UV Spectrophotometric Determination of Trace Amounts of Doxycycline in Water with Separation and Enrichment by Gas Floatation

Trace amounts of doxycycline (DXCC) in water sample were separated and enriched by gas floatation with hydrophilic solvent mixture of n-propanol and absolute alcohol(4+1),from a solution adjusted to pH 8 with 0.01 mol·L-1 NaOH solution.Sodium chloride was added as phase separating agent,and 1×10-4mol·L-1 Fe(NO3)3 solution was added to react with DXCC forming a hydrophobic complex,which was floated into the organic phase.Absorbance of the organic phase was measured photometrically at the wavelength of 383 nm.Linear relationship between values of absorbance and concentration of DXCC was obtained in the range of 3.1×10-7-2.0×10-5mol·L-1.Detection limit (3S/N) of the method found was 2.6×10-7mol·L-1.A self-made floutation installation was used in the determination.Samples of water from different sources were analyzed by the proposed method,and test for recovery was made by standard addition method using these samples as matrixes,giving values of average recovery of 99.7% and RSD′s (n=5) less than 2.5%.