title: A cut-off in ocular chemesthesis from vapors of homologous alkylbenzenes and 2-ketones as revealed by concentration-detection functions.
abstract: Studies of homologous series of environmental vapors have shown that their chemesthetic (i.e., sensory irritation) potency increases with carbon chain length (that is, their detection thresholds decrease) until they reach a homolog that fails to be detected, even at vapor saturation. All ensuing homologs cannot be detected either. In this investigation, we measured concentration-detection (i.e., psychometric) functions for ocular chemesthesis from homologous alkylbenzenes (pentyl, hexyl, and heptyl benzene) and 2-ketones (undecanone, dodecanone, and tridecanone). Using a three-alternative forced-choice procedure against air blanks, we tested a total of 18 to 24 subjects, about half of them females, average age 31 years, ranging from 18 to 56 years. Stimuli were generated and presented by a computer-controlled, vapor delivery device whose output was quantified by gas chromatography. Exposure time was 6 s and delivery flow 2.5 L/min. Within the context of present and previous findings, the outcome indicated that the functions for heptylbenzene and 2-tridecanone reached a plateau where further increases in concentration did not enhance detection. We conclude that: a) a cut-off point in ocular chemesthetic detection is reached along homologous alkylbenzenes and 2-ketones at the level of heptylbenzene and 2-tridecanone, respectively, and b) the observed effect rests on the homologs exceeding a critical molecular size (or dimension) rather than on them failing to achieve a high enough vapor concentration.
authors.affiliation: Chemosensory Perception Laboratory, Department of Surgery (Otolaryngology), University of California San Diego, La Jolla, CA 92093-0957, USA. ecometto@ucsd.edu
authors.forename: J Enrique
authors.initials: JE
authors.lastname: Cometto-Muñiz
authors.forename: Michael H
authors.initials: MH
authors.lastname: Abraham
mesh_terms: D000293:Adolescent; D000328:Adult; D001554:Benzene / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D005123:Eye / Q000187:drug effects*; D005260:Female; D006801:Humans; D007509:Irritants / Q000633:toxicity*; D007659:Ketones / Q000633:toxicity*; D008297:Male; D008875:Middle Aged; D013329:Structure-Activity Relationship; D014835:Volatilization
chemical_list: D007509:Irritants; D007659:Ketones; D001554:Benzene