Use of a constant current ohmmeter as a biamperometric endpoint

Use of a Constant Current Ohmmeter as a Biamperometric Endpoint Indicator Recent method development in our laboratory for the analysis of pyruvic and lactic acid analogs included an indirect oxidimetrie titration of excess vanadium oentoxide with ferrous ammonium sulfate in a strona- sulfuric acid solution. Cnlorimetrir endooint determinations were imoossihle to ~ e r f o r mbecause of the intense and verv similar hlue-ereen ~

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and inexpensive method was devised. The B and K Precision Model280 Digital Multimeter, is a linear or constant current instrument when used as an ohmmeter. When connected to two platinum wire electrodes, the Model 280 supplies a constant current of 100 wi and displays a voltage which indicates the polar&tian of the platinum electrodes. ~ u r i n g t h etitration of the excess vanadium pentoxide with ferrous ammonium sulfate, the ohmmeter reading exhibits a gradual change until a sharp break occurs at the endpoint. The reristnnce mav.. then he olotted versus the volume added to locate the endooint or the second derivative method of ~~. endpctlnl lcmtwn ma" be usrd in lieu i d the graphic n~etlwd. \Ve hare t w n d this tv be a q u c k , accurate alternative tu traditional h~nmpenmetricprwedurea. Its low ro-Land ?me of handling qhotrld make it very adsptahle toqunntitntrve analysis lahoratur).cxperimentr whwh illuitratc the yritwiplci of redox titrations and hiamperometric endpoint detection ~

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Institute of Organic Chemistry Syntex Research Palo Alto, California

484 1 Journal of Chemical Education

C. E. Weingartner D. A. Robertson