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Environmental Instruments
Water Analysis Instruments
1 of 4
Conductivity of
Water USP <645>
Key Words
• Conductivity
• USP <645>
• Deionized Water
• Purified Water
• Water for
Injection
• Conductivity Cell
Star Series
Method Note
M-1700
Introduction
is method describes the technique for measuring the direct conductivity of purified water and water for
injection based on Stage 1 of USP <645> Water Conductivity procedures. e ermo Scientific Orion
stainless steel conductivity probe, Cat. No. 013016MD, with a cell constant of 0.1 cm
-1
is used for this
analysis. is method is intended for general field or laboratory use when measuring low conductivity or
pure water samples such as deionized water.
Recommended Equipment Cat. No.
Conductivity Application Kit (includes listed items with a Cat. No.) 1010152
1. 5-Star Plus benchtop pH/ISE/DO/conductivity meter 1119000
2. Star Plus Navigator 21 and 21 CFR Part 11 software 1010017
3. Conductivity probe with flow cell 013016MD
4. ROSS Ultra® combination pH electrode 8102BNUWP
5. Stirrer probe (or magnetic stir plate and bar) 096019
6. Swing arm electrode stand 090043
7. Conductivity resistor calibration kit 1010001
8. 150 mL beakers
Required Solutions Cat. No.
1. 100 μS/cm conductivity standard, 5 x 60 mL bottles 011008
2. pH 4.01 buffer, 475 mL bottle 910104
3. pH 7.00 buffer, 475 mL bottle 910107
4. pH 10.01 buffer, 475 mL bottle 910110
5. pH electrode storage solution, 475 mL bottle 910001
6. ROSS electrode filling solution 810007
7. Deionized water
Note: e stirrer probe, Cat. No. 096019, has been added as optional equipment for Stage 2 if the measured
conductivity does not meet the requirements of Stage 1 of the USP <645> Water Conductivity procedures. A ROSS
Ultra pH electrode and pH 4.01, 7.00 and 10.01 buffers have been included in this kit for Stage 3 if the measured
conductivity does not meet the requirements of Stage 2.
Calibration Standard Preparation
Two 60 mL bottles of the 100 μS/cm conductivity standard are required. One is used for rinsing the
conductivity probe and the other is used for checking the calibration of the conductivity probe. Open the
first bottle of the 100 μS/cm conductivity standard and use it to rinse the probe. A calibration check can
then be performed by inserting the probe directly into the second 100 μS/cm conductivity standard bottle.
Standards may be reused once for rinsing; however, a fresh bottle of 100 μS/cm conductivity standard
should be used each day.
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