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Abstract
A quick, noninvasive method based on 31P NMR spectroscopy to measure the pH of samples containing phosphate buffer is presented. By taking advantage of all four phosphate species populated at acidic, mildly acidic, mildly alkaline and alkaline pH, the method is aplicable over a wide range of pH values, from 1 to 13. This tool is most precise at pH values near the pKa values, namely from 5.8 to 8.0 and 10.6 to 13.0. To facilitate its use, a web application is presented that calculates the pH value directly from phosphate 31P chemical shift (ppm): (https://rmni.iqf.csic.es/software/31phnmr/). In addition, the potential of this approach to monitor reactions which generate or consume H+ is illustrated.
Supplementary weblinks
Title
31pH NMR
Description
This webpage allows the user to input a 31P phosphate NMR chemical shift value (ppm), which was obtained at 5 ºC or 25 ºC and indirectly referenced to the 1H trimethyl signal of DSS, and obtain the pH.
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