A Spectrochemical Procedure of General Applicability EDWIN K. JAYCOX Bell Telephone Laboratories, Inc., M u r r a y Hill,
N.J. There are, of course, niany good spectrochemical procedures available for the quantitative analysis of almost any material. Hundreds of such methods can be found in the literature, and recently Committee E-2 of the American Society for Testing Materials (ASTRI) has published over 50 suggested spectrochemical methods (1). The majority of these methods, howevcr, are specific for the analysis of specific materials for certain elements. All require reliable standards for each matrix involvcd. Many of these standards are not readily available, and some cannot be made easily in most laboratories, especially for those techniques utilizing metal rods or disks. I n any case, where it is required t o analyze a wide variety of materials, many sets of standard samples must be kept on hand or made or purchawd as required. Somewhere between the qualitative and the accurate quantitative procedures there is a need for a reliable, objective, semiquantitative procedure with precision \Tithin better than =t250/,, one which would be applicable to the analysis of a wide variety of samples for most of the common elements. Such a method would be very useful for the analysis and classification of steels, brassev, bronzes, lead, tin, aluminum, magnesium- and zinc-base alloys, ceramics, paint pigments, and other materials. T h a t a need does exist for a general method of spectrochemical analysis is evidenced by the fact that Group L-I, Subcommittee I1 of AC3TRIE-2, is engaged in a project to evaluat,e the various general procedures that have thus far been developed (5-5, 7 , 10-13). Many of these procedures are not truly general in scopr, but are usually confined to some area of analysis such as that of geological materials, or ceramics, or certain classes of alloy.. Xevertheless, they do contain some of the essential factors necessary for wider application. One of the chief obstacles to devising a universal method is the marked effect of different matrix materials on the behavior of tllr spectral lines of each individual element to be determined. Far esample, if iron is determined in a sodium chloride matrix, the transmittance of the iron lines d l be very different than if tht. matris had been zirconium dioxide, lead, copper, or some other base material. The logical approach t o the elimination of this strong matrix effect is to dilute heavily or buffer samples with some common base material. I n this manner the behavior of the elements to be determined will approach that of their behavior in the pure buffer base. What buffer materialshould be chosen? For widest scope, it should be an element whose oxides and salts behave in an average manner. I t s excitation potential and its melting and boiling points should be somewhere in the miadle range of a l l the elements. The extremes of the alkali metals and the high[>. refractory compounds such as those of zirconium or thorium would obviously be poor choices. Elements and their compounds, such as those of lead, bismuth, tin, germanium, copper, iron, and nickel, should be satisfactory from the standpoint of desiralile behavior. It has been found in this laboratory that graphit? powder, cupric oxide, lead sulfate, and germanium dioxide are excellent buffer materials, with cupric oxide best for use as an internal standard because of its good distribution of spectral lines in the region from 2100 to 5000 Graphite powder is always used with the other buffers. 411 materials used for buffering must be extremely pure. A number of papers have been published by workers in thia laboratory in which buffers play an important role as an aid to diminishing the matrix effect. The first of these concerned the analysis of copper-base alloys in which brasses and bronzes
Spectroscopists have been endeavoring for years to devise a reliable semiquantitative or quantitative spectrochemical procedure which will have universal applicability for the determination of the metallic constituents-particularly the major componentsof almost any material, based on the use of a single set of standards and capable of an accuracy of better than 5 5 0 % for all determinations. .iprocedure is described which fulfills most of these requirements. By the judicious use of germanium diouide as a filler and cupric oxide and graphite as buffere,, in both samples and standards, it is possible to establish a common base so that the emission lines used in the analyses are comparable in all kinds of samples and in the standards. Powdered samples are used, but metals, liquids, and metal-organic materials can be readlily converted to a powdered salt or oxide. Once standard curves of concentration us. some function of the iritensitj of the line of the element to be determined have been established, individual samples can be analyzed with moderate speed.
S
PECTROSCOPISTS have been striving for many years to devise a spectrochemical procedure that would have general applicability-one that would be capable of analyzing any sample n i t h moderate accuracy for one or all of its metallic ion constituents, without the necessity of employing separate sets of standards for each basic matrix material involved. Ideally, one would like t o be able to do this using only a single spectrogram. For any isolated spectrogram this has not been generally pos&le, beyond an estimate of the order of magnitude of each element present, even if the absorbance or per cent transmittance of the analytical lines involved is measured accurately. Further information is required, such as kiiowledge of the liehavior of the various element lines in the particular matrix of the spectrogram in question and the energi rePponse chamcteristics of the emulsion or photorweiver.
Table I.
Schedule of Estimated Ranges Per C e n t
Principal component Alajor components Minor components Impurities Traces Slight traces Very slight traces
> 10 > 1
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