Sub-microgram-scale analysis by coulometry at controlled potential

The considerations which determine the success of controlled-potential coulometric analyses on the submicrogram level are discussed, and it is shown that the ultimate sensitivity of the method is governed by the accuracy with which the requisite background corrections, especially that for the charging quantity of electricity, can be determined. A method for the coulometric determination of zinc based on these considerations is shown to contain a limiting uncertainty of ± 0.2 mμF_y, so that as little as 0.07 μg of zinc can be determined within about ± 10%, while quantities of zinc exceeding about 10 μg can be determined with an accuracy and precision of ± 0.1% or better. Possible techniques for the further extension of controlled-potential coulometric analysis into the millimicrogram range are briefly discussed.