GB/T 13528-2015 "Paper and board — Determination of surface pH" specifies the method for determining the surface pH of paper and board, applicable to various types of paper and board. A pH meter with a flat electrode and temperature compensation function is used, with readings accurate to 0.01. Samples are collected according to GB/T 450, and after conditioning under standard temperature and humidity conditions, a small amount of distilled water is dripped onto the sample surface. The flat electrode of the pH meter is then placed in contact with the surface, and readings are taken at specified intervals. The average of multiple measurements is calculated to ensure accurate determination of surface acidity or alkalinity, providing a basis for quality control of paper and board.