High sensitive and simultaneous determination of chlortetracycline hydrochloride and tetracycline hydrochloride residues in water using zero-crossing first derivative synchronous fluorescence spectrometry

The weakly fluorescent of chlortetracycline hydrochloride (CTC) and tetracycline hydrochloride (TC) were alkalized under sodium hydroxide (NaOH) to produce products with strong fluorescence. When the two products were coated with cetyltrimethyl ammonium bromide (CTAB) micelles, the fluorescence intensity was further enhanced, which greatly improved the detection sensitivity. Since the conventional fluorescence spectra of CTC and TC alkaline hydrolysis products-CTAB overlapped seriously, synchronous fluorescence spectra scanning were performed at the wavelength difference (Δλ) was 43 nm to simplify the spectra. Then the two synchronous fluorescence spectra were treated with the first derivative. When λ= 350.6 nm, CTC was measured, here the relative fluorescence intensity of TC was 0. Similarly, so did TC at 360.4 nm. The zero-crossing determination was skillfully utilized to eliminate the mutual interference between the two drugs. Moreover, the fluorescence intensity of water sample background was suppressed to nearly 0 at the zero-crossing. The result showed that detection limit of CTC and TC were 0.2593 ng·mL −1 and 0.2199 ng·mL −1 . Recoveries of CTC and TC in water were 86.42 %-99.17 % and 90.56 %-97.79 %, respectively. The new first derivative synchronous fluorescence spectrometry had the merits of speed, simplicity, sensitive, good selectivity and high accuracy, and it was also environmentally friendly.