Trends in Quantitative Analysis A Survey of Papers f o r the Year 1946 FREDERICK C. STRONG, Villanova College, Villanova, P a . In order to help decide what methods of quantitative analysis will be important in the future and to compare future use of classical and newer instrumental methods, all research papers published in 1946 and covered in Chemical Abstracts prior to September 1947 were studied. Though the largest number of papers is on titrimetry (volumetric analysis), the number on colorimetry is almost as great; 56% of all papers are on instrumental methods of analysis,
C
principally coloriyetry, spectrophotometry, emiesion spectrography, instrumental titrimetry, and polarography; among preliminary steps described by research papers, chromatmgraphy is numerically outstanding; next to English, more 1946 papers are written in Russian than in any other language; 58% of the papers devoted to quantitative analysis during 1946 are concerned with the determination of organic compounds. PROCEDURE
OLUbINS and editorials in ANALYTICALCHEhrIsTRY and
the correspondence they quote show that many chemists &reasking, “Where is analytical chemistry heading, technically and professionally?” This paper is concerned with the technical side of the question applied to quantitative analysis. Though many teachers of quantitative analysis are adding a8 much material on the newer instrumental methods of analysis a8 time and equipment permit (I, $, 6, 9),there are many.shades of opinion on what is significant enough to include and whether the new methods are important enough to be given a t the expense of material on the classical methods. Some teachers of analysis, either willingly or unwillingly, leave instruction in physicochemical methods of analysis to courses in physical chemistry. The uncertainty about what to teach is reflected in the number of queries addressed to Muller’s column on “Instrumentation” in ANALYTICAL CHEMISTRY (11). Because facts are of greater value than opinions, a convenient and objective indication of the future practical importance of the various analytical methods can be obtained by a statistical study of the research papers now appearing in the journals, To some extent, the present importance of a method can also be measured, aince many papers describe improvements of procedures now in wide use. Of course, conclusions must be drawn with care; not all discoveries and improvements will be adopted, and those that are adopted will not be equally valuable. Ileepin‘g these limitations in mind, partial answers to the above questions can be obtained. Better anawers could be given if similar studies could be made periodically and then correlated with one another and with industrial practice. However, no recent paper of this sort that would permit correlation could be found. With very little additional labor, other useful or a t least interesting information is obtainable from a literature survey, and is presented in this paper. Consider first the languages in which the papers are written. There is much discussion in educational circles today of the relative importance to scientists of the various languages, especially Russian (2, 7). Though this study is limited to only very recent publications in the field of quantitative analysis, it can yield data of value in discussing this question. Also of interest but strongly affected by the war is a list of countries in which the research was done, with a total of papers from each. Furthermore, a rough estimation of the proportion of 1946 papers which are on quantitative analysis can be made by combining the data of this survey with those of Crane (3)on the number of abstracts that have appeared each year in Chemical Abstracts. Lastly, in order to see whether modern quantitative analysis is more concerned with determining organic or inorganic substances, a count can be kept of this aspect, The present trend is toward making organic analysis part of analytical chemistry rather than organic chemistry (10).
General. The most convenient period for a survey of papers is a complete year, and in order to cover as recent a period as possible, 1946 was chosen. The main source of material was, n a b urally, Chemical Abstracts. Since its index is not designed for such a search, it was necessary to skim briefly through each page. omitting a few sections very unlikely to contain analytical papers. It, is possible that a few were missed. At times more were found outside Section 7 than in it. Summer issues of Chemical Ab stracts for 1947 show a decrease to a small fairly constant number of 1946 papers. An arbitrary stop was made with No. 16, 1947, because it was felt that it would be some time before 1946 papers ceased appearing entirely and the relative results would probably be unaffect,ed by a delay in the summat,ion of results. When the abstract of a paper did not give sufficient information t o classify it, the paper itself was consulted if available. To be included in the study, a paper had to be concerned, in whole or in part, with quantitative analysis. I t could be a complete determination or a step such as sampling, filtration, or distillation, provided that it was specifically applied to analysis. Also included were patents on analytical apparatus and reviewe of methods. Reports of analyses by known methods were not included if they did not contain significant research on the methods used. As for the nomenclature used in the tables, the author feels that a paper of this sort is not the place to standardize terminology. Rather, all terms found to be in general use in the papers surveyed should be given. In no case did the number of interchangeable terms exceed two. Equivalent terms are given in parentheses in the tables and throughout the discussions. When a group name was desired and could not be found in the papers, the terminology of ,CAemical Abstracts was followed. Some method names-cg., chronometric, microscopical-were taken from Kolthoff and Sandell (8). Classification of Papers According to Method Used. Some papers contained research on more than one method, usually a comparison. If the methods m r e in different classifimtionse.g., colorimetry and gravimetric analysis-the paper was counted in both classifications. Classifications given a t the bottom of Table I were not included in the calculations. Therefore the total of figures in column 2 is not the same as the total number of papers covered by the survey. The percentage of papers in each classification (column 3) i m s calculated from the column 2 total. When large numbers of methods of different types were covered in one paper (extensive reviews, collected official niethods, etc.), the paper was called “many methods’’ and no addition was made to the figures for those methods; it was felt that they did not deserve the weight of papers entirely on one or two methods. A classification of ‘“preliminary steps and methods of seps968
DECEMBER 1947
969
Table I. Methods Pitrimetry (volumetric analysis) Colorimetry Gravimetic analysis Spectrophotometry Emission spectrography and automatic spectrometry (the latter a new methnd) Polarography Biological assay Miscellaneous methods General quantitative ana1ysi.Q Manometric methods Combustion analvsis Iass spectrometfy and spectrograph) F luorometry c: as analysis bsorption spectrometry and spectrograph) urbidimetry racer analysis (radioactive and nonradioactive isotopes) L>ensitometry Emission flame photometry, spectrophotometry, and spectrography X-ray di5raction spectrography
% of Total
323 29 1 108 72
25.6 23.0 8.5
67 51 46 32 29 22 21 21 20 18 17 14
5.3 4.0 3.6 2.5 2.3 1 .i 1 .i 1.i 1.6 1.4 1 :3 1.1
14 11
1.1 0.9
i 7
0.6
5.7
0.6
.
hlethodp Thermal conductivity Refractometry Electroanalysis Microscopical analysis Chronometric methods Electrical conductivitv Volume of liquid distnled (including entrainment methods) Critical solution temperature (cloud point) Nephelometry R a m a n spectrographv Viscometry (viscosiketry) hlelting point and freezing point Thermometric analysis Volume oi precipitate Dispersion hIagnetic susceptibility Optico-acoustical analysi? Polarimetry Capillary analysis Electrographic analysis (new method) Neutron capture (new method) Evolution Total
No of Papers 6 6 6 6 5
9% of Total 0.5 0.5 0.5 0.5 0.4
1
0.4
5 4 4 4 3 3 3 2
0.4 0.3 0.3 0.3
2 2 2 2 2 1
1
1 1266
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1
0.1 100 4
papers on preliiiiinary steiJs and separation methods (107),many method* (43), unclassified (36)
Not included:
Table 11.
Classification of Analytical Papers According to Method S o . of Papers
Instrumental
us.
Noninrtrumental illethodh
Pioninstrumental Methods Titrimetrv (volumetric analv-is). visi181 Gravimetiic analysis Biological assay Colorimetry, matching Total
No. of Paper251 1OS 46 34 -
43R
liistruniental A l e r t i d Colorimetry a Photoelectric Visual. instrumental Jpectrophotometry Emission spectrography Titrimetry (volumetric analysis) Potentiometric Amperoinetric Conductometric Thermometri’c Polarography Combustion Mass spectrometry a n d spectrograph? Fluorometry Gas analysis ibsorption spectrometry and vx=rtrop-
133 69 )
2UP
72 A:
41) ri(l
2,
d1
21 21 20 18 li 14
Total
.?a
Summary Noninstrumentel lnntrumental
439
563 Total number of papere
1002
2 4 8 pntwrs on colorimrtry mere not c:as$ifiPd tii either i n ~ t n i m r n t n lo r uoninstrumental. Probably they would almost all be found injtrunientiil
ration” was created to contain papers on such subjects as qampling, filtration, extraction, etc. Papers classified as miscellaneous were principally on complex methods for which no name has been proposed and which could not be described by a short phrase. Papers announcing new methods of analysis were so designated in Table I. * Papers on the Dumas determination of nitrogen were classified as “combustion” papers rather than “manometric (gasometric)” as is sometimes done. Since carbon-hydrogen combustion determinations may be concluded by either weighing or titration, but are not classified as “gravimetric” or “titrimetric,” this seemed to be more logical. Papers on the determination of rarbon in steel by combustion were counted under combustion. Kjeldahl determination papers were counted under both “titrimetric-visual” and “separation methods-distillation.” The titrimetric method of Jensen and Parrock has been given no specific name and hence was counted as conductometric. It is a new method.
Instrumental us. Noninstrumental Methods. A8 pointed out by hluller ( l a ) ,a truly instrumental method is entirely automatic, from putting in the sample to getting the result “printed on B ticket.” However, though colorimeters are seldom made direcb reading, we think of a determination with a colorimeter as intrinsically instrumental. Hence, for want of a better term, “instrumental” was taken to refer to such methods as spectrophotometry, colorimetry, and polarography. Table I1 was compiled to compare the number of papers on classical noninstrumental methods with those on the newer instrumental methods. Because of difficulty in classifying some of the less numerous methods,, they were omitted; their number is so small that their effect on the result would be negligible. Subdivisions of papers on preliminary steps were made in Table 111. To be consistent with the practice of counting a paper on two methods under both methods, it seemed necessary to take note of papers describing research on a determination where the novel feature lay in a preliminary step. Such papers vere counted under both the specific preliminary step and the final analytical method used. This accounts for the large nrimher of papers covered in Table 111, while the number listed at the bottom of Table I under “preliminary steps and separation methods” is small, since those included there were general in nature and applied to no specific method of determination. Compilation of Tables IV, V, and V I was simple and straightforward. Some paper? had to be classified in both groups in Table VI.
Table 111. Classification of Papers on Preliminary Steps and Separation Xlethods Preliminary Step or Separation hlethod Adsorption Chromatography 45 Ion exchange 91 Other 81 Extraction Precipitation Distillation Miscellaneous Sampling Filtration Diaestion (wet oxidation) Complex ion formation Reduction Centrifuging Dissolving Dialysis
No. of Papers
Total
% of Total
62
28.6
40 39 22 15 10 i 6 4 4 3 3 2 217
18.4 18.0 10.3 6.9
-
4.6 3.2 2.8 1.8 1.8 1.4 1.4 0.9 100.1
-
V O L U M E 19, NO. 1 2
970 Table IV. Language English Russian French Spanish Italian German Swedish Dutch (Flemish) Danish Japanese Norwegian Czech Jugoslavian
No. of Papers 870 153 137 57 31 23 19 16
% of Papers
32
?I 1
66.2 11.6 10.4 4.3 2.4 1.7 1.4 1.2 0.2 U.Z
0.1 0.1 0.1 99.9
~
Total Unclassified
Table V.
Languages of Analytical Papers
22
CALCULATION AND DISCUSSION OF RESULTS
The total number of quantitative analysis research papers found to be published in the year 1946 was 1336. Of these, 34 are patents. A small number of 1946 papers are bound to appear in coming issues of Chemical Abstracts, but in order to apply the results to the future, it is necessary that 1946 be not too far in the past, The relative results should not be affected by this omission, except to increase slightly the percentage of foreign articles. Turning first to Crane’s ( 3 ) graph of papers abstracted each year in Chemical Abstracts, if we reduce the figure for papers abstracted last year to alloff for the acquisition of back number journals unobtainable during the war, we arrive a t the approximate figure of 35,000 papers deemed suitable for inclusion iq Chemical Abstracts. AIaking the assumption that this number is roughly the same as the number published in 1946, we can compare r,his with the 1336 analytical papers found by this survey and conclude that 1 paper in 26 is on quantitative analysis research. This is rather interesting, though not of great significance. Methods of Quantitative Analysis. The most striking part of Table I is the high standing of colorimetry, a close second to titrimetry (volumetric analysis). Combining it with its close relative, spectrophotometry, puts the combination in first place. I t is raised still more if the closely related classification of absorption spectrometry and absorption spectrography is included. The high standings of eniission spectrography, polarography, and biological assay are worthy of note. This table should prove useful in revamping the content of advanced courses in quantitative analysis. Instrumental 2’s. Noninstrumental Methods (Table 11). The fact that 56% of 1946 analytical papers are on instrumental methods of analysis indicates their future practical importance, Colorimetry, spectrophotometry, emission spectrography, instrumental titrimetry (volumetric methods), and polarography shoJy up,as the “big five.” On the other hand, it must be admitted that noninstruniental methods will probably be widely used for some time to come. Preliminary Steps and Separation Methods (Table 111). The usual separation methods (extraction, precipitation, distillation, and filtration-in order of frequency) are topped by adsorption, with chromatography the principal subdivision. So many 1946 papers are on chromatography that it is reasonable to recommend that advanced analytical courses contain class and laboratory instruction in this important method of separation. The preliminary step receiving the greatest attention is sampling. Languages in Which Analytical Papers Are Written. The contention that knowledge of the Russian language is and will be important to analytical chemists is borne out by Table IV; Russian papers are nest to English in frequency, though one sixth of their number. French is a close third. The theory that because of Russia‘s economic problems, its research would be thoroughly practical in nature, was found untrue in analytical chemistry, numerous theoretical papers of high caliber being
Countries in Which Research for Papers Was Done
Country United States Great Britain Union of Soviet Socialist ReDublics France Sweden Italy Switzerland Spain Netherlands India Australia Canada Belgium Argentina Brazil
KO.of Papers
Germany Norway Greece Hawaii Chile Romania Japan Jugoslavia Czechoslovakia Rlexico China Palestine Peru Puerto Rico Egypt Hungary British West Indies Irish Free State
2 2
2 2 2 1 1 1
Total Unclassified
Table VI.
% of Papers
549 192 162 105 43 33 31 29 24 23 19 14 13 12 12 10 7 4 4 3 3 3 2 2
1 1 1 1 1 1 1318 18
-
Division of Papers According to Nature of Substance to Be Determined
Nature of Substance Organic Inorganic
No. of Papers 654 473 Total 1127
% of Papers 58
42 100
Metal organic (8),general (1681, unclassified (16).
noted. Of course, in evaluating the importance of a language to chemists, the extent of past literature as well as of the present and future must be considered. This consideration applies especially t o Russian and German. The huge quantity of captured German research reports together with previously available German literature will serve to maintain fcr some time its position as the foreign language of greatest use to English-speaking chemists
(6). Countries in Which Research for Paper9 Was Done. Table V requires little comment. Present dominance of the I-nited States is evident. Following Great Britain but well ahead of France is the Soviet Union. Sweden is in fifth place. Organic us. Inorganic Substances. The previous conviction of this author concerning the importance of the quantitative determination of organic compounds is verified by Table VI, which shows that the majority of 1946 papers were on the determination of organic compounds. Though it is probably correct to attribute this partly to the existence of many satisfactory methods for the determination of inorganic substances, it seems justifiable to conclude that teachers of analytical chemistry should place more emphasis on quantitative organic analysis than at present and not leave instruction in this growing branch of analysis to the teacher of organic chemistry. SUMMARY
h statistical survey of quantitative analysis research papers published in 1946 uncovered the following facts: Though the largest number of papers arc in the classical field of volumetric
971
D E C E M B E R 1947 analysis or titrimetry, colorimetry is a close second, and if combined with those on the very similar method of spectrophotometry, exceeds every other method. Instrumental methods of analysis comprise 56% of all papers, the first five being (in decreasing order) colorimetry, spectrophotometry, emission spectrography, instrumental titrimetry (volumetric analysis), and polarography. Statistically outstanding steps preliminary t o the final determination are (in decreasing order) adsorption (especially chromatography), extraction, precipitation, distillation, sampling, and filtration. Next to English, the language in which most 1946 analytical papers are written is Russian: French, Spanish, and Italian follow in that order. Tabulation of the countries in which the research for papers was done gives, in decreasing order, United St,ates, Great Britain, V.S.S.R., France, Sweden, etc. More than half of the papers (5S%j are on the determination of organic compounds.
ACKNOWLEDGMENT
The author is indebted to Earl J. Serfass for his interest in the progress of this paper and for his helpful advice and criticism. LITERATURE CITED
(1) Conklin, R. B . , J . Chem. Education, 24, 271 (1947). (2) Ibid., p. 272. (3) Crane, E. J . , Chem. Eng. Sews. 24, 3353 (1946).
(4) Dunkelberger, T. H . , J.Chem. Education, 24, 383 (1947). (5) Green, J. C . , Chem. Ene. News,25, 1335 ( 1 9 4 7 ) . i(1947). (6) Hallett, L. T., ANAL.CHEM.,19, No. 1, 17 ; (7) Harris, R. L . , J . Chem. Education, 24, 392 (1947). (8) Kolthoff, J . SI., and Ssndell, E. B., “Textbook of Quantitative Inorganic Analysis,” N e w York, Macmillan Co., 1936. (9) Lambert, R . H . , J . Chem. Education, 23, 2, 610 (1946). (10) Muller, R. H., Ari.4~.C H E M . ,19, No. 1, 24 -1,(1947). (11) Ibid., KO.5, 26 A (1947). (12) I b i d . , KO.1, 2 3 A (1947). RECEIYEDOctober 6 , 1947.
Determination of Olefinic Unsaturation Cooperative Evaluation of Nitrogen Tetroxide Methods E. T, SC.iFE AKD JOHN HERSI.4N, Research and Development Laborutories, Socony-Vacuum Oil Co., Paulsboro, N.J . G. R. BOND, JR., Houdry Process Corporation of Pennsylvania, W‘Vilmington, Del., AND’ COOPERATORS1
Two standardized procedures for the determination of olefins by reaction w-ith nitrogen tetroxide were cooperatively evaluated by an A.S.T.Rl. group. The results of this work indicate that the methods give a satisfactory value for total olefin content of hydrocarbon mixtures i n the gasoline boiling range which contain other than highly branched olefins. Further work is planned on highly- branched olefins of the
D
URIXC: the war, Subcommittee XXV \vas organized under Committee D-2 of the American Society for Testing
Materials for the purpose of developing methods of analysis of petroleum products for hydrocarbon types. Of particular interest to this group was the reaction of nitrogen tetroxide with olefin hydrocarbons as a possible basis for a procedure for quantitative determination of the olefin content of hydrocarbon mixtures. Previous work by Bond (3) indicated that, under certain prescribed conditions, nitrogen tetroxide was void of the conflicting reactions associated with halogen titration procedures, and two general procedures utilizing nitrogen tetroxide were outlined Tvhich were proposed as possible replacements for, or supplements to, the commonly used bromine number methods for determination of olefins. The evaluation and standardization of these procedures were placed under the jurisdiction of Section B of Subcommittee XXV. The work undertaken by this section involved (1) improvement of the design of apparatus and operating technique, and (2) cooperative evaluation of standardized procedures as test methods for determination of olefins. Sine laboratories cooperated in this phase of the work. The present paper presents in some detail the present statu? of the development work, and the limitations and precisions of the methods as interpreted from the data and contributions of the cooperators. 1
E . L. Baldeschwieler, Standard Oil Development C o . L.31. .Henderson, Pure Oil Co. S.S. Kurtz, Jr., Sun Oil Co. H. Levin, The Texas Co. C. E. Starr, Standard Oil Co. of New Jersey, Louisiana Division E. B. Tucker, Standard Oil Co. of Indiana F. D. Tuemmler, Shell Development Co.
di- and triisobutylene type. The need for estimating olefin molecular weights, required with bromine number methods, is eliminated. Method 4 provides an olefiwfree portion of the test sample which is suitable for additional analysis for other hydrocarbon types. Future work will further improve the precision and accuracy of the methods and extend their applicability to highly branched olefins, OUTLINE OF METHODS
Method A. Steam-Distillation Procedure. Gaseous nitrogen tetroxide is passed into the chilled sample to react with the olefins. At the end of the reaction, an aqueous solution of urea is added to decompose the excess nitrogen tetroxide. The mixture is steam-distilled, the unreacted hydrocarbons being removed as the distillate. The content of total olefins is obtained from the difference in volume of the unreacted hydrocarbons and the volume of the original sample. This procedure, in addition to determining the olefin content, produces an essentially olefin-free portion of the sample, which may be used for determination of other hydrocarbon types. Method B. Direct Volumetric Procedure. Gaseous nitrogen tetroxide is passed into the chilled sample to react with the olefins. The nitrosates formed react with 70mm.O.D. alcoholic potassium sulfide solution, permitting the measurement of the unreacted portion of the test sample. The content of total olefins is obtained from the difference in volume of the unreacted portion of the test sample and the original volume of test Sam le.Tfis method is applicable where only the total olefin Figure 1. Treating-Discontent of the sample is retilling Flask quired.
1
