Method 8330B and Nitroguanadine

[Room 101]

I am trying to develop a method for the analysis of Nitroguanadine. Using EPA method 8330B as a starting point, I so far cannot get Nitroguanadine to separate from my solvent front. I am using an Acclaim E1 Explosives column, my standards are in Acetonitrile and I have played around with various versions of MeOH/Water and ACN/Water mobile phases. Any suggestions?

Thanks!

[Vlad Orlovsky]

Here is previous discussion on the subject.

viewtopic.php?t=11830&highlight=nitroguanidine

RP chromatography and HILIC are not going to work. You need to use normal phase approach. Send me your email and I will provide you with the method

[bisnettrj2]

FYI, NP is a pain in the rear. Using 95:5 isooctane:ethanol at 1 mL/min, I was able to inject 1 uL of water with 2 ppm Nitroguanidine, and I got a decent peak at around 5 minutes (started a gradient to 50:50 at 2.5 min) on a Kinetex 50x4.6mm HILIC (bare silica) column. I only get to mess with NP for a while, but I couldn't inject enough water extract to get a decent peak at my low standard without have a massive pressure spike. I had to set the analysis aside for other work, but it's not too promising at this point.

I think the solution may be to concentrate my water extracts in order to correlate to a higher standard in my calibration while still maintaining my current reporting limits, but that adds a whole other bag of cats to the problem.

[bisnettrj2]

Room 101 - I've had custom standards made in 100% H2O, and have injected them on a PFP, YMC AQ ODS, C18, Cyano, Acclaim E1 and E2, all running 100% H2O. Normal phase is the way to go, but tweaking the analysis to find the right parameters is the problem (at least for me). Good luck.

[Vlad Orlovsky]

You cannot blame normal phase chromatography in your case. It is known for longer time then RP chromatography, and people used it for various compounds in various matrices

Here are problems with your analysis:
• Your column is not the most polar column on the market, so you are pushed to use higher isooctane concentration to gain retention
• You are running gradient with isocratic conditions at the beginning, when there is absolutely no reason to do this. Your compound is almost not moving at this high concentration of isooctane, because when you start your sharp gradient it takes another 2.5 minutes to elute it from the column
• High octane concentration (see above) prevents you from injecting aq. sample. At this point you K' is 9. Why do you need gradient to achieve such long retention (void on this column is about 0.5 min)?

I would suggest that you revisit your method
• Increase amount of alcohols in the mobile phase
• Move away from gradient run to isocratic
• Dissolve you sample in alcohol, or add alcohol to it (or THF)
• Consider extraction with organic solvent

NP is no more painful than RP or ion-exchange. You just need to totally understand what needs to be done, and may be listen what people done so far (just to save money for your company) and adopt it to your case. Now, almost 2 month later you don’t have a good method and also trying to discourage people from solving their problem.

[bisnettrj2]

Vlad:

Thanks for the tips. I'm not trying to discourage anyone else, it's just been a pain for me. Did I not say "Normal phase is the way to go, but tweaking the analysis to find the right parameters is the problem (at least for me). Good luck"? Is that discouraging this person from trying it? I think not. Also, it's not like I've been working on this for two months non-stop, it's something I play with when I have the time, and have probably spent about a grand total of a day on the NP portion.

The gradient I ran was the Phenomenex-recommended gradient for their HILIC column (in HILIC-mode, that is, but I used it just for starters). And I'll take a k' of 9 any day when the normal k' for nitroguanidine is less than 1, and more like 0.

[Vlad Orlovsky]

having K' of 3 -4 is very good, anything else (for one compound) is waste of time, solvent and money. If you have a method in which one compound elutes at 2 minutes and second one at 10 minutes, then you are wasting at least 7 minutes (not you but ay other analyst). In my opinion K' of 2-2.5 is good for single compound, assuming that matrix effect is eliminated.

P.S. I started writing my message before you posted yours.

[bisnettrj2]

Understood Vlad. Thanks again for the tips, when I get back around to playing with the analysis, I'll probably start with try to extract with an alcohol instead of water, to get around the incompatibility with isooctane. Need to find a solubility chart on nitroguanidine again to decide which solvent is best, outside of water. I'll ask Google.

[bisnettrj2]

Room 101 - See the "Polar analyte analysis" thread on this forum for the progress I've made on nitroguanidine as of 02/02/2010.