A New Approach to Total Organic Carbon Analysis Using Closed-loop Photocatalytic Oxidation

TOC is the acronym for total organic carbon. The first TOC methods were developed to correlate information obtained from chemical oxygen demand (COD) and biochemical oxygen demand (BOD) tests in drinking and wastewater. Today new government regulations are making TOC analysis a standard test for all industry water types. This paper discusses the principles of operation of common TOC methods and outlines a new methodology for TOC analysis using closed-loop photocatalytic oxidation. The new TOC methodology includes a titanium dioxide slurry and a 400 nm light source for the oxidation process. The closed-loop TOC system incorporates a closed-loop design to eliminate the need for carrier gases and uses what is called dynamic endpoint detection, where all of carbon in the sample is oxidized to completion. The reaction is measured using a non-dispersive infrared (NDIR) detector. This new technology can directly measure TOC from a single sample eliminating the loss of purgable organics and results in comparable recoveries of various organic compounds when compared to the combustion TOC method. This new methodology can be used for the same applications where the traditional TOC methods have been employed. INTRODUCTION TOC is the acronym for total organic carbon. The first TOC methods were developed to correlate information obtained from chemical oxygen demand (COD) and biochemical oxygen demand (BOD) tests in drinking and wastewater. The TOC methods were designed to be more efficient than the COD and BOD tests, which required the use of hazardous chemicals and multiple days to complete. Today new government regulations are making TOC analysis a standard test for all industry water types. The Environmental Protection Agency (EPA) has instituted rules to monitor municipal drinking water systems. The main reason for measuring TOC in drinking water is that chlorine, the primary drinking water disinfectant, has the potential to react with some organic compounds in the water to form chlorinated hydrocarbons which have been associated with carcinogenic activity. Drinking water is the feedwater for most water purification systems. Monitoring this feedwater is critical to maintaining the overall efficiency of any water purification process. The water’s characteristics such as hardness, particulates, bacterial levels, conductivity, and TOC levels significantly influence downstream processing. The power generation industry recognizes organic carbon as a significant corrosion contributor. Some carbon compounds found in water are a source of corrosive acids that can reduce the life of boilers, reactors and turbine blades. High-purity water is necessary for continuous operation of power facilities. TOC levels in ultrapure water such as that used in the semiconductor industry have been found to be a major contributor to increased product defects. Today, device geometry reductions accompanied by increases in circuit densities are imposing challenging demands on the purity of water used. Semiconductor manufacturers must monitor TOC levels in all stages of the water purification, most importantly at the point-of-use. Since even the slightest change in TOC levels can affect production yield, the industry has incorporated on-line TOC monitoring to provide trend information throughout the entire water purification process. Today, TOC levels in semiconductor process water are being controlled to below 1 ppb. Finally, and most recently, TOC regulations are now a part of the pharmaceutical industry. The United States Pharmacopeia (USP) has made TOC analysis a standard test for production of Purified Water and Water For Injection. Measurement of TOC is a direct reflection on the quality of the water being produced and can have a significant impact on the manufacturing process of drug products. This paper discusses the principles of operation of common TOC methods and outlines a new methodology for TOC analysis using closed-loop photocatalytic oxidation. COMMON METHODS FOR MEASURING TOC TOC methods share the same basic chemistry of converting all the carbonaceous material in a given sample to a form that is more readily measures, such as CO2. The oxidation and detection technologies vary based on the specific analysis method, and each technique is appropriately applied to different TOC concentration levels. COMBUSTION OXIDATION The combustion method measures total carbon (TC). It requires samples injection by syringe into a hightemperature furnace with a platinum or cobalt catalyst. This process oxidizes all of the carbon materials present to CO2. The CO2 is swept into a non-dispersive infrared (NDIR) detector by a carrier gas usually nitrogen for final measurement. The amount of CO2 measured is directly proportional to the amount organics present in the original sample. A variation of this method employs a stream splitter, which directs equal parts of the sample to two furnaces at different temperatures. One furnace at 150o C measures the total inorganic carbon (TIC) present and the other at 950o C measures the total carbon (TC) present. The final total organic carbon (TOC) amount is then calculated by: