I have a plant sample to which I want to find organic carbon percentage. The literature says that Wakley blank method is a good option whereas analysis through TOC analyser is also an option. which method should I go for?
Use TOC methods from Beckmann.
Total Organic Carbon (TOC) Analyzers (beckman.com).
If we assume that all carbon in the plant is in organic form, carbon measurement with a TC analyzer is an option. In our laboratory, we use TC and TIC analyzers from ELTRA.
* Determination of organic carbon in soil and plant material
- July 2006 by K. SHAW
- European Journal of Soil Science 10(2):316 - 326
Summary
A wet-oxidation technique for determining organic carbon in soil, plant material, and aqueous plant extracts is described. The oxidation is carried out by heating the soil or plant sample (containing 50–100 mg. carbon) with a mixture of potassium dichromate, sulphuric, and phosphoric acids for 10–15 min., and the carbon dioxide liberated is determined gravimetrically after absorption in soda-lime. With slight modifications, the method has proved useful for the determination of carbon in plant extracts and would also appear suitable for a soil extract. A method is described for the removal of carbonates without loss of organic carbon. It is shown that heating a wet soil at 105° C. causes considerable loss of organic carbon. Inert carbonaceous material, such as coal or charcoal, is oxidized by this wet-digestion method, thus producing erroneously high results for the carbon content of soil organic matter.The method is at least as accurate as the conventional dry- combustion technique, and is less time-consuming, only one hour being required for a determination. The apparatus is of simple design and with the exception of the needle valve can be readily constructed from normal laboratory glassware. The method can deal with fairly large samples of materials, thus preserving an essential feature of established macro-methods.This technique of determining carbon is convenient for the fairly rapid analysis of soils and plant materials where an accurate total-carbon value is required.
* Comparison of three carbon determination methods on naturally occurring substrates and the implication for the quantification of ‘soil carbon’
M. K. Conyers et al....
Soil Research 49(1) 27-33 https://doi.org/10.1071/SR10103 Submitted: 14 May 2010 Accepted: 17 August 2010
Accounting for carbon (C) in soil will require a degree of precision sufficient to permit an assessment of any trend through time. Soil can contain many chemically and physically diverse forms of organic and inorganic carbon, some of which might not meet certain definitions of ‘soil carbon’. In an attempt to assess how measurements of these diverse forms of C might vary with analytical method, we measured the C concentration of 26 substrates by three methods commonly used for soil C (Walkley–Black, Heanes, and Leco). The Heanes and Leco methods were essentially equivalent in their capture of organic C, but the Leco method captured almost all of the inorganic C (carbonates, graphite). The Heanes and Walkley–Black methods did not measure carbonates but did measure 92% and 9%, respectively, of the C in graphite. All three of the common soil test procedures measured some proportion of the charcoal and of the other burnt materials. The proportion of common organic substrates (not the carbonates, graphite, or soil) that was C by weight ranged from ~10% to 90% based on the Heanes and Leco data. The proportion of the organic fraction of those same substrates, as measured by loss-on-ignition, that was C by weight ranged from 42% to 100%. The relationship between Walkley–Black C and total C (by Heanes and Leco) showed that Walkley–Black C was a variable proportion of total C for the 26 substrates. Finally, the well-known, apparent artefact in the Cr-acid methods was investigated: dichromate digestion should contain at least 7–10 mg C in the sample or over-recovery of C might be reported. Our observation that common soil C procedures readily measure C in plant roots and shoots, and in burnt stubble, means that there will likely be intra-annual variation in soil C, because avoidance of these fresh residues is difficult. Such apparent intra-annual variation in soil C will make the detection of long-term trends problematic.
You can choose either of the two.
if TOC analyser is available you can opt for that.
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