Determination of pH in Detergents and Soaps (10-percent Solution): Guidelines in Accordance with ASTM D1172 and ISO 4316
The pH value of detergents and soaps is a crucial quality parameter in terms of both product performance and skin compatibility. The pH value of a cleaning product directly influences foam formation, dirt-removing power, its effect on textiles or surfaces, and its compatibility with the consumer’s skin. Therefore, pH determination for detergents and soaps is an indispensable part of routine quality control.
In accordance with international standards, the pH of detergents and soaps is typically measured using a 10-percent aqueous solution (10 g sample / 100 ml water). This concentration corresponds to the product’s typical conditions of use and ensures comparable results across different products. In this article, we will explain how pH determination is performed using a 10-percent solution, which standards apply, and what services Nano-Test offers in this area.
Why is a 10 percent solution used?
In their pure form, detergents and soaps can be so concentrated or viscous that measuring their pH is not possible. In addition, the product’s pH value may change upon dilution (especially in formulations with low buffering capacity). Therefore, the standards require that the measurement be performed at a specific dilution ratio.
A 10-percent solution is the most widely used reference concentration in the industry. This ratio provides both a scenario that closely resembles the product’s practical application and improved reproducibility across different laboratories. With soaps in particular, high concentrations can lead to problems such as increased viscosity and electrode clogging, which is why a 10-percent dilution ensures optimal measurement conditions.
Relevant International Standards
The most important standards used as a reference for determining the pH in detergents and soaps are as follows:
| Standard | Title | Scope of Application |
|---|---|---|
| ASTM D1172 | Standard Guide for the pH of Aqueous Solutions of Soaps and Detergents | Standard Guide for the Preparation and pH Determination of Aqueous Solutions of Soaps and Detergents |
| ISO 4316 | Surfactants – Determination of the pH of Aqueous Solutions – Potentiometric Method | Determination of the pH of aqueous surfactant solutions using the potentiometric method |
| TS 6365 EN 1262 | Surfactants – pH Determination | Turkish Standard for Determining the pH of Surfactants |
| GB/T 13531.1 | pH Measurement in Cosmetics and Detergents | Chinese Standard for Determining pH in Cosmetics and Detergents |
ASTM D1172 describes in detail the preparation procedures, particularly for soaps and detergents, while ISO 4316 establishes the framework for the potentiometric method, which is applicable to all products containing surfactants.
Method for Determining pH Using a 10-Percent Solution
The procedure, conducted in accordance with ASTM D1172 and ISO 4316, consists of the following steps:
1. Sample Preparation and Solution Preparation
- Weighing: Weigh 10 ± 0.05 g of the sample on an analytical balance.
- Dissolution: Transfer the sample to a 100-ml Erlenmeyer flask and make up the volume with approximately 60–70 ml of pure, carbon dioxide-free water.
- Mixing: The sample is mixed on a magnetic stirrer or in an ultrasonic bath until it is completely dissolved. If necessary, it may be gently heated (to a maximum of 40 °C).
- Make up the volume: After the solution has cooled to room temperature, add pure water to bring the volume to 100 mL.
2. Calibrating the pH meter
- The pH meter is calibrated using at least a two-point calibration procedure before taking a measurement.
- pH 4.00, 7.00, and 10.00 buffer solutions are typically used for calibration.
- Calibration must be performed at the measurement temperature (typically 25 ± 1 °C).
- The glass electrode is rinsed with pure water before and after calibration and gently dabbed dry with blotting paper (do not rub).
3. Measurement
- The prepared 10-percent solution is transferred to a clean beaker.
- The pH electrode is immersed in the solution and stirred gently with a magnetic stirrer.
- Wait to take the measurement until the value has stabilized (usually 30–60 seconds).
- The result is recorded with an accuracy of 0.1 pH units.
- The measurement is repeated at least twice, and the average of the results is calculated.
4. Temperature Correction
pH measurement is temperature-dependent. ASTM D1172 and ISO 4316 recommend performing the measurement at 25 ± 1 °C. When using pH meters with automatic temperature compensation (ATC), the temperature difference is automatically corrected.
Expected pH ranges depending on product type
The pH levels of laundry detergents and soaps vary depending on their intended use:
| Product Type | Typical pH range (10% solution) | Scope of Application |
|---|---|---|
| Bar Soap (Classic) | 9.0 – 10.5 | Hand and Body Hygiene |
| Liquid soap | 5.5 – 8.5 | Hand Wash, for Sensitive Skin |
| Shampoo (Baby) | 5.5 – 7.0 | Gentle, eye-friendly formula |
| Laundry Detergent | 9.0 – 11.0 | Dry Cleaning, Stain Removal |
| Dishwashing detergent | 7.0 – 9.0 | Grease solution, contact with hands |
| Surface cleaners | 10.0 – 12.0 | Industrial Cleaning, Disinfection |
GLP-Compliant pH Testing Services with Nano-Test
For manufacturers of cleaning products and soaps, pH testing forms the basis for both product quality and compliance with legal regulations. With its GLP-compliant analytical services, Nano-Test is a reliable solution partner for the cleaning products industry in this area.
Description of Nano-Test Services
Nano-Test offers a pH determination service for laundry and soap products using a 10-percent solution. Our analyses are conducted in full compliance with the ASTM D1172, ISO 4316, and TS 6365 EN 1262 standards.
Our service process:
- Sample preparation: Weighing, dissolving, and diluting in accordance with ASTM D1172.
- Potentiometric measurement: Measurement using high-precision pH meters and calibrated electrodes.
- Calibration: Two- or three-point calibration using certified buffer solutions.
- Temperature control: Measurement at 25 ± 1 °C, automatic temperature compensation.
- Reporting: The measurement results are provided along with standard deviation and repeatability data.
All of our analyses are presented as GLP-compliant reports that have been approved for testing and in which data integrity (ALCOA+ principles) is ensured.
Benefits of Nano-Test's pH Analysis Service:
- Accredited Infrastructure: Internationally recognized test reports with ISO/IEC 17025 accreditation.
- Compliance with Standards: Full compliance with ASTM D1172, ISO 4316, and the corresponding national standards.
- Fast results: Reports are available within 2–3 business days for standard pH analyses.
- Comprehensive scope: All product types, including bar soap, liquid soap, shampoo, laundry detergent, and surface cleaners.
- Expert Team: A team with experience in analytical chemistry and the regulatory requirements for cleaning products.
Determining the pH of detergents and cleaning agents is a critical step in quality control for assessing the product’s performance, stability, and skin compatibility. Potentiometric measurement using a 10-percent solution provides internationally recognized, reliable results when performed in accordance with ASTM D1172 and ISO 4316.
With its accredited laboratory infrastructure, expert staff, and GLP-compliant processes, Nano-Test fully meets the pH testing requirements of detergent and soap manufacturers. Partner with Nano-Test to improve the quality of your products and accelerate their time to market.