Determination of 9 Haloacetic Acids in Air and Exhaust Gas by Adsorption Tube Sampling Gas Chromatography

Nine halogen acetic acids in air or waste gas were collected with an adsorption tube packed with silica gel, desorbed with water and then determined simultaneously by gas chromatography. At the front and the end of the adsorption tube, 200 mg and 100 mg of silica gel were packed separately and the tube was connected with the air-sampler to collect the halogen acetic acids at an air flow-rate of 0.5 L·min^-1 for 40 min. The silica gel with the adsorbed acids were transferred to 2 test tubes separately and each of the silica gel was desorbed ultrasonically twice in succession with 5 mL of water and for 5 min in each desorption. The two desorption solutions were transferred to a separatory funnel in which 30 mL of water were added previously. 2 mL of H₂SO₄ acid were added to make the acidity of the solution less than pH 0.5, thus to keep the analytes in their forms of acid molecules. After adding 8 g of NaCl, 4 mL of internal standard solution (containing 4.00 mg·L^-1 of 1,2,3-trichloropropane which was used as internal standard) were added and extracted for 3 min. After staying and phase-separation, 3 mL of the upper etheric phase were taken and placed in a separatory funnel, 3 mL of a freshly prepared H₂SO₄-CH₃OH (2+8) solution were added, and esterification was performed at 50℃ for 2 h under tightly sealed condition with constant magnetic stirring. After cooling, wash the reaction mixture successively with 7 mL of 250 g·L^-1 NaCl solution and 1 mL of sat'd NaHCO₃ solution. The upper etheric solution was taken for GC analysis as described in the instrumental-working condition. It was shown that linear relationships were found between mass concentrations of the 9 halogen acetic acids (i.e., monochloro acetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid, tribromoacetic acid, monobromomonochloroacetic acid, monobromodichloroacetic acid and monochlorodibromoacetic acid) in the same range of 0.001-2.0 mg·m^-3 and the ratios of peak areas of the respective methyl halide to the internal standard. Detection limits (3S/N) for the 9 compounds were found in the range of 0.2-1.0 μg·m^-3. Tests for recovery and precision were made separatly, giving values of recovery in the range of 91.6%-116% and of RSDs (n=6) in the range of 4.3%-7.9%.