Trifloroacetic acid

The most common HPLC solvents used for LC NMR are acetonitrile and water. Both protonated and deuterated acetonitrile and water are commercially available and routinely used, where cost is a major consideration in minimizing the utility of deuterated solvents in HPLC experiments. Commonly, a low percentage of trifloroacetic acid (TEA) is also added to the HPLC solvent system to improve the LC peak lineshape. In some cases, a methanol water solvent mixture replaces the water-acetonitrile system if the compound of interest does not behave well (low solubility, aggregation, broad peak shape). If an MS system is attached to the LC-NMR to monitor the molecular weight than formic acid is preferred as a modifier. Table 12.9 provides a Kst of commonly used hyphenated techniques and their advantages and disadvantages. 

CHjCN or CHjOHiHjO with trifloroacetic acid or formic acid as a modifier. 

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