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Abstract
Organic amines are important pharmaceutical molecules and appropriate reversed phase HPLC methods for quality control are desirable for them. The development of IP-RPLC methods is challenging for complex profiles of organic amines. Mobile phase pH and ion pair reagent concentration are two important factors affecting the retention behavior of organic amines in IP-RPLC. Loratadine and its eight related compounds were used as the model compounds for studying their retention behavior and the elution profile using a gradient IP-RPLC condition. The parameters examined included the mobile phase pH and the concentration of an ion pairing reagent, SDS. The chromatographic separation and retention factor (k) of each analyte were monitored at different SDS concentrations (0 to 20 mM) and different pH values (6.2 and 3.0). Due to the basicity of the nine compounds in the study, each compound responded differently to the varying ion pairing reagent (SDS) mobile phase concentrations at different pH values. The ionized analytes had increasing retention factors with increasing SDS concentration, while the non-ionized analytes had nearly constant retention factors as a function of the SDS concentration. For the nine organic amines studied, optimal overall separation and resolution were achieved at 3 mM SDS under pH of 6.2 and at 1 mM under pH 3.0, respectively.
Notes
a The approximate pKa's were estimated from the respective chemical structure of each compound by the software ACD/Lab [15, http://www.camsoft.co.kr/chemnews/art/70.htm].