Determination of tetracycline and 4-epimeric tetracycline by TLC-fluorescence scanning densitometry

A newly sensitive TLC-fluorescence scanning densitometer (TLC-F) is described for the simultaneous determination of tetracycline (TC) and 4-epimeric tetracycline (4-ETC), using a mobile phase system of chloroform: methanol:acetone:1% aqueous ammonia (10:22:53:15, v/v) and a silica gel thin-layer, previously treated with 0.27 mol/L sodium EDTA solution adjusted to pH 9.0. The TC and 4-ETC were well separated and their R-f values are 0.64 and 0.24, respectively. The excitation wavelength was set at 365 nm. The linear ranges are 0.96 similar to 96.2 ng for TC and 0.96 similar to 48.1 ng for 4-ETC. The limit of detection for TC and ETC are 0.31 ng and 0.57 ng respectively. The epimeric reaction between TC and 4-ETC was studied. Their recoveries in urine are 97%similar to 106% and the relative standard deviations (RSDs) of both are less than 4.0%.