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USP MEASUREMENT
USP MEASUREMENT
USP MEASUREMENT
USP MEASUREMENT
USP MEASUREMENT
Pharmaceutical laboratories working in the US market are obliged to respect
the regulations set down by the US Pharmacopoeia. The 5
th
supplement of
USP24-NF19
lays down the rules for checking the quality of pure or fully
deionized water used for the production of injection products.
The conductivity of water provides information on its chemical composition. It
is therefore logical that makes this the main parameter to measure.
The conductivity of a water is a measure of the ion mobility through this water.
The conductivity partly depends on the pH, the temperature and the amount
of atmospheric carbon dioxide, witch has been dissolved in water to form ions
(intrinsec conductivity). The conductivity also depends on the chloride, sodium
and ammonium ions initially present in water (extraneous conductivity).
The conductivity (intrinsec and extraneous) of the water is measured at first
stage and compared to values listed in a table to evaluate if the studied water
is suitable or not for use in pharmaceutical applications. If the sample fails
stage 1, additional tests have to be performed (Stage 2 and 3) in order to
determine if the excessive conductivity value is due to intrinsec factors or
extraneous ions.
USP Requirements
Automatic temperature correction must not be used.
Instrument specifications
Minimum resolution of 0.1
m
S/cm on the lowest range. Excluding the cell
accuracy, the instrument accuracy must be ±0.1
m
S/cm.
Meter calibration
It is accomplished by replacing the conductivity cell with precision resolution
traceable to primary standards (accurate to ±0.1 % of the stated value) or
an equivalently accurate resistance device.
Cell calibration
Meter conductivity must be measured accurately using calibrated instrumen-
tation. The conductivity cell constant must be known in ± 2 %.
Before starting water analyze calibrate the EC lowest range or set the probe
cell constant (enter the value written in the calibration certificate delivered
with the probe).
Stage 1
Determine the temperature and conductivity of the water.
• Rinse the probe carefully with deionized water. Check that the 4 rings and
the temperature sensor are immersed in the sample and that no air bubbles
