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26_LC-page11 - •  These can be a bit more complex than...

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Unformatted text preview: •  These can be a bit more complex than with GC systems. •  If you attempted a manual syringe injection, expect to find the plunger shot into the ceiling - you might be working with pressures as high as 5000 psi. A very common approach is the use of sampling valves and loops. sample sample vent vent •  A simple approach would be to stop the flow and inject manually - not too good. column solvent You must use ‘zero dead volume’ valves. solvent Automated syringes syringe Manual and automated valve systems are available. Major limitation is fixed sample size. The loop must be changed in order to alter sample size - does not require that the flow be stopped. •  A small column added between the injection system and the analytical column. •  It helps prevent entry of materials that might want to stay on the column from your sample or solvent. •  Used to extend column life •  Should be the same packing as the analytical column. check valve This method allow for adjustment of sample size. The motor driven syringe can provide sufficient pressure to inject sample past the check valve. HPLC has seen significant improvement over the last 10 years primarily due to improved column technology. Packings are more uniform and smaller. Phases are commonly chemically bound to the packing. Packing methods have improved. ...
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