tailieunhanh - Chemical Pollutants in Air, Water, Soil, and Solid Wastes Phần 5

Phổ biến nhất trong các loại chất ô nhiễm đất là hydrocacbon, kim loại nặng, MTBE, thuốc diệt cỏ, thuốc trừ sâu, và các hydrocacbon clo hóa. | PHENOLS Phenols are organic compounds containing an -OH group attached to an aromatic ring. The structure of phenol the prototype compound of this class is OH Although the presence of other substituents in the ring can produce an array of diverse compounds of entirely different properties the chemical analysis of most phenols however can be performed in the same way. Tins is attributed to 1 the acidic nature of the phenolic -OH group and 2 that the -OH group can form derivatives. Trace amounts of phenols may occur in many natural waters as well as in domestic and industrial wastewaters. Chlorination of such waters can produce chlorophenols. Several phenolic compounds occurring in industrial wastewaters soils sediments. and hazardous wastes are classified as . EPA priority pollutants. These are presented in Table . The total phenolic compounds in an aqueous sample can be determined by a colorimetric method using 4-aminoantipyrine. Tins reagent reacts with phenolic compounds at pH 8 in the presence of potassimn ferricyanide to form a colored antipyrine dye. the absorbance of which is measured at 500 mn. The antipyrine dye may also be extracted from the aqueous solution by chloroform. The absorbance of the chloroform extract is measured at 460 nm. The sample may be distilled before analysis for the removal of interfering nonvolatile compounds. The above colorimetric method determines only ortho- and meta-substituted phenols and not all phenols. When the pH is properly adjusted certain parasubstituted phenols which include methoxyl- halogen- carboxyl- and sulfonic acid substituents may be analyzed too. 1997 by CRC Press LLC .