Determination of stability constants of copper(I) chelates with 1,10-phenanthroline by thermal lensing

Using investigations of the copper(I)-1,10-phenanthroline system as an exam ple, it is shown that thermal tensing can be used for determining stability constants at a level of concentrations one-two orders of magnitude lower c ompared to conventional spectrophotometry, with better precision of measure ments. The values of stability constants are log beta (2) = 11.7 +/- 0.7 wi thout regard for stepwise chelation, and logK(1) = 5.9 +/- 0.3, logK(2) = 5 .4 +/- 0.3, and log beta (2) = 11.3 +/- 0.6 taking into account stepwise ch elation. It is shown that, when shifting from microgram to nanogram amounts of reactants in the determination of stability constants by thermal lensin g, changes in the kinetic parameters of the reaction studied should be take n into account. The thermal-lens limit of detection of copper(I) is 2 x 10( -8) M; the linear calibration range is 4 x 10(-8)-2 x 10(-5) M (488.0 nm, p ump power 120 mW). The data obtained were used for determining copper(I) in the hydrogen sulfide layer of the Baltic Sea.