[2] Elimination of a metals

This chapter discusses the elimination of adventitious metals. The two methods reported in this chapter, dithizone extraction and ion exchange with a chelating resin, have been used extensively in numerous laboratories and have proven to be necessary in all aspects of work, involving the replacement or depletion of the metals in metalloenzymes. Diphenylthiocarbazonc (dithizone) is a complexing agent soluble in organic solvents that reacts with various metals to form organic soluble chelates. Upon rectal complexation, the bright green color of its solutions turns red, the color change serving as a sign of metal contamination. It is stressed that nothing supplants the verification of any procedure used for the elimination of adventitious metal. Hence, actual metal analysis of solutions, using methods, such as atomic absorption spectroscopy, is desirable subsequent to metal extraction. It is very easy to recontaminate solutions or to have such procedures go awry; therefore, if one or more metals are of particular concern, its presence or absence should be verified when possible.