Honey has variable moisture (10-20)% and this can be determined using a
high-solids refractometer. Another useful measure is enzyme(diastase)
activity which will tell you if heating has broken down some of the sugar
and therefore changed the composition.
The sugar d18O in unaltered honey will closely mimic the d18O in plant
nectar, which is the same as the d18O in the C3 or C4 cycle. This value is
rarely affected by the prevalent water supply, except in deeply depleted
areas (like the Pacific coast).
The Journal of the AOAC has published a few good stable-isotope
investigations on honey focussed on detecting adulteration with sugar,
between about 1990 and 2002. Their website will link you to the journal
search engine: www.aoac.org and I wish you luck.
University of Toronto