A new chemiluminescence system for determination of cobalt.
The chemiluminescence of the reaction of tartaric acid with hydrogen peroxide in the presence of Co(II) in alkaline buffer media has been examined. The maximum emission wavelength is 460 nm. The kinetic curve of the chemiluminescence system has been modelled with a computer, and the reaction conditions have been optimized. Foreign ions, such as Fe(II), Cr(III) and Mn(II), interfere when present in more than 10-fold ratio to Co(II), but several ions can be tolerated when present in higher ratios to Co(II). The concentration range of linear response is from 3.5 x 10(-9) to 2.0 x 10(-6) g/ml, and the detection limit is 4 x 10(-11) g/ml. The procedure has been satisfactorily applied to determine trace cobalt in human blood serum.
Determination of cobalt by pyrogallol chemiluminescence.
The chemiluminescence reaction involving pyrogallol in alkaline hydrogen peroxide solution is described. With reaction conditions selected for the determination of Co(II), the detection limit for Co(II) was at least two orders of magnitude below the detection limit of all other species tested. The results suggest that Ca, Mg, Mn, and Fe are the most likely interferents for environmental and biological samples. The log-log calibration graph for Co(II) is linear from a detection limit of 0.5 ng/ml up to 10 microg/ml.
Effects of polymeric charge variations on the proton-metal ion equilibria of humic materials
Except for specific molecular weights, humic materials have many of the chemical and physical characteristics of enzymes. Thus modified equations from the biochemical literature can provide a theoretical description of proton-metal ion interactions on humic substances. For a given ionizable group type, the members of the group are chemically identical within experimental error, and the observed variations in dissociation of humic acid and bonding strength of metal ion as a function of pH are quantitatively related to the electrostatic interaction between the cationic species and the negatively charged humic polyion. This approach allows experimental determination of intrinsic constants for dissociation of acid and formation of metal ion, i.e. equilibrium constants which are independent of all electrostatic effects. The intrinsic constants obtained for a few humic materials are compared to those of possible monomeric units. In addition, the intrinsic constants have been coupled with other experimental parameters to predict the concentration of metal ion bound to humic materials as a function of pH.