Figure 2. Phosphorescence decay curve plots of logarithm of the phosphorescence signal GS. time after termination of excitation for a mixture of 4-chlorobiphenyl (2.0 X 10-6M), 4-bromobiphenyl (5.0 X 10-6M), and 4-iodobiphenyl (5.0 X 10-6M). Ethanol was the solvent Key: Sweep time of 20 msec A Sweep time of 80 msec 0 Sweep time of 1280 msec
no attempt was made to also determine 3-chlorobiphenyl because of its low phosphorescence quantum yield (therefore, poor phosphorimetric limits of detection, about 1000-fold worse than the 2-chloro and 4-chloro species). Although the structural difference between 2-chlorobiphenyl and 4chlorobiphenyl is small and the phosphorescence spectra (also absorption and fluorescence spectra) are almost identical, the phosphorescence lifetimes and, therefore, the phosphorescence decay curves are quite different. This is another excellent example of a mixture analysis which would be difficult to perform by normal spectroscopic measurements but not by pulsed source, time resolved phosphorimetry. As long as the phosphorescence lifetime ratio of any two species is two or greater, phosphoroscopic resolution is possible via time resolved phosphorimetry. In conclusion, pulsed source, time resolved phosphorimetry is a useful method for the analysis of structurally and therefore spectrally similar molecules. Not only is it possible to obtain quantitative information, but also it should be possible to qualitatively identify some species with the assistance of the species phosphorescence lifetimes. For very complex mixtures, a simple thin layer or gas chromatographic separation prior to analysis may also be needed, but overall, the time for analysis of a multicomponent mixture should be considerably reduced as compared to methods previously used. It should also be possible to measure longer-lived phosphorescence species, e.g., species with lifetimes exceeding 1 sec, in a mixture also containing shortlived species as well as other long-lived species. Such studies are currently in progress.
biphenyl as well as 4-chlorobiphenyl) was similarly measured by pulsed source, time resolved phosphorimetry, and the results are also given in Table I1 errors of 5.4z and l o % , respectively). Again, this mixture cannot be readily measured by conventional phosphorimetry because of the similarity of the phosphorescence spectra. It should be pointed out that
RECEIVED for review July 25, 1972. Accepted November 16, 1972. Research was carried out as part of a study on the phosphorimetric analysis of drugs in blood and urine, supported by a U S . Public Health Service Grant (GM-11373-10).
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Novel Wet-Digestion Procedure for Trace-Metal Analysis of Coal by Atomic Absorption A. M. Hartstein, R . W. Freedman, and D. W. Platter Pittsburgh Mining and Safety Research Center, Bureau of Mines, US.Department of the Interior, Pittsburgh, Pa.
COALWORKERS’ PNEUMOCONIOSIS, its causes and cure, is the subject of intensive studies by different laboratories throughout the world. This form of pneumoconiosis is believed to be caused by the inhalation and retention of respirable coalmine dust (
