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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 results being accurate or reproducible. Check the manual for more information on each ISE about the expected stability. | 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. | ||
- | ===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 discarding, whereas diluted standards treated with ISA/pH buffer should be prepared weekly. | ||
- | ===How do you store the electrodes? | + | ====How do you store the electrodes?==== |
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, | 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, | ||
- | ===Can you do temperature compensation with ISE?=== | + | ====Can you do temperature compensation with ISE?==== |
Yes, it is possible, but somewhat difficult. | Yes, it is possible, but somewhat difficult. | ||
- You have to know the isopotential point for a given electrode system. | - You have to know the isopotential point for a given electrode system. | ||
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- The temperature of the sample can not exceed the operational temperature range of the ISE. | - The temperature of the sample can not exceed the operational temperature range of the ISE. | ||
- Very little isopotential point data for ISE's is available at this time. | - 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. | + | **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?=== | + | ====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. | 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?=== | + | ====Which standards should be used with the ISE?==== |
The most obvious choice will be determined by what | The most obvious choice will be determined by what | ||
concentration units are desired (e.g. ppm as what?). Also, if | concentration units are desired (e.g. ppm as what?). Also, if | ||
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sulfate with a lead electrode), use a stock standard of the | sulfate with a lead electrode), use a stock standard of the | ||
ion to be measured (e.g. sulfate). | ion to be measured (e.g. sulfate). | ||
- | ===Why buy a combination electrode instead of seperate | + | ====Why buy a combination electrode instead of separate |
- | Advantages: no external reference electrode needed more economical than price of both one less electrode to fit in the process. | + | Advantages: |
+ | * no external reference electrode needed | ||
+ | * more economical than price of both | ||
+ | * one less electrode to fit in the process. | ||