Analyzing Pesticides in Food or Plant Samples

Standard Preparation

  • For each component, 17 component pesticide standards need to be obtained at 300 μg/mL concentration.
  • 5 μL of each stock solution should be diluted in 195 μL of acetonitrile (0.1% acetic acid) to create 7.5 μg/mL spiking solution.

Sample Preparation

  • 15 g of desired food/plant sample should be weighed out with an OHAUS Analytical Balance and placed into a 50 mL polypropylene centrifuge tube along with 15 g of 3 mm zirconium beads (Product # 30391408).

It is not necessary to dice the samples. For larger quantities, a larger container may be used and reagents should be adjusted accordingly.

  • 200 μL of pesticide spiking solution should be added to each sample, creating a final solution of 100 ppb.
  • The tubes should be rocked at 15 rpm for 1 minute using the OHAUS Open Air Rocker, ensuring that the pesticide solution is dispersed evenly.
  • The samples then need to be incubated overnight at 4 °C.

Homogenization

  • Approximately 4–6 mL of Acetonitrile (0.1% acetic acid) should be added to each of the samples.
  • The samples should be homogenized for 3 minutes at 1300 rpm (preset#3) using the OHAUS HT Lysing Homogenizer

Samples may be homogenized together but ensure that they are secured safely in the homogenization tray. There are no restrictions given by the manufacturer.

Pesticide Extraction

  • 10 mL of Acetonitrile should be added to the homogenate followed by 6 g magnesium sulphate and 1.5 g sodium acetate.
  • The sample should be gently homogenized at 300 rpm for 1 minute using the OHAUS HT Lysing Homogenizer.
  • The samples should be centrifuged for 2 minutes at 3000 rpm on the OHAUS FC5714 centrifuge with a compatible rotor for 50 mL conical tubes.
  • The supernatant should be removed and placed in a 15 mL centrifuge tube along with 1.2 g magnesium sulfate, 400 mg PSA, 400 mg C18 and 400 mg graphitized carbon.
  • Using the OHAUS Mini-Vortex Mixer gently vortex for 1 minute.
  • To pellet the solid material centrifuge for 2 minutes at 1500 rpm on the OHAUS FC5714 Centrifuge with a compatible rotor for 15 mL conical tubes.
  • 500 μL of the supernatant should be extracted and placed into an autosampler vial for GC/MS analysis.

OHAUS Products Used Within this Procedure

Analytical Balances

Analytical Balances

FC5714 Centrifuge

FC5714 Centrifuge

Open Air Rocker

Open Air Rocker

Mini-Vortex Mixer

Mini-Vortex Mixer

HT Lysing Homogenizer

HT Lysing Homogenizer

About OHAUS Corporation

OHAUS Corporation manufactures an extensive line of weighing products, laboratory equipment and analytical instruments that meet the weighing and measurement needs of virtually every industry.

They are a global leader in the laboratory, industrial and education channels, as well as a host of specialty markets, including the food preparation, pharmacy and jewelry industries. An ISO 9001:2008 manufacturer, OHAUS products are precise, reliable and affordable, and backed by industry-leading customer support.


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Last updated: Nov 5, 2019 at 7:40 AM

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