Vertical vs Horizontal Furnaces: The Dumas Method for Protein Determination

LECO Organic Consumables collageOver the last thirty years, the Dumas combustion method for analyzing protein content in food has been gaining popularity against the classic Kjeldahl wet chemical digestion and titration method. The Dumas method has several advantages over the Kjeldahl method: it is much faster, with much lower operating costs, no real safety issues, and no toxic waste produced. However, there is a debate over which of the two main approaches to the Dumas method is better: a vertical or a horizontal combustion furnace.

LECO’s FP828 and FP928 nitrogen determinators are both well-suited for rapidly handling the Dumas method. The 828 Series is designed for small-sample (approximately 250-500 mg) use with tin capsules or foils in a vertical combustion furnace, while the 928 Series uses open ceramic boats with macro sample sizes (up to 3 g, depending on system configuration) with a horizontal combustion tube system.

Determined to settle the question on which method is more precise and offers the most advantages, LECO chemists analyzed many sample types in both an FP828 and an FP928. Flours, milk, hot dogs, orange juice, specialty beers, tobacco… a variety of different samples with a wide range of complexity and protein content put the instruments and the test through their paces.

Graph depicting Nitrogen levels in various samples
Nitrogen Levels, as determined by FP928 and FP828 using different containers

Even at low nitrogen levels, the results from both sample introduction approaches were comparable across the instruments. The larger samples in the FP928’s horizontal furnace and open combustion boats had a tighter precision, but there was little difference in the results.

For a more detailed breakdown of the results and a look at more of the samples used in this experiment, read Michael Jakob’s article in the September 2021 issue of eFood-Lab International.