Figure 2.

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.