2-picolylamine derivatization for high sensitivity detection of abscisic acid in apicomplexan blood-infecting parasites

We have developed a new liquid chromatography-electrospray ionization tandem mass spectrometry methodology based on 2-picolylamine derivatization and positive ion mode detection for abscisic acid (ABA) identification. The selected reaction leads to the formation of an amide derivative which contains a highly active pyridyl group. The enhanced ionization allows for a 700-fold increase over commonly monitored unmodified ABA, which in turn leads to excellent limits of detection and quantification values of 0.03 and 0.15ngmL-1, respectively. This method has been validated in the highly complex matrix of a red blood cell extract. In spite of the high sensitivity achieved, ABA could not be detected in Plasmodium falciparum-infected red blood cells, suggesting that, if present, it will be found either in ultratrace amounts or as brief bursts at defined time points within the intraerythrocytic cycle and/or in the form of a biosynthetic analogue.