Systems and methods for establishing and/or maintaining the accuracy of a
multivariate calibration model designed for quantitative optical
spectroscopic measurement of attributes or analytes in bodily tissues,
bodily fluids or other biological samples, which are particularly useful
when the spectral absorbance of the attribute or analyte is small
relative to the background. The present invention provides an optically
similar reference sample to reduce the effect of instrument or
environment variation on the measurement capability of the model. The
optically similar reference can be a gel composition having scattering
particles suspended therein. The reference gel can be directly applied to
a spectroscopic instrument sampler, or can be in a container specifically
designed for optimal coupling to a spectroscopic instrument.