Thermo Scientific Orion 9409BN Fluoride Electrode with BNC Connector, 5 to 7 pH Fluoride ion selective electrode (ISE) measures fluoride (F-) concentration in water, stack emissions, dental care products, and other aqueous solutions Solid-state sensor allows for dry storage and eliminates the need for membrane replacement Epoxy body for impact resistance and durability Measurement range is saturated to 0.02 ppm, and main interfering ion is OH- Electrode is 12mm in diameter and 110mm long, and is available with a screw cap connector or a BNC connector for attaching to compatible meters