Comparison of in-line connected diode array and electrochemical detectors in the high-performance liquid chromatographic analysis of coenzymes Q(9) and Q(10) in food materials

In-line connected electrochemical (EC) and diode array (DAD) detectors were compared in the reversed-phase high-performance liquid chromatographic (RP -HPLC) analysis of coenzymes Q(9) and Q(10) in some food materials (beef st eak, beef heart, Baltic herring fillet, and rye flour). Coenzymes Q(9) and Q(10) were extracted from the samples using a 5:1 n-hexane-ethanol mixture. Coefficient of variation (CV%) of quadruplicate or quintuplicate determine d samples for coenzymes Q(9) and Q(10) was < 10 by both EC detector and DAD . Responses of the detection systems were linear in the range evaluated, 10 -200 ng/injection, and had correlation coefficients exceeding 0.999. Recove ries of added coenzymes Q(9) and Q(10) varied 73-105% for DAD and 74-103% f or EC detector, respectively. Detection limits for coenzymes Q(9) and Q(10) using the DAD system were 4 and 6 ng/injection, respectively, and 0.2 and 0.3 ng/injection by EC detection. Results derived from the two detection sy stems were generally similar. However, although EC detector was 20-fold mor e sensitive, the selectivity was, in some cases, poorer than that of DAD.