It is hardly possible to give an answer without knowing your experimental setup: column (s), eluent composition, flow, type of detector.What do you mean with "the results are not good"? Do you mean the peek form, separation of peaks or are your results below the detection limit? What about your sample preparation? Did you filter your samples prior to the measurement? Keep in mind that most of PO43- might be in particulate form. Moreover, at pH 11 i would expect most NH4+ as NH3. 

Best wishes   

to be able to help you can you elaborate more on how you filtered your samples to remove the matrix, what kind of water did you use for dilution, what was the conductivity of your samples after dilution, why do you have to control the pH of your water sample

I use 883 basic IC plus of metrohm.We can change the column as per wish. Now i am using cation column of flow rate 0.9, pressure 7-8 mpa, conductivity 600-700 µS/cm, eluent composition is 1.7 mM HNO3 + 0.7 mM PDCA/ 1 l ultra pure water. I use 0.20 µm cellulose filter and use ultra pure water for dilution.

For now i am using synthetic waste water considering only ammonium ions....My real waste water contains around 9000 ppm of ammonium ion and some nitrate and sulphate ions under which i will be working soon. The bottom line is i want to utilize ammonium ions to precipitate struvite by adding MgCl₂.6H₂O and Na₂HPO as suggested by Michael Päch. I want to optimize pH and molar ratio. so i want to know the change in the concentration of Mg²⁺ ,NH₄⁺,PO₄³¯ ions. I analyse only supernatant solution of my sample.

When you say you do not get a good result upon dilution, what specifically is problematic about your result? Are you observing low recovery for ammonia? If so, the problem could be your filter material. Most natural materials contain cation-exchange sites due to oxidation and/or scission of chemical bonds during the preparation process. You might improve the situation by acidifying the sample with MSA.

you need to check fraction of particle size,adjust ph,flow rate,and filtration media especially in different toxic state waste water.

You can use theoretical method of pC-pH diagram about NH+ and PO4-P at first.  And then,according to this result you can  compare with analytical result. 

For NH4 determination it is important that your finally diluted sample is slightly in the acidic pH range. If the sample stays alkaline ammonium might evaporate.

Please also check back with your Metrohm represenative (JLScience) for further application support.

Thank you all for your wonderful comment..

recently i got real waste water which is NOx scrubbing waste water.. it has high NH4+ concentration around 12000 mg/l and pH range 10-10.5. when i dilute the sample 1000 times ph reduce to 9. so should i acidify my sample with the help of HNO3 or HCL? because i worry if HNO3 will interfare NH4+ of my sample.. 

i use standard of 1,5 and 10 ppm.. should i use standard of 50 ppm??

If you dilute with e.g. 2 mmol/L nitric or add the repsective volume of 2 mol/L no problem will occur.

dear markus

thank u ..i will follow this instruction and see the result. i have one more query..can we use only nitric acid as eluent for cation without PDCA? i previously used 1.7 mm/l HN03 and 0.7 mm/l PDCA. 

PDCA actually has an effect on calcium elution. Therefore I did not mention it. But of course you may use your eluent.

i tried once with only nitric acid (1.7 ml of 1 M HNO3 in 1 l solution) but the conductivity decresed to 370 and ic could not show any result.

can we use only nitric acid solution as eluent?if so then i dont know the exact concentration of nitric acid to be used in 1 liter solution..

Dear Thapa,

Actually I don't know the method you have been using but something is striking to me. Your samples' pH s are changing between neutral to basic. And you are using NaOH to control the sample pH. This means you are making your samples basic. Instead, you had better use dilute nitric acid for pH control. Since you do not need NO3 ion and you use nitric acid as mobile phase. Please first check working pH range of the column you used and then try slightly acidic samples. I hope this helps!

I am trying with acidic sample.. hope it will help me get good results. thank you Duran karakas

please help me with the following question:

do we need to measure standard solution everytime we change the eluent or can we use single calibration curve over the period?

Dear Shanti

To your 1.7 mmol/L nitric acid eluent: you shoud get a conuctivity of approx. 500 µS/cm or above. you also may higher concentration if retention times sre too long.

About measuring standards after eluent change: I would recooemd to check the background conductivity of the new eluent. If it is the same as with the previous eluent, there is a good chance that the elution and response stays the same. Anyway an injection of a check standard with known concentration is recommended. Ifyou get differences to the expected concentrtion a calibration is required.

My conductivity ranges from 658-662 µS/cm. After using only nitric acid as eluent, peaks of mg and ca has exchanged along with increased retention time which my IC operator told is normal. Anyway i will calibrate and measure the sample again and compare the results. 

Thank you Markus for the help :) 

Conductivity is OK. Switching from an eluent with dipicolinic acid to one without definitely will change the elution of Ca and Mg. Therefore recalibration is a must in this case.

About dipicolinic acid in the eluent: dipicolinic acid is a quite strong complexing agent which complexes e.g transition metal cations very well. Adding it to an eluent has two effects.

1. trivial: it encreases the H1 concentration and therefore increases the eluent strength.

2. It complexes or partially complexes divalent metal cations. Transition metals are almost fully complexed and if available in the sample are elutes in the front. Calcium builds a neutral 1:1 complex. Under the eluent condictions Ca is not fully complexed and the ligand exchange is fast. Therefore we get an earlier elution of calcium. As Mg is almost not complexed by dipicolinic acid its retention time is only little influenced. and depending on the concentration of the dipicolinic acid we can get an inversion of the retention times.

Thank you so much Markus for very clear and concise information.. 

Concerning Ammonia high concentration, it is advisable to use the vacuum distillation technique for comparison, using mild conditions in order to avoid any contamination from labile nitrogen containing organic compounds.

I suspect that your problem is caused by the low solubility of magnesium phosphate and magnesium carbonate.  Try removing magnesium with a hydrogen form cation-exchange resin sample prep cartridge prior to injection for anion analysis.  It may also be necessary to remove phosphate prior to injection of the sample for cation analysis depending upon the eluent system you are using and whether or not you are using a suppressor.  If necessary, try using an anion exchange sample prep cartridge in the acetate form prior to injection.