Washing on-line

Compressor Wash. When should the eompressor be washed on-line, and when should an off-line eompressor wash should be eonsidered. 

Polymer particles are suspended in water (25% MeCN) and then slurry-packed into stainless steel columns (250 mm x 4.6 mm i.d.) using an air-driven fluid pump (Haskel, Burbank, CA, USA) and water (25% MeCN) as the packing solvent. The packed columns are washed on-line on a Beckman HPLC system (comprising a solvent module 126 and diode array detector 168) using MeCN (20% acetic acid) to remove the print molecule until a stable base line is obtained. The mobile phase is then changed to a citrate buflfer (pH 3.0, 25 mM citrate) containing 10% MeCN (v/v) at a flow rate of 1 ml. min . For a test of chiral resolution, a racemic mixture of (+)- and ( )-isoproterenol (20 pL at 2 mM in the mobile phase) is injected, and the elution monitored at 280 nm. Acetone can be used as a void marker for the calculation of capacitor factor (k ) and separation factor (oc). 

The system incorporates nine solvent/reagent reservoirs to enable delivery of the NMP main wash, neat piperidine deblock (diluted with main wash on line), 0.45 M HBTU-HOBt-DMF activator solution, 2.0 M DIPEA-NMP, MeOH final wash, DCM wash, alternative activators (e.g. 1.0 M DCC-NMP), capping solution, and solvent exchange for Fmoc/rBu chemistry. In the case of Boc/Bzl-based methods, DCM and NMP are used as the main wash solvents, TFA (diluted with DCM on-line) for deblock, 1.0 M DCC-NMP and 1.0 M HOBt-NMP for activation, DMSO-NMP (4 1) for improved solvation, acetic anhydride for capping, and MeOH for final wash. A gas positive-pressure chemical delivery system controls the flow of all reagents and solvents. Gas pressure is provided by an external tank of nitrogen. 

Jeffs, E., 1992, Compressor Washing On Line for Large Gas TVirbine, TVirbomachineiy International, Vol. 33, No. 6, September/October 1992. 

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