Analytical variables affecting analysis of Fisoprostanes and Fneuroprostanes in human cerebrospinal fluid by gas chromatography/mass spectrometry

Fisoprostanes (FIsoPs) are a gold marker of lipid peroxidation in vivo, whereas Fneuroprostanes (FNPs) measured in cerebrospinal fluid (CSF) or brain tissue selectively indicate neuronal oxidative damage. Gas chromatography/ negative-ion chemical-ionization mass spectrometry (GC/NICI-MS) is the most sensitive and robust method for quantifying these compounds, which is essential for CSF samples because abundance of these compounds in CSF is very low. The present study revealed potential interferences on the analysis of FIsoPs and FNPs in CSF by GC/NICI-MS due to the use of improper analytical methods that have been employed in the literature. First, simultaneous quantification of FIsoPs and FNPs in CSF samples processed for FNPs analysis could cause poor chromatographic separation and falsely higher FIsoPs values for CSF samples with high levels of FIsoPs and FNPs. Second, retention of unknown substances in GC columns from CSF samples during FNPs analysis and from plasma samples during FIsoPs analysis might interfere with FNPs analysis of subsequent runs, which could be solved by holding columns at a high temperature for a period of time after data acquisition. Therefore, these special issues should be taken into consideration when performing analysis of FIsoPs and FNPs in CSF to avoid misleading results.