Oxidative mode, liquid chromatography

The sulfonate content was determined either by the well-known technique of two-phase titration with hyamine or by liquid chromatography (HPCL). Nonionic surfactants were analyzed by HPLC (16) in the reverse or normal phase mode depending on whether the aim was to determine their content in effluents or to compare their ethylene oxide distribution. 

The direct coupling of liquid chromatography with proton NMR has been attempted numerous times. Early experiments of coupled HPLC- H-NMR were conducted in a stop-flow mode or with very low flow rates [193-195]. This was necessary to accumulate a sufficient number of spectra per sample volume in order to improve the signal-to-noise ratio. Other problems associated with the implementation of on-line HPLC-NMR have included the need for deuterated solvents. However, with the exception of deuterium oxide, the use of deuterated eluents is too expensive for routine analysis. Therefore, proton-containing solvents, such as acetonitrile or methanol, must be used. To get rid of the solvent signals in the spectra, the proton NMR signals of the solvents have to be suppressed. 

Many simple carbohydrates and other polyhydroxy compounds can be oxidized at a silver oxide surface. The oxidation is via an electrocatalytic mechanism involving a Ag(I) oxide. This forms the basis of a flow stream detector operated in an amperometric mode which may be used for either flow injection or high performance liquid chromatography (HPLC) applications. The title electrode has been applied to the detection of simple carbohydrates, triglycerides and nucleic acid components. 

Figure 6.13. Separation mode selection guide for TLC. LSC = liquid-solid chromatography on an inorganic oxide adsorbent BPC = liquid-solid chromatography on a chemically-bonded sorbent RPC = reversed-phase chromatography with a water-containing mobile phase and chemically-bonded stationary phase IPC = ion-pair chromatography with reversed-phase separation conditions and PC = precipitation chromatography. (From ref. [151] Elsevier)...

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