Light absorbed or emitted in nature reveals information about objects in, on, and around Earth, even into space. To analyze atmospheres and objects, scientists use both ultraviolet (UV) and visible (Vis) light, which have wavelengths of 10-400 and 380-740 nanometers, respectively. Portable tools to detect these wavelengths provide even more information, because a scientist can take the device where it’s needed.
Some scientists make use of UV-Vis devices across their careers. Kimberly Strong, professor and chair of the department of physics at the University of Toronto, first used UV-Vis spectrometers in 1992. She started using UV-Vis detection during her post-doctoral work at the University of Cambridge and York University, and she continues to use this technology in many different ways. As she says, “I have worked with ground-based, balloon-borne, and satellite-based UV-Vis instruments.”
Other scientists also benefit from portable options. “We use the portable UV-Vis spectrometer whenever testing gemstones, usually colored stones, for our clients onsite—that is when we are testing abroad, for example, at our booth in trade shows,” says Michael Krzemnicki, director of the Swiss Gemmological Institute SSEF in Basel, Switzerland. The device that he uses sits on a table and is connected to a laptop. Although it’s not handheld, Krzemnicki calls it “portable and easy to use.”
How portable a device needs to be depends on the application. The portability of commercial devices ranges from being easy to move around to actually being handheld. In some cases, any mobility is enough; other times, scientists really need a UV-Vis device that can be carried in one hand.
The right fit for the project
When asked why she picked UV-Vis detection, Strong says, “The UV-Vis spectral range includes absorption features of a number of trace gases, making it well suited for retrieving their atmospheric abundance from atmospheric absorption spectra.” As examples of trace gases, she mentions ozone, several halogen gases involved in ozone chemistry, nitrogen dioxide, and several other gases that affect air quality, as well as aerosols. “UV-Vis instruments are relatively compact, making them suitable for deployment on high-altitude balloons and satellite platforms, as well as on the ground as part of long-term global networks, such as the Network for the Detection of Atmospheric Composition Change and the Aerosol Robotic Network, AERONET,” Strong explains.
Krzemnicki and his colleagues use this technology for items on or in the earth. “The UV-Vis absorption spectra—and the UV-emission spectra, which we also can take with the same instrument—provide us with principle information, [like] spectra, about the color of gemstones.”
These scientists use the spectrum to learn more about a stone. The analysis “may help to identify the material—for example, sapphire or blue glass, copper-bearing ‘Paraiba’ tourmaline or blue tourmaline without copper, blue spinel that is colored mostly by iron or cobaltspinel.” Krzemnicki and his colleagues also use UV-Vis detection to deduce how a stone has been treated, such as distinguishing green-dyed jadeite from naturally chromium-colored jadeite or heated from unheated spinel. “And finally,” he says, UV-Vis analysis “may support us in deducing the geographic origin of a colored gemstone—for example; sapphire from Kashmir versus sapphire from a Basaltic deposit, such as in Pailin, Cambodia; or emerald from Colombia versus emerald from Afghanistan.”
Picking a product
In selecting the right portable UV-Vis device, start by knowing how you plan to use it. “Know your measurement requirements,” Strong says. As she points out, this should include the required spectral range, spectral resolution, spectral stability, integration time, measurement frequency, temperature stability, and factors associated with the type of detector, including quantum efficiency, signal-to-noise ratio, and cooling.
“There are trade-offs between handheld UV-Vis devices and larger UV-Vis spectrometers,” Strong says. “Each has its benefits and disadvantages.” In some situations, scientists develop a custom solution. As an example, Krzemnicki says, “What we use is a portable and lightweight UV-Vis absorption spectrometer, which we (SSEF) developed in collaboration with the physics department of the University Basel.”
When asked what a scientist should look for in a UV-Vis device, Krzemnicki says, “Buy quality!” It’s important, he says, to purchase a device with a very sensitive detector and “an excitation lamp with a broad and strong emission spectrum ranging deep into the UV range—down to about 300 nanometers.”
To me, a biologist with experience in the field and the lab, the possible uses of a portable UV-Vis detector are endless. It gets even better if the device is handheld—something that I can take with me and aim at whatever I see.
What light do different plants reflect? How about bird feathers? What about insects? There is nothing in nature that I can’t point the device at and learn something. What will I learn? I’m not sure, but it’s a perfect tool for exploring. Any number of spectral readings from nature could trigger more questions, followed by experiments.
When a scientist needs to make UV-Vis measurements in the field, portability really matters. It’s not always possible to drag a big instrument to a site. Maybe a portable UV-Vis spectrometer is not as sensitive as a lab-based one. Maybe it lacks some of the fancy features that a bigger device delivers. But a scientist can take this device to the samples.
Those samples range from gases in outer space, to gems around the world, and anything else that a scientist wants to analyze. Some of the most exciting results might come from the completely unknown. Decades ago, Tom Eisner, the late chemical ecologist from Cornell University (Ithaca, NY), showed that insects home in on flowers by seeing UV patterns that look like a target. Who knows what else nature can teach us when scientists look deeper into places and things with UV-Vis spectroscopy. Portable devices will help us answer that question.