A mixture of 80% buffer containing 10.0 mMsodium phosphate monobasic and 0.50 mM sodium dodecyl sulfate(pH adjusted to 5.5) and 20% acetonitrile for 9 min at a flow rate1.0 ml min−1were used as a mobile phase and the analytes weredetected at 210 nm. The Hettich Zentrifugen (EBA20, Tuttlingen,Germany) was used for centrifugations