optical emission spectroscopy

optical emission spectroscopy
Name	Optical emission spectroscopy
Caption	Emission spectrum from a plasma source
Introduction	19th century
Related	Spectroscopy, Atomic spectroscopy, Plasma diagnostics

optical emission spectroscopy is an analytical technique that measures light emitted by excited atoms, ions, or molecules to determine elemental composition and plasma properties. It combines principles from Anders Jonas Ångström, Gustav Kirchhoff, Robert Bunsen, and Joseph von Fraunhofer's studies of spectra with instrumentation developed in the 20th century by groups at Bell Labs, National Institute of Standards and Technology, and industrial research labs such as Intel and DuPont. Widely used in laboratories, field monitoring, and industrial process control, it complements techniques employed at facilities like CERN and observatories such as the Palomar Observatory for related spectroscopic diagnostics.

Introduction

Optical emission spectroscopy (OES) arose from early spectral line observations by Ångström and systematic investigations by Bunsen and Kirchhoff which led to the first atomic emission identification schemes used by Robert Bunsen's laboratory. Subsequent instrumental advances at institutions including Bell Labs and the National Institute of Standards and Technology translated historical spectroscopy into quantitative analytical methods applied by companies such as Thermo Fisher Scientific and agencies like the Environmental Protection Agency.

Principles and Theory

The technique is founded on electronic excitation and radiative decay described by quantum mechanics developed by Niels Bohr, Werner Heisenberg, and Erwin Schrödinger, producing discrete emission lines cataloged in databases curated by NIST. Collisional excitation in plasmas follows kinetics studied by researchers at Lawrence Livermore National Laboratory and the Max Planck Institute; radiative transition probabilities (Einstein coefficients) and level populations can be derived using formalisms from Ludwig Boltzmann and Saha equations applied in stellar work at observatories like Mount Wilson Observatory. Line broadening mechanisms—Stark, Doppler, and pressure broadening—are interpreted using models developed by J. Stark and theorists at Princeton University.

Instrumentation and Experimental Setup

Core components—excitation source, collection optics, dispersion element, detector, and data system—reflect designs refined at MIT, Caltech, and corporate labs like Agilent Technologies. Common excitation sources include inductively coupled plasmas (ICP) pioneered in engineering groups at Imperial College London and direct current arcs used historically by Bunsen; glow discharges as developed in research at Siemens and laser-induced plasmas from groups at Lawrence Berkeley National Laboratory extend capabilities. Spectrometers use gratings from manufacturers linked to Zeiss and monochromators from Horiba Scientific, while detectors often include photomultiplier tubes (PMTs) and charge-coupled devices (CCDs) whose semiconductor physics was advanced at Bell Labs and Fairchild Semiconductor.

Sample Preparation and Measurement Techniques

Preparation methods depend on matrices studied by laboratories at US Geological Survey and industrial labs of BASF and Boeing. Liquids are nebulized for ICP systems using technology influenced by work at GE; solids may be ablated by lasers developed at Coherent, Inc. or introduced via glow discharge devices produced by companies such as Spectro Analytical Instruments. Calibration and standardization use reference materials from NIST and proficiency schemes run by organizations like ISO and American Society for Testing and Materials to ensure comparability across labs including Los Alamos National Laboratory and university facilities at University of Cambridge.

Applications

OES supports trace element analysis in contexts spanning environmental monitoring by the Environmental Protection Agency, metallurgy in plants run by ArcelorMittal and Tata Steel, semiconductor quality control at Intel and TSMC, and geochemical studies by USGS teams. In plasma diagnostics it is used alongside techniques at Culham Centre for Fusion Energy and fusion devices like JET; in archaeology and art conservation it complements work at institutions such as the British Museum and Smithsonian Institution for provenance studies. Clinical and forensic applications have been pursued at centers including Mayo Clinic and FBI laboratories.

Data Analysis and Quantification

Quantitative analysis employs calibration curves, internal standardization methods pioneered by analytical chemists at University of California, Berkeley and multivariate statistical models developed by researchers at Stanford University and Harvard University. Spectral libraries and line lists from NIST and astrophysical compilations used at European Southern Observatory are critical for peak identification. Software platforms from vendors like Thermo Fisher Scientific and open-source projects maintained by groups at Massachusetts Institute of Technology implement algorithms for baseline correction, deconvolution, and chemometric techniques such as principal component analysis inspired by work at Princeton University.

Limitations and Sources of Error

Accuracy can be limited by matrix effects studied by researchers at Argonne National Laboratory and spectral interferences cataloged by NIST; self-absorption, instrumental drift, and detector nonlinearity require controls instituted by standards organizations including ISO and ASTM International. Sample inhomogeneity encountered in field campaigns run by USGS and trace-level detection limits constrained by background continuum emission present practical challenges. Mitigation strategies reflect best practices developed at analytical centers like National Physical Laboratory and through round-robin studies organized by International Union of Pure and Applied Chemistry.

Category:Spectroscopy