than iron are not likely to be present in cracking catalysts in sufficient concentrations to necessitate separation. Iron is conveniently determined colorimetrically on a separate aliquot, and its concentration subtracted from the apparent aluminum result. T o afford an estimate of the precision of the modified method, 120 determinations of aluminum were macle by three analysts on a reference sample of silica-l3% alumina synthetic cracking catalyst. The average result was 13.14% Al20~(volatile-free basis), with a standard deviation of 0.047% A1203. On the same sample, 37 determinations by four analysts, using a classical gravimetric technique ( I ) employing single dehydration of silica, yielded an average result of 13.20% A1203) with a standard deviation of 0.19%. Despite the fact that one of the analysts participating in the complexometric cleterminations had had no previous laboratory experience, the precision of the complesometric results is significantly better than that of the graviiiietric results.
Table I.
Sample 7115 7148 7149 7175 6913 7140 7178 7224
Comparison of Gravimetric and Complexometric Methods
Type of Catalyst Virgin Virgin Virgin Virgin Equilibrium Equilibrium Equilibrium Equilibrium
% A1203Found, Volatile-Free Basis Complexometric Gravimetric Av. diff. 24.6,24 14.0,14 24.8,24 14.6,14 23 8 , 2 3 13.3,13 21.5,21 13.9,13
6 1 9 6
7 4
5 0
24.0 14.2 25.5 11.9 24.1 13.2 21.0 14.0
+0.6 -0.15 -0.65 -0.3 -0.35 $0.15 +0.5 -0.1 Av. 0.35
Table I shows a comparison of the results obtained by the complexometric and gravimetric methods in the analysis of several samples of virgin and used silica-alumina catalysts. The data exhibit reasonably good agreement. and there is no systematic trend.
of Kalco Chemical Co. (formerly S a tional Aluminate Corp.) for permission to publish this work.
ACKNOWLEDGMENT
(2)'S'anninen, E., Ilingbom, A., Anal.
LITERATURE CITED
(1) Catalyst Division, National Aluminate
Corp., Chicago, Ill., "Methods for th; Analysis and TeEting of Catalysts, 19.58.
The authors express their gratitude to STilliam Checovich, Richard W. Greene, Charles MT.Nesby, and Andrew J. Topps Jr. for performing some of the analyses, and to the Catalyst Division
Chim. d c t a 1 2 , 308 (1955). ARPADELO,JR. R. POLXY JOHN
Catalyst Division Kalro Chemical Co. 4001 West 71st St. Chicago 29, Ill.
Short-Term Determination of Carcinogenic Aromatic Hydrocarbons SIR: Present evidence indicates that in tobacco smoke condensate and air pollutants the polycyclic hydrocarbons represent a major group of carcinogenic substances. Thus, interest has been placed in analytical procedures that can accurately determine these compounds rvithin a short time. I n a n effort to meet this requirement we attempted to simplify our previous method ( 2 ) . METHOD
The variation between the methods is based on the fact that the polycyclic hydrocarbons from combustion and other materials can be enriched under ccparation from hydrophilic compounds 1,- partition between cyclohexane and n ater. We are indebted t o Grimmer for the suggestion of the partitions ( I ) . The partition coefficients for the pure polycyclic hydrocarbons between cycloh m m e and methanol-water (4 to 1) are above 13 (Table I) and, therefore, the loss of polycyclic hydrocarbons after eLtraction of the methanol phase with m-clohexane three times is less than 1%. 111 thc nest step a distribution between the CJ clohesane phase and nitromethane i q employed. Partition of pure poly(>> clic h ! drocarbons indicates that a t least 60% of these compounds are found in the nitromethane phase. Thus, four more extractions are necessary t o yield 99% in the nitromethane phase (Table I). The partitions vith the two sys-
Figure 1. Separation of constituents of cigarette smoke condensate
Table I. Partition Coefficients of Polycyclic Hydrocarbons (20"C.)
CJCm
Pyrene 150.0 Benzo(a)pyrene 14.9 Benzo(e)pyrene 14.5 Fluoranthene 140.0 Benzo(b)fluoranthene 14.7 Benzo(j)fluoranthene 14.8 Benzo(k)fluoranthene 14.9 Benz(a)anthracene 18.6 Dibmz(n,h)anthracene 14.9 Perylene 14.9 Benzo( g,h,i)perylene 11.6 Chryeene 14.6
Cn'Cc 4.40 1.53 1.68 1.80 1.94 1.75 1.76 1.75 1.80 1.69 1.77 1.65
C,. Concentration in cyclohexane. C,. Concentration in methanol-water 4:1. C,. Concentration in nitromethane. Coefficients are obtained after spectroscopic determination of concentrations.
tems were accomplished with solvents that nere pre-equilibrated nith each other. The distributions can be accomplished within 3 hours. After the partitions, column chromatography of the residue of the nitromethane extracts follon s. Here one needs only 30 to 40 parts of adsorbent (silica gel) per part of residue to achieve a sufficient separation before the final separation by means of paper chroniatography. The absorption chromatography can be readily accomplished within 4 hours. The paper chromatography (12 to 14 hours) was carried out according to our previously described method ( 2 ) . This analytical separation has been employed for the isolation of polycyclic aromatic hydrocarbons from Cigarette smoke condenbates, automobile eLhaust gas, and air pollutants. The purity of the organic solvents used n as ascertained by ultraviolet spectrometry. As far as possible, the procedure was performed under nitrogen. To prevent photodegradation, the light sources were covered with plastic sheets n-ith no transmittance belon470 mu. EXPERIMENTAL DATA
As a n example of the method, the analysis of a cigarette smoke condensate is dcscrihrd. VOL. 32,
NO. 2, FEBRUARY 1960
295
The condensate of the niain stream smoke of 260 long-size popular American nonfilter cigarettes was obtained in a fully automatic Ethel Mark VI smoking machine designed by Cigarette Components Ltd., of England. The part for the electrostatic precipitation of this machine was replaced by a cool-trap system for the collection of the condensate (trap 1, outside cooled by ice water; trap 2, by dry ice-acetone). All cigarettes were ignited n-ith a n electric lighter and smoked with a 35-ml. puff volume for 2 seconds every minute to a butt length of 23 mm. Before the analysis, the condensate was dried to constant weight over calcium chloride (7.32 grams). The separation is shown in Figure 1. The nitromethane e.xtract (0.82 gram) was chromatographed on 30 grams of silica gel (deactivated) ( 2 ) . Hexane was used for elution from fraction I through fraction VII, hexane and benzene (4 to 1) for fractions VI11 to X. Fractions I1 to VJII are named according to their major polycyclic hydro-
188.
carbon constituents. This does not exclude the presence of minute quantities of these hydrocarbons in the neighboring fractions. Benzo(a)pyrene, for instance, was found not only in fraction VI but also in small amounts in fractions V and VII. The corresponding bands from the paper chromatography fractions n-ere combined and rechromatographed for further purification. I n the case of benzo(a)pyrene only two chromatograms were usually necessary to obtain identical fluorescence and ultraviolet absorption spectra down to 250 mp by comparison with the authentic hydrocarbon. The loss of benzo(a)pyrene by the use of this method of separation amounts to about 30% as proved by the tracer technique ( 2 ) . From the smoke condensate 5.5 y of benzo(a)pyrene (0.75 p.p.m.) was isolated. The tracer method indicated a total of 7.9 y of benzo(a)pyrene (1.1 0.1 p.p,m.) to be actually present. Fluoranthene, pyrene, alkylpyrene,
*
chrysene, and alkylchrysene were found in the same amount as determined by the former method ( 2 ) . For the detection of benzofluoranthenes, bemanthracene, dibenzanthracene, benzo(e)pyrene, benzoperylene, and perylene we started with twice the amount of smoke condensate as used for the determination of benzo(a)pyrene. LITERATURE CITED
(1) Grimmer, Gernot, personal communi-
cation.
(2). Hoffmann, D., Wynder, E. L., “Isolation and Identification of Polynuclear Aromatic Hydrocarbons,” Cancer, in
press.
DIETRICHHOFFMANN ERNEST L. WYNDER
Section of Epidemiology Division of Preventive Medicine Sloan-Kettering Institute New York, N. Y.
Aluminum Boride, AIBlP
J. A. KOHN and D. W. ECKART, U. S. Army Signal Research and Development Laboratory, Fort Monmouth, N. J. postulating vacant sites in the structure; ALPHA-PHASE The powder diffraction data tabulated our data would necessitate -20 unbelow were obtained using filtered RYSTALS of a-A1BI2, as well as occupied sites per unit cell ( 4 ) ] . copper radiation with a Geiger diffracthose of D-AlBl2 (see next Formula Weight. 156.82. tometer. Single crystal diffraction insection), were recovered from the reacDensity. 2.557 0.003 grams per tensities were used to assist in the tion products of two different methods cc. (pycnometric in toluene). indexing of the powder lines, where of preparation. The first was a simple two or more calculated spacings showed melt reaction, using the elements; OPTICALPROPER TIE^ equally suitable agreement. Refractive Indices. w and e > 2.20 the second was an aluminothermic (by freezing in PbC12). reaction, using elemental aluminum Absorption Edge. Approximately and B2O8. Boride crystals were sepaCRYSTAL MORPHOLOGY 6500 A. (calculated energy gap, 1.8 to rated in each case by leaching with dilute Crystal System and Class. Tetrag1.9 e.v.). aqua regia. Both methods of preparaonal, pseudocubic [true symmetry first described by Halla and Weil @)I; tion have been described in detail (4). FUSION BEHAVIOR tetragonal trapezohedra1 class. Crystals of a-AlB12 were obtained Melting Point. 2150’ =t 50’ C. Form and Habit. Platelike along as tetragonal (pseudocubic), hematite(in helium at 50 p.s.i.). (101) = (111) cubic; crystals are like plates, up to 2 mm. in largest Oxidation Temperature. 700” C. essentially pseudooctahedrons, most of dimension. Very thin sections were them flattened along (111) of the wine-red to orange-red in strong transBETA-PHASE pseudocubic cell; forms observed are mitted light. This phase was first first-order prism ( 1101, ditetragonal Crystals of &4.lBI2 were obtained described in the early literature as a prism ( 3201, first-order bipyramid from the same reaction products as { 1111, second-order bipyramids ( 101 ) form of elemental boron, having been were those of &-AlBl2. Specimens were and { 201 ) , and tetragonal trapezotermed “graphite-like boron” (6). It hedrons (312) and { 314) ; { 101) is by orthorhombic (pseudotetragonal) biwas later shown to be aluminum boride, far most common, with (110) next; pyramids, up to 2 111111. in largest dimenMBiz (3). twinning on (101) is fairly common. sion, translucent to opaque, ranging in X-ray diffraction studies were carried Axial Ratio. c : a = 1.4050:l color from yellow to honey-yellow to out with copper radiation, using rota(morph.); 1.4057: 1 (x-ray). amber to brown. Until relatively retion and Weissenberg methods for cently (b), this phase was considered a single crystals and powder film and X-RAYDIFFRACTION DATA form of elemental boron (termed diffractometer techniques for polycrysSpace Group. P41212 or enantio“adamantine or diamond-like boron”) talline specimens. The Weissenberg morphous P4&2. or possibly a ternary borocarbide (1). patterns showed the following systemCell Dimensions. a = 10.161 f X-ray diffraction studies were carried 4n; atic absences: 001 with I # 0.001 A , ; c = 14.283 f 0.002 A. out using the same techniques as hOO, with h # 2n. This permitted an [a = 10.28 A.; c = 14.30 A. ( S ) ] . described for a-AIBlz. Weissenberg unambiguous determination of the space Formula Weights per Cell. 14.4 patterns showed the following systemgroup as P41212 (or enantiomorphous [Halla and Weil (2) explained this atic absences: hkl, with h k 1 # 2n; deviation from a reasonable integer by P43212).
C
*
+ +
296
ANALYTICAL CHEMISTRY
