Complex ionic, liquid chromatography

Nowadays, ESI is the leading member of the group of atmospheric pressure ionization (API) methods and the method of choice for liquid chromatography-mass spectrometry coupling (LC-MS, Chap. 12). [10-13] Currently, ESI and MALDI (Chap. 10) are the most commonly employed ionization methods and they opened doors to the widespread biological and biomedical application of mass spectrometry. [5,10,11,13-17] Moreover, ESI serves well for the analysis of ionic metal complexes [18,19] and other inorganic analytes. [20-22]... 

One of the most powerful separation techniques available is high-performance liquid chromatography (HPLC) [6], It has a broad range of applicability which also encompasses non-volatile substances such as ionic compounds (e.g. amino acids, proteins, metal complexes) or high-molecular weight compounds, such as... 

As a new class of materials, ionic liquids require special analytical methods. In the case of imidazolium halides and similar compounds the most common impurities are amines, alkyl halides and of course water. Seddon et al. described a method for the detection of residual amines using the strong UV absorbance of copper tetramine complexes. These complexes are readily formed by the addition of Cu2+ ions [24]. The detection of both amines and alkyl halides is possible by NMR spectroscopy but with limited resolution [25]. By far the most powerful analytical method is liquid chromatography combined with UV detection. This sensitive method allows the detection of traces of amines and halides [26]. Unreacted amines can be also detected by ion chromatography combined with a suppressor module. In this case detection is achieved using a continuous flow conductivity cell since amines are protonated and thus detectable. For traces of other ionic impurities ion chromatography is also the most powerful analytical tool [27]. Finally, residual water can be quantified using Karl Fischer titration or coulometry [28]. 

The most commonly used method for the analysis and purification of peptides mixtures is reversed-phase liquid chromatography (RPLC). The experimental system usually comprises an -alkylsilica-based stationary phase material from which peptides are eluted with gradients of increasing concentration of acetonitrile in the presence of ionic modifier, e.g., trifluoroacetic acid (TFA). With modern instrumentation and columns, complex mixtures of peptides can be separated and low picomole amounts of resolved components can be collected. Separations can be easily manipulated by changing the gradient slope... 

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