Fraunhofer Effect Atomic Absorption Spectrometry

Abstract

The dark lines in the solar spectrum were discovered by Wollaston and cataloged by Fraunhofer in the early days of the 19th century. Some years later, Kirchhoff explained the appearance of the dark lines: the sun was acting as a continuum light source and metals in the ground state in its atmosphere were absorbing characteristic narrow regions of the spectrum. This discovery eventually spawned atomic absorption spectrometry, which became a routine technique for chemical analysis in the mid-20th century. Laboratory-based atomic absorption spectrometers differ from the original observation of the Fraunhofer lines because they have always employed a separate light source and atomizer. This article describes a novel atomic absorption device that employs a single source, the tungsten coil, as both the generator of continuum radiation and the atomizer of the analytes. A 25-microL aliquot of sample is placed on the tungsten filament removed from a commercially available 150-W light bulb. The solution is dried and ashed by applying low currents to the coil in a three-step procedure. Full power is then applied to the coil for a brief period. During this time, the coil produces white light, which may be absorbed by any metals present in the atomization cloud produced by the sample. A high-resolution spectrometer with a charge-coupled device detector monitors the emission spectrum of the coil, which includes the dark lines from the metals. Detection limits are reported for seven elements: 5 pg of Ca (422.7 nm); 2 ng of Co (352.7 nm); 200 pg of Cr (425.4 nm); 7 pg of Sr (460.7 nm); 100 pg of Yb (398.8 nm); 500 pg of Mn (403.1 nm); and 500 pg of K (404.4 nm). Simultaneous multielement analyses are possible within a 4-nm spectral window. The relative standard deviations for the seven metals are below 8% for all metals except for Ca (10.7%), which was present in the blank at measurable levels. Analysis of a standard reference material (drinking water) resulted in a mean percent recovery of 91%. This report attempts to give an historical perspective on the development of a novel atomic spectrometer based on the Fraunhofer effect.

Principles and applications of Raman spectroscopy in pharmaceutical drug discovery and development

“…The concept of spectroscopy was born in 1801, when British scientist Sir William Wollaston discovered dark lines in the solar spectrum. Almost a decade later, scientist Joseph von Fraunhofer attributed these dark lines to the absence of a certain wavelength of light [2]. Austrian physicist Adolf Smekal provided the theoretical basis for inelastic light scattering in 1923 [3].…”

Fraunhofer-type absorption lines in double-pulse laser-induced plasma

“…After this publication, the absorption in LIP was mostly studied in the x-ray and deep UV spectral ranges addressing properties of excited atomic, molecular, and solid species [8][9][10]. In [11], atomic absorption spectrometry using a single device for both light source and sample atomizer has been described for the first time since the explanation of the Fraunhofer lines in the solar spectrum. Costello and coworkers [12][13][14][15] proposed a photoabsorption method for investigation of the laser plasma absorption in the vacuum UV.…”

Simultaneous determination of Cr, Ga, In and V in soil and water samples by tungsten coil atomic emission spectrometry

“…A programmable solid state DC power supply (BatMod, Vicor, Andover, MA, USA) provides the constant current to resistively heat the coil during the heating cycles. Both atomization cell and tungsten coil atomizer have been described in detail previously [12,13]. Radiation emitted by the atom cloud at high temperature is collected with a 25 mm diameter, 75 mm focal length fused silica lens.…”