Measuring and testing – Gas analysis – Gas chromatography
Patent
1992-02-28
1994-02-08
Williams, Hezron E.
Measuring and testing
Gas analysis
Gas chromatography
73 317, 128719, G01N 122, G01N 33497
Patent
active
052840549
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of preparing a gas mixture such as exhaled human or animal breath for subsequent analysis and to an apparatus for preparing this preparation.
BACKGROUND OF THE INVENTION
Analysis of a gas mixture is facilitated when the mixture is separated into various fractions before analysis proper. Illustratively a sample of respiratory air is prepared for mass-spectroscopy analysis in that the person from whom the alveolar air, that is the air from the actual lung, is to be investigated, is made to inflate a collecting pouch holding about 1 ltr.
Prior to being introduced into the ion source of the mass-spectrometer, the breath sample must be prepared physically. So far and illustratively this has been done using a cold-trap. The respiratory air to be analyzed first arrives at a trap cooled with frozen methanol wherein the water vapor is frozen out and then this air passes into a second trap cooled with liquid nitrogen where the carbon dioxide is frozen out. At this location the gas components that did not freeze, in particular nitrogen, oxygen and noble gases, are removed using a vacuum pump. Next the second cold trap is heated to allow the frozen carbon dioxide to evaporate, and it is then moved through an intake system into the ion source of mass spectrometer.
Especially with respect to routine use on a large scale, the above described method of sampling, storage and preparation incurs substantial drawbacks: sampled; however, the marked carbon dioxide does not necessarily accumulate in the lung in a uniform manner in time and space; in this respect the above method fails to be integrating. ml remains fairly large; this entails space problems if, for instance, eight samples are taken per patient and at the same time samples from several patients must be shipped and stored. medical labs and therefore entails special costs of operation. automated; ice formation at different sites makes is susceptible to malfunctions; in the event of malfunction, the entire analytical the system of cold traps is capital-intensive.
SUMMARY OF THE INVENTION
The method of the invention is especially advantageous when the approximate composition of a gas mixture is known by its classes of substances and if the fractionating of the gas mixture facilitates the ensuing detection or makes it possible at all or if a special gas component is to be separated for further analysis, for instance to determine isotope ratios.
The separation of a weakly adsorbed component from a mixture of more intensely adsorbed components by means of two beds of adsorbents is possible even when these beds are the same material and the pressures and temperatures are equal. Appropriately, the bed crossed first must be so sized in relation to the quantity of the gas mixture that only the weakly adsorbed component continues to flow to the second bed. More or less all components are adsorbed in the first bed, however, the component to be separated is adsorbed only to a slight degree. This component, on the other hand, is adsorbed in the second bed where it is present in its pure form.
As a rule, that gas component associated with one bed but flowing farther will interfere by displacement desorption with the adsorption in the next bed. A portion of the gas component already adsorbed in the bed is replaced by the gas component associated with the previous bed and thereby the intended separation of the gas components is partly negated. Accordingly, the invention proposes to so size the individual adsorbent beds with respect to quantity and approximate composition of the gas mixture and adsorbing power for the conditions of temperature and pressure prevailing in the beds that the gas component assigned to one bed shall not flow farther into the next. The quantity of gas is determined illustratively by the pressure and temperature in a reservoir from which this gas mixture is fed to the sequence of beds. Knowing approximately the composition of the gas mixture and from the adsorption isotherms of the adsorbents l
REFERENCES:
patent: 4327575 (1982-05-01), Locker
patent: 4759210 (1988-07-01), Wohltjen
"Prufrohrchen MeBtechnik", K. Leichnitz, Jun., 1981, p. 5, 24-29, 48 and 49).
"Organische Chemie", Hans Rudolf Christen et al., 1988, pp. 54 and 55.
"Methoden Der Organischen Chemie", Eugen Muller, 1953, pp. 31-41.
Farley Walter C.
Roskos Joseph W.
Williams Hezron E.
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