AUTOMATING LOSS-ON-IGNITION MEASUREMENTS FOR SEDIMENT CORES

MAHER, Louis J., Jr., Department of Geology and Geophysics, University of Wisconsin,

1215 W. Dayton St., Madison, WI 53706, maher@geology.wisc.edu

Loss-on-ignition (LOI) is used to estimate sediment moisture, organic matter, organic carbon, and carbonate content. Down-core changes in these properties complement environmental information from pollen and other microfossils. Although there are better techniques for determining some of these quantities, none does all as quickly and cheaply as LOI. One needs only a drying oven, a muffle furnace, a sensitive balance, and a tolerance for tedious work. With access to an electronic balance connected to an IBM (or clone) computer a lot of the drudgery can be avoided.

Most sediment is a mixture of clastic silicates and oxides, organic material, various carbonates, and water. If a sample is heated to 100°C in an oven, the weight loss measures its water content. The sample's dry weight is a useful base to which ignition losses are compared. Organic matter is consumed when the sample is heated to 550°C. If the ash is then heated to 1000°C further weight loss occurs as carbonates liberate CO₂ and clays yield water from their lattice structure. Although the absolute values of LOI data are subject to several uncertainties, the relative down-core changes are very useful in interpreting sedimentary sequences. The tedium of doing a LOI analysis lies in the repetitious weighing of each sample, reading and recording the data, and computing the final results.

A computer program called LOI-EZ is available either as a stand-alone DOS program or as BASIC source code that can be run with MicroSoft QuickBasic--or QBasic that comes with DOS 5 and 6. Different versions run on various models of Mettler Toledo and Fisher/Denver balances, and the source code allows you to tailor the program for your own needs or adapt it to other balances. DOS programs are small and fast, and they run on the oldest PC. LOI-EZZ.EXE is available as a self-unzipping package from http:/www.geology.wisc.edu/~maher/inqua.html.

LOI-EZ records the sample and crucible ID numbers and weights in a *.001 file. All recorded weights are the mean of ten stable measurements. After oven-drying the program requests each crucible by its ID number and records the dry weight data in a *.002 file. New *.003 and *.004 files are made after LOI. LOI-EZ uses these files to calculate the results, saving them either as a *.SUM file (derived data) or as a *.TOT file (both raw and derived data for archive purposes).