Gas-chromatographic determination of trace amounts of vinyl chloride and dichloroethenes in water after purge-and-trap preconcentration and conversion into their dibrominated derivatives

Abstract

A method for the quantitative preconcentration and determination of vinyl chloride (VC) and the three isomers of dichloroethene (DCE) in water is presented. After addition of 200 g CaCl2 · 2 H2O and 5.0 nmol of vinyl bromide (VB) as internal standard, the analytes are stripped from a 1 l sample with a helium flow of 500 ml/min over a period of 30 min. The analytes are adsorbed in an ice-cooled adsorption tube filled with 1.0 g of a carbon molecular sieve, subsequently desorbed with carbon disulfide and transformed into their 1,2-dibromo-derivatives by reaction with bromine water at 40° C for 30 min. These derivatives are consequently determined by capillary gas chromatography with electron capture detection. The detection limits were found to be 1.6 (VC), 3.9 (1,1-DCE) and 1.9 ng/1 (σ 1,2-DCE), respectively. The method was tested with spiked water and natural samples and exhibited a linear range over four orders of magnitude combined with an overall relative standard deviation of less than 8%. The average total analyte recovery was confirmed to be quantitative. The influence of different parameters, including purge-gas flow-rate, temperature, salt-addition, ultrasound application and presence of surfactants, on the volatilization of the analytes were examined in order to evaluate different preconcentration concepts. Several adsorbents were tested for their applicability.