Product Focus: UV-VIS Spectrophotometers

Despite the technique’s maturity, ultraviolet and visible (UV-Vis) spectroscopy has been a fertile area for innovation, both in terms of underlying technology and instrumentation.

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Still A Rich Area for Innovation

Despite the technique’s maturity, ultraviolet and visible (UV-Vis) spectroscopy has been a fertile area for innovation, both in terms of underlying technology and instrumentation. The continuous xenon light source, which operates from UV to near-infrared, has been an enabling technology for UV-Vis, says Michael W. Allen, Ph.D., marketing manager for NanoDrop UV-Vis and fluorescence products at Thermo Fisher Scientific (Madison, WI). Xenon lamps replace older tungsten and deuterium lamps, which require extremely stable power supplies to deliver quality data.

The xenon flash lamp, a full-spectrum single source, remains on only during data acquisition. “This makes it a very long-lived source,” says Dr. Allen. Thermo offers xenon flash lamps in most of its mid- to high-end UV instruments, as do most other vendors, who continue to sell tungsten and deuterium continuous- source lamps as well.

Thermo guarantees its lamps for three years, but the installation lifetime is almost twice that, according to Dr. Allen, thus saving customers the cost of replacing an expensive lamp. “Users in QA/QC labs can enjoy walk-up usage, without a warm-up period.”

Another push has been to make instrument footprints smaller. Part of that trend has been the introduction of micro-volume instruments that generate full UV-Vis spectra on microliter-sized samples. Avans Biotechnology, Quawell, GE Healthcare, and Thermo Scientific manufacture instruments within this category. Other companies, for example Agilent Technologies and Shimadzu, sell microliter-volume cells for their macro-scale spectrometers.

Speed and throughput vs. sample considerations

Micro-volume spectroscopy preserves precious samples, but that is not the driver for adopting this format, Dr. Allen tells Lab Manager Magazine. “The critical factor is the convenience of not having to prepare a cuvette, pipette in the sample, wait for the spectrum to run, and clean out the cuvette when it’s all over.” These workflow complications represent a barrier to fully utilizing traditional cuvette measurements for higher throughput applications, he says.

Instruments in Thermo Scientific’s NanoDrop line, for example, acquire a full spectrum in less than five seconds. After discarding the pipette tip and wiping the spectral window surfaces clean, the instrument is ready for the next sample.

Unlike methods such as infrared and chromatography-mass spectrometry, UV-Vis is suited to analyzing known compounds. “The method’s bread and butter is concentration measurements,” Dr. Allen explains. Obtaining more information out of a UV-Vis spectrometer, particularly in a field application, requires additional reagents or sample preparation. Even then, it comes nowhere close to “gold standard” techniques for unknown compound identification, like NMR and mass spectrometry.

Yet software and automation improvements have helped to turn UV-Vis instruments into true analyzers, as opposed to standalone instruments. This is one area where Thermo has excelled, particularly in the era of the nonspecialist instrument user and where the overwhelming percentage of instruments run dedicated methods.

Changing the user experience

“Instrument makers have to focus not on the science and the spectroscopy, but on helping users get answers. That’s where the field is going,” says Dr. Allen. Thermo’s CUE method development software, for example, which is packaged within the company’s INSIGHT analysis software, allows customers to design workflows in macro-like fashion and to design customized user interfaces.

For the vast majority of routine UV-Vis applications, adapting instrumentation for ease of use is the overriding trend.

According to Keith Bratchford, marketing director at Agilent Technologies’ Melbourne, Australia, facility, sample preparation and cuvette handling become limiting factors for high-throughput laboratories.

Agilent solves this problem through the use of fiber-optic probes that insert into the sample and take measurements directly. Similar to the micro-sample instruments, sample preparation and cuvette manipulation are eliminated. “Customers performing routine UVVis analysis are anxious to go in this direction,” Mr. Bratchford says.

Fiber-optic probes save space because the instruments can be placed anywhere, including upside-down, as on the ceilings of ocean-going research vessels. Probes hang down from the instrument, allowing true highthroughput testing of water samples. A similar configuration could be used in a quality or industrial test facility, or for in-line quality control. Similarly, in a biology laboratory, technicians can perform measurements on hundreds of samples without removing them from their containers.

Beam me up, Scotty

Miniaturization has been an exciting trend in UV-Vis spectrometry. Carl Zeiss introduced a miniature (but not quite handheld) instrument in 1992. “And we took off from there,” says Rob Morris, director of marketing at Ocean Optics (Dunedin, FL).

UV-Vis instruments have become smaller as a result of microelectronics miniaturization, but were always limited by the instrument’s “optical bench”—the components and pathways used for delivering radiation and measuring absorbance or transmittance. The most prevalent UV-Vis detectors are charge-coupled devices and photodiode arrays, which have become inexpensive due to high-volume applications like bar code scanners. Ocean Optics now uses a complementary metal-oxide semiconductor detector that allows true miniaturization. Three or four of the company’s STS microspectrometers, which are used mostly for embedded/OEM applications, fit into the palm of a hand.

Mr. Morris sees bright days ahead for even more miniaturization and integration into what he terms Star Trek “tricorder-like” devices. Such handheld instruments might use filtering technology or spectral sensing to monitor just a few wavelengths (versus providing a full spectrum) for niche field applications. Connectivity to the Internet and radically redesigned user interfaces could help create virtual UV-Vis networks from nodes around the globe, with spectral libraries residing in the cloud.

Another change he sees is bundling all computing with the handheld instrument to eliminate the computer box altogether. One could imagine creating a global map of atmospheric conditions, such as ozone concentrations, from strategically placed cell phonesized devices.

If Ocean Optics’ smallest handheld spectrometer is any indication, that day is not too far off. The device, which now connects via Ethernet but may one day incorporate wireless communications, looks more like a boom box than a scientific instrument.

For additional resources on UV-Vis spectroscopy, including useful articles and a list of manufacturers, visit www.labmanager.com/spectrophotometers.

Categories: Product Focus

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Published: September 9, 2011

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