The International Norm for the Measure of the TOC and the Carbons in Waters
Chronological and Critical Analysis

G. Visco, L. Campanella, V. Nobili

Department of Chemistry, Rome University "La Sapienza" P.le Aldo Moro 5, 00185 Rome

	The recent development of technologies applied to the environment follows the awareness of its protection as well as the improvement of a human life compatible with the ecosystem survival. The national laws, the community rules and the international conventions in this field, in strong evolution, induce a speeding up in the solution of problems related to the environment protection.
	In this connection some ecologists of both the industrial and research sectors demonstrated the interest to examine in detail measurable new parameters in the environment, descriptive of the quality of waters and useful in the control of the efficiency of  purifying treatments.
	In all the countries the analysis of the Total Organic Carbon (TOC) is recognised as the more suitable parameter for the control of civil and industrial wastes.
One of the more used analytical methods foresees the IR measure of the CO2 produced by the oxidation of the organic substances present in waters.
	The monitoring of the CO2, with the oxidative system, is the heart of TOC modern analysers. Taking into account the aggressiveness and complexity of some aqueous matrices, a CO2 detector must be robust and not subject to interference from other substances.
	IR spectrophotometry and conductivity measures are actually widely used thank to their sensitivity and selectivity (generally obtained by selective membrane in the case of conductivity) that resulted suitable for this kind of analysys.
	If corrosion processes are avoided, IR analysers result sensitive and stable (no measure drifts) devices with a linear answer in a wide range of measure. Among the IR detectors, in both portable and laboratory TOC analysers, NDIR (not dispersive infrared detector) is the more used as it ensures not only careful CO2 measures but also absence of interference from other gas heteroatomic as CO, NO, SO2 and NH3.
	Obviously, the accuracy of the measure depends very much from the efficiency of the oxidation system that differs as a function of the aqueous matrix and/or the aim of the analysis.
Mainly they are divided in “low temperature” (below 100 °C) and “high temperature” (680-1100 °C,) methods corresponding to different experimental procedures and technical instrumental specifications, further differences are due to different applications i.e. laboratory or “in situ” analysis, control of processes….
	It is certainly to mention the device based on the UV oxidation by a double wavelengths (254 and 185 nm) lamp that allows an oxidative different power.
	Many countries activated to create rules for the determination of the TOC in order to avoid that builders of scientific equipment manage at their commercial convenience on this field and, actually, builders must now follow rules imposed by internationally recognised organisms.
	The wide fields of application involving the TOC measurement render the TOC analysers indispensable not only for the "waters" (drinking, surface, waste) management but also for particular aims. Just as an example, some industries producing semiconductors or drugs need water of extreme purity. The international rules therefore impose the use of reference solutions, specific methods of measure and detection limits that must be respected by the instrumentation.
	For instance, since the January 1996 the analysis of the TOC (limit value 500 ppb) is compulsory for all the pharmaceutical waters due to the rules imposed by the USP (American Pharmacopoeia).
	At present, definitive rules on TOC measure are not laid down by law; so, we considered interesting to present the chronological list of the actual rules and of their content concerning the measurement method, the sensitivity and detection limit, the matrices that must be subjected to the control