By RM on Monday, May 31, 2004 - 10:38 pm:

Hi;

I am currently using ion chromotography and a conductivity detector to quantitate sulfate anions in water. I would like however to use a uv vis detector.

After reading "Analysis of Anions in Drinkign Water using HPLC" - Angelika Gratzfeld-Huesgen [Agilent] I got very excited.

It now seems I can not to find infornmation regarding the column I require. I know it is a low capacity styrene bead with a quarternary N... however this is about the extent of my knowledge.

Can anyone shed some light?

Thanking you
RM

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By Chris Pohl on Wednesday, June 2, 2004 - 02:25 pm:

I did a bit of digging around but could find no specifics on the column being used in the method cited above. The most recent Agilent literature connected to this application was published in 2001(http://www.metlab.co.uk/img/literature/ ... 883294.pdf ) where an example is shown on page 33. It appears that they were being intentionally vague about both the column and the mobile phase in order to sell the column and eluents in some sort of "kit". As far as I could tell, though, they do not sell the column or the eluent kit anymore.

The technique being used (Indirect Photometric Chromatography) was first developed by Hamish Small (Small, H. and Miller, T. E. Anal. Chem. 54: (1983) 462). By using a UV absorbing eluent component, UV transparent analytes are visualized as negative deflections in the baseline. Because the technique necessarily involves working with a high eluent background, system performance is typically inferior to that of conventional ion chromatography (e.g. temperature control requirements are much more stringent in order to obtain stable baselines). Furthermore, in order to obtain sufficient sensitivity, one typically uses a high potency UV absorbing eluent species in conjunction with a low capacity column. While this does help increase detection sensitivity, these two parameters also narrow the working range of the method, necessitating the use of the column under overload or near overlaod conditions in order to have a reasonable operating range. Note the poor peak shapes for phosphate in the reference cited above.

However, if you are determined to pursue this detection mode, I would suggest checking in the published literature for detailed information about this operating mode. The book: Ion Chromatography by Joachim Weiss, second edition or the book: Ion Chromatography by Paul Haddad both have many examples of this operating mode along with specific column information and details of suitable eluents.

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By Markus Laeubli on Thursday, June 3, 2004 - 04:53 am:

I totally agree with Chris. And I would go even a step further.
Your are using ion chromatography with conductivity dectection right now. This is the best what you can do with this application.
I tested a lot of methods in this area and found conductivity detection (suppressed or non-suppressed) always more sensitive than indirect UV detection.

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By Anonymous on Tuesday, June 8, 2004 - 07:17 am:

Markus, what do mean with a suppressor ?
Is the suppressor required for conductivity detection ?
How reliable / robust is it ?

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By Anonymous on Tuesday, June 8, 2004 - 04:06 pm:

Why this "suppressor-subject" now when they agreed to agree?

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By Chris Pohl on Saturday, June 12, 2004 - 02:30 pm:

A suppressor is a device which removes an ionic eluent from the mobile phase used in ion exchange separations while simultaneously converting the analyte to a more conductive form. For example, a commonly employed mobile phase is potassium hydroxide. If you are interested in separating chloride and sulfate using an eluent based on potassium hydroxide, it will be difficult to detect the chloride and sulfate in the presence of the background conductivity due to the presence of the potassium hydroxide. A suppressor placed after the separation column replaces (in this case) the potassium with hydronium producing water in the place of potassium hydroxide resulting in an eluent with an extremely low background conductivity facilitating detection of analyte anions. Simultaneously, the suppressor converts potassium chloride and potassium sulfate into HCl and sulfuric acid, increasing the conductivity response of both analytes. Of course, there are a wide variety of different types of suppressors available from a number of different manufacturers. The relative merits of different designs is too large a subject to cover in this forum. If you are interested in learning more about this topic I would encourage you to visit the web sites of Dionex, Metrohm and Alltech.

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By Anonymous on Saturday, June 12, 2004 - 04:52 pm:

Can you explain why are HCL and H2SO4 more conductive than chloride and sulfate? It seems like the ionic forms would be more conductive? Thank You

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By Chris Pohl on Saturday, June 12, 2004 - 04:57 pm:

HCl and sulfuric acid are more conductive than potassium chloride and potassium sulfate because the conductivity is a function of both the anion and the cation of the electrolyte in question. Since hydronium has a much higher mobility than potassium, converting a strong acid anion to the acid form will result in a significant increase in the conductivity when compared to the corresponding salt.

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By RM on Thursday, June 24, 2004 - 05:05 pm:

Hi guys;

Sorry for my radio silence, I have been on holidays and then I forgot what I named my query and couldn't find it ;)

I will digest these replies and then get back.

Thanks
RM
p.s I am Australia - hence the weird posting times.