Identification vs. Detection – Analysis Based on Concentration

For first responders the “unknown” can sometimes be the only “known” when responding to a chemical emergency.  With so many methods and tools at their fingertips, how do they know what to grab first?  Once a scene is cleared for initial hazards such as explosivity, flammability, radioactivity, and corrosivity, the initial personal protective equipment (PPE) can be selected. Next, the responder needs to quantify and classify or identify the chemical threat, if any, to determine toxicity.  This is generally initiated using clues such as victim symptomology, confirmed odors, colors, containers, and other key visual indicators. Unfortunately, this is often not enough information.

Identification for High Concentration Levels

A bulk chemical analysis tool, usually based on either Raman or Fourier transform infrared (FTIR) spectroscopy, for chemical identification is one of the first instruments pulled from the responders’ toolkit following initial scene reconnaissance. These handheld instruments may help identify the majority chemical constituents (i.e., components that are present in greater than 5-10%). Obviously, like any tool, not all chemicals are easily detected using Raman or FTIR spectroscopy and identification will only occur if the material is in the instrument’s library.


Raman Spectroscopy for Identification

Raman spectroscopy is especially useful as a first instrument of use post recon as it can scan through translucent packaging to analyze liquids, solids, powders, gels, and pastes.  Raman spectroscopy uses a laser to interact with molecular components and the resulting inelastic Raman scattering provides information about the molecule.  Raman scattering is used to generate a spectrum that is unique to the material scanned, like a fingerprint.  The spectrum is compared to a library of known compounds within the instrumentation, and if there is a match – the identification is determined. 

Detection for Low Concentration Levels

But what if the chemical in question is present in an extremely low concentration (such as <5 %)?  We know that some of the most dangerous chemicals and chemical combinations can be fatal at low levels of the active ingredient.  Fentanyl is one example of a chemical that can be harmful in doses generally too small to be seen by Raman and FTIR spectroscopy.   This is when a non-visible, or trace, analysis method can be pulled from the toolkit to detect the presence of a chemical.  There are many options available for trace detection, from colorimetric screening testing kits to mass spectrometers that can detect down to the ng or lower level.


Colorimetric Kits for Detection

Colorimetric detection involves the reaction of a chemical reagent to an unknown material or sample and observing the subsequent color change.  The color change indicates the presence of a common chemical functional group within a material.  

The Power of both Detection & Identification

Rigaku Analytical Devices has combined the power of both methods onto their handheld 1064 nm Raman unit so that it can be used to provide both detection and identification.  With the QuickDetect feature, users can swab a surface that may not have any visible material on it with a colorimetric kit that can then be scanned with the on-board camera of the Rigaku CQL Raman unit.  The Rigaku device can also be used to scan substances through packaging to identify a higher concentration of an active ingredient against a library of over 13,000 materials.

When would a user use the QuickDetect Feature vs. a Raman Scan?

  • To screen samples for threats in trace levels
  • As a complementary technique to Raman
  • For surfaces not in an optimal position relative to the unit’s laser focal point
  • As an alternative for potentially thermally sensitive material