Multiwavelength photometry of thermochromic indicator solutions for temperature determination in multicuvettes

If buffer/indicator systems are used as optical thermometers in multicuvettes, the temperature resolution is limited by errors of optical measurements produced mainly by variations of pathlength and blank transmittance of the wells. Theoretical and practical approaches show that, in multicuvettes, a between-well temperature resolution of < 0.05 degrees C can be achieved by multiwavelength photometry with use of the Tris/cresol red indicator system. Using up to three absorbances (A0, A1, A2) measured in the same well at different wavelengths for calculation of differences, quotients, and quotients of differences, we found the optimum temperature signal to be In(A1/A2), with equal-ranking absorbances changing with temperature in opposite directions. We have used the method successfully to measure the temperature profiles and temporal dynamics of temperatures at all positions in two types of multicuvettes under controlled conditions, or not controlled thermostatically.