TOC Analysis Moving from Laboratory Testing to On-line Analysis

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c) Verifying the TOC calibration against USP-traceable TOC standards The GMP-critical on-line TOC analyser is used to demonstrate that the TOC level in the PW or WFI water system is 85%
e) Verifying the UV lamp Correct operation of the UV lamp is fundamental to the TOC analysis. Robust on-line TOC analysers will measure the UV lamp output and have main and stand-by UV lamps to ensure 100% up-time should one of the UV lamps fail. When UV lamps age, their UV output falls and TOC oxidation times are extended. The on-line TOC analyser must be designed to monitor the oxidation process and adjust it’s oxidation cycle time to allow for varying amounts of TOC and ageing UV lamps, otherwise the TOC analyser will report incorrect TOC levels. Either using an external UV meter, or using the analyser’s built-in diagnostics, verify that the main and standby UV lamps are working correctly. CONCLUSION TOC Analysis – Moving from laboratory to on-line monitoring. March 2008 by Hach Ultra Figure 10: Verify the Main and Standby UV lamps are working correctly When moving from laboratory-based TOC analysis to on-line TOC analysis, it is important to consider the type of TOC analyser to be used. The complex design used in the wide-ranging membrane conductivity lab-based TOC analyser is not suitable for un-manned, on-line TOC analysis for the following reasons: Laboratory membrane-based TOC analysers: • Calibration is not stable and frequent re-calibration is required • Not possible to verify the calibration of the conductivity cells used to measure TOC • Not possible to verify or validate the calibration of the temperature compensation sensors • TOC result affected by flow rate changes caused by pressure fluctuations in PW or WFI system • TOC result dependant on UV lamp age, i.e. it is a flow-through design and the water is exposed to the oxidising UV lamp for a fixed period, so, as the lamp intensity decreases with age, the TOC analyser will tend to under-report the TOC present in the water Direct Conductometric TOC analysers are stable and robust and the Anatel PAT700 is specifically designed to support compliance and allows verification and calibration to all the pharmacopoeial requirements: Direct Conductometric on-line TOC analysers: • Calibration is stable and supports 6-monthly re-calibration intervals • The calibration of the conductivity cell used to measure TOC can be verified • The calibration of the temperature compensation sensor can be verified • TOC result is not affected by flow rate changes caused by pressure fluctuations in PW or WFI system (the Anatel takes a sample aliquot and fully oxidises the TOC content) • TOC result is not dependant on the level of the UV lamp output, i.e. the water sample aliquot exposure to the oxidising UV lamp is extended until all the TOC is fully oxidised. So, despite the lamp intensity decreasing with age, the TOC analyser will always report the correct TOC present in the water • UV lamp monitoring and ‘main’ and ‘standby’ UV lamps to ensure that lamp failure is detected and that the analyser provides 100% up-time using the ‘standby’ UV lamp whilst the maintenance teams arrange the failed lamp replacement. 7 of 7
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TOC Analysis Moving from Laboratory Testing to On-line Analysis

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