Practical Protein Chemistry - A. Darbre 1989

Current state of automated liquid-phase amino acid sequence analysis
Major problems encountered when using an automated sequencer
Valves

The reagent and solvent delivery valves used in the 890C model are a subject of considerable debate. The shortcomings of these valves have led many laboratories to retrofit them using the Wittman-Liebold method. When continuously monitoring instrument performance, a drop in step-wise yield is a reliable indicator of valve malfunction. Most frequently, the decrease in process efficiency is caused by Diaphragm cracking. While diaphragm failures are well known to any Sequencer user, few are familiar with simple techniques for checking diaphragm integrity. In our laboratory, this is tested by applying a vacuum to the sequencer Reactor and monitoring for the presence of Reagents in the supply lines leading from closed valves. Each supply line is sequentially filled with its respective reagent (or solvent). Subsequent application of a vacuum draws the liquid out of the line, which should appear completely dry. During vacuum drying steps performed after each cycle stage (PTC coupling, ATZ Cleavage, extractions), leaks must be entirely absent, especially in the reagent supply lines, as this can severely compromise the process. Cracks or other defects on the valve Contact surfaces will also result in leakage.

The flow-switching valve (manifold-to-waste) is rarely a source of operational issues unless an automatic fraction collector is used. On the sequencer, failures of various solenoid valves—such as Swelling or sticking of the sealing gaskets—are frequent, leading to an interruption in reagent delivery. Restoring valve functionality requires frequent replacement of worn components with spare parts.