Principle of Polyacrylamide Purity Test by Ignition Method

Polyacrylamide purity is a core concern for customers, as it directly affects product pricing, chemical dosage and actual water treatment efficiency. Higher-purity PAM delivers stable flocculation and sedimentation effects, while excessive impurities will increase consumption costs and weaken overall treatment performance. Therefore, customers attach great importance to accurate purity detection. We would like to introduce one simple way of purity test, which doesn’t require much equipment or device. It is Ignition Method.

This method is based on the characteristic that polyacrylamide completely decomposes into volatile gases at high temperatures. A precisely weighed polyacrylamide sample is placed in a pre-weighed crucible and ignited in a muffle furnace at a specific temperature until constant weight is achieved. During ignition, the polyacrylamide molecular chains break down, decomposing into small molecular gases such as water, carbon dioxide, and ammonia, which escape, leaving inorganic ash as the residue. The organic content in the sample is calculated from the mass difference before and after ignition, and the purity of polyacrylamide is subsequently derived. The calculation formula is:

• Standard Operating Procedure

1. Sample Pre-treatment‌: Dry solid PAM sample at 105℃±2℃ to constant weight to eliminate moisture interference, ensuring dry-basis measurement;

2. Weighing and Loading‌: Accurately weigh 2–3 g of dried sample into a pre-weighed porcelain crucible; record initial mass;

3. Carbonization‌: Heat gently on an electric stove (~300℃) until no smoke is emitted, preventing splattering during high-temperature ignition;

4. High-Temperature Ignition: Transfer crucible to a muffle furnace and ignite at ‌850℃±50℃‌ for ‌2–3 hours‌ until constant weight is achieved (mass change ≤0.3 mg);

5. Cooling and Weighing‌ Cool crucible in a desiccator to room temperature, then weigh the residue.

• Applicability and Limitations‌

This method is suitable for‌: solid powdered or granular PAM with no significant moisture or volatile solvent residues. While it is not applicable to‌: liquid PAM, solvent-containing systems, or formulations with volatile organic additives (e.g., surfactants).

• Interfering Factors‌:

1. High content of inorganic additives (e.g., sodium sulfate, ammonium chloride) leads to elevated residue, ‌underestimating purity‌.
2. Incomplete drying causes water evaporation to be misinterpreted as organic loss, ‌overestimating purity‌.
3. Sample heterogeneity or weighing error >0.1% significantly affects accuracy.

• Advantages and Standard Compliance‌

Advantages‌: Simple equipment (muffle furnace, analytical balance), low cost, high reproducibility — ideal for industrial quality control.

Standard Reference‌: China National Standard ‌GB/T 31246-2025‌ “Water Treatment Agents — Cationic Polyacrylamide” formally adopts the ignition residue method for solid content and purity assessment.