Measurement of urinary F₂-isoprostanes by gas chromatography-mass spectrometry is confounded by interfering substances

Abstract

Analysis of F₂-isoprostanes in urine using gas chromatography-mass spectrometry is confounded by the presence of endogenous compounds interfering with the internal standard, 15-F_2t-IsoP-d₄ (m/z 573). Previous efforts to resolve the 15-F_2t-IsoP-d₄ from co-eluting peaks with different solid phase extractions were unsuccessful. This study has now used a highly-deuterated, d₉-analogue of the derivatization agent N,O-Bis(trimethyl-d₉-silyl) trifluoroacetamide (BSTFA-d₉) yielding trimethylsilyl ethers, but this was not successful in resolving the 15-F_2t-IsoP-d₄ from co-eluting peaks. It was hypothesized that interfering peaks at m/z 573 could be the tetrahydro analogue of 15-F_2t-IsoP. However, using an authentic standard showed the interfering peaks are not due to this metabolite. In subsequent experiments good resolution was shown of the 15-F_2t-IsoP peak using 8-F_2t-IsoP-d₄ (m/z 573) as the internal standard. These data show that care must be taken when using GC-MS for quantitation of F₂-IsoPs to prevent interfering substances affecting the results.

Keywords::

• Isoprostanes
• GC-MS
• 15-F_2t-IsoP

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

This paper was first published online on Early Online on 19 November 2009.