65
Chloride Standards
You will need:
• Solid sodium chloride or a certified 1000 mg/L chloride solution from a supplier
• Magnesium sulfate
• High-purity water
• A good quality analytical balance
• 1000 mL volumetric flask
• An accurate 10 mL measuring devices
• And 1000 mL glass or plastic storage vessels
1000 mg/L
Standard
1.
Accurately weigh 1.655 grams of anhydrous sodium chloride and transfer into a 1000 mL volumetric flask.
2.
Add 0.5 grams of anhydrous magnesium sulfate to the flask.
3.
Add 500 mL of water to the flask, swirl to dissolve all of the reagents, then dilute to the volumetric mark with water.
4.
Mix well by repeated inversion, then transfer the 1000 mg/L standard to a storage bottle.
5.
Rinse the flask extensively with water prior to its use in the preparation of the 10 mg/L standard. Alternatively, simply add 0.5
grams of magnesium sulfate to a liter of a 1000 mg/L chloride standard from a certified supplier.
10 mg/L Standard
1.
Accurately measure 10 mL of the above 1000 mg/L standard solution into a 1000 mL volumetric flask.
2.
Add 0.5 grams of anhydrous magnesium sulfate to the flask.
3.
Add 500 mL of water, swirl to dissolve the solid reagents, then dilute to the volumetric mark with water.
4.
Mix well by repeated inversion, then transfer the 10 mg/L standard to a storage bottle.
Sensors, Calibration, and Maintenance
ISE Maintenance
ISE sensors are shipped with their tips in a dry storage bottle. Keep this bottle for long-term storage. A soak for several hours in a
high concentration standard solution is necessary to rehydrate the sensor before calibration and use.
Sensor Maintenance
Ammonium or Nitrate sensor:
When deposits, biofouling, or other contamination
appear on the membrane, users should
gently
remove them with a fine jet of
deionized water or rinsing in alcohol followed by soaking in the high standard
calibration solution. Gently dab dry with a lint-free tissue.
Chloride sensor:
When deposits, biofouling, or other contamination appear on
the membrane, users should
gently
remove them by washing with alcohol and/
or gently polishing with fine emery paper in a circular motion to remove deposits
or discoloration, then thoroughly washing with deionized water to remove any
debris.
NOTICE:
The ion-selective membranes are very fragile. Do not use coarse materials
(e.g. paper towels) to clean the membranes, as these could permanently damage
the sensor. The exception is fine emery paper for the chloride sensor, noted above.