Irreversible optical test strip for mercury determination based on neutral ionophore

A test strip for the determination of mercury in aqueous solution has been developed. It has a circular sensing zone containing all the reagents necessary to produce a selective response to mercury and formed by plasticised PVC incorporating the cation-selective neutral ionophore 1,4,7,10-tetraazacyclododecane, the chromoionophore 9-dimethylamino-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanonadecyl)phenylimino]benzo[a]phenoxazine and tetrabutylammonium tetraphenylborate as lipophilic salt. The measurement principle is based on an ion-exchange mechanism. When the sensor is introduced for a period of time depending on the mercury content into a water sample at a pH of 4.7, there is a colour change from blue to red, making it possible to use absorbance at 670 nm as the analytical signal. All experimental variables that influence the test strip response, especially in terms of selectivity and response time, were studied. The sensor responded linearly to mercury concentration in the range 0.3 and 5.1 (mu)M with a reproducibility in mid-calibration of 1.6% relative standard deviation (R.S.D.) for 60 min agitation. Similarly, it responded linearly to concentrations in the range 7.9–108 (mu)M with a mid-range R.S.D. of 1.8% (for 5 min without agitation). The procedure was applied to the determination of mercury in different types of waters (tap, mineral and spring), validating the results against a reference procedure.