Determination of trace amounts of thiabendazole in fruit juices using internal standard-based SERS method

Thiabendazole (TBZ) is widely used as a fungicide to prevent mold on citrus fruits. Uncontrolled use of TBZ can potentially harm the human health and contaminate the environment of aquatic organisms. In this work, we have developed an ultra-sensitive and low cost quantitative method for the determination of TBZ in juices (orange, apple, and peach) using surface-enhanced Raman scattering (SERS) on CaCl2-agglomerated silver nanoparticles. The recovery of analyte from juice with ethyl acetate was performed using liquid-liquid extraction. We used nitrothiabendazole (NTBZ), a closely related compound to TBZ, as an internal standard for improving accuracy and reproducibility of the results. This compound was obtained through a simple synthesis procedure. The structural similarity between TBZ and NTBZ allowed to obtain a practically identical recovery rate during the extraction and a relatively equal concentration dependence in the SERS mode. Application of NTBZ as an internal standard allowed to obtain a linear dependence of the SERS intensity signal at the TBZ concentration ranging between 100 and 1000 nM (R2 =0.9907). The recovery rate was between 90% and 113%, RSD was less than 3.5%. The LOD for TBZ specifically in juice samples was calculated to be between 1.2 and 5.1 nM. The dependence of the TBZ signal on the acidity of the medium was also studied. The enhancement factor was evaluated at 1.57 * 107.