Patent ID: 7451634

Claim:
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.