From: PO3::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 01:56:53.03 To: sweets@ucs.indiana.edu CC: Subj: LOI I would like to know how other listmembers feel about the Loss-on- ignition (LOI) assay for measuring the organic content of lake sediments. In LOI, sediment samples are precisely weighed, dried at 100 degrees C to drive off all free water, reweighed, and then baked at 500 C and reweighed again. The assumption is that any weight loss resulting from the 500 C sessions represent ignition of all organic compounds in the sample. However a ceramic analyst from our Archeology Dept. tells me that some clays (especially kaolinite) will lose structural water at temperatures as low as 450 degrees C. This could result in an artificially high LOI reading. What do you think? Is LOI accurate? Does one need to identify which clays are present before conducting an LOI? Is there a more reliable test for organic percentage in sediments that is as easy and inexpensive as LOI? Jim Hasbargen Laboratory of Paleoecology Northern Arizona University From: PO3::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 04:28:14.08 To: sweets@ucs.indiana.edu CC: Subj: Re: Loss-On-Ignition Jim Hasbargen Wrote >I would like to know how other listmembers feel about the Loss-on- >ignition (LOI) assay for measuring the organic content of lake sediments. >In LOI, sediment samples are precisely weighed, dried at 100 degrees C >to drive off all free water, reweighed, and then baked at 500 C and >reweighed again. The assumption is that any weight loss resulting from >the 500 C sessions represent ignition of all organic compounds in the >sample. However a ceramic analyst from our Archeology Dept. tells me >that some clays (especially kaolinite) will lose structural water at >temperatures as low as 450 degrees C. This could result in an artificially >high LOI reading. >What do you think? Is LOI accurate? Does one need to identify which clays >are present before conducting an LOI? Is there a more reliable test for >organic percentage in sediments that is as easy and inexpensive as LOI? This true that some kaolinite lose structural water at 'low' temperatures but a lot of hydrated, hydroxyde and sulfurs minerals do the same. By instance : goethite (Fe2O3,H2O),Diaspore (AL2O3,H2O) gypsum (CaSO4,2H2O), gibbsite Al(OH)3, FeS,... Those minerals often occur in lake sediments. Conclusion : LOI is probably not a good way to measure organic content in lake sediments. A cheap but long method (chemical titration) exists to make those measurements. (For instance WALKLEY AND BLACK (1934) Journal of Soil Sciences, 37:29-38.) Pierre FRANCUS Universite catholique de Louvain Institut de Geologie - Unite PAGE Place L. Pasteur, 3 B-1348 Louvain-la-Neuve Belgium tel: 32.10/47.28.42 fax: 32.10/47.25.56 e-mail : francus@page.ucl.ac.be From: PO3::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 06:19:06.90 To: sweets@ucs.indiana.edu CC: Subj: Re: LOI LOI overestimates organic carbon by about 100% compared to chromic acid oxidation (Schollenberger wet oxidation) for sediments, primarily silts and clays, we have processed from cutoff meanders. Our chemist puts the difference down to water held in the clays, as you indicated. Cheers, Ralph Ogden Archaeology and Natural History, RSPAS Australian National University From: PO2::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 06:38:10.07 To: sweets@ucs.indiana.edu CC: Subj: P.S. Re: LOI Oops---should have mentioned that the organic content of the cutoff meander seds ranges around 4-8% dry weight. Ralph Ogden Australian National University From: PO3::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 04:28:14.08 To: sweets@ucs.indiana.edu CC: Subj: Re: Loss-On-Ignition Jim Hasbargen Wrote >I would like to know how other listmembers feel about the Loss-on- >ignition (LOI) assay for measuring the organic content of lake sediments. >In LOI, sediment samples are precisely weighed, dried at 100 degrees C >to drive off all free water, reweighed, and then baked at 500 C and >reweighed again. The assumption is that any weight loss resulting from >the 500 C sessions represent ignition of all organic compounds in the >sample. However a ceramic analyst from our Archeology Dept. tells me >that some clays (especially kaolinite) will lose structural water at >temperatures as low as 450 degrees C. This could result in an artificially >high LOI reading. >What do you think? Is LOI accurate? Does one need to identify which clays >are present before conducting an LOI? Is there a more reliable test for >organic percentage in sediments that is as easy and inexpensive as LOI? This true that some kaolinite lose structural water at 'low' temperatures but a lot of hydrated, hydroxyde and sulfurs minerals do the same. By instance : goethite (Fe2O3,H2O),Diaspore (AL2O3,H2O) gypsum (CaSO4,2H2O), gibbsite Al(OH)3, FeS,... Those minerals often occur in lake sediments. Conclusion : LOI is probably not a good way to measure organic content in lake sediments. A cheap but long method (chemical titration) exists to make those measurements. (For instance WALKLEY AND BLACK (1934) Journal of Soil Sciences, 37:29-38.) Pierre FRANCUS Universite catholique de Louvain Institut de Geologie - Unite PAGE Place L. Pasteur, 3 B-1348 Louvain-la-Neuve Belgium tel: 32.10/47.28.42 fax: 32.10/47.25.56 e-mail : francus@page.ucl.ac.be From: PO2::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 13:13:31.08 To: sweets@ucs.indiana.edu CC: Subj: Re: LOI Dean, 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: 242-248. This paper suggests a small overestimate may occur in some particularly clay-rich sediments; nevertheless, LOI is still the cheapest method around. | Ian D. Campbell o8o | | Canadian Forest Service 8Oo8oOoO | | 5320-122 St. Edmonton, AB ^ oO8O88o8o8 | | Canada T6H 3S5 ^^^ o8Oo8ooOooO ^ | | Tel: +1-403-435-7300 Fax: +1-403-435-7359 ^^^^^ 88oo8O88 ^^^ | | e-mail: icampbell@nofc.forestry.ca ^^^|^^^ || | | From: PO2::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 13:42:22.53 To: sweets@ucs.indiana.edu CC: Subj: Re: LOI In low-carbonate lake and bog sediments, LOI and nitric acid digestion techniques produce curves over the whole range of organic contents (1-90+%s) that are almost indistinguishable. The "almost" is usually due to the amount of charcoal in the sediment that is not oxidized by the nitric acid, but is burned during LOI. I think LOI is a good quick lab measure of organic carbon - we measured the range of values in 10 replicates of +/- 3%, with a standard deviation of +/- 0.99% and a standard error of +/- 0.31%. You do have to desiccate samples while they are cooling after drying and after burning, before weighing. Weighing should be done only when cool. Handling of crucibles should be done by calipers, not by fingers, and the crucibles should be cleaned, dried in a drying oven overnight, and desiccated before weighing at the beginning of the procedure before the sample is put into them. Marge Winkler Center for Climatic Research Univ. of Wisconsin-Madison (608) 262-0775 mwinkler@macc.wisc.edu From: PO2::"quaternary@morgan.ucs.mun.ca" 6-FEB-1995 16:45:07.37 To: sweets@ucs.indiana.edu CC: Subj: Re: LOI (1) I should think that it would be easy to take some pure, wet kaolinite and run it through the LOI procedure to see just how much H2O it does lose -- say x proportion (or x*100 percent) (2) After running LOI analyses on sediments, take the estimated inorganic content and multiply it by x -- to get at least a rough idea of how much in error your estimated of organic content could be. If H2) loss from kaolinite is really the major cause of LOI organic content error, then this method should give a conservative measure (i.e., overestimate) of the error in the organic content (because it would be unlikely that ALL of the inorganic material in the sediment would have the same capability as kaolinite to bind water). (3) Consider this "possible error value" as more or less the "detection limit" of organic matter via the LOI method, and do not over-interpret values that are close to this level (or below, obviously). Surely step (1) above must have been done by *someone*, hasn't it? Jim Almendinger USGS--WRD Mounds View, MN From: PO2::"quaternary@morgan.ucs.mun.ca" 9-FEB-1995 13:42:53.56 To: sweets@ucs.indiana.edu CC: Subj: Re: LOI The quick answer is, no, there probably isn't a cheap alternative to LOI unless you have a lab that provides free labor and materials. LOI has been accused of driving off the water in some clays at 550C, but it will be a small variation compared to organic ashing, unless you have very inorganic samples and are looking for a signal in minor changes in LOI. I have looked at late-glacial lakes that have considerable inorganic material and find that the LOI curve matches the % water curve (based on wet weight/dry weight differences). I have also burned material at 900C to ash the carbonates, and see little subsequent change in the LOI signal at core levels where I expect higher clay amounts. Marine-based samples may be very different, because the clay composition is variable compared to lake cores and the clay fraction is large compared to organic content. Soory I don't have any references to provide just now - but I'm sure a lot of comparative studies have been done on this. You might start by looking at the Berglund Handbook of Holocene Paleoecology and Paleohydrology. I'd be interested in hearing more about this. Lisa From: PO2::"quaternary@morgan.ucs.mun.ca" 24-MAR-1995 19:34:32.73 To: sweets@ucs.indiana.edu CC: Subj: Comments on LOI of sediment Apparently from the February comment some people have not appreciated Walter Dean's 1974 paper in the Journal of Sedimentary Petrology 44:242-248. His empirically-derived conversion of Organic Matter (measured at LOI 550) to organic C is by dividing the OM by 2.13. This value comes from regression of LOI values with wet combustion values. The basis for this 2.13 divisor lies in the composition of organic matter which has the general formula of CH2O; thus CH2O plus O2 plus heat yields CO2 plus H2O. To convert OM to organic C, the H2O must be factored out by dividing by 2.5, the proportion of the atomic weight of CH2O to C. What accounts for the difference between the empirical 2.13 and the calculated 2.5? It is that organic matter contains elements other than C, H, and O, such as P, K, I, N, S, Ca, Mg, Fe, Si, Al, etc., which constitute the residual ash. Structural water is probably insignificant, but this assertion deserves the Jim Almendinger kaolinite test. Dean also produced a factor for the percent CaCO3 from the weight lost between 550 and 1000 C, namely 0.44 as calculated from atomic weight of the reaction: CaCO3 plus O2 plus heat yields CaO plus CO2. We compute percent OM, percent CaCO3, and percent 'Silicates' from our sediment cores. I suspect the 'Silicates' are largely the more common crustal elements Si, Al, and Fe. We have replaced our analog (dials) furnace with a digital furnace which is more precise and efficient. Ramping and weighing at successively higher increments of 50 degrees shows that OM is done at 450 and CaCO3 is done at 850 (higher temperatures for longer times are a waste of energy and time). For sediment samples of 1 cc, drying at 100 is over in 1 hour and the hotter reactions are over in 30 minutes. Using a desiccator and tongs is a waste of time unless you require high precision. We have a problem explaining values over 500 C for some sediment which result in a weight gain; perhaps pyrite is involved. Finally, can someone tell me of 'off the shelf' racking for crucibles in the furnace? J. McAndrews docjock@utcc.utoronto.ca From: PO3::"quaternary@morgan.ucs.mun.ca" 27-MAR-1995 15:23:25.58 To: sweets@ucs.indiana.edu CC: Subj: Re: Comments on LOI of sediment I thought I might add one more comment regarding LOI analysis. Carbonates are not appreciably lost (calcined) at temperature of about 500 or 550 C, but they begin to be lost at temperatures well below 900 C. So -- when determining organic matter by LOI, make sure that your temperature gauge is accurate, and that temperatures do not exceed 550 C, or else you may be losing carbonates and thus overpredicting organic content. Guess how I found this out... (our gauge was reading about 100 C too cool). Jim Almendinger ALMENDIN@maildmnspl.cr.usgs.gov U.S. Geological Survey, WRD JDINGER@vz.cis.umn.edu 2280 Woodale Dr. 612-738-3253/fax 612-783-3103 Mounds View, MN 55112 ********************* This message is being posted to obtain or provide technical information relating to my duties at the U.S. Geological Survey.