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Direct injection.. when do we use this?

12 Nov 2009

diagram

Direct injection is obtained when all the sample injected in the liner is evaporated instantly and directly sent to the column. If the column is set at a low temperature, focusing can be obtained for components with higher retention. The solvent peak will usually be very broad. To eliminate condensation effects for the solvent, the column must be set at a temperature where the solvent will be in gas phase, so usually near or above the boiling point of the solvent.

Direct injection is done : (1) if we need to measure sub ppm amounts in a matrix which is problematic with Splitless injection (2) if Splitted injection is discriminating to much. Special Uniliners are available which make a perfect seal for direct injection.

for best possible result: - Inject fast and smallest possible amount - Use 0.32/0.53mm columns for high flow - Use 2 mm or < liner ID - use column with thick film for retention Applications: traces of volatiles in high boiling and/or polar solvent