Determination of Active Matter in Liquid Detergents: Test Methods, Standards, and Technical Requirem

Active matter content is the single most important quality and performance indicator for liquid detergents, directly determining cleaning power, formulation cost, and regulatory compliance. This technical article explains how the anionic, nonionic, cationic, and amphoteric active ingredients in liquid detergents are measured, covering internationally recognized methods such as ISO 2271, GB/T 13173, and ASTM D3049. Whether you are a manufacturer performing quality control or sourcing products through an accredited third-party laboratory, this guide outlines the sample types, testing items, analytical procedures, and acceptance criteria involved.

Technical Overview

Active matter refers to the surface-active substances in a detergent formulation that provide the primary cleaning function, mainly including anionic surfactants such as linear alkylbenzene sulfonate (LAS), alcohol ethoxysulfate (AES), and alpha-olefin sulfonate (AOS), nonionic surfactants such as fatty alcohol ethoxylates (AEO) and alkyl polyglucosides (APG), amphoteric surfactants such as betaines, cationic surfactants, and fatty acid salts (soap). The total active matter content is typically defined as the ethanol-soluble residue of the sample minus sodium chloride and other inorganic salts.

For liquid detergents, active matter determination serves as the core chemical index in product standards, factory quality control, incoming raw material inspection, and market surveillance. Insufficient active matter reduces detergency and foaming performance, while inaccurate labeling of active content can result in non-compliance with national and industry standards. Established methods are gravimetric extraction for total active matter and two-phase titration for specific ionic classes of surfactants, supported by instrumental techniques for complex formulations.

Testing Samples

Liquid Laundry Detergents

Standard and concentrated liquid laundry detergents, laundry capsules, and pre-treatment sprays are tested for total active matter as well as the individual distribution of anionic and nonionic surfactants to verify detergency performance and compliance with industry standards such as QB/T 1224.

Dishwashing Liquids

Hand dishwashing liquids are typically formulated with high levels of anionic surfactants (LAS, AES) blended with nonionic amine oxides or APG, and are tested to confirm active content, foaming capacity, and label claims.

Hard Surface and Multi-Purpose Cleaners

Kitchen degreasers, glass cleaners, floor cleaners, and all-purpose cleaners contain mixed surfactant systems, requiring separate quantification of anionic, nonionic, and occasionally cationic components, especially for disinfectant-type cleaners.

Surfactant Raw Materials

Incoming inspection of purchased surfactant lots, such as sodium dodecylbenzene sulfonate, sodium laureth sulfate, and alcohol ethoxylates, uses the same active matter methods to verify supplier specifications and active concentration.

Testing Items

• Total active matter content (ethanol-soluble matter minus sodium chloride)
• Anionic active matter content
• Cationic active matter content
• Nonionic active matter content
• Amphoteric surfactant content (for example, cocamidopropyl betaine)
• Soap content (fatty acid salts)
• Ethanol-insoluble matter
• Sodium chloride and inorganic salt content

Testing Methods

Total Active Matter by Ethanol Extraction (Gravimetric Method)

The sample is dissolved in 95% ethanol under heating, and the ethanol-insoluble fraction, mainly inorganic salts and insoluble fillers, is removed by filtration. The ethanol extract is evaporated to dryness and weighed to obtain the ethanol-soluble matter. Chloride in the residue is then determined by titration with standardized silver nitrate solution and converted to sodium chloride, which is subtracted from the ethanol-soluble matter to yield the total active matter content. This procedure follows the principles of GB/T 13173 for detergent testing and ISO 4321 for active matter determination.

Anionic Active Matter by Two-Phase Titration

Anionic surfactants are titrated in a water-chloroform two-phase system with a standardized cationic titrant, typically benzethonium chloride (Hyamine 1622), using a mixed indicator of dimidium bromide and disulfine blue. The endpoint is detected by the transfer of the indicator color from the aqueous phase to the organic phase. This classical method is specified in ISO 2271, GB/T 5173, and ASTM D3049. A potentiometric two-phase titration variant, which eliminates subjective visual endpoint judgment, is also available and is referenced in standards such as ASTM D4251 for anionic active content.

Cationic Active Matter by Two-Phase Titration

Cationic surfactants in disinfectant cleaners and fabric softener formulations are titrated with a standardized sodium dodecyl sulfate (SDS) solution using a similar two-phase indicator technique, following ISO 2871-1 and ISO 2871-2, which distinguish between different cationic molecular weight ranges, as well as GB/T 5174.

Nonionic Active Matter by Weibull Method or Spectrophotometry

Nonionic surfactants are separated from ionic species by ion exchange and determined gravimetrically according to the Weibull method described in ISO 2268. For routine quality control of ethoxylated nonionics, the cobalt thiocyanate spectrophotometric method provides a rapid colorimetric alternative based on the formation of a colored complex with the polyoxyethylene chain.

Instrumental and Supplementary Methods

• HPLC with UV, evaporative light scattering, or mass spectrometric detection for quantification of individual surfactant homologs
• Ion chromatography for determination of chloride and inorganic salt content
• Near-infrared (NIR) spectroscopy as a rapid, non-destructive screening tool calibrated against classical reference methods
• Determination of soap content by acidification and titration of liberated fatty acids

Applications

Active matter determination is applied across the full detergent value chain. Manufacturers use it for batch release testing, formulation cost optimization, and verification of surfactant blending accuracy. Regulatory bodies and market surveillance programs rely on it to verify compliance with mandatory and voluntary product standards. Importers, brand owners, and retailers commission accredited third-party laboratories to perform active matter testing for supplier qualification, private-label product development, and competitive benchmarking. The data also supports environmental labeling declarations and resolves quality disputes between trading parties.

FAQ

What is the required minimum active matter content for liquid laundry detergents?

Under the Chinese light industry standard QB/T 1224, standard liquid laundry detergents are generally required to contain no less than 15% total active matter, while concentrated products require a higher minimum level, typically no less than 25%. Similar minimum requirements exist in other jurisdictions, so the applicable product standard should always be confirmed.

Why is sodium chloride subtracted in the total active matter calculation?

Ethanol extraction dissolves both surfactants and certain inorganic salts such as sodium chloride. Because sodium chloride is not a surface-active substance, its content, determined separately by silver nitrate titration, must be deducted to obtain the true active matter value.

Can two-phase titration be used for formulations containing mixed surfactant types?

Yes, but with care. Soaps and amphoteric surfactants can interfere with the two-phase endpoint. In such cases, prior separation, pH adjustment, or complementary instrumental methods such as HPLC are recommended to obtain accurate results for each surfactant class.

How much sample is required and what is the typical testing cycle?

For liquid samples, approximately 100 to 250 grams is generally sufficient for a full active matter test suite. Classical gravimetric and titration methods typically require three to seven working days, while rapid screening by NIR can provide results within hours once a calibration model is established.

Which standards are most commonly cited in test reports?

Frequently cited references include GB/T 13173 for detergent testing methods, GB/T 5173 and ISO 2271 for anionic actives, GB/T 5174 and ISO 2871 for cationic actives, ISO 2268 for nonionic actives, and ASTM D3049 for anionic active matter by two-phase titration.