Total organic carbon (TOC) analysis measures the carbon content of dissolved and particulate organic materials in water. It’s nonspecific, meaning it tells how much organic carbon is present without identifying the contaminant. The carbon measured in TOC analysis may arise from any combination of living or dead organisms and chemical contamination.
Water utilities use TOC to monitor by-products of chlorination or ozonation. TOC often serves as a surrogate for more difficult measurements, for example, contamination from petrochemicals, solvents, pharmaceuticals, chlorinated industrial chemicals, and pesticides. It can also act as a screen for additional analysis. For example, pharmaceutical manufacturers might use liquid chromatography- mass spectrometry to analyze water samples containing unacceptable TOC values.
The two main approaches to TOC measurement involve either initial removal of inorganic carbon (mostly carbonate) followed by TOC measurement, or the subtraction of inorganic carbon from total carbon present. The four steps in TOC measurement are acidification to remove inorganic carbon, purging to release volatile organics (which are measured separately), oxidation of the remaining carbonaceous material, and detection. The latter two operations form the heart of TOC analysis. Several types of oxidation may be used: high- or low-temperature combustion, catalytic oxidation, photo-oxidation, thermochemical oxidation, or electrolytic oxidation.
Detection limits for TOC depend on the measurement technique used and the type of analyzer. Hightemperature (up to 950ºC) oxidation produces a sensitivity of 0.1 mg/L of carbon, while low-temperature methods (below 100ºC) are five times as sensitive, to about 0.02 mg/L. Response times for TOC analyzers vary widely, but instruments generally take five to fifteen minutes to report stable readings.
Online TOC analyzers are capable of continuous, unattended operation, but regular calibration, inspection, and maintenance by skilled technicians is required for reliable operation.
TOC analyzers are reasonably priced as lab instruments go. A basic unit costs approximately $20,000. Autosamplers will add to the cost, as will the addition of detectors for nitrogen or isotopic carbon.
“Over the past decade, the popularity of TOC analysis has been driven by regulations,” notes Steve Poirier, VP of business development at GE Power and Water (Boulder, CO). “Every pharmaceutical company that ships drugs into the U.S. and Europe is required to measure TOCs to certain specifications.” In the drug industry, high-purity water is used both for cleaning and in sterile drug products. The second regulatory front is the environment. According to Poirier, every municipality of greater than 10,000 population is required to control TOC to specified levels in drinking water.
“Additionally, some companies have demonstrated equivalency between TOC measurements and other tests and use TOC as the primary regulatory assay for releasing wastewater,” Poirier adds. The advantages are that TOC analysis is straightforward and does not require the specialized skill set of chromatography. “But in the end, most purchase decisions are based on productivity, and that comes down to analysis time or throughput,” Poirier says.
9210e
• Ensures processed and purified water is safe for human consumption
• Maintains excellent long-term calibration stability, providing accurate and dependable data with minimal maintenance
• Created using reagentless electrochemical oxidation technology developed for use on the International Space Station
• Efficiently oxidizes organic compounds using hydroxyl radicals, peroxides and ozone
OI Analytical
www.oico.com
Sievers InnovOx On-Line
• Supercritical Water Oxidization (SCWO) technique offers enhanced reliability, ease of use and low maintenance
• Handles difficult samples such as brine, humic acid and cellulose
• Features a dynamic linear working range of 0.5 to 50,000 ppm
GE Healthcare
www.geinstruments.com
Fusion
• Employs UV Persulfate oxidation for increased carbon liberation from challenging matrices
• Uses static pressure concentration (SPC) technology, for low-end sensitivity from a NDIR detector
• Allows unattended auto-calibration monitoring and automated self-diagnostic tools
Teledyne Tekmar
www.teledynetekmar.com
astroTOC UV Turbo
• Features a response time of less than 5 minutes with 100% oxidation
• Multi-point calibration compensates for background TOC in make-up water
• Available in ranges of 0-2000 up to 0-50,000 µg/l
• Housed in a spacious, robust, dual-compartment enclosure
Hach Company
www.hach.com
