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Guidelines for Choosing CG Columns

Guidelines for Choosing CG Columns

SGE Environmental GC Columns
Guidelines for Choosing GC Columns

Stationary Phase
• Select the least polar phase that will perform the separation you require.
• Non-polar stationary phases separate analytes predominantly by order of boiling point.
• Increase the amount of phenyl and/or cyanopropyl content in the phase, and the separation is then influenced more by differences in dipole moments or charge distributions (BP10 (1701), BPX35, BPX50, and BPX70).
• To separate compounds that differ more in their hydrogen bonding capacities (for example aldehydes and alcohols), polythylene glycol type phases are best suited - SolGel-WAX™, BP20 (WAX).

 

Internal Diameter

• The smaller the diameter the greater the efficiency, hence better resolution. Narrow columns (0.1 mm ID) are used for faster analysis because the same resolution can be achieved in a shorter time.
• The larger the diameter the greater the sample capacity.

 Column Length
• Always try to select the shortest column that will provide the required resolution for the application. If the maximum column length available is being used, and resolution of the sample mixture is still inadequate then try changing the stationary phase or internal diameter.
• Resolution is proportional to the square root of the column efficiency. Therefore, halving the column length will only decrease the resolving power of the column by approximately 40 %.

Film Thickness
• For samples with a variation in solute concentration, a thicker film column is recommended. This will reduce the possibility of broad overloaded peaks co-eluting with other compounds of interest. If the separation of two solutes is sufficient and co-elution is still unlikely, even with large differences in concentration, then a thinner film can be used. The greater the film thickness the greater the retention of solutes, therefore the higher the elution temperature. As a rule, doubling the film thickness results in an increase in elution temperature of approximately 15-20 ° under isothermal conditions. Using a temperature program, the increase in elution temperature is slightly less.

• From the phase ratio value ß, a column can be categorized for the type of application it would best suit. The smaller the ß value, the greater the ratio of phase to the column inner diameter, making it better suited for analyzing volatile compounds. Columns which have thin films are generally better suited for high molecular weight compounds and are characterized by large ß values. Maintaining phase ratio among different ID columns to yield similar chromatography.

Recommended Column by Application