I an new to NMR and am about to conduct (after a scant training) some quantitative proton-NMR in D2O to determine the SDS concentration from the solution. I am told that DSS (2,2- Dimethyl- 2- silapentane- 5- sulfonic acid or it's Na Salt) can be used as an internal standard to quantify the solute (SDS in this case). I am wondering if this standard will have some interaction with SDS (compound of interest) and shift the chemical shift in any way. Does anybody has any experience in this field and can help me get answer to this question. I appreciate any help. Thank you.
Mrs/Miss/mr. Rajopadhye,
Quantification by any methods is carried out in triplicate. So you not only should measure samples using bothneutral and Na-salt of the standard, but this should be done in triplicate. In addition the data should be interpreted using chemometric methods as well.
As both SDS and DSS are comparable small molecules I would not expect an interaction between them. On the other hand, SDS might form micelles which could have an effect on its relaxation properties once these become too big. This might lead to reduced peak intensity and thus disturb your quantification. I would only use this method if you work with SDS concentrations below the CMC.
I would not expect any interaction between SDS and DSS. From a spectroscopic point of view the methylgroups of DSS are sufficiently separated from SDS to allow a accurate integration. The alpha methylene signal of SDS is also out side of any region where DSS signals occur. Whereas there is the possibility of overlap of the other signals. Make sure that the regions used for integration belong to one compound only.. In other words make sure all signals of SDS and DSS are accounted for. For quantification with the highest precision you will also have to account for the 13C satellites or use 13C decoupling during data acquisition.
Hello all, thank you so much for the inputs. I appreciate that.
@Ivanova, y es, all the measurements are planned in triplicates.
@Jonas, i am g going to have to do the quantification over a range of concentration, so there will be some concentrations below the CMC. A few ( at least one) would be above.
@Clemence, thanks for the suggestion of using 13C satellite . As I mentioned in the question, I have read about the 13C satellites and decoupling but do not hold quite grasp over the subject. However, in that case, I will speak with my colleague in the NMR lab to get his hello on this.
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