Preventive Maintenance

Nitrogen-phosphorus detector (NPD)

All collectors should be washed off with GE grade hexane or a similar solvent before reinstalling in the instrument to remove any grease, fingerprints, or other contaminants. Soak the entire collector in a vial of hexane for several minutes (2-10). Remove the collector, touching only the top portion, and scrub the lower, outer collector tube with a clean wipe soaked with hexane. Dry off the excess hexane solvent.

Place a new O•ringon the collector and place it into the collector body assembly from the top. Carefully position the collector tube so that the bevel on the outer tube is positioned properly in relation to the bottom edge of the collector body. Tighten the collector holding screw firmly against the collector tube. This connection is both a mechanical connection and an electrical contact.

Complete the collector assembly as follows: Wear clean, lint•freegloves to avoid contaminating the collector assembly; (1) make sure the O•ring is depressed into the groove in the collector body; (2) examine the collector sealing gasket for wear or cracks and replace if necessary; (3) place the stainless steel spacer/spring onto the collector/body assembly;

(4)place the Teflon spacer on top of the spring•the side with the groove faces up; (5) if necessary, replace the bottom transformer secondary wire into the hole in the collector body and tighten the setscrew onto the wire connector.

Attach the brass collar to the top of the collector tube and tighten the collar•holdingscrew. The smaller hole in the brass collar faces up.

Insert the top transformer secondary wire into the slot in the brass collar and tighten the wire•holdingscrew on the bare wire. This must be a good electrical connection, but take care and do not completely cut the wire with the screw.

Carefully position the transformer/collector body assembly into the cover and fasten the Teflon insulator of the collector body in place with the two screws. Do not overtighten the screws into the Teflon and strip the threads.

Carefully position the transformer with both end covers in place between the threaded standoffs and fasten in place with the two screws. Place the assembled detector cover in place onto the detector base and fasten in place with the three screws.

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