We continue in this second volume the plan evident in the first; i.e., of presenting a number of well-rounded up-to-date reviews of important developments in the exciting field of ion-selective electrodes in analytical chemistry. In this volume, in addition to the exciting applications of ISE''S to biochemistry systems represented by the description of enzyme electrodes, there is featured the most recent development in ISE''S, namely, the joining of the electrochemical and solid state expertise, resulting in CHEMFETS. The scholarly survey of the current status of ISE''S will undoubtedly be welcomed by all workers in the field. Tucson, Arizona Henry Freiser vii Contents Chapter 1 Potentiometric Enzyme Methods Robert K. Kobos 1. Introduction . . . . . . 1 2. Soluble Enzyme Systems . . . 5 2.1. Substrate Determinations 5 2.2. Enzyme Determinations . 13 2.3. Inhibitor Determinations. 18 3. Immobilized Enzyme Systems . 19 3.1. Methods of Immobilization. 19 3.2. Characteristics of Immobilized Enzymes 23 3.3. Analytical Applications with Ion-Selective Electrodes 23 4. Enzyme Electrodes 31 4.1. Urea Electrodes 35 4.2. Amygdalin Electrodes 39 4.3. Glucose Electrodes . 40 4.4. Penicillin Electrodes 40 4.5. Amino Acid Electrodes 41 4.6. Nucleotide Electrodes 46 4.7. Uric Acid Electrode 47 4.8. Creatinine Electrode 48 48 4.9. Acetylcholine Electrodes. 4.10. D-Gluconate Electrode 49 4.11. Lactate Electrode 49 4.12. Inhibitor Determination 50 4.13. Substrate Electrodes 50 4.14. Current Trends . . . .