Cyclic oligomers ranging from tetramer to octamer and a tetramer plus –NH(CH2)2CH3 in ethanol extract of polyamide-6 (PA) were identified by HPLC/MS and MS/MS. An HPLC method was developed to detect the residues of the cyclic oligomers in tea catechins isolated by PA column. It showed that catechins had interference on HPLC analysis of the cyclic oligomers, but the interference could be eliminated using polyvinylpolypyrrolidone as an adsorbent to remove catechins in the sample. It is found that pretreatment of PA using 95% (v/v) ethanol was an effective method to eliminate cyclic oligomers residues in the final products isolated by PA column.
Key words: Tea catechins, polyamide-6, cyclic oligomer, residue, high-performance liquid chromatography (HPLC), mass spectrometry (MS).
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