Preventive Maintenance
Nitrogen-phosphorus detector (NPD)
180
2. a. Using compressed air or N , blow out loose material from inside
the collector. Do this carefully so as not to disturb the active
element.
Caution
Do not attempt to clean the inside of the collector by inserting objects
such as wires or brushes; to do so may damage the active element.
b. Wash the collector in hexane or isooctane. Then carefully dry the
collector using compressed air or N
.
Caution
Avoid polar solvents, especially water; polar solvents may dissolve the
rubidium salt coating on the active element.
Note: Avoid touching the lower end of the collector itself (end nearest the
jet); fingerprints and/or other contamination may cause baseline drift and
noise.
3. If worn or cracked, replace the collector sealing gasket (Part No.
0905•0915;see Figure 8•11).
4. Using a 1/4•inchhex nut driver, unscrew (counterclockwise) and
remove the jet from the detector base (see Figure 8•12).
5. The jet exists in two sizes: 0.018•or 0.011•inch.Use a cleaning wire
(0.016•inchod, 12•inchlength, Part No. 18765•20070)to
loosen/remove internal deposits. Be careful using the wire with the
0.011•inchjet.
Wash both the internal bore and exterior of the jet with a 1:1 (V/V)
solution of CH
OH (methanol) and (CH ) CO (acetone). Dry the jet
with compressed, clean air or N
and heat in an oven at 70 C for at
least 1/2•hour.
6. Clean the detector base cavity using solvents, a swab, and compressed
air or N
.
7. Reinstall the jet, tightening it to finger•tightness,and then an
additional 1/8•turn.
