Solid phase extraction (SPE) is among the most widely used sample preparation techniques for chemical and biological analyses. SPE is used to purify a compound by concentrating liquid phase components onto a solid phase substrate and extracting the target analytes. Greater sample complexity and more sensitive instrumentation have driven the need for SPE advancements. Also fueling developments are SPE’s use prior to LC/MS analysis, particularly for fast growing application areas such as food analysis and proteomics. Progress in SPE has included automation and miniaturization. In this article, IBO looks at three products resulting from latest developments in SPE.

As evidenced by the number of recent product introductions, one of the fastest growing areas of SPE is QuEChERS (quick, easy, cheap, rugged, effective, safe). The two-step process combines liquid-liquid extraction and dispersive SPE (dSPE). In dSPE, the SPE sorbent is added to a portion of the sample’s extract. QuEChERS uses less solvent, less glassware and is faster and easier, with less steps, than previous methods for sample preparation prior to multi-residue analysis of pesticides in agricultural products. Other applications include the analysis of drug residue in animal tissues and the extraction of contaminants from environmental samples.

Consistent with the demand for automated SPE solutions, Teledyne Tekmar recently introduced the AutoMate-Q40 automated workflow platform, which uses a dedicated liquid handling platform. It automates all steps of QuEChERS methods AOAC 2007.01 and EN 15662.2008. “Once the user has loaded the AutoMate-Q40 with homogenized samples, the platform fully automates the extraction workflow all the way up to providing the solvent extract for analysis by LC/MS/MS or GC/MS,” explained Thomas Harlein, AutoMate-Q40 product manager at Teledyne Tekmar. “The workflow automation is accomplished through the integration of a series of modular devices that cap and de-cap sample centrifuge tubes, dispense solvents and standards, add salts, shake, vortex and centrifuge as required, detect the desired liquid layer from others for pipetting (patent pending) and clean up via dSPE.” VialVision technology identifies the liquid layers in a sample extraction tube and calculates volumes.

Although part of QuEChERS’s advantages are its speed and simplicity, the process can benefit from automation, said Mr. Harlein. “By automating the entire workflow, improvements can be made, not only reducing the need to conduct tedious manual labor but achieve improved reproducibility as well, regardless of technician’s level of training or experience.” Automation also increases throughput. “Furthermore, as the acceptance and popularity of the QuEChERS technique increases, the number of samples that laboratories will be confronted with will see a proportionate increase creating new bottlenecks or exacerbating those that already exist.”

Asked about other products that automate the QuEChERS procedure, Mr. Harlein told IBO, “Currently, there are no other systems specifically designed to automate the QuEChERS extraction workflow. Although there are larger complex robotics-based platforms that can be configured to perform these extractions by integrating and testing additional preparatory modules, doing so comes at considerable cost and effort.” He added that the AutoMate-Q40 is configured “out of the box.” He noted that the system’s use of pre-mixed reagents in bulk contributes to cost savings. “Additionally, the automated dispensing station can be adjusted to deliver varying volumes. Lastly, the end-user will no longer have to spend time opening and pouring reagents which can be messy and a potential hazard to the laboratory environment.”

The AutoMate-Q40 is designed for food testing labs of all sizes. “We anticipate the primary users will be those conducting food safety testing including regulatory and commercial testing laboratories, as well as food producers, processors and their supply chains,” said Mr. Harlein. The system also represents a bit of a departure for Teledyne Tekmar, which primarily provides automated sample preparation solutions for environmental testing using GC. ”Although this system is designed to extract semi-volatiles, the techniques and technology required for the application fit very well with our existing core competencies, enabling us to expand our product offering in the exciting food safety arena,” he explained.

Capitalizing on the demand for the miniaturization of SPE, SGE Analytical Science’s MEPS (Micro Extraction by Packed Sorbents) technology. First commercialized in 2007, MEPS products include both SGE-branded systems and products the company manufactures for other vendors. “The MEPS technology is simply a miniaturized form of the standard cartridge SPE where the ‘cartridge’ is a modified needle assembly of an analytical syringe,” explained Andrew Gooley, PhD, director of SGE’s Chromatography Business Unit. “This has two immediate advantages—the first being that all of the liquid handling steps needed for SPE, such as sample aspiration, washing of the stationary phase and elution of the target analyte, are integrated into the one device. Second, being an analytical syringe, the technology can be seamlessly integrated into the automated injection systems on any instrument platform that supports an analytical syringe.” MEPS works with sample volumes down to 10 µL.

According to Dr. Gooley, the technique is advantageous for samples in complex matrices, such as urine, blood and saliva, where sufficient sample amounts can be difficult to obtain. “However, the fundamental advantages that are emerging in the literature are that the very fact the SPE is miniaturized enables rapid method development, fast extraction (in some cases, less than five minutes), reduced sample volume and reduced reagent volumes,” he said. “This has a significant impact on laboratory efficiency and hence introduces a broader scope for improved experimental design.”

Since its introduction, MEPS has added different sorbent phases. “While launched with a standard array of stationary phases such as C18, C8 and the anion exchanges, the simplicity of the BIN [barrel insert and needle assembly] design has encouraged users to trial a number of different materials including Molecular Imprinted Polymers, polymeric materials, such as DVB [divinylbenzene], as well as an expansive range of silicas to optimize their particular sample preparation.” The BIN is reusable and is washed between uses, with a typical usage of 40–50 samples.

The technique’s evolution has also involved automation options. Among them is semi-automated MEPS using SGE’s eVol digital syringe. “A number of recent publications in 2012 have realized the benefit of having a fully programmable handheld solution for micro SPE, eliminating the risk of intra- and inter-operator errors associated with complex SPE protocols,” said Dr. Gooley. EVol MEPS can be used for method development. For full MEPS automation, SGE and CTC offer a kit for CTC’s PAL Series of autosamplers, enabling on-line SPE and injection.

The applications of MEPS have been wide ranging, according to Dr. Gooley. “Given the inventor was in a large pharmaceutical at the time he developed the technique, it was no surprise that drug metabolism studies in complex matrices such as urine was an initial field of interest,” he said. “Over the past three years, there have been more than 40 publications where the major fields of study are drug metabolism in blood, plasma and urine, environmental pollutants in waste water, food and beverage analysis, and a number of method development papers.” Newer applications include the analysis of dried blood spots.

MEPS development is ongoing. For the eVol MEPS, Dr. Gooley described an application of a “lab-in-a-syringe” concept. “One such example is ‘at-line’ MS analysis, which was recently published in the Journal of Separation Science—fundamentally a microSPE-ESI MS technique, which was demonstrated to be a fast screening technique for drug metabolites extracted from urine.” Also, he noted the development of single-use MEPS cartridge. “[M]any scientists have asked for a single-use version to completely eliminate the risk of carryover, particularly in the fields of forensics, diagnostics and medico-legal analysis. SGE is well down the development path of a single-use version of the MEPS technology.”

Miniaturization is also the result of DPX Lab’s SPE technology. The company’s DPX (disposable pipette eXtraction) tips are available for traditional SPE and QuEChERS. Products are sold by the firm and through regional distributors. “It is a dSPE method in a pipette tip,” explained William Brewer, PhD, founder and president of DPX Labs. “It provides rapid extractions and is readily automated with robotic liquid handlers.” In the tip, loose sorbent mixes with the sample and air bubbles, providing faster, more efficient extraction. The extraction is based on equilibration time rather than flow rates. “Extractions generally take from 30 s to 4 min to perform, depending on the application/method,” said Dr. Brewer. For multiple samples, the company’s manual 24- and 96-sample Lever Press Extractors control flow rates. Gerstel provides an automated solution using its MPS MultiPurpose Sampler. Using the MPS DualRail, the analyte can be introduced directly into a GC or LC.

Dr. Brewer told IBO that commercial sales began in 2007, with one product available for one application. “We started with just RP (styrene divinyl benzene) and a 5 mL tip,” he said. “Now we offer two different sizes of 1 mL tips, tips for specific automation platforms and six different solid phase sorbents.” Asked about applications, he said, “Analysis of pain management drugs in urine, opiates and benzodiazepines in urine and comprehensive analysis of drugs of abuse in oral fluid are the most popular applications currently. We also have products for food safety applications that are increasing in popularity.” However, the technology continues to evolve to enable more applications. Describing future products, he said, “Smaller tips for rapid high-throughput testing are currently being developed. Also, additional products that permit high selectivity for specific applications are also being developed.”