Stationary phase column cleaning

One solution is to replace the column, but a less expensive approach is to attempt to clean the column. Baking is one approach that removes some forms of contamination, but also shortens the column life because it removes some of the stationary phase. A solvent rinse is the most effective means of cleaning a bonded or cross-linked phase column. Solvent rinse kits are available with instructions from most column manufacturers. The procedure involves forcing solvents through the GC column, usually in the following order—water, methanol, methylene chloride, and hexane—using 10-15 psi back pressure. 

Five synthetic and five natural colorants were identified and quantified in lyo-philized dairy products and fatty foods using an automatic method based on solid phase extraction using a stationary phase followed by RP-HPLC C,g columns for the sequential retention of colorants and diode array detection. Lyophilization of the samples coupled with the separation procedure provided clean extracts despite the complexity of the food matrices and preserved the sample for at least 2 months without changes in colorant concentrations. The detection limits achieved for the colorants were found in a wide range from 0.03 to 75 pg/g of the lyophilized sample, according to the limits established by the European Union. ... 

Aspec is designed to receive up to 108 samples. The system is compatible with most standard disposable extraction columns. Analytichem Bond-Elut Baker SPE, Supelco Supelclean, Alltech Extract Clean, etc. There is a choice of more than 20 different stationary phases. 

The early developments of on-line LC-GC have been reviewed by Davies et al. [496] and Koenigbauer and Major [497]. The selectivity characteristics of the mobile and stationary phases can be optimized to give both a cleaned-up sample and group separation by heart-cutting the desired fraction prior to GC analysis. The LC is usually interfaced to the GC by an uncoated, deactivated GC capillary precolumn to transfer the heart-cut from the LC. This heart-cut from the LC is vaporized to focus the solute at the head of the GC column [498]. The volume of the GC precolumn, the volume of the heart-cut, the GC oven temperature, and carrier gas flow for the concurrent solvent evaporation are carefully matched [499,500]. 

When an amino-type column becomes contaminated by physically adsorbed, non-polar materials, it may be cleaned by washing with acetonitrile, hexane, and dichloromethane. If column failure is due to covalent interactions, or to dissolution of the stationary phase, there is very little that can be done to regenerate it. Samples should therefore always be cleaned up, and a pre-column and a saturator column should always be used with the analytical column. 

The column should permit the modulation of retention behavior over a very wide range of conditions. This requirement in fact means that the stationary phase is inert, that is it does not facilitate specific interactions with certain molecular functions of solute molecules with the concomitant advantage of a relatively clean and rapid adsorption-desorption kinetics. Preferably then the stationary phase has no functional groups such as fixed charges that would have strong affinity to counterionic solutes and exclude solutes of co-ionic nature. In this regard the properties of well-prepared hydrocarbonaceous bonded phases indeed approach those that we would expect from an ideal phase. 

Coating the inside of a capillary tube requires pretreatment of the silica so that the liquid will wet the surface and stick to it.1112 Stable stationary phases have been attained recently by bonding the liquid to the silica and/ or crosslinking it, using a variety of methods including gamma irradiation.13 The crosslinked bonded phase OT columns are very stable and can even be washed with (liquid) solvents for cleaning. 

The concept behind the invention is shown in Figure 9.36. It operates with two mechanisms—size exclusion and reverse phase bonded sorption. The purpose is to facilitate the injection of plasma samples without prior clean up to remove proteins that normally clog a reverse phase column. The pore size of the stationary phase is small enough that the large protein molecules cannot enter and the outer surfaces to which they are exposed do not retain them at all, so they are eluted off the column... 

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