Patent ID: 7663755

Claim:
A method for determining the optical pathlength through a liquid-containing sample comprising: a. placing the liquid-containing sample in a sample holder which provides a substantially vertical light path through the sample, said vertical light path having an unknown optical pathlength through the sample, and said liquid-containing sample having an unknown absorbance; b. transmitting light through the sample along the vertical light path, the light comprising a first calibration wavelength and a second calibration wavelength; the first calibration wavelength and the second calibration wavelength having been preselected within the range of wavelengths of 750-2500 nanometers to provide two characteristic light signal values for the liquid with a predetermined relationship between them and with the vertical optical pathlength through the sample; c. determining measured light signal values at the first calibration wavelength and at the second calibration wavelength; and d. determining from the measured light signal values, and the predetermined relationship, the vertical optical light path length through the sample.