Hexaldehyde and nonanal are both products of the oxidation of common cooking oils, such as olive oil. We detect these by EPA method TO-11A (aldehydes) and many VOC tests, such as EPA TO-17 with Tenax TA or even the now historical OSHA 7. Come to our presentation later this month at the AIHA meeting in Phoenix to learn more. I'll be speaking Tuesday, May 23 at 11:15 am - hope to see you there.