Analytical Laser Atomic Spectrometry

Abstract

The uses of laser excitation in analytical spectrometry will be discussed and compared. The analytical techniques include atomic fluorescence spectrometry, atomic ionization spectrometry, and atomic photothermal spectrometry. The ultimate and practical detection limits for each of these methods based upon signal-to-noise ratios will be given and will be compared with experimental values obtained in our laboratory and in other laboratories. Factors limiting the linear range of response (signal vs concentration or amount) for each of the laser based methods will be given as well as magnitude for the linear ranges. The shape of growth curves in atomic fluorescence and atomic ionization will be discussed. Other figures of merit, including the relative standard deviation and the selectivity of measurement, will be discussed. The relative standard deviation involves measurements at concentrations or amounts at least 100 x above the detection limit. The selectivity of measurement is determined by both sample matrix interferences and spectral interferences. Sample matrix interferences are primarily related to the sample cell, flame, plasma, furnace, etc. Whereas spectral interferences are intimately related to the width of the spectral absorption lines, the presence of background atomic and molecular species, and the selectivity possible with dye laser excitation. Sequential excitation with 2 dye laser wavelengths can greatly increase the spectral selectivity and thus the system resolving power. Typical instrumental systems for each of these laser based analytical methods will be briefly mentioned and compared and analytical figures of merit for them will be given. Potential analytical applications for these approaches which require standard samples/solutions will also be considered. Dye laser excited fluorescence, ionization, and photothermal detection also have potential use for measurement of absolute concentrations of species, such as atomic (molecular) species in flames, hot gases, furnaces, and plasmas. The difficulties and requirements of such measurements will be considered.