Sample Prep for LC, GC, and SFC at Pittcon® 2013

At Pittcon® 2013, sample prep stood out as a major focus, perhaps because of the few advances in chromatography instrumentation. In addition, some sample preparation is spilling over into other technologies, including optical spectroscopy and mass spectrometry. In this report, I endeavor to cover sample prep that is not directly coupled to a particular technique. For example, headspace sample preparation is uniquely tied to GC and is thus covered in the GC review (http://www.americanlaboratory.com/913-Technical-Articles/136800-Advances-in-Gas-Chromatography-Instrumentation-at-Pittcon-2013/).

Sample preparation is still the slow runner in the race to deliver actionable information to the decision-maker. Plus, automating sample prep usually reduces variance attributed to humans and thus improves data quality. The best approach seems to be: 1) reduce human involvement; 2) use design-of-experiments, including factorial design, to estimate experimental variables; and 3) once the design is verified, adopt a “trust, but verify” approach.

Accelerated evaporation system

Horizon Technology Inc. (www.horizontechinc.com) provides an example of the “trust, but verify” approach in sample prep, particularly for environmental samples for chromatography. The XcelVap™ automated benchtop Evaporation/Concentration System is designed for simultaneous evaporation of up to 54 samples and can prepare samples for a chromatography system in a wide variety of markets, including environmental, clinical, and toxicology. Sample volumes can range from less than 1 mL up to 200 mL. If concentration is performed manually, sample uniformity usually suffers compared to automated technology. Pressure profiling is automated to gradually increase the evaporation gas flow, so splashing and cross-contamination are avoided and the optimum evaporation time is achieved.

Sample concentrator

Also for sample concentration by evaporation, Fluid Management Systems (FMS; www.fmsenvironmental.com) introduced the SuperVap™ concentrator for controlled sample concentration directly in the sample vial. The SuperVap directs a stream of heated nitrogen indirectly into each GC sample vial. The heating cycle can be programmed for maximum efficiency. Up to six samples can be processed in parallel. Endpoints are detected, which triggers shutdown of the flow and alarm. This prevents overdrying and excessive heating of the sample. The volume range for vials is 500 μL–220 mL. Target applications include pesticides; herbicides; persistent organic pollutants (POPs); polychlorinated biphenyls (PCBs); polyaromatic hydrocarbons (PAHs); pharmaceuticals, including excipients; and personal care products. Additionally, reports on the processing of each sample may be reported to a LIMS.

Dried blood spot analysis system for LC/MS

Interest in dried blood spots continues to increase since they are smaller and easier to handle than blood in collection tubes. CAMAG (www.camag.com) introduced the DBS-MS 500 dried blood spot analysis system for LC/MS. The robotic sample processor selects the card from a 100-position sample tray, reads the identification, and compares it with the expected identity. The next station applies the internal standard. The card is then transferred to the extraction station, where analytes and internal standard are eluted from the card and passed to the sample loop of the LC. The volume is typically 20–200 μL. Following injection, the sample loop is thoroughly washed to avoid carryover. Analysis of replicates shows a reproducibility of better than ±3% for peak area ratios. This is but one example of improved data quality delivered by automating, with thoughtful design, what is often a manual process.

QuEChERS sample prep workstation

Sample preparation utilizing QuEChERS protocols is very popular. Typically, QuEChERS involves several manual steps. As with any manual protocol, one can expect improved quantitative consistency if the human factor is reduced. Human implementation involves several steps, but these are not very sophisticated and hence are suitable for automation. With the popularity of QuEChERS, the engineers at Teledyne Tekmar (www.teledynetekmar.com) saw a need and opportunity—hence the AutoMate-Q40 sample prep workstation. The AutoMate-Q40 automates all of the sample preparation protocols, including liquid dispensing; vortex mixing; shaking, removal, and resealing of vials; addition of solids; estimation of liquid levels; centrifugation; matrix spiking; and label identification via barcode. Upon installation, the Q40 is programmed to prepare pesticide residue samples according to AOAC 2007.01 (Pesticide Residue) and EN 15662.2008.

Robotic sample processor

For decades, CTC Analytics AG (www.palsystems.com) has provided a series of prep-and-load sample processors. The open design has made the “PALs” an easy choice for many labs. This year, CTC introduced the PAL RTC, where the RTC stands for “robotic tool change.” Tools include a liquid syringe, solid-phase microextraction (SPME), and headspace. The robotic arm selects the correct tool dictated by the protocol. Other modules include a vortex mixer, agitator, SPME fiber conditioner, injection and switching valves, and Fast Wash. The GC version was in the booth; the LC version is close behind.

Automated operational qualification of instruments

Multiple-well plates are rapidly replacing sample vials for automated assays. Many autosamplers have adopted this format. Automated sample prep usually relies on liquid handling for reagent addition and dilution for generating calibration curves, but for quantitative work, one needs assurance that automated reagent addition is reproducible and accurate. Artel (www.artel-usa.com) has extended its range of Multichannel Verifi cation Systems (MVS®) to include several solvents. The MVS checks the performance of multiple-well (1, 2, 4, 6, 8, 12, 16, 24, 96, and 384) liquid handlers that are used in preparing and transferring samples. In 2013, the list now includes 100% DMSO, which is commonly used as the primary solvent for stock solutions of analytes and metabolites.

Stationary phases

I recall my wild enthusiasm when introduced to the concept of molecularly imprinted polymers (MIPS) over 25 years ago. This was followed by decades of disappointment as the technology continuously failed to live up to expectations. However, as with many inventions in science, patient visionaries make the difference. Polyintell (www.polyintell.com) was founded in 2004 to develop intelligent polymers for use in sample prep of analyte classes and even specific analytes, even isotopes such as 18F. One of the problems with MIPS was leakage of the imprinting reagent that provided a high background concentration during use in assays. Polyintell responded with MIPS that had a similar shape and enhanced selectivity as the target analyte, but had a significantly different structure. This removed ambiguity of the origin of the analytes. The company published a 56-page applications notebook with methods. Most offer greater than 90% recovery of spiked analytes.

SiliCycle (www.silicycle.com) is rapidly expanding its product line in sample preparation. SilaPrep™ cartridges and multiple-well plates are available in a range of bed sizes. Sorbents include silica, reversed-phase liquid chromatography (RPLC), ion exchange, and several specialty items. If silica is a problem, then SiliCycle recommends SilaPrepX™, which are filled with beads of organic polymers.

Supelco (www.sigmaaldrich.com) introduced three sample prep products: 1) Supel™ QuE Z-Sep sorbents for QuEChERS dispersive solid-phase extraction use zirconia-coated silica particles to remove lipids and pigments from samples prior to pesticide residue and POP analysis. These sorbents provide more robust LC/MS and GC/MS analyses. 2) Supel Tox SPE cartridges reduce sample prep time for chromatographic mycotoxin analysis, provide better reproducibility, and are easier to use than the industry-standard immunoaffinity columns. 3) Supel Sphere Carbon/NH2 SPE cartridges for pesticide residue analysis contain both spherical carbon and aminopropyl silica particles, improving flow characteristics and allowing for sample preparation in half the time.

Phase separator

Biotage® (www.biotage.com) introduced the Universal Phase Separator for solvent extraction. Conventional phase separators work only for nonpolar solvents with a density higher than the aqueous phase. The Universal Phase Separator has a phase-separating membrane tube concentric to the outer reservoir. Just pour your two-phase mixture into the outer annulus, and the organic washes through and down the center tube to a receiver. Once separated, pour out the aqueous solution. So simple–bye bye glass extraction flasks!

Carbon SPE

United Science (www.uniscicorp.com) introduced CarbonX SPE cartridges with graphitized carbon black (GCB) deposited on porous silica, alumina, clay, and iron. GCB has unique selectivity for geometric isomers. It is highly retentive of hydrophilic hydrogen bond acceptors and polar analytes. For SPE, three phases are offered: 1) CarbonX COA, a polar adsorption phase; 2) CarbonX COS, an acidic polar adsorption phase; and 3) CarbonX Plus, for basic polar analytes. All are available in beds of 100 mg–5 g.

Conclusion

Gone are the days when sample prep was driven by reduction in cost. As was evident at Pittcon 2013, the concerns today are improving data quality and time to result. I expect that novel materials and excellent engineering will improve work flows for the next few years, or longer. So, come to Pittcon 2014 and see the latest.

Robert L. Stevenson, Ph.D., is a Consultant and Editor of Separation Science for American Laboratory/Labcompare; e-mail: rlsteven@comcast.net.

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