Investigation of the reaction of copper(I) with 2,9-dimethyl-1,10-phenanthroline at trace level by thermal lensing.

The stability constants for copper(I) chelate with 2,9-dimethyl-1,10-phenanthroline are determined by thermal lensing, and the advantages over spectrophotometric determination of stability constants are shown. Changes in the photometric reaction when moving from the microgram to the nanogram level of reactants are discussed. The conditions for the thermal-lens determination of copper are optimized. The limit of detection of copper is 3x10(-8) mol dm(-3), and the linear calibration range 1x10(-7)-1x10(-5) mol dm(-3).

Thermal lens studies of the reaction of iron (II) with 1,10-phenanthroline at the nanogram level.

The determination of iron(II) with 1,10-phenanthroline in aqueous solutions was carried out exemplarily by thermal lens spectrometry. The peculiarities of analytical reactions at the nanogram level of reactants can be studied using this method. Under the conditions of the competing reaction of ligand protonation, the overall stability constant for iron(II) chelate with 1,10-phenanthroline was determined at a level of n x 10(-7) mol L(-1), logbeta3 = 21.3+/-0.1. The rates of formation and dissociation of iron(II) tris-(1,10-phenanthrolinate) at a level of n x 10(-8) mol L(-1) were found to be (2.05+/-0.05) x 10(-2) min(-1) and (3.0+/-0.1) x 10(-3) min(-1), respectively. The conditions for the determination of iron(II) with 1,10-phenanthroline by thermal lensing were reconsidered, and ascorbic acid was shown to be the best reducing agent, which provided minimum and reproducible sample pretreatment. Changes in the conditions at the nanogram level improved both the selectivity and sensitivity of determination. The optimum measurement conditions for thermal lensing were determined not only by the absorption of the analyte and reagents, but also by the background absorption of the solvent. The limits of detection and quantification of iron(II) at 488.0 nm (excitation beam power 140 mW) are 1 x 10(-9) and 6 x 10(-9) mol L(-1), respectively; the reproducibility RSD for the range n x 10(-8)-n x 10(-6) mol L(-1) is 2-5%.

The studies of the reaction of bismuth(III) with iodide at nanogram level by thermal lensing.

By the example of the analytical system based on the reaction of bismuth with iodide, it is shown that thermal lens spectrometry can be used for studying changes in analytical reactions at the nanogram level of reactants. The stability constants of bismuth(III) iodides at the concentration level are found. The solubility constants of iodides of metals interfering with bismuth determination are estimated. It is shown that the due regard to the new conditions could enhance the sensitivity and selectivity of determination.

Investigation of adsorption of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) on glasses and silica by thermal lens spectrometry.

Thermal lens spectrometry is used for studying adsorption equilibria in aqueous solutions at the level of nanogram quantities of iron(II) tris-(1,10-phenanthrolinate) as a model system. The kinetics of the sorption of the chelate on silica is studied and adsorption isotherms are built. Thermal lensing is used as a method for direct determination of the chelate concentration adsorbed on a quartz surface. The detected amount is 4.1x10(-15) mol at the area irradiated by the excitation beam. The adsorption of iron(II) tris-(1,10-phenanthrolinate) on laboratory glassware at the nanogram level is characterised by measuring the residual concentration of the sorbate in solution. A procedure for handling and cleaning the laboratory glassware for determining nanogram amounts of iron in aqueous solutions is proposed. The sensitivity of thermal lensing both in measuring adsorption on silica and glass and quartz surfaces is 100-fold higher than diffuse-reflectance measurements under the same conditions.