Chromatography Forum

I have been running the equipment in my lab for a year now, and still consider myself a noob. I have no chemistry background and no "official" training on our Dionex IC (GP50, AS50. EG50). I was trained to use the machine by our former technician, and still have questions b/c he didn't teach me any of the theory behind the science of the machine. We test ground water for Cl, SO4, NO3, PO4 using KOH eluent cartridges. We are running samples that contain higher levels for determining road salt contamination, and not trace levels

I have been browsing posts here and see several that comment about type of eluent being used, and several mention bicarb/carb eluent. I literally have no idea why it would make sense to use KOH over the bicarb/carb type. some posts indicate that PO4 is more difficult on the KOH and so the bicarb/carb type should be used.

Could anyone give me background on this? Our PO4 QC's always come back low (std 5ppm, result of ~4ppm), but it's it known that it happnes like that and we can't do anything about it.

Thanks!

Hi labmonkey208

Using hydroxide or carbonate/bicarbonate eluents are mainly given by the used column or application. There are special hydroxide and carbonate selective columns available. Using a EG (eluent generator) KOH is usually used. In this case you need only water as eluent without manual preparation of any eluent. There are several individual advantages using KOH or Carbonate/Bicarbonate. In general hydroxid eluents are (easier) gradient compatible and you'll have the corresponding benefits.
However, PO4 in mg/l range is for booth eluents possible without any problems and should be done easily (depending on the other ions).
I recommend to contact your support representative, invest a little money to receive some background info from him/her.

Regards

Thanks for the reply Stefan!

We don't ever use our eluent using the gradient technique, so i wonder if using the carbonate/bicarbonate type eluent would be a good option for us.

Yes, if you are working under isocratic conditions the carbonate/bicarbonate eluent with the appropriate column works perfect.

Merry christmas.