Eliminate interfering ions by sample pre treatment with  guard cartridges.

How well resolved are the peaks in low anion concentration? May be you can lower the strenght of your mobile phase to increase retention times and better resolve the peaks.

Colorimetric/spectrophotometric methods are more specific for analyzing NO3 or NO2 in the present of other ions. These methods are routinely used for analysis of nutrients in seawater.

Choose any bidentate ligand or tridentate ligand to react with only NO3 or NO2 not react with chlorine or phosphate. you will develop a colour and go to UV spectrophotometric method and measure the absorbence and calculate your analysts. OR Chlorine and phosphate react with any ppt reagent to form a precipitation. Remove that ppt. And go to above UV method

Thank you very much for all the comments and suggestions.

You can used capillar electrophoresis, it is simple y non expensive. As well, the anions can be determined by HPLC. This method is slower than the first. Finally the by ioinic crhomatography, but to do it is somehow more expensive. In all cases, the reproducibility and sensibility are high

Regards

J Gomez 

I use suppressed IC to separate F, Cl, NO2, Br, NO3, PO43-, SO4 using Dionex high capacity column, a 9mM carbonate buffer, and microbore Dionex chromatographic system. These anions resolve very well in aqueous samples that have disparate concentrations of the anions:  high choride and sulfate (up to 400 ppm), low nitrate/nitrate (less than 3 ppm).

Hello Tran,

I will send you via email a manuscript where you can find the IC conditioins I use to resolve by IC the F, Cl, NO2, Br, NO3, PO43-, SO4  even in the presence of high amounts of Cl, PO43-, and SO42-.  Cheers.

Thank you Mr J Gomez and Ms Maria Martinez.

The spectrophotometric (Colorimetric) methods are well established to measure nitrate and nitrate in seawater which contains high concentrations are Cl and other cations and anions. In case of nitrate, it has to be reduced to nitrite using cadmium-Hg or Cd-Cu amalgamation column and then measure the converted nitrite following Azodye method. I is quite accurate and can measure up to 0.02 uM.

In addition to the above comments you can also try an off line matrix clean up to remove much of the Cl in the sample with the single use  Dionex OnGuard II Ag cartridges.  They are simple to use with a syringe and will decrease the level of Cl in your sample suffiently to allow you to resove your Nitrate and nitrite peaks.  It would be a good idea to run a few standards through the cartridges to confirm that you are still getting complete recovery of the Nitrate and nitrite with the column. 

No matter that chlorides and phosphates occur high, is a selective determination and if you determine as nitrites nitrates do not interfere other ions, determination can make use of a uv-vis spectrophotometer.

I am also experiencing the same problem. I was trying to analyse the amount of nitrates in water but am getting two peaks. does anyone knows what could be the problem? I have prepared my standards twice because i thought it might be a contamination but am still getting two peaks. please help

The use of Dionex OnGuard II Ag cartridges to remove the excess of Cl is a good approach but you can also use high capacity column designed for matrices with disparate concentrations of anions such as the ionPac  AS9-HC:

http://www.dionex.com/en-us/webdocs/4347-MAN-Dionex-IonPac-AS9-HC-031267-EN.pdf

In my lab nitrate and nitrite are measured by HPLC or capillar electrophoresis. Write to Dr. Cuervo-López ([email protected]) or Dr Texier ([email protected]) for details

I am also looking good suggestions. How to use Ion Chromatography to analyse NO3, NO2, NH4, PO4, Br, F, I for high salinity groundwater (EC ~ 10000 to 25000 microS/cm). High dilution reduces the concentrations of these parameters. Sometimes, these are BDL due to high dilution.

Any good suggestions?

You might want to look into using high capacity ion exchange columns for IC. The analysis of minor components requires the injection of your samples at lower dilutions. You need the high capacity to retain the minors still, though the conductivity trace of your chromatogram on a first glance will only show the majors. For anion exchange, I would recommend looking into high capacity anion exchangers and use suppressed conductivity in conjunction with UV-detection. While the major components like chloride and sulfate are not absorbing UV-light, others like nitrite nitrate, bromide and iodide are. You will be able to analyze them even at lower concentrations. The elution of iodide might become tricky, but depending on your instrument capabilities you could think about running gradient elution using a high capacity column with less hydrophobicity.

Analyzing phosphate with ion chromatography using conductivity detection will become a challenge, as we cannot exclude the presence of metals (e.g., iron) in the groundwater. As IC only determines the soluble o-phosphate, the irons content determines what the recovery of ortho-phosphate will be. While there are solutions in IC to access this parameter, I think that a conventional photometric determination might be in order. If you have to analyze many samples, an automated device (e.g., a discrete photometric analyzer) could help.

The determination of ammonium in the presence of high concentrations of sodium is one of "the" challenges in IC. I assume you will have to run trace levels (how much?) of ammonium. While for the anions we can use simple to apply specific detectors, we will have to see if

a) isocratic elution using a high capacity cation exchanger will be sufficient

b) gradient elution will be needed

c) if we would need to look into alternative detection like fluorescence.

While a) and b) are rather simple to realize, c) would require quite some effort, and before crossing that bridge, I'd instead think that photometry would help. As you expressed only interest in one cationic component (ammonium), it might be an idea to question, if IC is the best choice in this scenario.

I am adding some links to applications below, and they could serve as starting points of your evaluation. There is more on these topics on the Internet, and Dr. Google helps. ;-)

something to read:

https://assets.thermofisher.com/TFS-Assets/CMD/manuals/Man-065711-IonPac-AS23-4um-Man065711-EN.pdf

https://assets.thermofisher.com/TFS-Assets/CMD/Application-Notes/AN-141-IC-Inorganic-Cations-Ammonium-Waters-IonPac-CS16-AN71549-EN.pdf

https://appslab.thermofisher.com/App/133/an239-determination-iodide-seawater-other-saline-matrices-using-a-reagentfree-ion-chromatography-system-with-suppressed-conductivity-uv-detections

Hello Tran, for separation and quantification of nitrogen ions in samples with high chloride, phosphate, and sulfate, we use suppressed ion chromatography with conductivity detection. Our system is a Dionex ThermoScientific ICS 6000. The analytical column, an IonPac 9AS-HC column. he method is provided by the factory and is a standard method approved by EPA for water quality. Cheers, Maria Martinez