Yokogawa EXA SC202 2-Wire Conductivity Transmitter/Analyzer - Manual (Page 72)

IM 12D08B02-01E
USP 9-1
9. USP WATER PURITY MONITORING
9-1. What is USP ?
USP stands for United States Pharmacopeia and it is responsible for issuing guidelines for the pharma-
ceutical industry. Implementing these guidelines is highly recommended for companies wishing to mar-
ket drugs in the US. This means that USP is important for pharmaceutical companies worldwide. USP
recently issued: - USP - recommendations for conductivity measurement. This new USP, aims at the
replacement of 5 antiquated laboratory tests by simple conductivity analysis.
9-2. What is conductivity measurement according to USP?
Life would be easy, if the limits for the conductivity of injection water were set to be 1.3 μS/cm at a refer-
ence temperature of 25°C. However, the committee (PHRMA WQC) who made the USP recommenda-
tions, could not agree on a simple Sodium Chloride model for water quality determination. Instead, they
chose a Chloride-Ammonia conductivity-pH model in water atmospherically equilibrated (CO
2
) at 25 °C.
The objective of the WQC was to find an easy way to establish the water quality, so on-line analysis at
process temperature was a necessary requirement. However, if it is not possible to choose one temper-
ature response model to work to, then it is also not possible to choose one temperature compensation
algorithm.
We as a manufacturer of analytical equipment do not want to go into the details of whether the limiting
conductivity values for water quality are based on the Chloride model or the Ammonia model. Our job is
to develop on-line analyzers that make it simple for our customers to meet the water quality that is speci-
fied as “stage 1: Conductivity Limit as a Function of Temperature.”
If the water exceeds the limits of stage 1, then it can still be acceptable, but requires the customer to
proceed to Stage 2, and possibly Stage 3, to validate the water quality. It is our objective to assure that
our customers do not exceed the limits in stage 1 to avoid them having to carry out the complicated
laboratory checks in Stages 2 and 3.
9-3. USP in the SC202
1. In SC202 we have defined an Error Code: E13. This is independent of what range the customer is
measuring or what temperature compensation method he is using for water quality monitoring. When
the display shows E13, then the water quality exceeds the USP limits, and the FAIL flag on the
display is activated to signal that the system needs urgent attention.
2. We have introduced uncompensated conductivity in the DISPLAY menu. In the LCD display the user
can read the temperature and the raw conductivity to compare his water quality with the USP table.
3. We have kept all the EXA functionality: It is even possible to have the mA Output and Display
readings in resistivity units. Most users will have very good water quality and in the resistivity mode
they will have better resolution on the recorder or DCS. The readings are simply the reciprocal
values of the conductivity values. In the example mentioned above the contact will close at an
uncompensated resistivity of 1/1.76 μS/cm. = 0.568 MΩ·cm.