Technologies for the extraction of solid materials have come a long way since the advent of the Soxhlet extractor, particularly in the automation of solid sample preparation techniques. In comparing this year's reader survey on sample preparation trends (4) to the last reader survey (5), the techniques of supercritical fluid extraction (SFE), pressurized-fluid extraction (PFE), and microwave-accelerated (or assisted) extraction (MAE) have all shown substantial growth. Of the readers surveyed, SFE usage went from 1.9% to 3.7%, PFE from 5.8% to 8.0%, and MAE from 2.6% to 8.0%. All three techniques haven't surpassed more popular techniques such as solid-phase extraction (SPE) and solid-phase microextraction (SPME) but have established themselves in the environmental, food safety, and natural products markets in particular. To bring us up-to-date in SFE, Professor Larry Taylor of the Department of Chemistry, Virginia Tech, Virginia, USA, provides a good perspective on why this extraction technique, so popular in the 1990s, is coming "back to the future" by providing a safer, greener, and rapid method for not only non-polar compounds but also for polar compounds. Part of the answer lies with the introduction of the latest generation of supercritical fluid chromatography (SFC) instrumentation. On the PFE front (also referred to as accelerated solvent extraction [ASE]), Aaron Kettle from Thermo Fisher Scientific reviews the latest instrumentation developments as well as selected applications of this rapid extraction technique. For MAE, Greg LeBlanc and coworkers from the CEM Corporation provide an in-depth update on greatly improved instrumentation in the field as well as some novel applications.
Since the last special issue, the movement towards green chemistry has been a driving force in chemistry in general and analytical chemistry and sample preparation in particular. Professor Douglas Raynie and his graduate student Victor Essel from the Department of Chemistry and Biochemistry, South Dakota State University, South Dakota, USA, discuss green chemistry perspectives on analytical extractions. Reduced solvent consumption, safer solvent alternatives, and reasonable energy demands all contribute to a greener environment. In that respect, Professor Roger Smith of the Chemistry Department of Loughborough University in the United Kingdom has a lot of experience in the use of superheated water as an extraction solvent and it is amazing the dissolution power that this entirely safe solvent can provide for organic compounds when heated well above its boiling point. He will provide a nice overview of the role of this novel extraction solvent in sample preparation.Finally, if sample loads eventually increase enough, safety concerns arise, or labour costs become an issue, automation becomes a necessary part of the sample preparation portion of the analytical cycle. Most chromatography laboratories use autosamplers as the standard form of sample injection but modern instrumentation permits automation beyond injection. Edward Pfannkoch from Gerstel USA has a good handle on the role of sample preparation beyond the autosampler and will discuss the various steps prior to injection that are now automatable, freeing up the user to perform less routine tasks.
If you are faced with sample preparation challenges in your own laboratory, I hope you find something of interest in this special issue of LCGC Europe.
(1) R.E. Majors, Ed. "Current Trends and Developments in Sample Preparation", LCGC 16(5S), S1–S60 (1998).
(2) R.E. Majors, Ed. "Sample Preparation of Solids", LCGC 17(6S), S1–S44 (1999).
(3) R.E. Majors, Ed. "Sample Preparation for Volatile Compounds", LCGC 17(9S), S1-S36 (1999).
(4) R.E. Majors, LCGC North Am. 31(3), 190–203 (2013).
(5) R.E. Majors, LCGC 20(12), 1098–1113 (2002).