Reversed-phase high-performance liquid chromatography analysis of 1,3- and 1,2(2,3)-positional isomers of palm-based diacylglycerols
2013
Lo, S. K. | Tan, C. P. | Lai, O. M. | Amir Hossein Saberi | Beh, B. K.
Reversed-phase high-performance liquid chromatography method using charged aerosol detector was developed for separation of 1,3- and 1,2(2,3) positional isomers of palm oil- and palm kernel oil-based diacylglycerols (PO-DAG and PKO-DAG, respectively) with different equivalent carbon numbers(ECN) and without the need of sample derivatisation. In this method, step-wise gradient of acetone and acetonitrile was used and a total retention time of 28 min was attained. Identification of PKO- and PODAG molecular species was accomplished using synthetic DAG standards. Completeness of separation as well as identification of PKO- and PO-DAG molecular species including positional isomers with different ECN values were verified where similar elution patterns as well as the same number of identified peaks were observed for the chromatograms of PKO-DAG and PKO-DAG standards, as well as the PO-DAG and PO-DAG standards. Among the 1,3-DAG species and/or 1,2-DAG species, as ECN value of their fatty acid constituents increased, their corresponding retention time always increased. However, among the PKO- as well as PO-based synthetic DAG with the same ECN values, 1,3-DAG were always found to elute earlier than the respective 1,2-DAG. Furthermore, some exceptional examples were observed among the PKO- as well as PO-based synthetic DAG standards with the different ECN values where a few of 1,3-DAG with the relatively higher ECN values eluted earlier than 1,2-DAG with relatively lower ECN values. The last two observations evidence the defect of ECN-based prediction for identification of DAG positional isomers with the same ECN as well as for different ECN values.
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