Bicarbonate Assay by HPLC-UV

[MestizoJoe]

Hello,

I am trying to do a bicarbonate assay by HPLC-UV (210 nm). I've tried SAX with pH 12.5 phosphate buffer and did not get retention. I also tried using only NaOH at 4 - 10 mM and no retention and poor peak shape.

Apart from that I tried a normal phase column with ~80% acetonitrile and 20% pH 7.5 buffer and had no retention. I was trying to imitate HILIC chromatragraphy using a silica column.

I also tried pH 7.5 with a C18 and CTAB for ion pairing. This also did not acheive retention. The CTAB also made detecting the carbonate more difficult.

I was wondering if anyone had advice for this. I can't do titration because the matrix of the sample interferes.

Thanks,

[Gerhard Kratz]

I would recommend Ionchromatography. Maybe indirect UV detection. It is challenging.
Good luck.

[KM-USA]

What levels of bicarbonate or carbonate? If high enough, consider the antiquated but effective Chittick Apparatus. We use that for bicarb in laundry products.

[MestizoJoe]

My bicarbonate (carbonate in diluent) is 0.25 mg/mL. I think the Chittick Apparatus but I sure would like to avoid that if possible. Ha ha.

I don't have an ion chromatograph, but I do have a strong anion exchange column. I think I do not understand something about the retention mechanisms involved in IEC. I have carbonate at high pH which should have a 2- charge making it retain on such a column and maybe even enhancing it's absorbance in UV, but I am having a rough time with this.

Thanks,

[Markus Laeubli, Metrohm]

I would recommend to use titration.

Using ion chromatography I would recommend ion exclusion chromatography with conductivity detection after chemical suppression. Here a cation exchange column is requied. This is the only method I know to get reliable carbonate results (total of carbonate and hydrogen carbonate).