Extracted ion chromatogram of mass transition 351→271 in an 8-hour synovitis sample. The separate peaks show excellent chromatographic resolution of geometrical isomers prostaglandin E2 (PGE2) and PGD2. The low-abundant peak at 351→175 (inset) coincides with the first peak of the main trace, confirming the identity of this analyte as PGE2 rather than PGD2. Note the difference in scales of the left y-axis (showing ion count for PGE2) and the right y-axis (PGD2). cps, counts per second; m/z, mass/charge.
de Grauw et al. Arthritis Research & Therapy 2011 13:R123 doi:10.1186/ar3427