Coupled solid phase extraction–supercritical fluid extraction–on‐line gas chromatography of explosives from water

Abstract

Abstract A method has been developed for the quantitative extraction of nitrotoluenes (2,3‐dinitrotoluene, 2,4‐dinitrotoluene and trinitrotolugene) from water using a Bakerbond TM phenyl sorbent. The average solid phase extraction recoveries for spiked standards ranged from 80 to 95 percent for reagent water and 52 to 95 percent from well and surface water in the low ppb and ppt levels. After the nitrotoluenes had been trapped on the solid sorbent they were quantitatively eluted using SFE. Adding toluene to the extraction cell increased the rate of extraction, but did not improve analyte recovery versus unmodified CO 2 . The extracts were analyzed off‐line with GC–ECD using an internal standard. Extraction losses were due to analyte breakthrough, and not from poor SFE recoveries. This demonstrates that supercritical fluid extraction is a suitable elution technique for analytes trapped on solid phase extraction sorbents. Also, a method for the direct on‐line coupling of SPE to GC, using SFE, has been developed and evaluated. Supercritical CO 2 is ideal for directly coupling SPE to GC, since carbon dioxide is a gas under ambient conditions. One potential problem of on‐line SPE–SFE–GC is the presence of residual water trapped on the active sites of the Bakerbond 13 phenyl sorbent. This problem was dealt with by using a split interface previously described by Hawthorne . From the results of this study, the relative standard deviation of the on‐line SPE–SFE–GC interface was determined to be between 4 and 10 percent. In addition, there was no significant difference in the precision of the method with or without the use of an internal standard. A calibration curve was also constructed ( r 2 = 0.995) from spiked controls, demonstrating that the method is quantitative.