Sweeping under controlled electroosmotic flow and micellar electrokinetic chromatography for on-line concentration and determination of trace phlorizin and quercitrin in urine samples.

A novel sweeping under controlled electroosmotic flow scheme was developed for preconcentration and determination of neutral compounds by micellar electrokinetic chromatography (MEKC). An anionic surfactant, sodium dodecyl sulfate (SDS), was added into the buffer for sweeping and separation. By controlled electroosmotic flow (EOF) equal to the counter electrophoretic flow, the surfactants were at an immobile state in capillary. The neutral analytes with sample solution was injected electroosmotically into capillary and swept by SDS micelle for essentially an unlimited volume. The injected sample plug lengths for phlorizin and quercitrin under 18 kV for 70 min were experimentally estimated as 1532 cm, corresponding to 51-fold the effective capillary length. The sweeping under controlled EOF scheme resulted in increased detection factors for phlorizin and quercitrin of 2.3 × 104 and 2.1 × 104 using 70 min injection relative to a traditional pressure injection. The proposed method has been adopted to analyze trace phlorizin and quercitrin in urine samples successfully.

Bioavailability of phloretin and phloridzin in rats.

Phloretin is a flavonoid found exclusively in apples and in apple-derived products where it is present as the glucosidic form, namely, phloridzin (phloretin 2'-O-glucose). In the present study, we compared the changes in plasma and urine concentrations of these two compounds in rats fed a single meal containing 0.25% phloridzin or 0.157% phloretin (corresponding to the ingestion of 22 mg of phloretin equivalents). In plasma, phloretin was recovered mainly as the conjugated forms (glucuronided and/or sulfated) but some unconjugated phloretin was also detected. By contrast, no trace of intact phloridzin was detected in plasma of rats fed a phloridzin meal. These compounds presented different kinetics of absorption; phloretin appeared more rapidly in plasma when rats were fed the aglycone than when fed the glucoside. However, whatever compound was administered, no significant difference in the plasma concentrations of total phloretin were observed 10 h after food intake. At 24 h after the beginning of the meal, the plasma concentrations of phloretin were almost back to the baseline, indicating that this compound was excreted rapidly in urine. The total urinary excretion rate of phloretin was not affected by the forms administered, and was estimated to be 8.5 micromol/24 h in rats fed phloretin or phloridzin. Thus, 10.4% of the ingested dose was recovered in urine after 24 h.