Optical kinetic method for calibration of spectrophotometer temperature: demonstration with the Cobas-Bio analyzer

The pseudo-first-order rate constant for the Jaffé reaction with creatinine varies logarithmically with temperature and was calibrated in the range 25 to 37 degrees C to measure the temperature of the liquid in the lightpath of spectrophotometric instrumentation. The reagent concentrations can be adjusted to permit rate-constant measurements in time intervals from a few seconds to several minutes. The temperature increment that can be resolved is limited only by the analytical imprecision of the instrumentation used to measure the rate constant and the calibration temperature. In this investigation, a temperature SD of 0.03 degrees C could be measured. Two Cobas-Bio centrifugal analyzers, used to demonstrate the utility of this technique, were found to have temperature errors from -1.0 to -1.7 degrees C in the 30 to 37 degrees C range and overall temperature SD of 0.19 and 0.36 degree C, respectively, at 37 degrees C. Analysis of variance gave between-rotor SD of 0.14 and 0.34 degrees C and within-rotor SD of 0.13 and 0.11 degree C, respectively. We found temperature differences of 0.3 degree C between cuvets in a rotor, and gradients of 0.3 and 0.4 degree C, respectively, from the top to bottom of an individual cuvet in the two instruments.