An apparatus configured to separate specific compounds in a gas mixture, the apparatus comprising: - a line for delivering a pressure-controlled neutral carrier gas, - a sample chamber of specific volume for collecting a gas mixture to be examined, the sample chamber being removably connectable to the line, - means for injecting the gas sample into said line when the sample chamber is connected to said line and pressurized by said pressure-controlled carrier gas, - a temperature-controlled separation capillary column arranged to receive the gas sample injected into said line; - a gas sensor at the outlet of the capillary column; and - a data processing system which comprises a micro-controller configured to automatically control the measurement sequence; characterized in that: - said line includes a bypass for the pressure-controlled neutral carrier gas; - the sample chamber is removably connectable in the bypass of the line in a bypass configuration relative to the line for pressurizing the gas sample in the sample chamber before injection of the sample into the line, - and in that the apparatus further comprises: - means configured to inject the pressurized gas sample from the bypass into said line during a pre-set injection time, typically between 0.5s and 3s, when the sample chamber is connected in the bypass of said line and has been pressurized by said pressure-controlled neutral carrier gas; and - the data processing system is configured to automatically control the measurement sequence including the sample injection, the injection time and the measurement time. - a line for delivering a pressure-controlled neutral carrier gas, - a sample chamber of specific volume for collecting a gas mixture to be examined, the sample chamber being removably connectable to the line, - means for injecting the gas sample into said line when the sample chamber is connected to said line and pressurized by said pressure-controlled carrier gas, - a temperature-controlled separation capillary column arranged to receive the gas sample injected into said line; - a gas sensor at the outlet of the capillary column; and - a data processing system which comprises a micro-controller configured to automatically control the measurement sequence; - said line includes a bypass for the pressure-controlled neutral carrier gas; - the sample chamber is removably connectable in the bypass of the line in a bypass configuration relative to the line for pressurizing the gas sample in the sample chamber before injection of the sample into the line, - and in that the apparatus further comprises: - means configured to inject the pressurized gas sample from the bypass into said line during a pre-set injection time, typically between 0.5s and 3s, when the sample chamber is connected in the bypass of said line and has been pressurized by said pressure-controlled neutral carrier gas; and - the data processing system is configured to automatically control the measurement sequence including the sample injection, the injection time and the measurement time. - means configured to inject the pressurized gas sample from the bypass into said line during a pre-set injection time, typically between 0.5s and 3s, when the sample chamber is connected in the bypass of said line and has been pressurized by said pressure-controlled neutral carrier gas; and - the data processing system is configured to automatically control the measurement sequence including the sample injection, the injection time and the measurement time.