lower amounts of beryllium. The limit was about 2 mg of beryllium in about 100 ml of precipitating solution. The use of smaller volumes would probably lead to difficulties with real samples, since the other dissolved metals would be more concentrated . The analysis of the NBS alloy yielded results that were in good agreement with the published value of 1.770 f 0.0043 %.
Our values were 1.761 + 0.0071 by the gravimetric method and 1.762 0.0079% by the coulometric method, The precision was reasonably good as indicated by the standard deviations.
*
RECEIVED for review March 27,1972. Accepted July 20,1972.
Application of Coulostatic Charge Injection Techniques to Improve Potentiostat Risetimes James E. Davis and Nicholas Winograd Department of Chemistry, Purdue University, West Lafayette, Ind. 47907 The design of a potentiostat is given which is capable of applying large amounts of peak power (300 watts at 1 psec) to an electrochemical cell. The design incorporates the use of a coulostat to initially charge the double layer while the potentiostat supplies the relatively small current needed to sustain any electrode processes. For systems with rather high resistances and large capacitances, time improvements of more than an order of magnitude are indicated with this device. Current-time data are presented on the oxidation of ferrocene-carboxylic acid in acetonitrile which agree with the theoretical values to 10 psec. In addition, internal reflection spectroelectrochemical experiments at optically transparent electrodes follow predicted behavior to less than 4 psec. This time improvement will greatly extend the use of potentiostatic methods for fast reaction rate studies to highly resistive nonaqueous solvent systems.
THEINVESTIGATION of rapid kinetic reactions associated with heterogeneous electron transfer processes has long been an important application of potential step techniques ( I ) . Many workers have presented detailed analyses of constructed instruments with special emphasis on frequency response, compensation for unwanted solution resistances (2-5), and cell geometry (6, 7). With the advent of cheap, readily available high performance operational amplifiers, potentiostats capable of applying controlled voltage steps in times on the order of 1 psec are presently being designed. Nearly all of these studies have been concerned with “small signal” conditions, that is instruments which are neither limited by current, voltage, nor slew. These conditions generally require very small applied voltage steps (
