potassium dichromate in H2S040.01 N and by nicotinic acid in HC10.1 N. On the basis of the results obtained, the values reported here may contribute to the elaboration of two new RMs spectrophotometrically usable for the control of the spectrophotometers intended for practical use.
ACKNOWLEDGMENT We wish to thank F. Bonifati for helpful technical assistance. LITERATURE CITED (1) G. Haupt, J. Res. Nafl. Bur. Stand., 48, 414 (1952). (2) Phofoelec. Specfrom. Group. Bull., 18, 456 (1965).
(3) J. R. Edisbury, “Practical Hlnts on Absorption Spectrophotometry”, Hilger Watts, London, 1966, p 186. (4) 0. Menis and J. I. Schults, Ed., Nafl. Bur. Stand. Tech. Nofe, 544, 19, 22 (1970). (5) G. Kwtiim,~dorimetrie,‘‘Photometric und spektrometrie”, 4th ed.,Springer Verlag, Berlln, 1962, p 302 (and literature quoted there). N. T. Gridgeman, Phofoelec. Specfrom. Group. Bull., 4, 67 (1951). J. A. A. Ketelaar, J. Fahrenfort, C. Haas, and G. A. Brinkman, Phofoelec. Specfom. Group. Bull., 8, 176 (1955). J. M. Vendenbeit, J. O p f . Soc. Am., 50, 24 (1960). K. M. Sappenfield, G. Marinenko, and J. L. Hague, Nafl. Bur. Stand., Spec. Pub/., 32, 260-264 (1972). (IO) 0. Menis and J. I. Schults, Ed., Nafl. Bur. Stand. Tech. Nofe, 584, 27 (197 1).
RECEIVED for review October 29,1976. Accepted January 31, 1977.
Application of the Fundamental Parameter Method for the Determination of Major and Minor Elements on Fused Geological Samples with X-ray Fluorescence Spectrometry Christ1 Palme” and Emll Jagoutz Max- Planck-Institut fur Chemie, Abteilung Kosmochemie, Saarstrasse 23, 6500 Mainz, Federal Republic of Germany
An x-ray fluorescence spectrometrlc method for the determination of major and minor elements In rock samples Is presented. The method has been elaborated for accurate analyses of small sample slres (max. 100 mg), and with the alm to measure both major and trace elements on the same samples. The samples were fused In a flux of L12B407and NaNO, wlth a dilution of approxlmately 1 : l O . No heavy absorber was added. To avoid contamlnatlon, the glass beads were formed within the cruclble. Problems of homogenelty of the glass beads are dlscussed. For correctlon, the fundamental parameter method was applied. The parameters entering the correction program were verified wlth synthetic standards.
The research in the Department of Cosmochemistry at the Max-Planck-Institute in Mainz is directed toward the analysis and interpretation of extraterrestrial materials, like lunar and meteoritic samples. As these samples are rare in most cases, the analytical methods have to be sample-saving. Nondestructive neutron activation analysis is a well established analytical method in the department, but several elements, like P and S, are not accessible with neutron activation; for other elements this technique has poor sensitivity and large errors. Therefore it was decided to develop a x-ray fluorescence analysis method with the following objectives: 1) to do the analysis with small quantities of material (max. 100 mg), 2 ) to obtain results with high accuracy, and 3) to measure major and trace elements on the same samples. For the sample preparation a fusion method has been adopted; it is considered to be easier and more reproducible than a powder-pellet method. In contrast to the widespread Norrish and Hutton method (I), less amount of sample quantity is taken and no La203 is added to the flux, as La would lower the sensitivity for the trace element analysis. As the fusions are only moderately diluted and without a heavy
absorber, a considerable matrix correction is necessary; for this reason, the fundamental parameter method has been chosen. It is considered to be more general and more flexible for application on samples with wide concentration ranges.
EXPERIMENTAL Apparatus. The measurements were made with a Philips PW 1410/10. A W and a Cr x-ray tube were available. LiF, PE, RAP, C, and Ge crystals were used for the analyses. A 12-fold sample changer has been adapted to the instrument. The conventional sin 0 potentiometer with subsequent single-channel analyzer has been substituted for by a 20-channel analyzer (2). The spectral range covered by this analyzer is fixed by the independently adjustable upper and lower level. The range between the two levels is divided into 20 equidistant channels. After each counting interval, the content of the 20 counters-corresponding to the 20 channels-is transferred to the memory of the on-line computer (Intertechnique,Multi 20,16K). Position and width of the optimal window is calculated by the computer software. The on-line computer also controls the sequence of the measurements: the sample changing mechanism, the goniometer control,and the mA setting of the high voltage. The net-peak intensities calculated from the 20-channel analyzer were punched on paper-tape and then processed by a TR 440 computer for matrix corrections. Sample Preparation. A mixture of approximately 100 mg of sample, 1300 mg of H3B03,400 mg of LiC03(H3B03and LiCOs in the proportion of Li2B407),and 200 mg of NaN03 was fused at 970 “C for 20 min in a Pt-5%Au crucible. The dilution of the sample in the glass bead was approximately 1:lO. The beads were formed by letting the fusions cool inside the crucible. The bottom of the crucible had been previously flattened. The diameter of the beads is 20 mm and their thickness is 1.2 mm. So for the shortest wavelength, which occurs in the determination of major elements (Fe Ka),the beads can be considered as infinitely thick. This procedure for the sample preparation had been developed by E. Jagoutz (3). Data Evaluation. The fundamental parameter method ( 4 ) was used for correction of the measured intensities. They were corrected for absorption and enhancement effect according to the formulas published by Sherman (5) and Shiraiwa and Fujino (6). The parameters entering the calculations were taken from the ANALYTICAL CHEMISTRY, VOL. 49, NO. 6,MAY 1977
717
1,Ol I ID0
F
e
melt1
2
K
3
4
a
Table I. Recision of the Analysis of Standard Rock BR Sample Mg Si Ca Ti Fe 17.87 9.86 1.57 9.03 BR bead 1 7.94 18.10 9.86 1.58 9.05 BR bead 2 8.02 18.01 1.57 9.01 9.86 BR bead 3 7.95 17.75 9.83 1.57 BR bead4 8.01 8.96 18.04 9.83 1.57 BR bead 5 8.01 9.05 Meanvalue 7.99 17.95 9.85 1.57 9.02
L
5
without Na20
Confidence level 95%
I with addition of NazO Figure 1. Fe K a intensities of fused Fe203-Li2B407 beads. The points of the first plot correspond to five consecutive melts of a bead without Na,O, the points of the second plot to five consecutive melts of a bead with addition of Na20 following sources: spectral distribution: T. C. Loomis and H. D. Keith (7); absorption coefficients: W. H. McMaster et al. (8); the values were fitted with the approximation, ~1 (X) = C X3 - N X4, so, two pairs of constants C,N were obtained, one for the K absorption and one for the L absorption (9). For the K-shell fluorescence yields and absorption jumps, averages from the different literature data have been used (10-15). A Fortran program was written for the correction. It calculates the correction integral over X of the formulas of Sherman and Shiraiwa (5,6). The measured intensities divided by these integrals, Z’,are proportional to the concentrations of the measured elements I,’= kc, + d , where k and d are calibration constants. From the corrected intensities of standard rocks and their element concentrationstaken from the publication of F. J. Flanagan (161, the calibration constants were determined. The element concentrations of the unknown samples were then calculated with the calibration constants and the known sample to fusion ratio. As the correction integrals depend on the sample compositions, three or four iterative steps were necessary.
RESULTS AND DISCUSSION Reproducibility of t h e Sample Preparation. An example for the reproducibility of the sample preparation is shown in Table I. Five independently fused samples of standard rock BR were measured for some elements in a routine run. With a confidence level of 9 5 % ) the average precision is 0.5%. This includes sample preparation and the measurement itself.
Sample without No2 0
t
t
0.98%
0.21%
0.35%
0.51%
The NaN03 has been added to the fusions to provide oxidizing conditions for the determination of sulfur (I). Experiments showed that 200 mg of NaN03 are sufficient to oxidize all sulfur. Another reason for the addition of NaN03 is the effect of Na on the homogeneity of the fusions. In the case of some elements, e.g., Fe and Si, it was noted that the counting rate changed slightly, when the beads were remelted, especially when no NaN03 had been added. Already Norrish and Hutton mentioned problems they had with the determination of Fe (1). So the system FezO3-Li2B40, was studied in detail. Two samples containing about 5.7% Fez03fused in Li2B407 were prepared. In addition, one of them had 7% NazO, corresponding to 200 mg of NaN03. The Fe K a intensity was measured and afterward the samples were remelted and the Fe Ka intensity was measured again and so on. If the bead had been homogeneous the counting rate should not change. The results are shown in Figure 1. The sample without NaN03 shows variations of 2-3%; after it had been remelted several times, the counting rate approximated a constant value. The counting rate of the NaN03 containing glass is practically constant. The same samples were analyzed with a microprobe. The distributions of the Fe K a intensities across the profiles of the glass disks are shown in Figure 2. The first bead had been melted only once. One can observe an enrichment of Fe at the lower surface. The second sample is also without NaN03, but it has been remelted several times, and each time it was turned upside down in the crucible. The Fe concentrated in the center of the sample. The NaN03-containing sample is nearly homogeneous. The borate-glass structure can be considered as an irregultlr three-dimensional B203network. No information about the function of Fez03in a B203network could be found in the literature. But phase diagrams of some alkaline earth and alkali oxides in boric acid exist (17). Other oxides, as alkali or alkaline-earth oxides weaken the BzO3 network and are called modifying oxides (18-20). With alkaline-earth oxides present in high boric acid concentrations, generally two liquid phases are formed and these melts on cooling will form glasses
Sample without No20 remelted several times
t
0.59%
t
Sample with addition Of No20
t
t
irradiated surfaces Flgure 2. Distribution of the Fe K a intensity across the profiles of fused Fe2O3-LI2B4O7 beads determined by the microprobe. In the abscissas are plotted the Fe K a intensities and in the ordinates the positions in the beads 718
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
of the used constants, standards were synthetized consisting of one or two element oxides and Li2B407. At first the application of the absorption correction will be shown. In Figure 4 measured vs. calculated Fe K a intensities are plotted. All samples have the same Fe concentration: 3.2%, they only differ in their matrix compositions. In addition to Li2B407, the matrix contains one other element in variable concentrations which acts as absorbing element. The added elements are indicated in Figure 4. Another example is given in Figure 5. Fe203-Li2B407 samples with Fe concentrations varying between 0 6 4 % were prepared. The majority of them also contain Na20, and to three of the samples CaO was added in the concentration range of 1.0 to 5.6%. The open circles represent the measured intensities, whereas the filled circles, the stars, and the asterisks represent the corrected intensities. All intensities have been normalized to the highest value. The relative deviations from the calibration line for the corrected intensities can be seen in Figure 6. Nearly all data points lie within a limit of 1%. The same synthetic standards were used to test the correction method based on the empirically determined influence coefficients a (25). A t first the a’s were determined experimentally and afterward they were compared with a’s calculated from fundamental parameters (26). The results are shown in Table 11. With the known concentrations c, and the measured intensities IFe for the 14 standards the a matrix is overdetermined and canbe calculated by multiple regression analysis. The experimental a’s obtained in this way have very large errors. The theoretical a’s were determined by the formalism of the fundamental parameter method. P F J C F ~ is the integral correcting for absorption ( 4 ) and has been calculated from the known compositions of the standards.
two liquids
Figure 3.
Glass-forming region in the system Li20-Bz03-Si02
appearing opaque or cloudy (20,22). Alkali oxides in highly concentrated boric acid form clear glasses. But on looking at clear Na20-B203 glasses with the electron microscope, even those glasses showed a phase separation of Na-rich droplets in a B2O3 phase (22). It has been shown that the tendency toward immiscibility increases with increasing ionic potential of the constituents (20,21). The alkali oxides can be used to homogenize phase-separated melts, and for this purpose Na has a major effect compared to Li because of its larger atomic radius and smaller ionic potential (21). The effect of two immiscible phases for the ternary system Li20-B2O3-SiO2has been described by Sastry and Hummel (23). The region of homogeneous glass formation in this system is shown to be rather small; it is located around the composition of Li2B407,as can be seen from Figure 3. At lower Li20 concentrations, the tendency toward liquid immiscibility increases and at higher Li20 concentrations devitrification will occur. This type of phase separation in the system NaiO-B2O3-SiO2 is used for the production of Vycor glasses (24). T e s t of t h e Correction Method w i t h Synthetic Standards. To test the correction program and the quality
1
/
/
Kp‘ 0.5
/
/
/
/
/-
All samples have the same content of Fe:3.2%
0.5
1
Fe -intensity calculated Figure 4. Measured vs. calculated Fe K a intensitles for samples with different 3.31%; Mg: 2.56%; AI: 2.42%; Si: 1.11%; Si: 2.11%; Si Na: 3.84% 3.55 U/o
+
matrix compositions. Concentrations of the added elements: Na: + 1.11%; K: 6.02%; P: 2.71%; Ca: 2.97%; TI: 1.11%; Mn: ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
719
/
% rdative
/?
-3 -
a
Flgure 7. Relative deviatlons from the calibration lines. (0)intensities corrected with experimentally determined a coefficients. (X) intensities corrected with theoretical a coefficients.
I
!
I
1
I
L 6 e Yo concentration of Fe in the sample Flgure 5. Fe K a intensities vs. Fe concentration. (0) uncorrected intensities: (0,+, *) intensities corrected with the fundamental parameter method. ( 0 )Fe,03, Na,O, Li2B407samples, (+) CaO, Fep03,Na,O, LiPB40, samples. (*) MnO, Fe,03, NazO, Li2B407 samples
2
YOrelative
1
2
3
L
5 %Ca
Ca K a intensities corrected for absorption vs. Ca concentrations. (+) CaO, Li2B407samples, (0)Fe,O,, CaO, Li2B407 samples Flgure 8.
OO /
Fe
correlation coefficient 0,9999L
Flgure 6. Relative deviations from the calibration line for the intensities corrected with the fundamental parameter method. Symbols used as in Figure 5
Table 11. Determination of CFeb - CFe
cy
Coefficients
&!Fed = PFeC a , ( ~t cyFe~cFeet a N a ~ c N a f
IFea
+ “CaACCag) Experimental
Calculated by the fundamental parameter method a o / g F e = 1.9856 * 0.0008 a,,= 0.066 * 0.02 a~~ = 5.992 i 0.001 CYF =~7.45 f 0.75 1.404 i 0.011 cy^^= 0.81 c 0.81 aca= 9.722 * 0.018 a C a = 11.79 t 1.3 a Measured Fe K a intensity; Fe concentration; Fe K a intensity calculated by the fundamental parameter method, formulaof Qiss and Birks ( 4 ) ; constant, e A C F ~ CFe= CFe, CFe= O.@O; LAC,,= CNa- CNa, C N ~ O.023ig = ACca= Cca- Cca, cca=0.025. Finally the a’s were also obtained by regression analysis. It can be seen that these now theoretically determined a’s are similar to the experimental a’s, but their standard deviations 720
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
are much smaller. In Figure 7 the results with the experimental and theoretical a’s are compared. The experimental a’s give no satisfactory result, whereas the correction with theoretical a’s is identical to the result obtained previously by the fundamental parameter method. Finally in Figure 8 an example of our correction program applied for enhancement is shown. On some of the previous samples-CaO and Fez03 fused in LizB407-CaKa has been measured. If for the correction only absorption is taken into account, the data points of the Fe-containing samples fall above the calibration line of pure Ca samples. But if the correction for enhancement is included, these points fall on the same line. The quality of the enhancement correction depends essentially on the values for the fluorescence yields. In our fusions of geological samples, the enhancement correction normally is less than 170of the absorption correction. Only in a few cases, e.g., for the determination of Cr in Fe-rich samples, the enhancement correction is larger than 1% of the absorption correction. So, in most cases, a big error in the fluorescence yield is tolerable. Results for Terrestrial Standard Rocks. The accuracy of our analyses can be judged from a comparison of our results with concentrations reported by Flanagan (16).Results of MgO, A1203, SiOz,CaO, TiOz,Cr, MnO, and Fez03are shown in Tables I11 and IV. For the major elements Mg, Al, Si, Ca, Ti, and Fe, there are only a few values deviating more than 2% from the Flanagan concentrations. Especially the Mg values for some standard rocks with low Mg content show larger deviations. For Mn the accuracy is about 5% and for Cr, 7% in the concentration ranges given. No comparisons
Table 111. Results for MgO, Al,O,, SiO,, and CaO in Comparison with F. J. Flanagan (16) MgO, % A1,0,, % SiO,, % This work Flanagan This work Flanagan This work Flanagan AGV-1 1.61 1.53 17.21 17.25 58.65 59.00 BR 13.11 13.28 10.06 10.20 38.39 38.20 BCR-1 3.46 3.46 13.47 13.61 54.23 54.50 BM 7.29 7.46 16.17 16.20 50.20 49.60 Mica-Fe 4.66 4.60 19.40 19.40 34.68 34.40 TB 1.91 1.94 20.55 20.55 60.54 60.30 w-1 6.62 6.62 14.78 15.00 52.04 52.64 DTS-1 49.93 49.80 0.25 0.24 39.93 40.50 GA 0.97 0.95 14.65 14.50 70.01 69.90 -_15.40 0.81 0.76 69.49 69.11 G-2 0.37 0.38 13.95 13.50 GM 73.47 73.55 -_0.96 15.20 15.25 66.84 67.38 GSP-1 43.18 43.18 0.73 0.74 40.85 41.90 PCC-1 Table IV. Results for TiO,, Cr, MnO, and Fe,O, in Comparison with F. J. Flanagan (16) TiO,, % MnO, % This work Flanagan This work Flanagan This work Flanagan AG V- 1 1.04 1.04 12.2 12.2 0.096 0.097 Br 2.62 2.60 403 420 0.20 0.20 BCR-1 2.21 2.20 18.1 0.19 0.18 17.6 BM 1.13 1.14 120 123 0.15 0.15 Mica-Fe 2.43 2.55 95 90 0.35 0.35 TB 0.90 0.93 85 0.05 0.05 80 114 w-1 1.08 118 1.07 0.18 0.17 DTS-1 0.017 4070 4000 0.013 0.11 0.11 GA 0.37 11 10 0.38 0. os 0.09 G-2 0.50 7 I 0.50 0.036 0.034 GM 0.21 11 10 0.21 0.04 0.04 GSP-1 0.67 13.5 0.66 12.5 0.042 0.042 PCC-1 0.019 2680 2730 0.015 0.11 0.12 " Fe total as Fe,O, Table V. Major Element Data (wt %) for the Apollo 17 Mare Basalt 70215 Method Mg A1 Si Ca Duncan et al. XRF 4.82 4.69 17.72 7.70 LSPET XRF 5.14 4.64 17.39 7.45 Rhodes et al. XRF 4.77 4.77 17.98 7.82 Rose et al. XRF 5.63 4.65 17.58 7.73 Wanke et al. IFNAA 4.98 4.57 17.90 Wanke et al. ITNAA 7.42 This work XRF 5.03 i 0.10" 4.64 i 0.09" 17.82 i 0.36" 7.62 i 0.15a Mean value 5.06 i: 0.13c 4.66 f 0.03c 17.73 i: O.0gc 7.62 i 0.07c " Accuracy 2%. accuracy 3%. standard deviation.
CaO, % This work Flanagan 4.99 4.90 13.80 13.80 7.02 6.92 6.45 6.44 0.42 0.45 0.14 0.30 11.00 10.96 0.12 0.15 2.44 2.45 1.95 1.94 1.01 1.02 2.01 2.02 0.54 0.51
Fe203,%a This work Flanagan 6.83 6.76 12.90 12.88 13.31 13.40 9.59 9.68 25.80 25.75 6.91 6.92 11.03 11.09 8.64 8.64 2.80 2.83 2.68 2.65 2.03 2.02 4.37 4.33 8.45 8.35
Ti 7.84 7.88 7.48 7.91 7.70 7.30 7.53 i 0.23' 7.66 t O.0gc
Fie 15.51 15.25 15.08 14.94 15.70 15.27 15.83 i 0.47' 15.37 * 0.12c
Table VI. Minor Element Data (ppm) for the Apollo 17 Mare Basalt 70 215
a
Method P S Duncan et al. XRF 500 1880 LSPET XRF 390 1800 Rhodes et al. XRF 430 1700 Rose et al. XRF 300 ITNAA Wanke et al. This work XRF 440 i 40" 1620 i 160a 1750 i 6OC Mean value 412 t 33c Accuracv 10%. accuracv 5%. standard deviation.
'
are shown for K, S, and P, because for K and S we used well analyzed lunar samples as standards, and for P we used our trace element correction program. Results for Lunar Samples. In Tables V and VI a comparison of results on one lunar sample (anApollo 17 mare basalt) with other literature data is shown (27-30). In the publications of Duncan, LSPET, and Rhodes a method similar to the Norrish and Hutton method has been applied. They take 280 mg of sample and add La203to the flux. The data
K 340 330 415 660 340 407 i 20b 415 i 5OC
Cr 2950 2870 2670 2800 2680 2820 t 140' 2798 f 44c
Mn 2044 2170 2250 2090 1940 2020 f 100' 2086 i 45c
of Wanke et al. are from our Institute, obtained by neutron activation analysis. In most cases our data fall within the standard deviation of the mean value. In all cases the error bars overlap. The data for P and K are relatively wide spread. As these elements are mainly concentrated in the late crystallizing accessory minerals, they may be inhomogeneously distributed in samples of small size. Further results of our analyses on lunar samples have been published in the Proceedings of the Lunar Science ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
721
Conferences 6th and 7th (31,32).
ACKNOWLEDGMENT The authors thank H. Kruse for writing the computer programs. LITERATURE CITED (1) K. Nwrish and J. T. Hutton, Geochlm. Cosmhlm. Acta, 33, 431 (1969). (2) E. Jagoutz and C. Palme, work to be published, Max-Planck-Institut fur Chemie, Mainz, 1976. (3) E. Jagoutz, thesis, Mainz, 1976. (4) J. W. Criss and L. S. Birks, Anal. Chem., 40, 1080 (1968). (5) J. Sherman, Spectrochlm. Acta, 7, 283 (1955). (6) T. Shiraiwa and N. Fujino, Jpn. J. Appl. Phys., 5, 886 (1966). (7) T. C. Loomis and H. D. Keith, X-Ray Spectrom., 5, 104 (1976). (8) W. H. McMaster et ai., UCRL - 50174 (1969). (9) J. A. Victoreen, J. Appl. Phys., 20, 1141 (1949). (IO) C. Broyles et ai., Phys. Rev., 89, 715 (1953). (11) F. D. Davidson et ai., J. Appl. Phys., 33, 3528 (1962). (12) R. W. Fink et al., Rev. Mod. Phys., 38, 513 (1966). (13) P. Suortti, J. Appl. Phys., 42, 5821 (1971). (14) W. Bambynek et ai., Rev. Mod. Phys., 44, 716 (1972). (15) H. U. Freund, X-Ray Spectrom., 4, 90 (1975). (16) F. J. Fianagan, Geochim. Cosmochim. Acta, 37, 1189 (1973). (17) E. M. Levin et 81. “Phase Diagrams for Ceramists”, American Ceramic Society, Columbus, 1964.
(18) P. W. McMilian, “Glass Ceramlcs”, Academic Press, London and New York, 1964. (19) H. Scholze, “Gias”, Friedr. Vieweg & Sohn, Bsaunschweig, 1965. (20) H. Rawson, “Inorganic Glass-Forming Systems”, Academic Press, London and New York, 1967. (21) L. Shartsis et ai., J. Am. Ceram. Soc., 41, 507 (1958). (22) W. Skatuila et al., Slllkattechnik, 9, 51 (1958). (23) B. S. R. Sastry and F. A. Hummel, J. Am. Ceram. SOC.,43, 23 (1960). (24) T. J. Rockett and W. R. Forster, J. Am. Ceram. Soc., 49, 30 (1966). (25) S. D. Rasberry and K. F. J. Helnrich, Anal. Chem., 46, 81 (1974). (26) W. K. de Jongh, X-Ray Spectrom., 2, 151 (1973). (27) A. R. Duncan et ai., Proc. 5th Lunar Sci. Conf., Geochlm. Cosmochlm. Acta, Suppl. 5, 2, 1147 (1974), Pergamon Press, Elmsford, N.Y. (28) J. M. Rhodes et ai., ref. 27, p 1097. (29) H. J. Rose et ai., ref. 27, p 1119. (30) Lunar Sample Preliminary Examination Team, Science, 182, 659 (1973), (31) H. Wanke et ai., Proc. 6th Lunar Sci. Conf., Geochim. C o s m h i m . Acfa, Suppl. 6, 2, 1313 (1975), Pergamon Press, Elmsford, N.Y. (32) H. Wanke et al., Proc. 7th Lunar Sci. Conf., Geochlm. Cosmochlm. Acta, Suppl. 7, 3, 3479 (1976), Pergamon Press, Elmsford, N.Y.
RECEIVED for review November 9,1976. Accepted January 18,1977. The paper was presented at the 25th Annual Denver X-Ray Conference, August 4-6,1976, University of Denver, Denver, Colorado. The financial support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.
Determination of Composition and Molecular Weight of Polyester Urethanes by High Resolution Proton Magnetic Resonance Spectrometry F. W. Yeager” and J. W. Becker Elastomer Chemicals Department, E. I. du Pont de Nemours a n d Company, ExperimentalStation, Wiimlngton, Delaware 19898
The compositional analysts of a polyester urethane and number average molecular weight of the polyester moiety can be determined directly by 220 MHz ‘H NMR. Accuracy of both measurements was wlthln the preclslon llmlts (217) of the method. Precision of the ’H NMR composltlonal analysis for a polybutylene adlpate-TDI or -MDI polymer was f2.5 Yo relative for 1,4-butanedIol, f4.3 % relatlve for adlplc acld, and f19% relative for TDI or f13% relative for MDI. The precision for the number average molecular weight determination was f 1 8 % relatlve for a polyester of about 1000 Mn and f15% relative for one of 2000 Mn.
Proton nuclear magnetic resonance spectroscopy (‘HNMR) is used extensively in our laboratories for both the qualitative and quantitative analysis of polyesters, polyester urethanes, and polyether urethane polymers. Early workers in the field of ‘H NMR established the general utility of this technique for the analysis of polyester polymers (1-5). Proton NMR methods for the identification and compositional analysis of polyester and polyurethane polymers are described in a review by Kasler (6). Brame, e t al., describe the application of ‘HNMR for the analysis of both polyether and polyester urethane polymers (7). This paper gives a table of chemical shift correlations and describes the quantitative analysis of these polymers. Quantitative data from the ‘HNMR analysis of a polyester urethane polymer are compared with data obtained by wet chemical analysis of the same polymer. The application of ‘H NMR for the determination of the number average molecular weight of isocyanate terminated 722
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
linear polyurethanes has been reported (8). Here, the end groups are reacted with dimethylamine and the number average molecular weight of the polyester urethane determined from the ratio of NMR absorptions of the chain segments in the polymer backbone to those of the dimethylurea end groups. In this paper, we describe the application of ‘HNMR (220 MWz) for the compositional analysis of polyester urethanes and for the determination of the number average molecular weight of the polyester moiety. Both precision and accuracy of the ‘H NMR technique are reported. EXPERIMENTAL Polybutylene Adipate-MDI Based Polyester Urethane Polymer. The polybutylene adipate-MDI polymer used for the accuracy determination was prepared from a commercial grade polybutylene adipate having a number average molecular weight of 883 g/mol as determined by hydroxyl number analysis and a commercial grade methylene-bis(4-phenylisocyanate)(MDI). Solid MDI (54.4g, 217.6 mmol) was added to a stirred, nitrogen-blanketed reaction flask containing (250g, 283.1 mmol) polybutylene adipate at 55 “C. The mixture was heated to initiate the reaction. After the reaction exothermed, the product was cast into pans coated with Teflon non-stick finishes. The polybutylene adipate-MDI based polymer used for the precision determination was a commercial polymer and was not modified in any way for this study. Polybutylene Adipate-TDI Based Polyester Urethane Polymer. The polybutylene adipate-TDI based polymer was obtained from a commercial source and used in this work without further modification. Sample Preparation for ‘H NMR Analysis. The polymer samples were prepared for ‘HNMR analysis by dissolving 0.1 g of the polyester urethane polymer in 1 mL of AsC& solvent containing 1% of either tetramethyisilane (TMS) or hexa-
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