Comparison between THE oven and THE Karl Fischer methodS for THE determination of the moisture content of maize (Zea mays L.) and soya (Glycine max (L) Merrill) seeds

Abstract

The objective of the present paper was to compare the seed water content of maize and soya, obtained by the oven method at different temperatures and the Karl Fischer method. The water contents used were 11.2 %, 12.8 % and 16.2 % for maize and 10.7 %, 12.4 % and 16.0 % for soya. Samples were dried for a sufficiently long time in order to obtain the same results in both methods. The results indicate that the official method for seed moisture determination (105oC oven method) should be revised in order to obtain more reliable results. The drying time in the oven varied according to the seed water content and the temperature used.<br>O objetivo da pesquisa foi comparar os teores de água de sementes de milho e de soja obtidos pelos métodos da estufa e de Karl Fischer. Os teores de água utilizados foram 11,2% 12,8% e 16,2% para sementes de milho e 10,7%, 12,4% e 16,0% para sementes de soja. Para as determinações dos teores de água nas sementes foi utilizado o método da estufa com diferentes temperaturas, sendo as amostras secadas por um período suficiente para obter os mesmos resultados obtidos pelo método de Karl Fischer. Os resultados indicaram que o método oficial para a determinação do teor de água em sementes (método da estufa, a 105oC) precisa ser revisado para a obtenção de resultados com maior precisão. O tempo de permanência das sementes na estufa, para a determinação da umidade, varia conforme o teor de água das sementes e da temperatura utilizada

Restrictions to use oven in determining water content for Brazil nuts

“…Based on the results for water content in samples submitted to oven at 105°C for 24 hours, in comparison to those obtained submitting the samples to Karl Fisher titration, there is statistical differences between the methods, being the contents obtained by oven higher (p< 0,05) than those obtained by titration, that was the reference method (Table 1). Tillman;Cicero, (1996) comparing water contents for maize and soybeans using oven at 105°C with the contents determined by Karl Fisher titration, cites that to water contents higher than 16%, for both products, the oven method overestimates its parameter. Hart et al (1959) mentions that products with high oil content may present oxidation on its lipid portion during the heating of product into an oven, and it may be a source of error to this method.…”

“…Using a Karl Fisher titrator, a solution containing the samples is titrated and the reagent amount is related to water content in the product (INSTITUTO ADOLFO LUTZ, 2008). Considering that it is a chemical method based on the amount of water in the samples, it may be used as a reference method to calibrate or verify the accuracy of other methods (TILLMAN;CICERO, 1996;HART et al 1959).…”