Preparation of packed columns

The field of aqueous SEC is of growing interest and also represents an area of active development by several companies, with Polymer Laboratories included. In this area, contrary to the organic SEC scenario, a variety of polymer chemistries are employed in the preparation of the column packing materials. This fact alone makes the practice of aqueous SEC more difficult than its organic counterpart and requires the suppliers of such columns to offer a good level of technical support to the column user. This chapter outlines the characteristics and applications of PL aquagel-OH aqueous SEC columns. 

Enantiomeric separations have proven to be one of the most successful applications of packed column SEC. Despite initial reluctance, many analysts now use SEC routinely for both analytical and preparative chiral separations. Additional studies of chiral recognition in SEC and continued improvements in instrumentation will ensure a prominent role for SEC in chiral separations methodology in the future. 

Slurry packing techniques are required for the preparation of efficient columns with rigid particles of less than 20 micrometers in diameter. The same general packing apparatus. Figure 4.8, can be used to pack columns by the balanced-density slurry, liquid slurry, or the viscous slurry techniques. Down-fill slurry packing is the method of choice for small bore columns and packed capillary columns. 

Equation (11) shows that ko increases rapidly with increasing porosity (i/). For columns used in HPLC, e is usually about 0.40 and seems not to depend on the material and the packing technique used for the preparation of the column (22). For e = 0.40 the equation predicts that A — I x I0" in agreement with experimental observations. In order to achieve the very homogeneous packing necessary for a good colunin efUciency, (he... 

S. Scalia and D.E. Games, Determination of free bile acids in pharmaceutical preparation by packed column supercritical fluid chromatography, J. Pharm. Sci., 82 44 (1993). 

For the preparation of capillary columns for gas chromatography, the fused silica column wall is deactivated using polysiloxanes, and modified with a suitable stationary phase. Hetem19 discussed the use of polymethylhydrosiloxanes (PMHS) for deactivation and subsequent coating with a polymerized C18-type silane for stationary phase formation. Stationary phases used in packed GC are analogous to HPLC. 

Another approach to the preparation of a column of low hydrophobicity is to use an organosilane with a short C-chain, e.g., trimethylchlorosilane. However, Nice et al. 40) found that such a column (Hypersil SAS) deteriorated rapidly over 24 h when used with an aqueous mobile phase. The aged column exhibited loss of retention for polypeptides, and analysis showed an increase in the silanol content of the packing. 

Instead of packed columns, monolithic (continuous bed), analytical, or capillary columns in the form of a rod with flow-through pores offer high porosity and improved permeability. Silica-based monolithic columns are generally prepared by gelation of a silica sol to a continuous sol-gel network, onto which a Cjg or another stationary phase is subsequently chemically bonded. Such columns provide comparable efficiency and sample capacity as conventional columns packed with 5-pm particle materials, but have three to five times lower flow resistance, thereby allowing higher flow rates and fast HPLC analyses. Rigid polyacrylamide, polyacrylate, polymethacrylate, or polystyrene monolithic columns are prepared by in sim polymerization. 

Inverse gas chromatography has proven to be a particularly important technique for the investigation of polymers, with most studies making use of packed columns. IGC also has been recently extended to the investigation of fibers and of polymers coated on capillary columns. The preparation of each of these columns is very important to overall success. 

GC can achieve the highest resolution of the essential oils, but there are some significant limitations with regards to preparative scale separations. Typically, as the sample capacity is increased, the resolution of the chromatographic separation is reduced. On a lab scale, equipment is available that permits 24-hour automated and unattended separations, however, the recovery yield and sample resolution are still problematic [57]. Capillary column GC has become so routine for essential oil analysis that one rarely finds a lab without that capability. A multitude of detectors exist for GC thermal conductivity (TCD), flame ionization (FID), flame photometric (FPD), thermionic specific (TSD), photoionization (PID), electron capture (ECD), atomic emission (AED), mass spectrometry (MS), and infrared spectroscopy (FTIR) [58,59]. The TCD is used primarily with preparative-GC (packed column) because it is... 

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