[Reader Insight] Insights into the Application and Expansion of QuEChERS Technology

This article is submitted by expert chromatographer OU Shuo-Jun. Welch Materials, Inc. is authorized to translate this article to English and publish it on behalf of the author.

QuEChERS technology, first developed in 2003, has been a cornerstone in sample preparation for over 20 years. Its methodology revolves around four essential components: water, acetonitrile (organic solvent), salts, and solid-phase extraction agents.

Today, I’d like to share some practical experiences and insights into optimizing QuEChERS technique, aiming to help users better master its application.

QuEChERS is widely used for analyzing pesticide residues in fruits and vegetables, veterinary drug residues in meat and dairy products, and active or prohibited substances in dietary supplements and other samples. Generally, water and acetonitrile are used for extraction, though specific cases may require substituting the solvent to achieve better results.

The process then involves salting-out and solid-phase extraction for purification. Here are critical considerations:

1. Target compound polarity: The target should not be too polar and must dissolve in the organic phase. Acetonitrile is commonly sufficient, but for compounds with a higher logP (octanol-water partition coefficient), a less polar solvent may be needed. Conversely, highly polar targets may render the method unsuitable.
2. Salt concentration: Ensure the organic phase precipitates completely.
3. Solid-phase extraction (SPE): Minimize target compound adsorption by the SPE agent.

When these conditions are met, the method is considered viable for further experimentation.

Preliminary testing is recommended to evaluate these points individually while controlling variables. For example, to determine if the target dissolves in acetonitrile, experiment with a standard solution using only water and the organic solvent to assess recovery rates without adding the matrix or SPE agent.

Predicting outcomes based solely on theoretical knowledge or experience is rare, even for seasoned experts.

Expanding QuEChERS involves improving the method for cases that deviate from the three key conditions above, primarily addressing issues with compound polarity and SPE adsorption.

For instance, in determining alkylamines (compounds shown in the above figure), the seven compounds analyzed have two amine groups each. While their alkyl chains contribute hydrophobicity, shorter chains like 1,4-butanediamine exhibit significant water solubility, violating the first condition (target compound polarity).

Since substituting acetonitrile with a solvent of higher polarity that also allows salting-out is impractical, the chosen solution to reduce the target compound’s polarity is derivatization.

For alkylamines, derivatization not only reduces target polarity, improving solubility in acetonitrile, but also increases molecular weight, enhancing stability, instrumental response, and secondary mass spectral fragmentation.

However, several factors require attention:

• Timing of the derivatization reaction: In this study, derivatization agents were added directly to acetonitrile for simultaneous extraction and derivatization. Notably, matrices like food packaging materials are less complex and exhibit minimal matrix effects. In other food samples, competing reactions between the matrix and the target compound may hinder derivatization, necessitating purification beforehand. Post-purification derivatization must be evaluated for necessity and effectiveness.
• Aqueous phase composition: A 1.5% Na₂CO₃ solution, instead of pure water, was used to accelerate the derivatization reaction. Since Na₂CO₃ is a salt, careful control of salt concentration is essential to prevent premature precipitation of acetonitrile, which can compromise reaction efficiency and increase deviations.
• Residual derivatization agents: Derivatization agents often dissolve in the organic phase, potentially entering analytical instruments. Solutions depend on agent volatility: volatile agents can be removed via nitrogen blowdown, while SPE can be applied on non-volatile agents. If feasible, a six-way valve can be integrated before the mass spectrometer to switch between flows.

The above study explores the extended application of QuEChERS technology by incorporating acetonitrile-based derivatizing agents for simultaneous extraction and derivatization. Depending on the nature of impurities and byproducts, purification methods can be tailored.

For example, a similar approach is used in determining fatty acids in powdered milk. This involves methanol and toluene for extraction, with the aqueous phase mixed with salts. During the process, toluene extracts fatty acid methyl esters while the aqueous phase simultaneously removes methanol, acetyl chloride, and hydrochloric acid. Although differing slightly from QuEChERS, the principles align. Interested readers are encouraged to explore these methodologies further.