Gas Chromatography-Mass Spectrometry Paired with Total Vaporization Solid-Phase Microextraction as a Forensic Tool

The TV-SPME protocol is significant because it can analyze a wide range of samples, including drugs, racing fuels, explosive materials, and polycyclic aromatic hydrocarbons. No filtration is needed because only volatile analytes will vaporize. So dirty samples or suspensions can be analyzed.

Very simple matrices can be used, including organic or aqueous solvents. The main advantage of the TV-SPME technique is its high sensitivity. TV-SPME demonstrates better sensitivity than standard liquid injection, headspace SPME, and immersion SPME.

TV-SPME also has the benefit of utilizing large sample volumes without any changes to the GC instrumentation. TV-SPME is a very simple technique to perform. The main difficulty comes from ensuring the proper volume has been delivered.

The use of small manual or electronic syringes can help, as well as taking your time while sampling. It can also be difficult to ensure the fiber maintains its coating, so fibers must be monitored closely for degradation. Visual demonstration is crucial because both manual and robotic manipulations are required to be successful.

To begin, extract or dissolve the solid sample in enough solvent to reach the desired concentration. After ensuring that the sample is fully dissolved, calculate the volume needed to fully vaporize it at the chosen temperature. Transfer the sample volume into a headspace vial, and secure the cap.

If derivatizing the sample, prepare the proper derivatization agent by placing approximately one milliliter of the agent into a headspace vial. Set the proper incubation and extraction temperature, ensuring total vaporization, sufficient sample extraction, and complete derivatization. Select GC-MS parameters based on the class of the compounds of interest.

Ensure that the proper inlet liner is in the GC inlet and that the SPME fiber has been properly conditioned and is in good working order before beginning the analysis. Prepare a sample of gamma-hydroxybutyrate or gamma-butyrolactone in water, with a concentration of less than one part per million. Transfer one microliter of the sample to a 20-milliliter headspace vial, and cap the vial immediately.

Place one milliliter of BSTFA with 1%trimethylchlorosilane into a separate 20-milliliter headspace vial, and cap it. Create a GC-MS method by setting the initial oven temperature to 60 degrees Celsius for one minute, the oven program to 15 degrees per minute, the final oven temperature to 280 degrees for one minute, the flow rate to 2.5 milliliters per minute, and the inlet and transfer line temperatures to 250 and 280 degrees, respectively. Ensure a narrow SPME inlet liner has been placed inside the GC inlet and that the PDMS/DVB SPME fiber has been properly conditioned and is in good working order.

Then run the GC-MS on the sample. A GBL volume study was performed to demonstrate the sensitivity of TV-SPME compared to headspace and immersion SPME. Overall, sample volumes that allowed for TV-SPME demonstrated more sensitivity than headspace or immersion SPME for GBL in water.

A comparison of the chromatograms for each method is shown here. Samples of wine spiked with an effective dose of GHB and GBL were analyzed. These samples also show the interconversion of GBL and GHB.

When TV-SPME is performed properly, a sharp abundant peak is observed. TV-SPME has high sensitivity. Therefore, proper concentrations should be used as to not overload the column.

Peak asymmetry occurs when high concentrations are present. In these cases, diluting the sample or using a split injection can improve peak shape. TV-SPME could be paired with liquid chromatography, which would dramatically expand the range of detectable analytes.