Experiments 28 HPLC techniques, analysis

DOSY is a technique that may prove successful in the determination of additives in mixtures [279]. Using different field gradients it is possible to distinguish components in a mixture on the basis of their diffusion coefficients. Morris and Johnson [271] have developed diffusion-ordered 2D NMR experiments for the analysis of mixtures. PFG-NMR can thus be used to identify those components in a mixture that have similar (or overlapping) chemical shifts but different diffusional properties. Multivariate curve resolution (MCR) analysis of DOSY data allows generation of pure spectra of the individual components for identification. The pure spin-echo diffusion decays that are obtained for the individual components may be used to determine the diffusion coefficient/distribution [281]. Mixtures of molecules of very similar sizes can readily be analysed by DOSY. Diffusion-ordered spectroscopy [273,282], which does not require prior separation, is a viable competitor for techniques such as HPLC-NMR that are based on chemical separation. 

Experiment 27. Ion pair chromatography of vitamins Experiment 28. Techniques in HPLC analysis of analgesics Experiment 29. Analysis of amino acids as their DNP derivatives Experiment 30. Analysis of paraben preservatives by HPLC with photodiode array detection... 

Experiment 28. Techniques in HPLC analysis of analgesics [13,14] Object... 

We were interested in examining the corresponding monolayer photolysis products of the diazenes as a function of surface pressure. This goal was not reached due to our inability to collect enough material from the film balance experiment (typically, 1016 molecules per run) for HPLC analysis. However, the physical data acquired by interfacial techniques has given information about the nature of the aggregates and their diastereoselectivity. 

Phylloquinone has been extracted from powdered infant formula using supercritical carbon dioxide at 8000 psi and 60°C for 15 min (65). The extracted material was readily recovered by depressurization of the carbon dioxide across an adsorbent trap and then washed from the trap with a small volume of dichloromethane/acetone (1 + 1) to give a sample suitable for direct HPLC analysis. Trial experiments gave recoveries of 92% of phylloquinone from a Chro-mosorb W matrix. A similar technique was applied to the extraction of retinyl palmitate from cereal products (90). 

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