Organic ICP-OES Phosphorus FACT Modeling Application

The Cu peak is 213.598nm and the P peak is 213.718nm. That means the Cu peak is 20 picometers to the left and the resolution of the instrument is very good so you can actually obtain baseline resolution of the 2 peaks with fitted background correction. Therefore you really do not need FACT, you can use fitted background correction. With FACT, it is dangerous to use a multielement standard for both the analyte and interferent models. You really need a single element P solution in kerosene for the analyte model, and a single element Cu solution for the interferent model. Here is a calibration curve for P 213.718nm using organometallic multielement standards in an organic matrix and Fitted background correction. 

Thank you for the response, Tina. When we began working on our method, we were recommended FACT due to matrix effects from the oxygenated nature of our oil. Do you think this is not a factor for this specific analyte at this wavelength? Also, at sub-ppm measurements, the P peak seems to drift upward in wavelength. Would FACT with the correct interferent/analyte solutions be better than fitted for sub-ppm measurements due to the nature of the curve? And one last question, I see the P curve you provided is a quadratic regression. Would a quadratic regression be a good fit for the range of 0.1 - 10 ppm, or is the linear regression model sufficient? I am not familiar with different regressions using ICP-OES, so any insight would be appreciated. 

Thank you!
Kyle Bell

When performing sub-ppm analyses in an organic matrix, yes the background structure of the ,carbon-based matrix can become an issue. FACT can be used to remove some of this background structure, but you need good models. So I would definitely recommend single element solutions for both your analyte and interferent models. You can easily change from fitted to FACT to see which one is better, and it may be wavelength dependent. If you have done a recent wavelength calibration, and the temperature and pressure in your lab is stable, then you should not see peaks "drifting". It could be that you have interference from background structure. Also, on the configuration tab of your worksheet, make sure "Drift correction" is OFF. This is very important in organic analyses because carbon emission wavelengths may interfere with the argon drift correction lines used for correction, and this may cause an apparent shift in wavelength position. 

With respect to which regression fit is better, experiment with different ones to see which is better. I would expect 0.1 to 10ppm to be linear for most wavelengths, as long as you have "weighted fit" checked. I hope this helps!