eBook: TOC and Microbial Detection Monitoring - 5

Real-Time Compliance

TOC Measurement Technologies
All TOC technologies for Pharmaceutical regulation requirements
use UV to oxidize the organic carbon to CO2 in the measured water
sample. The resultant CO2 is measured by a conductivity cell. The
level of pre and post oxidation conductivity, along with temperature, is used for calculating the level of TOC present in the
sample.
Many on-line TOC technologies for Pharmaceutical compliance
use batch measurements for analysis. In these systems an aliquot
of water is brought into a measurement chamber where the sample
is oxidized and then analyzed. Depending upon system type and
water sample conditions, time for analysis is usually 5 to 20 minutes before a result is reported. Batch measurements therefore only
analyze a small portion of an entire water system and at an infrequent interval when compared to the total volume. The time delay
can be significant depending on the location of the TOC analyzer
and it is important to understand that during the unattended period regulated water systems may be exposed to undetected
incursions.
Unlike other systems, METTLER TOLEDO Thornton's TOC technology analyzes a continuously flowing sample for continuous measurements. Systems use a differential conductivity and a dynamic
UV oxidation process where a water sample continuously passes
through the sensor in a flowing stream at 20mL per minute.
Conductivity is measured every second with an initial conductivity
sensor at the beginning of the oxidation chamber. Water flows
through a quartz coil and is irradiated with high energy UV light.
This exposure to intense UV radiation results in organic molecules
present in the solution breaking down into CO2 and water. The
CO2 generated during UV exposure partially dissolves in water to
form carbonic acid. The post-oxidation conductivity is then measured with a second sensor. TOC content is calculated using the
difference in conductivity before and after oxidation. MT Thornton
dynamic oxidation method measures TOC 400 times faster than

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traditional batch type TOC analyzers which require analysis times
of 5-20 minutes. In the Thornton design, the sample flow process
is continuous; the sensor keeps repeating the measurement of the
two conductivity cells. The TOC value is updated every second with
a new aliquot of a continuously flowing sample.
METTLER TOLEDO TOC systems are unique in their ability to
measure this constant flow of water through the sensor providing
the ability to measure a process change in a very brief time so that
an excursion can be rapidly identified. This allows the operator to
immediately respond, preventing OOS water from being used in the
production process or contaminating the return loop to the UPW
storage tank.
Continuous Measurements Reduce the Uncertainly of
Organic Breakthrough
"An increase in TOC concentration can be the result of an increase
in potable water TOC or a decrease in water purification efficiency.
This decrease in efficiency can be due to the degradation of water
distribution components such as ion exchange resins, pump lubricating oils, polymer material dissolution, polishing resins, stagnant water zones and membrane erosion among other contributing
factors." (1)
TOC breakthrough resulting from deionization or mixed bed regeneration or ruptured RO membrane can give TOC spikes that are
quite small. These brief spikes are easily missed with on-line
sampling that is not frequent enough. Installation of new filters
with their required rinse-down process can cause a TOC spike lasting only a few hours. Unless the batch measurement coincides
within the few hours of the filter installation, this increase in TOC
can easily be missed and not detected. A continuous flow TOC detection device provides better resolution with data that is only a few
seconds apart enabling real time tracking of the water system
process and mitigating uncertainty associated with organic breakthrough missed by traditional batch systems.

eBook: TOC and Microbial Detection Monitoring

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