a 30-cc/min helium carrier gas flow rate, and flame ionization detectors. A 1O:l splitter divided the effluents between the flame ionization detector and the infrared cell. Ten parts went to the infrared cell and one part to the flame ionization detector. ?'he spectra were recorded on a Honeywell Visicorder recording oscillograph. Figures 10 and 11 show data obtained when this system was used to analyze 2 p1 of a synthetic mixture containing 10 acetone, 10 n-butyraldehyde, 10 % isovaleraldehyde, 20 diethyl ketone, 10 n-heptane, 20% toluene, and 20% butyric acid. Figure 10 displays the gas chromatogram. Figure 11 shows seven selected scans obtained by the Model 563 spectrometer on samples corresponding tu those observed in Figure 10 at points A , B , C , D , E, F, and G, respectively. Each of these spectra is labeled with a letter from A to G in accordance with the point in Figure 10 to which it corresponds. Spectra A , B, and C indicate that the first three peaks in the gas chromatogram are acetone, n-butyraldehyde, and isovaleraldehyde. During the rise and fall of each of these three G C peaks, several more IR spectra were recorded and were characterized by coincident rise and fall of all observed infrared peaks. This behavior indicates that these first three G C peaks are homogeneous and probably pure. The fourth peak in Figure 10 is impure, containing both diethyl ketone and n-heptane. The chromatogram shows no evidence of this impurity but the infrared spectra provide clear proof of it. The infrared spectra of the effluents of the leading edge of this peak are qualitatively different from those of the trailing edge. The differences are illustrated by
z z
z
z
spectra D and E of Figure 11. Each of these tracen represents a spectrum of a mixture of diethyl ketone and n-heptane. However, the concentration of the ketone can be seen to be much greater in D than E and the hydrocarbon is more concentrated in E. Fifteen other spectra were recorded between D and E. In these 17 spectra (along with a few before and after them), all infrared peaks can be seen to rise and fall with the ketone peaks rising and falling before the hydrocarbon peaks. The fifth and sixth G C peaks in Figure 10 are produced by toluene and butyric acid, respectively. This is indicated by spectra F and G in Figure 11. Qualitative similarity within the group of spectra produced by the fifth G C peak and within the group of spectra produced by the sixth G C peak indicates that each of these two G C peaks is homogeneous. CONCLUSIONS
This preliminary investigation indicates that rapid on-thefly infrared scanning is potentially capable of yielding useful information to help identify G C effluents. Ability to detect unresolved G C peaks appears to be a particularly valuable feature of this analytical method. Chemical sensitivity varies widely with the G C peak width and flow rate, and with the molecular weight and the infrared transition probabilities of the sample. Samples used in this study were of a size that may be employed in larger packed columns.
RECEJVED for review December 31, 1968. Accepted March 10, 1969.
Activation Analysis of Halogens in Photographic Emulsions Using a Neutron Generator E. P. Przybylowicz,' Gilbert W. Smith, J. E. Suddueth, and S. S. Nargolwalla Institute f o r Materials Research, National Bureau of Standards, Washington, D. C. 20234 A nondestructive neutron activation technique for the analysis of chloride and iodide in a silver bromide matrix is described. Chlorine was measured after activation with 14.7-MeV neutrons. The 3.1-MeV gamma rays from were measured without interference. Calibrations were carried out using photographic emulsions containing 10 to 200 mg of chlorine. The relative standard deviation of a single determination at the 10 mg level is 5%: at the 200 mg level it approaches 1%. Iodine was measured via lZ8l produced by (n,?) activation with 2.8-MeV neutrons. A straight line curve was established for 2 to 420 mg of iodine. The relative standard deviation of a single determination at these two levels was 20% and 1%, respectively. The method offers an attractive alternate to existing chemical and instrumental methods for the determination of iodide and chloride in silver halide mixtures because it has the potential for providing rapid analyses with reasonably good precision.
MANYANALYTICAL PROCEDURES have been reported for the determination of chloride, bromide, and iodide in mixtures. The abundance of methods testifies to the importance of the problem and is tacit proof that no accepted methods exist Research Associate from the Eastman Kodak Company, Rochester, N. Y . , at the National Bureau of Standards, 1968.
for the halides which can be applied directly to a variety of matrices. Because the primary light-sensitive properties of a photographic emulsion are determined by the composition of the silver halide component, a need exists to have accurate and rapid methods of analysis for the halides in this matrix. Several methods have been applied to this problem, however, none of these provide the desired speed, coupled with acceptable accuracy. One of the earliest analytical methods used for halides in photographic emulsions was the potentiometric titration with silver nitrate ( I ) . This procedure, while capable of high accuracy and precision, is very lengthy. An alternate titrimetric method which has been used is based upon the automatic coulometric titration of the halides with silver after separation by differential oxidation (2). The method is somewhat faster than the potentiometric procedure, however, because iodide, which is often a minor component, is determined by difference, the relative standard deviation for its measurement is large. Russell (3) reported a specific method for iodide in emul~
(1) W. Clark, J. Chem. SOC.,1926, 749. (2) E. P. Przybylowicz, A. J. Moyse, and T. N. Tischer, unpub-
lished work, 1964.
(3) G . Russell, Sci. Ind. Photogr., 28, 297 (1957). VOL. 41, NO. 6, MAY 1969
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sions based on the oxidation of iodide to iodate, followed by its polarographic measurement. The method is not rapid and is subject to errors from a variable matrix and the irreversible nature of the iodate reduction. Another method which has been used for these measurements is X-ray emission spectrometry. While accurate methods have been reported for the individual halides in organic matrices (4, 5), the attenuation problems in a silver halide matrix are appreciable and variable depending upon its exact composition. These problems are most severe for chlorine and least, for iodine. The purpose of the present study was to examine the potentialities of a nondestructive, rapid neutron activation technique for this analysis. It was expected that in contradistinction to the X-ray emission technique, matrix problems would be considerably reduced with the higher energy gamma rays and, therefore, the analysis would be less dependent upon the composition of the matrix. A survey of the literature indicated a number of thermal neutron activation methods for the analysis of halogens in mixtures which involve radiochemical separation of the individual halides after reactor activation (6-8). This approach is not attractive for routine use in an industrial application where the speed of analysis is often a prime consideration. Several reports are available on the use of small neutron generators for halogen analysis. Atchison and Beamer (9) used a van de Graaff accelerator for the thermal activation of individual halogens in organic matrices. Johnson and Gordon (10) measured chlorine cia 38Clresulting from neutron capture. Lbov and Naumova (ZI) used the 35Cl ( n p ) *?P reaction induced by 14-MeV neutrons to measure chlorine in polymers, paraffin, and graphite. These determinations, however, required 12- to 14-hour irradiations and were followed by radiochemical separation of the phosphorus as Mg2P207. Broadhead and Shanks (12) used 2.8-MeV neutrons for the determination of bromide in sodium chloride utilizing the reaction 79Br (n,n’y) 7gmBr. The lower detection limit for bromine was about 0 . 2 z . A study was made of the possible nuclear reactions using 14-MeV neutrons for the halogens of interest in this study, as well as for the other constituents of a photographic emulsion. The cross section values and decay data were taken from a tabulation of Kenna and Conrad (13) and the “Table of Isotopes” (14). It is clear that the presence of nitrogen in the sample precludes the analytical utilization of many of the
isotopes produced by activation with 14-MeV neutrons because of the positron annihilation peak at 0.51 MeV from 14N (n,2n) 13N and the resulting Compton and bremsstrahlung radiations at lower energies. Only those isotopes giving high intensity photopeaks above 0.51 MeV were considered useful. With this limitation, there are only two isotopes which can be used for the measurement of c h l 0 r i n e - ~ ~ ~ C 1and 37S. Because the cross section and half-life for production of the latter were more favorable, the reaction *7Cl(n,p)33 was chosen for further study. The photopeak at 3.1 MeV from should be essentially free from interference by the other matrix constituents, and being high in energy, less subject to matrix attenuation effects. The measurement of iodide in this matrix with 14-MeV neutrons is not straightforward with present technology. lZ61produces useful radiations at 0.67 MeV; however, this is seriously interfered with by lo8Ag, S0Br, ’*As, loeRh, and Compton continuum from and 3 4 W l . Thus an alternate approach was used for the measurement of iodide. The reactions induced with the elements of interest by 2.8-MeV neutrons produced from the reaction of 150- to 200 keV deuterons with deuterium (12, 15) were examined. While the d,d reaction produces 2.8-MeV neutrons, it is recognized that some of the neutrons are degraded in energy due to scattering and that the neutron energy is a function of the angle of emission. The nuclear reactions induced with the elements in this matrix are n,y and n,n‘y. The 2.8-MeV neutron energy is below the threshold energy required for activation of nitrogen and oxygen, thus one is no longer limited to the use of gamma energies above the 0.51MeV annihilation radiation. The 0.44-MeV photopeak of 281 would be useful for analytical measurements provided the rates of production of lOSAg, lloAg, and 80Brare small in comparison with that for 1281. This was demonstrated to be the case experimentally, although n o specific measurement of cross sections was made. The focus of the work reported here was the development of calibration data for the nondestructive measurement of iodide in silver bromide-silver iodide emulsions, and chloride in silver chloride-silver bromide emulsions. We were not directly concerned with the measurement of bromide, for it is usually a major constituent and its concentration can be obtained by difference once the other halides and the silver have been determined. EXPERIMENTAL
(4) J. F. Cosgrove, R. P. Bastian, and G. H. Morrison, ANAL. CHEM.,30, 1872 (1958). ( 5 ) H. J. M. Bowen, Biochem. J . , 73, 382 (1959). (6) R. A. Duce. J. T. Wasson, J. W. Winchester, and F. Burns, J . Geophys. Res., 68, 3943 (1963). (7) P. Belkas and A. G. Souliotis, Aiialyst (London), 91, 199 (1966). (8) G. G. Goles, L. P. Greenland, and D. Y . Jerome, Geochim. Cosmocliim. Acta, 31, 1771 (1967). (9) G. J. Atchison and W. H. Beamer, ANAL.CHEM.,28, 237 (1956). (10) R. A. Johnson and B. E. Gordon, Tram. Amer. Nucl. Soc., ‘ 7, 328 (1964). (11) A, A. Lbov and I. I. Naumova. J. Nucl. Enerav. -_ Part A ., 12., ‘ 85 (1960). (12) K. G. Broadhead and D. E. Shanks, Int. J . Appl. Radiat. Isotopes, 18, 279 (1967). (13) B. T. Kenna and F. J. Conrad, SC-RR-66-229, “Tabulation of Cross Sections, Q Values and Sensitivities for Nuclear Reactions of Nuclides with 14-MeV Neutrons,” Sandia Corporation, June, 1966. (14) C . M. Lederer, J. M. Hollander, and I. Perlman, “Table of Isotopes,” 6th Ed., Wiley, New York, N. Y . , 1967. I
820
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ANALYTICAL CHEMISTRY
Equipment. The neutron activation facility used consisted of a Cockcroft-Walton generator rated at 2.5-mA beam current and a dual sample rotating assembly. The detector system used in this study consisted of two 4-inch by 3-inch NaI(T1) detectors coupled to a 400-channel pulse height analyzer. Throughout this study the sample and standard were counted sequentially. Details of the program sequencer and sample irradiation assembly have been reported (16, 17). The targets used in the neutron generator were loaded with either 5 Ci/in2 tritium or 6 cc/in2 deuterium. In converting from tritium to deuterium targets, the entire front end of the drift tube assembly was exchanged. Thus there was no possibility for gross tritium contamination in the experiments (15) D. J. Hughes and R. B. Schwartz, “Neutron Cross Sections,” BNL-325, U. S. Government Printing Office, Washington, D. C., 1958. (16) S. S. Nargolwalla, M. R. Crambes, and J. R. DeVoe, ANAL. CHEM.,40, 666 (1968). (17) F. A. Lundgren and S. S . Nargolwalla, ibid., p 672.
Table I. Typical Elemental Composition of Emulsions Used Emulsion #I Silver iodide-silver bromide Grams Element Iodine 0.0043 Bromine 0.2702 Silver 0.3681 Nitrogen 0.0719 Oxygen 6.7730 Carbon 0.2120 Hydrogen 0.8702 Total weight 8.5697
0
2
7s
E 2K )r
e c
W
.-c
Emulsion #2 Silver chloride-silver Element Chlorine Bromine Silver Nitrogen Oxygen Carbon Hydrogen Total weight
3 L
W Q
i
v)
e
c
0
- IK 0
e
I-"
I.o 2.0 Gamma Energy
- MeV
3.0
4.0
Figure 1. Normalized gamma-ray spectra of 14-MeV neutron irradiated silver chloride-silver bromide emulsion
with deuterium targets. In these experiments, the average flux at the sample position was estimated to be 5 X l o 8 n.cm-2 sec-1 for 14-MeV neutrons and 1 x 106 nscm-* sec-' for 2.8-MeV neutrons. Chemicals. All chemicals used in these experiments were either ACS reagent grade or in the case of the organic compounds, Eastman White Label chemicals. The calibration curves were obtained using fine-grain photographic emulsions which had been analyzed chemically for their composition. These consisted of individual emulsions of each silver halide suspended in gelatin. Sample Preparation. Emulsions containing different levels of iodide and chloride in silver bromide were prepared by weighing out varying amounts of the emulsions in screw-cap bottles and melting the mixture by immersing the bottles for 1 hour in 50 to 60 "C water contained in a n ultrasonic stirrer. The composition of two typical emulsions used in these studies is given in Table I. Samples were placed in our standard 2-dram plastic vials (Z1/,-inch long X 5/5-inch in diameter) for irradiation and counting. Powdered samples and flux monitors were packed into the vials using a hand-operated plunger which ensured uniformity of compaction. The photographic emulsions were encapsulated using a different technique. Although the emulsions are set up at room temperature, they melt readily above 40 "C to give a thin liquid. Provided the emulsions are stirred and not held for long periods of time at elevated temperatures, no settling of the silver halide grains is observed. This is true for fine- and medium-grained emulsions, but caution should be exercised with certain large-grained emulsions. Once melted, the emulsions can be encapsulated using the same technique employed for liquids. The vials are first sealed with a hot soldering iron, then the sample is injected into a weighed vial with a hypodermic syringe. After cooling, the sample is weighed and the small needle hole is sealed with a hot iron. The emulsion samples weighed about 9 grams.
bromide Grams 0.0234 0.3199 0.5030 0.0655 6.9212 0.1932 0.8874 8.9136
Chlorine Determination. Chlorine was measured by irradiating the sample along with a flux monitor, which was a full capsule of chlorobenzoic acid, in the dual sample irradiation assembly. The pair was irradiated for two minutes a t full beam (2.5 mA) and allowed to decay for two minutes. The sample was then counted for 10 minutes followed by a five-minute decay. Finally, the flux monitor was counted for 10 minutes. The particular counting sequence used here is not optimum from the standpoint of minimizing analysis time. Although a 10-minute count is desirable for the sample, the flux monitor could be counted for only two minutes after only a one-minute delay, without significantly increasing the overall counting errors. The counting was carried out with the 400-channel analyzer in a pulse height mode, with the gain set such that 0 to 4 MeV was contained in 200 channels. This permitted sample and flux monitor to be counted without the necessity of reading out the data between counts. The readout format consisted of printed data and punched paper tape. Subsequent data handling was accomplished ria a computer. The energy interval from 2.69 to 2.75 MeV was used as a measure of bremsstrahlung from the sample whereas the chlorine peak was integrated from 2.75 to 3.30 MeV for both sample and flux monitor. Iodine Determination. Iodine was measured by irradiating the sample, along with a capsule of ammonium iodide as a flux monitor. The timing sequence included a 30-minute irradiation, one-minute decay, 30-minute sample count, oneminute decay and a five-minute flux monitor count. The analyzer settings were such that gamma energies from 0 to 1 MeV were displayed in 100 channels. Thus, two samples plus their respective flux monitors could be analyzed before readout was necessary. The area integrated for the measurement of iodine was from 0.4 to 0.5 MeV. Correction for bremsstrahlung contribution was made by measuring the counts in the energy interval between 0.58 and 0.67 MeV and then using a measured ratio on pure bromide to correct for its contribution in the 0.4 to 0.5 MeV region. RESULTS AND DISCUSSION
Determination of Chloride in Silver Chloride-Silver Bromide Emulsions. Figure 1 illustrates a series of gamma-ray spectra from the irradiation of the individual elements present in a silver chloride-silver bromide emulsion with 14.7-MeV neutroins. The spectra have been normalized to the same VOL. 41, NO. 6, MAY 1969
821
0.
/
I Sld. Error o f the Mean
[ 4 oetn's] Slope 0,00330 0.000084 ( m i ' ) Inlrrcept 0.00912 f 0.005790
*
0
-v;g
I/
E
0.
0 L
.-c 0 e
s
k
IOK[
X
0.
1 )
.N
0
E
0
0
I.o
0.5 Gommo Energy- MeV
0.
a e
Figure 3. Normalized gamma-ray spectra of 2.8-MeV neutron irradiated silver iodide-silver bromide emulsion
e E)
0
.-ug
o
B
V
I 0
Sld. Error o f the Mian
[2
Del"'$]
Slope 0.0295 f0.00013 (rnp.') Inlorcepl 0,0240kO.01344
0.0 50
100
Milligrams
IS0
200
Chlorine
Figure 2. Chlorine calibration curve flux, counting time, and weight of element to facilitate comparison. The spectrum of I6N (from oxygen) is not included because a two-minute decay time was used after irradiation, before counting. It is clear from an examination of these curves that the measurement of the peak from chlorine at 3.09 MeV will contain a minor contribution from bromine. The contribution from bromine under the chlorine curve is due to bremsstrahlung from the high energy beta particles from '*As decay. This contribution can be accurately subtracted from the counts due to chlorine by establishing the ratio of counts in a background region to those in the peak region for a pure bromide sample. In the analysis of a sample, the measurement of the background can then be used to correct for the contribution in the peak region. The results of the series of calibration experiments are shown in Figure 2. Four determinations were used to
Table 11. Results of Analyses on Emulsions Milligrams of halogen Coulometric Activation Emulsion Analysis valuevalueb 16.7 i 1 . 5 18.8 f 2 . 5 A Iodine 29.6 f 1 . 4 29.8 i.2 5 B Iodine 45.9 f 2 5 C Iodine 44.8 i 1 . 4 76 4 f 0 . 4 76.4 f 2 . 7 D Chlorine 75.6 f 0 . 2 75.8 f 2 . 7 E Chlorine a Results are based on the scatter from triplicate determinations. b Results are the weighted means of duplicate determinations. The errors are the weighted mean standard errors of the weighted means.
822
ANALYTICAL CHEMISTRY
0
100
zoo
300
400
MilliQramr Iodine
Figure 4. Iodide calibration curve establish each point on the calibration curve. A weighted mean was then calculated for each point along with the propagated statistical error. The error limits shown on the calibration points are weighted 1 u values; the line is a least squares fit to the points shown using the Gram-Schmidt Orthonormalization calculation. The line has a slope error of about 2.5z (relative) which is somewhat larger than expected on the basis of the statistical error of each point. The magnitude of this slope error and the fact that the calibration line does not intercept the origin, may indicate some inhomogeneity problems with the calibration standards. By using this line, two different chloride containing emulsions were analyzed. The results of these analyses are shown in
Table I1 along with results obtained by a chemical analysis of these emulsions. The agreement between the chemical method and the activation method is considered good. Determination of Iodide in Silver Iodide-Silver Bromide Emulsions. Figure 3 illustrates a series of gamma-ray spectra from the irradiation of the individual elements present in a silver iodide-silver bromide emulsion with 2.8-MeV neutrons. Here again the spectra have been normalized to the same flux, counting time, and weight of sample to facilitate comparison. In the analysis of the samples, the amount of silver present yields an insignificant amount of activity in the region of the iodine peak. The Compton continuum from the 0.51 and 0.62 MeV 60Brpeaks, however, contributes significantly to the iodine peak and therefore must be accurately corrected for. This is done by measuring the g0Br peak at 0.62 MeV using an energy window from 0.58 to 0.67 MeV and multiplying the counts found in this region by a factor which ratios these counts to those in the iodine peak (0.40 to 0.5 MeV) from the irradiation of a pure bromide sample. The calibration curve for iodide is shown in Figure 4. Two determinations, statistically weighted, were used to establish each point on the calibration curve. The error limits shown on the curve are weighted 1u limits and the line is a least squares fit. The error of the slope is less than 0.5 (relative) which is considered excellent for this analysis. Results for the analysis of three silver iodide-silver bromide emulsions are given in Table I1 along with chemical analyses on these same emulsions. It will be noted that the relative standard errors (lu) for both methods overlap for each sample indicating that results by the two methods, for the number of determinations made, are statistically indistinguishable.
Neutron Attenuation and Sample Self-Absorption Effects. It has been well recognized (16) that neutron attenuation and gamma ray self-absorption effects must be corrected for in order to obtain accurate results in neutron activation analysis. With the comparative analytical technique used in these studies, it is important that all points on the calibration line, as well as the sample subsequently analyzed, have approximately the same attenuation. This would permit direct analytical use of the calibration curve without the necessity of correcting for attenuation differences. In order to check whether this was the case for these samples, attenuation factors were calculated for two points on each calibration curve (the lowest and highest points) and for one of the unknown samples for both chlorine and iodine determinations used procedures previously reported (16). The total correction factor was then calculated for two of the points using the lowest point on the calibration line as a reference point. These calculations showed that the maximum error which would result if no attenuation corrections were made is about 0 . 5 z . In all cases in this study, correction for attenuation was neglected without introducing a significant error. ACKNOWLEDGMENT
The authors thank T. Whitely of the Eastman Kodak Research Laboratories for supplying the photographic emulsions used in these studies. They are also indebted to D. Bush and T. Tischer of the Kodak Laboratories for providing chemical analyses on these emulsions. Computational assistance of Sheryl Birkhead of the National Bureau of Standards is gratefully acknowledged. RECEIVED for review November 18,1968. Accepted February 6, 1969.
Effect of Selected Solvents on the Viscosities and Oxygen Contents of Asphalts M. A. Abu-Elgheit,' C. K. Hancock,* and R. N. Traxler Hightvay Research Center, Texas A&M Uniaersity, College Station,Texas 77843 Estimation of the effect of aging, during service, on the properties of asphalts in asphalt-aggregate mixtures is a problem faced by highway engineers. It i s not feasible to measure these properties in situ. Current practice is the solvent extraction of the asphalt from the mixture and subsequent removal of the solvent by distillation. Benzene (a), benzene-ethanol mixture (b), trichloroethylene (c), and l,l,l-trichloroethane (d) were used to determine their effects as solvents on a series of six asphalt cements used in the construction of bituminous pavements. Magnitude of hardening (measured by viscosity at 25 "C) increased in the order (a) through (d). Oxygen content was determined by neutron activation analysis in original and recovered asphalts. In general, the recovered asphalts had lower oxygen contents than the reference asphalts.
ASPHALTSare extracted from mixtures with stone (paving mixtures) for two reasons. First, to determine the amount of asphalt in the mixture and second, to determine changes in consistency and composition of the asphalt that may have occurred during service life in the pavement. In order for this
procedure to be valid, the solvent must not cause a significant change in the consistency or composition (especially the oxygen content) of the asphalt and the recovery from the solution must be carefully conducted to ensure that the asphalt is not markedly hardened by oxidation and over-heating during the recovery process. EXPERIMENTAL
Apparatus. A vacuum rotary thin film evaporator was used to remove the solvents from the extracted asphalts and to protect each recovered bitumen against damage by temperatures above 100 "C (1). 1 Present address, Department of Chemistry, Faculty of Science, Alexandria University, Alexandria, Egypt, U.A.R. Present address, Department of Chemistry, Texas A & M University, College Station, Texas 77843
(1) R. N. Traxler, Proc. Assoc. Asphalt Pacing Technol., 36, 546 (1967). VOL. 41, NO. 6,MAY 1969
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