Septum bleed during GC-MS analysis: utility of septa of various makes.

The significant presence of septum-related ghost peaks, causing interference in routine gas chromatography-mass spectrometry analyses at sample injection port temperatures above 100°C, is demonstrated. A comparative study with commonly employed septa of various types and makes under varying analytical conditions, e.g., injection port temperature, carrier flow rate, capillary column type and oven heating rate reveal that long-chain hydrocarbons, substituted phthalate derivatives and silanes (silicon compounds) are responsible for such interferences, which is confirmed from their respective peak fragmentation patterns after comparison with standard mass spectrometry library data. Consequently, prior blank studies at actual analysis conditions may become mandatory for quantification and reduction of such interferences, ignoring septa quality and performance claims.