Columns packed versus capillary

If 10,000 theoretical plates can be generated on a packed column and 250,000 theoretical plates can be generated on a capillary column assuming k = 5, what selectivity is required on each column to obtain a resolution greater than 1.5 Use this to explain why 10 times more different liquid phases have been used for packed column GC versus capillary GC. 

C22. Cramers, C. A., Rijks, J. A., and Bocek, P., Packed versus capillary columns in gas chromatography. Clin. Chim. Acta 34, 159-168 (1971). 

Figure 4.5 Plate height versus linear carrier gas velocity for a packed versus a capillary GC column.

Trends The results of a survey of 12 leading experts in gas chromatography appeared in 1989 and outlined their thoughts on projected trends in gas chromatographic column technology, including the fumre of packed columns versus capillary columns (1). Some responses of that panel are... 

Contaminant by-products depend upon process routes to the product, so maximum impurity specifications may vary, eg, for CHA produced by aniline hydrogenation versus that made by cyclohexanol amination. Capillary column chromatography has improved resolution and quantitation of contaminants beyond the more fliUy described packed column methods (61) used historically to define specification standards. Wet chemical titrimetry for water by Kad Eisher or amine number by acid titration have changed Httle except for thein automation. Colorimetric methods remain based on APHA standards. 

Figure 5 Comparison of chromatograms for different volume injections but constant mass (800 amol) of met-enkephaUn (peak indicated by arrow). Injections were 10 nL of 80 nM (A), 100 nL of 8.0 nM (B), and 1000 nL of 0.80 nM (C). Capillary column was 8 cm long, 25 im i.d. fused silica capillary packed witb 5 (im Alltima C-18 reversed-phase particles. After loading sample, the column was rinsed with 5% solvent B-95% solvent A for 5 min before gradient elution started. Gradient elution started at 5% solvent B, linearly changed to 50% solvent B in 5 min, kept at this composition for 2 min, and then stepped back to 5% solvent B. Solvent A was 1 mM phosphate buffer in 10 mM sodium sulfate adjusted to pH 7.0. Solvent B was 40% (v/v) of solvent A with 60% acetonitrile. Detection utilized a 9 (im diameter by 2 mm long C-fiber eleetrode inserted into the outlet of the column. Detector electrode potential was set at +1.0 V versus Ag/AgCl reference.

This simple illustration shows how the basic choice of capillary versus packed columns determines the nature of the resulting separation and how optimization of flow and temperamre can produce further improvements. Now we will leave packed columns behind and consider in more detail the various avenues available for optimization of capillary-column separations. 

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