The paper reports on new determinations at INRIM of the triple point temperature of pure neon isotopes Ne-20 and Ne-22, obtained on samples sealed in cryogenic cells and measured with an uncertainty much lower than that of the previous determinations The experimental technique is the same used at INRIM for recent studies on neon of natural-isotopic composition, showing an expanded uncertainty of approximate to 30 mu K for a single cell and approximate to 50 mu K for the comparison of sample pairs The determinations were mainly intended to obtain a more accurate value of the temperature difference for the two pure isotopes, found to be 0 14660 K with an expanded uncertainty of 0 00007 K The temperature values were found to be 24 5422 K for Ne-20 and 24 6888 K for Ne-22 on ITS-90. but each with a larger expanded uncertainty, 0 00032 K This is mainly caused, contrarily to the difference, by each of these values being affected by the present ambiguity of the ITS-90 definition This definition refers to neon generically to 'natural' composition, while its uncorrected variability heavily affects the uncertainty of the thermometer calibrations. These results for pure isotopes are compared with those recently obtained at INRIM on samples of commercial neon of natural composition and with literature data. The problems involved in the correction for the residual content of isotopic impurities and for chemical impurities are discussed (C) 2010 Elsevier Ltd All rights reserved