Chromatography Forum

Does anyone know what is plunger seal wash do? And what would be the preferred plunger stroke volume? Thanks!

Plunger seal wash is a second seal behind the main high-pressure seal. You pass a wash solution between the two seals. When you pump buffers with nonvolatile salts, you can get a salt buildup on the plunger (also called piston) that abrades the high-pressure seal. The plunger seal wash keeps the plunger clean and the seal wetted, and thereby increases the service interval.

Most pumps don't have any ability to set the stroke volume. The few that do also have automatic settings that work well in almost all situations. You might want a smaller stroke volume if you are trying to reduce the gradient delay volume to the minimum possible.

Plunger seal washes are typically a gravity/siphon system of tubes that allows water to pass between your main plunger seals and a second set of seals, the object being to rinse any salts from the plunger surfaces before they can crystalize and trash your main seals. They are highly recommended if you have phosphate or other salts in your mobile phase. As tehy are typically a passive system, there is no stroke volume to set.

Some pumps can be setup to deliver a couple of different stroke volumes (large for higher flow rates, small for low flow rates). This can be done by altering the plunger setup so that they do not fully retract (leads to shorter stroke volume with added pulsation noise) or by swapping out plungers and seals for ones with a different diameter (a larger chore, but better results).

Thanks DR and Mark Tracy!

I just got several Alliance HPLC systems (Waters) and I am trying to figure out the parameter setup. we normally set our flow rate at 0.5ml/min with 0.1M Sodium Phosphate buffer. Do you think the default stroke volume (130uL) is too high for my flow rate?
Thanks again!

Unless you have some sort of problem related to flow noise or gradient delay, stick to the default. The engineers designed the control software to optimize performance over the great majority of conditions. They give you this option so you can make adjustments in unusual cases. (Marketing likes to have something to talk about too.)

Use the default values for stroke volume.
Use 10% methanol in water or 5% Acetonitrile in water as the plunger seal wash. You need the organic in there to keep bugs from growing. It is easy to forget that bottle is up there, so check it once in a while.

To AA: we use 10%IPA/H2O as our piston wash solution.

To Mark Tracy: with regards to your advice about sticking to the default stroke volume unless gradient delay causes a problem, could you please elaborate on a problem Could a difference in retention time when the same method is run on HPLCs by two different manufacturers be linked to this gradient delay due to the plunger stroke volume The flow rate setting is ~1ml/min.

Differences in retention times between the equipment of two different manufacturers can be due to differences in gradient delay volume, temperature differences or potentially, but rarely, the precision of the mobile phase composition, in that order.

Gradient delay is usually only a significant issue at low flow rates. Suppose you have a gradient method running at 0.3 mL/min, and the original instrument where it was developed has a gradient delay of 0.9 mL; the gradient delay is 3 min. Now you transfer it to a different LC with a gradient delay of 1.1 mL; the new delay is 3.7 min, and some of the peaks will miss their retention windows. If the second instrument could change its stroke and reduce the delay volume to 1.0 mL, the delay is 3.3 min, and the peaks now hit their retention windows.

Of course, that is not the usual way that transfer is done, but it would work.

Thanks DR and Mark Tracy!

I just got several Alliance HPLC systems (Waters) and I am trying to figure out the parameter setup. we normally set our flow rate at 0.5ml/min with 0.1M Sodium Phosphate buffer. Do you think the default stroke volume (130uL) is too high for my flow rate?
Thanks again!

stroke volume of 130µl is indeed default, but for a flow <0.53ml a stroke volume of 25µl is suggested in the instrument method editor.

Bart