Chromatography Forum

HELLO EVERYBODY
I need to determine the percentage of sulphur in a lotion hair by HPLC.
I have only this information:
use sodium peroxide to oxidaze the S to sulphate,
Recuperate the sulphate with water
And the quatitative Analysis is carried out using ionic HPLC.
Calibration is made with a standard of sulphate solution)

Please anyone can anyone to suggest me an HPLC system?

A column SAX can be useful?

Can anyone suggest me more details for the sample treatment?

What kind of sulphate solution can be used for calibration ?

Many thanks for all and best regards.

Paul.

You will need a system set up for "ion chromatography". This usually implies conductivity detection.

If you already have an HPLC system, you might be able to get away with RI detection (if the level is high enough), or set up for "indirect UV" using something like a phthalate buffer in the mobile phase.

And yes, the column used would typically be a SAX column.

Something like Na2SO4 should work just fine for a standard.

Do a Google search for "sulfate" and "ion chromatography" and you should come up with plenty of references. Also contact Dionex and Metrohm, both of which supply IC instruments.

thanks Tom.

I do not have conductivity detection.

I have an Hplc with DAD .

Please ,what do you mean with "indirect uv".

An by the way a question:
-0.02 M phtalic acid-sodium borate solution at pH 6.0 -
I should preparate this mobile phase by mixing of 0.02 M phtalic acid solution and 0.02 M sodium borate solution in proportion (1:1) ?

And please,can you give an idea of how can i correlate a sodium sulfate of standard solution and sulfate obtained of the sample .

Thanks again for your collaboration.
Paul

If you use phthalic acid for the eluent, I would bring the solution to the respective pH with NaOH solution.

Equilibrate the eluent on the anion exchange column. In the DAD detector you will find very high absorption. As you inject now ions e.g. sulfate, sulfate ions will replace phthalate ions due to the ion exchange process. The solution then will have lower absorption according to the concentration of sulfate. You will get negative peaks – this is indirect UV detection.

While indirect UV detection can and does work, I would strongly recommend obtaining a conductivity detector if you need reasonable sensitivity. In my experience, they tend to be quite rugged, so if money's a concern you can obtain an old one cheaply and still do quite well. I have an old Waters 431 (circa 1991-2, perhaps) and it works very well when needed. At one point, it was stashed in a cabinet for 8 years and when I pulled it out and started it up, it ran perfectly.