The growing interest in green chemistry requires fresh perspectives on analytical extractions. Reduced solvent consumption,
alternative safer solvents, and reasonable energy demands must be balanced with traditional analytical considerations such
as extraction yield and selectively. This article introduces some of the concepts behind green chemistry, and discusses green
solvent selection and extraction techniques. An overview of alternatives to conventional solvents, new green solvents, ionic
liquids, and other solvent options are also described.
The history of modern analytical extractions mirrors the development of green chemistry. For nearly a century Soxhlet extraction,
combined with shake-flask methods, was the standard method for the isolation of analytes from solid samples, while multiple
liquid–liquid extractions (LLEs) using separatory funnels was the method of choice for liquid samples. In the mid-1980s, new
forms of analytical extractions were developed and popularized — such as supercritical fluid extraction (SFE), pressurized-fluid
extraction (PFE), solid-phase extraction (SPE), solid-phase microextraction (SPME), microwave-assisted extraction (MAE), single-drop
microextraction (SDME), and ultrasonic extraction. These new extraction techniques had benefits such as faster times, lower
cost for each extraction, improved yield and reproducibility, and lower solvent volumes. Lower solvent volumes provide significant
environmental advantages. Extraction solvents generally provide the bulk of the waste encountered in any analytical method
and often have health and safety concerns, such as toxicity or flammability.
In parallel with these developments, the concept of green chemistry emerged. This culminated in the statement of the 12 principles
of green chemistry in 1998, which are shown in Table 1 (1). The goals of green chemistry are to address environmental, health,
and safety concerns when planning a chemical process rather than after it has been performed. Despite the fact that modern
extraction technologies and green chemistry are contemporaries, the two fields have advanced independently of each other.
The green advantages of newer extraction methods are widely promoted, but they are rarely placed in the context of the green
Table 1: Principles of green chemistry. Adapted from reference (1).
Green chemistry in the chromatography laboratory was recently reviewed and this article described ways to save on solvent
consumption, alternatives to using acetonitrile in liquid chromatography (LC), and how to assess the "greenness" of analytical
methods (2). These topics will not be repeated in this review.