Methods and Techniques - Soils and Sediments - Loss-on-ignition

Ball, D. F. 1964

Loss-On-Ignition as an Estimate of Organic Matter and Organic Carbon in Non-Calcareous Soils. Journal of Soil Science 15(1):84-92.
Ball describes the "usual procedure" for LOI as ignition of an oven-dried sample in a muffle furnace of half an hour at 850°C. He notes that this procedure does not attempt to distinguish what component of the sample is contributing to the weight loss. He indicates that "elemental C" (i.e., contained in coal or charcoal or other carbonized material) is destroyed at ignition temperatures of 375° and 850°C. He cites older work (Keeling 1962) that shows that heating at 375°C for 16 hours removes "carbonaceous material" without loss of structural water from clays. He states that the greatest loss of water from clays occurs in temperature range 450°C to 600°C. He tested low temperate ignition using non-carbonate-rich soils. Concluded that accuracy (as measured against chemical digestion/titration procedures for organic C) was better for the lower temperature ignition (375°C). States that this ignition "must be maintained for a much longer time than the 850°C ignition". However, there are no data presented to justify the 16 hour recommendation.

Beaudoin, A. 2003

A Comparison of Two Methods for Estimating the Organic Content of Sediments. Journal of Paleolimnology 29(3):387-390.
AEU SCI QE 39.5 P3 J86

Bengtsson, L., and M. Enell 1986

Chemical Analysis. In Handbook of Holocene Palaeoecology and Palaeohydrology, edited by B. E. Berglund, pp. 423-451. John Wiley & Sons, Chichester, England, UK.
AEU SCI QE 741 H236 LOI procedure is discussed on pp. 426-428. Oven-dry sample at 105°C for at least 12 hours, 550°C ignition for a minimum of 2 hours, 925°C ignition for minimum of 4 hours. They note that the crucible should be ignited in furnace at 550°C for 1 hour before procedure begins. They also note that in highly organic samples, the crucible may need to have a lid on to prevent loss through ash drifting from crucible. (This would probably limit oxygen to the sample and hence reduce combustion rate). They also note that, if the sample is still black after 2 hours of 550°C ignition, then combustion is incomplete. They recommend igniting for a further 30 minutes, after a chemical treatment of the cool residue with "1 or 2 drops" of 20 g/100 ml w/v NH₄NO₃ (ammonium nitrate) solution. They indicate that the values given by LOI provide an approximation for organic matter in the sample. They also make caveats about calcareous samples.

Dean Jr, W. E. 1974

Determination of Carbonate and Organic Matter in Calcareous Sediments and Sedimentary Rocks by Loss on Ignition: Comparison with Other Methods. Journal of Sedimentary Petrology 44(1):242-248.
AEU SCI QE 420 J86 States that OM begins to break down at 200°C, ignition complete by 550°C. Breakdown of calcium carbonate to release CO₂ by 850°C, though dolomite breaks down at 700 - 750°C. Dean's recommended procedure therefore is: oven-drying sample overnight (so all computations are done on an oven-dry basis - the standard for oven-drying is 105°C). Muffle furnace for 1 hour heated to 500°C (weight difference gives OC). Muffle furnace for 1 hour heated to 1000°C (weight difference gives measure of carbonate minerals). He points out that clay minerals contain interstitial water, and therefore part of the high-temperature weight loss will be due, not to carbonate breakdown, but to loss of water from clays. This can be significant where clays are a large component of the sample (e.g., in many lake sediments).

Heiri, O., A. F. Lotter, and G. Lemcke 2001

Loss on Ignition as a Method for Estimating Organic and Carbonate Content in Sediments: Reproducibility and Comparability of Results. Journal of Paleolimnology 25:101-110.
AEU SCI QE 39.5 P3 J86

Keeling, P. S. 1962

Some Experiments on the Low-Temperature Removal of Carbonaceous Material from Clays. Clay Minerals Bulletin 28:155-158.
Describes experiments to distinguish the weight loss on ignition due to "carbonaceous material" to that from clay minerals. Notes that clay minerals show little breakdown below 400°C. Showed that around 90% of carbon was removed after heating at 375°C. This only applies if the clays are not carbonate-rich. Samples were left in the furnace for 16 hours. However, there is no discussion of why 16 hours was the optimum time, just that the samples were heated overnight.

White, E. M., and L. A. Hannus 1981

Approximate Method for Estimating Soil Charcoal Contents. Communications in Soil Science and Plant Analysis 12(4):363-371.
Describes a method for estimating the charcoal content of "soil" or sediment, especially applicable to archaeological sites where charcoal can be significant component. Point out that it may be difficult to tell is a "soil" layer is black because of soil OM or because of finely-divided charcoal. Treatment with hydrogen peroxide (H₂O₂) is used to remove soil OM. However, peroxide does not remove charcoal. Their method also recommends a pretreatment with 4 N HCl to remove "soluble compounds that might react with" peroxide (presumably this would be carbonates, both primary and secondary), and a post treatment with 48% HF acid to remove silicates. (NB: HF is an extremely hazardous material!) The water-washed residue (on a filter paper) is weighed then ignited in a muffle furnace. Charcoal content is estimated by the weight loss. The paper does not indicate the temperature or length of time of ignition.