Question about high pH buffer in HPLC separation

[squall]

Hi All,

I am going to do some RPLC separation using mobile phase having pH~10. Before the experiment starts, I got some concern about the pH. Will the connection tubing (fused silica) or column get partially dissolved at this pH condition?

I know some people doing the high pH separation, not sure whether this could be a problem or not

Thanks

[tom jupille]

Most connecting tubing in HPLC is stainless steel or PEEK. Fused silica *is* available, but it is relatively rare. The fused silca will probably etch somewhat pH 10.

pH 10 will *definitely* hurt the majority of bonded-phase packings, which are silica-based. There are some end-capped packings which may get up there, but even that is pushing it. The major exceptions would be the "hybrid" packings (XBridge, Gemini, etc.), PS-DVB packings, and "bidentate" bonded phases on silica hydride.

[silmartras]

You can use steel or peek tubing. But be sure that the column resist this pH. Luna columns works well at this pH for example. The temperature is also important. Some columns can work at pH 10 but at low temperatures.

[HPLCaddict]

pH itself is not the only thing to consider concerning column lifetime. Which buffer do you use (organic high pH buffers are usually more column-friendly than inorganic; phosphate is supposed to be especially corrosive)? As already mentioned, which temperature? Lower temperatures will extend column lifetimes. Gradient or isocratic? Isocratic is more column friendly. Which ion-strength of buffer? Try to keep it low.
Be also aware that addition of organics will shift the pH of the buffer. (Yes, I know, pH is only defined in purely aqueous media...please don't start a thread on this again...)

I have made some pretty good experiences with the Waters XBridge and high pH-buffers. Stable like charm, even with 20mM phosphate pH11 at 50°C.
Disclaimer: I don't get any money from waters (unfortunately ).

[uzman]

Also be careful about the system parts at pH 10.
Vespel rotor seals at your injector can not handle this pH at a long time.

Detector lenses are another concern if you are using uv, fluorescence or RI detectors.

[squall]

Thanks all for the suggestions!

[Rob Burgess]

Just to add from my experience, organic buffers at high pH tend to be stronger UV absorbers than inoragnic one, so much so that they can swamp baselines when looking for minor components in impurity analyses. If it is just a main peak assay you are looking it then that may be fine.

Try it and see, and get back to the forum about how you get on. When I tried it, the high baseline absorbtion from the gradient analyses cancelled the excellent peak shapes we got for our basic main peak compound. We also tried on X-bridge. In the end we went back to a low pH acidic mobile phase for this particular application.

[danko]

Hi Uzman,

How could any buffer at any pH, influence/corrupt the lenses of the detector – UV, or Fluorescence, or whatever?

Best Regards

[uzman]

Hi Danko ,

Detector manufacturers warn people about using high pH mobile phases in their instruction manuals.
I think , quartz lenses are some sort of silica , used in UV, fluorescence and RI detectors , so general rules for silicas and high pH may apply for, transmission may decrease.

[danko]

Hi Uzman,
I never heard of manufacturers advise against buffers at pH 10 nor 11 or 12 for that matter - in relation to the detector optics.
And I understand you were thinking about the flow cell being corrupted. If so, I can assure you that you don't need to worry – quarts has a different structure from silica (the material used for making stationary phase support) and it's far more stable.

Best Regards

[uzman]

Hello Danko,

How about this :

http://www.starnacells.com/d_download/Starna.pdf

At the bottom of page two , it says :

'' strongly basic solutions ( pH 9.0 and above ) will etch the surface of windows and shorten the usefull life of the cells .''

Starna is a producer of quartz and glass spectrophotometer cells ( same material as detector cell windows ) and warning against high pH.

If pH 9.0 is to be avoided , pH 10 ( 10 times more OH- ) seems very dangerous.

Warmest Regards.

[danko]

pH 9 - strongly basic?

Thanks for the warning. So, now I know that there are some ignorants working for the company in question

10s of thousands of chromatographers work with basic mobile phases but I never heard of someones flow cell being compromised.

Best Regards

[uzman]

Theory vs practice