title: The choice of a masking agent in the histochemical staining of metals.
abstract: The masking effects of standard masking agents (aminopolycarboxylic acids, carboxylic acids and phosphates) have been investigated in both test-tube experiments and tissue sections in order to ascertain the factors which must be considered when choosing a masking agent for the histochemical staining of a metal. The masking effects in vitro were determined by spectrophotometry through the complexing of the dye Chrome Azurol S with aluminium, beryllium, and iron at pH 5 and 7. The effects were also examined by staining metal-containing tissue sections in a Chrome Azurol S masking agent system at the same pH values. In many cases, the masking effects observed in sections did not agree with those obtained in the test-tube experiments. This means that the published values of stability constants are not a sufficient guide for choosing a suitable masking agent for the staining of metals. The discrepancy is mainly attributable to the presence of protein in a solid state when metals are stained in sections. Therefore, in the future, consideration should be given to a metal-protein or masking agent-protein interaction using a model compound such as a chelate resin. The polyphosphates are among the most useful masking agents for metal staining in acidic solutions from a practical standpoint.
mesh_terms: D000818:Animals; D002264:Carboxylic Acids / Q000494:pharmacology*; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006651:Histocytochemistry / Q000379:methods; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000032:analysis*; D004369:Pentetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology*; D051381:Rats; D013194:Staining and Labeling / Q000379:methods
chemical_list: D002264:Carboxylic Acids; D008670:Metals; D010710:Phosphates; D004369:Pentetic Acid; D004492:Edetic Acid