Tea Analysis with eXtreme|FV® by GC-MS
This method investigates whether SPE is required for the analysis of pesticides in green tea leaves using GC-MS. To simplify the comparison, the method utilizes an existing validated ISO method for the analysis of pesticides in food and natural products. The method is comprised of two sections: first, the extraction of the pesticides from the sample; second, the sample clean-up required for GC/MS.
Sample Preparation for Green Tea Leaves
- Current method uses a salt extraction followed by SPE clean-up.
- Improved method uses a salt extraction followed by Thomson eXtreme|FV® clean-up.
- One large sample is extracted and then split in half. Half the sample goes through SPE and the other half through the eXtreme|FV®.
- 2.0g of commercially available Green Tea is spiked with 0.2mL of 1.0 ppm pesticide standard mix containing 87 pesticides in a 40mL vial for a final concentration of 0.050 ppm.
SPE Cleanup Prior to Analysis - 6 mL Combo SPE Cartridge
- Wash one 6 mL Combo SPE Cartridge (packed with 200 mg CarboPrep 200 and 400mg PSA) with acetonitrile.
- Add the 10mL portion of the re-suspended residue from the flask labeled “for SPE” to the SPE cartridge.
- Elute the sample from the cartridge with 50mL of acetonitrile.
- Concentrate the eluted sample to 10mL using a Turbovap II concentrator.
- Filter sample with a syringe and syringe filter, PTFE 0.45μm and elute into autosampler vial
Thomson eXtreme|FV® Cleanup Prior to Analysis
- Add 400μL of the re-suspended residue from the flask labeled “for Thomson eXtreme|FV® to the shell of one Thomson eXtreme|FV® 0.45μm.
- Insert plunger completely.
Samples were analyzed utilizing an Agilent Technologies GC/MS, 7000 Triple Quad system equipped with a 7890A GC system and 7693 auto sampler.
fig.1Pesticides in Green Tea Comparison of SPE to eXtreme|FV®s.
The results for the green tea can be seen in Table 1, Pesticides in Green Tea Comparison of SPE to eXtreme|FV®s and Fig. 1, Pesticides in Green Tea Comparison of SPE to eXtreme|FV®s, below, shows the recoveries for both clean-up methods: SPE and syringe filter (PTFE 0.45µm) and Thomson eXtreme® Filter Vial. The results show Thomson eXtreme® Filter Vials offer a viable alternative with higher recovery and less preparation time compared to SPE for the sample clean-up of tea leaves and for the clean-up of samples prior to pesticide analysis.
|Compound/Sample Name||SPE Clean-up Average ppm||eXtreme|FV® Clean-up Average ppm|
|BHC-alpha (benzene hexachloride)||0.037||0.037|
|Endosulfan II (beta isomer)||0.032||0.036|
|Permethrin II (trans)||0.058||0.61|
SPE -vs- eXtreme|FV®
The results clearly show Thomson eXtreme|FV®s, 0.45µm, PTFE Filter Vials (Thomson # 85540-500) offer a viable alternative with equivalent recovery and significantly less preparation time and solvent usage compared to sample clean-up with SPE for the preparation of green tea samples prior to pesticide analysis. Future testing is required to further streamline this method by re-evaluating the extraction procedure, specifically the need for the concentration/re-suspension steps.