A Multi-Residue Method Choice-QuEChERS
Originally designed to analyze fruits and vegetables, QuEChERS now includes a variety of products. Since being developed and released by scientists at the United States Department of Agriculture in 2003, QuEChERS has gained increasing popularity as a method of selection. It combines several sample preparation steps and extends the range of analytes recovered by older boring extraction methods. The growth of QuEChERS benefits from the emerging requirements for the determination of trace analytes in high-throughput environments.
The matrix includes:
• animal products – meat, fish, kidneys, chicken, milk, honey
• grains and cereal products
• food – wine, fruit juices, fruits and vegetables
The extension of the QuEChERS method not only demonstrates its function in sample extraction and purification, but also addresses concerns about detecting large quantities of pesticides, herbicides, fungicides, antibiotics, and other compounds throughout the food supply.
The basic form of QuEChERS consists of three steps:
1. Liquid microextraction
2. Solid-phase cleaning
3. LC/MS/MS or GC /MS analysis
QuEChERS continued to improve the sample preparation of analytes in various samples. QuEChERS has now become a generic technology, with many modifications, each variant designed to do one thing: rapid sample extraction and clean up.
These modifications include:
• increase the flux of samples while reducing the cost
• minimize degradation of susceptible compounds, such as base and acid-unstable pesticides
• extend the range of matrices applicable to this approach
Three main QuEChERS approaches
1) the original QuEChERS method (by Anastassiades, Lehotay et al.)
• sodium chloride is used to reduce polarity interference
• provides the cleanest extraction because it USES less reagent
• does not use acetic acid which may be problematic in GC/MS analysis
• dispersive clean-up procedures are used
• use 1% acetic acid in acetonitrile and sodium acetate buffers to protect base-sensitive analytes from degradation
• a USDA study showed that this method provided an excellent recovery rate for ph-sensitive compounds compared to the other two QuEChERS methods
• the method uses acetic acid in the extraction step. Acetic acid may overload the PSA adsorbent used in the purification process, rendering it ineffective and possibly causing GC separation problems
3) EN 15662
• European methods include sodium chloride to limit polarity interference, and several buffers to retain alkali-sensitive analytes
• sodium hydroxide should be avoided in the citrus step as it may increase impurities in the extract and damage the adsorbent used in the purification step
Sample preparation and extraction
• freeze the sample to -20°C
• Take dry ice to homogenize and stops when the free-flowing powder is formed.
Then the sample is
1) extract into the solvent
2) clean it by dispersive or cartridge SPE
Characteristics and influence
QuEChERS greatly improved laboratory efficiency and throughput. An analyst can produce a batch of 20 extracts in less than 60 minutes. This procedure requires only a few milliliters of solvent, and for many compounds suitable for GC and LC, the recovery rate can reach 90-110% when RSD < 5%.
Extraction and cleaning.
• solvent extraction techniques are designed to remove as many analytes as possible from the base matrix.
• solvent selection is important to minimize the co-extraction of compounds.
• samples must be cleaned to reduce interference.
• interference can damage analytical instruments and complicate the identification and quantification of analytes.
Extraction reagent and its function
Anhydrous magnesium sulfate – promotes solvent distribution and improves recovery of polarity analytes.
Acetic acid – used to regulate pH.
Acetonitrile – an organic solvent that provides the best properties to extract the largest number of pesticides and the smallest number of co-extracts.Suitable for LC and GC analysis.
Buffer – prevents pH-sensitive analyte degradation by maintaining optimum pH value.
Sodium chloride – reduces the amount of polarity interference.
Purification reagent and its functions
Aminopropyl – removes sugars and fatty acids, with the same function as PSA, but is unlikely to catalyze the degradation of base-sensitive analytes. The cleaning capacity of aminopropyl is lower than that of PSA.
ChloroFiltr- polymer adsorbent for the selective removal of chlorophyll from acetonitrile extracts without loss of polar aromatic pesticides.
C18- removes long-chain fat compounds, sterols, and other nonpolar disruptors.
Graphitized carbon black (GCB) – strong adsorbents for the removal of pigments, polyphenols, and other polar compounds: examples of planar (polar aromatic) pesticides that can be removed: bacillin, crop, hexachlorobenzene, thiazulin, terpene phosphorus, and Quinto.
Anhydrous magnesium sulfate – removes water from the organic phase.
Persecondary amine (PSA) – used to remove sugars and fatty acids, organic acids, lipids and certain pigments. When used in combination with C18, other lipids and sterols can be removed.