SummaryTagging techniques with reagents used for fluorescent detection for short and long-chain fatty acids using high-performance liquid chromatography are evaluated in terms of the tagging reactions, handing, flexibility, stability of the reagents. Emphasis is given to the applications of the tagging techniques to relatively high molecular mass fatty acids. The fatty acids or carboxyhc compounds were derivatized to their corresponding esters with 9-(2-hydroxy ethyl )-carbazole (HEC) in acetonitrile at 60 ~ with N, N'-carbonyldiimidazole (CDI) as a coupling agent in the presence of 4-dimethylaminopyridine (DMAP). A mixture of esters of C1-C20 fatty acids was completely separated within 45 min using gradient elution on a reversed-phase Cls column. The maximum fluorescence emission for the derivatized fatty acids is at 365 nm O~ex 293 nm). Studies on derivatization conditions indicated that fatty acids react rapidly and smoothlywith HEC in the presence of CDI and DMAP in acetonitrile to give the corresponding sensitively fluorescent derivatives. The application of this method to the analysis of long chain fatty acids in plasma is also investigated. The LC separation shows good selectivity and reproducibility for fatty acids derivatives. The relative standard deviations (n = 6) for each fatty acid derivative are < 5.0%. The detection limits are at 38 -57 fmol levels for C14-C20 fatty acids and lower levels for < C14 fatty acids.

SummaryWe report four new derivatization agents, acridone-N-acetic acid (ARC), carbazole-9-ylacetic acid (CRA), carbazole-9-ylpropionic acid (CRP), and 2-methyl-2-carbazole-9-ylacetic acid (MCRA), with strong fluorescence emission which has low dependence on solvent polarity. The emission maxima for ARC, CRA, CRP, and MCRA were 430 nm ()~ex 404 nm), 368 nm ()~ex 335 nm), 356 nm ()~ex 340 nm) and 360 nm @ex 330 nm), respectively. The effects of mobile-phase composition, pH, and temperature on the liquid chromatographic retention behavior of the four fluorescence agents were investigated. An experimental model was established for calculating the inclusion constants of cyclodextrin (CD) complexes in the dynamic state, using [3-cyclodextrin (~-CD) and hydroxypropyl-[~-cyclodextrin (HP-~-CD) as examples, and different mobilephase compositions. On the basis of the model, the inclusion constants of the solutes in pure water (Kfw) were determined by extrapolation. The thermodynamic parameters (AH ~ and AS ~ and dissociation constants Kam for the solutes in this chromatographic system were obtained by means of capacity factor (k) values using a corresponding model formulation.

The aim of this work was to investigate the microbial diversity characteristics and driving factors in a high elevation drop river and to analyze the potential risks of river microorganisms to human health. In March 2019, we analyzed the microbial diversity characteristics in surface water and sludge from the Huotong River using high-throughput sequencing. The Huotong River is of great importance to the production and life of the people living along this river. The sampling points were set at the estuary of the river, on a downstream section of the river, on an upstream section of the main river, at one tributary flowing through a town, at one tributary with a barrage, and at the source of one tributary. The results showed significant differences in bacterial diversity in different areas of the river. For example, actinomycetes were less abundant in water samples from the headwaters of tributaries and more abundant upriver. The results revealed that different intensities of human activities had significant different effects on functional flora. Anthropogenic disturbance and human activities reduced the abundance of probiotic bacteria and increased the abundance of pathogenic bacteria in the river. The changes in functional floral diversity may pose potential threats to human health.