High-performance liquid chromatography experiment

In a high-performance liquid chromatography experiment, the dependence of the retention parameter, k, on three factors was investigated. The factors were pH (factor P), the concentration of a counter-ion (factor T) and the concentration of the organic solvent in the mobile phase (factor C). Two levels were used for each factor and two replicate measurements made for each combination. The measurements were randomized. The table below gives the average value for each pair of replicates. 

Compounds 23a-23d were tested as tryptophan carriers across bulk model membranes. Transport was conducted with a U-tube that contained a dichloromethane phase between two water phases. At 1 mM concentration, 23a transported 12% of available Trp with only 20% enantioselectivity after 2 h. Increasing transport times led to even less enantioselection. Compounds 23b-23d behave similarly in Trp transport under these conditions. However, reducing the concentration of 23a to 125 XM resulted in greatly enhanced enantioselection (73% ee), though with a reduced rate of transport. These results suggest that 23a can select for the matched L-isomer of tryptophan, but competition with the D-isomer occurs when the concentration of L-Trp becomes depleted. Indeed, HPLC (high-performance liquid chromatography) experiments revealed that near the membrane interface the concentration of L-Trp is diminished... 

The second set of experiments describes the application of high-performance liquid chromatography. These experiments encompass a variety of different types of samples and a variety of common detectors. 

B. Waiczak, L. Morin-Allory, M. Chrdtien, M. Lafosse and M. Dreux, Factor analysis and experiment design in high-performance liquid chromatography. III. Influence of mobile phase modifications on the selectivity of chalcones on a diol stationary phase. Chemom. Intell. Lab. Syst., I (1986) 79-90. 

These experiments were carried out mainly by NMR spectrometry ( H and ljC) and high performance liquid chromatography. Stopped-flow and low temperature techniques were used in some of the NMR experiments. In all cases the reactions were aimed at monitoring the half-life of the starting materials as well as monitoring the products which were formed. Detailed procedures will appear shortly [15]. 

Walczak, B., Chretien, J.R., Dreux, M., Morin-Allory, L., and Lafosse, M. (1987), Factor Analysis and Experiment Design in High-performance Liquid Chromatography. IV. Influence of Mobile Phase Modifications of the Selectivity of Chalcones on an ODS Stationary Phase, Chemom. Intel. Lab. Sys., 1, 177-189. 

To suppress enamine-derived side products, we explored addition of benzotriazole (BtH) to the reaction mixture. The premise behind these experiments was the ability of BtH to form stable adducts with imines,23,24 thereby blocking tautomerization of 19 to 20 through in situ formation of the benzotriazolyl derivative 21. It was hoped that subsequent hydride displacement of the Bt moiety would afford the desired mono alkylated products 23. Indeed, analytical high-performance liquid chromatography (HPLC) revealed a remarkable improvement in terms of product purity, especially for reactions carried out at room temperature, with the desired secondary anilines 23 being essentially the only products detected. In... 

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