How to Use a GC-IR Hyphenated System to Distinguish Structural Isomers


Problem: Legally sold as “Vanilla Sky” and “Ivory Wave,” bath salts have become very popular for the very dangerous “high” they are providing. Packets of bath salts containing mostly white powder can be purchased at truck stops and convenience stores throughout the U.S. This “super coke” is said to contain Lidocaine and Methylenedioxypyrovalenone (MDPV), a non-schedule drug with very powerful stimulant properties. MDPV provides sensations similar to those experienced through cocaine use, such as euphoria and physical and mental stimulation. However, there is also a wide range of undesirable side effects, such as chest pains, increased blood pressure, increased heart rate, agitation, hallucinations, extreme paranoia, delusions, and fiending.

In the U.S., southern states have begun to ban bath salts due to numerous incidents linked with its ingestion, snorting, smoking or injection and criminal cases involving the use of bath salts are increasing rapidly. For proper criminal proceedings, identification of active ingredients and other species in the seized drug samples of bath salts must be definite and conclusive. In particular, analogs (for example, positional and stereo isomers) of controlled substances must be properly identified.

For conclusive qualitative analysis, The Scientific Work Group for the Analysis of Seized Drugs (SWGDRUG) requires: (1) a minimum of two analytical methods to form an acceptable analytical method, and (2) that each method must yield conclusive and definite results (precluding false positives). Many labs use GC-MS hyphenated systems coupling gas chromatography (GC) and mass spectrometry (MS) for their resolution, sensitivity in analysis, and high level of availability. However, these systems do not fully meet the two criteria set forth by the SWGDRUG. For the identification of structural isomers, MS only provides information consistent with isomer class identification, proving to be inconclusive for the identification of individual isomers. Therefore, isomer retention time as determined through GC is the only true means of differentiating one isomer from another within a class when using a GC-MS hyphenated system. In these cases, access to another detection method besides MS—one which would provide complementary, “orthogonal” information—would be extremely useful in confidently identifying an isomer’s structural assignment.

Spectra Analysis Instruments’ DiscovIR system.

Solution: Spectra Analysis Instruments, Inc. has developed DiscovIR™, the first commercially available hyphenated system with infrared spectroscopy as the detection module and gas or liquid chromatography as the separation module. With the DiscovIR, individual isomer identification is made possible through definitive retention time values as well as individual IR spectra. When connected to the outlet of a GC column, the DiscovIR deposits GC eluants as a continuous solvent-free track on an infrared transparent substrate. The built-in interferometer simultaneously captures a set of time-ordered infrared spectra from the deposition track. Because of the unparalleled specificity of infrared spectroscopy, the GC-IR hyphenated system enables sharp discrimination among structural isomers and provides conclusive identification of each substance being tested.

To add to this, the DiscovIR automatically generates full IR spectra for each eluant or peak which can be compared to the solid-phase IR libraries. The included library of over 10,000 compounds can be expanded through access to private or commercially available libraries, and compounds can be added by the user as they are encountered. Another key feature of infrared analysis is that absorption at a certain wavelength is in direct proportion to the amount at hand. Therefore, relative quantities can be determined with confidence, avoiding errors due to disparity in ionization or presence of chromophores.

The DiscovIR meets both criteria set forth by the SWGDRUG in one single instrument and is able to perform definitive qualitative analysis and identification of bath salts as well as other illegal substances.

For more information about the DiscovIR, go to: or contact us at +1.508.281.6232

Categories: How it Works

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Published: September 9, 2011

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