Method for calibrating a device for measuring the concentration of creatinine

A method for recalibrating the sensitivity of one or more sensors in a measuring device for measuring concentration of creatinine (Crn) using one or more calibration solutions, wherein the method comprises:

• providing the measuring device for determining concentration of Crn in a solution, wherein the measuring device comprises the one or more sensors having the sensitivity in need of recalibration;
• providing the one or more calibration solutions comprising one or more of a creatine (Cr) calibration solution and/or one or more of a Crn calibration solution for the one or more sensors, wherein the one or more calibration solutions has been stored at at least one unknown temperature after an initial time;
• receiving concentrations at the initial time of Cr and/or Crn in the one or more calibration solutions;
• receiving outputs of the measuring device at an end time;
• calculating concentration of Cr and/or Crn in the one or more calibration solutions at the end time using a two-temperature temperature model, rate equations for an equilibrium reaction of Cr and Crn, and the Arrhenius equation;
• wherein the two-temperature temperature model indicates an estimation of temperature of the one or more calibration solutions from the initial time to the end time, and wherein the two-temperature temperature model includes a variable parameter, and
• wherein the two-temperature temperature model is determined by at least calculating the variable parameter,
• wherein said calculating the variable parameter comprises solving an analytic expression comprising the rate equations for the equilibrium reaction of Cr and Crn, the two-temperature temperature model, and the outputs of the measuring device;
• determining the sensitivity of the one or more sensors based on a relationship between the outputs of the measuring device and the calculated concentration of Cr and/or Crn;
• and
• recalibrating the sensitivity of the one or more sensors for subsequent determination of the concentration of Cr and/or Crn in a sample.