Quechers: a detailed survival guide

Quechers: a detailed survival guide

Posted by Maxi Scientific on Jul 18th 2024

QuEChERS, which stands for Quick, Easy, Cheap, Effective, Rugged, and Safe, is a widely adopted sample preparation method in analytical chemistry. Developed in the early 2000s, this technique has revolutionized the way laboratories analyze pesticide residues in food and agricultural products.

What is QuEChERS?

QuEChERS is a multi-step process that involves:

  1. Sample extraction using an organic solvent (typically acetonitrile)
  2. Liquid-liquid partitioning with salts
  3. Cleanup using dispersive solid-phase extraction (d-SPE)

This method allows for the simultaneous extraction of a wide range of pesticides from various sample matrices, making it highly versatile and efficient.

Who Uses QuEChERS?

QuEChERS is primarily used in:

  1. Food safety laboratories
  2. Agricultural research facilities
  3. Environmental testing labs
  4. Government regulatory agencies
  5. Pesticide manufacturing quality control labs

Applications of QuEChERS

The main applications of QuEChERS include:

  1. Pesticide residue analysis in fruits and vegetables
  2. Detection of veterinary drug residues in animal products
  3. Analysis of environmental contaminants in soil and water samples
  4. Mycotoxin detection in grains and cereals

Best Practices for QuEChERS

To ensure optimal results when using QuEChERS:

  1. Choose appropriate extraction solvents and salt mixtures based on the sample matrix and target analytes.
  2. Use high-quality, pesticide-grade reagents to minimize interference.
  3. Optimize the cleanup step by selecting suitable sorbents for d-SPE.
  4. Validate the method for each specific matrix-analyte combination.
  5. Regularly maintain and calibrate analytical instruments (e.g., LC-MS/MS, GC-MS/MS) used for quantification.

Detailed QuEChERS Procedure

  1. Sample Preparation:
    • Homogenize the sample (e.g., fruits, vegetables) using a blender or food processor.
    • Weigh out a representative portion (typically 10-15 g) into a centrifuge tube.
  2. Extraction:
    • Add acetonitrile (usually 10-15 mL per 10 g of sample).
    • Shake vigorously for 1 minute to ensure thorough mixing.
  3. Salt-Out Partitioning:
    • Add a salt mixture, typically containing:
      • Magnesium sulfate (MgSO4): Acts as a drying agent
      • Sodium chloride (NaCl): Helps control polarity
      • Citrate salts: Buffer the pH
    • Shake immediately after adding salts to prevent clumping.
    • Centrifuge the mixture (typically at 3000-4000 rpm for 5 minutes).
  4. Aliquot Transfer:
    • Transfer an aliquot of the acetonitrile layer (usually 6-8 mL) to a clean tube.
  5. Dispersive Solid-Phase Extraction (d-SPE) Cleanup:
    • Add sorbents to the aliquot. Common sorbents include:
      • Primary Secondary Amine (PSA): Removes fatty acids, sugars
      • C18: Removes non-polar interferences
      • Graphitized Carbon Black (GCB): Removes pigments, sterols
    • Add additional MgSO4 to remove residual water.
    • Vortex the mixture for 30 seconds to 1 minute.
    • Centrifuge again (typically at 3000-4000 rpm for 5 minutes).
  6. Final Extract Preparation:
    • Transfer the supernatant to a vial.
    • If necessary, add an internal standard for quantification.
    • The extract is now ready for instrumental analysis.
  7. Instrumental Analysis:
    • Analyze the extract using techniques such as:
      • Liquid Chromatography-Mass Spectrometry (LC-MS/MS)
      • Gas Chromatography-Mass Spectrometry (GC-MS/MS)

Important Considerations:

  • The exact amounts of sample, solvents, and salts may vary depending on the specific QuEChERS method version being used (e.g., AOAC 2007.01, EN 15662).
  • Some laboratories modify the procedure based on their specific needs or the properties of target analytes.
  • The choice of d-SPE sorbents can be tailored to the sample matrix and target compounds.
  • pH adjustment may be necessary for certain pesticides that are pH-sensitive.

This detailed procedure highlights the simplicity and efficiency of QuEChERS, allowing for rapid sample preparation and analysis of multiple pesticide residues in a single run.

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