pH 4.01 Buffer Solution at 25C is primarily used for calibration and verification of pH meters and electrodes especially for measurements in the acidic range.

It provides a stable known reference value of pH 4.01 at 25C allowing accurate and reproducible pH measurements. It is commonly used as part of one- two- or multi-point calibration.

It is a standardized acidic buffer solution with a specified pH of 4.01 at 25C (typically within a small tolerance such as 0.02). Temperature is important because buffer pH varies with temperature.