Lars Alf Jensen in the group of Associate Prof Frans Mulder at the University of Aarhus, Denmark has made an easy-to-use online tool for tracking impurities in 1H and 13C NMR spectra of small molecules. The tool builds on two very well-known papers [1,2] that tabulate chemical shifts, J-patterns for common impurities that often present themselves in organic and organometallic synthesis chemistry, in a number of solvents. In addition, they have extended that database to include data for a number of common impurities in biochemistry laboratories.
 NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities. Gottlieb HE, Kotlyar V, Nudelman A. J Org Chem. 1997 Oct 17;62(21):7512-7515
 NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist
G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb, A. Nudelman, B. M. Stoltz, J. E. Bercaw, and K. I. Goldberg Organometallics 2010 29 (9), 2176-2179