MEETINGS Workshop on Spark Source Mass Spectrometry at the National Bureau of Standards in Gaithersburg, Md., Nov. 13 and 14, 1967
Reported by A. J. Ahearn and P. J. Paulsen, National Bureau of Standards, Washington, D.C.
Wanted: on Spark Source Mass AWORKSHOP Spectrometry sponsored by the Na tional Bureau of Standards was held at the Bureau's Gaithersburg, Md., lab oratories on November 13 and 14, 1967. Seventy people from 43 institutions (7 U. S. government laboratories, 9 uni versities, 2 research institutes, 5 instru ment makers, 20 industrial laboratories) participated in the discussions of prob lems. The purpose of this workshop was to examine the factors that influence the precision and accuracy attainable in analytical determinations by this spark source technique. The workshop, open to all engaged in spark source work, promoted discussion of basic problems, and exchange of ideas, experiences, techniques, etc. Among the basic prob lems, those directly bearing on calibra tion, quantitation, and standard refer ence materials suitable for spark source work were of particular interest. The agenda consisted of topics se lected by questionnaire. Discussion leaders were used. Short informal so licited talks were given. More than 50% of the time was allotted to discus sion. This proved to be barely ade quate. The first topic, led by Ε. Β. Owens (MIT Lincoln Laboratory), considered the analysis of a mass-resolved ion sample recorded on an ion-sensitive emulsion. This topic included alterna tive analytical forms for this emulsion characteristic and alternative methods of determining ion intensities from mass spectra recorded. Replicate mass spectra yield numbers for the ions pro ducing the mass lines that fluctuate about an average value with a standard
deviation of at least a few per cent. The second topic, led by J. M. MeCrea (U. S. Steel Corp.)", dealt with the background problem of mass spec tra recorded on ion-sensitive plates. This includes diffuse background from ion scattering in transit, secondary products generated by ion impact, etc., and mass line background due to instru ment memory, residual gases, etc. Among the methods of minimizing diffuse background is the magnetic shim—a sheet of magnetic material placed behind the ion-sensitive plate. The reduction achieved, presumably caused by suppression of secondary products, varies considerably among in struments. The third topic, led by R. E. Honig (RCA Laboratories), was concerned with the fidelity with which the ion sample represents the solid sample. This degree of fidelity is generally much higher than, for example, in thermal ion source mass spectrometry. Nevertheless, Relative Sensitivity Fac tors in many cases are significantly dif ferent from unity and cannot be ig nored. This topic included questions like 1 ) how does the fidelity depend on spark parameters?, 2) can it be cal culated from properties of the solid sample? Relative Sensitivity Factors (RSF) were calculated assuming that they were inversely proportional to the prod uct of the heat of fusion, heat of va porization and the first ionization po tential of both the element and the matrix in question. They agreed rea sonably well for the case of artificially doped samples of rare earths. The fidelity problem in the ion sam-
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VOL. 40, NO. 3, MARCH
1968
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