Comment on: ‘A simple cryogenic method for efficient measurement of triple oxygen isotopes in silicates’ by Ghoshmaulik et al. (Rapid Commun Mass Spectrom. 2020;34(18):e8833)

A response to the comment on ‘A simple cryogenic method for efficient measurement of triple oxygen isotopes in silicates’ by Ghoshmaulik et al. by Martin F. Miller, Ryoji Tanaka and Richard Greenwood

“…We thank them for a detailed and critical evaluation of our work and acknowledge their appreciation. MTG 1 point out that the ẟ 17 O and ẟ 18 O precisions reported by us 2 are similar to those reported by Miller et al 3 20 years ago using a similar technique. However, the precision reported for ∆′ 17 O was only ~24 ppm, 3 whereas the precision obtained in our study is 4 ppm because of a tight coupling of the ẟ 17 O and ẟ 18 O values.…”

“…Notwithstanding the efficacy of this procedure, we agree that using NBS‐28 as an anchor for working standard oxygen calibration might compromise the accuracy of our method. Therefore, we accept the suggestion of MTG 1 to use SCO or UWG‐2 (University of Wisconsin‐Gore Mountain Garnet #2) for calibration. Between the two choices, we would like to use SCO for reasons discussed here.…”

“…The comparison of isotopic ratios of international standards by MTG 1 shows that despite VSMOW (Vienna Standard Mean Ocean Water)‐SLAP (Standard Light Antarctic Precipitation) correction, the laboratories engaged in this research did not achieve consensus on the ∆′ 17 O values. The available ∆′ 17 O values of UWG‐2 show large inter‐laboratory variations.…”

“…Miller, Tanaka and Greenwood (MTG) 1 have critically assessed our article Ghoshmaulik, Bhattacharya, Roy and Sarkar (GBRS) 2 in a recent issue of Rapid Communications in Mass Spectrometry . We thank them for a detailed and critical evaluation of our work and acknowledge their appreciation.…”

“…In our work, 2 we calibrated the ‘working standard’ gas O 2 through NBS‐28 using oxygen isotope ratios reported by Wostbrock et al 8 MTG 1 point out that the NBS‐28 standard is not an optimal choice because its ratios are not well constrained (Miller et al 9 reported an unacceptably large variation in the NBS‐28 values). It is possible that the quartz grains of NBS‐28 are difficult to fluorinate completely by laser heating due to sputtering during burning.…”