Comparisons of Karl Fischer Method with Oven Methods for Determination of Water in Forages and Animal Feeds

Abstract

In a comparative study of the Karl Fischer method with oven methods for determination of water in forages and animal feeds, oven methods yielded the following relative recoveries (expressed as a percentage of the recovery obtained by the Karl Fischer method) for hay, haylage, and corn silage, respectively: (1) drying at 135°C for 2 h (AOAC 930.15), 113,162, and 133%; (2) drying at 104°C for 3 h (AOAC 935.29), 96,122, and 113%; and (3) drying at 104°C for 6 h, 97, 129, and 117%. Relative recoveries for nonurea-containing and urea-containing feed, respectively, were as fol lows: (1) drying at 135°C for 2 h (AOAC 930.15), 116 and 2746% (2) drying at 104°C for 3 h (AOAC 935.29), 88 and 239%; (3) drying at 95°C for 5 h under vacuum (AOAC 934.01), 83 and 727% (4) drying at 104°C for 6 h, 90 and 427%; and (5) drying at 110°C for 3 h, 94 and 425%. Preliminary near-infrared reflectance calibrations for water (moisture) based on the Karl Fischer method were promising (r2 = 0.98; standard error of calibration = 0.20).

Challenges in measuring moisture content of feeds

“…During oven drying, volatile substances other than water are lost and side chemical reactions occur during the heating process. Windham et al (1987) and Thiex and Van Erem (1999) reinforced Mo and Tjornhom's findings, suggesting no progress on improvement of moisture testing over two or more decades. Even though oven methods are prone to error, they remain commonly used because the determinations are fast and inexpensive to perform.…”

“…Since the instrument is programmable, the laboratory may have used either the 104°C or 135°C temperature; however, the data suggest that only the 104°C data are being reported. (1987) and the second was that of Thiex and Van Erem (1999).…”

“…The forages evaluated by Thiex and Van Erem (1999) included hay, haylage, and corn silage. Hay materials included four each of grass hay, legume hay, and legume-grass mix.…”

“…Six feeds containing urea and ten feeds containing no urea were compared by Thiex and Van Erem (1999). The feed materials were ground to pass a 1mm sieve in a Retsch centrifugal mill, except for the soybeans and cat food, which were ground using a Tecator Knifetec mill.…”

“…All four samples had been analyzed by oven method P. Windham et al (1987Windham et al ( , 1991 had established NIR as a valid technique for moisture determination in forages. The potential for extending an NIR method for moisture in forages to determine moisture in feeds was reported by Thiex and Van Erem (1999). Evaluation was based on a standard error of calibration (SEC), correlation coefficient, and partial least squares calibration.…”