Principles
Infrared (IR)-spectroscopy has been used for a long time for the quantitative analysis of gas mixtures, i.e. the determination of the concentration of certain gases in other gases. In conventional IR-spectroscopy, the IR-absorption of a sample is measured when the sample is being irradiated by the light from the narrow-band light source. This narrow band is usually provided by a dispersive element (e.g. grid, interferometer).
Contrary to the conventional method, Kibion® Dynamic uses with non-dispersive IR-spectroscopy (ND-IR) a broad-band light source and acousto-optical detectors which are sensitive only to those wavelengths at which the gases to be measured are IR-absorbing. With two such detectors, individually sensitive to the absorption spectra for 12CO2 and 13CO2, the concentrations of these two gas components to be related to each other for 13C/12C-isotope ratio determination are measured. The IR-absorption spectra of the asymmetrical stretch oscillation modes of both the 13CO2– and 12CO2-molecules are separated almost completely.
NDIR-spectroscopy, utilizing all the absorbing lines of an individual gas component for its detection, has a high sensitivity combined with a very good linearity in measuring individual gas components, a presupposition for determining the 13C/12C-isotope ratio which in breath gas are in the range of 50 to 500 ppm, where 12CO2 accordingly is at concentration of 0,45 to 4,5 Vol.%.
Within that device, every measurement of the gas components IR-absorption is related to a full energy measurement of the IR-light source, available by a reference gas cell filled with the non-IR-absorbing gas. Such, an internal compensation for any instability of the light source is applied, and 13C/12C-isotope ratios are determined down to 0,1 ‰ (per mille) related to ratios near 1,1, % (percent). In absolute terms, that measurement by NDIR-spectroscopy does provide a sensitivity of 1/104 x 1/102 = 1/106 for the isotope ratio, and as demonstrated on IRIS®-systems also has stabilities within ± 0,2 ‰ (per mille) on real life breath samples over the CO2-concentration range between 0,5 to 6 Vol.%.
That capacity is the base that for any 13C-breath test done on an IRIS™ system the amount of 13C-substrate to be used on man needs to contain not more than 15 mg of carbon 13C as the label, to constitute a quantitative test result within reasonable limits of uncertainty.
Calibrations of Kibion® Dynamic demand one breath sample provided from the operator to contain 5 Vol.% of CO2 or more, to allow for the “Concentration Calibration” with automated dilutions by “zero gas” over the range between 5 to 0,3 Vol.%, and one more “operator’s standard breath sample” at about 3 Vol.% of CO2, to adjust and check final calibrations. The daily calibrations require 5 minutes of instrument time, and the monthly total check of calibrations is to be completed within 30 minutes in an automated mode which does not require more than the operator’s samples to be attached and calibrations to be started.
The very heart of Kibion® Dynamic is an analyzer principle which is in use successfully through several of its generations for quantitative analysis of CH4, CO, CO2 and many other gases (“URAS” by ABB, formerly Hartmann & Braun, Frankfurt/Main, Germany) and has been modified for 13C/12C-isotope analysis by the group of Prof Hering and Dr Haisch, University of Düsseldorf, Germany in cooperation with Wagner Analysen Technik GmbH, Bremen, Germany.