Scopolamine analysis in beverages: Bicolorimetric device vs portable nano liquid chromatography

Scopolamine (SCP) is often involved in sexual assaults and robberies, particularly in recreational environments. Therefore, analytical tools are required for the analysis of this compound amenable for the field. In this work, a sensor for SCP is described based on the entrapment of KMnO₄ into polydimethylsiloxane (PDMS). The possibility of using KMnO₄ in combination with the reagent 1,2-naphtoquinone-4-sulfonate (NQS) giving a double sensor acting as a bicolorimetric device is also demonstrated. In contact with the sample, the PDMS composite delivers MnO₄^-, which reacts rapidly with SCP under basic conditions causing a change of the color of the solution that can be related to the concentration of drug using both, absorbances and color coordinates, while the NQS part of the sensor remains unchanged. After an exposure time to the sensors of 10 min, satisfactory linearity was obtained for concentrations of SCP up to 865 μg/mL, being the limit of detection (LOD) 108 μg/mL. A method using a portable nano liquid chromatograph with detection at 255 nm has been also developed; in this case the LOD was 100 μg/mL and the working linear interval was 250-2000 μg/mL. The precision, expressed as relative standard deviation (RDS), was ≤8% for both methods. Different beverages (cola, cola-whisky, tonic water-vodka, red wine and green tea) were assayed. The potential of the two proposed approaches for on-site tests is discussed.