The analysis of pergolide residues in horse plasma by LC with fluorescence detection

Pergolide is used to treat pituitary pars intermedia dysfunction (equine Cushing's disease) a neurodegenerative condition associated with loss of dopaminergic inhibition of the pituitary in horses. After oral administration, only low concentrations of the drug are achieved in plasma, making drug detection and quantification difficult. While direct analysis of plasma using sensitive MS/MS techniques is possible, dirty plasma samples and mobile phase buffers can cause instrumentation to become rapidly incapacitated. A method using LC with fluorescence detection was developed for pergolide analysis. The limit of quantitation (LOQ) for the instrumentation was 2 ng/mL when using direct injection of horse plasma samples, while interferences from the matrix were nominal. The use of SPE provided cleaner extracts and increased the LOQ in plasma samples to 0.15 ng/mL. The LC method developed allowed high sample throughput before pre-columns required replacement, which was extended when SPE cleanup was used. The effectiveness of SPE for the cleanup and pre-concentration of plasma samples containing pergolide was demonstrated with spiked and naturally incurred samples, and LC-MS/MS was used to validate the SPE method against direct injection samples.