Abstract
Mass loss at specified temperatures has been used widely to determine amounts of organic matter and carbonate in sediment samples. The loss on ignition (LOI) method is cheap and simple, but is time-consuming and provides information only for specific, pre-determined temperatures. It also requires relatively large sample sizes and is destructive. Thermogravimetric analysis (TGA) is an alternative method for determination of organic and carbonate content in sediment samples, and provides accurate and precise data in a time-efficient manner. We compared results from these two thermal analysis techniques, which were applied to sediment samples from a submerged landscape (Doggerland). An organic-rich peat sample and a silty fine-sand sample were used. An unpaired t-test was used to test agreement and repeatability of the two analytical techniques. One advantage of being able to monitor mass loss throughout the analytical operation is that free and bound moisture losses can be distinguished. TGA is less time-consuming, involves automated sample handling (minimising operator error), and can yield reliable data from sample masses (typically 30–50 mg), which are much smaller than those needed for LOI (typically 3–5 g). The unpaired t-test, along with precision and repeatability analyses led us to conclude that TGA can be used instead of LOI to provide reliable measures of organic matter and carbonate content in sediments, and has several advantages over LOI.
Highlights
Loss on ignition (LOI)Heating of samples to specified temperatures has been used widely to measure organic matter and carbonate content in sediment, soil and coal fly ash samples (Bengtsson and Enell 1986; Heiri et al 2001; Santisteban et al 2004)
The standard LOI method presented by Konare et al (2010) used three different temperatures under an air atmosphere: (1) the sample was first heated to 150 °C during which mass loss was attributed to water, (2) the temperature was raised to 550 °C which combusts organic matter in the sample, yielding ash and carbon dioxide, and (3) the sample was heated to 950 °C, the temperature at which carbonates were decomposed to produce carbon dioxide
LOI and Thermogravimetric analysis (TGA) results for core ELF002 and ELF009 sediments are shown in Tables 2 and 3, respectively
Summary
Heating of samples to specified temperatures has been used widely to measure organic matter and carbonate content in sediment, soil and coal fly ash samples (Bengtsson and Enell 1986; Heiri et al 2001; Santisteban et al 2004). Weight losses during each heating stage can be used to calculate the amount of moisture, organic matter and carbonate in the sample (Ben-Dor and Banin 1989; Santisteban et al 2004; Heiri et al 2001; Virkanen et al 1997). There are, some drawbacks to the approach, such as the large sample size required, typically 3–5 g. This may consume a substantial proportion of the sample and has the associated disadvantage of requiring more time for mass loss to occur. Other considerations associated with the LOI approach include furnace type, position of samples in the furnace, exposure time at temperature, and the potential for operator error during the weighing process (Heiri et al 2001; Fan and Brown 2001)
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