The Shimadzu PPSQ-31A protein sequencer uses the Edman degradation reaction method. The sequencer separates PTH-Amino acids isocratically providing more stable retention times. Analysis in isocratic mode also allows for eluents to be recycled, thereby reducing the cost and disposal of the mobile phase. The 31A has one reactor and the cycle time is 47min/cycle. Glass fiber disks or PVDF membrane may be used for sample immobilization.