Patent ID: 8035816

Claim:
A method for measuring optical absorption of samples, comprising: directing light from a radiation source at a sample to be examined and at a reference sample; modulating the light transmitting the sample to be examined with a first frequency and modulating the light transmitting the reference sample with a second frequency, the first frequency being different from the second frequency; converting the radiation intensity transmitted from the sample to be examined and from the reference sample into an electrical mixed signal via a photoelectric converter; increasing the electrical mixed signal in a pre-amplifier; converting the increased electrical mixed signal into a digital mixed signal in an analogue-to-digital converter; separating the digital mixed signal, with regard to the first frequency, into a measurement signal associated with the sample to be examined and, with regard to the second frequency, into a reference signal associated with the reference sample using a digital lock-in amplifier; and forming a quotient from the reference signal and the measurement signal as a measurement for the concentration of the sample to be examined in such a way that the reduction in the intensity of the radiation due to absorption leads to an increase in sensitivity.