Determination of carbon monoxide with a modified zeolite sorbent and methanization-gas chromatography

The purpose of this study was to develop an alternative sorbent sampling technique to concentrate CO from an air sample for subsequent instrumental analysis. Y52 zeolite doped with 9.4 wt % cuprous ions was found to have high capacity, stability to air, and thermal reversibility for CO. The Cu(I)-modified zeolite was packed in glass tubes, preceded by a drying tube containing silica gel. Air was sampled through the tubes at the flow rate of 100 mL/min. Collected CO was thermally desorbed at 300 degrees C and determined by gas chromatography with reduction of CO to methane and flame ionization detection (TD-GC-CH4-FID). Breakthrough capacity of the sorbent was found to be 2.74 mg CO per gram of sorbent. For 2-L air samples containing 12.5 to 100 ppm CO and 50% relative humidity at room temperature, recovery of CO was found to be 96.6% with pooled relative standard deviation of 5.8%. The estimated detection limit for a 2-L sample was 0.2 ppm. Collected CO was stable at room temperature for 1 day and up to 7 days at 4 degrees C if the sorbent tube was flushed with helium before storage. In field testing, the ratio of CO measured by the new technique and by a reference technique was found to be 0.93 with pooled relative standard deviation of 6.3%. This unique new sorbent coupled with TD-GC-CH4-FID shows promise as a sensitive and specific alternative for measurement of CO in air.