Patent ID: 7003337

Claim:
A method of non-invasive measurement of a concentration of a target analyte in a fluid within a sample matrix, the method comprising the steps of: directing a combined beam of electromagnetic radiation at the sample, the combined beam including at least two repetitive periods of radiation having different wavelengths, the target analyte having different absorption coefficients for two of the different wavelengths, the two wavelengths forming a wavelength pair; while the sample is at a first sample fluid state having an initial amount of fluid, detecting the combined beam with a sample detector arranged to detect a portion of the radiation transmitted through or reflected by the sample to generate an output signal proportional to the intensity of the combined beam at each of the two repetitive periods of radiation of the wavelength pair; subjecting the sample to a second sample fluid state to change the amount of fluid within the sample; measuring the output signal of the sample detector and obtaining an estimate of the amount of fluid in the sample while the amount of fluid in the sample varies from the initial amount in the first fluid state to a second amount in the second fluid state; and combining the measured output signal from the sample detector with the estimate of the amount of the fluid containing the target analyte to produce an estimate of the concentration of the analyte in the fluid; wherein during one of the sample fluid states, the detected intensities at each of the at least two repetitive periods of radiation are made substantially equal by adjusting the intensity of at least one of the repetitive periods of radiation entering the sample.