The odor of an alcoholic beverage is noted as an indicia of intoxication in your client. This indicia is unreliable because “…even under optimum laboratory conditions, breath odor detection is unreliable…” according to the study Police Officers’ Detection Of Breath Odors From Alcohol Ingestion by Herbert Moskowitz, Marcelline Burns, and Susan Ferguson that appeared in Accident Analysis Prevention 31 (1999) 175-180.
The odor of an alcohol beverage is primarily due to congeners. Congeners include fusel oils which are alcohols. There are more than 45 different alcohols that can be congeners. They are mostly aliphatic alcohols. They are not ethyl alcohol but they would be detected on GC/MCS.
Additionally, other volatile organic compounds other than ethanol exhibit Infrared (IR) absorption bands that overlap a 9.5 µm wave length. Wave length on infrared (IR) spectroscopy. Dominic A. Labianca, How Specific for Ethanol is Breath-alcohol Analysis Based on Absorption of I.R. Radiation at 9.5 Micrometers? , and Journal of Analytical Toxicology, vol. 16, November/December 1992, pgs. 404-405.
Furthermore, the odor of alcohol on the breath is only qualitative, not quantitative. The presence of such an odor does not equate to intoxication. Additionally, it may indicate the presence of gastroesophageal reflux.