Dear AMMRLers,
We have been evaluating four quantitative NMR methods:
1. Internal reference standard method, classical analysis, primary method
2. External reference standard method
3. ERETIC using absolute integral values
4. ERETIC using relative integral values
Below are some of our observations on the methods outlined above. For those of you who are interested in quantitative NMR, would you share some of your observations in this area? Aside from this general question, two specific questions are:
1. What may cause a bias when using ERETIC with absolute integral values?
2. What may cause this same bias, with a loss in precision, when using ERETIC with relative integral values?
If you are interested, please contact me and I will supply you with plots of some of these data. Note, we are using the current Bruker version of ERETIC, which consists of inserting a computer-generated signal into the spectrum.
We have looked at 10 replicate preparations of a test solution containing the internal reference standard and analyte.
The internal reference standard method gave us what we would expect:
* The precision over the ten samples at a given time was ~ 0.4%.
* The reproducibility for a single sample over four weeks was ~ 0.1%.
* These numbers indicate that larger source of error was from the sample preparation (from weighing).
For the external reference standard method, the reference signal in the first spectrum was used to calibrate the analyte signals in all subsequent spectra.
* The precision over the ten samples at a given time was ~ 0.4%.
* The reproducibility for a single sample over four weeks was ~ 0.3%
* These results showed good instrument stability over four weeks.
For the ERETIC method using absolute integrals:
* The precision over the ten samples at a given time was ~ 0.7%.
* The reproducibility for a single sample over four weeks was ~ 0.3%
* There was a negative bias by ~ 2% when compared to the results from the internal reference method.
For the ERETIC using relative integral values (intended use):
* The precision over the ten samples at a given time was ~ 0.7%.
* The reproducibility for a single sample over four weeks was ~ 1.5%
* There was a negative bias by ~ 2-6% when compared to the results from the internal reference method.
Regards,
Joe Ray / Christina Szabo
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G. Joseph Ray, PhD
Senior Research Scientist/Technology Resources/PCS
Baxter Healthcare Corporation
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Received on Fri Oct 15 2010 - 10:08:43 MST