1. What specific ion are you interested in measuring? 2. What is the concentration of this specific ion in your sample? 3. What other ions are present in your sample? What is the concentration of each of these other ions? 4. Is your sample totally aqueous or is any organic solvents present? 5. Is your sample at room temperature or another temperature? 6. What is the pH of your sample? 7. What level of accuracy do you require in the measurement? 8. Have you used ISE's before? Are you familiar with their use? 9. How do you currently measure the specific ion in your sample? 10. Are there any other special requirements for your application?