Thermo Scientific™ Orion™ Green Electrodes are the first lab electrode to contain no lead, mercury or other hazardous substances and are completely ROHS compliant. GD9156BNWP is a refillable electrode that provides reliable and accurate measurements of routine samples but are best suited for treated effluent, distilled water and wastewater. GD9106BNWP and GS9106BNWP contain a low-maintenance gel that is best suited for field or plant use and educational institutes, where minimal maintenance is required.