Determination of free hydroxyproline and proline in human serum by high-performance liquid chromatography using 4-(5,6-dimethoxy-2-phthalimidinyl)phenylsulfonyl chloride as a pre-column fluorescent labelling reagent.

A fluorescent labelling reagent, 4-(5,6-dimethoxy-2-phthalimidinyl)phenylsulfonyl chloride, was designed for the determination of amines by precolumn HPLC and was applied to the simultaneous determination of hydroxyproline and proline in serum. The reagent reacted with hydroxyproline and proline at 30 degrees C for 10 min to produce the fluorescent derivatives, which were separated on a reversed-phase column by gradient elution with phosphate buffer (1 mmol l-1, pH 7) and acetonitrile and detected by fluorescence measurement at 315 nm (excitation) and 385 nm (emission). The detection limits (signal-to-noise ratio = 3) for both hydroxyproline and proline were 10 fmol per injection. The within-day (n = 10) and day-to-day (n = 5) relative standard deviations using human sera were less than 2.16% and 2.75%, respectively, for hydroxyproline and less than 2.30% and 3.25%, respectively, for proline. The concentrations of free hydroxyproline and proline in normal human sera (n = 13) were 5.6-18.0 and 137.6-252.6 mumol l-1, respectively. The proposed method was also applied to the determination of hydroxyproline and proline in sera from patients with chronic renal failure. The mean concentrations of hydroxyproline and proline in chronic renal failure were about 2.6 and 1.6 times higher, respectively, than those in normal human sera.