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Analysis of pyrethrins in extract of Tanacetum cinerariifolium using Raman spectroscopy

Dalmatian pyrethrum (Tanacetum cinerariifolium /Trev./ Schultz Bip (Asteraceae), the species native for East Adriatic coast, is known as the main source of pyrethrin, which is mixture of six active compounds (pyrethrin I and II, cinerin I and II and jasmolin I and II), acting as natural insecticide. Quality of the natural pyrethrin is expresed as pyrethrin I/pyrethrin II ratio (Grdiša et al., 2014). The aim of this paper was to describe possibilities of using Raman spectroscopy, as fast and sensitive method in screening and differentiation of six pyrethrin components of the extract of T. cinerariifolium inflorescence. The plant material was collected from ten indigenous populations in Croatia. Ultrasound assisted extraction (UAE) was used for extraction of pyrethrins from samples of dried flowers of Dalmatian pyrethrum. Isolation and purification of six compounds from pyrethrine active substance was performed using liquid chromatography (HPLC-UV/VIS-DAD). Raman spectroscopy of the extracts and pyrethrins was performed in the range 500–1800 cm-1 with XploRA Raman spectrometer (Horiba Jobin Yvon). Raman scattering was excited by a frequency- doubled Nd/YAG laser at a wavelength of 532 nm (maximum output power 20-25mW), equipped with a 600 lines mm-1 grating. Spectra were analysed using Origine Pro 8.6 software (OrigineLab, USA). Figure 1 represents Raman spectra in the spectral region from 500-1800 cm- 1 of extracts of T. cinerariifolium (Figure 1.1- 10), as well as pyrethrins (Figure 2.1-6) which were used as standard chemicals. Due to the high percentage of pyrethrins in the drug extracts, the Raman spectra (Figure 1) actually represent the profile characteristic for this compound. This was evidenced through high similarity of obtained Raman spectra of the extracts and the isolated (standard) pyrethrins (Figures 1 and 2). The region between 600 and 1710 cm-1 of Raman spectra exhibited significant structural information, and therefore informative in distinguishing the variances among extracts originating from different populations (Figure 1). High intensity bands at 1634 and 1437cm-1 can be attributed to the six individual pyrethrins, as well as bands at 1703 cm-1 (Figure 1.1-10). In addition, the prominent bands at 1646, 1273 and 956 cm-1 cm-1 indicated the presence of jasmolin and cinerin I (Figure 2b, c), the band at 1259 and 1295 cm-1 indicates the presence of pyretrin I (Figure 2a), 1414 cm- 1 cinerin I, II, (Figure 2c, f). These preliminary results showed that Raman spectroscopy can be used as a screening method for the pyrethrins in extracts but should be combined with HPLC for more precise determination of quality and quantity of extracts.

Dalmatian pyrethrum ; Raman spectroscopy ; pyrethrin I, II ; cinerin I, II ; jasmolin I, II

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