Determination of Crude Fiber – Filtration Method

1. Principle

The sample after defatting is sequentially treated with boiling dilute sulphuric acid, and with boiling potassium hydroxide solution. The loss in mass resulting from incineration corresponds to the mass of crude fiber.

2. Scope

The method described is applicable for determination of feeds with a crude fiber content

Higher than 1%. If sample contains >10% fat, extract fat with petroleum ether prior to

Beginning analysis.

3. Responsibilities

Laboratory Analysts shall perform the analysis as per this method. It is the responsibility of the Laboratory Analyst to ensure that all conditions laid down in the method are met and strictly adhered to. Any deviations from the prescribed method shall be recorded and supervisor notified.

4. Equipment

4.1 Analytical balance, accurate to 0.1 mg.

4.2 Glass filter crucibles, P100.

4.3 Heating apparatus.

4.4 Filtration equipment, connected to a vacuum system, for example a Fiber system.

4.5 Desiccator.

4.6 Drying oven ventilated, capable of being maintained at a temperature of 103 ± 2 °C.

4.7 Muffle furnace, capable of being maintained at a temperature of 550 ± 20 °C.

5. Reagents

5.1 Petroleum ether (boiling point 40 to 60 ˚C).

5.2 Sulphuric acid, 0.15 M.

5.3 Acetone technical quality.

5.4 Potassium hydroxide, 0.23 M.

6. Procedure

6.1 Pretreatment

6.1.1 To each P100-crucible (4.2) weigh 1 g of the sample to the nearest 0.1 mg (W1).

6.1.2 Place the crucibles in the filtration equipment (4.4) and add approximately 30ml of petroleum ether (5.1) to each crucible and filter using vacuum.

6.1.3 Repeat the washing two times.

6.1.4 Dry the residue in air and transfer quantitatively to a beaker.

6.2 Digestion

6.2.1 Add to each beaker 150 ml sulphuric acid (5.3) and boil for 30 ± 1 minutes. If foaming occurs, add a few drops of anti-foaming agent.

6.2.2 Filter the mixture through a crucible (4.2) using vacuum (4.4).

6.2.3 Wash the residue 5 times, each time with 10 ml of hot distilled water.

6.2.4 Add a volume of acetone (5.4) to just cover the residue. Remove the acetone after a few minutes by applying slight suction.

6.2.5 Transfer the residue quantitatively to a beaker.

6.2.6 Add to each beaker 150 ml potassium hydroxide (5.1.8) and boil for 30 ± 1minute.

6.2.7 Filter the mixture through a crucible (4.2) using vacuum (4.4).

6.2.8 Wash the residue with hot distilled water until the rinsing’s are neutral

6.2.9 Wash the residue 3 times under vacuum, each time with 30 ml of acetone (5.4).

Dry the residue by suction after each washing.

6.3 Drying and incineration

6.3.1 Put the crucibles in an oven (4.6) adjusted to 103 ± 2 °C and dry for 4.0 hours.

The drying time starts when the oven has reached 103 °C.

6.3.2 Place the crucibles in a desiccator and allow to cool.

6.3.3 Weigh the crucible directly after removing from the desiccator (4.5) to the nearest

0.1 mg (W2).

6.3.4 Place the crucibles in a muffle furnace (4.7), and incinerate the samples for

2 hours at 550 ± 20 °C. The incineration time starts when the furnace has

reached 550 °C.

6.3.5 Place the crucibles in a desiccator (4.5) and allow to cool.

6.3.6 Weigh the crucible directly after removing from the desiccator to the nearest

0.1 mg (W3).

7. Calculation

Percent Crude fiber (% CF):

% CF = (W2 – W3) x 100 / W1

where,

W1 = weight of the sample (g),

W2 = weight crucible and residue after drying (g), and

W3 = weight crucible and residue aft