Thermo Fisher Scientific ORION Calcium Ion Activity Electrode Plastic Membrane Thermo Fisher Scientific Scientific Accessory. Combining top-notch and uncompromising quality with an affordable price the Thermo Fisher Scientific ORION Calcium Ion Activity Electrode Plastic Membrane Accessory 932001/ 34109-576 can fulfill your laboratory needs while still offering a great value for the money. Product Category Description: Suitable for direct measurement of fluids and for potentiometrically determining the end point of calcium titrations made with EDTA. The electrode is 50 times more sensitive to calcium than to magnesium and approximately 1000 times more sensitive to calcium than to sodium or potassium. Can be used with samples as small as