New liquid-membrane electrodes for direct determination of atropine in pharmaceutical preparations

Solutions of atropinium 5-nitrobarbiturate in n-octanol and atropinium picrolonate in p-nitrotoluene are used as novel liquid ion-exchangers in electrodes that respond to the atropine cation. The performance characteristics of the two electrodes are almost identical: the response is linear for 10(-5)-10(-2)M atropine with a slope of 56.5 +/- 1 mV/concentration decade. The static response times are 30-90 sec and the potential readings are stable over the pH range 3-8. There is negligible interference from a number of inorganic and organic cations, and some common excipients. In the direct determination of 1-200 mug/ml of atropine, the average recovery with both electrodes is 98% (mean standard deviation 1.7%). Atropine has been determined in some pharmaceutical preparations with an average recovery of 98% (standard deviation 1.9%), the results being in agreement with those obtained by standard methods.