Determination of natural pyrethrins by liquid chromatography-electron ionisation-mass spectrometry

Pyrethrum extract is a mixture of six insecticidal compounds from the flower heads of Chrysanthemum cinerariaefolium L.. Since they only have low to moderate mammalian toxicity they can be used as natural insecticides in agriculture or to develop low cost and safe dermatological formulations. Because of the thermal instability of pyrethrins, analytical methods based on liquid chromatography (LC) are preferred over those based on gas chromatography (GC). A few applications using LC with mass spectrometry detection are presented in the literature. Current protocols for their characterisation by LC rely on the use of less sophisticated detectors such as UV detection.

To develop the first liquid chromatography-electron ionisation-mass spectrometry (LC-EI-MS) method for pyrethrins detection and quantitation in pyrethrum extracts.

A commercial pyrethrum extract and various samples of flower heads from C. cinerariaefolium L. were investigated using reversed-phase nano-liquid chromatography coupled to direct electron ionisation-mass spectrometry (nanoLC-direct EI-MS). The eluted compounds were identified through searches of the US National Institute of Standards and Technology (NIST) library, exploiting the direct EI capability to produce high quality EI mass spectra.

The method demonstrated satisfactory sensitivity (limit of detection (LOD) range: 0.04-0.38 mg/g), linearity (R² range: 0.9740-0.9983) and precision (RSD% range: 4-13%) for the quantitation of the natural pyrethrins in extracts from C. cinerariaefolium L.

The nanoLC-direct EI-MS technique can be a useful tool for the detection of pyrethrins.