Study On Analytical Methods Based On Spectral Signal Weakening And Their Application In The Food And Pharmaceutical Analyses

Application status of fluorescence and resonance light scattering analyses were summarized. Some new methods based on spectral signal weakening effect were proposed based on the previous work in this paper. Firstly, it’s the fluorescence quenching between fluorescent compound and the charge transfer complex which was formed by the reaction of media lacking of binding and analytes with electron-rich molecule structure and N element. New analytical methods were established based on a good linear relationship between amount of analytes and the weakness of fluorescence. Secondly, it’s the other fluorescence quenching of fluorescent compound made by analytes whose maximum absorption wavelength were the same to the excitation light in fluorescence analysis. Related analytical methods were obtained based on a good linear relationship between amount of analytes and the weakness of fluorescence. Thirdly, it’s the second-order scattering reduction because of adding analytes to the solution composed of rare earth ion and surfactant. What’s more, it showed good linear relationship between amounts of analytes and the weakness of second-order scattering. Results were satisfactory when these methods were applied to determine samples in commercial. At last, the mechanisms were explored preliminarily. Details were as follows:1. This study shows that alizarin red (AR) only slightly quenched fluorescence for acridine orange (AO) in an AR/AO mixed solution at pH=5.0-6.0 The reduced fluorescent signal was closely and linearly associated with the level of matrine (MT) added to the system, which is the basis for a new quantitative MT assay method using the fluorescence quenching reaction in the AO-AR system. The results show that under optimal conditions, this method had a 14.9-43.5 mg·L-1 linear detection range with a 1.38 mg·L-1 detection limit and 1.2% precision. In addition, this method was used to determine the MT levels in the commercially available MT-containing pesticides and suppositories, which showed a 96.6～103% recovery. Therefore, this method has multiple advantages, including simple and fast operation, high accuracy and low cost. Moreover, herein, we investigated the underlying mechanism in-depth using an ultraviolet (UV) spectroscopic technique.2. It was found that less energy transfer could occur between the acridine orange and AR under the conditions of pH=6.0. An appropriate amount of melamine (M) added could react with AR to form a charge transfer complex, in which M was an electron donor because of its rich electronic structure and the AR was an electron acceptor. Since the maximum absorption wavelength of the complex and maximum emission wavelength of acridine orange were about the same, the effective energy transfer could occur between the acridine orange and the complex so that fluorescence quenching of the system was more. Fluorescence quenching degree of the system had a good linear relationship with the amount of added M. Accordingly, a novel fluorescence quenching method for the determination of melamine was established. Under the optimum conditions, linear range was 4.26×10-2-30.3 mg·L-1 and the detection limit was 1.29 ×10-2 mg·L-1. RSD was 1.1%. The method was used to determine the melamine in commercial milk and milk powder with recoveries of 97.7～102%. The method is low cost, simple, fast and accuracy. Furthermore, the method mechanism was further explored by UV spectroscopy.3. The study shows that the fluorescence for levofloxacin could be reduced obviously by promethazine hydrochloride (PMH) at 500nm emission wavelength with 300nm excitation wavelength in the solution of pH=2.8. Fluorescence reduced degree of the system had a good linear relationship with the amount of added PMH. Accordingly, a novel fluorescence quenching method for the determination of PMH was established. Under the optimum conditions, linear range was 1.41-84.6 mg·L-1 and the detection limit was 0.426 mg·L-1. RSD was 2.3%. The method was used to determine the PMH in pharmaceutical formulations in commercial with recoveries of 98.2～103%. The method is low cost, simple, fast and accuracy.4. It was found that the fluorescence for levofloxacin could be reduced obviously by pyritinol hydrochloride (PTH) at 500 nm emission wavelength with 295 nm excitation wavelength in the solution of pH=4.6. Fluorescence reduced degree of the system had a good linear relationship with the amount of added PTH. Accordingly, a novel fluorescence quenching method for the determination of PTH was established. Under the optimum conditions, linear range was 3.93×10-2～33.1 mg·L-1 and the detection limit was 1.19×10-2 mg·L-1. RSD was 0.7%. The method was used to determine PTH in commercial pharmaceutical formulations with recoveries of 97.5～105%. The method is low cost, simple, fast and accuracy. Furthermore, the method mechanism was further explored by UV spectroscopy.5. This study shows that the second-order scattering signal (SOS) of the particles which was composed of La3+ and Sodium Dodecylbenzenesulfonate (SDBS), could be weakened by levodopa (L-DOPA) at 600 nm emission wavelength with 300 nm excitation wavelength. The reduced SOS signal of the system had a good linear relationship with the amount of added L-DOPA, which is the basis for a new quantitative L-DOPA assay method using the SOS weakening reaction in the La3+-SDBS system. The results showed that under optimal conditions, this method had a 0.178～39.0 mg·L-1 linear detection range with a 5.39 ×10-2 mg·L-1 detection limit and 2.7% precision. In addition, this method was used to determine L-DOPA levels in the commercially available L-DOPA-containing pharmaceutical formulations, which showed a 99.0～102% recovery. Therefore, this method has multiple advantages, including simple and fast operation, and low cost. Moreover, we investigated the underlying mechanism in-depth using an ultraviolet (UV) spectroscopic technique.