Predicting aquisition time needed depending on sample concentration

0	Hi , is there a way of predicting aquisition time needed depending on sample concentration in order to get a decent spectrum for a 2D experiment for example? 2D aquisition bruker topspin asked Dec 18 '14 at 02:47 gravatar 83

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It is difficult to answer your question for any type of sample since the concentration is not the only parameter that will affect the S/N. T2 (size) and p90 length (salt concentration) are two of the factors that would have a big effect on S/N.

In case you do have a reference sample with properties similar to those of the molecule in question, you can collect a spectrum, choose the weakest peak that you are interested in and calculate its S/N (use the SINOCAL AU program).

Keeping in mind that S/N of 2-3 is close to the minimum that you can reliably use and the fact the S/N is increasing linearly with concentration, you can calculate the minimum concentration you can use with the same number of scans.

Now if you want to increase the experiment time keep in mind that S/N is analogous to the square root of the number of scans. So to double the S/N you need to quadruple the number of scans.

I hope this helps.

Best regards

Manolis

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answered Jan 14 '15 at 08:33

Manolis Matzapetakis
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Hi, sorry my response took this long.Can you explain to me how to use SINOCAL au exactly? It asks for left and right limit of signal range and noise range which I understand; but then it asks about noise width which I do not completely understand. - gravatar (Mar 12 '15 at 09:35)

gravatar, I believe this is how the noise width works: You specify a lower and upper limit from which it can sample the noise. The noise width is the window within those limits that the program uses in the calculation... - clemistry (May 19 '15 at 14:32)

...The program uses various positions of the noise width you specified and calculates the S/N. It returns the best value that it finds. **Note: You can sometimes get an idea of how the au program works by typing edau (edit au). There's often comments at the beginning. - clemistry (May 19 '15 at 14:36)

Hello, ... such a feature in Bruker software I also miss a bit! This one is already implemented in VnmrJ 3 and 4. Calculation are done via estimation by signal to noise measurements of defined compounds.

Sorry, I haven't found anything comparable at TopSpin.

Uli

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answered Dec 22 '14 at 01:29

Ulrich Haunz
210

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Asked: Dec 18 '14 at 02:47

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Last updated: May 19 '15 at 14:36

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