This Standard Reference Material (SRM) is intended for use as an analytical standard of known purity. It is intended primarily for use in the calibration and standardization of procedures for potassium (K) and chloride (Cl-) determinations employed in clinical analysis, including those using ion-selective electrodes, and for routine critical evaluation of the daily working standards used in these procedures. This lot of potassium chloride (KCl) was prepared to ensure a material of high purity and homogeneity and has been assayed after heating at 110 degrees C to 120 degrees C. A unit of SRM 918c consists of a single glass bottle containing 30 g of the material. This data is public in the Certificate of Analysis for this material.