I have some samples containing phosphorus. I need NMR spectra of these. How can I measure spectra? Should I use an internal/external reference or none? Will I make a mistake about 31P chemical shifts if I use none?
This depends how accurately you need the chemical shifts. If you know one of your components in the sample, you can use that. For example you can use the phosphate resonance (if that is in your sample).... however, that is pH and temperature sensitive. So you have to know (and correct for those). The simplest thing to do is to make a capillary (sealed) with 85% phosphoric acid and use that as your standard.
... there is always indirect chemical shift referencing.
+1 with Markus, you will also need or the laboratory that you are using for NMR, a P NMR probe.
.. and one more thing. If you want to decouple 1H from 31P you need only very little power if your H-P couplings are on the order of 10Hz or so. (e.g. nucleic acids). The 90 deg decoupling pulse can be easily around 200us or more; IF the shift range is small waltz16 and such a long pulse will do fine. If you have a huge shift range and large couplings then you need to be more careful.
Re probes: Most Bruker X probes (BBI, BBO) etc go from Ag to 31P. Clearly, a BBO (x observe) would be best but 31P is easily observed in an inverse probe.
First you need a broadband probe to tune in the 31P Larmor frequency and as Markus already stated you need internal or external reference, such as the sealed capillary including 50 microL or like that amount of 85% phosphoric acid, insert it in your NMR sample tube and run the scans to determine 31P species in your sample. Also find a good 31P NMR data table to make notice the type of 31P nuclei present chemically to compare.
Check as well if you have the correct filter (λ/4) for 31P. Proceed as Markus and Hiram stated. If you are determining the changes of hexagonal/lamelar membrane drug influence I send you some recent articles on this subject.
Article Nimesulide interaction with membrane model systems: Are memb...
As far as referencing of the chemical shifts is concerned, either put into your sample a concentric capillary containing 85% H3PO4 or just measure your deuterated solvent with the H3PO4 capillary and remember the frequency of the reference (to be used later also with other samples in the same solvent without need of the capillary). Or apply the IUPAC-recommended method (chi-value). Most importantly, however, you have to describe what you did so that others can reproduce your experiment.
Also, external references (capillary) require a susceptibility correction [which takes into account the different magnetic susceptibility of your solution or solvent and your reference material]. The sign and magnitude - generally less than 1 ppm - of this correction depend on the direction of your sample with respect to the direction of the magnetic field (iron or superconducting magnet), see textbooks.
For a very detailed treatment of the chi-value of orthophosphoric acid, see Magn. Reson. Chem. 1992, 30, 850-854 (by H. T. Edzes).
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