By K.J. Ingolic
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Extra info for Organotellurium Compounds, Vol. E12b
Solvents for hplc should be of high purity and again many suppliers provide special'hplc grade' solvents, wh ich have been purified and filtered to remove contaminants which might degrade hplc columns. 4. 5% purity) solvents. It is good practice in general to use high quality solvents for the purification of your products, and it is particularly important to use pure solvents when purifying sampies for microanalysis. In most cases purification of a solvent simply involves drying and distilling it, so the next sections are devoted to drying agents and methods used for drying common solvents, and the final section contains descriptions of typical continuous stills.
It is important when using such lines, you ensure that oil bubblers or similar devices do not suck back when the still is cooling. This often happens as a result of the gas volume of the still contracting as it cools, which creates a partial vacuum in the system. It is simply remedied by turning up the flow rate of the inert gas for the period whilst the still is cooling. It is also important that you do not heat up the still system without some mechanism for allowing the increase in gas volume to be released otherwise an explosion may result; this is prevented by incorporating an oil bubbler in the gas line (see Chapter 8).
A yellow colour indicates the presence of low concentrations of peroxides whereas a brown colour indicates high concentrations. Low concentrations of peroxides must be removed before further purification and a number of methods have been suggested4 • One frequently recommended procedure is to shake the solvent with concentrated aqueous ferrous sulphate. Ethers are usually pre-dried over calcium chloride or sodium wire, and rigorously dried over sodium-benzophenone. Careful preliminary drying is necessary because all of these solvents can dissolve substantial quantities of water.