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The behavior of calcium has been investigated in the interference systems: hydrochloric acid/calcium, sodium chloride/calcium, acetic acid/calcium, aluminum/calcium, and phosphate/calcium. Possible mechanisms are detailed and corrective procedures tested. In general, presence of a concomitant in high concentration depresses calcium signals at different calcium concentration levels. These depressions are observed both with total consumption burners and laminar flow burners. In cases of heavy interference, protectors and releasers have been studied. With ethylenediametetraacetic acid, protective action is effective when only moderate concentrations are involved but is somewhat less desirable at higher concentrations because of the increase in burner contamination by the organic material. The presence of lanthanum is very helpful in such cases, and this approach has become routine in some applications. Strontium has been used in a similar manner and provides satisfactory results in many analyses. However, strontium appears to be less effective than lanthanum and usually is required in higher concentrations to provide equivalent protection. The nitrous oxide-acetylene flame has proven particularly useful even for the more difficult systems such as aluminum/calcium and phosphate/calcium. Addition of an ionization inhibitor such as potassium has also been investigated in connection with the high-temperature flame tests.
air-acetylene flame, atomic absorption, calcium, flame photometry, interferences, laminar flow burner, nitrogen oxide-acetylene flame, protectors, releasers, analyzing, tests
Ulrich, W. F.
Manager, Beckman Instruments, Inc., Fullerton, Calif.
Principal application chemist, Beckman Instruments, Inc., Fullerton, Calif.