stituents of a calculus are clinically significant. Considering the urinary tract medium in which calculi are deposited where all the above ions are constantly in contact Yith the nidus of the calculus once formed, i t is inevitable that these ions become either precipitated or adsorbed on the predominant calculus type. There is no difficulty in interpreting the spectra of the two organic calculus types most frequently found. They are individually distinct and characteristic and incapable of confusion. I n this limited series, no mixed calculi n-ere found. At present, no conclusions can be drawn concerning frequency of occurrence of the major calculus types, because a small series was examined. Additional work is in progress.
h
I
I
13
I
I
5
IP It Figure 10. Representative spectra
--
---
ACKNOWLEDGMENT
The authors are indebted to John Herman, Bronx Hospital, for his gift of natural fluorapatites, and to Herbert Jaffe, Rockefeller Institute for Medical Research, for helpful discussions. LITERATURE CITED
(1) Beischer, D. E., J . Urol. 73, 653 (1955). (2) Clark, C. C., Ph.D. thesis, Columbia University, New Pork, N. Y., 1950; Publ. 1838, Univ. Microfilms, Ann Arbor. Mich. (3) Colthup, X. B., J . O p t . Sac. Am. 40, 397 (1950). (4) Fischer, R. B., Ring, C. E., -1s.4~. CHEM.29, 431 (1957).
I
b
7
I
I
I
I
13
I
i
15
1-Cystine Pure cystine calculus
unt. J. >I., Turner, D . S.,Ibz‘d., 2 5 , (5!l% (1953). (6) Hunt, J. hf., Wisherd, &I.P., Boil ham. L. C., Ibid.,22, 1478 (1950). (7) Koegel, R. J., Greenstein, J . P..
(12) Prien, E. L., Frondel, C. J., ,J. Croi. 57, 949 (1947). (13) Randall, H. hl., Fowler, R. G.. Fuson. N.. Danol. J. R.. “Infrared Determination of Organic Structure,” pp. 121, 208, Van Sostrand, Self Tork, 1949. (14) Roberts, Glyn, Ax.4~. CHEX. 29, 911 (1957). (15) Romo, L. A., J . Am. Chent. SOC.76, 3924 f1954). . ,
.
RECEIVED for review October 20, 1958. Accepted February 26, 1959. Division of A1nalytical Chemistry, 135th AIeeting, .1CS, Boston, Mass , April 1959.
Winitz, hlilton, Birnbaum, S. XI., McCallum, R. *4.,J . Am. Chern. SOC. 77, 5708 (1955). (8) Kolthoff, I. XI., Sandell, E. B., “Textbook of Quantitative Inorganic Analvsis.” rev. ed.. D. 362. 1Iaemillan. Sew“York, 1947. (9) Leonard, R. H., Butt, A. J.. C h . Chem. 1 , 241 (1955). (10) Miller, F. A,, Wilkins, C. H.. A h i ~ CHEM.24, 1253 (1952). (11) Nicholas, H. D., CZzn. C h ~ i4 , 261 (1958).
Diffuse Reflectance Spectrophotometry in the Ultraviolet Using Powdered Salts T. R. GRIFFITHS, K. A. K. LOTT, and M. C. R. SYMONS Department o f Chemistry, The University, Southampton, England ,The spectra of a variety of powders have been studied b y diffuse reflectance methods in the 200- to 1000-mp region. Compounds whose spectra in the solid state are known were used to check the reliability of the method and it is concluded that, with appropriate precautions, the resulting spectra are trustworthy at least down to 220 mp. However, surface effects are of considerable importance. To illustrate the potentiality of the technique, a variety of compounds whose spectra in the solid state have not been previously reported were studied. These included certain periodates, iodates, sulfur-oxy ions, sodium superoxide, and ozonide.
1338
ANALYTICAL CHEMISTRY
visible and ultraviolet spectra of solutions has become a n important analytical tool. I n attempting to identify observed bands, i t is frequently of interest to study the role of the solvent and one relevant datum is the corresponding spectrum in the gas or solid phase. .\lso, for solids which are not soluble in readily available transparent solvents, a knowledge of the spectrum of the solid may lead directly to identification. By far the most satisfactory method for measuring the spectra of solids is to study single crystals in which the absorbing species has been diluted Kith an isomorphous material which is transparent in the spectral rcgion of EASUREMEST Of
interest. Hon ever, this procedure is always laborious and often impossible. I n alternative is to measure the diffuse reflectance spectra of the powdered solids, which have been diluted, if necessary, by mixing with another powder which has no absorption in the region to be studied. The purpose of this study was to examine this technique in an attempt to define the spectral region in which it may be used reliably with standard spectrophotometers, and especially to discover whether such spectra can justifiably be treated as characteristic of the bulk solid. Other aspects of this technique have been studied by various workers (9-12, 18, 23).
EXPERIMENTAL
The absorption spectra arise because multiple reflections of the incident light are accompanied by limited transmittance. They are measured by collecting monochromated light diffusely reflected from the powdered solid with a toroidal mirror which focuses the light onto the detector. This is compared with light reflected from a reference surface. The use of a photomultiplier attachment was essential in the ultraviolet region to obtain good reproducibility coupled with high sensitivity. The specific photomultiplier used v a s the Model S.Z.G. 500 (incorporating a l.P.28 multiplier phototube) manufactured by Pdzisimsmessgerate RST’, of Icking, Oberbayern, Germany. This n-as fitted to a Unicam SP. 500 spectrophotometer with an SP. 540 diffuse reflectance attachment. However, any spectrophotometer fitted with a photomultiplier would prove satisfactory. Magnesium oxide is generally used as a comparison surface. However, lithium fluoride was found to reflect between 10 and 20y0 more of the incident light, and this figure increased rapidly on going below 240 mp. The authors have also experimented with other reference surfaces but have always found lithium fluoride to be superior. Using lithium fluoride, readings have been obtained which appear to be reliable down to 210 mfi. Specimens, together with lithium fluoride diluent, were ground with an agate pestle and mortar to a homogeneous fine powder. The relative amount? of lithium fluoride required depended on the need to keep the final absorbance below 0.6. If these precautions are not taken, spurious peaks and spurious broadening may occur. (Other causes of spurious peaks are mentioned later.) The powder was immediately spread on the metal dish of the attachment to give a flat compact surface comparable with that of the reference surface. (Small differences in absorption in regions where no bands occur are due to differences in spreading, which are unavoidable.) Because coarse or inhomogeneous powders are less satisfactory ( M ) , this aspect of the problem was not studied. For hygroscopic salts it may be necessary to carry out these operations in a dry box. To avoid subsequent contact with water vapor the bottom of the specimen tray may be covered with silica gel-sodium peroxide did not pick up water in the cell housing and reproducible readings could be obtained after more than 12 hours. When spectra of compounds with high extinction coefficients were measured in the ultraviolet region, even undiluted specimens did not appear to be optically black and it was sometimes possible to describe peaks which subsequently were found to be spurious. Such peaks had an absorbance greater than 0.8 and did not decrease on initial dilution. The procedure, therefore, was
to dilute until further dilution resulted in the expected decrease in absorbance. Peaks that could be reproduced with differing dilutions of the compound with lithium fluoride (normally between 1 to 5 and 1 to 15 by volume) iyere regarded as real and all others as spurious. I n general, it is advisable to have absorbances less than 0.6 a t the peak maxima. Spectra recorded in Figures 1 to 3
n-ere obtained from specimens diluted with lithium fluoride. If, however, compounds with forbidden transitions are being studied. dilution is undesirable. A constant slit width was used when each spectrum was measured, the actual choice being made such that the instrument was as sensitive as possible in the R-ave length region to be investigated. I n the near ultraviolet and vis-
ARSORBANCE
200
300
Wave length 400 mJJ 2 0 0
Ib
1
400
300
Figure 1 . Diffuse reflectance spectra of salts homogeneously diluted with lithium fluoride a.
I. Potassium iodide (KI) 11.
I. Paraperiodic acid (HdO6)
b.
I!.
Cadmium iodide (Cdlz)
2a
Potassium periodate
ABSORBANCE
(K104)
2b
I
I
200
300
.
Wave length 40Q mIJ 300
400
Figure 2. Diffuse reflectance spectra of salts homogeneously diluted with lithium fluoride a.
b.
I. Potassium iodate (K103) II. Sodium paraperiodate (NazH3106) I. Commercial sodium peroxide (NazOz f about 10% 11. S2dium ozonide (NaOs)
0;)
VOL. 31, NO. 8, AUGUST 1959
1339
ible regions slit widths as small as 0.1 nim. could be used and in the 220-mp region slits of greater than 0.6 mm. were not necessary. The spectra were reproducible when plotted a t different slit widths. Sodium dithionite was a specially purified sample, the purity of which was estimated as 98.7%. Sodium ozonide was prepared by passing ozonized oxygen over powdered sodium hydroxide a t room temperature. Other chemicals were high grade commercial products and nrere not further purified.
ABSORBANCE
36
1
3b
0.2-
RESULTS A N D DISCUSSION
Some results which cover a range of inorganic compounds and illustrate a variety of points are given in the figures. Potassium Iodide. The spectra of single crystals a t room temperature show an intense, relatively narrow symmetrical band a t about 220 mp (6). The diffuse reflectance spectrum [Figure l,a(I)] besides being shifted 5 mp to lower energies is asymmetric, with a broadening on the lower energy side (this is more apparent using a n evtended abscissa). It is postulated that this difference arises because a relatively large fraction of the iodide ions responsible for the band is located on, or very close to the surface. Because the iodide band is very sensitive to environment (20), this could well result in a shift. The situation is similar to that which is found in single crystals containing negative ion vacancies. I n such crystals a small satellite band is found at about 230 mp, vhich is ascribed to those iodide ions which surround the vacancy (17). Cnder the conditions used, the authors did not obtain any resolution into discrete bands, and the spectrum is an average for all the iodide ions involved. Cadmium Iodide. Single crystals have bands a t 325 and 238 mp (3). The band a t 323 mp obtained by diffuse reflectance is accordingly ascribed to the bulk crystals but the bands a t 260 and 225 mp [Figure l,a(II)] must have some alternative origin. Cadmium iodide crystals may be described as semiionic, having a layer lattice (8). I n the gas phase, however, the linear molecules are covalent, and are characterized by intense bands a t 260 and 225 mp. Accordingly, it is postulated that the bands a t 260 and 225 m p detected from the powder are due to cadmium iodide molecules located on the surface of the crystals, but not directly part of the lattice. Chromate and Dichromate. The chromate ion in soIution has two symmetrical bands a t 373 and 270 mp, The ratio of the two heights of these bands is 4 to 3 for the solution and the powder, barium chromate [Figure 3,b(I)]. This result suggests
1340
ANALYTICAL CHEMISTRY
0.1-
200
300
Wave length 300
400 my
400
Figure 3. Diffuse reflectance spectra of salts homogeneously diluted with lithium fluoride a.
I. II. 111.
S3dum dithionite (NasSmO,) Sodium metabirulfite ( N a & O j ) Sodium dithionate (Na?StO&
that, although i t is impossible to edimate extinction coefficients for the bands recorded by diffuse reflectance methods, nevertheless relative band heights are reproduced accurately even in the 250mp region. iicid chromate and dichromate have weak bands in the 440-mp region and more intense bands a t 350 mu (1, 5 ) , It is suggested that surface changes are important and that exposure to the atmosphere may giye rise to acid chromate, dichromate, or some other ion of this type of the surface, thus accounting for the asymmetry of the powder spectrum [Figure 3 b(II)]. The spectrum of dichromate by diffuse reflectance is similar to the solution spectrum. None of the fine structure found in single crystals of chromate (16) is resolved by this technique. Periodate and Iodate. The spectra of single crystals of these compounds have not been studied. There are two remarkable differences betn-een t h e spectra of diluted powders and aqueous solutions: The bands found in the 300-mp region for potassium periodate [Figure l,b(II)], sodium paraperiodate [Figure 2,u(II)], and potassium iodate [Figure 2,a(I)] are not resolved at all in solution and the intense band at 222 mp characteristic of periodate in neutral solutions (4) is not found in solid potassium periodate. The issues involved in the latter observation will be discussed elsevhere. The point the authors wish to stress
b.
I. II.
Barium chromate (BaCrOJ Potassium chromate (K?CrOd
is that these simple evperiments have revealed absorption bands not recorded previously for these ions. Smith, honever, in these laboratories (191, has tentatively inferred their presence from a study of the long wave length edge of the spectra of aqueous solutions. From his results he has also constructed a spectrum for paraperiodic acid (periodic acid) which is in very good a,ereenient with the spectrum of the powder ivhich was obtained by the authors [Figure l,b(I)]. Sodium Ozonide and Superoxide. The yellow paramagnetic solid formed by passing ozone over pondered sodium hydroxide has been identified as sodium ozonide, Na03 (14, 22). The spectrum recorded [Figure 2,b(II)] is identical with that of a solution of potassium ozonide in liquid ammonia ( I C ) and is, therefore, due to an internal transition of the ozonide ion. Certain commercial varieties of sodium peroxide are pale yellow and are thought to contain about 10% of the superoxide ( 2 ) . There is a shoulder in the spectrum obtained from the powder in the 370- to 380-mp region (Figure 2,b(I)], which is almost certainly due to the superoxide ion, because the spectra of solutions of superoxide in liquid ammonia have a band in this region (21). This is a n example in which diffuse reflectance spectrophotometry has given useful information about very unstable compounds for which single diluted crystals would be very hard to obtain.
A knowledge of the spectra of these solids as well as their spectra in solution is of considerable use in understanding the origin of these spectra, because their similarity is such that the possibility that the absorption is due to charge transfer to solvent can be ruled out (20). Sodium Dithionite, Metabisulfite, and Dithionate. Spectra of single
crystals do not appear t o have been recorded. Aqueous solutions of dithionite are unstable, b u t are reported t o ha7.e intense bands at 313 and 250 mp (‘7, 13). The spectrum recorded [Figure 3,a(I)] s h o m no resolved band in the 313-mp rtlgion. Various explanations for this (’an be proposed, one possibility being that the surface of the solid dithionite has undergone extpnsive decomposition into nietabisulfite ( p y r o d f i t e ) and thiosulfate (15). Because metabisulfite has a peak a t 250 nip [Figure 3,a(II)1, a superimposition of the true ditliionite spectrum and that for metabisulfite could give the recorded spectrum, the 313-mp band being hidden under the tail of the metabisulfite band (thiosulfate has no absorption in this region). CONCLUSIONS
Band maxima can be reproduced with
fair accuracy down to 220 mp, and relative heights of different bands are measured reliably. Surface changes are readily detected and often give rise to spectra which are not characteristic of the bulk solid. This is a severe analytical limitation, but it could be of great use in studying surface phenomena. Because the method is very simple and reproducible results are readily obtained, it is strongly recommended as an analytical tool.
(8) Hiickel, TV., “Structural ,,Chemistry
of Inorganic Compounds, p. 592, Elsevier, New York, 1951. (9) Jahoda, F. C., Phys. Rev. 107, 1261
i 1957). (10) Kortum, G., Spectrochim. Acta, 1957 Supplement, 534. (11) Kortum, G., Kortum-Seiler, \I., 2. n’aturforsch. Za, 652 (1947). (12) Kortum, G., Schlotter, H., 2. Elektrochem. 57, 353 (1953). (13) Koson-er, E. M., Bauer, S. W.,
ACKNOWLEDGMENT
IT’th Intern. Congress of Biochemistry, Vienna, Austria, September 1958. (14) McLachlnn, A. I)., Symons, M. C. R., Tomnsend, 31. G., J . Chem. Soc., in press. (15) Meyer, J., 2. anorg. Chem. 34, 43
The authors thank C. A. Parker, who supplied the specially purified sample of sodium dithionite.
(1903). (16) Schaumann, H., Z. Physilz. 76, 106 (1932). (17) Seitz, F., Revs. M o d . Physics 26, 7 i -1R.54) ”--
(2) Bennett, J. E., Ingram, D. J. E.,
(18) Sh&ata, S., J . Biocheni. (Tokyo) 45, 599 (1958). (19) Smith, hI., Ph.D. thesis, Southampton University, 1958. (20) Smith, RI., Symons, 91. C. R., Trans. Faraday SOC.54, 338 (1958).
82 (1951). (5) navies, W. G., Prue, J. E., Trans. Faraday SOC.51, 1045 (1955). (6) Fesefeldt, H., 2.Physik. 64,623 (1930). (7) Hellstrom, H., 2. physiol. Chenz. 246, 155 (1937).
RECEIVED for review November 28, 1058. Accepted April 27, 1959. Research scholarships from the University of Southnmpton to T. R . G. nnd K. -1.K . I,.
LITERATURE CITED (1) Bailey, N., Lott, K. A. K., Symons,
11.C. R., J . Chern. SOC., to be published.
Symons, >I. C. R., George, P., Griffith, J., Phil. Mag. 46, 443 (1955). (3) Butkov, K., 2. Physik. 71,6i8 (1931). (4) Crouthamel, C. E., Hayes, A. >I., Martin, D. S., J . Am. Chem. SOC.73,
(21) Thompson, J. K., Kleinberg, J., J . Am. Chent. SOC.73, 1243 (1951). (22) Whaley, T. P., Kleinberg, J., Ihid., 73, 79 (1951). 123) Zeitlin. H.. Siimoto., A,., .Tuture 181, 1616(19%).
Determination of Manganese in Gasoline by X-Ray Emission Spectrography RICHARD A.
JONES
Research laboratories, Ethyl Corp., Detroit, Mich.
b A method has been developed for determining manganese in gasoline by x-ray emission spectrography. It was necessary to compensate for the interferences caused b y variations in gasoline base stock and in the concentration of certain additives. This method uses a compensative reference, which consists of an iron rod positioned in the liquid sample at a fixed distance from the specimen-holder window. The intensities of selected manganese and iron lines are measured, and the concentration of manganese i s calculated by comparing the manganese-iron intensity ratio for the sample to ratios obtained with known standards. Because the manganese-iron intensity ratio i s reasonably free from interferences due to the base stock or additives, a single calibration curve suffices for all gasoline samples. The time required for a determination i s approximately 15 minutes. Over
the range of 0.1 to 1.0 gram of manganese per gallon, the average standard deviation varies from 0.003 to 0.007 gram per gallon.
R
(methylcyclopentadieny1)manganese tricarbonj-1 has been developed by Ethyl Corp. as a n e x antiknock additive for gasoline. I t s use will require analytical methods for the determination of manganese in gasoline. This TTork was undertaken to devise a satisfactory x-ray emission method. X-ray emission spectrography has been very useful in the petroleum industry (2-7) and in the analysis of gasolines has been used for the determination of lead (2j 7 ) and of bromine (2, 6). The procedures developed for these determinations were complicated by absorption effects due t o variations in the composition of the matrix. ComECENTLY
pensation n‘as made for these absorption effects by devices such as a series of calibration curves, a correction based on density, or a n added internal standard. This paper describes a successful technique for dealing with absorption effects in gasolines. All necessary measurements are made with the x-ray instrument, and a single calibration curve applies to all gasoline samples normally encountered. d b o u t 15 minutes are required for a single determination. INSTRUMENTATION
The instrument used was a Norelco (Philips Electronics, Inc.) invertedsample, three-position x-ray spectrograph equipped with a Norelco FA-60 x-ray tube. A schematic diagram of the experimental setup is shown in Figure 1. The x-ray tube was operated at 45 ma. and 55 kv. t o excite to a suitable intensity the K , line of manganese at 2.103 A . and the K , line of iron a t 1.937 A. The liquid specimen holder supplied VOL. 3 1, NO. 8, AUGUST 1959
* 1341
