Perspectives in Quantitative Organic Microanalysis J. A. KUCK Microchemical Group, Stamford Research laboratories, Research Division, American Cyanamid Co., Stamford, Conn.
b Since Pregl’s time various instrumental techniques have appeared as potential competitors to his methods, Although each of these can enter the field, no one of them has thus far been sufficient in itself to supplant classical microanalysis. In the meantime the Pregl field has continued to advance in its own way, with more new possibilities and interesting refinements still to come.
T
HIS article
deals with contemporary developments in quantitative microanalysis and its future outlook. The author examines the present state of the field and speculates regarding directions which its continued growth may be reasonably expected to take. Since Pregl’s time others have followed with brilliant theoretical contributions in the field of physics, which have since had important application in analytical chemistry. Their discoveries contrast sharply with his original achievement, which represented no new scientific principle but only conclusions arrived at by a tedious method of trial and error. Indeed, so sensitive are some of the newer physical tools that one wonders about the actual survival of Pregl’s work. Can it be that quantitative organic microanalysis in the Pregl mode is already on its may out and that the day is not far off when it will be regarded as a chemical curiosity like the mineralogist’s old-fashioned blowpipe? With such a prospect, the present state of the Pregl field cannot be reliably appraised \Tithout taking the potential competition of certain new physical tools into account. These have important implications in both elemental and group analysis. SPECTROSCOPIC METHODS
Any survey of the recent tools of physics for chemical analysis begins with those that come under the title of spectroscopy: These deal with specific molecules. I n this category are the infrared, Raman, mass, ultraviolet, visible, and x-ray emission or absorption spectroscopies. S e w spectroscopies are being constantly devised, but all are alike in that they yield information concerning molecular structure, atomic linkages, and groups. Moreover, although they may be regarded as essentially qualitative, they are potentially 1552
0
ANALYTICAL CHEMISTRY
quantitative, and, in such capacity, can conceivably serve as tools for elemental analysis. This latter possibility appears especially in situations when the signal function contains some chemical element peculiar to it in the molecule alone. For instance, the >C=O is a strong absorber in the infrared: If oxygen is known to be absent elsewhere in the molecule, determination of carbonyl by infrared becomes a determination of oxygen as well. Thus a physical method can become a serious rival to the corresponding procedure in the Pregl field and the deciding factors in the contest for supremacy will be convenience, speed, accuracy, sample size, and sensitivity; in sum, it is a question of economics. Table I compares six common spectroscopic techniques with the determination of carbon by the Pregl carbon and hydrogen method. Much of what a given technique can do in a certain analytical situation depends upon a chance combination of favorable circumstances. Sometimes it can do very well; sometimes a single detail sharply restricts its usefulness. But as a general rule such a method does not have the precision of exact quantitative microanalysis and consequently we associate each technique in our minds with certain valuable confirmatory functions as shown in the table. Further details about spectroscopic methods are given in a recent book of 787 pages with each chapter written by a team of experts (4, 30). NUCLEAR TECHNIQUES
Sowadays two other analytical tools of physics should be of interest to analysts: nuclear magnetic resonance and radioactivation analysis. Both have one thing in common: They look a t the nucleus. Hence they are concerned with the fundament21 nature of the element under investigation and are therefore independent of the physical state of the analytical material. Furthermore, they are highly sensitive and should readily lend themselves to microanalysis. Suclear magnetic resonance may be summarized for the laity as follows: The magnetic property of the nucleus arising from its spin is the function measured. K i t h the nucleus spinning in a permanent magnetic field, its behavior in a superimposed radio-
frequency field (linearly polarized) is studied. The resulting induced signal is received and interpreted on an oscillograph tube (2, 3, 9). Experimental details can be obtained from two excellent sources (1, S I ) . The point of interest about nuclear magnetic resonance for the microanalyst is that small shifts in frequency can be correlated with chemical structure For example, working with hydrogen nuclei, the expert can distinguish betn-een the case of two >CH2groups in a structure or one -CH3 and a tertiary
I I
-C-H.
i l n attractive future applica-
tion of nuclear magnetic resonance is its possible application to conformational analysis, because it can distinguish between axial and equatorial hydrogens in a steroid or a sugar molecule. Investigation of the spins of nuclei other than hydrogen is probably not of too great concern t o the organic microanalyst. These include phosphorus, fluorine, boron, and sometimes less abundant isotopes of common elements not otherwise measurable. For example, carbon-13 and oxygen-17 can be measured, whereas their more familiar counterparts, carbon-12 and oxygen-16, cannot; the latter have a zero moment by virtue of their even atomic numbers and even atomic weights. But sometimes even elements of odd atomic number-like nitrogen, for example, atomic number 7-hare relatively small moments and hence are difficult to measure. Consequently, to carry out elemental organic microanalysis by measuring nuclear magnetic moments does not seem too practical just now, evcn though one laboratory is already attempting to determine carbon and hydrogen in hydrocarbons by a specid technique. Radioactivation analysis may be defined as the determination of the weight of element in the sample by measuring the intensity of its induced radioactivity ( 7 ) . The intensity of this radiation is directly proportional, subject to various conditions, to the weight of the element present. I n practice. atoms of the element in question are activated by appropriate nuclear bombardment. This means the use of a pile or an accelerator. The intensity of the radiation created in the
sample is compared with similar radiation from a standard of the same element that has been activated under identical conditions. The emitted radiation is usually measured by counting p-particles with a Geiger counter. Although sensitivity in a given radioactive procedure has to be defined in terms of whatever pile flux is available for activation, sensitivities for the elements of the periodic table under present-day pile facilities have been tabulated (8). As many as 80 elements have sensitivities to 10-7 gram or lower. This is a range far below the level of methods of organic microanalysis. Although a t first glance analysis by radioactivation has much to offer, it proves disappointing as far as the elements in Period 2 of the periodic table are concerned. Lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine have low absorption cross sections for thermal neutrons, even if not for fast neutrons. Therefore they exhibit comparatively weak radioactivity when activated with thermal neutrons and their sensitivities are poor. Consequently analysis by radioactivation does not seem to be a substitute for Pregl microanalysis, because Period 2 includes the three elementscarbon, nitrogen, and oxygen-with which the microanalyst is most frequently concerned. P-PARTICLE BACKSCATTERING
Radiochemistry has other techniques for bombarding atoms besides the use of neutrons. In bombardment with pparticles, the phenomenon utilized is not radioactivation, but the principle of “backscattering.” When 8-particles strike matter, a certain percentage of them are turned back in the general direction from which they come and the percentage returned is a cumulative function of the atomic numbers of the various kinds of atoms in the specimen. Apparently the p-particles are attracted and deflected in their path by the field of the nucleus and are also repelled by the extranuclear electrons. Nultiple scattering results and the analytical problem is in a sense the statistical one of counting how many electrons are returned. Muller (95) has developed the experimental method for this type of analysis and has shown that relative backscattering by various elements in the periodic table as measured by his method is a definite function of atomic number. Working with highly purified standards consisting of crystalline compounds as well as a few free elements, he has obtained a table of relative backscattering values from elements 2 through 83. For each
period of the periodic table his data fit a particular empirical straight-line equation with remarkable precision. From this information he can predict the per cent backscattering of any element on the basis of its atomic number. The usefulness of the p-ray backscattering technique for analysis, however, lies in the fact that backscattering of compounds as well as elements can be predicted with high precision. This is done through calculation of an “effective atomic number” for the compound based upon the intrinsic scattering of each element present and its weight fraction in the compound. Stated in another way, every compound will behave in backscattering as if it were a hypothetical element of atomic number 2, and when this number is substituted in the equation for the appropriate period, the per cent backscattering can be predicted. The presence of the element hydrogen in the compound constitutes an interfering effect in the above relationship, because hydrogen exhibits “negative backscattering”-Le., it absorbs pparticles. However, D. C. LIiiller ($4) has investigated this phase of the problem and has developed a positive correction for the empirical equation based upon the weight fraction of hydrogen present and the desired intrinsic scattering of hydrogen. With such correction a 2 value for any organic compound can be computed from its measured backscattering or rice versa. Measurement of 8-particle backscattering as a method of elemental analysis is too new to permit appraisal of its future. But because every compound and its isomer may be assigned an identification number, its 2 or “effec-
Table I.
tive atomic number,” measurement of p-particle backscattering is primarily an identification technique like the infrared. Its effectiveness is diminished, however, by the fact that many compounds can presumably qualify for the same Z number if their atoms are combined in suitable weight fractions to produce the same backscattering power. In other words, the Z number can never be the exclusive possession of any one compound alone. Consequently, although elementary qualitative analysis by p-ray backscattering may narrow down the list of possibilities considerably in the identification of an unknown, additional confirmatory evidence mould still seem necessary. On the other hand, it is conceivable that this new method is a potential tool of great speed and simplicity for furnishing what can serve as a useful alternative to an empirical formula in many instances. Because a microanalysis is usually needed for routine identification or establishment of purity, perhaps a quick measurement of 6-particle backscattering with an automatic counter may do just as well. G A S CHROMATOGRAPHY
Gas chromatography is another physical tool of interest to the microanalyst. It is quantitative and operates with micro samples. Although it has several experimental techniques (9, 26), it is always a kind of spectroscopy. The initial sample mixture is dispersed into its components a t different zones along the column with either a high or low “resolving power” according to various conditions. For qualitative analysis the number of peaks in the chromato-
Comparison of Six Common Spectroscopic Techniques with the Pregl Carbon and Hydrogen
Technique Infrared
Visible Ultraviolet X-ray emission
Time for Sample Rel. Size, Sensitivity, Ace. , Precision, Organic Micro Analysis, W Functions Llin. hlg. Y 70 /O Identification 12 0.5-5 5 1 0.1 group detn. (elemental anal.) Colorimetry 5-30 O,l/5ml. 0.1 3 1 3 0.1 1 1 Quant. anal. 5-20 unsaturation conjugation Elemental anal. 20 100 10 5 5 above At. Xo. 16
Identification 30-50 1-20 pl.5 0 .0 j b quant. anal. molecular wt. Gas chromatog- Identification 5-60 1-20 pl. 1 quant. anal. raphy Pregl micro C Elemental anal. 45 3-5 600 (in C H) Vapor pressure of at least 0.1 mm. a t 150’. * Assuming peak height of 20 divisions read t o =k 0.1 dipision.
+
1
1
2
1
0.5
1
VOL. 30, NO. 9, SEPTEMBER 1958
1553
gram usually gives the number of components in the sample. Such peaks can often be identified with known individuals run separately as standards. Because each component is retarded characteristically in the column before it ultimately emerges, the travel time through the column under specific conditions is also confirmatory evidence of a given individual if identical with that of a previously run standard. The quantitative usefulness of gas chromatography lies in the fact that the area under each peak in the chromatogram is a direct measure of the amount in the mixture of the substance represented. Here is an analytical method that is fast and highly sensitive. It has added value in that it can be combined with either the infrared or mass spectroscopy, if it is desired to recover fractions from the column for such examination. Thus the advantage of the high resolving power of gas chromatography can be coupled with the specific identification of the infrared or the molecular weight determination of mass spectroscopy. In fact, the use of rapid scanning infrared spectrometers for outlining the spectrum of each fraction while it is passing through the column has already been predicted. Gas chromatography may be useful to the microanalyst as a sensitive method for separating and determining the combustion products water, carbon dioxide, carbon monoxide, and nitrogen dioxide in the oxygen stream, as well as just a tool for isolating and purifying his analytical sample. (Whether gas chromatography can do this job as effectively as a series of sensitive infrared gas analyzers remains to be seen.) But if substitution of a chromatographic column for the conventional micro absorption train can enable one to determine these gases more rapidly and accurately than by weighing, a very significant improvement will have been added to the micro carbon and hydrogen determination, The tedious, time-consuming practice of weighing absorption tubes may be eliminated and along with it the familiar carbon dioxide and water weighing error or “blank.” Moreover, a fast analytical finish will be more appropriate for the “empty-tube” or “rapid” carbon and hydrogen method of Korshun and others (17), where an oxygen sweep of 30 to 50 ml. per minute is required and the carbon dioxide and water from the combustion must be determined as quickly as possible in order to begin the next run. The problem of nitrogen dioxide removal is another source of vexation in the carbon and hydrogen determination, which either gas chromatography or spectroscopy might remove. This could be done by eliminating need of our present lead dioxide reagent for retaining oxides of nitrogen. Most 1554
ANALYTICAL CHEMISTRY
objectionable among the drawbacks of this material is the fact that it cannot fix traces of nitrogen dioxide, even in a newly filled combustion tube. Furthermore, the N02/C02 ratio in the exit gas from the combustion tube as a result of this leakage is critically significant with sample weights below 2 mg. But if accurate determination of carbon dioxide and water by gas chromatography can be accomplished in the presence of other gases, perhaps interference by trace nitrogen dioxide may not apply. In fact, more selective absorption a t several points in the system may be the answer to a more accurate carbon and hydrogen determination for submicro samples, regardless of whether they contain nitrogen or not. If it turns out that small quantities of water and carbon dioxide can be determined more accurately by an instrumental method than by weighing in absorption tubes, a more practical approach to the much desired decimilligram carbon and hydrogen may likewise be offered. Up to now this has been blocked by inability to weigh light-weight tubes even on the quartz fiber balance with sufficient accuracy and reproducibility. SPECTROSCOPY vs. PREGL ANALYSIS
It still remains to be seen whether a complete spectroscopic identification is more positive than a total elemental microanalysis. Furthermore, the answer to this question depends in part upon one’s particular criteria of purity. Nevertheless, within the group of methods previously mentioned, each method has its own job to do and although any one may cut across the boundaries of the Pregl field on occasion, none is sufficient in itself to supplant the traditional Pregl analysis. In one case, that of gas chromatography, both techniques might be termed “synergistic”-Le., each may enhance the effectiveness of the other and microanalysis stands to gain something. In another case, that of p-particle backscattering, there may be serious competition with microanalysis, if research workers in the organic field can satisfy themselves with a quick determination of effective atomic number (without loss of sample) in lieu of several microanalyses to establish an empirical formula. RECENT ADVANCES I N THE PREGL FIELD
Within the Pregl field itself the most significant current development is perhaps the curious growth of “ultramicro” analysis (10, 23, 52). Often it might better be called “decimilligram analysis”-Le., analysis of tenth-of-milligram samples.
Ultramicro work begins with the ultramicrobalance. At present these are of the quartz fiber type, the sensitivity of balances with agate knives being unreliable below 10-6 gram. Quartz fiber balances, in contrast, can be built with sensitivities approaching lop9 gram, although for decimilligram analysis only from 10-7 to 10-8 gram is needed. Two general types of quartz fiber balance are now comniercial items for submicro work; they are exemplified in the balances of Rodder (27) and Garner (19). The former, Rodder Model E (Figure l), has evolved from an instrument originally described by Kirk (11 ) . It can be classified as a torsion balance of the twist fiber type and functions as a null-point instrument whereby the force of gravity acting upon the ultramicro mass is counterbalanced by a sufficient torque in the twisted fiber to restore the beam to its original horizontal position. This little balance is remarkably rugged, readily portable, fast, and easy to operate. The pan holder frames are easily removed and are convenient to pick up. The ratio of load capacity of the balance to its rated sensitivity (200 mg. to 0.05 y ) represents a factor of 4 X 106. The standard deviation for weighing a 300-mg. weight in a temperature-controlled room was 0.05 mg. (16) and the weighing range covered by the fiber is about 12 X lo4 times the sensitivity or 6 mg. Consequently, the Rodder balance is ideal for decimilligram samples, if no container heavier than 200 mg. is involved. The Garner balance (Figure Z), another of the twist fiber type, has the added feature of vertical support fibers to relieve the torsion system of the strain of supporting the masses being weighed. By this means as much as 7 grams or more can be borne by each arm of the balance, with little theoretical loss in sensitivity. Since its description in 1954, the Garner balance has been considerably modified in the light of experience and an improved form is still in the development stage. The Garner balance is designed t o do a difficult job: to weigh a much heavier load than the original Kirk balance, with about the same sensitivity and reproducibility. Nevertheless, if this can be accomplished-Le., to weigh a 7-gram load to 10-7 or 10-8 gram-a great contribution will have been made in decimilligram analysis. Scaleddown micro combustion boats, absorption tubes, and filters can be weighed. A gravimetric carbon and hydrogen determination will become possible. ULTRAMICRODETERMINATION OF CARBON A N D HYDROGEN
The maximum allowable error in
Figure 1.
Rodder Model E quartz fiber microbalance
weighing 0.5 mg. of acetanilide (il% carbon) for the carbon and hydrogen is 2 y, in order to get conventional 0.3%esrbon). acceptability of results (=t In order to maintain this same criterion (=t0.3%) when it comes to weighing the combustion products, 1.3 mg. of carbon dioxide must he weighed to within 2 ~ 5 . 5y and 0.3 mg. of water to =t 14 y. Rut in spite of the fact that the Garner balance in itself is sufficiently accurate for the work, preliminary attempts to use i t for this purpose have not been successful. Part of the trouble may have been in failure to get cleancut separations at the decimilligram level of carbon dioxide, water, and nitrogen dioxide during combustion, hut difficulty has also been encountered in meeting the tolerances for weighing carbon dioxide and water when the absorption tubes are reweighed after a blank run (20). This problem applies to small sealable absorption tubes as well as the diminutive Pregl type and until it is solved, no direct carbon and hydrogen determination a t the decimilligram level seems possible. Kirsten (J2) has been attempting elemental analysis in decimilligram samples hy combustion in a sealed tube. The sample (0.1 to 1 mg.) weighed on the Rodder balance is heated in a quartz capillary with lead chromate, copper gauze, and oxygen whereby halogen, sulfur, phosphorus, and alkali are fixed by the lrad chromate. The sealed capillary is then transferred to a gasometric apparatus and broken under vacuum, and the three combustion gases water, carbon dioxide, and nitrogen are successfully determined. Table I1 (J4) gives data for three typical analyses of decimilligram samples. For 12% hydrogen the hydrogen value is low, perhaps through absorption of moisture on glass walls. For 0% nitrogen a significant blank appears, p e r h p s from nitrogen in the oxygen supply. Nevertheless, the carbon determinations in such small samples are excellent. Elemental anal-
I
!
f
*I
Figure 2.
Garner heavy-duty quartz fiber microbalance
ysis at the decimilligram level has been accomplished.
can he measured more accurately than volume of solution.
OTHER DEClMlLllGRAM PROCEDURES
POSSIBLE FUTURE DEVELOPMENTS
Two other Pregl decimilligram procedures have been reported for Dumas (J6,18). In one the eamples were weighed with a knife-edge balance; in the other with the Garner balance. For l'regl sulfur there are also two decimilligram methods. One is the silver absorbent method (22), the sulfate uptake on the silver being weighed directly on the Garner balance. The other (f3)involves combustion in oxygen, then reductive combustion in hydrogen to hydrogen sulfide, and finally colorimetric determination of the hydrogen sulfide. The Pregl combustion of chlorine has likewise been scaled down to the decimilligram level ( S I ) . Here the chlorine after absorption in 1 to 1 1N sodium hydroxide-30% hydrogen peroxide is determined by potentiometric titration using the silversilver oxalate electrode system. This titration is very accurate for traces of chloride, although perhaps no more so than the coulometric method, as time
In view of the trend of microanalysis toward further method refinement, the l'regl field can hardly he regarded as static. Consequently, it is easy to foresee many new future developments. One can predict, for instance, that the present trend toward more new and improved equipment will continue. An obviously needed item here is a more durable electric microcomhustion furnace with certain improvements. It must be universally adaptable-Le., it should do equally well for the carbon and hydrogen, Dumas, sulfur, oxygen, or fluorine determinations. T o do this it must he able to operate with at least three selective operating temperatures: 750", 900", and 1125O C. A furnace l i e this ought to be equipped with a porcelain shell rather than aluminum and provided with a series of heavy platinum-rhodium thermocouples (5% rhodium-platinum to 20% rhodiumplatinum) and a selector switch for taking temperature at various points
TableII.
Decimilligram Carbon, Hydrogen, and Nitrogen Determination by Kirrten Technique' Sample, Theow, % Found, % ME. C H N C H N Acetanilide 0.0921 71.1 6.7 10.4 71.2 6.9 10.3 Lauric acid 0.1254 72.0 12.1 ... 71.8 10.8 0.4 Triiodophenol 0.11213 15.3 0.6 ... 14.9 0.7 0.9 Best analyses selected from list of 12 recently obtained by Kirsten a t MedicabChemical Institute, University of Uppsala.
VOL. 30, NO. 9, SEPTEMBER 1958
II555
along the heated zone. Heating elements must be more durable, being made, perhaps, of a larger diameter iiichrome resistance wire (Kanthal) or Carborundum glow bars, and these must be easily replaceable. Another badly needed tool for the microanalyst is a small, inexpensive, electric vacuum drying oven. This item should be mass produced, so that he can have a number of them. The oven should be cube-shaped for convenience in stacking and should have its individual temperature control. Search for a new and better combustion technique may be expected t o continue. Although the now familiar “rapid” method, which already represents a considerable departure from Pregl’s original ideas, seems well established today, pa-haps a fresh outlook is still worth while. One attractive lead along this line is a n adaptation of the metallurgist’s “heat extraction” procedure (5). For it should be possible by means of the mercury vapor pump to extract traces of carbon dioxide, water, or other combustion gases from a system after burning a small organic sample, as is now done with molten metal. Upon transfer of these gases to a suitable receiver, several possibilities for determination present themselves, Figure 3 is the delicate microOrsat apparatus of Feichtinger (@, which measures gas volumes from 0.05 to 2 ml. with an accuracy to 1 pl. It is now being used successfully in the analysis of metals. Alternatives in such gas microanalysis are the use of a manometric technique based on chemical separation, or a column for gas chromatography equipped with a sensitive gas density balance (balanced circuit). Another new development in combustion technique is the method of Schoniger (28, 29), which has already proved exceedingly useful. In many laboratories it is ’fast replacing conventional combustion procedures for halogen and sulfur in simple compounds on account of its speed and simplicity. Its future refinement, as well as its extension t o the analysis of other elements, can be expected. Its unusual accuracy points to successful scaleddown procedures and one can readily visualize a 5-ml, Erlenmeyer combustion flask with its 6-mm. ground joint stopper for ultramicro work. CONCLUSION
Because of its theoretical simplicity and relatively low cost, Pregl micro-
1556
ANALYTICAL CHEMISTRY
Maturing Marks
I Gar ion
7. Measurimg Chamber
Ccinbu8tIOn Chamber
Seal
Step
Absorptlon ~ e ~ Step ~
~
~
l
b
~
Micrometer
Figure 3.
Micro-Orsat apparatus of Feichtinger
analysis continues to perform a valuable function in organic research. The pharmaceutical and fine chemicals industries in particular, as well as universities and research institutes, will continue to avail themselves of its services. ACKNOWLEDGMENT
Bcknowledgment is hereby made to the following: C. RI. Judson, Stamford Research Laboratory, and group leaders associated with him for advice on physical methods; Jerome Rodder and T. H. Garner for information and material concerning their quartz fiber balances; and W. J. Kirsten for lastminute analytical data from his ultramicrocombustion.
(15) Kirsten, TI-. J., Greenbaum, B. W., AKAL.CHEJI.27, 1806-9 (1955). (16) Koch, C. W.,unpublished communi-
cation.
(17) Kuck, J. A,, Altieri, P. L., ilfikrochzm. Acta (Wzen) 1954, 17-24. (18) Ibad., 1956, 1550-64. (19) Kuck, J. A,, Altieri, P. L., Towne, A. IC., Ibtd., 1953, 254-65. (20) Ibzd., 1954, 1-15. (21) Kuck, J. A,, Daugherty, M., Ratdorf, D. K., Ibid., 1954, 287-307. (22) Kuck, J. A,, Grim, E. C., Ibid., 1954, 201-10. (23) Kuck, J. A., Kingsley, Alma, Kinsey,
Doris, Sheehan, Frances, Swigert, G. F., A s . 4 ~ CHEM. . 22. 604 (1950). (24) Muller, D. C.; Ibid.; 29,975-9 (1957). (25) RIuller, R. H., Ibid., 29, 969-75
(1957). (26) Munch, R. H., Record Chem. Progr. 18,69-lOl(1957). (27) Rodder, J., Sales Brochure, Micro-
tech Services Co., Berkeley, Calif.
128) Schonieer. LITERATURE CITED
( 1 ) Andrew, E. R., “Nuclear Magnetic
Resonance,” Cambridge University Press, London, 1955. ( 2 ) Block, F., Phys. Rev. 70, 460 (1946). ( 3 ) Bloembergen, N., Purcell, E. &I., Pound, R. V., Ibid., 73, 679 (1948). (4) Boaen, E. J., Nature No. 4572, 1205 (1957 i.
(5jFeiihtinger, H., Arch. EisenhiLttenw. 26, 127-30 (1955). (6) Feichtinger, H., Berg. u- hQttenmann. Monatsh. montan. Hochschule Leoben 100, 230-8 (1955). (7) Jenkins, E. N., Smales, A. A., Quart. Revs. (London)10,83-107 (1956). ( 8 ) Ibid., pp. 94, 95. ( 9 ) Jordan, L. A., Chem. & Ind. (London) 1957,316, 318. (10) Kirk, P. L., “Quantitative Ultramicroanalysis,” Wiley, Yew York, 1950. (11) Kirk, P. L., Craig, Roderick, Gullbere. J. E.. Bover. R. Q.. ANAL.CHEW
W.. Mikrochim. dcta
(29) Ibid.,-1956, 869-75. (30) Keissberger, A., et al., “Chemical Applications of Spectroscopy, Technique of Organic Chemistry,’ 1701. IX, Interscience, Ken, York, 1956. (31) Wertz, J. E., Chem. Revs. 55, 829953 (18.55’1 \ - - - - ,
(32)T’ilson,
C. L., Mikrochim. Acta (Wien) 1956, 91-103.
RECEIVEDfor review Rlarch 26, 1958. Accepted March 26, 1958. Division of Analytical Chemistry, Symposium on hficrochcmistry, 132nd Meeting ACS, Sew York, K.Y.,September 1957.
Pola rog r a phic Deter mina tion of Small Amounts of Ti n-Co rr ect io n
-
