Pharmaceutical Water Conductivity Checker (Three-Stage Test)
Stage 1 temperature table, Stage 2 at 25 °C and Stage 3 pH table, with a verdict.
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Conductivity verdict
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About the Pharmaceutical Water Conductivity Checker (Three-Stage Test)
Checks bulk purified water and water for injection against the three-stage conductivity test. Stage 1 compares the reading without temperature compensation with the limit for the temperature equal to or just below the one measured. If that is exceeded, Stage 2 takes the sample to 25 ± 1 °C and stirs it until the reading changes by not more than 0.1 µS/cm in 5 minutes: it must then be 2.1 µS/cm or less. If not, Stage 3 reads the pH of the same sample, with saturated potassium chloride added, and compares the Stage 2 reading with the limit for that pH, from 5.0 to 7.0.
The checker tells you which stage decides, the limit that applies and what to do next, for one sample or a list of points of use, and can check the conductivity cell's constant with a potassium chloride reference solution. These are the stage tables of the approach USP general chapter <645> describes, as the Brazilian Pharmacopoeia reproduces them; the Japanese Pharmacopoeia gives the same Stage 1 table and Stage 2 limit. Without a pass it shows a free preview: the method, the limits that apply and the verdicts, with every computed figure hidden; the margins, the working and the PDF, Excel and Print exports unlock with a Premium pass.
How to use it
- Choose the water and enter the temperature and the conductivity read without temperature compensation (Stage 1).
- If Stage 1 is not met, stir at least 100 mL at 25 ± 1 °C and enter the reading once it has settled (Stage 2).
- If Stage 2 is not met, add 0.3 mL of saturated potassium chloride solution per 100 mL to the same sample within 5 minutes and enter the pH (Stage 3).
- Optionally check the cell constant with one of the potassium chloride reference solutions, or switch to A list of samples and paste one point of use per line.
- Read the stage, the limit and the verdict. Without a pass the report stays a free preview with its figures hidden; the PDF, Excel and Print unlock with a Premium pass.
Examples
64.3 °C, 2.6 µS/cm · Stage 2: 2.0 µS/cm at 25.0 °C
Stage 1 limit at 60 °C: 2.2 µS/cm, exceeded · Stage 2: 2.0 ≤ 2.1 µS/cm, meets the requirement
25.0 °C, 2.5 µS/cm · Stage 2: 2.3 µS/cm · pH 6.65
pH read as 6.7, limit 2.6 µS/cm · 2.3 ≤ 2.6, meets the requirement at Stage 3
25.0 °C, 2.5 µS/cm · Stage 2: 2.3 µS/cm · pH 6.5
Stage 3 limit at pH 6.5: 2.2 µS/cm · 2.3 > 2.2, does not meet the requirement
Common uses
- Daily release of purified water and water for injection at the points of use.
- Checking an in-line reading taken without temperature compensation against the table.
- Working through Stage 2 and Stage 3 in the laboratory when Stage 1 is exceeded.
- Verifying the cell constant of a conductivity meter before testing.
Stage 1 limits (without temperature compensation)
0 °C 0.6 · 5 °C 0.8 · 10 °C 0.9 · 15 °C 1.0 · 20 °C 1.1 · 25 °C 1.3 · 30 °C 1.4 · 35 °C 1.5 · 40 °C 1.7 · 45 °C 1.8 · 50 °C 1.9 · 55 °C 2.1 · 60 °C 2.2 · 65 °C 2.4 · 70 °C 2.5 · 75 °C 2.7 · 80 °C 2.7 · 85 °C 2.7 · 90 °C 2.7 · 95 °C 2.9 · 100 °C 3.1 (µS/cm). Use the row at the temperature equal to or just below the reading’s, without interpolation: 24.9 °C is read against 20 °C, 1.1 µS/cm.
Stage 3 limits by pH
pH 5.0 4.7 · 5.1 4.1 · 5.2 3.6 · 5.3 3.3 · 5.4 3.0 · 5.5 2.8 · 5.6 2.6 · 5.7 2.5 · 5.8 2.4 · 5.9 2.4 · 6.0 2.4 · 6.1 2.4 · 6.2 2.5 · 6.3 2.4 · 6.4 2.3 · 6.5 2.2 · 6.6 2.1 · 6.7 2.6 · 6.8 3.1 · 6.9 3.8 · 7.0 4.6 (µS/cm). The pH is read to 0.1 unit; outside 5.0 to 7.0 the water does not meet the test.
Instrument and cell constant
The meter needs a resolution of 0.1 µS/cm and the thermometer 0.1 °C divisions. The cell constant must be known to within ±2 %, checked with a potassium chloride reference solution at 25 °C without temperature compensation: 0.01 mol/L 1412 µS/cm, 0.005 mol/L 717.5, 0.001 mol/L 146.9, 0.0005 mol/L 73.9 and 0.0001 mol/L 14.9. The actual constant is the one set on the meter times the solution’s conductivity divided by the reading.
Sources
- Brazilian Pharmacopoeia, 6th edition, English translation of volume 1 — 5.2.24 Water conductivity: the three steps, the tables and the reference solutions
- The Japanese Pharmacopoeia, English version — General Information, quality control of water for pharmaceutical use: Stages 1 and 2, based on USP general chapter <645>
Limitations
- Bulk water only: packaged waters and pharmacopoeias with another table or limit for a grade of water need their own monograph.
- In a list, a Stage 2 value is taken as read at 25 °C after stirring; record the Stage 2 temperature and the settling for each sample.
- Total organic carbon, microbial and endotoxin tests are separate requirements.
- Up to 300 samples at a time.
- MySmartCoPilot is not affiliated with or endorsed by the United States Pharmacopeia (USP).
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Frequently asked questions
What do I get without a pass?
Without a pass, Pharmaceutical Water Conductivity Checker (Three-Stage Test) shows the method, the limits that apply and the verdict for your input, with the first rows of a list; computed figures stay hidden until the pass. Until you unlock it, the result can’t be downloaded or printed. A Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
What is the conductivity limit of purified water at 25 °C?
At Stage 1, 1.3 µS/cm for a reading at 25 °C without temperature compensation. If it is exceeded, the water can still meet the test at Stage 2 (2.1 µS/cm after settling at 25 ± 1 °C) or at Stage 3 (the limit for the sample’s pH).
Why is the reading not temperature-compensated?
The Stage 1 table already holds a limit for each temperature, made for raw readings. Compensated readings are not comparable with it.
Which table row applies at 27.4 °C?
The 25 °C row, 1.3 µS/cm: the table temperature equal to or just below the measured one, never an interpolated value.
When do I need Stage 3?
Only when the Stage 2 reading is above 2.1 µS/cm. Within 5 minutes, on the same sample at 25 ± 1 °C, add 0.3 mL of saturated potassium chloride solution per 100 mL, read the pH to 0.1 and compare the Stage 2 reading with the limit for that pH.
How do I check the cell constant?
Read a potassium chloride reference solution at 25 °C without temperature compensation. The actual constant is the one set on the meter times the solution’s conductivity divided by your reading; it must be within ±2 %.