IUPAC has published a list of replacement weight ranges for hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium because the standard atomic weights are inappropriate for many applications in analytical science.

Isotope ratios of various elements are used in archaeology, food science, forensics and detection of counterfeit products in a wide range of industries. Citing the weights of these ten elements as an upper and lower limit, is expected to allow scientists to home in on the “origin” of a particular element in a much more straightforward manner.

• Atomic weights of the elements 2009 (IUPAC Technical Report)
  M. E. Wieser, T. B. Coplen,
  Pure Appl. Chem. 2010.
  DOI: 10.1351/PAC-REP-10-09-14