Column Precautions

B. Polymerization Procedure. Butadiene was used as a blend in hexane. Neat butadiene was treated with mercuric sulfate, washed with caustic and water, distilled and dried by passage through molecular sieves. At this point, the butadiene was blended with hexane, and the blend was passed through molecular sieve drying columns. Precautions were taken to avoid the presence of water, oxygen and other impurities which would inhibit the polymerization or react with the initiator. 

Before the whole-broth-solvent stream can be fed to the column, the packed bed must be converted to an expanded bed. This is done by pumping a solids-free liquid through the eolumn in an upflow direction and gradually increasing flow until the expanded bed is 1.5-3 times the packed-bed height and has stabilized. This liquid can be water or a water-solvent solution at the same ratio as the whole-broth-solvent feed. When forming an expanded bed in small-lab-scale columns, precautions should be taken to avoid accidentally introducing air into the bottom of the column since an air bubble may form across the... 

The effluent from a GC column is already in the gas phase and needs only to be mixed with argon makeup gas before passage into the flame. Precautions need to be taken to divert temporarily the GC flow when the first solvent peak emerges because it contains far too much material for the plasma to withstand. 

Fractionally distd below ISmm pressure, using packed column and taking precautions to avoid absorption of water. 

The dibutyl ether must be dry and peroxide-free. This can be achieved by filtering it through a large column of basic alumina, or by leaving overnight over sodium wire and distillation. If these precautions are not observed, low yields result. The checkers purified dibutyl ether by distillation from sodium hydride dispersion. 

Do not connect the column to the detector. This precaution will prevent any contaminants precipitating in the flow cell that could damage it. 

The lifetime for GPC columns used under high temperatures is lower than at room temperature. If higher temperatures are necessary, the user should look for special offers of high temperature columns or check which temperature interval is permitted for the selected column type. For a maximum lifetime a few precautions are advantageous ... 

If the liquids remain discolored even after these precautions, it is often possible to purify them further by first stirring with activated charcoal, followed by passing the liquid down a short column of neutral or acidic alumina as discussed in Section 2.1.3.2 [33]. 

Other modes of LC operation include liquid-liquid partition chromatography (LLC) and bonded phase chromatography. In the former, a stationary liquid phase which is immiscible with the mobile phase is coated on a porous support, with separation based on partition equilibrium differences of components between the two liquid phases. This mode offers an alternative to ion exchange in the fractionation of polar, water soluble substances. While quite useful, the danger exists in LLC that the stationary phase can be stripped from the column, if proper precautions are not taken. Hence, it is typical to pre-equil-ibrate carefully the mobile and stationary phases and to use a forecolimn, heavily loaded with stationary phase 9). 

The concentrations of nitrosamines were reduced to undetectable levels by ultraviolet treatment of the amine solutions and were not increased by addition of 2 ppm NaN02> indicating that the nitrosamines were present originally in the amines and were not formed in the GC injection port. Similar concentrations were found when the amine samples were analyzed using the column extraction method. Direct injection is appropriate for analysis of relatively simple mixtures, if adequate precautions are taken ( ), but can result in significant artifact formation in more complex systems (42). 

II What precautions do you think would be necessary when using 3x3 columns ... 

The in-line filter ahead of the column is a last-second filtering precaution, just in case particulates are introduced with the sample. 

Apparatus The introduction of sample(s) may be accomplished by using airtight syringes and a simple conventional gas chromatograph. Nevertheless, the equilibrium has got to be carried out in a separate chamber and the vapour phase is subsequently conveyed to the column taking necessary and every possible precautions so as to avoid any minute changes in the equilibrium. 

The following operating guides are recommended for maintaining reversed-phase columns. Consult the vendor s column instructions for precautions and column regeneration guides. 

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