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A new fluorescent labeling reagent, benzimidazo[2,1-<i>b</i>]quinazolin-12(6<i>H</i>)-one-5-ethyl-<i>p</i>-toluenesulfonate (BQETS) was designed and synthesized, and it was successfully applied to the determination of fatty acids with liquid chromatography. BQETS can easily and quickly label fatty acids within 20 min at 90 °C in dimethylformamide with K<sub>2</sub>CO<sub>3</sub> as catalyst. The derivatives exhibit high stability and strong fluorescence with excitation and emission wavelengths of 247 and 401 nm, respectively. The 24 derivatives of fatty acids were completely separated by gradient elution on a Hypersil GOLD C18 column. Excellent linear responses for all fatty acids were observed with correlation coefficients of >0.9991. The method also showed good sensitivity and precision, with limits of detection in the 0.0024-0.0206 μg g<sup>−1</sup> range and relative standard deviations ≤9.6 %. This is the first time that BQETS fluorescent probe and its applications for the determination of fatty acids have been reported. Moreover, this is the first report on the comparison of free fatty acids composition in the above-ground part of <i>Coriandrum sativum</i> L. from different habitats in China.
A simple, sensitive, and selective high-performance liquid chromatography (HPLC) method using 9-(2-iodoethyl)acridone (IEA) as a novel fluorescence derivatizing agent for the simultaneous determination of six thiophenols has been developed. An efficient Pb<sup>2+</sup>-modified OASIS-MCX cartridge was used and could get good recoveries. IEA was successfully used to label thiophenols with high sensitivity and excellent selectivity. The effects of different solvents, pH, and surfactants on fluorescence properties of derivatives were investigated. To obtain the best labeling efficiency, derivatizing parameters including pH value, temperature, and concentration of IEA, as well as types of catalysts were also evaluated in detail. Under the optimal conditions, the separation could be achieved within 12 min with limits of detection (LODs) in the range of 0.6-5.8 μg L<sup>−1</sup> and relative standard deviations (RSDs) < 3.9 %. This is the first time that IEA was applied to the analysis of thiophenols, and the established method has been successfully applied to the trace level detection of thiophenols in industrial wastewater samples.
In this work, we have developed an efficient method for the rapid extraction and separation of triterpene acids from 37 different varieties of raspberry via ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME). The triterpene acids were then determined by high-performance liquid chromatography (HPLC) with fluorescence detection using benzimidazo-[2,1-b]quinazolin-12(6H)-one-5-ethyl-p-toluenesulfonate (BQETS) as the labeling agent. Five triterpene acids, including asiatic acid (AA), maslinic acid (MA), corosolic acid (CA), oleanolic acid (OA) and betulinic acid (BA), were extracted by UA-DLLME using chloroform and acetone as the extracting and dispersing solvents, respectively. After extraction and nitrogen flushing, the extracts were simultaneously characterized by HPLC based on pre-column derivatization using BQETS, a new labeling agent synthesized in our laboratory. Several key parameters affecting the extraction efficiency and derivatization yields were investigated and optimized by response surface methodology (RSM) combined with Box-Behnken design (BBD). The method was further validated for linearity (correlation coefficient <i>R</i> <sup>2</sup> > 0.9979), precision (RSD = 0.23-2.45 %), and recovery (RSD = 90-106.5 %). The limits of detection (LODs) and the limits of quantification (LOQs) were determined to be within the range of 1.83-7.69 µg/L and 6.06-25.47 µg/L, respectively. This is the first report of the use of BQETS as a pre-column derivatization agent for the determination of triterpene acids in real samples. The proposed method has been applied to the determination of five triterpene acids in 37 different raspberry varieties with significantly increased sensitivity compared to other methods. The results obtained indicate that the contents of triterpene acids vary significantly across different raspberry varieties.