NMR Spectroscopy
Solution and Solid State
Scientific knowledge is a body of statements of varying degrees of certainty-some most unsure, some nearly sure, but none absolutely certain- Richard Feynman
1D 1H & 2D 1H 1H NMR Analysis
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Sample: 50 mg from the cooked pork bone reference sample and 100 mg of the ding sherd sample
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Soaked in 1 ml solution of CD3OD/CDCl3/D2O (1:1:.9) and extracted for 1 hr in a sonicator and subsequently centrifuged (Tanasi, et al., 2017).
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After centrifugation, the organic lipid layer of each sample (CDCl3 phase) was transferred into a 5 mm NMR tube and analyzed.
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1H NMR spectra were recorded at 300 K with a direct drive Agilent spectrometer operating at a proton frequency of 600.13 MHz. Scans of 256 and 512 were collected for pig bone and pig pottery samples, respectively, with a 1H pulse width of 10 µs and the recycle delay was 2 s.
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Spectra were acquired with a time domain of 32 k data points, were zero filled, and Fourier transformed with 64 k data points.
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Support of pig residue in the ding sherd from H31 was indicated by NMR spectra (see Fig. 4).
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The assignment of the major groups of signals is shown in the spectrum and is summarized in Table 1, highlighting in red the observed proton.
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The assignment of cholesterol (see Table 1 & Fig. 4) was based on the functional fragment’s main methyl groups (C18, C19, C21, C26, and C27) and their characteristic proton chemical shifts. Apart from the methyl group C18 at 0.67 ppm, the cholesterol molecules are not visible in the 1D 1H spectra.
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Many of the assignments were further confirmed by the use of a 2D 1H-1H TOCSY (see Fig. 5) acquired with 2 k and 1 k points in the F2 and F1 dimensions, using 32 scans. Spectra were processed and analyzed using Topspin, NMRPipe and Sparky.
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13C and 31P NMR analyses are also pending for both samples