Chromatography Forum

Hi,

This applies to those familiar with the Dionex PAD detector. Please forward to anyone that might be able to contribute to the information requested.

We are presently in need of troubleshooting advice. Recently, we have noticed a leak in the PAD cell of our BioLC system. The leaking occurs between the gold electrode block and the cell body (where the pH reference electrode is in place). More specifically, we have observed the formation of salt crystals on the side of the cell body, on the two wing nuts and between the cell body and the gold electrode block (around the gasket). With a 100 mM NaOH eluent, pressure is around 900 psi at a flow rate of 1 ml/min using a PA1 column (“250 x 4.6 mmâ€

Hello Marie Helene:

First, please try to make both the working electrode and counter electrode surfaces completely dry before reassembling and also use a new gasket.

Should the leaks continue, please check for scratches both on the working electrode and on the counterelectrode block. Scratches on the working electrode can be removed by polishing. Start out by using coarse and fine polishing compounds from Dionex. In case the surface is still not completely smooth, apply 600 grit sand paper and repeat the coarse and fine polishing.

If the counter electrode block is not smooth enough, I am afraid, you may have to buy a new counterelectrode.

Also, please be aware that the detector cells do not necessarily bear the same name as the technique (PAD).
For future reference, your cell fits the description of either PED (not PAD) or ED50 electrode cell. The PAD cell has four screws and there is no pH electrode available for PAD cells. The gasket thickness for a PED cell (3 mm gold electrode) is 140 um. Whereas, the ED50 cell is used with 25 um thin gaskets.

Best regards,
Petr

Petr.Jandik@Dionex.com

Marie Helene:

There is one more and very frequent cause of cell leaking.
It is an excessive pressure inside the cell usualy being caused by a deformed outlet fitting.

Please remove the column from the system and check the pressure with only the cell connected directly to the pump. If you see more that ca. 150 psi, redo the outlet fitting and check the pressure again. The cell outlet fitting should always be installed without using a wrench. "Fingertight" is just fine for that fitting since there is no backpressure at this point.

Best regards,
Petr