Determination of crude fiber by acid-base digestion method

Acid-Alkali Digestion Method for Crude Fiber Determination

‌Principle‌

The acid-alkali digestion method is a chemical analysis technique that separates crude fiber components from samples. Its core principle involves using acidic and alkaline digestion to remove soluble substances, with crude fiber content ultimately determined by gravimetric measurement. The measured crude fiber is not a single chemical compound but a composite indicator containing cellulose, hemicellulose, lignin, and other components.

‌Standards Compliance‌

The method primarily adheres to the following national/international standards:

GB/T 5515 Inspection of Grains and Oils: Determination of Crude Fiber

GB/T 6434-2006 Determination of Crude Fiber in Feed

ISO 6865:2000 Animal Feeding Stuffs: Determination of Crude Fiber

‌Operational Procedure‌

‌Sample Pretreatment‌: Grind samples to standardized particle size.

‌Acid Digestion Phase‌:

Boil in 1.25% sulfuric acid solution for 30 minutes.

Removes starch, partial proteins, and minerals.

‌Alkali Digestion Phase‌:

Boil in 1.25% sodium hydroxide solution for 30 minutes.

Dissolves proteins and partial hemicellulose.

‌Filtration Separation‌: Collect residues through specific-pore filter membranes.

‌Rinsing & Drying‌:

Rinse with ethanol to remove residual reagents.

Weigh after constant-weight drying at 105°C.

‌Ashing Correction‌: Incinerate at high temperature to eliminate organics, calculating actual crude fiber content.

‌Key Equipment‌

Crude fiber analyzer (e.g., CXC-06 model)

Ceramic heating digestion apparatus

Electronic balance (precision 0.0001g)

Muffle furnace

‌Technical Parameters‌

Batch capacity: 6 samples per run

Digestion temperature precision: ±1°C

Reagent dosing error: <0.2ml

Repeatability error: RSD ≤3%

‌Precautions‌

‌Environmental Control‌: Operate under constant temperature conditions.

‌Repeated Testing‌: Average ≥3 measurements per sample group.

‌Equipment Maintenance‌: Regularly calibrate sensor accuracy.

‌Safety Measures‌: Use fume hoods when handling organic solvents like petroleum ether.

‌Applications‌

Widely applied in:

Grain, feed, and food testing

Byproduct analysis of agricultural processing

Routine laboratory analysis in research institutions

ST116 Coarse Fiber tester tests raw fiber content according to acid and alkali boiling method.It adopts accurate concentration acid and alkali to boil samples in particular condition, then remove soluble substances by ether, deduct the amount of minerals by high temperature burning.