Solid-Phase Extraction Systems

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 Solid-Phase Extraction Systems

Size and simplification change how and where SPE can make the most difference

Getting the most out of sample analysis depends on preparation. “Any lab with complex sample matrices can use solid-phase extraction—anybody with a sample where they’re trying to isolate targeted compounds and increase the sensitivity, resolution, and robustness of analysis,” says Kim Haynes, SPE product marketing manager for Waters (Milford, MA). With solid-phase extraction (SPE) applied to complex samples, scientists can get more specificity than from most other forms of sample preparation.

Bioanalytical labs across a broad range of areas—academics, contract research organizations, forensics, pain-management, and pharmaceuticals—use SPE. “It comes down to how much matrix needs to be removed from a sample,” says Haynes. The more that a sample needs to be cleaned up, the more useful SPE becomes.

Making SPE even more useful also depends on improving technology. This article reviews some of the latest tools.

System sizes

Expanding the uses of SPE often depends on the system. For example, the ASPEC Extraction System from Gilson (Middleton, WI) comes in three sizes. “The smallest system, the GX-241, takes up 40 centimeters of linear bench space, and is designed for low-throughput application laboratories where budget is limited,” says Ronan Herry, product director for SPE at Gilson. “The GX-271 is a bit larger and more flexible, while the GX-274 is our high-throughput, fully automated ASPEC model with parallel extractions.”

Beyond the various sizes, these platforms can also be used for diverse applications. “These instruments can be used for SPE, liquid handling, and other sample-prep techniques, such as liquid–liquid extraction, filtration, supported liquid extraction, and derivatization. SPE can be performed in either batch or sequential mode to optimize efficiency,” Herry explains. “These instruments can accommodate 1-, 3-, and 6-milliliter polypropylene or glass columns on the same run, and they utilize positive pressure to improve reproducibility.”

The Gilson systems also allow a variety of applications—from method development to routine analysis, and from simple to multidimensional SPE. For instance, Herry points out, “The GX ASPECs contain on-bed reservoirs that allow access of up to seven solvents to automate any SPE protocol.” In addition, the GX-271 can be modified with an optional GX direct-injection module that allows on-line injections onto HPLC or LC/MS systems. Also, a precision syringe pump includes a pressure-sensing module that monitors pressure and can handle error conditions, including high cartridge pressure or clogged liquid lines.

According to Herry, top applications of the GX-ASPEC are food testing laboratories for detecting mycotoxins and multiresidue contaminants in food and the surrounding environment, and drug testing labs for screening trace amounts of drugs or signs of doping and for confirmation analyses.

The ASPEC Extraction Systems from Gilson come in three sizes, including the GX-271. (Image courtesy of Gilson.)

When asked about the newest system from Hudson Robotics (Springfield, NJ), Bruce Jamieson, director of sales and marketing, explained that his company developed its “positive pressure, 96-well-based ‘FilterPress’ for more accurate, reproducible extractions.” He adds that “positive pressure assures uniform flow between all 96 channels, and an optional flow controller can add even more control to the SPE process.”

Jamieson points out many applications for the system, including DNA purification, serum samples for preclinical and clinical trials, testing drugs-of-abuse, environmental analysis, testing pharmaceutical products for impurities, food-chemistry studies, and cleaning up biological fluid samples prior to HPLC and MS. This system is easy to use, Jamieson says, because “it generally is part of a robotic workcell that is configured for the customer’s method, and uses a Hudson PlateCrane to move the 96-well SPE blocks and sample microplates into and out of the FilterPress.” Plus, he says, “Our preconfigured SoftLinx software runs at the press of one button and is super easy to learn and use.”

SPE can include automation with added instruments, such as the Micro10x Reagent Dispenser. (Image courtesy of Hudson Robotics.)

Other SPE options

Various manufacturers create SPE systems and tools. Berlin-based Knauer designed the Online SPE System specifically for SPE used with its Azura HPLC system. The company notes that this combination reduces “analysis time and sample contamination” and provides “an increase of analyte yield.”

From Canada, Aurora Biomed notes that its VERSA Automated SPE workstations “fully automate SPE workflow from cartridge conditioning to sample derivatization on a single deck with innovative modules.” The company adds: “VERSA SPE workstations are highly scalable for different throughputs and budget, from the compact VERSA 10 to the highly customizable VERSA 1100, for applications in forensics, environmental samples, pharmaceutical compound analysis (ADME), clinical samples, and food safety.”

For SPE supplies, Kinesis (Vernon Hills, IL)—part of Cole-Parmer—makes microplates and cartridges. Georgia-based Sorbent Technologies also makes various kinds of SPE cartridges.

A variety of other devices can also be purchased. For example, ANPEL Laboratory Technologies in Shanghai offers an SPE vacuum manifold in 12-, 16-, and 24-port configurations.

Simplifying the steps

“Sometimes, other techniques are good enough, and sometimes people shied away from SPE because it seemed complicated and required expertise,” Haynes notes. So, in June 2015, Waters introduced the Oasis PRiME HLB reversed-phase products for acidic, basic, and neutral compounds. “This comes with defined protocols for a starting point, and, though it does a great job, sometimes a little optimization is needed to capture and recover specific compounds,” Haynes says. It also removes 95% of the contaminants—proteins, phospholipids, fats, pigments—that impact the analysis. Plus, this technique can reduce the typical five steps of SPE to as few as two.

In some applications—including drugs-of-abuse and pain-management—target molecules tend to be basic. To focus on these, Waters launched the mixed-mode Oasis PRiME MCX sorbent in January 2018, available in single-use cartridge and multiple-well plate formats. This form of SPE usually takes six steps, but the new Waters technique reduces that to three or four and removes 99% of the phospholipid matrix. As Haynes points out, the product is quality-control-tested with the protocol to ensure phospholipid removal performance.

These tools can be used as fit for purpose. “The first try is with Oasis PRiME HLB, and if you don’t get good capture and recovery of the basic compounds, then you can use Oasis PRiME MCX,” Haynes explains. “We always recommend starting with the simplest approach, and provide another option that is more specific but equally simple.”

This approach can be used with various detection methods. “Customers will be using it with ultraviolet detection and/or MS/MS,” Haynes says, “and this sample cleanup removes matrix interferences that can make quantification unpredictable and reduce sensitivity.” It also keeps columns cleaner and reduces the frequency needed for cleaning an MS platform. As Haynes concludes, “A little investment of work on the front-end increases confidence in the analytical results.”

Mike May is a freelance writer and editor living in Texas. He can be reached at [email protected]