On-line headspace-multicapillary column-ion mobility spectrometry hyphenation as a tool for the determination of off-flavours in foods.

In this work, an ion mobility spectrometer (IMS) with a tritium ionization source on-line coupled to a headspace (HS) autosampler and a multicapillary column (MCC) was evaluated for the monitoring of lipid oxidation products in milk with different flavours (cacao, fruits, cereals and nuts) and linseed oil samples enriched with omega-3 acids. In this combination, the multicapillary column is used as an interface between the HS and the IMS, providing the efficient separation of the volatile compounds. In this way, the proposed method permits the detection of hexanal, 2-butanone, acetone and dimethyl sulfide as representative degradation products. The limits of detection were in the interval 0.3 μg L(-1) (for hexanal in milk) to 3.0 μg L(-1) (for dimethyl sulfide in linseed oil) while the limits of quantification varied between 1.1 μg L(-1) (for hexanal in milk) and 9.6 μg L(-1) (for dimethyl sulfide in linseed oil). The precision of the method was evaluated as relative standard deviation and the values were better than 8% in all cases. The evolution of the volatiles profile during 36 days under different storage conditions (temperature, oxygen and light) demonstrates the capability of the HS-MCC-IMS coupling for the estimation of the degradation of the samples. After the degradation study, it can be concluded that the stability of the milk samples during storage is more affected by the light while temperature was more critical for oil samples.