Abstract: The continuous-addition-of-reagent technique was used as an effective means for enhancing the performance of energy transfer chemiluminescence-based determinations. For this purpose, the reaction between tertiary aliphatic amines and sodium hypochlorite in alkaline medium containing fluorescein as sensitizer was chosen. The influence of experimental variables such as the addition rate and sodium hypochlorite concentration, pH and fluorescein concentration on the maximum reaction rate was assessed and compared with that observed when using Rhodamine B as sensitizer. The method based on fluorescein exhibited the better analytical features (e.g. calibration graph for trimethylamine was linear over a wide such range as 10^-2500 nmol, with relative standard deviation of 2.6%). The proposed method allows the indirect determination of primary amines (viz. methyl- and ethylamine) and compares favourably with recent alternatives to the determination of trimethylamine in fish tissue (mean recovery 101.0% and standard deviation 2.7). Some aspects on the degradation during storage of fish samples are discussed.

Abstract: The continuous addition of reagent (CAR) technique was used as an effective means of improving the simultaneous reaction-rate determination of phosphate and silicate based on the formation of the corresponding heteropolymolybdates. The special features of the CAR technique allow the flexible manipulation of the reactant concentrations and reaction kinetics for controlling the classical synergistic effect involved in this reaction. Hence, resolution of mixtures of the two anions with phosphate-to-silicate ratios from 10:1 to 1:20 at the micromolar level can be resolved with good accuracy (errors less than 10% in most cases) and precision (relative standard deviations about 2.5-4.5%). The method compares favourably with existing reaction-rate alternatives, especially in the resolution of mixtures with excess of phosphate over silicate, which is reported in this paper for the first time. The determination of phosphorus and silicon in sunflower was selected to validate the proposed method for the analysis of real samples.