Importance and Limitations of the TOC analysis - Influences of the sample composition
The importance of TOC determination in medical technology
In medical technology in particular, TOC measurement plays a crucial role in checking the cleanliness of medical devices as part of the validation of cleaning processes and the monitoring of final cleaning. TOC determination helps by measuring the amount of organic residues that remain on the products after cleaning or that should no longer be present.
In addition, TOC determination is also used to monitor cleaning baths by regularly testing the cleaning medium for contamination with organic impurities. The continuous monitoring of cleaning media and systems is used for the early detection of problems and malfunctions before the cleanliness of the medical devices is impaired.
As part of the validation of manufacturer instructions for the reprocessing of reusable medical devices, the TOC determination also serves to check the effectiveness of the prescribed cleaning and disinfection without leaving significant and harmful organic residues.
The TOC value serves as a sum parameter for water-soluble organic residues. These residues can originate from cleaning agents and disinfectants or other process auxiliaries, among other things. Compliance with the cleanliness requirements in accordance with ISO 19227 and DIN EN ISO 10993-18 is essential for the safety of medical devices.
Technische Details zur TOC-Messung
Probenvorbereitung: Vor der TOC-Messung müssen die Proben häufig vorbehandelt werden, um anorganischen Kohlenstoff (TIC; Total Inorganic Carbon) zu entfernen. Dies geschieht durch Zugabe von Säure und Austreiben des CO₂. Anschließend wird der verbleibende organische Kohlenstoff (NPOC; Non-Purgeable Organic Carbon) oxidiert und gemessen.
Oxidationsmethode: Die TOC-Messung erfolgt häufig durch katalytische Verbrennung bei hohen Temperaturen (z.B. 680 °C bis 720 °C) oder durch UV-Oxidation. Bei CleanControlling wird die katalytische Verbrennung über einen Katalysator genutzt, um organische Verbindungen effizient zu CO₂ zu oxidieren.
Detektionsmethode: Die Detektion des erzeugten CO₂ erfolgt über einen nichtdispersiven Infrarotsensor (NDIR), bei dem die Absorption von Infrarotlicht durch CO₂-Moleküle gemessen wird. Diese Art der Detektion zeichnet sich durch eine hohe Empfindlichkeit und Genauigkeit aus.
The problem with TOC analysis
If a sample has a high salt content, a very high level of contamination with organic compounds or a strongly basic/acidic pH value, this can lead to considerable problems in the TOC determination. CleanControlling uses platinum wool as a highly sensitive catalyst in the TOC analyzer. The catalyst is crucial for the oxidation of organic compounds to carbon dioxide (CO₂). If such problematic samples are introduced into the catalyst, it can corrode or become contaminated and lose activity. This can damage the catalyst and lead to inaccurate measurement results.
Solution
In some cases, the samples can be diluted to protect the catalyst. It should be noted that if the dilution is too high, the TOC value may fall below the limit of quantification (LOQ), which means that quantification of the TOC is no longer possible. The procedure should therefore be agreed in advance with the laboratory's test management.
Conclution
The measurement of total organic carbon (TOC) is an indispensable method for ensuring the cleanliness of medical devices. Despite its widespread use and importance, TOC analysis can be significantly affected by various sample characteristics. High salt contents, strong organic impurities or extreme pH values can negatively influence the accuracy of the measurement and damage the sensitive platinum wool catalyst.
Careful sample preparation and an adapted procedure are required to ensure reliable and accurate measurement results. Dilution of problematic samples can be a solution, but must be carried out with caution and in consultation with the test supervisor in order not to fall below the quantification limit.
Overall, this means that despite its challenges, TOC analysis plays an important role in quality assurance and can be optimized through targeted measures.
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