Using Phosphoric Acid

[WK]

Hi All,
I have 0.15% w/v solution of phosphoric acid in HPLC water.
There are dark particles filling up in the lines to and from the vacuum degasser.
This does not happen with HPLC water, acetonitrile or 0.1%v/v TFA in HPLC water - which are in the other 3 lines.
Has anyone any idea why they appear?
Best Regards
WK

[HW Mueller]

Are these real particles that can be flushed out or microbial growth attached to the tubes?

[WK]

Hi HW,
They appear to be microbial type residues - but I wondered why do they occur at the inlet and outlet to the degasser and not in any other piece of horizontal tubing in the line? The residues are very dark - which is why I wonder if the phos acid has attacked the insides of the degasser in some way.

[HW Mueller]

You should try to find the sundry chains on this subject. Microbes always start at one point, usually creating a colony, probably at a dust particle, and spread from there. I suspect that your phosphate (pure phosphoric?) had some dust in it, or your plumbing. Highly pure phosphoric should have trouble supporting growth of organisms which need C, etc.
(It is tough to keep all organics out of things, but if you are the type who doesn´t make mistakes you can claim that you created an organism that lives on P. H, and O, nothing else.)

[WK]

Thanks HW,
Another question on phosphoric acid:
When 20mM H3PO4 is quoted in an application is it reasonable to assume that the 85% purity has already been factored in? To me it has to be. I wonder if everyone does though?
WK

[HW Mueller]

Lets put it that way: You better make sure that 20 moles of H3PO4 are in 1L of solution when you say that you have 20M H3PO4.

[Consumer Products Guy]

Like H. W. indicates: directions for stuff like this need to be explicit, not ambiguous. I've seen numerous papers where one must guess whether it's 850 ml A plus 150 ml B, or 850 ml A diluted to 1000 ml with B, or 150 ml B diluted to 1000 ml with A. Detailed (and correct) instructions would save a lot of time. Of course, I've also seen assays from suppliers where their analytical standard did NOT dissolve in their specified solvent, made me suspect everything from them. And I'm always wary of applications using 254nm, suspect they were never updated to more-modern variable wavelength detectors, and wary of some internal standard procedures, figuring that they were developed in the manual-injection days.

[tom jupille]

Amen, brother, amen!