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Logic Puzzle #42: How to Convert to PPM for NMR and MS Data? … Solution

June 11, 2013

Many analytical data rely on common calculations. This solution shows the formula used in the calculations.

NMR and MS data were collected on two unknown compounds. The TOF-MS data shows the [M+H]+ at m/z 300.0000 and 600.000 at an error of 0.001 Da. The 500 MHz 1H NMR spectrum shows two chemical shifts at 1500.00 and 3000.00 Hz referenced to TMS at 0.00 Hz.

The conversion for the mass accuracy of TOF data from Daltons to PPM is:

Error (ppm) = Error (Da) * 1,000,000 / (m/z for sample)

Error1 (ppm) = 0.001 Da * 1,000,000 / 300.0000 = 3.3 = 3 ppm

Error2 (ppm) = 0.001 Da * 1,000,000 / 600.0000 = 1.7 = 2 ppm

The conversion for the NMR shifts from Hz to PPM is:

Sample shift (ppm) = ( F(sample in Hz) – F(reference in Hz) ) / F(spectrometer in Hz) * 1,000,000

Sample Shift1 (ppm) = ( 1500.00 Hz – 0.00 Hz ) / 500 Hz = 3.00 ppm

Sample Shift2 (ppm) = ( 3000.00 Hz – 0.00 Hz ) / 500 Hz = 6.00 ppm

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