HCl solution just for 10 s and then washing with water. The sensor was used for the analysis of reference alloy samples and water samples with satisfactory results.