Moisture Control In Total Organic Carbon Analyzers

Total organic carbon (TOC) is a valuable parameter since it is present in every sample that is analyzed by laboratories in the analytical, environmental, and pharmaceutical industries. TOC is part of what is referred to as total carbon (TC). TC consists of TOC and inorganic carbon (IC). TOC can be further subdivided into purgeable organic carbon (POC) and non-purgeable organic carbon (NPOC), depending on the type of carbon and solubility in water.

TOC is mainly measured by using either catalytic combustion oxidation or wet chemical persulfate oxidation. Catalytic combustion oxidation involves combusting the sample at a high temperature in the presence of a catalyst, while wet chemical persulfate oxidation involves mixing the sample with a persulfate oxidizer, heated at 80 oC, and UV irradiated (1,2). During either process, moisture might be generated from the oxidation process. The oxidation process converts the carbon within the sample to carbon dioxide, which is later detected by either conductivity or non-dispersive infrared (NDIR) detectors.

NDIR detectors are considered more stable detectors than conductivity detectors and, as a result, are more popular. NDIR detectors are less susceptible to the interferences affecting sensitivity and results that afflict conductivity detectors. Interferences that affect the conductivity detectors include pH, temperature, and ions in solution that lead to high recoveries. Also, conductivity detectors are affected by interferences from gases such as chlorine dioxide, sulfur dioxide, or other noxious gases.

Whether measuring TC, IC, TOC, POC, or NPOC, using an NDIR ensures good reproducibility and accuracy of the data. During the oxidation process, moisture might be generated as mentioned earlier. The generated moisture can contaminate the detector and increase the required maintenance. Moisture can be removed using different dehumidifiers, such as the Peltier cooler and Permeation dryer.