Dear Wasiu,

I have been used ion chromagraphy to separated perchlorated compounds without suppression just using borate buffer and strong cation exchange colunm.

Talk to Waters assistence or Agilent to help you for better chromatographic column and buffer to your separation.

Dr. Marcelo Ribani

Thank you Dr Ribani

I am also currently using a borate buffer.What mobile phase do you use in conjunction?

I also think you can try to have your analyte concentrations increased and avoid small volume injections also would you apply polymer coated silica columns

Dear Wasiu,

without suppression the LOD for PFOS is critical. What kind of sample will you analyse?

Hi Waisu:

In principle, yes, non-suppressed conductivity can be used to detect perfluorinated acids. Generally speaking, the detection limits are inferior to suppressed conductivity. Using RP-HPLC for the separation, the analytes are charged, and therefore the retention is influenced by the ionization of silanol groups on the column. Therefore the mobile phase needs some form of pH control to stabilize the retention times. For modern C18 columns, very little buffering capacity is needed. I would suggest 0.03% acetic acid (5 mM) in the mobile phase as a reasonable starting point. If a gradient elution is needed, the baseline will have a large slope; adjust the acid concentrations in the aqueous and organic until the background conductivity is the same; blank subtraction may also help.

I need to mention that there are some under-appreciated aspects to this analysis. First, PFOA is a trace contaminant in many fluoropolymers used in the construction of HPLCs and other laboratory equipment; the latest manufacturing processes have eliminated its use, but discerning whether any given piece of plastic is contaminated is not easy. Second, perfluoro-acids stick to some surfaces and you can see problems with carryover or low recovery depending on the materials that the sample comes into contact with; this includes vials, filters, SPE cartridges, transfer tubing, etc. I have found PEEK and stainless steel reasonably safe. Do read the literature on this point. Third, common anionic surfactants like laureth sulfate, LAS or SDS elute in the same region as perfluoro-acids, and are also detected by conductivity; learn to recognize these interferences.