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LEDs light up the future of UV/Vis: UVC LEDs are proving their worth in UV/Vis spectroscopy applications by offering better performance, faster data acquisition and longer lifetimes.

Molecular spectroscopy techniques, such as UV/Vis, infrared and NMR, account for more than a third of a $10 billion market. Of these various techniques, UV/Vis spectroscopy is one of the most basic spectroscopy methods, and is used to perform analyses for a wide range of applications, including DNA quantification at micro volumes and prep HPLC. The majority of customers that intend to purchase UV/Vis spectrometers highlight the following key factors in their purchase decision:

* Performance (sensitivity, reproducibility, wavelength accuracy)

* Osage cost (ease of maintenance and use, low operating cost)

* Data acquisition (faster acquisition and data analysis)

* Instrument cost

DNA quantification relies on using absorption spectroscopy at 260 and 280 nm to determine DNA concentration and sample purity. Prep HPLC is commonly used for purifying proteins, isolating natural extracts and other routine measurements, and relies on absorption or fluorescence spectroscopy in the UV wavelength range for controlling fraction collection. Manufacturers of these instruments have traditionally chosen xenon flash and deuterium lamps as light sources for these applications. However, high performance UVC LEDs can address some of the key decision-making criteria owing to the inherent benefits of LEDs as a solid state light source.

Sensitivity, reproducibility and wavelength accuracy

Sensitivity and detection limits in absorption spectroscopy are related to light intensity; for the same system noise, a higher intensity light source allows for a shorter integration time for the photodetector and a lower detection limit. In fluorescent spectroscopy, a higher light intensity can enable detection of lower concentration of fluorophores. As seen in Figure 1, all of the light output of an LED is concentrated at the wavelength of interest. As a result, sensitivity and detection limits of LED-based spectroscopic instruments are almost always superior to plasma-based UV lamps.

Reproducibility and wavelength accuracy can be impacted by stray light from the instrument's light source. Stray light refers to radiation at wavelengths other than the bandwidth selected for measurement. Instruments based on UV lamps use monochromators to filter unwanted wavelengths. Still, imperfections in the dispersing element, which can increase over time with normal operating conditions, have been shown to lead to stray light. Because LEDs are monochromatic light sources, monochromators are not required to eliminate stray light.

Ease of use and maintenance

For decision makers of instrument purchases, ease of use and lowered cost can trump broad functionality and features of an instrument. Since prep HPLC and DNA quantification rely on a few or even a single wavelength for measurement, highly precise, reliable measurement provides more value than information at multiple wavelengths.

Maintenance and operating costs vary based on light source, with the most significant costs being replacement of the light source. Over a five-year operating period, a deuterium lamp will typically require a yearly replacement--a cost of $400 per replacement. Xenon flash lamps require replacement after 1E9 flashes (about three years) at a typical lamp cost of $450. UVC LEDs can exceed the lifetimes of deuterium lamps and xenon flash lamps (Figure 2)--making the replacement cycle far longer than either of the legacy technologies.

Faster data acquisition

Labs are looking to increase productivity in DNA quantification and prep HPLC without sacrificing quality of measurement. For these high-throughput applications, instruments using light sources that require a warm up period, such as deuterium lamps, are being replaced with instant on/off solutions like xenon flash lamps and UVC LEDs. Not only does this allow for walk-up usage, it also maximizes lifetime of the light source.

Miniaturization of electronics and processing equipment has allowed manufacturers to reduce instrument size for mobile instruments. Up to now, the limiting factor has been the physical size of the optical train--the components required for optical measurement. Reducing the footprint of these elements allows for further reduction of size to meet the expectations of the market. Instruments based on UVC LEDs require fewer components, which allows for more compact instruments. The ability to take accurate field measurements decreases analysis time by bringing the instrument to the sample instead of vice versa. For example, fluorescence spectroscopy of blood samples in the field reduces time for infection diagnosis and enables faster treatment.

Reducing components to save costs

As seen in Figure 1, deuterium and xenon flash lamps provide high light output across many wavelengths. However, these' applications require measurements of a single or few wavelengths, thus the rest of the light in unwanted wavelengths must be filtered out. These lamps require expensive, bulky power supplies, which limit cost effectiveness of the solution. Instrument manufacturers are addressing this by expanding their product portfolio to incorporate UVC LED-based devices--reducing instrument costs by 40 to 80 percent. Cost savings are also experienced by the end-user in drastically reduced operating and lamp replacement costs over a five-year period.

Instruments based on UVC LEDs can address primary decision drivers around performance, usage and data acquisition. With improved performance, manufacturers can provide products that offer longer lifetimes and better sensitivity than those based on deuterium or xenon flash lamps. Such trends are leading to the adoption of UVC LEDs as a core technology in UV/Vis spectroscopy applications.

by Hari Venugopalan, Director of Global Product Management, Crystal IS, Green Island, N. Y.
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Title Annotation:Separations & Spectroscopy: Feature
Author:Venugopalan, Hari
Publication:Laboratory Equipment
Date:Jan 1, 2015
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