Determination of Residual Chlorinated Solvents in Decaffeinated Coffee by Using Purge and Trap Procedure

Abstract

Abstract A purge and trap method developed for the analysis of volatile halocarbons (VHCs) in table-ready foods has been applied to the determination of residual chlorinated solvents in decaffeinated coffee. Samples are stirred in water and purged with nitrogen for 0.5 h in a water bath at 100°C. The analytes are collected on a duplex trap composed of Tenax TA and XAD-4 resin, eluted with hexane, and determined by gas chromatography (GC) with a thick-film, widebore capillary column and Hall electrolytic conductivity detector. The higher levels of residual chlorinated solvents are also confirmed by full scan GC/mass spectrometry. Samples are analyzed for several chlorinated solvents including methylene chloride, chloroform, 1,2-dichloroethane, methyl chloroform, carbon tetrachloride, trichloroethylene, and tetrachloroethylene. Eleven decaffeinated instant coffees and 14 decaffeinated ground coffees representing 9 different commercial brands were analyzed by this method. Residues of methylene chloride, chloroform, methyl chloroform, and trichloroethylene were found. Highest levels occurred in ground coffees—up to 640 ppb methylene chloride. Recoveries of these 4 chlorinated solvents detected from fortified samples ranged from 96 to 106%. Brews from 3 instant and 3 ground coffee samples contained up to 1.1 ppb and 4.8 ppb methylene chloride, respectively. In addition, the resulting grounds from the brewing process were analyzed and contained up to 14 ppb methylene chloride and up to 13 ppb trichloroethylene. The limit of quantitation for these coffee grounds was 4 ppb for methylene chloride. Chromatograms from this purge and trap method are clean, enabling levels of about 10 ppb and 0.4 ppb to be achieved for chlorinated solvents in decaffeinated coffees and their brews, respectively.