eBook: TOC and Microbial Detection Monitoring - 6

compounds are tested against competitive analyzers in order to
highlight weaknesses in one technology vs. another are typically
competitor-funded and often do not represent real-world use of a
TOC measurement system. Pure and Ultrapure waters may contain different organic compounds, each representing one of thousands that may be present in a water purification system and
make up the TOC measurement. Water purification systems do
not selectively remove one type of organic compound but let another one pass. TOC is a non-specific indicator of organic contamination just as conductivity is a non-specific indicator of ionic contamination.
The purity of the water sample being monitored should be considered when selecting a TOC instrument. Customers with concerns
about specific contaminants that may exist in their source water
are encouraged to evaluate the TOC system of their choice directly on their water system before dismissing any instrument's effectiveness.

Both sensor and analyzer configurations use proven technology to
reliably detect TOC of the measured sample when used according
to manufacturing guidelines. This multi-parameter approach
used by METTLER TOLEDO provides users with a variety of choices. Single or multiple TOC sensors can be connected or any combination of other sensor parameters such as conductivity, ozone,
pH, or flow, all commonly used measurement parameters for water
system monitoring.

Advantages and Disadvantages of a UV Detect Technologies
UV lamps used for oxidation typically emit two wavelengths: 185
nm and 254nm. Some TOC analyzers monitor only the loss of
potency of the 254nm wavelength during the typical lamp aging
process. This provides an incomplete and potentially inaccurate
picture since the aging of the 185nm and 254nm occurs at different

Do all TOC Sensors respond equally well to all compounds?
No single TOC system responds perfectly to all organic compounds and all TOC monitoring systems are susceptible to interferences. Laboratory generated studies where certain organic

TOC
Measurement
Device



Real-Time Compliance

Sensors and Analyzers: Is there a difference?
Some TOC technologies are promoted as "analyzers" with all of the
components in one device for the primary purpose of measuring
TOC. The METTLER TOLEDO design separates these components
into a TOC measuring "sensor" supported by a separate transmitting device, which by its design is capable of supporting not only a
TOC sensor but other sensors as well. Some TOC manufacturers
claim all TOC sensors are less accurate than TOC Analyzers but
these claims are misleading and far from the truth. As previously
noted, all TOC measurement devices (Figure 1) used for measuring
regulated water systems utilize UV oxidation and a differential
conductivity measurement of a pre and post sample to determine
TOC.

UV
Lamp

Conductivity
Sensors

Detection
Algorithms

Output
Device

Figure 1: TOC Measurement process for both sensors and analyzers

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eBook: TOC and Microbial Detection Monitoring

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