There are four methods to measure pH gradient by isoelectric focusing electrophoresis:

1. Cut rubber strip into small pieces, soak it in water, measure the pH value with precision pH test paper or imported slender pH composite electrode, and then draw a graph.

2. Directly measure the pH value of each part of the tape with the surface pH microelectrode, and then draw a chart.

3. Using a group of protein with known different pI values as the standard, determine the standard curve of pH gradient.

4. Freeze the adhesive tape at -70℃ and cut it into 65438±0mm slices, add 0.5 ml of 0.065438 0 m KCl, and measure its pH value with microelectrode.