What we use

Fourier-transform infrared (ATR-FTIR) spectroscopy is The Loop’s primary analysis method because it is fast, has a low cost-per-test and has excellent detection ability. The Loop use a Bruker Alpha FTIR spectrometer.


How it works

It works by shining different wavelengths of infrared light onto a solid sample which will partly absorb certain wavelengths according to its chemical structure. Because every drug has a unique chemical structure, the absorption behaviour is unique for every compound which allows us to plot a graph called an absorption spectrum. We can then use a computer algorithm to compare this unique absorption spectrum to a huge database of substances measured by labs around the world to locate the closest match with extreme accuracy. The database The Loop use is the TICTAC IR library from TICTAC Communications Limited. TICTAC has Europe’s largest and most up-to-date IR library for new psychoactive substances/legal highs, and this library is constantly updated to ensure validity.

The Loop uses an instrument with “Fourier-transform” technology which exploits the wave-like properties of light to generate many different shades (wavelengths) of the infrared light, and can therefore build up an extremely accurate absorption spectrum for a sample. A computer algorithm then examines the spectrum and does a full comparison to the database of verified analyses to find a match. It not only looks for the closest match, but uses further formulae to identify when two or more spectra may be overlaid (such as with a pill or adulterated substance). Thanks to modern computing techniques, these calculations take around 30 seconds and the software generates a list of likely matches, along with a probability that the spectrum was generated by the exact reference sample from the database. The scientist can then perform a conventional examination of the spectrum to manually screen for problems. If everything is as expected and the match probability is high, the sample is recorded as having a low likelihood of adulteration or contamination so that the results can be returned to the service user in the intervention.

If the match probability is not high, a number of further procedures can be followed. For medium match probabilities, a “subtraction analysis” is performed on the sample, where the computer is instructed that a mixture is suspected with the primary detection and others. This “subtracts” the spectrum of the primary compound to reveal underlaid spectra belonging to adulterants. This process will detect a 10% adulteration with ease, and depending on the adulterant can detect even lower adulterant concentrations. Depending on the nature of the result and the adulterant, this information will be returned to the drugs worker for feedback to the service user. For something like a clear contamination of cocaine with benzocaine, the exact details may be relayed, but in the case of a low match probability with an uncertain adulterant, the service user may be given less detail.

From here, the analysis path may continue. In the case of pills with a low match probability, it is common for the active components to be extracted with methanol to obtain a higher concentration sample for the process to be repeated.

In some cases it is possible that no compound is detected, in which case the sample will be tested with colourimetric reagents to screen for samples not in the IR library. These give a wide range of colour changes depending on the chemical bonds in a substance and although they are less precise than an objective computer readout, they do not rely on a library. If there is no change then the content is recorded as “most likely inactive” and this information is returned to the service user with the appropriate caveats.

If there is a result and FTIR has been unhelpful then the sample may be passed to the police for full analysis or destroyed, and the service user informed that the analysis was not able to reveal the contents. This situation tends only to arise in apparent cases of very obscure NPS, which service users so far have surrendered to us when informed.

In addition to this The Loop also use a quantitation method for ecstasy pills due to the threat presented by tablets with a high MDMA content. Once a pill is verified by FTIR to be likely unadulterated its mass is recorded and it is crushed and washed with methanol. A vast majority of pill binders and other excipients are very poorly soluble in methanol, but MDMA is very soluble. This means that with just a small amount of washing, the pill residue that remains is the mass of the original pill with the mass of MDMA subtracted, so the MDMA content is easily calculated. In some rare cases there may be excipients or dyes which are soluble in methanol. This could cause the recorded MDMA content of the pill to appear greater than it actually is, which would present an inaccuracy for the service, but is not likely to increase the risk that service users are exposed to. The results are checked against international pill databases recorded by EcstasyData to screen for this issue, and scientists may additionally use their own judgement to identify methanol soluble excipients. If a problem is suspected, the extract will be evaporated and washed with butanone, which dissolves many methanol soluble excipients but not MDMA.

Finally, in 2017 The Loop have introduced UV spectrometry for quantification of pills. This is a well-known technique which is more resistant to minor adulteration in pills because looks at the absorption of light at a single wavelength in the UV spectrum (286nm) which most other compounds do not absorb. It has similar “weaknesses” to the washing method, in that it can overestimate the MDMA content of a pill (if something else absorbs 286nm light) but is very unlikely to underestimate the MDMA content, but has the advantage of being quicker, simpler and more precise.


ATR – attenuated total reflectance. This refers to the type of sample stage used on the IR spectrometer. It means the beam of light is directed onto the sample and reflected off again, instead of being directed through the sample.

FTIR – Fourier-Transform Infrared spectroscopy.

UV – Ultraviolet spectroscopy.