Laser-induce mission Kenneth W, Marich, Peter W. Carr,l William J. Treytl, and David Glick Division of Histochemistry, Department of Pathology, Stanford University School of Medicine, Stanford, CaliJ 94305 The magnitude of the suppression of spectral emission of metallic elements by organic material in sampling and excitation with a ruby laser microprobe was studied in model systems in which intensities of spectral lines of silver and magnesium were measured in relation to the presence of bovine serum albumin and human serum. The silver emission was also investigated in the presence of sucrose, sodium acetate, and sodium sulfate. The sodium acetate and sulfate were included to represent a combined inorganic-organic compound and a totally inorganic compound. Methyl blue was used in an attempt to intensify the laser energy absorption by the sample, but it failed to increase, and in higher concentvations decreased, the silver emission. For all matrix materials increasing concentrations above a threshold value diminished the emissions. The threshold level varied with the nature of the emitting element and of the matrix. It was observed that, at constant laser energy, the presence of increasing concentvations of matrix progressively decreased the amount of sample vaporized.
LASERhlICROPROBE emission spectrometry has considerable promise as a means of microsampling and analysis of elements in biological material, e.g., body fluids, tissues, and single cells or their components (1). It has been demonstrated that the laser microprobe is capable of sampling with a resolution of 0.5 p (2). In some cases spectral emission may be so weak that auxiliary spark excitation is required (3-5); however, this results in poorer resolution, 10-25 p (6). With photographic recording of the more intense spectral lines, metals have been detected in the 10-50 pg range with use of cross-excitation (4). Detection limits without auxiliary excitation have not been so well investigated. Increase in detectivity by use of higher speed spectrographs and particularly of photomultiplier recording has been achieved ( I , 7j. This should extend the potential of the noncross-excitation technique. Several workers have shown that the staining of cellular structures with appropriate dyes aided in localizing the laser damage to these structures by increasing their energy absorption (8, 9). This prompted an investigation of whether stain1 Present address, Department of Chemistry, University of Georgia, Athens, Ga. 30601
(1) D. Glick, Ann. N . Y.Acad. Sci.,157, 265 (1969). (2) N. A. Peppers, E. J. Scribner, L. E. Alterton, R. C. Honey, E. S . Beatrice, I. Harding-Barlow, R. C. Rosan, and D. Glick, ANAL.CHEM., 40, 1178 (1968). (3) F. Brech, Appl. Spectrosc., 16, 59 (1962). (4) S. D. Rasberry, B. F. Scribner and IW. Margoshes, Appl. Opt., 6 , 81 (1967). (5) Ibid., p 87. (6) E. S . Beatrice, I. Harding-Barlow, and D. Glick, Appl. Spectrosc., 23, 257 (1969). (7) E. S . Beatrice and D. Glick, ibid., p 260. (8) R. Storb, R. L. Amy, R. K. Wertz, B. Fauconnier, and M. Bessis, J. Cell Biol., 31, 11 (1966). (9) M. W. Berm, D. E. Rounds, and R. S. Olson, Exp. Cell Res., 56,292 (1969).
ing analytical samples with methyl blue would increase the sampling efficiency in our work. Biological samples pose special problems. Many metals are present only in trace amounts and the total sample may be very small, e.g., single cells,
