charcoal and identical spectra were obtained, which indicates that the charcoal selectively removes the same components. To test this method under actual conditions the U.S. Coast Guard Research and Development Center at Groton, Conn., supplied us with oil samples collected from actual oil spills along with the oils from suspected sources. Figure 5 shows the Raman spectra of a spilled oil and two suspect oils. The spectrum of suspect A was by far the closer match to the spilled oil and it was later confirmed that suspect A was indeed the spill source. We have measured the Raman spectra of No. 2 fuel oils, kerosenes, lubricating oils, weathered oils, and actual spill oils and found that Raman spectroscopy provides a fast and simple method for the identification of petPoleurn products. It is highly suited for work with the lighter fuel oils where, because of the rapid changes which these oils undergo once they have been spilled, it is usually desirable to use several techniques to match them with their source.
i r
n
ACKNOWLEDGMENT We express our appreciation to the U.S. Coast Guard R&D Center for supplying actual spiIl samples and to Marshall Margolis for his helpful consultatioh. LITERATURE CITED
-&-----
IO00 FREQUENCY,
500 CM-’
(1) Chem. Eng. News., November 17, 1975, p 7. (2) C. W. Brown, P. F. Lynch, and M. Ahmadjian, Appl. Specrrosc. Rev., 9,223 (1975) (3) C.W. Brown, P. F. Lynch, M. Ahmadjian, and C. D. Baer, Am. Lab., 7, 59
Figure 5. Raman spectra of a spilled oil and two suspect oils (oils supplied courtesy of US. Coast Guard)
(1975). (4)C.W. Brown and P. F. Lynch, Anal Cherfi., 48, 191 (1978). (5) P F. Lynch, M. Ahmadjian, and C. W. Brown, Environ. Sci. Techno/., 7, 1123
oil was somewhat broader compared to the treated oil. Overall, the two chromatograms were similar to each other. The infrared spectra of the untreated and treated oil (Figure 4) showed a decrease in the bands a t 1700 and 740 cm-l. The 1700 cm-l band is characteristic of the oil’s oxidized components and the 740-cm-l band is due to aromatic substitution. Except for these two differences, the spectrum of the treated oil was identical to that of the untreated oil. The charcoal treatment induced very slight changes in the gas chromatograms and in the infrared spectra of the oil, but caused a drastic decrease in fluorescence. Evidently, only a very small fraction of the oil’s components were strongly fluorescent and these were readily removed by the charcoal. Three different samples of the same oil were treated with
(6)“industrial Applications of Laser Raman Spectroscbpy”, J. G. Grasselii, M. A. S.Hatle, and L. E. Wolfram, 1975 Paclfic Conference on Chemistry and
(1973). Spectroscopy.
Mark Ahmadjian Chris W. Brown* Department of Chemistry University of Rhode Island Kingston, R.I. 02881 RECEIVEDfor review January 29, 1976. Accepted April 1, 1976. This work was supported partially by Sea Grant (administered by the National Oceanic and Atmospheric Administration) and partially by the Office of Water Resources, Department of the Interior.
Synthetic Inorganic Ion Exchangers as Adsorbents for Gas Chromatography Sir: Gas-solid chromatography has some advantages over the gas-liquid technique, which can be summarized as follows: higher selectivity, i.e., high separation factors of compounds of similar structure such as isomers and even isotopes; high thermal stability, which allows the same column to be used for both low and high boiling compounds; and negligible bleeding of the stationary phase, as has been shown in various works (1-4). On the other hand, gas-solid chromatography with conventional adsorbents shows some disadvantages, such as irreversible adsorption of polar compounds and very high retention times, compared to gas-liquid chromatography. Thus, most work has been oriented to the search for homogeneous, nonspecific adsorbents, such as graphitized carbon blacks ( 5 ) ,that resulted in a wide use of these mate-
rials, either as such or modified by appropriate liquid phases. The best results have been obtained with the latter techniques, which permit the use of the same solid matrix to make “tailor made” columns (6) for certain specific separations, or columns of general use (7). The disadvantages of coating the adsorbent with a stationary phase may be overcome by looking for a material, whose chromatographic properties can be modified by changing some of its constituents so that the chemical properties, namely, the ability to elute polar compounds of different nature, are properly adjusted. Synthetic inorganic ion-exchangers belonging to the group of insoluble acid salts of polyvalent metals have received much attention since they have Seen obtained in crystalline form, having well-defined compositions, as reANALYTICAL CHEMISTRY, VOL. 48, NO. 8 , JULY 1976
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Table I. Retention Data for Some Saturated Hydrocarbons When Zr(KPO& or Zr(KAsO4)z (mesh range -300) Are Used as Stationary Phases at 155 "C Zr(KP0412 Zr (KAs04)2 Compound n-Cs n-Clo n-C11 n-C12 n-Cls ~-CM
Crystalline zirconium phosphate, -300 mesh. Glass column: 80 cm, 0.2-cm i.d. A& = 6 kg/cm2. Flow rate = 10 ml/min
Figure 1.
at room temperature (a) 80 OC isotherm. (1) Carbon tetrachloride,(2) Methylene chloride, (3)Chloroform. (b) 85 O C isotherm. (1) Methyl mercaptan, (2) Isopropyl mercaptan, (3) tertSutyl mercaptan, (4) sec-Butyl mercaptan, (5) Diethyl sulfide, (6) I+ Butyl mercaptan
'I
22
0 P
w v, Q
21
'I
Crystalline zirconium arsenate, -300 mesh. Glass column: 80 cm, 0.2-cm i.d. AfN2 = 6 kg/cm2. Flow rate = 10 ml/min at room temperature Figure 2.
(a) 185 O C isotherm. (1) n-Propionaldehyde, (2) Isobutyraldehyde, (3) n-Butyraldehyde; (b) 150 OC isotherm. (1) Benzene, (2) Toluene, (3) mxylene, (4) &Xylene and p X y l e n e ; (c) 205 O C isotherm. (1) Triethylamine, (2) Diethylamine, (3) n-Butylamine; (d) 130 O C isotherm. (1) Carbon tetrachloride, (2) Methylene chloride, (3)Chloroform
cently pointed out by Alberti and Costantino (8).Furthermore ion exchange (9) and sieving ( 1 0 ) properties of zirconium phosphate in molten salts were extensively investigated. T o date, gas-solid equilibrium studies on these exchangers, which have a layered structure including zeolitic type cavities ( 1 1 ) , have not been reported in the literature. Preliminary experiments (12) on the adsorption of polar gases from crystalline zirconium phosphate in the lithium, sodium, and potassium forms showed that, in all cases, a very 1260
ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
t , (min) 0.66
1.35 2.10 3.15 5.12 8.53
Vo, (ml) 0.61 1.25 1.94 2.91 4.74 7.89
t , (min) 0.34 2.08 4.14 7.44 11.69 18.60
V o , (ml) 0.31 1.93 3.83 6.87 10.80 17.20
small ammonia adsorption ( mol NHg/mol exchanger) occurred at room temperature. The very poor adsorption tendency of Zr(KP04)2 for polar gases as well as its high thermal stability and low surface area (12 m2/g) has prompted us to try possible applications of this material in gas chromatography. A glass column, 80 cm long, 2-mm i.d. was packed with microcrystalline Zr(KPO& without any attempt to have a defined mesh range. The dipotassium form of the crystalline zirconium phosphate was obtained by titrating its dihydrogen form prepared according to Ref. 13, and heating the hydrated compound a t 500 "C. The average particle size was around 300 mesh. In these conditions, the pressure drop is about 5-6 kg/cm2 and the flow rate 10 ml/min at room temperature. Experiments were first made on linear aliphatic hydrocarbons, and the results are reported in Table I. Symmetrical peaks have been obtained even for well-retained compounds, in a wide range of concentrations. Further experiments were made eluting alcohols, mercaptans, chlorocarbons, aliphatic amines, and aldehydes. The results obtained for mercaptans and chlorocarbons are reported in Figure 1. The other classes of compounds eluted gave unsymmetrical peaks, scarce separation, and nonreproducible quantitative determinations, although all these compounds were eluted. Two interesting features have to be considered, the linear elution of mercaptans with suitable separation factors, which has never been achieved before on a pure solid adsorbent to our knowledge, and the elution order of chlorocarbons, with CC14 being eluted first and CHC13 much later. This has not been observed before and implies a working mechanism completely different from the commonly used adsorbents. T o test the flexibility of the class of adsorbents considered, similar experiments were carried out with crystalline Zr(KAsO4)n (6.4 m2/g) which was prepared with the same procedure as for Zr(KP04)2. The results for hydrocarbons are reported in Table I, while the most significant chromatograms obtained are shown in Figure 2. Mercaptans gave very poor chromatograms (tailing peaks) with the latter solid support while, surprisingly, aliphatic amines gave symmetrical and quantitatively reproducible peaks, that could not be obtained with Zr(KPOd2. Aromatic hydrocarbons yield results similar to those on other adsorbents and a separation of m-xylene from the ortho and para isomers was obtained. Chlorocarbons give a nice separation with the same elution order as with Zr(KP04)2, but different separation factors. The separation of aldehydes is somewhat strange with an amazing separation between isobutyl and n -butyraldehyde resembling that found for chlorocarbons on Zr(KP04)2. The preliminary results reported here show that synthetic inorganic ion-exchangers can be successfully used for gas chromatographic separations and that, by changing some of the atoms, one can obtain peculiar stationary phases to be employed in particular separation problems. The unusu-
a1 behavior with amines (linearly eluted without any liquid modifier of the original material) and with chlorocarbons (having a quite peculiar separation order) makes necessary further and more detailed investigations on the gas chromatographic properties of these compounds. The gas chromatographic behavior of other salt forms of crystalline zirconium phosphate and arsenate are under investigation in our laboratories. LITERATURE CITED A. V. Kiselev and Y. I. Yashln, “Gas Adsorption Chromatography”, Plenum Press, New York, N.Y., 1969, Chap. 11, and references therein. F. Bruner, W. Bocola, and G. P. Cartoni, Nature (London), 209, 200 (1966). M. Novotny, J. M. Haves, F. Bruner, and P. G. Simmonds, Science, 189, 215 (1975). F. Bruner, C. Canulli, A. Di Corcia, and A. Liberti, Nature (London), 231, 175 (1971). F Bruner, P. Ciccioll, G. Crescentini, and M. Pistolesi, Anal. Chem., 45, 1851 (1973), and references therein. F. Bruner, P. Ciccioli, and F. Di Nardo, Anal. Chem., 47, 141 (1975). F. Bruner. P. Ciccioli, and G. Bertoni, J. Chromatogr., 90, 239 (1974).
(8) G. Alberti and U.Costantino, J. Chromatogr., 102, 5 (1974). (9) S. Allulli, A. La Ginestra, and N. Tomasslni, J. lnorg. Nucl. Chem., 36, 3839 (1974). (IO) S. Allulli and N. Tomassini, J. Chromatogr., 62, 168 (1971). (1 1) A. Clearfield and G. D. Smith, lnorg. Chem., 8, 431 (1969). (12) S. Allulli, unpublished results, 1975. (13) G. Alberti and E. Torracca, J. lnorg. Nucl. Chem., 30, 317 (1968).
S. Allulli N. Tomassini C.N.R. Laboratorio Metodologie Avanzate Inorganiche Via Montorio Romano 36 Rome, Italy
G. Bertoni F. Bruner* C.N.R. Laboratorio Inquinamento Atmosferico Via Montorio Romano 36 Rome, Italy RECEIVEDfor review February 17, 1976. Accepted April 2, 1976.
AIDS FOR ANALYTICAL CHEMISTS
Simple Bearing for High-Precision Grating Rotation J. P. Walters,’ B. D. Hollar,’ and D. M. Coleman Department of Chemistry, University of Wisconsin, Madison, Wis. 53706
Spectrometers that use a plane diffraction grating can provide a linear display of wavelength if the grating is rotated with a sine-bar mechanism (1,2).While the sine-bar linkage itself is straightforward to fabricate, the angular motion of the grating is so small for moderate wavelength displays that the bearings used for its support must be of high precision, e.g., A.B.E.C. class 7 or 9 tolerances. Concurrently, mounting these bearings requires sophisticated machining, usually a t jigboring tolerances, to provide mounting holes of suitable concentricity and diametrical tolerance. Such fabrication typically exceeds the capacity of most university student shops, requiring instead tool and die grade service a t high expense. In this note, we communicate the essential details of a very simple bearing that provides smooth, low-speed rotation of heavy objects while still being sufficiently straightforward to allow fabrication in a student shop using only a tool-room lathe and production milling machine.
THE “NEST-OF-BALLS” BEARING The approach used follows from the realization that a plane diffraction grating, when used in a Czerny-Turner or Ebert configuration, rotates only over a limited angle (usually less than 60’) and at low rates. Thus, the features of a conventional high-precision ball bearing are largely wasted in this application, except for the sphericity of the balls and smooth surface finish of the races, which combine to allow rotation without cogging or jerking. It then is reasonable to discard all the parts of the bearing except the balls themselves and to eliminate the actual rotation of the balls, since neither wear nor speed of rotation need be considered. Present address, Union Carbide Corporation, Kenmore, N.Y.
When all rotation of the balls in a bearing is eliminated, then a configuration such as shown in Figure 1is possible. For example, in Inset A, three large balls are set with their centers at 120°, and they remain stationary. A smaller ball is placed in the center of this nest. It becomes the non-rolling, rotating member of the bearing. The stationary balls are held as shown in Figure 1,Inset B. A hole is cut in a base plate of suitable shape and the balls are simply dropped into it. A shaft is fixed to the rotating ball by first turning a smooth, but untoleranced, cone into the end of the shaft stock. Then, a small amount of epoxy glue is placed a t the bottom of the cone. The ball is pushed into the cone until it firmly contacts its machined sides and is held thus while the epoxy sets. If the shaft stock is round, then the center of the ball will coincide with the centerline of the shaft to good tolerances (e.g., f O . O O 1 inch or f0.03 mm) with only routine machining care, i.e., a collet in the spindle of the lathe to hold the shaft and a center-drill in the tail-stock to start the cone.
BEARING ASSEMBLY AND ROTATION To assemble the bearing, the shaft and cemented ball are lightly pushed into the center of the nest of stationary balls until they move out and contact the edge of the hole in which they are resting. The stationary balls are then fixed in position. A three-point contact is established between the stationary balls and the rotating ball. This three-point contact behaves as a sliding “surface” for bearing motion when the shaft is rotated. The rotation will be free of cogging, jerking, and wobble if the sphericity of all of the balls is high and if their surfaces are smooth. Balls that are micropolished, surface hardened, and spherical to tolerances of less than 0.001 mm are readily available in a variety of toleranced diameters a t ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
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