EPA Method 1650 Adsorbable Organic Halides by Adsorption and Coulometric Titration

The standard "EPA Method 1650 Adsorbable Organic Halides by Adsorption and Coulometric Titration" published by the Environmental Protection Agency, known as EPA for short, is for the determination of adsorbable organic halides (AOX) and other organic halides amenable to combustion and coulometric titration associated with the Clean Water Act, the Resource Conservation and Recovery Act, and the Comprehensive Environmental Response, Compensation, and Liability Act. This method is designed to meet the research and monitoring requirements of the Environmental Protection Agency (EPA).

This method is applicable to the determination of adsorbable organically bound halogens (AOX) in water and wastewater. This method is a combination of several existing methods for organic halide measurements.

The method can be used to measure organically bound halides (chlorine, bromine, iodine) in dissolved or suspended form. Results are reported as organochlorides. The detection limit of the method is generally due to interferences rather than instrumental limitations. A method detection limit of 6,6 µg/L and a minimum level of 20 µg/L can be achieved without any interference.

This method may be used by or under the supervision of analysts experienced in the use of combustion/micro-coulometry. Each laboratory using this method must demonstrate the ability to produce acceptable results using the procedures described in this standard.

Before this method is applied, any remaining chlorine that may be present is removed by adding sodium thiosulphate. The pH of the samples is adjusted to a maximum of 2 and kept between 0 and 4 until analysis.

Organic halide in water is determined by adsorption on granular activated carbon, washing the adsorbed sample and granular activated carbon to remove inorganic halide, burning the sample and granular activated carbon to form hydrogen halide, and titration of hydrogen halide with a micro-coulometer.

The micro-coulometer (detector) works by maintaining a constant silver ion concentration in a titration cell. An electric potential is applied to a solid silver electrode to produce silver ions in the cell. When the hydrogen halide formed by the combustion of the organic halide enters the cell, it partitions into an acetic acid electrolyte where it precipitates as silver halide. The current produced is integrated over the combustion period. The electric charge is proportional to the number of moles of halogen trapped in the cell. The mass concentration of organic halides is reported as the equivalent concentration of organically bound chloride.

Adsorbable organic halides are defined as the analytes measured by this method. The nature of the organo-halides and the presence of semi-removable material affect the amount measured and the interpretation of the results.

At the time of collection, if the sample is known to contain free chlorine, the chlorine should be reduced to eliminate any positive interference that may result from continued chlorination reactions. Knowledge of the process by which the sample was collected can be valuable in determining whether dechlorination is necessary. The sample should be tested for residual chlorine immediately after collection.

During the acidification process, the pH value of aqueous samples is adjusted with nitric acid to a maximum of 2. Acidification inhibits biological activity and stabilizes chemical degradation, including possible dehalogenation reactions that may occur at high pH. Acidification is necessary to facilitate extensive adsorption.

During the cooling process, samples are kept at a temperature of 0 to 4 degrees from the moment of collection until analysis.

The sample amount is collected in an amber glass bottle of appropriate size for all quality control tests, not exceeding three days or six months from the collection date required for analysis. Samples are analyzed within a minimum of three days and a maximum of six months after collection.

Each laboratory using this method must operate a formal quality assurance program. The minimum requirements of this program consist of an initial demonstration of laboratory capability, ongoing analysis of standards and blanks as ongoing performance tests, and analysis of matrix spike and matrix spike replicate samples to assess accuracy and precision.

Our organization has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. Among the numerous test, measurement, analysis and evaluation studies provided for businesses in various sectors, there are also testing services in accordance with the standard "EPA Method 1650 Adsorbable organic halides by adsorption and coulometric titration".