Chromatography Forum

Hi,
I can determine Cl, NO3 and NO2 by using C18 column with the eluent n-Octylamine at 220 nm. However, I want to measure Sulfate additionally.

My methode is below

Column Eurosil Bioselect 300-5 C18, 120 x 4 mm
Eluent A 0.01 M n-Octylamine, set to pH 4
Flow rate 1.0 ml/min
Injection volume 5 µl
Column temperature 40 °C
Detection UV at 210 nm

Do you have an application to measure sulfate nitrate and nitrite together with HPLC-UV
Thanks

What else is in your mobile phase that you neglected to mention? Cl- is pretty much transparent at UV wavelengths, so you are *not* detecting it directly at 210 nm. Sulfate has the same issue: it does not absorb UV light.

Chloride and sulfate can be done via indirect UV (for example: http://www-user.uni-bremen.de/~koelling/so4.html) but it's much more straightforward with an ion-exchange column rather than ion-pair.

Hi Tom. Mobile phase is 0.01 M n-Octylamine at pH 4. But Once I checked Cl. I saw peak.

Hi Tom. Mobile phase is 0.01 M n-Octylamine at pH 4. But Once I checked Cl. I saw peak.

Probably the solvent front?

That size column would have an internal volume of around 1 mL. At 1 mL/min, that makes the dead time about 1 minute. Certainly anything eluting before 2 minutes is t0 noise. It's not good practice to quantitate any peak eluting with a k' less that 2 (in this case, retention time less than about 3 minutes).

Ion exchange with conductivity detection is the simplest solution to this and an old conductivity detector should be easy enough to find and wouldn't cost much. I've run the same unit on and off for 20 years, have never done a thing to it, and it runs fine.

For $500, it'll be less expensive than spending half a day working on your RP method:

http://www.ebay.com/itm/Waters-431-Cond ... 3cd2df570d

Hi Alpher,

I would have to concur with the previous comments above. Have you considered IC? Specifically designed for what you are trying to do...

http://www.dionex.com/en-us/products/io ... 72590.html

Thanks

To add up an other IC player:

View Metrohm's IC

I've seen this done with a C18 "permanently coated" with some quaternary ammonium modifier with hydrophobic arms. The column never lasts long.

Friend, you could probably separate sulfate, nitrite, nitrate on a SAX guard column. Why re-invent wheel?

ELSD with one of our columns will address the issue:
http://www.sielc.com/Compound-Nitrate.html
http://www.sielc.com/Compound-Sulfate.html