Susmita very able replies have been given my two colleagues,  Jenkins and Ewald. Since you are working on soil samples rich in phyllites , sandstone and quartzite , probably  you need higher temperature for ashing ( somewhere 5000C) . The temperature  limit is largely dependent upon the soil composition . The work of D. Storer (1984) is worth referring with a title  , A simple high sample volume ashing procedure for determination of soil organic matter   published in  Communications in Soil Science and Plant Analysis 15(7) : 759-772.

That is an optimal temperature range. Is there any logical reason why those ranges might be or not be a problem? Temperature is one factor and the time the soil sample will be left under such temperature is yet another factor couple with the soil type, texture, moisture content, and the available soil organic matter. I think the decision is left with you, but whatever you turn out to take, you just need to justify that.

the main criteria for temperature and time is the completeness of ashing. Often oxygen in the initial phase of burning is a limiting factor, you can easy see it when you get dark yellow flames and thick black fumes immediately after ignition. The muffel furnaces used are usually designed to provide reducing conditions for metallurgical experiments and not oxidising for ashing, in so far they are contraproductive for total C determination by ashing. The risk is that under lack of oxygen in the first moments after ignition very heat resistant carbon structures are formed, which can only be combusted at very high temperatures. What to do: leave the door of the muffel furnace ajar until the samples have ignited or at least 30 minutes to provide enough oxygen in the oven chamber, and use smaller amounts of sample material. Also crusing the ash once or twice during the process by means of a steel needle helps. An indicator for a complete ashing is always awhite-grey colour of the ash.

Read this:

Parameters influencing the calcination of plant materials in muffle furnaces and their importance for micronutrient analysis

E. Schnug & S. Haneklaus; Communications in Soil Science and Plant Analysis

Volume 27, Issue 5-8, 1996 ; pages 993-1000;

sorry, forgot it: we do it at 550C in porcelain crucibles!

Thank you very much.

Susmita very able replies have been given my two colleagues,  Jenkins and Ewald. Since you are working on soil samples rich in phyllites , sandstone and quartzite , probably  you need higher temperature for ashing ( somewhere 5000C) . The temperature  limit is largely dependent upon the soil composition . The work of D. Storer (1984) is worth referring with a title  , A simple high sample volume ashing procedure for determination of soil organic matter   published in  Communications in Soil Science and Plant Analysis 15(7) : 759-772.

550 C 

Between 60 and 70 °C

Ms.Maria,the temperature you suggested is for drying plant samples in oven.In the literature, I have come across temperatures ranging from 375 to 550 C.800 C is too high for ignition of organic matter in soils.There may be incomplete oxidation of carbon in some soils at lower  temperatures(360-375 C).This method is not suitable for calcareous soils.One should have knowledge of the amount of carbonates in the soil before choosing this method. Dr.Schnug suggested the temperature of 550 C(which appears to be o.k).He has also given several other suggestions which may help .Even porcelain crucible need to be dried at the same temperature for one hour before cooling in  the desiccator and weighing. The period of keeping in muffle furnace is also important. Probably different workers suggested 8-16 hours(overnight).The sample size 5 g soil passed through 2 mm sieve.

Susmita - por precaução utilize sempre a maior temperatura possível com teu equipamento.

Com solos sobre os materiais assinalados - filitos, arenitos, metarenitos e quartzitos a probabilidade de encontrar  carbonatos é 0%.  . 

420ºC and 4 hours. More information http://gsrpdf.lib.msu.edu/ticpdf.py?file=/1990s/1993/930331.pdf

 Mr.Andres,the literature attached by you is useful.The American Society for Testing and Materials,ASTM prescribes two methods-one for peat materials for fuel purpose at temperature 440 C and another for geotechnical and general classification at 750 C.The first one,the peat, is predominantly organic material and the second one,geotechnical, is probably predominantly inorganic material.For mixed material /matrix like mineral soil,muffle temperature range of 440 to 550 C may be o.k.

To our experience where soil samples derived from dominant rock types like phyllites, sandstone and quartzite , the muffle temperature ranged between 470-540 degree celcus is the best.

We normally run LOI as follows: (1) dry 5-10 g air-dried soil for 2 hours at 105 C in a crucible; (2) weigh to get dry weight; (3) heat at 360 C for 2 hours after temperature reaches 360 C; (4) cool to less than 150 C; and weigh again. See the attached publication that we use for soil testing in the north central US.

Dont you think that everything what Susmita wants and needs to know is already said many times? Such continuous ruminating on a question is very tiredsome amd unproductive dear colleagues! Thats why suggested somewhere else in RG to install a termination switch which ceases endless Q/A tapeworms!

Difficult to answer because it depends from the used devices and the aim of your reserach. For most practical application in soil assessment mass losses between 105 (absolute drying to reduce disturbances from clay) and 550 °C (T behind this limit increase the risk for decay of carbonates) are frequently a good solution. But this holds true for limited aims only.

For example, for soil organic matter detection in soils temperatures behind 550 °C may not useful because you will capture carbonate carbon. If you need to capture all organic and inorganic (carbonate) carbon the final temperature should be much higher than 550 °C and behind 1000 °C plus a oxygen athmosphere.

May be, following papers could be helpful for you:

Ghabbour EA, Davies G, Cuozzo NP, Miller RO. Optimized

conditions for determination of total soil organic matter in diverse

samples by mass loss on ignition. J Plant Nutr Soil Sci. 2014;

177(6):914–9

Hoogsteen MJJ, Latinga EA, Bakker EJ, Groot JCJ, Tittonell PA.

Estimating soil organic carbon trough loss on ignition: effects of

ignition conditions and structural water loss. Eur J Soil Sci.

2015;66:320–8.

Pribyl WD. A critical review of the conventional SOC to SOM

conversion factor. Geoderma. 2010;156:75–83

I recommend this publication:

"Optimizing the weight loss-on-ignition

methodology to quantify organic and carbonate

carbon of sediments from diverse sources"  by Wang and others

Environ Monit Assess (2011) 174:241–257

DOI 10.1007/s10661-010-1454-z

It gives both times and temperatures and points out risks.

I work mainly on salt marsh sediments and go with 550 for 2.5h.

Let me know nif you cannot find a copy..

Dear colleagues we have sufficiently discussed the topic and gathered sufficient ,pertinent and useful information.