↑ R. M. Silverstein, G. C. Bassler and T. C. Morrill, Spectrometric Identification of Organic Compounds, 5th Ed., Wiley, 1991. ↑ The Theory of NMR - Chemical Shift ↑ US patent 4110681, Donald C. Hofer; Vincent N. Kahwaty; Carl R. Kahwaty, "NMR field frequency lock system", issued 1978-08-29 ↑ Balci, M., in "Basic 1H- and 13C-NMR Spectroscopy" (1st Edition, Elsevier), ISBN 978-0444518118. ↑ Gottlieb HE; Kotlyar V; Nudelman A (October 1997).