150mV Mono/Reference 300mV Combination SENTEK Unit 6 & 7 Crittall Court, Crittall Drive, Springwood Industrial Estate, Braintree, Essex, CM7 2SE Tel: +44 (0) 1376 340 456 Fax: +44 (0) 1376 340 453 Email: [email protected] Operating Instructions Potassium Ion Selective Electrode This Document includes operating instructions for two types of Ion Selective Electrode. A single sensing Half Cell Potassium Electrode which requires a separate Reference Electrode, and a Combination Potassium Electrode which has the Reference built into the outer shaft. For extremely low level work the Half Cell plus Reference Electrode should be used. For general applications the Combination is more convenient. Depending on the type of ISE chosen you will need to disregard some information for instance if you have the Combination Electrode then disregard any comments about reference electrodes. A quick guide is included with a more involved section following. SENTEK Unit 6 & 7 Crittall Court, Crittall Drive, Springwood Industrial Estate, Braintree, Essex, CM7 2SE Tel: + 44 (0) 1376 340 456 Fax: +44 (0) 1376 340 453 Email: [email protected] Quick Guide to Potassium ISE The combination ion selective electrode has a solid state PVC polymer membrane with an integral driTEK reference electrode. The electrode is designed for the detection and analysis of Potassium ions in aqueous solutions and is suitable for use in the field in the laboratory and in on line analyzers. Installation Connect the ISE to the mV or ion meter. Remove the black protective cap and keep it in a safe place. The ISE can be used immediately but pre soaking for 5 minutes in a 100ppm Potassium solution is recommended. The ionic strength of the standards and solutions should be kept constant between all standards and samples. This is achieved by the simple addition of an Ionic strength adjustment buffer (ISAB). Lithium Acetate is ideal. A typical addition would be 1 ml of 1 molar ISAB to 100 ml of standard and sample. For low level measurements below around 50ppm in relatively pure samples no ISAB is needed. No temperature correction is necessary however standards and samples should be measured at the same temperature. Begin calibration from the lowest concentration standard to avoid cross contamination. Calibration should cover the anticipated range of the samples. Rinse tip with de-ionised water between measurements. Avoid strongly acidic or alkaline samples, strong detergents and organic solvents. Storage and Maintenance Avoid touching the membrane surface. After use rinse with de-ionised water, replace protective cap and store dry in its box. If performance becomes sluggish, rinse with dilute detergent, rinse with de-ionised water and immerse the tip in a 1000ppm Potassium solution for 1 hour. Rinse with de-ionised water and resume your normal calibration routine. Specification Parameter Specification Overall length Body Diameter Cap Diameter Connector Cable length Resistance at 25 Deg C 155 mm 12 mm 16mm BNC 1000 mm < 10 Meg Ohm Concentration Range Slope Potential Drift Operating pH range Temperature range Endpoint time Interferences: Ions with coefficients above 0.001. 0.04 to 39,000 ppm 57 +/- 2 mV per decade 1 mV per 8 hours 1 to 9 5 to 50 Deg C Typically 10 to 30 seconds Caesium Ammonium For advice on methodologies and analytical hints and tips contact your local distributor. Operating Instructions for Potassium Ion Selective Electrode 1. Introduction 1.1 Construction The electrode consists of an inert fluorocarbon body with a detachable PVC membrane unit, on the end of which is glued the ion-selective membrane. Inside the membrane unit, an internal filling solution makes contact between the membrane and the internal silver/silver chloride reference element. The sensitive membrane consists of liquid ion exchange material immobilised in a poly-(vinyl chloride) matrix. Connection to a millivoltmeter is via a BNC plug, though an alternative plug may be specified. 1.2 Operating Principles The electrical potential of an ion selective electrode is a function of the activity of certain ions in an aqueous solution. This potential can only be measured against a reference electrode, such as a saturated calomel electrode (SCE), placed in the same solution. Because leakage of KCl form the SCE junction will alter the potassium ion activity of the sample solution, a saturated sodium nitrate salt bridge should be placed between the SCE and sample.