No abstract

The complexation of Tl(III) and Cr(III) with groundwater humic acids (HA) was investigated at pH 4.5 and pH 5.5 using different fluorescence methods. These comprised both quenching measurements of the continuous and synchronous fluorescence of the HA ligand and an ion competition method based on the time-resolved laser-induced fluorescence of HA-bound Eu(III). Modeling of the experimental data using an electrostatic discrete site approach (Model V), yielded comparable values of intrinsic binding constants for each of the studied metal, independently of sample conditions (pH, metal:ligand ratio) and fluorescence method used. The results confirmed the validity of fluorescence techniques in the analysis of low concentration metal ion−HA interac tions and indicated that, beside the aquo ion and the first hydroxo complex, other species may also bind to humic acids.

The simultaneous determination of potassium nitrate and sodium monofluorophosphate in dentifrices by single column ion chromatography is described. Nitrate and monofluorophosphate are extracted from the dentifrice with deionized water and separated by a low capacity anion separator column with 0.2% sodium benzoate (adjusted to pH 5.8 +/- 0.1 with formic acid) as the mobile phase. A conductivity meter is used for concentration measurements. The method has been applied to commercial dentifrices containing both potassium nitrate and sodium monofluorophosphate. The mean recoveries for potassium nitrate and monofluorophosphate from spiked samples were 99.0% and 99.2%, respectively, with corresponding standard deviations of 1.73% and 2.55%. The minimum detectable concentration is 5 micrograms/ml for both nitrate and monofluorophosphate.

No abstract

No abstract