Effect of mobile phase composition on the separation of thyrotropin-releasing hormone and some metabolites by reversed-phase ion-pair chromatography.

Sodium dodecyl sulphate was used for the separation of thyrotropin-releasing hormone (TRH) and the related compounds deamido-TRH (TRHOH), histidylprolinediketopiperazine, proline and prolineamide by reversed-phase ion-pair chromatography. The effects of mobile phase composition on retention and selectivity were determined. The parameters studied included acetonitrile, pairing ion and salt concentrations, salt type and pH. The results show that the separation of TRH and its analogue TRHOH can be easily adjusted by small modifications of the pH in the vicinity of pH 2. A remarkable improvement of peak width and peak shape was observed for some analytes when a potassium salt was added to the mobile phase.