Spectrochemical vs. Wet Methods in Routine Industrial Analysis RONALD B. SPACHT1 The National Aluminum Cylinder Head Company, Cleveland, Ohio
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N THIS article I would like first to discuss the
present and probable future status of spectrochemical analysis and its effect on traditional chemical methods, then submit some questions for consideration in the organization of postwar courses in analytical chemistry. With the advent of the war and the requirement of analyses on most products, war plants found q e m selves without personnel and without laboratory space to meet these increased demands. Under these conditions the logical question to ask was, "Is there a shorter method by which these analyses can be done accur a t e l y ? ' T b e answer to the above problem was found to be the spectrograph. The methods of quantitative spectrographic analysis had been worked out in the years preceding the war. It remained to adapt these methods on a large scale to war products. The greatest advances have been made in the analysis of alloys of iron, aluminum, and magnesium. It had been known for a long time that the spectrograph was well adapted to the qualitative and quantitative analysis of metals from less than 0.01 per cent to 1 per cent. In the past few years, spectrographic techniques and equipment have been improved to such an extent that the upper limits to which the spectrograph can be used are constantly being extended. In our laboratory the range of the analyses of a single aluminum alloy XA142 runs from Mn 0.01-0.04 per cent, to Cu 3 . 7 4 . 5 per cent. In between we determine Ti 0.07-0.17 per cent, Cr 0.1Fr0.25 per cent, Si 0.06-0.60 per cent, Fe 0.20-0.80 per cent, Mg 1.20-1.70 per cent, and Ni 1.80-2.30 per cent. Thus by a single photograph with a proper selection of lines, elements may be determined from traces up to 5 per cent. Other laboratories have worked out procedures for high percentages of other elements. Hasler and Harveya and also Coulliette3 report spectrographic determinations of nickel and chromium in stainless steel up to 20 and 28per cent, respectively, with an accuracy which compares favorably with routine wet methods. These are but two of some recent articles which show that spectrographers are no longer thinking in limits of 1 or even 5 per cent, but of complete analyses of minor constituents regardless of the quantity present. 'Formerly Assistant Professor of Chemistry at Kent State
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TTniversitv -----, HASLEn, M. F.. AND
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To be conservative, however, it would appear that most analyses up to 5 per cent can be done spectrographically. The accuracy usually claimed for spectrographic methods is 5 per cent of the amount of the element present, with most determinations falling much closer than this but an occasional determination being in error by as much as 10 per cent of the amount present. Duplicate and triplicate determinations reduce this error to less than 2 per cent of the values obtained by wet chemical methods. Sawyer4 makes the statement that spectrographic analysis is more accurate than chemical methods below 0.5 per cent, has about the same accnracy as chemical methods between 0.5 and 5 per cent, while above 5 per cent chemical methods are more accurate. My experience with copper determinations a t the 4.5 per cent level is that spectrographic and chemical results compare favorably in most cases; however, the higher the percentage of an element being determined by the spectrograph the more frequently should be the chemical checks upon such analyses. Qualitative analysis by the spectrograph is very easily done on metal samples, salts, and mixtures of metallic compounds. With many instruments now being furnished with master scales locating the principal lines of the common elements, i t takes but a few minutes to identify the main metallic constituents of most chemical compounds or mixtures. It usually remains for the chemical laboratory to identify the anion constituents unless the anion is composed of a metalloacid element such as silicon or related elements. Elements such as carbon, sulfur, phosphorus, and other nonmetals are analyzed by the usual chemical methods in most cases. This represents the most severe limitation of the spectrograph in routine analysis, especially of iron and steel. The chief advantages of the spectrograph over chemical methods of quantitative analysis are many: It is more accurate for identifying small quantities of trace elements which may be detrimental to certain alloys even when present in very small amounts. It is much faster, hence the saving of labor costs. Fewer highly trained technicians are needed since most of the routine work can be handled by any intelligent person after a few hours of instruction. One trained spectrographer can usually handle the technical work required for the ordinary plant such as preparing
C . E. HARVEY, "Quantitative analysis
of stainlesssteels."Ind. Eng. Chene..Anal. Ed..15,102-7 (1943).
a COULLIBTTB, J. H., "Spectrographic determination of nickel and chromium in stainless steel," ibid.. 15,732-4 (1943).
SAWYER, R. A,, "Experimental spectroscopy," Prentice-Hall. Inc., New Ymk, 1944, p. 309.
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curves, repairing equipment, etc., unless an unusual number and variety of samples are to be analyzed. Capital outlay for spectrographic eqitipment, while initially rather high, compares favorably with that of a chemical laboratory, since maintenance costs are low and much floor space is saved. The amount of sample is very small and in many cases metallic parts may be tested directly without the need ' of a special sample. Working conditions in the spectrographic laboratory are more pleasant and more healthful than in the usual chemical laboratory. Then, too, the tedious tasks of drilling samples, washing dishes, etc., are eliminated. The time-saving feature of spectrographic analysis is probably the outstanding selling point from the standpoint of the industrialist. To illustrate from the author's personal experience, our laboratory runs only one aluminum alloy, XA142. Eight elements are determined. We commonly get around 60 samples daily, which means 480 analyses. These are done by 22 man hours of labor, which includes my time as supervisor, very little of which is spent in the routine operations. Thus each analysis takes only three minutes to complete, including keeping records, repairing equipment, checking bad results, preparing working curves, etc. Previous to the installation of the spectrograph it took eight men working 10 hours a day to complete the above work. Roughly about 60 man hours of labor were saved daily. Because of the speed, spectrographic methods lend themselves very well to control operations. Analysis of metal being held in the furnace may be had in the melting room in eight minutes after the sample is taken. As industry returns to competition after the war, I feel spectrographic methods which were adopted as a war measure will be retained. Also, those plants not
being able to secure spectrographic equipment during the war will purchase such equipment. In view of the above situation what should the postwar college course in quantitative analysis consist of? Should it be reorganized with emphasis on the analysis of the nonmetals and those things not done by the spectrograph, or should the course continue along traditional lines, with emphasis on the theoretical aspects and the teaching of important laboratory techniques, both of which are important to the student wishing to continue his study of chemistry? How are we to meet the common criticism by many students that our analytical courses are too theoretical and not practical, and a t the same time satisfy the student who wishes to enter chemical research? Can it be done by proper choice of subject matter in one welkorrelated course or by offering special courses to each group of students? Many short courses of this type have been organized for war purposesshould they be continued? Should the chemistry department of a college plan to keep its courses in touch with modern industrial methods? I do not attempt to answer the above questions but submit them as food for thought in the organization of postwar chemistry courses, particularly in the analytical field. It is my opinion that in the years immediately following the war many of our college students will want a quick practical education and it will be the duty of the colleges and uni~ersitiesto work out such courses as will meet the students' needs. It will be well to have these courses as well planned as possible before the msh of students back to college begins. To determine the needs of students it would be well for the organizers of courses to become acquainted with changes in industrial requirements brought about by the war. The above brief description of spectrographic analysis is just one such example of the changing needs of the college-trained chemist.
