Chromatography Forum

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,

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

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

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,

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).