Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation methods
Brodie, Chris R., Leng, Melanie J., Casford, James S.L., Kendrick, Christopher P., Lloyd, Jeremy M., Yongqiang, Zong, and Bird, Michael I. (2011) Evidence for bias in C and N concentrations and δ13C composition of terrestrial and aquatic organic materials due to pre-analysis acid preparation methods. Chemical Geology, 282 (3-4). pp. 67-83.
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This study is the first systematic comparison of the effect of acid treatment methods on the reliability of organic carbon [C] and nitrogen [N], and carbon isotope (δ13C) values on a range of terrestrial and aquatic, modern and geological environmental materials. We investigated the 3 most common methods; (i) acidification followed by sequential deionised water rinses ("rinse method"); (ii) acidification in silver capsules ("capsule method"); and (iii) acidification by exposure to an acid vapour ("fumigation method"). We also investigated the effect of sample size and capsule type (silver and tin) on C/N ratio and δ13C values. We find (i) that %C, %N, C/N and δ13C showed significant within and between method variability; (ii) disproportionate and non-linear offsets of %C, %N and C/N values after acidification within and between methods and within and between sample materials; (iii) that alterations in %C did not necessarily manifest themselves in shifts in δ13C, and vice-versa; (iv) that small (~ 90 μg C) sample sizes showed consistent overestimations and inaccuracies after acidification; (v) that the effect of capsule type was not significant on most samples, but did show a notable effect on our aquatic materials, generally increasing %C and %N, and producing depleted δ13C values. These findings raise cause for concern on the interpretative nature of C/N ratios and their support for carbon isotope values. The comparability between laboratories (different preparation methods) and environmental settings (amount, type and nature of OM) is also likely to be problematic. We conclude that the response of C and N concentrations in organic matter to acid treatment in environmental materials is neither negligible nor systematic.
|Item Type:||Article (Refereed Research - C1)|
|FoR Codes:||04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 100%|
|SEO Codes:||97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%|
|Deposited On:||26 Mar 2012 17:15|
|Last Modified:||17 May 2013 01:47|
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