Honey adulteration particularly by adding cheap sugars such as High Fructose Corn Syrup (HFCS) and cane sugar syrup into natural honey is widespread. This study reports (C-13/C-12,parts per thousand) patterns of 31 authentic honey samples obtained from different sources and regions of Turkey as well as 43 commercial honey samples to determine the adulteration using mass spectrometer coupled to elemental analyzer (EA-IRMS). The analyses indicated that the ranges of (C-13/C-12, parts per thousand) values of honey and protein fractions of Turkish honey are from -23.30 to -27.58 parts per thousand and -24.13 to -26.76 parts per thousand, respectively. These values for commercial honey samples were determined to range from -11.28 to -25.54 parts per thousand and -19.35 to -25.61 parts per thousand, respectively. The numbers of adulterated commercial honey samples were found to be 10, which corresponds to 23% of the total number of the samples. Diastase activity, HMF content, electrical conductivity and moisture content of honey samples were also determined. Method validation and uncertainty budget calculations were also reported. (C) 2011 Elsevier Ltd. All rights reserved.