Pumps that drive the liquid phase through the column should be capable of achieving the appropriate pressure for your intended use. For example, a UHPLC column with a narrow i.d. and very small sorbent molecules will require differ- ent pressures than a larger diameter column with larger sorbent molecules. Both smaller sorbent particles, and smaller column internal diameters, require greater pressures from the pump to drive the solvent through the column.
A pump’s ability to maintain enough pressure to drive the solvent through the column at a steady rate is important. UHPLC systems can run at pressures up to 15,000 psi. Much greater pressures are possible—even up to 100,000 psi using submicron sorbent particles—but these are not common.
UHPLC detectors There are many kinds of detectors possible for UHPLC, and your choice of detector will depend on your planned usage. Examples of detector types are listed below.
• UV-VIS detector: The commonly used ultraviolet-visible light detector (with single- or multiple-wavelength capabilities)
Table 1 – UHPLC system manufacturers Agilent Technologies Dikma Technologies EMD Millipore
Fortis Technologies
detects absorption of light in the UV-VIS wavelength range.
• Photodiode array detector: This detector also detects absorption of light in the UV-VIS range, but does so using multiple arrays that obtain measurements over a wide range of light wavelengths.
• Fluorescence detector: Best for detecting samples that fluoresce, fluorescence detectors are also among the most sensitive detectors because, generally, impurities do not emit fluorescent light, so the signal-to- noise ratio using this method is high.
• Single and tandem quadrupole mass spectrometry detectors: These detectors are best for detecting molecules in UHPLC fractions according to their mass.
Other detection methods are suitable for particular types of samples, such as chiral compounds. For samples that are not detect- able by conventional UV-VIS light absorption methods, consider refractive index detectors, evaporative light scattering detectors, and charged aerosol detectors.
• Circular dichroism detector: Designed for those working with chiral compounds, circular dichroism detectors also detect UV- VIS light absorption for nonchiral compounds.
• Refractive index detector: An RI detector detects compounds based on the measured refraction of light in an aqueous solution.
• Evaporative light scattering detector: This type of detector is usually at least several times more sensitive than a refractive index detector, and works by atomizing the sample, illuminating the resulting particles, and then detecting the light that they scatter.
• Charged aerosol detector: Using a method similar to an evaporative light scattering detector, a charged aerosol detector ionizes the atomized particles with charged nitrogen gas and then detects them electrically.
More tools and technology:
Santa Clara, CA Lake Forest, CA Billerica, MA Cheshire, U.K.
Hitachi High Technologies America Schaumburg, IL JASCO Knauer
Easton, MD
Optimize Technologies PerkinElmer Phenomenex Restek Corp. Shimadzu
Thermo Fisher Scientific Waters Corp. ZirChrom
Berlin, Germany Oregon City, OR Waltham, MA Torrance, CA Bellefonte, PA Columbia, MD Waltham, MA Milford, MA Anoka, MN
www.agilent.com
www.dikmatech.com www.emdmillipore.com
www.fortis-technologies.com www.hitachi-hta.com www.jascoinc.com www.knauer.net
www.optimizetech.com www.perkinelmer.com www.phenomenex.com www.restek.com
www.ssi.shimadzu.com www.thermoscientific.com www.waters.com www.zirchrom.com
AMERICAN LABORATORY • 21 • SEPTEMBER 2013
The future of UHPLC Although conventional HPLC is still more com- monly used, UHPLC is becoming increasingly powerful as researchers refine its methods. In fact, some chromatography systems, such as the X-LC from JASCO (Easton, MD; www.
jascoinc.com), offer both conventional HPLC and UHPLC in one instrument. Others, such as the Shimadzu Nexera X2, have modular designs so that researchers can tailor the features of their chromatography system according to the func- tions they need. Thus, the technology and tools for UHPLC are likely to grow in both number and specialization in the future.
Please see Table 1 for a list of manufacturers of UHPLC systems. More information is available at
www.labcompare.com.
Caitlin Smith is a freelance science writer who has a Ph.D. in Neuroscience from Yale Univer- sity and postdoctoral work in Electrophysiology and Synaptic Plasticity; e-mail:
caitlin.smith@
comcast.net.
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