A METHOD FOR THE IDENTIFICATION AND ELIMINATION OF CONTAMINATION DURING CARBON ISOTOPIC ANALYSES OF EXTRATERRESTRIAL SAMPLES

• Published in: Meteoritics
• Main Authors: Swart, P.K., Grady, M.M., Pillinger, C.T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1983
• Subjects: General Earth and Planetary Sciences; General Environmental Science; Antarc*; Antarctic
• Online Access: http://dx.doi.org/10.1111/j.1945-5100.1983.tb00584.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1945-5100.1983.tb00584.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1945-5100.1983.tb00584.x

The study of carbon abundance and isotopic composition in extraterrestrial samples is fraught with problems related to contamination in the terrestrial environment and during sample handling. A stepped combustion method is described which demonstrates that progress can be made towards resolving the indigenous species from contamination which for the most part burns at low temperature (< 425 ± 25 ±C). The proposed method is not applicable to samples which have indigenous phases burning at low temperatures e.g. the C1 and C2 carbonaceous chondrites. A number of examples where its application is possible are given. Even meteorites collected immediately after their fall, such as Allende, contain a proportion of extraneous carbon which has deleterious effects on any bulk estimate of isotopic composition. “Falls” which have spent a considerable time in museum collections and “finds” (other than Antarctic samples) can be considered as grossly contaminated. Bulk isotope and carbon abundance measurements in the literature for most samples having less than 1 wt% C are thus of questionable value. Antarctic samples have much less contamination of an organic nature but all seem to contain a weathering component which can be easily recognised and hence disregarded in estimates of bulk composition. Stepped combustion, applied to an Apollo 11 lunar soil which has not been specially stored and which now contains, due to contamination, nearly twice as much carbon as when originally collected, can still afford data closely resembling those obtained from the sample when it was first returned to Earth.