Vortex mixer

A sequential liquid-liquid extraction was performed using 1) petroleum ether, 2) diethyl ether 3) hexane, 4) ethyl acetate and 5) methanol. The selected solvents ranged in polarity starting from non-polar (petroleum ether, diethyl ether and hexane) to more polar solvents (ethyl acetate and methanol) to take advantage of their different properties.
Briefly, 1 ml of petroleum ether was added to the capped glass tube containing 1 g of L. rhinocerus extract. The mixture was then vortexed for 1 min using a vortex mixer (Westbury, New York, USA), followed by centrifugation (Centrifuge Universal 32R, HettichZentrifugen, Germany) at 700 × g for 5 min. The supernatant was aspirated before being transferred (100 μl) to a new auto-sampler vial for GC-MS injection. The residue was used for subsequent extraction using diethyl ether followed by hexane, ethyl acetate and finally, methanol, as previously described for petroleum ether. Following extraction by each solvent type, the samples were individually injected into the GC-MS system in duplicate. Each sample was analyzed against a blank organic solvent containing a similar type of organic solvent used in the extraction process each time.

To extract four pesticides, 10 g of homogenized lettuce sample was weighed in a 50-mL polypropylene centrifuge tube. The sample was extracted with 10 mL of acetonitrile and vortexed for 5 min using a digital Vortex-Mixer (Velp Scientifica, Usmate, Italy). After vortexing, salts containing 4 g magnesium sulphate, 1 g sodium chloride, 1 g trisodium citrate dihydrate and 0.5 g disodium hydrogen citrate sesquihydrate were added. The tubes were immediately shaken for 1 min, vortexed in a Vortex-Mixer for 5 min at 4500 rpm and then centrifuged at 10,000 rpm (Hettich, Tuttlingen, Germany). The upper layer (acetonitrile extract) was transferred into the dSPE tubes containing 150 mg anhydrous MgSO₄ and 25 mg PSA. The tubes were vortexed for 30 s and centrifuged at 5000 rpm for 5 min. One millilitre of the final extract was filtered through a 0.2-m hydrophilic PTFE filter, transferred into the appropriately labeled autosampler vial and subsequently analysed using LC–MS/MS (Fig. 2).Fig. 2

Sample preparation of lettuce and instrumental analysis. Where: 1) Lettuce sample; 2) After vortexing salts containing 4 g MgSO4, 1 g NaCl, 1 g trisodium citrate dihydrate and 0.5 g disodium hydrogen citrate sesquehydrate were added; 3) Vortexed in a Vortex-Mixer for 5 min; 4) Final extract; 5) LC-MS/MS analysis