Calcium by IC using Waters system

[GaryR]

I’m trying to set up a new method to determine calcium in CaCO3 tablets.
The method was provided by a sister company using a shimadzu IC.

I am trying to run this using the shimadzu column but on a Waters system using an Alliance and 432 conductivity detector.

The column is a Shim-Pak IC-C3 100 x 4.6mm with guard column.
The mobile phase is a mixture of a solution of tartaric acid (3 in 2000) and dipicolinic acid (1 in 3000) (1:1)
The standard is around 20ppm Ca, and also contains some Na from solvent.

The problem is that I am getting no peaks at all, other than an injection peak.

I have tried making a mobile phase of 2.5mM oxalic acid, as used in the manufacturers example chromatogram, but I’m still not getting any peaks.

I have injected my stock std solution (200ppm Ca) and still see no peaks.

Wondering if anyone has any suggestions on what to try next?

[Mark Albertson]

Hi Gary,

Try injecting 20 ppm of Na or Li as these ions are more monovalent and should elute quickly, if you still have no signal at all take out the column and replace it with some backpressure restriction coils. Then inject 10ppm of nitric acid onto the 432 if it is working you should get a response in seconds. Note non suppressed Cations will elute with negative inflection so your polarity needs to be reversed.

Cheers

Mark Albertson

[Mark Albertson]

Hi Gary,

Apologies for the back pressure coil flow through test use only DI water

Cheers

Mark

[Markus Laeubli, Metrohm]

Dear Gary

In the non-suppressed mode you will get negative peaks. Make sure that the polarity on the detektor is switched.
You are working on a high background. Therefore also make sure that the signal is zeroed.