Amperometric sniffer based on electrodes supported on ion-exchangers for monitoring the state of turning rancid of lipids

A porous gold electrode supported on one face of an ion-exchange membrane, acting as a solid polymer electrolyte (SPE), is proposed as an amperometric sniffer for monitoring the aldehyde content in the headspace in equilibrium with lipid samples, in order to gain indication of their state of turning rancid It was used as a detector for a flow injection system in which aldehydes were injected, after preconcentration by solid phase microextraction on a SPME fiber from the gas phase standing above thermostated samples and subsequent desorption by heating. Repeatable (± 4.5%) sharp peaks were detected over a wide linear concentration range (0.5-200 ppm). A detection limit of about 0.03 ppm was inferred for a signal-to-noise ratio of 3, referred to hexylaldehyde (used as prototype) dissolved in squalene or vegetable oils samples. This approach was applied to the determination of volatile aldehydes from some partially oxidized cereal oils and the results found were compared with both the corresponding peroxide values and their aldehyde content determined by a conventional spectrophotometric method.