Prime The Needle Wash Pump - Waters Alliance e2695 Operator's Manual

6. To prevent a compression test from running, leave the Compression Check check box blank
the first time you use the system.
Note: Calibrate the seal pack before running a compression test or it will likely fail.
7. Press OK.
3.5.2

Prime the needle wash pump

The needle wash pump flushes the needle in the sample management system, preventing
carryover of sample between injections. The needle wash also extends the life of the injector seals
by flushing buffered mobile phase and sample from the needle.
3.5.2.1 Select a needle wash solvent
Use a needle wash solvent based on the sample and mobile phase chemistries, making sure all
solutions and buffers are miscible and soluble.
A gradient separation typically involves the initial use of a weak solvent combination, whereas final
conditions usually combine stronger solvents. In general, it is best to choose a needle wash
solvent similar to final gradient conditions. For example, in a separation with an initial gradient of
80% water/20% methanol, and a final gradient of 10% water/90% methanol, an effective needle
wash solvent would be 20% water/80% methanol.
The choice of a needle wash solvent similar, but not equivalent, to final gradient composition
ensures solubility of early eluting peaks. When sample solubility in the mobile phase is
pH-dependent, choose a needle wash solution that is similarly pH-adjusted, unless using buffer
solutions that are pH-adjusted containing nonvolatile salts.
If acids are used, avoid long-term exposure of the needle wash system to halide-containing acids.
Using samples containing strongly hydrophobic components can require experimentation to
determine the best needle wash solvent. In these cases, the use of a needle wash solvent such as
20% water/80% methanol with tetrahydrofuran (THF) or dimethylsulfoxide (DMSO) [1-5 mL THF or
DMSO/99-95 mL needle wash solvent] may be superior.
The following table lists some needle wash solvents recommended for use with certain mobile
phase conditions. High sample concentrations can require other needle wash solvents.
Notice: Use separate solutions and containers for needle wash and plunger seal wash. The
solutions' functions differ, so using one solution for both functions can compromise the
effectiveness of needle or plunger-seal washing.
February 27, 2018, 715003794 Rev. C
Page 60