Chapter 1

How the food detectives optimized solvent extraction for food analytics

🗂 Case overview: The seven detectives are about to start working on their very first cases in food analytics. The agency is already full of requests on how to detect contaminants and residues in different food groups. But before they get started, Shallot Holmes gathers his colleagues for a brief overview of their available tools and methods. Today, the team sits down to explore how to set up their solvent extraction process to achieve fast and reliable results.

Shallot Holmes takes a sip of his tea and jumps right into the day’s challenge: optimizing their solvent extraction method.

First order of business for the detectives is to figure out how to reach exhaustive extraction in minimal time. The team begins to discuss which parameters ensure fast extractions with accurate and reproducible results. Everyone, from Eggcule Poirot to Nancy Beef, contributes some excellent points, which Shallot Holmes compiles in a list. The list looks as follows:

Parameters that influence solvent extraction results

Polarity – A solvent with a similar polarity to that of the analyte should be chosen. As there is no universal ideal solvent, publications and standard methods will need to be consulted on case-by-case basis. Eggcule Poirot makes a note that their extraction glassware should be made of resistant materials, such as borosilicate glass. Such equipment would guarantee that they can safely work with best suited solvents, such as organic solvents or water.

Temperature – Typically, a temperature increase of 10°C doubles the solvent extraction speed. However, limitations regarding degradation of heat-sensitive compounds and possible side reactions must be taken into consideration.

Solvent turnover/number of solvent extraction cycles – The evaporation rate should be > 10 mL/min. The heating power should be chosen based on boiling enthalpy, the ambient temperature and the altitude.

Extraction method – Extraction efficiency should be optimal. The most appropriate solvent extraction method should be chosen for maximal turnover of solvent or contact time with sample matrix. Eggcule Poirot suggests using a universal extractor with flexibility in the choice of solvent extraction methods to include Soxhlet, Soxhlet warm, Hot extraction, Twisselmann and Continuous flow extractions.

Sample type – Preferably, dry and dispersed samples should be used. Thanks to their larger surface, these samples have a larger contact area with the solvent, which increases solvent extraction efficiency. Miss Mapple suggests using consumables filled with Celite® or quartz sand to dry and disperse samples.

Next, the detectives turn their attention to analyte safety during solvent extraction. Shallot Holmes invites Eggcule Poirot to discuss this with the rest, as he is the reputable expert on the topic.

Eggcule Poirot pulls on his moustache and explains that to obtain reliable results, it is crucial that the analytes are not deteriorated, especially when solvent extraction is used as a sample preparation step. He then moves to the whiteboard, uncaps a black marker and jots down important points on analytical safety. His list, enhanced by comments from the other detectives, looks as follows:

Four key steps in analyte protection during solvent extraction

1. Choose the most suitable solvent and extraction temperature to prevent side-reactions or deterioration of the analyte. In some cases, you must also take measures against oxidation and sun-light exposure. Nancy Beef suggests using extraction systems with inert gas supply to reduce oxidation and an analyte protection sensor to prevent heat deterioration.

2. Apply the same conditions to all sample replicates and blanks within one batch and from one batch to the other. These conditions include the number of cycles, as well as contact time between solvent and sample.

3. Avoid contamination from pervious samples, the laboratory environment or leaching materials. Clean or pre-extract all of the materials in contact with the sample and analyte. Miss Mapple points out that use of resistant or inert materials and equipment that is easy to disassemble and clean can be very helpful in working contamination-free.

4. Use the appropriate sample size. The ideal sample weight is determined by analyte concentration and homogeneity. Small sample amounts reduce solvent consumption and shorten Soxhlet cycles. But you should use sufficient sample and large sample volume options on your extraction unit to reach low detection limits and high reproducibility.

The meeting concludes with Shallot Holmes handing out some more useful material relating to solvent extraction to his colleagues. They are invited to read though an Extraction Pocket Guide full of tips on how to achieve fast and flexible solvent extraction.

The detectives grab their coats and head out into the fresh spring evening, chattering amongst themselves about starting on their first case. Shallot Holmes locks up the bureau and sighs relieved that their first meeting has gone so well. Despite his satisfaction, he cannot shake off a feeling of unease that Nancy Beef will take offence at their first case. 🕵🏽‍♂️🕵🏼‍♀️