Teledyne Tekmar recently released a new guide that compares Total Organic Carbon analysis techniques. The guide provides important details for users and recommends the best instrument for your specific application. TOC analysis, which is used in a variety of labs, is a technique employed to determine water cleanliness and purity. It is a required test by the United States Pharmacopoeia (USP), European Pharmacopoeia (EP) and Japanese Pharmacopoeia (JP), and is frequently used to monitor wastewater, soils and drinking water safety.
Carbon analysis started in the 1630s when scientist Jan Battist Van Helmont discovered Carbon Dioxide. In 1756, Joseph Black discovered a way to measure Carbon Dioxide, and the method became more refined in 1924. American Cyanamid developed the infrared gas analyzer in 1948, and in 1967, DOW chemical patented a carbon content measuring system that manually injected aqueous samples directly into a gas stream of oxygen. Since that time, manufacturers have made a number of technology advances to continue to meet customers changing needs.
Labs in the biotech and pharmaceutical industries use TOC in cleaning validation procedures, including Clean-in-Place. TOC concentration levels can also be used to track success of cleaning procedures to ensure there is no cross-contamination. Protecting drinking water is a major focus for local, state and national organizations and governments, and TOC analysis popularity has increased because of the need to test wastewater and municipal water for organic matter. The guide reads, “When high organic content water is subjected to the disinfection process during normal purification, it will create disinfection by-products, which are carcinogenic. It is important to make sure the TOC is low in water coming in and water leaving the water treatment facility to ensure public safety.”
The guide reviews three primary oxidation techniques used by TOC analyzers today:
- Catalytic combustion – sample is injected into a catalyst packed tube, which is enclosed in a furnace at 680 ̊C -1000 ̊C. The combination of the temperature, an oxygen-rich environment and a catalyst oxidize the carbon in the sample to C0 The C02 is then swept to the Non-Dispersive, Infrared (NDIR) detector.
- UV persulfate – an aliquot of sparged sample is transferred to a UV reactor where the oxidation power comes from a combination of sodium persulfate and UV light.
- High temperature ceramic – sample is injected into a furnace up to 1800 ̊C with a stream of oxygen. There is no catalyst needed for this oxidation process. The CO2 is then swept to the NDIR detector.
The guide also reviews they types, strengths and weaknesses of NDIR detectors, including their inability to handle halogenated compounds and their challenges with moisture. Teledyne also highlights other detection methods, including:
- Conductivity – Measures the sample before and after oxidation with the difference yielding the amount of TOC
- Membrane conductivity – Uses hydrophobic gas permeation membrane for greater discrimination for dissolved CO2 over other chemical compounds.