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=====Frequently Asked Questions (Ion-selective electrodes)===== | =====Frequently Asked Questions (Ion-selective electrodes)===== | ||
- | ===How often do you need to calibrate? | + | ====How often do you need to calibrate?==== |
- | Recalibrate at least once a week, or daily if in doubt of your | + | Recalibrate at least once a week, or daily if in doubt of your results being accurate or reproducible. Check the manual for more information on each ISE about the expected stability. |
- | results being accurate or reproducible. | + | ====How long after being opened or made are standards good?==== |
- | ===How long after being opened or made are standards good?=== | + | The stock standard will last at least six months before discarding, whereas diluted standards treated with ISA/pH buffer should be prepared weekly. |
- | The stock standard will last at least six months before | + | ====How do you store the electrodes?==== |
- | discarding, whereas diluted standards treated with ISA/pH | + | It is best to store them dry when they are not to be used in the next week or so. Empty out the filling solution in the gas-sensing electrode. For shorter periods, store in dilute standard approximating the sample concentration, |
- | buffer should be prepared weekly. | + | ====Can you do temperature compensation with ISE?==== |
- | ===How do you store the electrodes? | + | Yes, it is possible, but somewhat difficult. |
- | It is best to store them dry when they are not to be used in | + | - You have to know the isopotential point for a given electrode system. |
- | the next week or so. Empty out the filling solution in the | + | - The concentration of the sample has to be similar in concentration to the isopotential point or else the temperature correction will be very inaccurate. |
- | gas-sensing electrode. For shorter periods, store in dilute | + | - The temperature of the sample can not exceed the operational temperature range of the ISE. |
- | standard approximating the sample concentration, | + | - Very little isopotential point data for ISE's is available at this time. |
+ | **It is best to standardize and measure samples at the same temperature without using temperature compensation.** | ||
+ | ====Can you do in-line continuous ISE measurement without treating the sample? | ||
+ | Yes, direct measurement is possible in many cases without ISA/buffer addition to the sample stream. However, Fluoride, Sulfide, Ammonia, and Sodium Electrodes do require pH adjustment and must have ISA/ buffer added to the sample stream. | ||
+ | ====Which standards should be used with the ISE?==== | ||
+ | The most obvious choice will be determined by what | ||
+ | concentration units are desired (e.g. ppm as what?). Also, if | ||
+ | an electrode is being used to measure another ion (e.g. | ||
+ | sulfate with a lead electrode), use a stock standard of the | ||
+ | ion to be measured (e.g. sulfate). | ||
+ | ====Why buy a combination electrode instead of separate ones?==== | ||
+ | Advantages: | ||
+ | * no external reference electrode needed | ||
+ | * more economical than price of both | ||
+ | * one less electrode to fit in the process. |