15
If calibration fails, the followings should be checked:
• The DI blank is being contaminated.
• The 100 ppb PTSA standard solution is decayed or being contaminated.
• The light shield cover is not in the closed position.
• The sample vial compartment is blocked with debris, water, or other materials.
The 100 ppb standard solution shall be stored in a brown or black opaque bottle.
Exposing the PTSA standard to light will cause the standard losing the PTSA
concentration. Many substances, such as quaternary amine cause a negative
interference. Many other substances such as laundry detergents that contain optical
brightener will cause a significant positive interference.
4 Fluorescein Measurement
4.1 Fluorescein Measurement
1. Fill the 10 ml sample vial with the test solution and tightly cap the sample vial.
2. Place the sample vial into the sample vial compartment and slide the light shield
cover to the closed position.
3. Press the M-F on the main page, then press the OK button, the SP-910 will start to
measure the fluorescein concentration in the sample.
4. The SP-910 will display the fluorescein concentration in ppb.
Figure 8 Fluorescein Measurement
For best results, ensure that the sample vial is clean. Wipe off water on the outside
wall of the sample vial using a lint-free tissue paper. Fill the sample vial to the 10 ml
mark. If the sample contains air bubbles, tap the sample vial gently to remove the
bubbles before placing the sample vial to the sample vial compartment.
4.2 Fluorescein calibration (Firmware version before v1.0r295)
Deionized water (DI) as the blank calibration solution and the 20 ppb fluorescein
calibration standard solution are needed.
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