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

Abstract

SummaryA method has been developed for the quantitative extraction of nitrotoluenes (2,3-dinitrotoluene, 2,4-dinitrotoluene and trinitrotoluene) from water using a BakerbondTM 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 COz. 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 COZ 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 BakerbondrM 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 (2 = 0.995) from spiked controls, demonstrating that the method is quantitative.

Approaches for on-line coupling of extraction and chromatography

“…The solvating properties of the fluid are also decreased substantially during the depressurisation. Many SFE-GC applications have been published [128,129,130,131,132,133,134,135,136,137,138,139,140,141], and a few SFE-SFC [143,144,145,146] and numerous SFE-LC [147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173] applications have been reported. SFE-SFC applications are not covered in this review.…”

Multidimensional Chromatography: Forensic and Toxicological Applications

“…In his comprehensive text, Taylor provides an excellent description of the principles and applications of SFE (44), while Pawliszyn presents a description of the supercritical fluid as the mobile phase in his development of a kinetic model for the extraction process (45). Slack et al have provided an example one of of the many types of forensic and related analyses that can be performed by using SFE -GC (46). These authors analyzed several explosives from water using on-line SFE -GC and describe several of the method development considerations.…”

Supercritical fluid extraction strategies of liquid-based matrices

“…Slack et al [58] have used a phenyl sorbent contained within an SFE vessel for the analysis of explosives in water. With this arrangement water samples were aspirated through the support media prior to SFE.…”

“…Slack et al [58] added 20 ml of saturated sodium sulphate per litre of water prior to sample preconcentration using a phenyl sorbent. However, no details of improved extraction efficiency of explosives from water were reported.…”

“…Slack et at. [58] used a hot air gun to prevent the fused-silica restrictor from plugging, despite having vacuum dried the phenyl sorbent used for extracting explosives from water for 15 min prior to SFE. The incorporation of a stainless-steel collection chamber (heated to 100°C) between the extraction vessel and fused-silica restrictor eliminated freezing problems, allowing Ong et at.…”