RESULTS AND DISCUSSION Since no such interferences were present in air samples, future work will be performed with a single channel chopped source and a lock-in amplifier with a probable increase in sensitivity. The Glan-Taylor polarizers used in this system absorb in the 217 nm region, so the 283.3 nm line had to be used. This resulted in decreased sensitivity. For the standard curve shown in Figure 2, lead was added to the graphite crucibles as lead nitrate solution. One of the advantages of this type of furnace is the fact that chemical matrix effects are minimized and within experimental error the response for a given quantity of lead does not vary regardless of its chemical nature . Plots of the variation of the concentration of lead with time can be seen in Figures 3 and 4. Figure 3 represents samples taken on the Montana State University campus on June 8, 1971, which was during the week of final examinations, therefore traffic was not expected to be very heavy. The winds were out of the west at about 5 miles per hour and the temperature was about 75 OF. It can be seen from the figure that the levels of lead were rather low in the morning, averaging 0.1 microgram per cubic meter, but were generally higher in the afternoon with sharp increases at 3 : 05,4: 30, 5 : 00, and 5:30. These levels are generally consistent with the traffic flows that were observed. Figure 4 was taken at North Seventh Avenue and Main Street in Bozeman. Traffic from the interstate highway as well as traffic going to Yellowstone National Park must pass this point. The samples were taken on June 1 1 , 1971, and it was sunny, calm, and dry all day.
Again the levels of lead are consistent with observed traffic flows. The samples were taken during noon hour rush and there are noticeable increases in the lead concentrations at 12 : 00 and at 12 : 50. The sensitivity of this technique, based on a scale deflection of lx, is approximately 5 x gram per sample. Preliminary experiments with a standardization technique have resulted in a coefficient of variation of 1 . 2 z . This method of sampling should prove useful for most particulate impurities found in the air, within the limits of the sensitivity of the instrument and the size of the particles. The extreme sensitivity of the method of analysis combined with the sampling technique should make it valuable for spot checks as well as for determining the background levels in places where the concentrations would not be expected to be very high. ACKNOWLEDGMENT
The authors are indebted to Wayne Fagan of Poco Graphite Inc. for his technical advice,
RAYWGQDRIFF JEROME F. LECH Department of Chemistry Montana State University Bozeman, Mont. 59715 RECEIVED for review January 25, 1972. Accepted March 28, 1972. Work supported by Grant No. GP-28055 from the National Science Foundation.
Infrared Spectra of Stoichiometric Oxides of Vanadium SIR: Research at present in progress in this laboratory on the activity of vanadium-oxide-based catalysts has led to the recording of the infrared spectra of the oxides of vanadium, Vz03, V2O4, and V205. The spectra were recorded between 1100 and 300 cm-1 (which corresponds to the spectral zone in which the compounds exhibit absorption bands) directly on finely ground, pure powders, using a Perkin-Elmer 457 spectrograph. V Z O ~and V204 were supplied by Schuchardt, V205 by Carlo Erba (RS). The spectra recorded for the three oxides are shown in Figure 1, and the positions of the bands and estimated peak intensities are summarized in Table I alongside the wavenumber of absorption maxima and intensities deduced, for the same compounds, from the figures of the well-known paper of Frederickson and Hausen ( I ) on the spectra of vanadium compounds. According to the data of Table I, particularly in the case of vzo3 and V204, the spectra obtained by us are quite different from those reported in the cited work ( I ) . In view of the fact that the data supplied by Frederickson and Hausen ( I ) have recently been used by many authors
Table I. Positions of Absorptions Maxima and Relative Intensities for V 2 0 3 ,v204, and VzOs, in cm-' Present work v203
995 vs
Frederickson and Hausen' 980 w 860 vw 825 vw 800 vw
775 w 540 s VzOa 980 vs 890 vw 850 vw 810 vw
710 vw
vzoj
530 m 1022 vs 980 w 840 vs 665 610 vs 515
1020 w 980 w 950 w 880 s 850 m 725 m 1020 vs 830 vs
475 w (1) Leo D. Frederickson, Jr., and D. M. Hausen, ANAL.CHEM., 35,
a
See Ref. (I).
818 (1963). ANALYTICAL CHEMISTRY, VOL. 44, NO. 7, JUNE 1972
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(2-6) as a basis for the interpretation of spectroscopic data pertaining to vanadium-oxide-based catalysts, and hence as a starting-point for discussion of the behavior of these catalysts in practical applications, it seems of interest to make our findings known.
GIANFRANCO FABBRI PIETROBARALDI
t
w
0
z
Figure 1. Infrared spectra of vanadium-oxides
2 c
fz
d e
Istituto di Chimica Fisica Laboratorio di Chimica Fisica Applicata Universith di Modena 41 100 Modena. Italv RECEIVED for review December 6, 1971. Accepted February 7,1972.
x
I
(2) S. Yoshida and K. Tarama, Bull. Inst. Chem. Res. Kyoto Uniu., 47, 246 (1969). (3) K. Tarama, S. Teranishi, and S. Yoshida, ibid.,46, 185 (1968). (4) G. Blyholder and M. C. Allen, Inorg. Chem., 9, 302 (1970). ( 5 ) Y. Kera, S. Teratani, and K. Hirota, Bull. Chem. SOC.Jup., 40, 2458 (1967). (6) Y. Kera and K. Hirota, J . Phys. Chem., 73, 3973 (1969).
AIDS FOR ANALYTICAL CHEMISTS Determination of Fluoride in Vegetation Using the Specific Ion Electrode R. L. Baker Research Department, Chemetals Division, Diamond Shamrock Chemical Co., 711 Pittman Road, Baltimore, Md.
SOLUBLE FLUORIDES and atmospheres containing fluorine compounds cause damage to and, in severe cases, destruction of plants and plant tissue. Until the present, the Willard and Winter distillation ( I , 2) and modifications thereof and subsequent titration or colorimetric determination have been used extensively for fluoride analyses in vegetation. This procedure is somewhat time-consuming and requires a great deal of apparatus if a number of determinations are to be run at once. I have developed a method for the determination of fluoride combining a NaOH fusion with the technique of standard addition and employing the fluoride specific ion electrode for measurement of the fluoride ion. Baumann (3) and others have described various standard addition techniques using the fluoride ion electrode. The technique by its very nature cancels out the effects caused by differing pH and ionic strengths encountered between standards and actual samples. With these effects eliminated, the observed potential changes can be related directly to concentration rather than ionic activity. The calibration curve, as it were, is prepared in the sample solution. (1) H. H. Willard and 0. B. Winter, IND.ENG.CHEM., ANAL.ED.,5 7 (1933). (2) Association of Official Agricultural Chemists, “Official Methods of Analysis,” 1965 Ed., p 360, sec. 24.029. (3) E. W. Baumann, Anal. Chem. Acta., 42, 127 (1968). 1326
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EXPERIMENTAL
Apparatus. The Orion 9409A Fluoride Electrode with a Leeds & Northrup Calomel reference electrode and a Leeds & Northrup Model 7403 meter were used in this work. A supply of 50-ml plastic beakers is necessary. Reagents. FLUORIDE STANDARD SOLUTION.A 1 OOO-pg/rnl F- solution is prepared by adding 2.211 grams of NaF to water and diluting to 1.00 liter in a volumetric flask. SODIUM HYDROXIDE SOLUTION.Six hundred seventy grams of NaOH pellets are dissolved in water and diluted to 1 liter. A blank consisting of 10.0 ml of this solution should be taken and carried through the entire procedure. If F- is found, a correction can then be made in the final results. I found none in my solutions. Procedure: A 25- to 30-gram sample of vegetation is collected at the sampling site and sealed into a plastic bag. The sample is then refrigerated and analyzed as soon thereafter as possible. In the laboratory the sample is cut into -1-inch lengths and mixed to produce a sample as nearly uniform as possible. Ten grams of the sample is weighed to the nearest 0.01 gram and set to dry at 110 “C for 24 hours. At the end of that time, the sample is reweighed and the dry sample weight calculated. Another portion of the sample (5-10 grams depending on the amount of F- expected) is weighed to the nearest 0.01 gram and transferred to a 50-mI Ni crucible. Ten milliliters (6.7 grams) of NaOH is added to the crucible and the sample is dried for 2 hours at 150 “C. At the end of the drying time, the sample is transferred to a 550 “C muffle furnace and the sample fused for 2 hours. After fusion, the
