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Conductivity of
Star Series
Method Note
Water USP <645>
M-1700
Key Words
Introduction
This 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. The Thermo Scientific Orion
• Conductivity
stainless steel conductivity probe, Cat. No. 013016MD, with a cell constant of 0.1 cm
analysis. This method is intended for general field or laboratory use when measuring low conductivity or
• USP <645>
pure water samples such as deionized water.
• Deionized Water
Recommended Equipment
• Purified Water
Conductivity Application Kit (includes listed items with a Cat. No.)
• Water for
Injection
1. 5-Star Plus benchtop pH/ISE/DO/conductivity meter
• Conductivity Cell
2. Star Plus Navigator 21 and 21 CFR Part 11 software
3. Conductivity probe with flow cell
4. ROSS Ultra® combination pH electrode
5. Stirrer probe (or magnetic stir plate and bar)
6. Swing arm electrode stand
7. Conductivity resistor calibration kit
8. 150 mL beakers
Required Solutions
1. 100 μS/cm conductivity standard, 5 x 60 mL bottles
2. pH 4.01 buffer, 475 mL bottle
3. pH 7.00 buffer, 475 mL bottle
4. pH 10.01 buffer, 475 mL bottle
5. pH electrode storage solution, 475 mL bottle
6. ROSS electrode filling solution
7. Deionized water
Note: The 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.
1 of 4
is used for this
-1
Cat. No.
1010152
1119000
1010017
013016MD
8102BNUWP
096019
090043
1010001
Cat. No.
011008
910104
910107
910110
910001
810007
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Summary of Contents for Thermo Scientific Orion Star Series
- Page 1 Conductivity of Star Series Method Note Water USP <645> M-1700 Key Words Introduction This 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. The Thermo Scientific Orion • Conductivity stainless steel conductivity probe, Cat. No. 013016MD, with a cell constant of 0.1 cm is used for this analysis. This method is intended for general field or laboratory use when measuring low conductivity or • USP <645> pure water samples such as deionized water. • Deionized Water Recommended Equipment Cat. No. • Purified Water Conductivity Application Kit (includes listed items with a Cat. No.) 1010152 •...
- Page 2 Conductivity of Water USP <645> Sample Preparation 1. Using a 150 mL beaker, collect about 100 mL of purified water or water for injection and measure it immediately (within 5 seconds). Alternately, use the flow cell that is included with the conductivity probe. 2. Repeat step 1 for additional samples. Results Five aliquots of deionized water were measured and the obtained conductivity results demonstrated good repeatability. The temperature value was 22 °C for the above results. From the Physical Tests, <645> Water Conductivity Stage 1 Table for Temperature and Conductivity Requirements, 1.1 μS/cm is the limit at 20 °C. Better results may be obtained using the flow cell included with the 013016MD conductivity probe if the measured conductivity is less than 1 μS/cm. If the measured conductivity is higher than the table value, proceed with Stage 2 as described in the USP <645> Water Conductivity procedures. Deionized Water Conductivity (µS/cm) Sample # 1: 0.09 Sample # 2: 0.07 Sample # 3: 0.08 Sample # 4: 0.08 Sample # 5: 0.07 Mean: 0.08 Standard Deviation: 0.01 % CV 10.73 Stage 1 Table for Temperature and Conductivity Requirements – For non-temperature compensated conductivity measurements only Temperature Conductivity...
- Page 3 Conductivity Probe Storage 1. For overnight and longer, cell should be stored clean and dry. 2. Storing the probe in water is acceptable between measurements. Equipment Set Up Electrode Setup – Conductivity Probe 1. Thoroughly rinse the conductivity probe with deionized water. Gently shake off any excess water. 2. Enter the cell constant value that is printed on the cable of the conductivity probe. a. I n the measurement mode, press the LINE SELECT key until the arrow icon points to the middle line, press the UP ARROW key until the μS/cm or mS/cm icon is shown and press the CALIBRATE key. b. T he manual calibration screen will display the cell constant on the top line, a conductivity value on the middle line and “CELL” on the bottom line. To change the cell constant, within 5 seconds press the DIGIT key until the first digit to be changed is flashing, press the UP/DOWN ARROW key to change the value of the flashing digit and continue to change the digits until the value matches the cell constant printed on the cable. Once the value is set, press the DIGIT key until the decimal point is in the correct location. c. Press the MEASURE key to save and end the calibration. Note: In the calibration screen, start changing the cell constant within five seconds or the meter will proceed to the automatic/direct calibration screen.
- Page 4 Calibration Check and Analysis 1. Allow the conductivity standards to reach room temperature for precise measurements, since conductivity measurements are temperature sensitive and the conductivity temperature compensation is off. 2. 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 for each new calibration. 3. Rinse the probe with the first bottle of standard and place the probe into the second bottle of standard, as stated above. 4. In the measurement mode, press the MEASURE key. The μS/cm icon will flash as the measurement is being made. The μS/cm icon will become solid and the display value will freeze when a stable reading is achieved 5. Record the measured conductivity value and temperature and compare it to the conductivity values in Table 2. If the results are within 2% of the expected conductivity value, the calibration check passed. If the results are outside 2%, try the following: a. Review the Meter Setup section to verify that the parameters are set properly. b. Rinse the conductivity probe and soak it in deionized water for 5 minutes. Repeat steps 3 through 5. c. Clean the probe with warm water and alkaline detergent for 10 to 30 minutes while stirring and repeat step b. d. Re-enter the cell constant value as described in the Electrode Setup section. 6. Rinse the probe thoroughly with deionized water. Remove excess solution from the probe by gently shaking it. 7. Prepare a sample as described in the Sample Preparation section. The sample must be measured immediately after being collected and the probe must be immersed in at least 2 inches of sample. 8. Place the probe in a prepared sample with the tip fully immersed in the solution. Press the MEASURE key. The μS/cm icon will flash as the reading stabilizes. The μS/cm icon will become solid and the value will freeze when a stable reading is achieved. 9. Use the Stage 1 Table to find the temperature value closest to the sample temperature that is not greater than the sample temperature. The corresponding conductivity value is the conductivity limit for the sample at the measured temperature. If the measured conductivity value is not greater than the table value, the water meets the requirements of the USP <645> test for conductivity. If the conductivity is higher than the table value, proceed with the Stage 2 USP <645> Water Conductivity. 10. R epeat steps 6 through 9 for additional samples. When all samples have been measured, rinse probe with deionized water and store the probe according to the Probe Storage section.
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