Determination of the lipid peroxidation product trans-4-hydroxy-2-nonenal in biological samples by high-performance liquid chromatography and combined capillary column gas chromatography-negative-ion chemical ionisation mass spectrometry.

trans-4-Hydroxy-2-nonenal (HNE) is an aldehyde end-product of lipid peroxidation in biological systems which is capable of producing a range of powerful biological effects. We wish to describe a sensitive and selective strategy for the determination of HNE in biological samples. The method is based on the formation of the O-pentafluorobenzyl (O-PFB) oxime derivatives of HNE and its deuterated internal standard which, after sample clean-up by solid-phase extraction and purification by high-performance liquid chromatography (HPLC), were derivatised further to trimethylsilyl ethers. Subsequent capillary column gas chromatography-negative-ion chemical ionisation mass spectrometry (GC-NICIMS) using selected-ion monitoring allowed quantitation in the low ng/ml range. The use of an internal standard and the O-PFB oxime derivatives circumvented the problems encountered previously by other workers because of the volatility and instability of HNE. The syn-isomer of HNE O-PFB oxime followed the anti-isomer on the HPLC and GC columns used, giving a distinctive pair of peaks of characteristic relative proportion. Moreover, the NICI mass spectra of the geometrical isomers were significantly different, providing further evidence to validate the identity of any endogenous HNE recovered. The method was used to identify and quantify HNE in platelets, monocytes, plasma and oxidised low-density lipoprotein.