Total organic carbon
[1] For marine surface sediments average TOC content is 0.5% in the deep ocean, and 2% along the eastern margins.
Another common variant of TOC analysis involves removing the TIC portion first and then measuring the leftover carbon.
This method involves purging an acidified sample with carbon-free air or nitrogen prior to measurement, and so is more accurately called non-purgeable organic carbon (NPOC).
One analysis technique involves a two-stage process commonly referred to as TOC differential method.
The remaining non-purgeable organic carbon (NPOC) contained in the liquid aliquot is then oxidized releasing the CO2 gases.
Modern TOC analyzers perform this oxidation step by several processes: Prepared samples are combusted from 1000 up to 1200 degrees C in an oxygen-rich atmosphere.
[6] A manual or automated process injects the sample onto a catalyst in a combustion tube operated from 680 up to 950 degrees C in an oxygen rich atmosphere.
The major drawback of HTCO analysis is its unstable baseline resulting from the gradual accumulation of non-volatile residues within the combustion tube.
To avoid this problem the manufacturing industry has developed several concepts, such as matrix separation,[8] ceramic reactors,[9] better process control or methods without catalysts.
Limitations include the inaccuracies associated with the addition of any foreign substance into the analyte and samples with high amounts of particulates.
Performing "system blank" analysis, which is to analyze then subtract the amount of carbon contributed by the chemical additive, inaccuracies are lowered.
Conductivity and non-dispersive infrared (NDIR) are the two common detection methods used in modern TOC analyzers.
A region of absorption of infrared light specific to CO2, usually around 4.26 μm (2350 cm−1), is measured over time as the gas flows through the detector.
A second reference measurement that is non-specific to CO2 is also taken[clarification needed] and the differential result correlates to the CO2 concentration in the detector at that moment.
As the gas continues to flow into and out of the detector cell the sum of the measurements results in a peak that is integrated and correlated to the total CO2 concentration in the sample aliquot.
A variation described as "membrane conductometric detection can allow for measurement of TOC across a wide analytical range in both deionized and non-deionized water samples.
Modern high-performance TOC instruments are capable of detecting carbon concentrations well below 1 μg/L (1 part per billion or ppb).
[12] Gulf Coast Waste Disposal Authority (GCWDA), Bayport Industrial Wastewater Treatment Plant in Pasadena, Texas sponsored and conducted this test in 2011.
Field tests were conducted for a period of 90-days and used laboratory conformance measurements once per day to compare with analyser output to demonstrate the instrument's overall accuracy when subjected to many simultaneously changing parameters as experienced in real-time monitoring conditions.
After removal of inorganic carbon persulfate is added and the sample is either heated or bombarded with UV light from a mercury vapor lamp.
TOC is the first chemical analysis to be carried out on potential petroleum source rock in oil exploration.
TOC detection is an important measurement because of the effects it may have on the environment, human health, and manufacturing processes.
In addition, low TOC can confirm the absence of potentially harmful organic chemicals in water used to manufacture pharmaceutical products.
Some detergents, pesticides, fertilizers, herbicides, industrial chemicals, and chlorinated organics are examples of synthetic sources.
Safe Drinking Water Act in 2001, TOC analysis emerged as a quick and accurate alternative to the classical but more lengthy biological oxygen demand (BOD) and chemical oxygen demand (COD) tests traditionally reserved for assessing the pollution potential of wastewaters.
Recently published analytical methods, such as United States Environmental Protection Agency (EPA) method 415.3,[17] support the Agency's Disinfectants and Disinfection Byproducts Rules, which regulate the amount of NOM to prevent the formation of DBPs in finished waters.
Numerous evaluation methods have been introduced, including these based on wireline logs and in situ techniques.
[21] For this reason, TOC has found acceptance as a process control attribute in the biotechnology industry to monitor the performance of unit operations comprising water purification and distribution systems.
As many of these biotechnology operations include the preparation of medicines, the U.S. Food and Drug Administration (FDA) enacts numerous regulations to protect the health of the public and ensure the product quality is maintained.
Due to the quality requirements of semiconductor water, TOC must be monitored at the parts per billion level.
