Wet-column

May incorporate device for continually wetting column High loadings of particulates may plug unit with packing... 

It is always desirable to use a wet column once a column has been used, this condition prevails. It is advantageous to admit a little xylene while regulating the heater, before addition of the reactants. 

Dry-column chromatography is another approach to the separation of large quantities of a mixture of products. I think it s easier than wet-column chromatography, though more limited. 

HPLC. Is it high-performance liquid chromatography or high-pressure liquid chromatography or something else It s probably easier to consider it a delicate blend of wet-column chromatography and gas chromatography (see Chapters 20 and 24, respectively). 

Air bubbles are the nasties in HPLC work. They cause the same type of troubles as with wet-column chromatography, and you just don t want them. So there s usually a bubble trap (Fig. 112) before the eluent reaches the pump. This device is quite simple, really. Bubbles in the eluent stream rise... 

Once the sample is in the column, there s not much difference between what happens here and what happens in paper, thin-layer, vapor-phase (gas), wet-column, or dry-column chromatography. The components in the mixture will stay on the stationary phase, or move in the mobik phase for different times and end up at different places when you stop the experiment. 

A novel development for HPLC is something called bonded reversed-phase columns, where the stationary phase is a nonpolar hydrocarbon, chemically bonded to a solid support. You can use these with aqueous eluents, usually alcohol-water mixtures. So you have a polar eluent and a nonpolar stationary phase, something that does not usually occur for ordinary wet-column chromatography. One advantage is that you don t need to use anhydrous eluents (very small amounts of water can change the character of normal phase columns) with reversed-phase columns. 

The liquid may flow in a turbulent layer over an inclined or vertical surface (wetted columns, Votator). Discontinuities in the surface may cause periodic mixing of the liquid layer during its flow (packed columns). 

Chromatography is perhaps the most useful means of separating compounds to purify and identify them. Indeed, separations of colored compounds on paper strips gave the technique its colorful name. Although there are many different types of chromatography, all the forms bear tremendously striking similarities. Thin-layer, wet-column, and dry-column chromatography are common techniques you ll run across. 

Wet-column chromatography, as you may have guessed, is chromatography carried out on a column of adsorbent, rather than a layer. Not only is it cheap, easy, and carried out at room temperature but also you can separate large amounts, gram quantities, of mixtures. 

Occasionally, you ll be asked to clean and/or dry your product using column chromatography by pipet. It s a lot like large-scale wet-column chromatography. 

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