Effects of pH buffer substances on pM

Although most of the chelating agents used in metal-ion buffers are also capable of serving as pH buffers, their values do not usually lie in the required pH range. For example the pATa values of NTA, tartaric acid and citric acid are too remote from pH 7 for them to be used as pH buffers in near-physiological media. Similarly A-hydroxyethyl-ethylenediamine triacetic acid (pATa 5.33), EDTA (pATj 6.13) or trimethylenediamine tetraacetic add (pATa 7.91) are of only limited use for this purpose. 

Hence it is ordinarily necessary to control the pH of metal ion buffers by adding conventional buffering materials. Most of these, including acetate, borate, phosphate, bicarbonate 

The computer programmes COMICS (Perrin and Sayce, 1967) and HALTAFALL (Ingri et al., 1967) are convenient if more detailed compositions of metal-complex mixtures have to be calculated. They also make possible the rapid screening of chelating agents that are potentially of use in this way. 

For further reading on metal-ion buffers, see Chaberek and Martell (1959). Raaflaub (1956) described two examples of pCa-enzyme activity studies, and Wolf (1973) has very recently given a mathematical treatment of two-metal-ion buffer systems. 

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