Which water do you use for Mobile Phase prep?

[Apple_insci]

I am just wondering what kind of water do people use for HPLC mobile phase preparation? bottled HPLC grade water? MilliQ water? or PURELAB® Ultra Analytic water? Pros and cons for each kind?

Thanks!

Apple

[HW Mueller]

We use an old MilliQ (4 component cartridge), the last time this was tested against commercial HPLC water (~ a year ago, UV at 220 or 210nm, pressure vessel, just an empty prep column, filled with water, evacuated 10 min, pressuriced with N2, connected to UV detector, flow rate ~1-2mL/min, usually 34 bar resistor after detector), it was better than that well known brand. So I think one can hardly beat those modern water purification systems which produce water with very low organics concentration, see for instance, application lit on the Millipore net.

[Jeff Brewer]

My labs use an Elix system from Millipore to prepare the tap water into a reagent grade water which we then clean with a UV light source and a Milli-Q UHP system. This produces 18 meg water which we use for all our lab work including standards, sample prep, IC eluents/reagents and HPLC mobile phase. We have used other systems and water purification products like resin beds as initial prep but these did not work anywhere close to the same levels as our Millipore products. (Millipore service has also been excellent).

Jeff

[rhaefe]

I use and have used the following: old MilliQ system (4cartridges), Barnstead EasyPure, Purelab (with and without UV oxidation, with and without ultrafiltration cartridge).

All of them work very well (of course they have to be properly maintained). I did run into problems with bottled HPLC water in the past and try to avoid it.

Best regards,

Robert Haefele
Hamilton Company

[DR]

All of them work very well (of course they have to be properly maintained). I did run into problems with bottled HPLC water in the past and try to avoid it.

That's pretty much my experience. I've recently had a house DI fed Purelab Ultra Analytic and I'm currently using MilliQ Gradient A10s fed Elix treated city water. Both systems work well. My impression of the consumables is that Millipore is a little more conservative on their specifications meaning that if they say "change it avery 6 months" you will get away with going a little longer. With U.S. filter consumables, you had better have replacements on hand at 6 months, because that's all you'll get. The only thing I don't like about either company is the way they talk about each other (at least in my area).

[Bruce Hamilton]

Used old three cartridge blue Milli-Q ( 1978 vintage ) till last year, fed with distilled water. Only change was to replace final filter with newer model Millex as old one no longer made. It's still in use, and cartridges/filters last a year without apparent increase in TOC or UV, although the initial carbon cartridge can acquire slime if not used regularly - doesn't seem to affect final water TOC much though.

Bought an A10 Milli-Q Gradient system last year, also fed by distilled water. Very impressed, easy to use, and based on my experience with older instrument, didn't see need for all the sophistication of some of the TOC meter/trace organic models.

My only comment would be to not skimp on capacity, having high flows means that you can rinse everything out multiple times without worry, and it's great to fas -flush HPLC solvent lines when non-volatile buffers have been used without worrying about water use.

Also, even if you don't change the cartridges frequently, do keep an eye on the final filter ( 0.22um ), and replace that annually, at least.
Lab water treatent companies make their money on the consumables, so the highest quality feed to the system will protract consumable life.

I tend to replace any untreated water in HPLC reservoirs every second or third day, but in my experience having 30mm of 10 thou PTFE capillary as the solvent resevoir vents virtually precludes wildlife and moisture ingress for weeks.

Bruce Hamilton

[rc_12321]

what should be the ideal Ph range for Milli Q water to be used for mobile phase preparation?

[HW Mueller]

pH? That of pure water, of course.

[Ron]

My general rule is to use water from a high quality water system whenever possible. Pure water is a very aggressive solvent, and will degrade surprisingly quickly when stored in glass. The only time I use bottled water is for troubleshooting purposes, using a grade of water from a supplier I trust to eliminate a varialbe.

[HW Mueller]

I hear that a lot around here, that pure water is an aggressive solvent... what does that mean?

[Ron]

There was an article in one of the general publications several years back, possibly American Laboratory, where water from a recirculating purification system was stored in new, cleaned glass bottles, then periodically analyzed for purity. The result was that over a period of a few months the level of dissolved solids, primarily silica and trace metals from the glass, increased significantly. I wish I could give you the reference but it has to have been at least 15 years since I saw the article.

I believe that the properties of "polywater" were also shown to be the result of high purity water leaching material from the walls of the capillary tubes used in the experiment.

My understanding of the phrase "agressive solvent" is that high purity water will tend to leach components from the container so that after a period of a few weeks to a few months it will no longer meet the purity specifications it met at the time of production at the time of production.

[HW Mueller]

OK, it seems that pure water would leach most substances, if not everything, the least effectively. For instance, a basic aqu. solution will leach out silica much faster. It must be that this "aggressiveness" of pure water arose through the fact that water at equilibrium does not "show" what is going on.

Thought that polywater was researchers sweat. Also wonder why nobody uses levitated water in HPLC.

[Bruce Hamilton]

My understanding was that pure water is called aggressive because it dissolves many containers ( glass/metal ) faster than buffered water ( aka tap water ).

If exposed to the air the pH can drop down to 5.x, but even when not exposed, will quickly dissolve many ions, especially if flowing, as it is also low in other dissolved gases, such as oxygen, preventing some protective oxide films from forming on metals.

IIRC, polywater was attributed to dissolved silica from the reserachers' capillary tubes.

Bruce Hamilton

[HW Mueller]

One can see some problems if bulk movement prevents equilibrium to be attained. In practis it appears that either equilibria are attained very slowly or are lying far on the side of pure water. This statement is based on experience with UV detection. This was mentioned before: A physicist (doing metal trace anal.) in this house shook his head when he saw me come with a glas bottle, trying to borrow some high purity water, I shook my head when he recommendet his plastic containers... I guess it´s ok to call ANY water aggressive.... for instance, it violently attacks Na°. Super acids are then.....?