Errors in Atomic Absorption Analysis for Metals in Surfactant Solutions.

摘要

Aqueous solutions in the pH range 2to 4.5containing 3micrograms/ml of copper with varying concentrations of the anionic surfactant sodium dodecyl sulfate (SDS) were analyzed for copper. At pH 2the cationic surfactants dodecyl pyridinium bromide (DPB) and tetradecylpyridinium bromide (TPB) were also used. Enhancement of instrument response was observed with SDS at pH values of 2, 3and 3.4,but a depression of instrument response was observed at pH 4.5. Much less signal enhancement was observed at pH 2with DPB than with SDS and no significant enhancement was observed with TPB at this pH. The same type of enhancement of instrument response is observed for magnesium and cadmium,and has already been reported for nickel at pH 2with SDS as the surfactant. Thus,the signal enhancement seems to be rather general for divalent metals at low pH with this particular surfactant which is quite similar to the surfactant in many commercial detergents. Viscosity and density changes observed for such solutions are far too small to cause the effects observed. Surface tension does not appear to be a major factor in producing the enhancement or depression of signal. It is doubtful if such errors would be significant in routine analyses unless the samples were at rather low pH.