Evaluierung eines konventionellen Raman- und SERDS-Spektrometers für den mobilen Einsatz zur Detektion von Gefahrstoffen

Kurzfassung

Raman spectroscopy has gained increasing importance in the field of hazardous sub stance detection over recent decades, particularly through the use of portable Raman spectrometers for the contactless analysis of explosives with minimal sample prepara tion. However, challenges arise when investigating fluorescent samples, such as soil samples, since fluorescence signals can strongly interfere with Raman analysis. To minimize this effect, a handheld Raman device based on the principle of shifted-exci tation Raman difference spectroscopy (SERDS) was used. The aim of this study was to evaluate the SERDS-based handheld Raman device Pen dar X10 with regard to the influence of various measurement parameters, the detection of substance mixtures, and the identification of hazardous substances in combination with fluorescent materials. The older handheld Raman device First Defender® RM, which is not based on the SERDS principle, served as the comparison system. The investigations revealed significant differences in the laser beam profiles of the two devices. The Pendar X10, in particular, features a highly focused laser beam that can contribute to intense signals. However, the signal intensity decreases noticeably as the measurement distance increases. This loss can be partially compensated for only by extending the measurement time, which decisively improves the quality of the Raman spectrum. Furthermore, an incidence angle of 90 ° has a positive effect on the signal intensity for solid samples. In contrast, the First Defender® RM, exhibits a rather inho mogeneous beam profile; here, higher laser power and longer measurement times lead to increased signal intensity, but the detector quickly becomes saturated, especi ally for Raman-active substances, so that improved detection is not necessarily achie ved. Furthermore, it was found that both devices experienced difficulties in detecting sub stances in mixtures with mass fractions below 20 %, both for Raman-active substances such as ammonium nitrate (AN), and for less Raman-active substances, such as low density polyethylene (LDPE) and polymethyl methacrylate (PMMA). In addition, signal intensity generally increased with increasing concentration of the respective sub stance. For the detection of polyvinylidene fluoride (PVDF), which was manually added to both device libraries, the First Defender® RM achieved better results than the Pendar X10. The differences between the two systems became particularly evident in the investiga 8 tion of fluorescent soil samples and minerals in combination with AN. Due to the use of the SERDS principle, the Pendar X10 was significantly more capable of detecting AN even at lower concentrations, whereas the First Defender® RM was strongly limited by intense fluorescence signals, especially at high laser power. Overall, it was de monstrated that the SERDS-based Pendar X10 offers advantages in the analysis of fluorescent samples and is therefore better suited for corresponding applications in hazardous substance detection, although it also showed difficulties in detection at low concentrations (< 20 %).