Method for calibrating spectrophotometric apparatus

A method of determining the concentration of at least one Analyte in a Sample in a second apparatus comprising:

• (i) providing the second apparatus having at least one upgraded primary calibration algorithm for each of the one or more analytes, the at least one upgraded primary calibration algorithm developed by combining some, or all of an original primary calibration data set obtained from one or more first apparatus for at least one wavelength of a standard set of wavelengths, with additional data from the second apparatus, the additional data obtained using a smaller similar primary calibration set, a subset primary calibration set, or both, for at least one wavelength of a standard set of wavelengths, wherein the one or more wavelengths of the standard set of wavelengths are the same as, or different from, wavelengths of a wavelength calibration table for the first apparatus, the second apparatus, or both the first and the second apparatus;
• (ii) measuring absorbance values of the sample at one or more wavelengths from the standard set of wavelengths, on the second apparatus;
• (iii) calculating a concentration of the one or more Analyte in the sample, by applying the at least one Primary Calibration Algorithm to the order derivative of the absorbance measurements of step (ii).