Patent Document ID: 4442353
Application ID: 06275164
Patent Flag: 1

Claim One:
1. In a high-precision method for measuring in situ concentrations of gases and volatile products emanating from any natural or industrial source at a varying flow rate and at a varying pressure above atmospheric pressure before being fed to a mass spectrometer via an input duct and an intermediary expansion closure while maintaining optimal pressure values within said spectrometer and said expansion enclosure by means of vacuum pumps, the method comprising the steps of: continuously sampling over very long periods of time the gases in which variations of concentrations thereof are to be measured; introducing the gases into the expansion enclosure; automatically controlling the rate of flow of the gases into the expansion enclosure to maintain therein a constant pressure between about 10.sup.-2 and 10.sup.-1 millibar by means of: a pressure-limiting valve (12) between said duct and said enclosure (11), and a pressure gauge (16) measuring the pressure in said expansion enclosure for controlling the operation of said valve (12) as a function of said pressure; feeding the expanded gas into the analysing chamber of a mass spectrometer; and automatically regulating the flow of the gas from the enclosure into said analysing chamber to maintain in said chamber a stable pressure of between about 10.sup.-8 and 10.sup.-7 millibar by means of: a piezo-electric valve (22), between said expansion enclosure (11) and the analysing chamber (19) of said mass spectrometer (20), for controlling the gas flow from said enclosure (11) into said analysing chamber, and means for controlling said piezo-electric valve (22) as a function of the pressure in said analysing chamber.