Dionex AXP/AXP-MS Manual
2.5 Instrument Installation
2.5.1 Mobile Phase Reservoirs
The mobile phase reservoir should be placed at the same level or
slightly higher than the pump, never below the pump, and the inlet
tubing should be as short as practical. These steps minimize pressure
losses on the inlet side of the pump during refill and help to avoid
bubble formation. These steps are particularly important when using
high vapor pressure solvents (hexane, methylene chloride, etc.).
Mobile phases should be degassed, filtered, and covered (see Section
2.4).
2.5.2 Self-Flush Solution
Self-flush heads require 250 to 500 mL of 20% methanol in water as
a flushing solution. A pH indicator that will indicate the concentration
of salts in the solution is recommended as a reminder to change the
solution. This flush solution should be replaced with a fresh solution
weekly to avoid frequent pump maintenance.
2.5.3 Inlet Tubing and Filters
The replacement parts list shows the inlet tubing and filter used in the
Dionex AXP/AXP-MS pump. All inlet lines are 30 in. long and are
made of a fluoropolymer material.
2.5.4 Outlet Tubing
Outlet tubing (not supplied with the pump) should have a 1/16-in.
outer diameter. It is available in PEEK with a 0.020-in. inner diameter
and is normally used before the injection valve. Tubing with a 0.010-
in. inner diameter is normally used after the injection valve. The
tubing must be cut squarely and with no burrs. The tube itself should
not be crimped and the center hole must be open. PEEK tubing may be
cut with a plastic tubing cutter or razor knife.
If the Dionex AXP is being used as a sample loading pump for trace
ion applications, the convoluted diaphragm will cause sample
contamination. Remove the convoluted diaphragm as described in
Section 5.2.1. Once the diaphragm is removed, the seal wash feature
cannot be used; if it is, wash solution will drain past the piston
retainer. Rotate the flush housing 180 degrees so that the self-flush
outlet tubing is facing down. This will allow any leaks from the high
pressure seal to drain from the head assembly.
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