New filtration equipment was developed to improve the acid-detergent method of fiber fractionation. This apparatus incorporates a vacuum manifold with an air metering device that provides the operator very precise control over the partial vacuum, permitting a very gradual change in vacuum level as needed for proper filtration. The partial pressure is provided by a water aspirator. A hot water jacket permits a continuous flow of hot water around the sample during the filtering process to keep the sample hot. This speeds filtering on practically all samples and is essential for reliable results on samples high in carbohydrates and salts. As a result of this new filtration equipment we do not need asbestos for a filter aid. This eliminates the need for duplicate acid-detergent fiber analyses when using 72% H2SO4 for the cellulose and lignin determinations. Six independent analyses were performed on each of 9 samples (3 feces, 3 orts, and 3 feeds) for the determination of acid-detergent fiber and its constituents. The average maximum differences for these analyses indicate that this filtration apparatus and the method are reproducible and have reduced the filtration time from several hours, on some samples, to 15 min.
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David O Holst (1973) studied this question.