Tip # 118: Optional Seal Wash Systems and Flushing the HPLC
Many vendors offer an HPLC Pump
"Seal Wash" option. If you often operate your instrument with high
concentrations of aqueous salt buffers (e.g. Protein, Peptide Separations), then an
optional seal wash system might be something you want on your HPLC system. When combined
with daily flushing of the HPLC system to remove buffers, it can extend the life of and
reduce the maintenance needed on your HPLC system.
To prevent the
build up of salt crystals inside of the narrow bore tubing, pump and other HPLC components
I strongly recommend that you wash the system down each day, after use. I routinely see
HPLC systems with white fluffy crystals built up around the pump heads, pistons and
various fittings from lack of maintenance on a daily basis. High concentrations of mobile
phase buffer in your system (e.g. 0.1 M is considered 'high', but all buffers should be
flushed out) can damage the pump pistons, pump seals, injector parts and are corrosive to
the stainless steel used. The resulting damage can lead to expensive repairs.
(1) Flushing the
HPLC Flow Path: Potential damage from salts can be avoided if you remember to always flush
down the entire flow path of your HPLC each day (and anytime it may sit unused) with a
proper mixture of HPLC grade water and some organic (to prevent the growth of 'critters').
Flush the column down first with an appropriate solution and then remove it from the flow
path. Next flush the entire HPLC system down to rinse it of any remaining deposits
(sometimes the column can be left in-line and flushed with the system. Consult your column
manufacturer for advice). The exact mixture to use will depend on the exact type of mobile
phase you are using. You want to select something which will dissolve the buffer used in
your mobile phase into the solution plus incorporate some organic solvent component to
reduce the surface tension and also deter the growth of bacteria over time. For example: A
common Reverse Phase (RP) solution of 80% HPLC Grade water and 20% Methanol can be used in
many applications. If you have an automated HPLC system, then this entire process can be
stored as a "Flush" method and programmed to run at the end of each day's
sequence or series of runs so you do not have to remember to do it manually.
(2) Seal Wash System Use: A second level of flushing buffers from the system involves the
use of "seal wash" pump. These pumps are often small peristaltic pumps with
silicone tubing connected to them (Some are simply gravity fed systems where the wash
solvent bottle must be kept elevated and waste tubing kept low to function). The tubing is
connected to a metal ring which surrounds the back of the main pump's piston in such a way
that it can wash liquid over it and remove these deposits. When run with buffers, the main
HPLC pump pistons receive a thin coating of the solution each time they complete a full
stroke. Over time, the liquid evaporate and a film of buffer salts deposit on the sapphire
pistons. These salts accumulate and can scratch the pistol surface allowing air to enter
the system or leaks to results. Premature replacement of the pump head seals and pistons
often results from this damage. Washing the internal flow path of the HPLC system (as
described in section #1 above) does not wash away these salt deposits which occur outside
on the piston surface. A "seal wash" system can be employed to assist to deal
with the problem. The seal wash pump's inlet line can be placed in a bottle with fresh
wash solution and through either an automatic timer feature set in the pump's software or
through the operator manually turning the wash pump on and off, it can wash the back of
the piston to remove these deposits. The solution used to wash the pistons will again
depend on the type of mobile phase you are using (just like the HPLC flushing solvent).
For most RP applications, I recommend a mixture of 80% HPLC Grade water and 20% Methanol.
Another common seal wash solution is 90% HPLC Grade water and 10% IPA. For most
applications, I prefer using Methanol over IPA because it is much better at dissolving the
buffers used. A third option would be to use a wash solvent which is the same as your
mobile phase, but without any buffers added. Again, you must review your own method to
determine which wash solution is best as their is no such thing as a 'universal' wash
solution that can be used with all methods.
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Bill Letter, 08/24/2012
