It is shown that thermal lensing can be used for studying the peculiarities
of reactions at the level of nanogram quantifies of the reactants. The exa
mples of determination of absorption parameters, acidity constants, overall
and stepwise stability constants of complexes, characteristic rate constan
ts, solubility constants, and other parameters from thermal-lens experiment
s are shown. In a number of cases, the due regard of the reaction condition
s at the nanogram level improves analytical parameters of the determination
.