A system is described which can be used to semi-automate the gas chromatographic headspace analysis of acetaldehyde (AA) in polyethylene terephthalate (PET) beverage bottles. The system centers around a 16-port multiposition valve controlled by a digital valve sequencer. Some beverage producers have placed limits on the concentration of acetaldehyde in a capped/stored PET bottle. Quality control of the AA in these beverage bottles by headspace gas chromatography has placed a considerable work load on the manufacturers of these bottles. A typical bottle producer may test 50,000 bottles per year for AA content. The system described here could result in a cost savings of approximately 58 man hours per 1,000 bottles analyzed. In addition, the system has the potential to serve as an automated device for other types of headspace gas chromatography or for automated gas stream monitoring of on-line process.