Chromatographers dealing with volatile compound determination know very well how popular the static headspace technique is in many application fields since it offers benefits of ease-of-use, low cost of operation and high degree of automation.
Forensic and toxicology laboratories are taking advantage of the simplicity of this technique as well, particularly for the analysis of volatiles in biological samples, with almost no sample manipulation. In fact, headspace-GC analysis is the gold standard for automating volatiles extraction and quantitation from biological fluids and tissues, for intoxication assessment or for post-mortem studies.
Nevertheless, forensic labs need more than highly-automated and reliable sampling solutions. Of course, extended unattended workflows are a plus to support the laboratories in keeping up the high demand for services, but this would not be enough without assuring highly accurate and defensible data.
Alcohol is one of the most widely-tested chemicals in forensic laboratories and the numerical analytical results carry probative weight of evidence in driv
ing under influence (DUI) or driving while intoxicated (DWI) cases, impacting on prosecutor decision. Measured Blood Alcohol Concentration (BAC) is therefore required to be reliable, accurate, precise, repeatable, traceable, verified and true. The legal limit for alcohol concentration in blood is usually expressed in grams per deciliter (g/dL) and local legislation imposes acceptable limits before a person is charged with a crime.
The average BAC permitted across the majority of the EU Countries is 0.05% (0.05 g/dL of blood), with some countries as England and Wales allowing 0.08%, as well as in the majority of the US. Sweden and Norway have more stringent limits to 0.02%. In some countries like Brazil, zero-tolerance BAC laws are enforced.
The method of choice -- almost accepted world-wide -- uses a static headspace sampling followed by a GC-FID or GC-MS analysis, which allows for fast qualitative and quantitative analyses.
The most affordable solution is represented by a dual column/dual FID configuration run in isothermal conditions to combine the maximum throughput with ID confirmation in the same run. The sample is actually split into the two analytical columns after the injection. The two dedicated columns, having different stationary phases with different polarity, provide different separation and different retention time for the same analytes. This approach is helpful not only for ID confirmation of the ethanol peak with two RT values, but it is also useful to figure out possible interferences and coelution. Besides, the analysis is performed in an isothermal condition for a faster analytical cycle time, with the separation obtained in less than three minutes.
One of the main challenges related to BAC determination is to assure no carryover from previous injections, possibly leading to overestimation or, in some cases, to false-positive results after running high concentrated samples. Another possible issue can be related to a non-linear ethanol calibration, due to poor instrument performance or inadequate method optimization.
The Thermo Scientific™ TriPlus™ 500 Headspace autosampler
, based on valve and loop technology and featuring an innovative direct column connection design, offers forensic laboratories high performance in terms of repeatability, linearity, no carryover and excellent recovery for accurate quantitative data.
You can learn more about the method and the achievable results in this dedicated Application Note.
Such superior performance has been recently confirmed once more in our Centre of Excellence in the UK
, during a successful demonstration to an important forensic laboratory.
The key benefits for the customer were the high vial capacity of the TriPlus 500 HS (240-vials) to support high sample throughput, the Barcode Reader capability which saves data entry time and eliminates sample loading errors, higher data quality, extended calibration range (1-1000 mg/dL) and lower carryover.
On top of the analytical advantages, the lab greatly valued the Thermo Scientific™ Chromeleon™ CDS
, offering time-saving tools, advanced reporting options and full traceability of the results.
Additionally, different carrier gas options have been demonstrated, offering an alternative cost-saving solution with Nitrogen carrier gas (full baseline separation of all components in 3 min) or a throughput boost solution with hydrogen carrier gas with a completed separation in 1.5 min, with no compromise in the data quality.
With no doubts, forensic laboratories can rely on innovative technology to ultimately improve productivity and data traceability while supporting results defensibility in DUI and DWI cases.