YSI TruLine 400357 pH 21 Single Junction Combination pH Electrode w/Epoxy Body, Spear Tip Membrane, BNC Connector, 1m Cable. The TruLine series of combination ISEs is designed to meet the most demanding challenges of determining effective ion concentration in the laboratory setting. The TruLine ISEs can be connected to the YSI TruLab 1320(P), the YSI MultiLab 4010-2/3 (with BNC adapter) and other ISE instruments that feature BNC connection. The TruLine ISEs are refillable and feature a built-in double-junction reference system, allowing for a long electrode life and optimum performance in the lab.