text: 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 concentration of carbon dioxide generated is measured with a non-dispersive infrared (NDIR) detector.
  Oxidation of the sample is complete after injection into the furnace, turning oxidizable material in the sample into gaseous form.  A carbon-free carrier gas transports the CO, through a moisture trap and halide scrubbers to remove water vapor and halides from the gas stream before it reaches the detector. These substances can interfere with the detection of the CO gas. The HTCO method may be useful in those applications where difficult to oxidize compounds, or high molecular weight organics, are present as it provides almost complete oxidation of organics including solids and particulates small enough to be injected into the furnace. The major drawback of HTCO analysis is its unstable baseline resulting from the gradual accumulation of non-volatile residues within the combustion tube. These residues continuously change TOC background levels requiring continuous background correction. Because aqueous samples are injected directly into a very hot, usually quartz, furnace only small aliquots (less than 2 milliliters and usually less than 50 - 100 microliter, with a maximum of approximately 300 - 400 micro-liters under special conditions; such as repetitive injections) of sample can be handled making the methods less sensitive than chemical oxidation methods capable of digesting as much as 10 times more sample. Also, the salt content of the samples do not combust, and so therefore, gradually build a residue inside the combustion tube eventually clogging the catalyst resulting in poor peak shapes, and degraded accuracy or precision, unless appropriate maintenance procedures are followed. The catalyst should be regenerated or replaced as needed. To avoid this problem the manufacturing industry has developed several concepts, such as matrix separation, ceramic reactors, better process control or methods without catalysts.