Sample preparation has often been viewed as the bottleneck in analytical procedures. Surveys have shown that time is typically the most frequent problem area for sample preparation procedures and that analysts can easily spend a majority of the total analysis time on sample preparation. While newly developed extraction techniques address time, modern chromatography advances are also moving toward faster separations. Based on these considerations, what is high-throughput sample preparation? Do modern extraction methods adequately address the issue of time? How can we address the analytical need for speed?
The self-proclaimed world's greatest rock and roll band famously sang, "You can't always get what you want." It's easy to apply the Rolling Stones admonition to analytical sample preparation because surveys (1–3) have consistently shown that time, along with cost and solvent use, is among the most significant desires of analysts. Traditional sample preparation methods are often the rate-limiting step in the overall sample analysis process. We can envision three approaches for addressing the desire for high-throughput sample preparation: parallel sample processing, automation, and improvements in the process kinetics.
Evolution of High-Throughput Analysis from MicroplatesOver the past several years, we've heard increasing calls for high-throughput sample preparation. But what is high-throughput sample preparation? It many cases, high-throughput stems from the high-throughput screening approach to combinatorial chemistry. This approach is the most established, based on the 96-well plate format. These microplates have been established for two to three decades. Key considerations for the acceptance of this approach are standardization of microplate dimensions and attributes by the Society for Biomolecular Screening and development of ancillary devices like repeating pipettes, vacuum manifolds, and more. Countless vendors are involved. Sample preparation and analysis using microplates includes liquid–liquid extraction (LLE), protein precipitation, solid-phase extraction (SPE), fluorescence, matrix-assisted laser desorption–ionization mass spectrometry (MALDI-MS), and separations.
Wells (4) presented a list of some of the uses of filtration microplates in pharmaceutical development, including
As we can see, the development of 96-well plates and the major applications of this approach are in bioanalysis of liquid samples. This is because the transfer of liquid samples from analytical operation to another is somewhat straightforward. Recently, Scoffin (5) reviewed liquid transfer in high-throughput systems. These liquid-handling systems operate either by air displacement or positive displacement and can reliably work with microliter volumes of volatile or viscous liquids. Other combinations of liquid handling and sorbent-based extraction, including solid-phase microextraction (SPME), automated disposable pipette extraction, and microextraction by packed sorbent have also been used in high-throughput approaches (6,7). By combining these solvent-free, sorbent-based extractions with syringe-needle or pipette configurations, direct extraction and liquid transfer is accommodated.