Chromatography Forum

Don Risely at Eli Lilly has done quite a bit of work in this area using HILIC with ELSD or CAD. His matrices were primarily pharmaceutical formulations. I have looked at this as well using UV or ELSD (depending on the ions) and any HILIC column will separate anions and cations in a single gradient run. Which ions will be resolved depends on the column and the mobile phase conditions. If you have a silica column you can convert it to HILIC mode (if in normal phase solvent) by flushing with IPA (reduced flow due to BP, 15 column volumes) then ACN (15 column volumes) then 20% ACN 80% buffer (20 column volumes). Re-equilibration to starting gradient mobile phase takes much longer than in RPLC so use at least 15 column volumes if starting your gradient at 85% ACN. Increase the equilibration volume as you increase the initial %ACN. A gradient from 85% ACN to 30% ACN typically did the trick but this again depends on the column and buffer concentration, salt and pH. The final %ACN needed also depends on the ions you want to elute. As the charge increases from monovalent to trivalent retention increases.

For good selectivity and sensitivity, ion chromatography is often for ion analysis.
If for some reason, A HPLC method is desired, you can consider use the Acclaim Trinity P1 (http://www.dionex.com/en-us/webdocs/707 ... 239-02.pdf). This column is specifically designed for ion analysis in pharmaceutical applications, such as pharmaceutucal coounterions analysis as well as API and counterion analysis. This column combines anion-exchange, cation-exchange and reversed-phase interaction and provides much better results than HILIC colulmns (http://www.dionex.com/en-us/webdocs/874 ... 731-01.pdf). Some peer-reviewed journal articles are listed below for your reference.
1. K. Zhang, L. Dai, N. P. Chetwyn, Simultaneous determination of positive and negative pharmaceutical counterions using mixed-mode chromatography coupled with charged aerosol detector, J. Chromatogr. A 1217 (2010) 5776 – 5784.
2. X. Liu, C. Pohl, HILIC behavior of a reversed-phase/cation-exchange/anion-exchange trimode column, J. Sep. Sci. 33 (2010) 779–786.
3. B. N. Tran, R. Okoniewski, R. Storm, R. Jansing, K. M. Aldous, Use of Methanol for the Efficient Extraction and Analysis of Melamine and Cyanuric Acid Residues in Dairy Products and Pet Foods, J. Agric. Food Chem. 58 (2010) 101 – 107.

One of the probles I see of using convenctional HPLC for IC using exchange columns, is the material of the pathway. HPLC use metal tubing (specially Agilent, that you use) components, if you are thinking in very low concentrations this could generate some interference. Dedicated IC systems are te best solution, of course your problem is that you don't have one.

jvjkorn, could you expound on this, I don´t understand what is behind your statement.

Thank you of all for the responses!

Let me to explain my idea . In our lab we make soil analysis of nutrition elements by so called wet chemistry. These are time consuming and low sensitive methods. Since 2 years ago we bought Agilent 1200 with UV DAD.
And than I ask myself if could be make this analysis on HPLC. In literature I found more ways for determination these compounds, such as IC, spectrophotometric , ICP ( for metals) and other. I know that IC is more power technic for these kind analysis, but we haven't got this sistem. Than I had readed one article for simultaneously determination of cations and anions by IPC UV. This had attracted my attention and becauce I haven't more expirience in this field I have desided to ask this qouestion. Here is a link http://www.springerlink.com/content/j128g60h7v2hh560/ of the article.

Regards!!!!! Ana

Hello Ana,

what kind of extraction do you perform for the soil samples?

are you using photometric techniques or strictly wet chemistry?

I own 2 chromatographs, one for anions and one for cations. I do not use them for soil extracts because the IC columns are very expensive and could be easily damaged by soil extracts. For now it seems more cost effective to use chromatometric techniques with a UV-Vis instrument and test kits.

If you need all the cations and the anions though, IC could be a solution but a costly one.

The ICP is definately a good solution for soil analysis, for metals.

By the way ion pair chrom. with on column derivatization sounds like lots of trouble to me and perhaps quite a few blockages of the column and fittings. I'd rather not try that..
Can I ask you a few questions about your lab? Can I contact you somewhere please?

jvjkorn, could you expound on this, I don´t understand what is behind your statement.

I think what he is saying is that the flow of the buffer solution will pick up traces of metal ions from the column material (which is SS instead of plastic on most IC columns) and that will affect the conductivity detector and give faulse data.

Not having had experience with a conductivity detector that is just the kind of thing I don´t understand: It doesn´t work if traces of stainless derived ions are passing?

Well a conductivity detector has a flow cell which measures the conductivity of the mobile phase that passes through it. So the stainless steel obviously is metal and traces of that metal dissolved in the flow would cause contamination and consequently rise in conductivity disturbing your measurements.

That said I have seen anion exchange columns made of SS...

How many more ions does a typical IC mobile phase have compared to the Fe ions shed by the system?

I can give first-hand assurance that stainless steel does not cause any problems with conductivity detectors. We were doing single-column IC (HPLC system + ion exchange + low conductivity buffers + conductivity detector) back in the early 80's. Worked fine.

Actually what I would be more worried about would, is the fact that metal ions from the column should show great affinity with the column packing material causing deterioration of the column's separation ability eventually, when aggressive and strong eluants are being used.

Ion chromatography is a preferred method for ion analysis, for its high sensitivity (with suppressed conductivity detection) and high selectivity. A non-metallic ion chromatogragh should be used to avoid metal contamination espacially for the separation column. Dionex offers an array of ion chromatographs from low to high end with a collection of matching separation columns.

The stainless steel liquid chromagraphy system is not recommended for ion chromatography analysis when using corrosive mobile phase, such as MSA or NaOH, is used. When the mobile phase is compatible with the column chemical stability and detection method, ion analysis could be realized on a SST chromatograph as Tom suggested. However, even assuming the the mobile phase matches the column chemical stability and detection method well, metal contamination still occurs due to the accummulation of metal ions from mobile phase, SST column body and SST system during the use. The observation will be broadened and/or distorted peak shape. In this case, the column should be periodically cleaned with a chelating agent containing solution to restore its performance.