V O L U M E 2 6 , NO. 9, S E P T E M B E R 1 9 5 4 The incandescent light source is operated a t full voltage to obtain the closest approximation to I.C.I. Illuminant C. Each of the three tristimulus filters of the instrument is adjusted to read 100% transmittance for the standard liquid followed by measurement of the per cent transmittance obtained upon replacing the standard with the sample. Ordinarily, no difficulty is encounteied in obtaining results reproducible to 0.2 unit on the scale ranging from 0 to 100 units. ACKNOW LEDGV ENT
The authors wish to acknowledge the contributions made during the course of this work by many members of the California Research Corp. staff, especially 11. T. Sigh for assistance in evaluating the procedure for inorganic sulfate; R. D. Clark for the ultraviolet spectral analysis associated with the procedure for low molecular weight sulfonates; and A. C. Ettling for preparation of some of the alkyl aryl sulfonates used in the investigation. LITERATURE CITED (1) (2) (3) (4) (5) (6)
(7) (8) (9) (10) (11)
Alicino, J. F., ANAL.CHEY.,20, 85 (1948). Am. Sac. Testing Materials, Philadelphia, Pa., D 885-52T. Ibid., D 95. Analyst, 76, 279 (1951). Balthazar. J., Ing. chim., 32, 169 and 183 (1951). Barr, T., Oliver, J., and Stubblings, W. XI., J . SOC.Chem. Ind., London, 6 7 , 4 5 (1948). Bell, R. N.. ANAL.CHEM.,19, 97 (1947). Blank, E. I\'., and Tray, A , Oil & Soap, 2 3 , 5 0 (1946). Bronell, G., J . Am. Oil Chemists' SOC.,26, 427 (1949). Brunjes, H. L., and Manning, AI. J., IND.ENG.CHEM.,-4h-a~. ED.,12, 718 (1940). Compton, J. W., and Liggitt, L. M.,J . Am. 022 Chemists' SOC.,
28, 81 (1951). (12) Epton, S.R., Trans. Faraday SOC., 4 4 , 2 2 6 (1948). (13) Gdby, J. A., and Hodgson, H. IT., M / g . Chemist, 21, 371, 423 (1950). ANAL.CHEM.,25,897 (1953). (14) Gordon, B. F., and Urner, R. S., (15) Hallet, L. T., and Kuipers, J. IT., ISD.ESG. CHEM.,ANAL.ED., 12,360 (1940). (16) Hardy, -i.C., "Handbook of Colorimetry," Cambridge, Mass., N . I . T . ,The Technology Press, 1936. (17) Hartley, G. S., and Runnicles. D. F., Proc. Roy. SOC.,168A, 424 (1938). (18) Hintermaier, A , Fette u. Sez/en, 52, 689 (1950).
1497 (19) (20) (21) (22) (23) i24j
Hunter, R. S., Natl. Bur. Standards, Circ. 429 (July 30, 1952). Jones, J., J . Assoc. Ofic.Agr. Chemists,28,398 (1945). Jones, L. T., I N DESG. . CHEM.,ANAL.ED.,14,538 (1942). Joustin, D., Chim. anal., 34, 34 (1952). Karush. F.. and Sonenbere. M.. A N ~ LCREM.. . 22, 175 (1950). Kelley, R. M., and Blank, E. W., J . Am. Oil Chemzsts' SOC.,
26, 685 (1949). (25) Klevens, H. B., ANAL.CHEY.,22, 1141 (1950). (26) Lambert, J. I f . ,J . Colloid Sci., 2 , 479 (1947). (27) Lee, S. W.. Wallace, J. H., Jr., Hand, W.C., and Hannay, N. B., IND.EKG.CHEM.,ANAL.ED.,14, 838 (1942). (28) Lewis, G . R., and Nerudon, L. K., Sewage and Ind. Wastes, 24, 1456 (1952). -, (29) Xlahoney, J. F., and Michele, J. H., IND.ENG.CHEM.,ANAL. ED., 14, 97 (1942). (30) Marron, T . U., and Schifferli, J., Ihid., 18, 49 (1946). (31) Meader, A. L., private communication. (32) Miller, W. J., J . Am. Oil Chemists' SOC.,27, 348 (1950). (33) Munger, J. R., Yippler, R. W., and Ingols, R. S., A K ~ LCHEM., . 22, 1455 (1950). (34) Newhall, S. Ll.,Nickerson, D., Judd, D. C., and Judd, D. B., J . Opt. SOC.Amer., 33, 385 (1943). (35) Ogg, C. L., Willets, C. O., and Cooper, F. J., As.iL. C H E M . ,83 ~~, (1948). (36) Quimby, 0. T., Chem. ReE., 40, 141 (1947). (37) Raistrick, B., Harris, F. J., and Lowe, E. J., Analyst, 76, 230 (1951). (38) Salton, M.R. J., and Alexander, A. E., Research, 2 , 247 (1949). . 5 , 403 (1933). (39) Schroeder, W.C., IND.ENG.CHEM.,A N ~ LED., and Koester, 1%'. K., J . Am. Oil Chemists' SOC., (40) Schuck, N. W., 27, 321 (1950). (41) Sheen, R. T . , and Kahler, H. L., ISD. ENG.CHEM.,ANAL.ED., 8 , 127 (1936). (42) Stupel, H., and van Segesser, H., Fette u . Sei/een, 53, 760 (1951). (43) Sundberg, 0. E., and Roger, G. L., ISD. ESG. CHEM.,ANAL. ED., 18, 719 (1946). (44) Van der Hoeve, J. A . , Rec. trav. chim., 67, 649 (1948). (45) Weatherburn, A. S., J . Am. Oil Chemists' SOC.,28,233 (1951). (46) Weiner, S., Chemist Analyst, 42, 9 (1953). (47) Wijga, P. W. O., Chem. Weekblad,45,477 (1949). (48) Wurzschmitt, B., Chem. Ztg., 74, 16 (1950). \
RECEIVEDfor review March 2 2 . 1954. Accepted July 17, 1954. Presented before the Dirision of Industrial and Engineering Chemistry, Symposium on Synthetic Detergents, a t t h e 125th Meeting of t h e AMERICAN CHEMICAL SOCIETY,Kansas City, K a n . , RIarch 1954. Other paper8 from t h e symposium were published in Industrial & Engineerina Chemistry, September 1954.
New Molecular Addition Compounds of 2,4,7=Trinitrofluorenone DONALD E. LASKOWSKI and WALTER C. MCCRONE Armour Research Foundation, Illinois Institute of Technology, Chicago,
The iniestigation was undertaken to determine the types of benzene derivatives capable of forming molecular addition compounds with 2,4,7-trinitrofluorenonein the microscopic mixed fusion technique. From the large number of compounds tested, it can be concluded that those substituent groups known to release electrons to the benzene ring either by an inductive mechanism, or by a resonance mechanism generally lead to 2,4,7-trinitrofluorenone addition compound formation. Conversely, those substituent groups know-n to withdraw electrons from the benzene ring do not allow addition compound formation to occur. In polysubstitution, positional isomerism does not appear to influence addition compound forming tendencies to any great extent except that in certain instances of para disubstitution (hydroquinone,p-aminophenol, and p-diphenylbenzene) addition compound formation does not occur while other positional isomers of these compounds do form addition compounds. This work should be useful in qualitative organic analysis involving microscopic techniques.
I
111.
T WAS reported recently (3) that 2,4,7-trinitrofluorenone (TKF) is able to form molecular addition compounds with
certain benzene derivatives as well as with polynuclear aromatic compounds. Since this fact is of extreme importance in the use of the microscopic mised fusion method of analysis ( S ) , it was decided to survey a large number of compounds to determine the extent of this reaction. As a result of this investigation, it was hoped to be able to formulate rules for predicting the possibility of formation of molecular addition compounds between 2,4,7-trinitrofluorenone and benzene derivatives. EQUIPMENT AND REAGENTS
A polarizing microscope fitted with a 16-mm. objective and a 1OX eyepiece was used in these experiments to detect addition compound formation. A Kofler hotbar, such as that supplied by W. J. Hacker and Co., Inc., New York. K.Y., was used to prepare the mixed fusions. The 2.4,7-trinitrofluorenone was supplied by Dajac Laboratories, Division of hlonomer Polymer, Inc., Leominster, Mass. It used without further purification. No special attempt was made to purify the chemicals used in these experiments; for the most part, they were Eastman Kodak
ANALYTICAL CHEMISTRY white label products. Only compounds judged by their behavior on melting and solidification to be relatively pure were used. EXPERIMENTAL
I n order to survey a large number of benzene derivatives to determine 2,4,7-trinitrofluorenone addition compound forming tendencies, mixed fusions were conducted as described previously ( 2 ) 3 ) . The preparations were then observed microscopically as the slide cooled to room temperature. If an addition compound formed, its color and pleochroism were noted. If the crystal fronts of the benzene derivative and 2,4,7-trinitrofluorenone grew together m-ithout the formation of an addition compound, it was concluded that this particular compound would not form a 2,4,7-trinitrofluorenone addition compound.
Table I.
Many compounds in this series formed supercooled zones of mixing in which the crystal fronts grew very slowly. I n such a case, the preparation was allowed to incubate at an elevated temperature on the hotbar until either the addition compound formed or the two crystal fronts grew together. With all liquids and some solids, if no addition compounds appeared either immediately or after incubation a t elevated temperatures, the preparations were refrigerated at 0' C. for about an hour. Each preparation was then removed and observed microscopically as it warmed to room temperature. If no addition compound appeared under these conditions, it was concluded that the substance under investigation would not form a 2,4,7-trinitrofluorenone addition compound. In every case in which the two crystal fronts grew together without the formation of an addition com-
Aromatic Benzene Compounds Forming 2,4,7-Trinitrofluorenone Addition ComDounds ~
Compound Amine derivatives Aminobenzene Diphenylamine N-Phenylbenzamide 1.2-Diaminobenzene 1,4-Diaminobenzene 2-Aminophenol 3--4niinophenol 2-hlet hoxyaminobenzene 4-Methylaminobenzene 4-N,A'-Diethylaminochlorobenzene 4 - N ,X-Dimethylaminobromobenzene 2-Chloroaminobenzene 3-Chloroaminobenaene 2-Ni troaminobenzene 3-Nitroaminobenzene 4-Nitroaminobenzene 4-n'itro-N, N-dimethylaminobenzene 2-Aminobenzoic acid 3-Aminobenzoic acid 4-Aminobenzoic acid 4-Aminoethyl benzoate 4-ilminoacetophenone 2,5-Dichloroaminobenzene 2-Amino-4-nitrotoluene 4-N,N-Diethylaminobiphenyl 4,4'-Diamino-3,3'-d1methylbiphenyl
1,3-Benzenediol 3-hlethoxyphenol 2-hlethylphenol 3-Methylphenol 4-Rlethylphenol 4-Bromophenol 4-Hydroxy-n-butyl benzoate 2-Hydroxybenzoic acid 2-Hydroxymethylbenzoate 2-Hydroxybenzamide 1,3-Diliydroxy-4-chlorobenzene 2-Hydroxy-l,3-dimethylbenzene 2,4-Dihydroxybenzoic acid 4-Hydroxybiphenyl 2-Hydroxybensoxazole 2,4,6-TrimethylphenoI Halogen derivatives Bromobenzene Iodobenzene 1.4-Dibromobenzene green 3-Chlorobromobenzene 1,2-Dichlorobenzene 1.3-Dichlorobenzene 1,4-Dlchlorobenzene 2-Chloromethylbenzene 4-Chloromethylbenzene 2-Iodomethylbenzene
a b c
Color
Addition Compound Pleochroism
Red Purple Yellow Red-brown Deep purple Dark redbrown Red-orange Red-brown Red Red-brown
Strong, red t o pale Moderate, purple t o pale brown Strong lemon yellow t o clear Strong: light red-brown t o dark brown Strong, purple t o pale brown
Red-brown
Strong, red-brown to pale brown
Red Red Orange Orange Red Deep red
Moderate, red t o pale orange hloderate, red t o transparent Moderate, orange t o yellow Ifoderate, orange t o yellow Strong, deep red t o orange
Red Red Red Red Red Red Orange Purple Brown
Strong, red t o yellow-orange Moderate, red to yellow-orange Strong, red to pale orange Strong, red t o pale yellow Strong, red t o pale orange Moderate, red t o pale orange Moderate, pale orange t o red Moderate purple t o red-brown Moderate: dark brown t o light tirown
Yellow Red" Orangeb Orange Orange Orange Yellow Red-orange Yellow Pale yellowgreen Yellow-green Yellow-green Yellow Yellow-orange Orange
C
Noderate, red-orange t n ornnpe 3lo.ier3te, red-brown to light brown ?trunc.. deep red ro pale orange-brown Strong. deep red-broan to pale hrown
C
Strong, pale orange t o deep red Moderate, orange t o yellow-green Moderate, yellow t o pale yellow-green Strong, red-orange to light yellow Strong deep yellow t o clear Weak, 'yellow-green t o clear C
Weak, yellow-green to clear C
Moderate, yellow-orange t o yellow Moderate, orange to yellow-green C
Moderate, red-orange t o yellow Weak yellow-green t o brown Strong, red-orange to deep red Colorless Colorless Pale yellow-
Weak. pale brown t o colorless Weak, colorless to pale yellow-green Weak, yellow-green t o colorless
Pale yellow Colorless Yellow-brown Pale yellow Pale green Pale yellow Yellow-green
Weak, pale yellow to clear Weak, pale yellow t o colorless Moderate. vellow-brown to colorless
Yellow Pale yellowbrown Yellow-green Yellow Orange Yellow Pale yellow Colorless Yellow-orange Deep yellow
Moderate, yellow to dark yellow-green Moderate, pale yellow-brown to colorleea
Moderate, yellow-green t o colorless Yellow t o yellow-green Strong, orange to yellow-green Moderate vellow-green t o colorless Strong, pal; yellow t o brown Weak. pale yellow t o colorless Xoderate, yellow-orange t o yellow green Strong, yellow t o colorless Moderate, yellow t o pale green Yellow -.. Addition compound on 2,4,7-trinitrofluorenone side of preparation. Addition compound on 1,2-benzenediol side of preparation. Pleochroism not detected.
V O L U M E 2 6 , N O . 9, S E P T E M B E R 1 9 5 4
1499
Table 11. Compounds Yielding Colored Mixing Zones with 2,4,7-Trinitrofluorenone Color of hlising Zone Yellow Yellow Purple Deep red-orange Orange Deep orange Yellow Red Yellow Yellow-orange Yellow Yellow Yellow-green Orange-yellow Deep yellow
Compound N-Acetylaminobenaene 4-Bromo-~V-acetylaminobenzene 4-N, N-Dimethylamino-1%”-acetylaminobenzene 4-Ethoxy-~Y-acetylaininobenzene Thiobenzani!ide Dibenzylamine Tribenaylamine 4,4’-Bisdimethylaminodiphenylinethane Resorcinolmonobenzoate Resorcinolmonoacetate 2,2‘-Dihydroxybenzophenone 3-Methyl-4-tert-butylphenol n-Amyl2-hydroxybenzoate 1,4-Diphenylbenzene Cinnamic alcohol
pound, it was concluded that no addition compound could form vith this substance. EXPERIMENTAL RESULTS
Table I contains a list of the substances investigated that form 2,4,i-trinitrofluorenone addition compounds. A41thoughsome of the compounds investigated did not form 2,3,7-trinitrofluorenoneaddition compounds, they did give rise to a colored noncrl-stalline zone of mixing. Special attempts were made to induce the formation and growth of the possible addition compounds with these compounds. These attempts included prolonged incubation a t several temperatures, seeding the addition compound by scratching, seeding with crystals of both components of the mixed fusion, and prolonged refrigeration. There are several possible causes of a colored mixing zone without the concomitant formation of a molecular addition compound. These include formation of a loose addition compound in the liquid phase which is incapable of existing a s a solid (1); abnormal tendency of the addition compound to supercool; slight thermal decomposition of a t least one of the two components of the mixed fusion; slight solubility of the colored 2,4,7-trinitrofluorenone in the colorless benzene derivative melts; and presence of slight amounts of impurities which form noncrystalline addition compounds in the melt. Table I1 contains a list of the investigated compounds which yielded a colored zone of mixing but no addition compound. A large number of the tested compounds did not form 2,4,7trinitrofluorenone addition compounds and did not yield colored zones of mixing. Table I11 contains a representative list of these compounds. Although Table I11 does not list all of the tested compounds that failed to form 2,4,i-trinitrofluorenone addition compounds, it does contain enough of the data to warrant the conclusions drawn later. DISCUSSION
Originally, it was hoped that 2,4,7-trinitrofluorenone would form addition compounds only with polynuclear aromatics. If this were so, an unknown aromatic compound could be classified immediately as being either mononuclear or polynuclear. The observation that 2,4,i-trinitrofluorenone forms addition compounds with certain benzene derivatives obviates this hope; however, this observation vastly extends the field of applicability of 2,4,i-trinitrofluorenone as a microscopic fusion‘reagent. The observations reported are all empirical; hence any deduction from them must of necessity be empirical. The rules for 2,4,7-trinitrofluorenone addition compound formation, deduced from the data in Tables I, 11, and I11 are as follows: ( a ) Benzene monosubstituted with the -NH2,
-OH,
-Br,
H
-1,
-0 -A ,
= CH2, and -0CHa
(-OR)
form a 2,4,7-trinitrofluorenone addition compound.
groups will
( b ) Benzene monosubstituted with the -NO*, 0 0 0 0
I1
-C-H,
-C=S,
II
-C-OR.
11
-C-R,
II
--NHC-R,
-COOH,
-0
0
8
R,
I/
--CKH2, -Cl,. +Ha, --CH,OH, or --CH,OR groups will not form a 2,4,i-trinitrofluorenone addition compound. ( c ) Benzene disubstituted with any two of the groups listed under (a)will form a 2,4,i-trinitrofluorenone addition compound with the exception of the para effect discussed below. In addition, two or more methyl groups, two chloro groups, one chloro group and any of the groups listed under (a), and one methyl group and any of the groups listed under ( a ) will lead to addition compound formation. ( d ) Benzene disubstituted with one amino group and any of the groups listed under ( b ) will form an addition compound. Benzene disubstituted with one hydroxy1 group and any of the 0 groups under ( b ) , with the exception of --SO2, -0-C-R, 0
I1
/I
-C-R, and -C=S, will form a 2,4,i’-trinitrofluorenone addition compound. (See, however, discussion of the para effect.) ( e ) If benzene is substituted with two or more nitro groups and any of the other groups, it will not form a 2,4,i-trinitrofluorenone compound. (f) If benzene is substituted with three or more halogen groups, it will not form a 2,4.i-trinitrofluorenoneaddition compound. ( 9 ) Compounds in which coplanarity of the molecule is impossible will not form 2,4,i-trinitrofluorenoneaddition compounds. ( h ) Benzene substituted with bulky groups will not form 2,4,i-trinitrofluorenone addition compounds. The justification for Rules (a)and ( b ) is self-evident. I t should be noted that all of the groups leading to addition compound formation are classified in modern organic chemical theory as electron donating groups ( 4 ) ; while the groups that do not lead to addition compound formation are classified as electron withdrawing groups, with the exception of the chloro group and the methyl group.
Table 111. Compounds That Do Not Form 2,4,7-Trini1:rofluorenone Addition Compounds in a Mixed Fusion Benzene Pyridine Toluene Nitrobenzene Chlorobenzene Benzonitrile Benzaldehyde Phenyl methyl ketone Benzyl alcohol Benzyl acetate Benzyl propionate Benzyl n-butyl ether Phenyl ethyl alcohol Phenyl acetic acid Benzoic acid Benzamide Phenyl benzoate Benzouhenone Benzil 4,4‘-Dimethylbenzophenone Phthalic acids ( 0 , m, and p ) Phthalic anhydride N-P henyl p hthalimide Benzyl phthalate
Diethyl phthalate Diphenylmethane Triphenylmethane Diphenyl carbinol DiDhenyl acetic acid Dibenzyl sulfide Dip henylsulfoxide 2,4-Dinitroaniline 2-h-itrophenol 4-Kitrophenol 2,4-Dinitrophenol 3-Bromobenzoic acid 4-Bromobenzoic acid 3-Sitrobromobenzene 4-i‘iitrobromobenzene 4-i‘iitrochlorobenzene Resorcinol-dibenzoate Resorcinol-diacetate 2-Nitroacetanilide 2-Cyanobenaamide 1,3,5-Tribromobenzene 1,2,4,5-Tetrachlorobenzene Hexachlorobenzene
Rule ( c ) is amply justified by the data reported. In the case of para disubstitution, particularly 1,4-dihydroxybenzene and 4hydroxyaminobenzene, it was impossible to determine if addition compound formation occurred. An intensely colored zone of mixing appeared in the mixed fusion preparation with these compounds, but even on prolonged incubation or refrigeration, only a few crystals separated. I t was impossible to determine whether
1so0
ANALYTICAL CHEMISTRY
these crystals were due to thermal decomposition of the benzene derivative or were actually an addition compound of the original material. These two compounds are not reported in the tables, and, a t least for the present, they must be listed as unknown. In the case of 1,4-diphenylbenzene, there was no such doubt; no addition compound formed with this substance. Addition compounds were formed in several cases of 1,4-disubstitution, such as 1,4-dimethylbenzene, 1,4-diaminobenzene, 4-methylaminobenzene, and 4-aminobenzoic acid. From these facts, it must be concluded the effect of 1,4-disubstitution is unpredictable, Kot all of the cases under Rule ( d ) have been tested, but sufficient data have been obtained to warrant prediction as to the cases not tested. Since the amino group is the most powerful addition compound promoting group, and since 2,4-dinitroaminobenzene did not form a 2,4,7-trinitrofluorenoneaddition compound, Rule ( e ) can be considered to hold. Rule ( f ) follows from the fact that 1,3,5-tribromobenzene and 1,2,4,5-tetrachlorobenzenedo not form addition compounds. Rule ( 9 ) is deduced from the fact that diphenylmethane and triphenylmethane as well as dibenzylamine and tribenzylamine do not form addition compounds although the groups are electron donating groups. I n these compounds because of the tetrahedral nature of the central atoms, coplanarity is impossible. I n the case of 3-methyl-4-tert-butyI phenol, an addition compound should form, since all of the groups are electron donating. It is assumed that the addition compound does not form with this substance because of the bulky tert-butyl group, therefore, Rule ( h ) has been formulated. Since only one compound has been tested, Rule ( h )can be only tentative.
It is not possible a t this time to make statements regarding the theoretical interpretation of the above results. Equilibrium constants, composition diagrams, and thermodynamic data must be determined before quantitative statments can be made regarding the effects of substituents on addition compound formation. These electronic properties of the substituents may be taken as a clue to the necessary requirements for addition compound formation. Work is in progress to determine the thermodynamic data and phase diagram data for this class of compounds. ACKNOWLEDGMENT
The authors gratefully acknowedge the generous supply of 2,4,7-trinitrofluorenone donated by the Dajac Laboratories, Division of Monomer Polymer, Inc., Leominster, Mass. LITERATURE CITED
(1) Hildebrand, J. H., “The Solubility of Sonelectrolytes,” 3rd ed.,
New York, Reinhold Publishing Carp., 1950.
(2) Kofler, L., and Kofler, A, “Mikromethoden eur Kennzeichnung
Organischer Stoffe und Stoffgemische,” Innsbruck, Universitatsverlag Wagner, 1948. (3) Laskowski, D. E., Grabar, D. G., and McCrone, W. C., ANAL. CHEM.,25, 1400 (1953). (4) Remick, A. E., “Electronic Interpretations of Organic Chemistry,’’ New York, John Wiley and Sons, 1949. RECEIVED for review April 15, 1954. Accepted June 17, 1954. Based upon a part of t h e thesis t o be submitted b y Donald E. Laskowski t o the Graduate School of Illinois Institute of Technology in partial fulfillment of t h e requirements for the degree of doctor of philosophy.
Determination of Traces of Copper in Germanium By Activation Analysis GUSTAV SZEKELY Physics Laboratories, Sylvania Electric Products, lnc., Bayride,
The electrical characteristics of germanium are affected by the presence of copper in the germanium lattice. By y of copper in an activation analysis as little as germanium can be determined. The neutron irradiation of germanium samples, containing copper, results principally in the formation of radioactive isotopes of germanium, arsenic, and copper. Copper-64 is separated chemically, and the activity due to it serves as a measure of the copper content of the samples analyzed. The method is specific, and the result of the analysis is not affected by contamination introduced by sampling or during the chemical procedure.
T
HE electrical characteristics of semiconductor devices, such as transistors, are highly sensitive to the presence of traces of impurity atoms in the semiconducting material. The presence of copper in pure germanium renders the latter a p-type conductorthat is, conducting by means of holes. Furthermore, the operation of a transistor depends upon a certain minimum lifetime which the current carriers must possess; the presence of copper in germanium was found to increase the rate of recombination of holes and electrons ( 2 ) . Because copper can readily enter the germanium lattice [large diffusion coefficient (3,b ) , abundance of sources of copper contamination], this element is recognized as an important contaminant in germanium.
N. Y.
In attempting to find an analytical method applicable to the submicrogram range, one is confronted by the limit of detection of the more usual methods, such as absorption or emission spectroscopy. The activation analysis, described here, is specific and can be used to determine as little as lo-‘ y of copper in germanium. PRINCIPLES
The principles of activation analysis are now well known (1). Briefly, a sample is bombarded by nuclear particles-e.g., neutrons-at a flux for a period of time sufficient to produce an optimum amount of a radioisotope from the trace constituent to be determined. The decay rate of the isotope, registered by a counter, serves as a measure of the quantity of trace constituent originally present in the sample. Frequently, the major and other minor constituents also become activated during bombardment, which may necessitate a separation of extremely small amounts of the radioisotope t o be counted from large amounts of other radioactive isotopes formed. One way to achieve this is to effect chemical separations after adding a known amount of the stable element (“carrier”) to entrain its radioactive isotope. The stable isotopes thus carry the radioactive trace through the chemical procedure. From the yield with which the carrier is recovered and its counting rate, the quantity of radioactive trace present may be
