Continuous gradient method in flow microcalorimetry

A flow microcalorimeter operating in mixing mode generates a type of “continuous titration” when one of the feeding pumps is connected to a continuous gradient generating device. The proper correction of the instrumental signal for the thermal lag of the calorimeter can be performed by chemical calibration, through an evaluation of the parameters of Tian's equation, modified for the microcalorimeter. This equation relates the instrumental signal to the actual power developed by the reaction. This paper shows how a continuous exponential gradient method can be applied to the determination of the enthalpy changes of metal-ligand-proton equilibrium reaction in solution. The enthalpies obtained for the protonation of D-cycloserine and for the formation of CuL and CuL2 complexes in the Cu(II)-Glycine system are in substantial agreement with published values. The computer programs, in BASIC language on an IBM-XT PC, used to process gradient data, are presented.