Principles and Problems of Cadmium Analysis

Numerous scientific reports have been published, in which reported levels of cadmium are clearly, or very likely to be, erroneous. Normally, biological samples have to be digested in order to separate cadmium from the organic matrix before analysis. The basic principle is that cadmium forms a stable red-colored complex with dithizone at alkaline pH levels and that this complex can be extracted into chloroform or carbontetrachloride. The nonspecific absorption can thus be measured and the signal proportional to the actual cadmium concentration is measured as the difference between the total and nonspecific absorption. Cadmium has a number of stable isotopes. Neutron irradiation yields new radioactive cadmium isotopes. Cadmium levels can be determined using various types of electrochemical methods, e.g., classic polarographic methods and the more developed differential pulse anodic stripping voltammetry, and selective ion electrodes. Different electrochemical methods are of particular value for measurement of cadmium in solutions.