Determination of pH in Cosmetics
The methodology for determining the pH of cosmetics can be divided into two techniques: dilution method and direct testing method. For powders, ointments, and water-in-oil emulsions, direct testing cannot be utilized.
Dilution Method:
Accurately weigh 1 part of the sample (precise to 0.1g) and add 9 parts of experimental water with a conductivity less than 5µS/cm and free of carbon dioxide. Heat to 40°C (104°F) and stir the sample thoroughly before testing. If the sample has a high oil content, heat it to 70 to 80°C, then remove the oil chunks after cooling for testing. For powdered samples, allow them to settle and then filter before testing.
Direct Testing Method:
Place an appropriate amount of the sample from the packaging container into a beaker or directly open the seal for testing.
Considerations During Measurement:
• Ensure the pH meter is calibrated prior to measurement.
• The temperature difference between the sample to be tested and the standard buffer solution used during calibration should not be excessive.
• The sample needs to be thoroughly stirred during measurement.
• The result of the measurement should be based on the average of two measurements.