Hi all,
I would appreciate if you could guide me.
My solution contains 2500ppm calcium, 5000ppm sulphate, 8000ppm sodium, 8000ppm chloride and I add 10ppm NTMP (nitrilotri(methylenephosphonic) acid) which is a phosphonic acis at pH 7 to this solution. I want to measure the concentration of NTMP in this solution. Can NMR help me and be accurate?
In theory you could use NMR for the quantification of substances in your sample. However, I see two obstacles here:
1.) Sensitivity is a big issue in NMR. If you want to avoid overlong measurement times, you should not have too low concentrations of your analyte. You say you have 10 ppm NTMP in your solution, so this corresponds to 10 mg per litre - or 10 µg per millilitre. So this is way to little substance for a decent NMR measurement, for structure elucidation you normally use a few mg of your substance. If you want to do QNMR, you should consider increasing the NTMP concetntration.
2.) QNMR work quite good, but to use it, you have to calibrate your spectrometer accordingly and you have to have good environmental control (temperature, gas flow, high quality NMR tubes etc). I guess you will find useful information on that topic on the Bruker website.
To sum it up: I would suggest you use another method like e.g. MS or ICP-OES to do the quantification of NTMP. I guess you will have these methods available at LEeds, and maybe even a lab technician who can give you advise on which method to use and the sample preparation. Good luck!
I would suggest you to determine the P concentration using ICP OES or ICP MS if you are sure that the NTMP is the only source of P in the solution. And the adequate sample preparation is very important for the accuracy.
While other, more sensitive analytical techniques could provide a quick answer, you could still use quantitative 31P NMR.
If you can actually observe the 31P signal for NTP, then you should be able to quantify it.... with the following caveats:
1. Prepare a reference phosphate solution of similar concentration for calibration
2. Set the interpulse delay to a large value, based on the relaxation time of your molecule, to nsure full 31P raxation.
3. Set thenumber of scans, or transients, such that you get a decent S/N for integration. In this case you might need an overnight run on a 9.4T NMR instrument with an RT probe. It will, of course, be much faster if you are using a high field (18.8T-21.1T) instrument.
Additionally, if you have access to an instrument equipped with a cryoprobe, you will most likely, not have any issues with the low concentration of your compound.
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