ultraviolet–visible spectroscopy

ultraviolet–visible spectroscopy
Name	Ultraviolet–visible spectrophotometer
Type	Spectroscopic instrument
Invented	19th century
Makers	PerkinElmer, Agilent Technologies, Shimadzu, Thermo Fisher Scientific

ultraviolet–visible spectroscopy

Ultraviolet–visible spectroscopy is an analytical technique that measures absorption of electromagnetic radiation in the ultraviolet and visible ranges by chemical species. It provides information about electronic transitions, chromophores, and concentration through quantitative and qualitative analysis, and is widely used across chemistry, biology, and materials science. Instruments are produced by companies such as PerkinElmer, Agilent Technologies, Shimadzu, and Thermo Fisher Scientific, and techniques are taught in courses at institutions like Harvard University, Massachusetts Institute of Technology, University of Cambridge, and California Institute of Technology.

Introduction

Ultraviolet–visible spectroscopy emerged from 19th-century studies by scientists associated with institutions such as the Royal Society, University of Göttingen, and University of Paris, and was advanced through instrumentation from firms including Beckman Instruments and Hewlett-Packard. Key figures connected to the technique include Joseph von Fraunhofer, Gustav Kirchhoff, and Robert Bunsen for spectral analysis and later innovators at organizations like the National Institute of Standards and Technology and the American Chemical Society. The method is integral to laboratories at hospitals like Johns Hopkins Hospital, research centers such as the Max Planck Society, and industrial settings including BASF and DuPont.

Principles and Theory

Absorption of photons promotes electrons between molecular orbitals, an effect described by quantum models developed by scientists at institutions like the University of Oxford and Princeton University and formalized by researchers such as Niels Bohr and Erwin Schrödinger. Beer–Lambert law, historically associated with August Beer and Johann Heinrich Lambert, relates absorbance to concentration and path length and underpins quantitative measurements in laboratories such as those at Stanford University and Yale University. Electronic transitions (π→π*, n→π*) are interpreted using molecular orbital theory from contributors like Robert Mulliken and Linus Pauling, and spectra are compared with reference databases maintained by organizations including the National Institutes of Health and the World Health Organization.

Instrumentation

A typical spectrophotometer comprises a light source (deuterium lamp or tungsten-halogen lamp), monochromator (prism or diffraction grating), sample compartment, and detector (photomultiplier tube or photodiode array). Manufacturers such as PerkinElmer, Agilent Technologies, Shimadzu, and Thermo Fisher Scientific supply benchtop and portable instruments used by laboratories at Imperial College London, University of Tokyo, and ETH Zurich. Calibration standards and traceability often reference materials from the National Institute of Standards and Technology and procedures endorsed by the International Organization for Standardization and ASTM International. Components like double-beam optics and integrating spheres were developed alongside innovations at firms such as Carl Zeiss and Leica Microsystems, and detectors follow technologies advanced at Bell Labs and CERN.

Sample Preparation and Measurement Techniques

Samples may be liquids in cuvettes (glass, quartz, or plastic), solids as diffuse reflectance samples, or thin films on substrates used at facilities like CERN and SLAC National Accelerator Laboratory. Preparation protocols are taught in courses at Columbia University, University of California, Berkeley, and University of Chicago and follow standards from organizations such as ISO and ASTM. Techniques include baseline correction, blank subtraction using solvents from suppliers like Merck and Sigma-Aldrich, and use of flow cells in chromatography systems from Waters Corporation and Shimadzu. Special methods for biomolecules reference protocols from Cold Spring Harbor Laboratory and the Scripps Research Institute.

Data Analysis and Interpretation

Spectral processing involves baseline correction, smoothing (Savitzky–Golay filter), deconvolution, and fitting to models developed by scientists at institutions like the Max Planck Institute and Los Alamos National Laboratory. Concentrations are determined via Beer–Lambert law with standards traceable to NIST or certified reference materials from the European Commission's Joint Research Centre. Spectral libraries and chemometric methods (principal component analysis, partial least squares regression) are implemented with software from companies like Agilent Technologies, Thermo Fisher Scientific, and Bruker and are used in research groups at MIT, University of Cambridge, and University of Oxford.

Applications

Ultraviolet–visible spectroscopy is applied in pharmaceutical analysis at companies such as Pfizer, Merck, and GlaxoSmithKline for assay and dissolution testing; environmental monitoring by agencies like the Environmental Protection Agency and United Nations Environment Programme for water quality; clinical diagnostics at Mayo Clinic and Cleveland Clinic for hemoglobin assays; and materials characterization in research at IBM Research, Samsung, and Toyota Central R&D Labs. It supports studies in photochemistry linked to laboratories at Lawrence Berkeley National Laboratory and renewable energy research at National Renewable Energy Laboratory. Historical applications include pigment analysis at the Louvre and conservation science at the British Museum.

Limitations and Sources of Error

Limitations include deviations from Beer–Lambert law due to high concentration, chemical interactions, and scattering as encountered in atmospheric studies by NASA and ESA; instrumental stray light and bandwidth limitations as characterized by standards from ISO and ASTM; and matrix effects in complex samples addressed by laboratories like the Centers for Disease Control and Prevention. Common sources of error involve cuvette path length inaccuracies, lamp instability, temperature fluctuations (considered in protocols at WHO and CDC), and improper baseline correction, with mitigation strategies developed by research groups at University of Illinois and Carnegie Mellon University.

Category:Spectroscopy