Wavelength's UV/VIS Roundtable
This month's Technology Forum roundtable discussion covers UV/Vis - one of the longest standing spectroscopic techniques. As you’ll see from our panel’s comments, however, there is still a lot of activity in the field. Our participants this month are: Linda B. McGown, professor and chair of the Department of Chemistry and Chemical Biology at Rensselaer Polytechnic Institute; John Monti, senior scientist at Shimadzu Scientific Instruments; Shannon Richard, spectroscopy product manager at Shimadzu Scientific Instruments; David Clark, UV/Vis business manager for PerkinElmer Life & Analytical Sciences; and Dean Logan, UV-Vis-NIR/fluorescence product manager at Varian, Inc.
UV/Vis spectrophotometry is a mature analytical technique. Have there been any recent developments of significance in the field?
(McGown) Extensions to near-IR measurements come to mind, which are important for novel materials such as carbon nanotubes.
(Monti) Probably the most significant advance has been the introduction of xenon flash lamps as sources.
(Clark) Customer needs for UV/Vis instrumentation evolve continually just as they do for other analytical techniques. As a result, there are many new developments, which tend to focus on convenience, productivity, and ease of sampling.
(Logan) Adding versatility to a mature - and stable - analytical technique is an ideal strategy to address increasingly broad application needs without necessitating big changes in well-established methods.
UV/Vis instrumentation is used mostly for pharmaceutical, biotech, and academic applications. What other application areas can benefit from its use?
(Monti) UV/Vis is still the simplest, most cost-effective, and fastest method for quantification of analytes in liquid samples at concentrations in the ppm range. This could apply to innumerable situations in general industry, foods, cosmetics, optics, environment, and nutritional supplements, to name only a few. In addition, color and appearance are important measurements that are carried out using UV/Vis instrumentation.
(Richard) QA/QC, color analysis, film thickness, and even some applications in forensics have been seen throughout the years. We also see a lot of use in the optics industries.
(Clark) Due to the wide variety of applications and types of samples that can be measured, UV/Vis instrumentation is used in virtually every end-market. For example, PerkinElmer has many customers in the chemical, polymers, food and environmental markets, in addition to those mentioned. Also, one of our most important areas is materials science, which includes the glass, optics, coatings, and semiconductor markets.
(Logan) In fact, we find that of all the different products Varian manufactures, UV/Vis instruments address by far the broadest range of applications. Other areas include agriculture, food and beverages, environmental testing, chemical/industrial testing, and applications in the photonics/optics/semiconductor industries.
Can you discuss any research that has employed specialized spectrophotometry techniques (such as circular dichroism, spectropolarimetry, refractometry, etc.), or specialized instrumentation such as UV/Vis/NIR?
(McGown) Circular dichroism (CD) has been critical in academic studies of biomolecules, not only for structural characterization but also to study the effects of chemical modifications. CD also has important applications in nanotechnology. As mentioned earlier, the NIR region is important in studies of carbon nanotubes by absorption, CD, and fluorescence.
(Monti) CD/ORD (optical rotary dispersion) is finding more applications as we increase our understanding of the importance of conformational changes in proteins as underlying factors in many neurodegenerative diseases. The ability to quantify the active isomer in pharmaceutical preparations also has resulted in increased applications involving essentially a UV/Vis spectrophotometric liquid chromatography detector with a circularly polarized light source. The need for a more efficient, non-isotopic method for quantification of drug-receptor interaction has been met partially with the advent of surface plasmon resonance instrumentation, which employs highly sensitive measurements of changes in refractive index. The semiconductor industry has pushed the envelope for instruments with low UV (~165 nm) measurement capability while the communications industry has demanded NIR measurements at exceptionally high S/N. NIR has been at the forefront of process analytical technology (PAT) applications where the “spectrophotometer” is an integral unit of the manufacturing machinery, not only performing data measurements at high speeds but also communicating information derived from those data to other units such that process modifications and adjustments can be made in real time.
(Clark) Research on advanced materials for use in aerospace, telecommunications, automotive, and computer technology currently is thriving, and there is a strong demand for high performance UV/Vis and UV/Vis/NIR instrumentation to characterize new products. Researchers in these fields often require specialized optics and sampling systems.
(Logan) Perhaps the closest relative to UV/Vis spectrophotometry is fluorescence spectrophotometry, which extends UV/Vis techniques to greater levels of sensitivity and selectivity by the inclusion of a second monochromator positioned at right angles to the incident light in front of the detector. Using a fluorescence spectrophotometer along with a temperature-controlled multi-sample accessory and a variety of fluorophores, the Biochemistry team at Monash University in Melbourne, Australia has shown that it is possible to monitor subtle interactions between proteins - in intact, living cells using the fluorescence resonance energy transfer (FRET) technique. Physiological studies such as this are essential in helping to understand the absolute fundamentals of life science, and they cannot be performed in a gel, or on a column, or in a plasma, and so on.
Since scanning and photodiode array spectrophotometers can perform single wavelength analyses, is there a continued need for non-scanning systems?
(Monti) Yes, for rapid kinetics applications.
(McGown) This depends upon the quality of information available from non-scanning systems relative to the analytical needs of the experiment. Also, there will continue to be a need for non-scanning laser-based measurements in detectors, time-resolved measurements, and other specialized applications.
(Richard) Perhaps the biggest need for this type of instrumentation is in the PAT area, where monitoring at one single wavelength is all that is necessary for some applications.
(Clark) The demand for non-scanning systems probably is decreasing, except for very low-priced systems for applications such as colorimetry.
(Logan) Other than as an extremely low cost option, we believe that the days are numbered for non-scanning systems. Researchers tend to want to know more about their samples. Scanning UV/Vis spectrophotometers offer the ability to perform single wavelength reads at high speeds, but also give the flexibility of scanning for more sample information and quality control.
Are there any changes expected in the marketplace?
(McGown) Accessible laser technology will continue to have an impact.
(Monti) More low UV and NIR applications and more “applicated” instruments.
(Clark) Customers continue to ask for easier-to-use instrumentation that helps increase productivity. The UV/Vis market is no different from any other analytical technology in that respect. There are many ways to address these needs, through development of more user-friendly software, simpler, more automated sampling accessories, and more reliable instrumentation.
(Logan) The technique is mature and so is the market. I think it will continue to grow at a modest pace, although with such a large number of vendors it is reasonable to predict that some degree of consolidation will occur.
Anything else you’d like to add about UV/Vis?
(Richard) Although UV-Vis may be considered a mature market or product, it is a widely used technique for many applications. Quantitation, kinetics, and simple spectral scanning are just as useful to scientists today as they were years ago, and typically cannot be performed by other means. Some may also forget that spectroscopy is the cornerstone for detection in other instrumental methods such as HPLC, where the most common detectors are UV, photodiode array, and fluorescence detectors. Without the technological advances in spectroscopy, those other techniques might not have been so successful.
(Logan) I think UV/Vis spectrophotometry will continue to be a valued workhorse used in tandem with a variety of other techniques as we move forward. The key benefits of the technique are that measurements are simple, rapid and, perhaps most importantly, generally are not invasive or destructive to samples.
(Monti) To borrow from Mark Twain, “The reports of its death are greatly exaggerated.”