Tracer experiments for the other elements listed in Table I were not carried out, but good reproducibility was obtained regardless of whether the samples were passed through one or two HAP columns, This indicates that these elements are not retained by HAP, supporting Girardi's results. Very erratic values for potassium were obtained, and it was apparently partially retained on the column at times. This could have been due to co-crystallization with the solid NaCl observed with the heaviest samples. A similar problem w d S observed for strontium. By examination of the effluent samples after decay of all short-lived radionuclides, small amounts of Co and Ir could be detected, corresponding to about 20 ppb and 1 ppb, respectively. After decay of 24Na, some of the HAP columns were counted. lg2Ta was observed, consistent with Girardi's report that tantalum is retained by HAP. The Ta level was estimated to be about 0.1 ppm. Scandium-46 was observed in both the effluent and the HAP, n contrast to Girardi's data, but this is probably due to the
large differences (Le., high salt concentrations and HC104 residue) between his system and that resulting from the dissolution of the glass samples. In conclusion, the use of HAP provides a very powerful tool for the activation analysis of materials with high sodium content. Of the results reported in Table I, only those for gold could have been obtained without sodium removal. The procedure is quite simple and, with a little attention to technique, gives good reproducible results. RECEIVED for review July 1, 1970. Accepted September 17, 1970. Presented in part at the 158th National Meeting, ACS, New York, N. Y., September 1969. Certain commercial materials are identified in this paper in order to specify adequately the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the material identified is necessarily the best available for the purpose.
etermination o Tin in Copperectrometry P. A. Pella and J. R. DeVoe Institute for Materials Research, National Bureau of Standards, Washington, D. C. 20234
IN A PREVIOUS REPORT ( I ) , the critical Mossbauer spectral parameters which are pertinent for quantitative analysis were evaluated. Such factors as the source-sample-detector geometry, use of absorption filters, and the background radiation should be considered for the quantitative analytical application of this spectrometry. For absolute quantitative analysis where the sampling is nondestructive, accurate measurements of the Debye-Waller factors of the source and absorber are required. This may be accomplished through careful measurements of the absorption intensity over a wide range of temperatures. However, considering the presently available experimental methodology, these measurements are difficult to make. As an alternative to nondestructive sampling, analysis by this technique can be performed in a manner similar to analytical spectrophotometry. That is, the sample can be dissolved and the analyte incorporated into a reproducible matrix. A calibration curve can then be constructed using a standard in an identical matrix, Utilizing this approach, a simple and selective procedure is described for the determination of tin using NBS copper-base alloys as an example. In order to obtain a convenient concentration range, alloys with a tin content from 1 to 8 % were chosen. The method consists of the precipitation of tin as metastannic acid with nitric acid. The precipitate which contains a number of coprecipitated elements is ignited to stannic oxide and a portion mixed with aluminum oxide. The Sn02-A1203 mixture is then measured for its §no2 content by comparing the absorption intensity with an appropriate standard. An important feature of this method is (1) P. A. Pella, J. R.DeVoe, D. K. Snediker, and L. May, ANAL. CHEM., 41, 46 (1969).
that although the SnOz precipitate contains coprecipitated elements (about 6% by weight), it is possible to measure the §noz concentration without interference. The use of @-§n as an internal standard in these measurements is also demonstrated for the first time. EXPERIMENTAL
Apparatus. The source used in these experiments was 10 mCi of 119mSn as BaSn08. A 0.05-mm Pd foil was placed over the source to filter the 25-keV Sn X-rays. A cryostat for cooling the samples to 88°K has been previously described (2). The aluminum sample holder for mounting the powdered samples was essentially of the same design reported in a previous paper (3), but with the following modifications. The shim ring which determines the sample thickness was machined from a previous thickness of 3 mm to 0.5 mm. The area of the cell was 1.76 cm,2 and the Be windows were replaced with two 0.5-rnm lucite disks. The spectrometer and associated instrumentation have all been described (4). Treatment of Alloys. Known amounts of NBS alloys SRM 52c, 184, and 37e which contain Cu,Sn, Zn, Pb, Sb, Ni, P, Si, Mn, Al, and Fe were treated with 1 :4 nitric acid. The precipitates (about 300 mg each) were digested on a hot plate overnight, filtered, washed with hot 0.1% HNQI, and dried at 100 OC. The precipitates with filter papers were transferred to Pt crucibles. The filter papers were first charred at low temperature, and then the Pt crucibles were heated in an electric furnace at 1200 "C for 5 minutes. The (2) J. R. DeVoe, ed., Nat. Bur. Stand. (US.), Note, 421,8-15(1967). (3) L. May and D. K. Snediker, Nucl. Instrum. Methods, 183 (1967). (4) F. C . Ruegg, J. J. Spijkerman, and J. R. DeVoe, Reo. Sci. Insfrum., 36, 356 (1965).
ANALYTICAL CHEMISTRY, VOL. 42, NO, 14, DECEMBER 1970
e
1833
> k v, 2
W
with A12Q3 and casting the mixture in Koldmount. This procedure produces a solid disk about 0.5 mm thick by 3 cm2 in area. The tin content was about 8 mg/cm2. The areas of the SnQa and p-Sn absorption peaks were calculated by computer-fitting Lorentzian line shapes to the experimental data
1oo.oc
I-
5
(5,6).
W
? + 4, w
96.0C
n. 92.0C
88. oc
84.0( -4.00
-2.00
0.00
2.00
4.0C
VELOClTY (rnm/si
Preparation of Calibration urws. STANDARD A. A known amount of reagent grade tin metal was dissolved in %:4 WNOl and processed as in the above procedure. A calibration curve was prepared by measuring the ratio of the area of SnOs to that of P-Sn us. the SnOaconcentration. STANDARD B. A known amount of tin metal was added to the supernate obtained after the removal of the Sn02 precipitate from the dissolution of NBS alloy SRM 52c. Sufficient nitric acid was added to precipitate the Sn02 which was treated identically as the above precipitates. A second calibration curve was constructed where the weight of precipitate taken was corrected for the amount of SnQz known to be present.
Figure 1. Mossbauer spectra of §noo and p-Sn Experimental points - Computer-fitted Lorentzian function
RESULTS AND DISCUSSION
0
k 2 . 5 crn
Figure 2. Arrangement of moving source geometry using a liquid nitrogen cryostat Mijssbauer cryostat: A, dewar; B, mounting flange; C, 0.025-cm stainless steel wall; D, liquid nitrogen feed tube; and E , liquid nitrogen reservoir; F, aluminum yoke for mounting Mb'ssbauer source; G, H , K, copper flanges; I , Pb collimator placed over sample cell J ; L, p-Sn internal standard absorber; and M , NaI (TI) scintillation detector (Styrofoam insulation around cryostat is now shown) precipitates were weighed and then ground with a mortar and pestle. Sample mixtures containing from 6 to 12 mg of precipitate were prepared by adding the precipitate to enough AlzOa(ignited powder) so that the entire mixture weighed exactly 165 =t 1 mg. The mixture was then thoroughly mixed with an agate mortar and pestle, and transferred lo the sample cell holder. The thickness of the sample was 0.5 mm. Spectra were accumulated until a minimum of 7 X 10; counts per channel were obtained. The p-Sn internal standard was prepared by grinding a mixture of tin metal powder 1834
0
The base line of the Mossbauer spectrum represents the total transmitted intensity through the sample. This includes contributions from both the nonresonant radiation from the source and the unwanted background which cannot be resolved with NaI(T1) scintillation detectors. Pella et al. (1) have indicated that the unwanted background can arise from Compton scattering of higher energy photons from the source, and/or by X-ray fluorescence from the sample. The use of an internal standard should, in principle, cancel the effect of the base line and, hence, the background contribution from the measurement. This can be accomplished by measuring the ratio of the area of the analyte absorption peak to that of another compound added to the sample. Figure 1 represents a typical spectrum of Sn02 where @-tin was used as an internal standard. A schematic diagram of the geometry used in these measurements appears in Figure 2. A particular advantage of this scheme is that the internal standard can be mounted in the gamma-ray path as a separate absorber, physically independent of the sample. The spectrum of SnOz consists of a quadrupole doublet (7). Therefore, two Lorentzian line profiles were fitted to the SnOz data with the added constraint that their halfwidths be the same. The constrained& program used is described elsewhere (6). An estimate of the precision of mixing SnOa with Al2O3was obtained by making repetitive measurements on samples containing 13.0 i 0.05 mg of SnQz. The relative standard deviation of a single measurement om the area ratio was 1 based on 5 degrees of freedom. A least-squares fit to the experimental data for the calibration curves was performed using the expression
where A I and AZrefer to the areas of SnOz and P-Sn, respectively, C and K are the constants to be estimated, m is the mg of SnOz, and la(Km/2)is the Bessel function of imaginary argument of zero order. The values of C and K obtained for the fit to standard A were 0.03000 ct 0.00021, and 5.439 mg-' 10.034, respectively. The values for standard B were 0.03000 =k 0.00012, and 5.342 mg-' -I: 0.019, where the uncertainties refer to the residual standard deviations. In ( 5 ) J. R. DeVoe, ed., Nut. Bur. Stand. Note 404, 108-15 (1966).
(6) Ibid., 501, 19-28 (1969). (7) R. W. Herber and J. J. Spijkerman, J . Chem. Phys., 42, 4312 (1965).
ANALYTICAL CHEMISTRY, VOL. 42, NO, 14, DECEMBER 1970
~-
Table I. Results of Tin Analysis Alloy 52c Sna No. of Snh NBS found, % measurefound, Certified (mean) ments (mean) value % 7.66 & 0.05 12 7.82 f 0.05 7.85 Alloy 184 6.19 3t 0.06 6 6.31 =k 0.06 6.38 Alloy 37e 6 0.99 f 0.01 1 .oo 0.97 ic 0.01 a Standard A used for calibration. Standard B used for calibration. Uncertainties refer to the relative standard deviation of the mean
x
(i.e,, s/+i).
Table I is presented a summary of the results. The first column lists the mean values for the alloys using standard A for calibration. The results indicate a negative systematic error on the order of 3 % from the NBS certified values. The metrrstannic acid obtained from the dissolution of the alloys is heavily contaminated by the coprecipitation of such elements as Cu, Ni, Zn, Pb, Sb, and Fe. If these elements are merely admixed with SnOz, there should be no interference with the Mossbauer measurement. However, if the coprecipitated elements, especially during the ignition step, substitutionally replace the Sn4+ ions in the tetragonal lattice and/or are incorporated into cation vacant sites, the force constants of the -0-Sn-0- bonds may be affected (8). A
decrease in Debye-Waller factor for the SnOz containing coprecipitated elements will give a negative systematic error when compared to a “pure” SnQs lattice such as standard A. Another source of systematic error may arise if there are differences in the particle sizes of the SnOz containing coprecipitated elements and the SnO? standard. As a result, the dispersion of the two precipitates within the A1203 matrix will be affected (9). However, the systematic error should be eliminated through the use of a standard that is precipitated from the same environment as the sample and controlling experimental conditions so that the sample and standard are treated identically. In column three of Table I are the results for the alloys using standard B for calibration. An estimate of the precision of this analytical technique has been obtained by pooling the relative standard deviations of a single measurement and was 2.2 % based on 21 degrees of freedom. Of the many tin compounds that could be used as sample compounds for analytical Mijssbauer studies, SnQl is particularly suitable because of its sensitive analytical response in terms of the change in absorption intensity per unit change in concentration, In addition, since SnOs can be easily separated from a wide variety of matrices by precipitation with nitric acid, analysis with the Mossbauer spectrometric technique would be ideal in cases where the coprecipitation of other elements would normally interfere in other analytical methods.
RECEIVED for review June 29, 1970. Accepted September 23, 1970.
(9) J. S . Van Wieringen, Phys. Lett., 26A, 370 (1968).
(8) J. G. Mullen, Phys. Rev., 131, 1415 (1963).
n
m i
R. R. Turner, A. 6. Altenau, and T.C. Cheng The Firestone Tire and Rubber Company, Central Research Laborutories, Akron, Ohio 44317 NUMEROUS METHODS have been developed for determining the activity of organometallic compounds ; in particular, organolithiums with the alkyl lithium compounds receiving special attention. These procedures include thermometric titration with butanol ( I ) , oxidation with excess vanadium pentoxide, then titration of the reduced vanadium with sulfatoceric acid (2),reaction with excess iodine (3),reaction of disulfides with organometallic compounds and titration of the mercaptide formed with silver ion (4), and the use of certain compounds which when reacted with carbon-bound lithium will give color complexes that are used as indicators for subsequent titrations (5,6). The most commonly used method is, perhaps, (1) W. L. Everson, ANAL.CHEM., 36,854 (1964). (2) A. G. Clifford and R. R. Olsen, ibid., 32,544 (1960). (3) P. F. Collins, C. W. Kamienski, D. L. Esmay, and R. B. Ellestad, ibid., 33, 468 (1961). (4) C . A. Uraneck, J. E. Burleigh, and J. W. Cleary, ibid., 40, 327 (1968). ( 5 ) J. A. Dixon and R. L. Eppley, J. Organometul. Chem., 8, 176 (1967). (6) 9.F. Eastharn and S . C. Watson, ibid., 9,165 (1967).
the Gilman double titration (7) where the total base is determined by quenching the reagent with water, then titrating the base formed. The second titration involves destroying the carbon-bound lithium with a halide, such as allyl bromide, and titrating the free base. The carbon-bound lithium is determined by difference from the total and free bases. In a previous paper (B), a double titration procedure was used to determine the carbon-bound lithium polymer cements. We now use this procedure for determining the carbon-bound metal content of organometallic reagents. This procedure, as in the Gilman method, requires the reaction of a halide with the carbon-bound metal. Any reaction between the halide and any alkoxide present will affect the accuracy of the carbonbound metal determination. This paper studies the reactions of various alkoxides of lithium, sodium, and potassium with different alkyl halides (7) H. Gilman and F. K. Cartledge, J . Organometul. Chem., 2, 447 (1964). (8) R. R. Turner, L. J. Gaeta, A. G. Altenau, and R. W. Koch, Rubber Chem. Technol.,42,1054 (1969).
ANALYTICAL CHEMISTRY, VOL. 42, NO. 14, DECEMBER 1970
* 1835
