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IM 12D08N04-01E
10-4
10. Appendix
10-6. USP Item 645 Water Purity Monitoring
What is USP Item 645?
USP stands for United States Pharmacopoeia and it is responsible for issuing guidelines
for the pharmaceutical industry. Implementing these guidelines is highly recommended
for companies wishing to market drugs in the US. This means that USP is important for
pharmaceutical companies worldwide. USP recently issued: - USP 23 item 645 recom-
mendations for conductivity measurement.
This new USP item 645, aims at the replacement of 5 antiquated laboratory tests by
simple conductivity analysis.
What is conductivity measurement according USP?
Life would be easy if the limits for the conductivity of injection water were set to be 1.3
µ
S/cm at a reference temperature of 25
°
C. However, the committee (PHRMA WQC)
who made the USP item 645 recommendations, 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 temperature 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 specified as “stage 1:
Conductivity Limit at a given 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.
How have we accomplished this in SC402G?
1. In Software Rev. 1.2, (and later versions) 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 contact
closes 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 23 table.
3. We have added a USP function to the contact allocation. All 4 contacts can be
selected as USP alarms. The contact closes when the USP limit is approached. It is
possible to adjust a safety margin for the water quality. For example, if the
temperature is 64
°
C. and the safety margin is adjusted for 20%, then the contact
closes at 0.8 x 2.2
µ
S/cm. = 1,76
µ
S/cm. (2.2
µ
S/cm is the USP limit at 64
°
C).
4. 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
µ
S/cm. = 0,568 Mohm.