Heterogenic catalytic hydrolysis and analysis of natural pyrethrins in subcritical water coupled with solid phase microextraction (SPME) and GC-MS

Abstract

The natural pyrethrins, cinerin I, jasmolin I and pyrethrin I, have been hydrolyzed to chrysanthemic acid (CA) in subcritical water in the presence of basic alumina. The hydrolysis and extraction was performed in situ with subcritical water. The conversion to acid is reproducible at 200 °C and 30 min with an RSD of 19% (n = 16) at a concentration level of 1.2 × 10^–8 mol/L CA and 12% (n = 12) at concentration level of 1.2 × 10^–7 mol/L CA. An analytical method using Solid Phase Micro Extraction (SPME) combined with GC-FID or -MSD was developed and optimized. For SPME an equilibration time of 20 min at pH of 2 was required. Three fibers, 100 μm polydimethylsiloxane (PDMS), 85 μm polyacrylate (PA) and 65 μm carbowax/divinylbenzene (CW) were evaluated. The Carbowax/divinylbenzene fiber has the highest affinity for CA, but the capacity decreases significantly from experiment to experiment. The most reproducible and most stable one was the PDMS fiber. Two internal standards, octanoic acid and cis-chrysanthemic acid, were used because CA degrades slowly at 200 °C in water.

This method was applied to analyze some products which contain pyrethrum as an active ingredient, such as insect spray, shampoo against lice, and dried chrysanthemum flowers. The results are comparable to SFC-FID data and correspond to the values given by the manufacturer.