In addition to setting the chemical shift, the CSI in Chenomx NMR Suite allows calculating concentrations of compounds in your compound library. The ‘extra’ information that you need to enter about the CSI is what allows these calculations to occur.
Calculating the absolute concentration of any compound based on its signal intensities in an NMR spectrum requires the following information:
- The number of protons contributing to the signal from the compound
- The number of protons contributing to the signal from the reference compound
- The intensity of a signal from a reference compound
- The concentration of the reference compound
- The intensity of a signal from the compound
When you are using Chenomx NMR Suite, item #1 is stored in the compound signatures distributed in the Chenomx Compound Library, or any signatures that you might create yourself using Spin Simulator and Compound Builder.
#2 is built into the definitions for the supported CSI compounds (DSS, TSP and formate).
You define #3 and #4 when you process a spectrum in Processor, via the CSI editor. You set #3 when you fit the red CSI line to the spectrum using the CSI Editor, and #4 when you enter a CSI concentration in mM.
Finally, you manipulate #5 as you fit the compound in Profiler.
In short, the concentrations that you determine in Profiler depend on the number of protons (as you might expect), but they also necessarily depend on the concentration of the reference compound (as may be less obvious). It is not possible to calculate absolute concentrations using NMR without involving the concentration of a reference compound (in Chenomx NMR Suite, the CSI).