Dear Yael,
>What's a recommended 31P chemical shift reference standard for small organic
>molecules in D2O?
For acqueous solutions we use 85% H3PO4 as a primary chem shift reference
assigned to 0.00 ppm. This could be in a coaxially mounted capillary etc.
I assume you would have to correct for the susceptibility induced shift
(in a superconducting horizontal magnet) for highest accuracy.
However, usually we use secondary standards like phosphocreatine (-2.35
ppm), triethylphosphate, etc. I am not quite sure how much 100% D2O would
affect the shift (as compared with H2O). There would probably be
differences for 31P-nuclei near exchanging protons.
Inorganic phosphate in water has a positive and pH dependent (also D2O
effect) chemical shift separate from 85% H3PO4 (which is 0.00 ppm).
>I see 85% H3PO4 at zero ppm is the most referenced. But doesn't the amount
>of
>water present affect the 31P shift? (Sometimes I see just the acid given,
>sometimes I see aqueous given (no specific amount), sometimes I see the acid
>listed with D2O (no specific amount), the bottle of H3PO4 already states
>85%, . . .).
85% H3PO4 is straight from the bottle, no water added!
>In the NMR Encyclopedia (Vol 4, p. 2340, Table 2), I see listed PPh3 = -5.6
>ppm, but no literature reference as to details (assuming room temperature?
>in
>acetone-d6? still an okay external reference for organic molecules in D2O)?
I would not think so.
>I appreciate your assistance on this basic question.
Just my 2 oere.
73, Peter
_at_ _at_
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Received on Thu Jun 20 2002 - 20:42:28 MST