Report pubs.acs.org/jchemeduc
UV−Visible Spectrometers: Versatile Instruments across the Chemistry Curriculum Demetra A. C. Czegan* and Diana K. Hoover Division of Natural and Health Sciences, Seton Hill University, Greensburg, Pennsylvania 15601, United States ABSTRACT: This article describes a wide range of commercially available UV− vis spectrometers, with particular emphasis on educational models, and how this technique can be included in all aspects of the chemistry curriculum. Portable instrumentation and new software technologies are also highlighted.
KEYWORDS: Analytical Chemistry, Laboratory Instruction, Instrumental Methods, Laboratory Equipment/Apparatus, UV−Vis Spectroscopy FEATURE: Instrumentation Topics for theTeaching Laboratory
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typically consist of a tungsten lamp source, a grating monochromator, phototube detector, and LED or analog built-in display. One beam of light passes through one cuvette of sample and then onto the detector. These instruments require manual background adjustments for each wavelength and type of sample; therefore, it can be cumbersome to collect spectra, although it is quite practical for uses requiring multiple measurements at one wavelength, as in Beer−Lambert law experiments, for example. These instruments are also affordable, durable, semiportable, and, because of their inherent simplicity, can be starting points for students learning about spectroscopy. More modernized scanning versions of the single-beam instrument are now available and include automatic wavelength adjustment and computer interfacing. These instruments still have one light beam and one sample; however, the blank is zeroed over the selected spectral range and stored in the computer memory, and then subtracted from the sample spectrum. An example of this type of instrument is the PhotoLab 6600 manufactured by Global Water. Scanning single-beam instruments offer more functionality than the traditional nonscanning version, but also come with a higher price tag.
ltraviolet−visible absorption spectroscopy (UV−vis) was reported as the most common technique taught and employed in instrumental analysis courses in an article in this Journal, which asked undergraduate institutions to list the most important instruments in the chemistry curriculum.1 Here, we provide an overview of UV−vis spectrometers, representing the full continuum of commercially available instruments. A brief literature survey of the educational use of UV−vis in many of the courses in the chemistry curriculum is also included, as well as a characterization of the benefits and options of emerging technologies.
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WHAT IS OUT THERE? THE RANGE OF COMMERCIALLY AVAILABLE UV−Vis SPECTROMETERS A vast array of UV−vis spectrometers are available in the market, ranging dramatically in price, size, and functionality. Many are highly suited to academic uses, from high schools through university research laboratories. These instruments can be divided into three categories: single-beam, double-beam, and dispersive; variations occur based on five basic components: light source, light dispersing unit, sample holder, detector, and readout device. Almost all instruments use a cuvette-based sample holder; however, high-end instruments may have thermostatted sample chambers, flow-cells, or integration spheres. Tables 1 and 2 outline the features of several different instruments, providing a sampling from each category.
Double-Beam Spectrometers
Single-Beam Spectrometers
Scanning double-beam UV−vis spectrometers, such as the Perkin-Elmer Lambda series, are the most prevalent at colleges and universities. These instruments consist of two sample chambers, one for a blank and one for the sample. The light beam is divided, passes through each chamber, and the difference between the two beams is detected, allowing for instantaneous
The simplest type of UV−vis spectrometer is a single-beam, nonscanning model, such as a Thermo Spec20. These instruments
Published: January 25, 2012
© 2012 American Chemical Society and Division of Chemical Education, Inc.
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$5000 Portable Additional entrance slits, long-pass filters, optical fibers http://www.oceanoptics.com/ (accessed Jan 2012)
$500 Portable Optical fibers; LabQuest data logger (operation without computer) http://www.vernier.com/ (accessed Jan 2012)
http://www.spectralevolution.com/ (accessed Jan 2012)
5.5 × 2.5 × 6.5 USB interface (PC only) or Bluetooth wireless PDA interface $15,000 Portable Cuvette system ($2000)
Portable fiber optic-based spectrophotometer ideal for reflectance studies Dispersive Environmental and geological 310−1100 3.2 3.3 Tungsten halogen lamp; diffraction grating; Si diode array detector; fiber optic input
Spectral Evolution PSP1100
The instruments listed here were selected to provide a representative sample of the variety of UV−vis spectrometers available on the market; for a more complete list of manufacturers, refer to Table 3, and search online. bThese specifications were obtained from company Web sites or representatives and are meant for comparison purposes only. A detailed description of each instrument is beyond the scope of this article; please consult company Web sites and local representatives for more specific information. cThe costs shown here are approximate, provided for comparison purposes only; actual purchase prices will varyplease consult company Web sites and local representatives for more specific information.
a
Web Site URLs
Size, in. Interface and Computer Compatibility Cost, U.S. Dollarsc Portability Additional Options
Dispersive Research and teaching laboratories; Industrial 200−850 1.5 Variable (slit dependent) RF deuterium and tungsten lamps with cuvette holder; Czerny−Turner grating; linear CCD array detector 11 × 4 × 1.5 (combined) PC (Windows/Linux) and Mac with USB interface
Dispersive Educational 380−950 2.5 1.0 Tungsten halogen (Abs) and 2 LEDs for fluorescence (405 and 500 nm); diffraction grating; linear CCD array detector 6 × 3.5 × 1.5 USB computer interface (PC or Mac)
Type Primary Use Range, nm Resolution, nm Abs Max Source and Detector Components
Scientific-grade small footprint spectrometer and integrated sampling system source
Ocean Optics USB4000-UV−VIS and USB-ISS-UV−VIS
Affordable spectrophotometer and fluorometer
Vernier SpectroVis Plus
Description
Model Specificationsb
Table 1. Specifications of Dispersive UV−Visible Spectrometersa
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Global Water PhotoLab 6600
Portable spectrophotometer for both field and lab measurements Single-beam scanning Environmental (water testing) 190−1100 1 3.0 Xenon flashlamp; grating monochromator; photodiode detector 16 × 8 × 12.5 Integrated display and keypad (stand-alone); USB interface (PC only) $7500 Semiportable 12 V power supply adapter; barcode scanner http://www.globalw.com (accessed Jan 2012)
Thermo Scientific Spectronic 20D+
http://www.thermo.com (accessed Jan 2012)
$2000 Semiportable None
Low-cost, rugged, and reliable spectrophotometer Single-beam Educational and industrial 350−950 20 2.0 Tungsten halogen lamp; grating monochromator; phototube detector 16 × 8.5 × 13.5 Computer interfacing requires aftermarket adaptations
Shimadzu UV-2600/2700
http://www.ssi.shimadzu.com (accessed Jan 2012)
$15,000 Not portable Integration sphere ($8000)
18 × 24 × 9 USB interface, (PC only/Windows 7 [32 bit] compatible)
Double-beam scanning Research and teaching laboratories; industrial 185−900 0.1 >5.0 Deuterium and tungsten halogen lamps; single (2600) or double (2700) monochromator; photomultiplier detector
Double-beam scanning spectrometer
Perkin-Elmer Lambda 750 UV/vis/NIR
$40,000 Not portable Integration sphere ($15,000−30,000); Peltier accessories for thermostatting http://www.perkinelmer.com (accessed Jan 2012)
High-performance spectrophotometer for chemistry and materials science Double-beam scanning Research and industrial 190−3300 0.2 6.0 Deuterium and tungsten halogen lamps; doublebeam, double-monochromator; photomultiplier and Peltier-cooled PBS detectors 40 × 29 × 12 USB Interface (PC only/Windows95)
The instruments listed here were selected to provide a representative sample of the variety of UV−vis spectrometers available on the market; for a more complete list of manufacturers, refer to Table 3, and search online. bThese specifications were obtained from company Web sites or representatives and are meant for comparison purposes only. A detailed description of each instrument is beyond the scope of this article; please consult company Web sites and local representatives for more specific information. cThe costs shown here are approximate, provided for comparison purposes only; actual purchase prices will varyplease consult company Web sites and local representatives for more specific information.
a
Web Site URLs
Size, in. Interface and Computer Compatibility Cost, U.S. Dollarsc Portability Additional Options
Type Primary Use Range, nm Resolution, nm Abs Max Source and Detector Components
Description
Model Specificationsb
Table 2. Specifications of Single- and Double-Beam UV−Visible Spectrometersa
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Table 3. Representative List of Manufacturers of UV−Visible Spectrometers Available in the United States UV−Vis Instrument Line(s)
Instrument Web Site URLsa
Cary series (100) Astra UV−vis spectrometerc Customer-defined spectrometer systemsc Super Gamut seriesc DU 700 seriesd Jenway 6320Db; 7300 series; 6700 series; 6800 series; Genovad Buck Model 100/105b 1000 series;b Aurius series; Aquarius series Cole-Parmer spectrophotometers Cintra series PhotoLab seriesd U-5100;b U-2900/2910; U-4100, U-3900 JASCO V-600 series CHEM-4 series;b,c Red Tide series;b,c USB 2000 series;c USB 4000 seriesc LAMBDA Series UV-Series Spectrometers;b spectrophotometersb UVSB-061;e VS-071;b UVDB series; UVSB series; VSB series; VS series AquaMate;e BioMate;c Evolution series; Genesys series;e Spectronic seriese SpectroVis Pluse SpectroQuest series;e 1000 series;e 1100 series;e 1200 series; 2100 series
http://www.chem.agilent.com/ http://www.astranetsystems.com/ http://www.avantes.com/Avantes-USA/ http://www.bayspec.com/ http://www.beckmancoulter.com/ http://www.bibby-scientificusa.com/ http://www.jenwayusa.com/ http://www.bucksci.com/ http://www.cecilinstruments.com/ http://www.coleparmer.com/ http://www.gbcscientific.com/ http://www.globalw.com/ http://www.hitachi-hta.com/ http://www.jascoinc.com/Home.aspx http://www.oceanoptics.com/ http://www.perkinelmer.com/ http://www.ssi.shimadzu.com/ http://www.spectralevolution.com/ http://www.spectrophotometers.com/ http://www.thermoscientific.com/ http://www.vernier.com/ http://www.unicosci.com/
Manufacturing Company Agilent Technologies AstraNet Systems Ltd. Avantes, Inc. BaySpec, Inc. Beckman Coulter Bibby Scientific Ltd. Buck Scientific Cecil Instruments Cole-Parmer GBC Scientific Equipment Global Water Hitachi High Technologies America, Inc. Jasco Analytical Instruments Ocean Optics PerkinElmer, Inc. Shimadzu Spectral Evolution Spectrophotometers.com Thermo Scientific Vernier UNICO
b
a All sites accessed Jan 2012. bMiniaturized, highly portable, or fiber-optic based instruments. cInstruments designed for biological or life science applications. dInstruments designed for water or environmental analysis. eInstruments recommended by manufacturer for educational use.
An external computer interface is required for operation and collection of data. Small dispersive spectrometers are similar to the single-beam scanning models in that the blank signal is measured and stored for subtraction from the sample signal. At prices as low as a few hundred dollars and with a small size that is ideal for classrooms where space is an issue, these instruments are advantageous for the high school or small college level. Another benefit is rapid sampling times, with entire spectra being collected in less than a minute, making it possible to incorporate small experiments into short classes.
subtraction of the blank. These instruments have many variations in components in order to obtain different working wavelength ranges and resolutions; prices range from a few thousand dollars to tens of thousands of dollars. The doublebeam instrument is typically large and not portable, and is best suited for use in upper-level college courses or research laboratories. The light sources usually consist of a tungsten and deuterium lamp combination or a xenon lamp. The light is dispersed by a Chezny−Turner grating monochromator, with some high-end models containing double monochromators for better resolution. The double-beam system commonly consists of a chopping mirror, which alternates the light beam through the sample and reference cells, generating a sinusoidal signal that is monitored by a photomultiplier detector. Alternatively, some double-beam systems use a semitransparent mirror to split the beam into two beams that travel simultaneously through the sample and reference paths to individual photodiode detectors electronically coupled to monitor the difference between the two signals. The latter system is more simple and compact, while the former is generally considered the best for resolution and high-end use.
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WHAT CAN IT DO? INTEGRATION OF UV−Vis SPECTROMETERS IN THE CHEMISTRY CURRICULUM The nearly ubiquitous presence of UV−vis use in the chemistry curriculum has been documented extensively in this Journal, as well as others. UV−vis spectrometers are a natural component of the analytical chemistry laboratory,2−5 and are also commonly found in upper level undergraduate chemistry courses such as inorganic6−8 and physical chemistry.9−11 In organic chemistry, UV−vis instruments are occasionally used to study highly colored products,12,13 polymers,14 and have found some applications in green chemistry synthesis.15 Biochemistry relies on several techniques that are based on UV−vis absorbance measurements, including the classic Bradford16 and Lowry17 protein assays and nucleic acid extraction purity determinations.18 The study of enzyme kinetics is often possible through absorbance measurements of colored products.19−21 Historically, advanced instrumentation was often underutilized or missing altogether in first-year undergraduate chemistry courses; however, in the past two decades or so, this deficiency has begun to attract the attention of chemical educators and initiate discussions on this matter.22,23 Some examples of UV− vis spectrometry experiments developed for general chemistry
Dispersive Spectrometers
The third type of UV−vis spectrometer is a dispersive instrument, which is the newest in the market, using modern electronics to make small, highly portable sizes possible. Ocean Optics is a major manufacturer of these small, portable spectrometers and offers a wide range of customizable components for high-end research and industrial use, as well as educational models. These instruments use LED lamps or tungsten and deuterium sources. The light beam goes through the sample and is then dispersed, usually with a grating, onto a diode array detector, which measures the entire range simultaneously. The diode array detector is actually many small photodiodes assembled into an array; the number of diodes in the array determines resolution on these instruments. 307
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include examining coordination complexes,24 waters of hydration of cupric compounds,25 and household products, such as sunscreens.26 The impact of these versatile instruments does not stop at the boundaries of chemistry. There are many applications that appear in a variety of related fields, such as biology, environmental science, forensic science, and physics. For example, not only are many of the biochemical techniques previously mentioned used in molecular biology, but UV−vis spectrometry can be used to study more complex biological systems, such as photosynthesis in nongreen leaves.27 Many Environmental Protection Agency (EPA) methods used to determine water contaminants, such as inorganic ions and organics, are based on UV−vis measurements;28 heavy metal toxins (e.g., chromium) can also be determined in a similar fashion.29 Forensic science applications are typically based on comparing two or more samples. A spectrometer can be used to compare paint samples through reflectance30 or absorbance measurements,31 or to compare textile dyes in fibers.32 In physics, one of the obvious choices for the use of these instruments involves color and light. For example, photometry in an interesting Halloween-themed demonstration33 or in a color-mixing discussion34 may make these topics easier for students to fully grasp.
to increase student engagement in nonmajor science courses.36 Many of the examples of field trips given in the literature for chemistry courses include walking tours or other relatively passive activities. Allowing students the opportunity to collect data on site, using portable UV−vis instrumentation, could further enrich experiences, such as a trip to a local winery or water treatment plant. If time, financial, or geographical restraints preclude a field trip to an off-site location, the use of portable instrumentation can still enrich the curriculum without leaving campus. For example, the analysis of carotenoid and chlorophyll pigments in plants can be performed on site.37,38 The ability to perform an experiment on plant samples in the field would allow for quick sample preparation to analysis times, reducing impacts of degradation on results. As shown in Figure 1, students are able
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WHAT IS ON THE HORIZON? PORTABILITY AND TECHNOLOGY IN (AND OUT OF) THE CLASSROOM Development of portable instruments that can be used independently of cumbersome power sources and data recording systems drastically expands chemical measurements to a wide range of environments. Two major areas of innovation for UV−vis spectrometers include the ability to integrate mobile technology with existing instrumentation, as well as increasing portability of the measurement device itself. These instruments can be easily used with student-owned technology, including laptop computers, iPads, smart phones, and so forth. For example, several of the manufacturers mentioned in Table 1 are introducing the use of handheld devices used with portable instruments. Vernier portable instruments are used with Logger Pro software. This software, available with a generous site license, makes it possible to use student-owned laptop computers to actively collect and analyze data in real time. The Spectral Evolution portable spectroscopy systems can be operated wirelessly through a Bluetooth connection with mobile devices. Ocean Optics spectrometers can be used with Pasco’s DataStudio. This software suite is compatible with Mac or PC computer platforms, and has recently released a Bluetooth wireless capable interface. This system, in conjunction with the Sparkvue app (available from iTunes), makes it possible to collect data directly to a personal device, such as an iPad or iPhone. The ability to operate a UV−vis spectrometer wirelessly would permit one to take chemical measurements in awkward, extreme, or remote environments. While the average user may not have the opportunity to scale a volcano or set out to sea with a portable spectrometer, it would be possible to take advantage of this technological breakthrough in other ways. For example, when conducting sensitive experiments in a glovebox or hood, where limiting exposure to fumes or reagents is critical, a wireless UV−vis spectrometer would be ideal. Forest and Rayne35 discuss the important role that integrating field trips at the college level can play in student learning. The use of field trips have also been described in order
Figure 1. Photograph of students using a Vernier SpectroVis Plus VIS−NIR spectrophotometer to analyze chlorophyll in green plants. Reproduced with permission.
to take a UV−vis spectrometer outside to study chlorophyll samples extracted from different plants. In this case, students would be able to choose different plant species to test and compare, allowing for more flexible, student-designed experiments. UV−vis spectrometers have been useful tools for investigation and learning in chemistry courses for many years. Because of recent technological developments, these instruments are now more versatile and affordable than ever. We hope this will make exciting learning opportunities more accessible to a wider range of students.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected].
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ACKNOWLEDGMENTS We acknowledge the Spectroscopy Society of Pittsburgh (SSP) for funding to purchase portable Vernier instrumentation, some of which is referenced within the paper. We also thank Michelle Bushey, editor, for her helpful comments on the draft. Finally, we would like to thank Chelsie Binda, Kaitlin Martin, and Amanda Dumi for their assistance in preparing the figures in this manuscript.
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REFERENCES
(1) Girard, J. E.; Diamont, C. T. J. Chem. Educ. 2000, 77, 646−648. (2) Walters, C.; Keeney, A.; Wigal, C. T.; Johnston, C. R.; Cornelius, R. D. J. Chem. Educ. 1997, 74, 99−101.
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(3) McDevitt, V. L.; Rodriquez, A.; Williams, K. R. J. Chem. Educ. 1998, 75, 625 as described in . Harris, D. C. Quantitative Chemical Analysis, 7th ed.; W. H. Freeman: New York, 2006. (4) Adams, P. E. J. Chem. Educ. 1995, 72, 649−651. (5) Sigmann, S. B.; Wheller, D. E. J. Chem. Educ. 2004, 81, 1475− 1478. (6) Shtoyko, T.; Zudans, I.; Seliskar, C. J.; Heineman, W. R.; Richardson, J. N. J. Chem. Educ. 2004, 81, 1617−1619. (7) Hamilton, D. H.; Battin, E. E.; Lawhon, A.; Brumaghim, J. L. J. Chem. Educ. 2009, 86, 969−972. (8) Solomon, S. D.; Bahadory, M.; Jeyarajasingam, A. V.; Rutkowsky, S. A.; Boritz, C.; Mulfinger, L. J. Chem. Educ. 2007, 84, 322−325. (9) Minas da Piedade, M. E.; Berberan-Santos, M. N. J. Chem. Educ. 1998, 75, 1013−1017. (10) Lorigan, G. A.; Patterson, B. M.; Sommer, A. J.; Danielson, N. C. J. Chem. Educ. 2002, 79, 1264−1266. (11) Negri, R. M.; Prypszetejn, H. E. J. Chem. Educ. 2001, 78, 645− 648. (12) McCullagh, J. V.; Daggett, K. A. J. Chem. Educ. 2007, 84, 1799− 1802. (13) Mascarenhas, C. M. J. Chem. Educ. 2008, 85, 1271−1273. (14) Poon, T.; Eller, C. F.; Eller, L. R.; Jones, K. M.; Massello, W.; Norris, C. M.; Oelrich, J. A.; Pluim, T. A.; McIntyre, J. P.; Dorigo, A. E.; Davis, D. J.; Davis, M. A.; Izumi, H. K.; Kelley, K. H.; Melamed, M. L.; Poplawski, S. E.; St. Clair, J. M.; Stokes, M. P.; Wheller, W. C.; Wilkes, E. E. J. Chem. Educ. 1999, 76, 1523−1524. (15) Warner, M. G.; Succaw, G. L.; Hutchison, J. E. Green Chem. 2001, 3, 267−270. (16) Bradford, M. M. Anal. Biochem. 1976, 72, 248−254. (17) Lowry, O. H.; Rosebrough, N. J.; Farr, A. L.; Randall, R. J. J. Biol. Chem. 1951, 193, 265−275. (18) Glasel, J. A. BioTechniques 1995, 18, 62−63. (19) Howard, D. R.; Herr, J.; Hollister, R. Am. Biol. Teacher 2006, 68, 99−104. (20) Price, N. C.; Newman, B. L. Biochem. Mol. Biol. Educ. 2000, 28, 207−210. (21) Cochran, B.; Lunday, D.; Miskevich, F. J. Chem. Educ. 2008, 85, 401−403. (22) Steehler, J. K. J. Chem. Educ. 1998, 75, 274−275. (23) Bopegedera, A. M. R. P. J. Chem. Educ. 2011, 88, 443−448. (24) Fenk, C. J.; Kaufman, N.; Gerbig, D. G. J. Chem. Educ. 2007, 84, 1676−1678. (25) Barlag, R.; Nyasulu, F. J. Chem. Educ. 2011, 88, 643−645. (26) Moeur, H. P.; Zanella, A.; Poon, T. J. Chem. Educ. 2006, 83, 769. (27) Vartak, R. J. Biol. Educ. 2006, 40, 178−180. (28) United States Environmental Protection Agency. Approved General Purpose Methods. For example: Total Phosphorus (Method 365.4), Nitrate, Colorimetric, Brucine (Method 352.1), Phenolics, Total Recoverable (Method 420.1). http://water.epa.gov/scitech/ (accessed Jan 2012). (29) Kota, J.; Stasicka, Z. Environ. Pollut. 2000, 107, 263−283. (30) Hoffman, E. M.; Beussman, D. J. J. Chem. Educ. 2007, 84, 1806− 1808. (31) Kopchick, K. A.; Bommarito, C. R. J. Forensic Sci. 2006, 51, 340−343. (32) Eng, M.; Martin, P.; Bhagwandin, C. J. Forensic Sci. 2009, 54, 841−845. (33) Whitehead, L. A.; Mossman, M. A. Am. J. Phys. 2006, 74, 537. (34) Gilbert, P. U. P. A; Haeberli, W. Am. J. Phys. 2007, 75, 313. (35) Forest, K.; Rayne, S. J. Chem. Educ. 2009, 86, 1290−1294. (36) Peterson, K. E. J. Chem. Educ. 2008, 85, 645−649. (37) Miocha, R.; Martinez, G.; Lyons, B.; Long, S. Can. J. For. Res. 2009, 39, 849−861. (38) Lichtenthaler, H. K.; Buschmann, C. Curr. Protoc. Food Anal. Chem. 2001, Suppl. 1, Unit F4.3.1. http://www.nshtvn.org/ebook/ molbio/Current%20Protocols/CPFAC/faf0403.pdf (accessed Jan 2012).
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