Lysergic acid diethylamine (LSD), or «acid» as it is popularly known, is a Schedule 1 controlled substance responsible for potent euphoria-inducing and sensory-altering properties. Long lasting psychopathological consequences, such as auditory/visual hallucinations and psychoses, have been documented in vulnerable LSD users. LSD is typically spotted on colorful, absorbent «blotter» papers for sublingual and oral administration. Convenient detection of LSD requires a flexible system capable of trace detection of the target compound in the presence of potential interferents—including dyes, substrates, and solvents—with minimal sample processing. This Application Note describes real-world test simulations using SERS (Surface-Enhanced Raman Scattering) materials and test samples consisting of ink-printed and color dyed paper matrices spiked with LSD. Simple extraction procedures are highlighted to lift the target compound and remove fillers, inks and dyes that fluoresce or otherwise confound identification of LSD.

MISA (Metrohm Instant SERS Analyzer) and MIRA XTR DS (Metrohm Instant Raman Analyzer) are ideal solutions for rapid field identification of a range of illicit and dangerous chemical substances. Easy-to-use test kits and flexible sampling allow rapid and accurate interrogation of suspect materials with minimal time, training, and expense.

Raman spectroscopy is a superior method for detection of bulk materials and chemicals, although it lacks sensitivity for trace detection. When LSD-saturated paper products are interrogated with Raman, the spectrum is dominated by the substrate signal. SERS, however, is sensitive enough to detect the active ingredient in typical single-dose street samples containing 20–400 μg of LSD.

To evaluate the effects of colorants on SERS identification of LSD extracted from paper, the procedure outlined in the previous section was replicated with both paper laser-printed with colored toner and paper coated with a mixture of food dyes. As the bottom two spectra in Figure 2 show, both treatments significantly reduce the intensity and resolution of the LSD signal. This is largely due to the fluorescence emissions of colorants, which serve to lower the signal-to-noise (S/N) ratio of signature peaks.

A simple sample clean-up procedure based on liquid-liquid extraction improved signal intensity dramatically. In this modification of the extraction procedure, dried LSD-saturated paper was added to a glass vial containing 500 μL of water and 10 μL of 1 mol/L NaOH. This mixture was shaken gently, 500 μL of dichloromethane (DCM) was added, and the subsequent mixture was shaken again. After phase separation, the (bottom) DCM layer containing LSD was carefully pipetted to a fresh vial, the solvent removed by evaporation, and the remaining solid resuspended in a solution of 500 μL Ag colloid, 10 μL of 1 mol/L HCl, and 50 μL of 0.9% NaCl. The contents were gently mixed and measured with MISA.

This procedure converts LSD into its free base form, which is selectively solvated in DCM and can be separated from water-soluble toner and food dye interferents.

SERS capabilities on MISA and MIRA XTR DS provide rapid onsite identification of LSD in suspect street samples with simple, user-friendly procedures. Uniquely, this application provides alternative extractions as a way of addressing real-world situations while keeping sample clean-up as simple as possible. This provides a rapid and portable alternative to conventional analytical laboratory testing procedures and their associated expenses for time, materials, and personnel. Metrohm’s state-of-the-art test solutions continue to support detection and regulation of illicit substances.