Chromatographic methods for measuring impurities in a gas sample

A chromatographic method for measuring impurities in a gas sample having a gas background, said method comprising the steps of:

• a) providing a chromatographic system having a first sample loop, a first separation column, a second sample loop, a second separation column and a detector serially connected through a plurality of valves, said system being provided with a carrier gas and the gas sample;
• b) providing the second sample loop with the carrier gas for purging said second sample loop through a second loop venting line;
• c) isolating said second sample loop;
• d) providing said first sample loop with the gas sample for filling said first sample loop with a gas sample volume;
• e) injecting said gas sample volume into said first column to substantially separate the gas background from the impurities;
• f) venting said first column outside the system through a first column vent line for a predetermined venting period of time for eliminating at least a part of the gas background;
• g) connecting said first column to said second sample loop during a predetermined filling period of time for filling said second sample loop with a gas mixture comprising a carrier gas volume and a slice of the gas sample volume comprising at least one of said impurities;
• h) isolating said second sample loop;
• and
• i) injecting said gas mixture into the second column to separate the gas mixture into a plurality of baseline resolved peaks, thereby allowing measurement of the at least one of said impurities.