Ion chromatography

[Edwardchen]

My laboratory is currently considering setting up a quantitative assay for nitrate and nitrite. One possible method is Anion exchange chromatography. For sensitive and specific quantitative determination of nitrate and nitrite, is it the best method in terms of cost and ease of setup? In addition, I found that Waters has a system for IC which comprises an autosampler, a pump, a high capacity anion exchange column, a conductivity detector and an Alltech autosuppressor. I wonder if it is possible to use our existing Agilent 1100 autosampler and pump and then connect to the Waters conductivity detector. Besides, is the Agilent Chemstation data analysis software compatible with Waters system? According to the salesperson the Alltech autosuppressor is no longer available. Without this component, is the signal to noise ratio and hence sensitivity much lower? Are there any systems other than the Waters' that are suitable for my purpose? Could any expert please enlighten me? Thank you very much indeed.

[Kostas Petritis]

I suggest that you look at Dionex and Metrohm products for IC. The exact method will depend on the complexity of your matrix (i.e. what other components are there?).

[H.Thomas]

For Nitrate and Nitrite you dont need a conductivity detector. It's more sensitive with a UV-detector. Just buy an anion column and use your normal HPLC-equipment.
An altenative is photometric determination, possibly auomated by FIA. How many samples per hour do you want to measure?

[Bryan Evans]

This is an ion-pairing HPLC method for these anions on Unison UK-C18:
http://www.imtakt.com/TecInfo/TI298E.pdf

[Uwe Neue]

I just ran across the AOAC method for the determination of nitrite and nitrate in baby food [JOHN A. CASANOVA, LOIS K. GROSS, SARAH E. MCMULLEN, and FRANK J. SCHENCK, Journal of AOAC INTERNATIONAL | Volume: 89 (2006) | Issue: 2 | Pps: 447 – 451]. Might be helpful...

[Edwardchen]

For Nitrate and Nitrite you dont need a conductivity detector. It's more sensitive with a UV-detector. Just buy an anion column and use your normal HPLC-equipment.
An altenative is photometric determination, possibly auomated by FIA. How many samples per hour do you want to measure?

If a UV-detector is more sensitive, I don't have to buy a conductivity detector. Is it necessary to have an ion suppressor? Do you have any references for a method using HPLC-DAD? Thank you very much.

[Edwardchen]

This is an ion-pairing HPLC method for these anions on Unison UK-C18:
http://www.imtakt.com/TecInfo/TI298E.pdf

There is no method detail in the pdf except a chromatogram. Are there any detailed information please?

[Edwardchen]

I suggest that you look at Dionex and Metrohm products for IC. The exact method will depend on the complexity of your matrix (i.e. what other components are there?).

I work in a toxicology lab, so anything from vegetable to medicine will be my potential sample. I have no idea how the matrix affects the analysis.

[Edwardchen]

I just ran across the AOAC method for the determination of nitrite and nitrate in baby food [JOHN A. CASANOVA, LOIS K. GROSS, SARAH E. MCMULLEN, and FRANK J. SCHENCK, Journal of AOAC INTERNATIONAL | Volume: 89 (2006) | Issue: 2 | Pps: 447 – 451]. Might be helpful...

My institution have not subscribed this journal. Just registered at the Dialnet and don't know if I will have access to it. Thanks a lot!

[Consumer Products Guy]

Is it necessary to have an ion suppressor?

This may depend upon how sensitive you need to have your assay. We do plenty of IC here without suppressors. We use Agilent systems here with other companies' conductivity detectors; you can use anybody's detectors with agilent software if you have the 35900 A/D converter, either a board inside the computer (35900D) for older computers or external box (35900E) for newer computers and LAN-connected instruemnts. Contact your Agilent rep for those.

[Uwe Neue]

What is the matrix in which you need to determine the nitrate/nitrite?

[Kostas Petritis]

I suggest that you look at Dionex and Metrohm products for IC. The exact method will depend on the complexity of your matrix (i.e. what other components are there?).

I work in a toxicology lab, so anything from vegetable to medicine will be my potential sample. I have no idea how the matrix affects the analysis.

Uwe, more or less he said from very simple to very complex matrices... so it will probably be case by case scenario. I would imagine that he will get a lot of UV interference from the vegetable extract and probably some SPE will be necessary before analysis

[Uwe Neue]

Kostas, you're right - I had not seen this...

For complex matrices, I recommend the technique in the AOAC publication, since it is using a very specific detection technique that gets around the problem with intereferences: post-column derivatization. This technique is very specific, contrary to other more generic techniques, from UV detection to conductivity detection. Very little sample prep is required - essentially just to be free from stuff that would block the column. The detection at 525 nm is very specific.

[Bryan Evans]

Hi Edward -

The conditions are at the bottom of the chromatogram.
Perhaps this method was developed to compete with IEX
for nitrates & nitrites in water - I'm not sure.

Thi method uses relatively low UV @ 230.
The 525nm method will be more selective - but requires post
column derivatization. The IC folks will have options for you as
well.

It's up to you to figure out which method provides the best solution for
your needs (and budget) - that's the fun part!

[Edwardchen]

I suggest that you look at Dionex and Metrohm products for IC. The exact method will depend on the complexity of your matrix (i.e. what other components are there?).

I work in a toxicology lab, so anything from vegetable to medicine will be my potential sample. I have no idea how the matrix affects the analysis.

Uwe, more or less he said from very simple to very complex matrices... so it will probably be case by case scenario. I would imagine that he will get a lot of UV interference from the vegetable extract and probably some SPE will be necessary before analysis

I have got an HPLC-UV protocol which uses 0.045M potassium dihydrogen orthophosphate as mobile phase, Whatman Partisil 10 SAX 4.6x250mm column, simple sample preparation by boiling for 15 min and filtering, flow rate 1.2ml/min, injection vol:25ul, UV detection: 210nm. SPE by RPC18 only if interfering peak present. (Actually, I don't know how any interfering peak can be known as the UV scanning is made in one single wavelength).
Other methods exist such as binding of ion-pairing reagents to C18 column, which is hard to predict according to a review article. The post-column derivatization method may be too complicated because it involves additional hardware such as post-column pump, post-column derivatizing agent, post-column reactor, Teflon delay coil. I am entirely unfamiliar with these. I wonder if it is a good choice to select the strong anion exchange HPLC-UV method. Please comment. Thank you very much indeed.