Electrodes, Laboratory

pH Electrode Basics The Electrode Pair Sensing half-cell electrodes are the measuring portion of the electrode system and contain the pH sensitive membrane. Reference half-cells electrodes provide the reference potential needed for pH measurement. Most of the electrodes available at Cole-Parmer are combination electrodes that house both half-cells in a single probe. Bulb Material And Design The bulb or membrane is constructed of different types of glass, each with different useful properties. General-purpose glass: various pH ranges, temperatures to 212º F ( 100º C) . Blue glass: pH 0 to 14, temperatures to 230º F ( 110º C) . Amber glass: pH 0 to 14, temperatures to 230º F ( 110º C) , prevents Na+ error in high Na+ concentration solutions. The bulb shape can be modified to provide a semi-dome for increased ruggedness, a spear tip for penetration applications, or even a flat surface. Glass vs Epoxy Body Epoxy-body electrodes are impact resistant and are ideal for rough handling but should not be used at higher temperatures or for solvents. Note: Even though the body of an epoxy electrode is plastic, the bulb will still be glass. Glass-body electrodes withstand high temperatures and highly corrosive materials or solvents. Sealed vs Refillable Sealed ( also known as gel-filled) electrodes are easier to maintain than refillable liquid filled electrodes. However, they must be replaced when the fill material level is low. Refillable electrodes are long-lasting and provide a faster response. Single- vs Double-junction In combination electrodes, the reference junction allows H+ ions to pass freely between reference and sensing half-cells to complete the electrical circuit. A singlejunction design has one place where the H+ ions pass between half-cells. The junction is located so that contaminants in your sample can also pass into the reference chamber, leaving the potential for electrode failure due to reference contamination. A double-junction design restricts the reference behind a second junction; thus, it is twice as hard for reference contamination to occur. Selecting The Right Electrode Cole-Parmer offers a variety of laboratory electrodes for your general-purpose and specialty laboratory applications. The “ Application Guide” below provides information to help you find the electrode that best fits your application. The guide only offers suggestions— call our Application Specialists for more specific recommendations or clarification. Application Guide Biological samples, proteins, and tris buffer: Double-junction or ROSS® Pharmaceuticals: Double-junction or ROSS Hydrofluoric acid: Antimony or HF electrode Low ionic strength samples and acid rain: AccuFlow™ or Sure-Flow® styles Boiler feed water and distilled water: AccuFlow or Sure-Flow styles Drinking water: Standard Ag/ AgCl with single-junction Wastewater: Double-junction or ROSS Solutions with heavy metals: Double-junction Soil samples: Soil electrode or double-junction pH> 9 and high Na+ : Amber glass bulb, Ag/ AgCl High or rapidly changing temperatures: ROSS styles Moist, flat surfaces: Flat-surface Cheese, agar, paper, and skin: Flat-surface Semisolid samples: Spear-tip, Ag/ AgCl, ISFET Fruits, cheese, and meat: Spear-tip, Ag/ AgCl, ISFET Nonaqueous samples, solvents, and alcohols: AccuFlow styles, Sure-Flow styles, or double-junction Viscous samples, slurries, suspended solids, and sludges: AccuFlow styles, Sure-Flow styles, double junction, or ISFET Emulsions and oils: AccuFlow styles, Sure-Flow styles, double-junction, or ISFET Paints and inks: AccuFlow styles, Sure-Flow styles, double-junction, or ISFET Contact Us : 085218141054 E-mail : lab.naga@ yahoo.com Fax : 021 4788 3649 Jupentus Sinaga