Columns for chromatography can be small or big, according to the amount of material which needs to be loaded onto the column. Pictured below are three glass columns, two of which are used in the organic chemistry teaching labs at CU.
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The "column" on the far left in the photo is actually a Pasteur pipet. This size of column is suitable for 10-125 mg of material. The middle column is a 10 mL disposable glass pipet. You can load about a gram of material on this size column. The column on the right would be used for many grams of material.
Of the three columns pictured, only the column on the right is actually manufactured as a chromatography column. Note the stopcock at the bottom of the column. This is to control the flow of solvent through the column, important for gravity column chromatography applications. The middle column is used for gravity column chromatography in a few of the chemistry majors' laboratory courses (chem 3361 and 3381). Note the piece of flexible tubing which has been added to the bottom of the column.To control the flow of solvent, a pinch clamp would be placed on the flexible tubing at the bottom. The Pasteur pipet column is used for microscale gravity and microscale flash chromatrography procedures; these procedures (usually) do not require a means of control of gravity-induced solvent flow through the column. Much larger chromatography columns are available than the one on the right. The size employed depends on the amount of material which needs to be separated. Large-scale flash columns look like this column but have a standard taper connection at the top so they can be connected to a source of pressurized air. In the Organic Chemistry teaching labs at CU, the most frequently used column is the Pasteur pipet. They work well in microscale flash column chromatography procedures because a pipet bulb fits conveniently on top of them to serve as a source of pressurized air (when you press on the bulb!). Microscale procedures are used at CU Boulder whenever feasible to cut down on waste chemical production. Here is a picture of a packed column of the type on the right. |
Gravity columns are not used in any of the non-major organic lab courses at CU Boulder (chem 3321/3341). The majors (chem 3361/3381) do use this type of chromatography. Gravity columns are a lot slower to run than microscale flash columns. They also are more difficult to set up or "pack" with adsorbent.
Microscale flash chromatography is the method used almost solely in the organic chemistry teaching labs because it is both easy and environmentally friendly. The method is only limited by the fact that it can separate only small amounts of sample. It works best for 25 mg amounts, although we have pushed it to separate 125 mg mixtures if the TLC Rf's of the components of the mixture differ by at least 0.20.
