Dry-packing, columns

Dry column chromatography 494 Dry packing, columns (LC) 349 Dry test meter 843 Dual oven (GC) 62 Durapak phases (GC) 125 Dwell time, gradient elution, (LC) 489, 563... 

A useful LC modification is the quick clean-up column. The simplest of this is a capillary pipette plugged with glass wool and partially filled with packing material. The dry packed column is wetted with solvent, sample is applied, and... 

A dry packed column with porous material was used for the characterization according to size of the PVAc latex samples. The packing employed was CPG (Controlled Pore Glass), 2000 A, 200-400 mesh size. Deionized water with 0.8 gr/lit Aerosol O.T. (dioctyl sodium sulphosuccinate), 0.8 gr/lit sodium nitrate and 0.4 gr/lit sodium azide served as the carrier fluid under a constant flowrate. The sample loop volume was 10 pC A Beckman UV detector operating at 254 nm was connected at the column outlet to monitor particle size. A particle size-mean retention volume calibration curve was constructed from commercially available polystyrene standards. For reasons of comparison, the samples previously characterized by turbidity spectra were also characterized by SEC. A number of injections were repeated to check for the reproducibility of the method. 

The packing density is often an easy to measure parameter, particularly for dry-packed columns. However, the packing density does not correlate with plate count, although it does correlate with the void volume [92]. 

Adenosine (0.267 g, 1.0 mmol) was dissolved in 0.5 M HCI in DMA (2.5 mL) with warming and then the solution was cooled to rt. MCPBA (0.300 g, 1.74 mmol) in DMA (2 mL) was added and the solution was stirred for 2.5 h. Additional 0.5 M HCI in DMA (0.5 mL) and MCPBA (0.070 g, 0.4 mmol) were then added and the reaction was allowed to progress for an additional 1 h. The brown mixture was then evaporated to dryness and traces of DMA were removed by coevaporation from EtOH/xylene (1 2, 2x 3 mL). The gummy residue so obtained was dissolved in MeOH (3 mL) and H O was added. A white precipitate was formed which was filtered off and washed with HjO. The combined filtrate and washings were extracted with EijO (2x5 mL), the aqueous layer was concentrated to a small volume, silica gel (— 2 g) was added, and the evaporation was then continued to dryness. This material was placed on top of a dry-packed column (20 g) of silica gel and was developed first with 5% MeOH/CHCI, (500 mL) and then with 7% MeOH/CHClj. Fractions containing the required product were pooled and evaporated to dryness yield 0.151 g (50%). An analytical sample was obtained by crystallization (FtOH). 

To liquid NH, (150mL) in a stainless steel bomb was added the / -D-anomer (2.46 g, 0.0045 mol). The mixture was sealed in and allowed to stand for 25 h at rt. The NH, was then allowed to evaporate. The residue was treated with EtOH and aq 1 M NaOH (4.6 mL), and this mixture was evaporated to dryness. To the residue was added EtOH (10 mL) and silica gel (7 g) and this mixture was evaporated to dryness and the residue, absorbed on. silica gel, was applied to a dry-packed column (silica gel, 100 g). The column was washed with CHCl, (1 L) and CHClj/EiO.Ac (1 1. 1 L). and the washes were discarded. The product was eluted with EtOAc/MeOU (8 2) and evaporation of this solution followed by crystallization of the residue from EtOH (15 mL) gave 0.77 g (59%) of 2-chloro-2 -deoxyadenosinc. 

Dry packing is another very efficient way to pack a column. It is most often used in conjunction with regular or bonded silica gel. If done well, a dry packed column will give excellent resolution. As the name implies, dry packing... 

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