It is not obvious whether the previuos posting has been read or not. The term Chemical Potential is used whever a chemical enrgy is transformed into other forms of energy available for usefully extracting work. For example the magnetization build up does not any chemical energy getting transformed or briging about chemical changes. If the spin system energy is changed it is not obviuosly a Chemical Bond forming/breaking energies or even Chenge of state from Solid to liquid to gases which would involve intermolcular interactions. Since the number of spins available per mole of a chemical substance dpendes on the number of specified proton in the molecule there need not be always the same spin energy related to per mole of all substances. Thus trying to relate "concentration" dependence as the only criterion for depenedences of chemical potential in the case of spin system may not be all the time valid. Given the same strength of the Magnetization built up (eneregy of the spin system) the relaxation time may vary. Thus the relaxation time may be a measure of power deriverable rather than simply the total amount of energy available. Unless the relaxation time is related to its cause as a chemical transformation and that chemical transformation may relate to chemical potential and in favourable cases it may be possible to correlate the relaxation rates withy the chemical potentials. And, in this sense the caution expressed by evgeny is in place; that the chemical potential may not be directly readout from relaxation data. As far as Transverse relaxation time T2 is concerned, it is a change in the spin system ordering/aligning and no change energy is suppopsed to be associated with it. Then, changes in order a mere redistribution for the most probable state without energy changes corresponds to entropy change and the entropy change part is subtracted from the heat changes while calaculating Free energy which is related to Chemical potential. Aravamudhan