Analytical Results. T h e results of analyses are shown in Table V. Atomic absorption (X.4S) values are compared with the “true” value, which represents t h e batch composition, t h e chemically analyzed value, or an emission flame photometric value. The compositions of the glasses analyzed are indicated under “Glass Type.” Elements present, in excess of 1%, are listed in decreasing order of concentration. Using only results greater than one absolute per cent, the average relative differences from the “true” value for the alkaline earth oxides are as follows: MgO f 0.5yGJ CaO f l.570, and BaO 1.8%. The reasonably good results obtained on a wide range of sample compositions justifies the conclusion t h a t the recommended procedure successfully suppresses most interferences.
*
Table V.
Results of the Analysis of Diverse Glasses
Glass type Si A1 B Ti Mg Li Si A1 Na hlg K Si A1 M g Ti Si A1 Mg Na Li Si A1 Na Ti K Ca F Ba P Sr A1 Ca Mg Na F Ba P Sr A1 Ca Mg Na Ba Si B Zn A1 Ca Zr Si A1 Na Ca P Li Zr B h‘Ig Si Na Ca M g A1 Si A1 Li Zr Ti P A1 Na Zn B Ba Ca Si hlg Si A1 Li Ti Si La Li Ta Ba Sr Si A1 Ba Na Ti Ba Si B Zn A1 Ca F Ba P Sr A1 Ca M g Na Si A1 Na Ba Ti Si A1 Ba Na Ti Si Ba B Zn A1 Ca Mg Sb Si K Ba Na A1 Ca Mg F Si B Ba Ca Na P Si Na A1 Ba F Ti Si Na A1 F Ba Ti
Alkaline earth oxide determined MgO
CaO
SrO
BaO
Concentration, % ‘(True” AAS 3.17 3.65 14.7 4.36 3.64 5.49 10.7 1.52 3.43 5.46 0.56 2.65 LO0 2.95 0.15 0.5 20.04 10.76 12.94 32.9 8.73 6.04 4.37 4.33
3.18 3.66 14.7 4.28 3.64 5.49 10.8 1.54 3.45 5.28 0.45 2.71 4.98 2.65 0.19 0.48 20.0 10.7 12.2 32.3 9.09 5.98 4.36 4.35
LITERATURE CITED
(1) Adams, P. B., Williams, J. P., E-2 S l I 10-17 Methods for Emission Spec-
trochemical Analysis, 4th ed., Am. Soc. Testing Materials, Philadelphia, February 1964. (2) Baker, C. A,, Gorton, F. W. J., U.K. A t . Energy Auth. B e p l . AERE-R-3490
(1961). ( 3 ) Dean, J. A., “Flame Photometry,” McGraw-Hill, New York, 1960. ( 4 ) Dinnin, J. I., ANAL.CHEM.32, 1475 (1960).
(5) Gibson, J. H., Grossman, W. E. L., Cooke, W. D., Ibid., 35, 266 (1966). (6) Grewling, T., Chemist-Analyst 50, 40 (1961). ( 7 ) Herrmann, R., Alkemade, C. T. J., “Chemical Analysis by Flame
Photometry,” Interscience, New York,
Society Meeting, Bradford, Pa., Oct 9-12, 1963. (9) West, A. C., Cooke, W. D., ANAL. CHEM.32,1471 (1960). (10) Williams. C. H.. Anal. Chem. Acta. 22. 163 11960).
1963.
(8) Malenfant, A. L., Adams, P. B., Glass Division, American Ceramic
An Internal Image Discriminating Developer for Mass Spectrograph Plates SIR: The Nattauch-Herzog mass spectrograph, useful for the analysis of trace impurities in solids and, more recently, for high resolution organic work, uses a Schumann-type photographic plate in its detection system. There are several problems associated with the use of mass spectrograph plates. Three of these problems are: reproducibility of the plate response, both within a single plate and from plate to plate; sensitivity of the plate, since the spark source technique itself exists for the purpose of extending detection limits to lower and lower ranges; and problem of the signal-to-noise ratio of the plate. By signal, I mean the ideal positive ion image produced by the mass spectrograph, and by noise, I mean fog. Two types of fog may be considered-background fog, which covers the plate uniformly, and secondary emission fog which is associated with strong lines on the plate. Since one is dealing here with positive ions, the large store of photographic
knowledge based upon exposure of the emulsion by photons must be used with caution. I n a previous paper ( I ) , I reported some preliminary experiments using a surface image developer-Le., a developer which develops only the latent image residing on the surface of the silver halide grains in the emulsion. The more usual developer (typically, Kodak D 19 or Ilford I D 19) contains a stabilizer such as sodium sulfite. This stabilizer may dissolve the silver halide grain during the development process. Such dissolution can have two effects: first, a n image in the grain becomes developable regardless of its location with respect to the surface; second, the development process using a solventtype developer can be a combination of both chemical and physical development. A chemical development process is one in which the silver forming the visual image is obtained from the same silver halide grain on which the latent image resides. I n a physical develop-
ment process, the silver used to form the visual image is obtained from the developing solution itself. I n solvent developers the silver can be obtained from either source, thus resulting in a combination of physical and chemical development. Of the three processes, chemical, physical, or combination, the least easily controlled process is the combination. Therefore, it was decided to experiment with a surface developer in which the process would be confined to the chemical type in the hope t h a t the reproducibility of the process might be improved. This did turn out to be the case, but an additional advantage resulted, perhaps from the fact that the developer chosen acts somewhat less energetically than I D 19. Both the background fog and the secondary emission fog were reduced with respect to the desired image when using the surface image developer. The success in reducing fog through modifications in the development process led to the work reported here. It VOL. 30, NO. 4, APRIL 1966
633
EXPERIMENTAL
Table I.
Developing Techniques
D 19 developer 1. Develop 70" F. 3 min.-D
19 solution undiluted 2. Rinse H20 70" F. 30 sec. 3. Fix Kodak F5 bath 70" F. 1 min. 4. Wash H20 70" F. 20 min. Surface image developer 1. Develop 70" F. 4 min.
500 cc. Hz0 Ascorbic acid 10 g. Elon 2 . 5 g. Kodalk 35 g. Potassium bromide 1.O g. HzO to make 1 liter 2.-4. Follow steps 2-4 in D 19 developer above.
Internal image developer 1. Rinse H20 70" F. 30 sec. 2 . Bleach 70" F. 20 sec.
Potassium dichromate Sulfuric acid (conc.) Sodium sulfate (anhyd.) Chrome alum Silver nitrate H20 to make 3. Rinse H20 TO" F. 15 see. 4. Develop 70" F. 6 min. Hz0 Ascorbic acid Elon Kodalk Potassium bromide Sodium thiosulfate H20 to make 5 . Rinse H2070" F. 30 sec. 6. Fix 70" F. 30 see. 7 . Wash H2070" F. 20 min.
20 g. 2 cc. 4 g. 10 g. 1 g. 1 liter 800 cc. 10 g.
2 . 0 g. 35 g.
1 . 0 g. 10 g. 1 liter
was felt that the latent image of the agents responsible for both types of fog might well reside on the surface of the silver halide grains rather than in the interior. If the positive ions which produce the desired image on the plate were sufficiently energetic to produce an image in the interior of the grain, it might be possible to remove a surface image by a bleach and subsequently to develop the internal image. The result of such a process would be to remove much of the useless noise on the surface and to preserve the useful information in the interior of the grain. Studies based on these ideas show that this indeed is possible. Nearly all of the useful information is duplicated in the internal image while much of the fog resides only on the surface.
Table II.
Ch. curve slope Rel. mean deviation for ch. curve Background transmission Visual sensitivity (coulombs) 70Transmission to produce visible image
634
ANALYTICAL CHEMISTRY
The development process is shown in Table I. The exposed plate is initially rinsed to moisten the gelatin and then bathed in the bleaching solution. The bleach composition was derived from a composition reported by Stevens (4). d second rinse is followed by a conventional developing procedure. The developer used is that reported previously ( I ) to nhich 10 grams per liter of hypo is added to partially dissolve the silver halide grain, and thus expose the internal image to the developing solution. I n principle, D 19 could be used as a developer in this process, but in actual fact, a t full strength it produces a high background fog and thus seems too energetic. The times given in Table I for the prerinse, the bleach bath, and the developing bath were obtained from experiments using Kodak SWR plates exposed to light from a xenon flash lamp to avoid excessive time on the mass spectrograph. Experiments with Ilford &I1 plates exposed to positive ions showed that these times were satisfactory for mass spectrograph plates. The amount of hypo in the developing solution was adjusted to prevent the clearing of Ilford &I1plates during the developing process. Some Kodak SWR plates actually did completely clear using the composition liqted in Table I. For these plates, a composition with tpvo grams of hypo per liter would be preferable. I n the event that the emulqion completely clears in the developing solution, the only developing which can then take place is pure physical development. The result is a plate with a dark brown image nhich can easily be rubbed off the surface of the plate. & i n attempt was made to separate the hypo from the developer-Le., to rinse the plate in hypo and then to develop the plates in a pure surface developer. The resulting plates were excellent from the standpoint of fog, but the sensitivity had been reduced by a factor of lo2. RESULTS
Two techniques are used in our laboratory for evaluating spark-source mass spectrograph plates: the visual technique in which comparisons are made of lines on the plate of equal density and the photometric method in which the density of each line is meas-
Developer Comparison
D 19
Surface image 0.74
Internal image 1.06
5.39
4.01 8370
1 70 S8%
0.50
I
7870
x 10-14 95-97y0
1
x
10-14
98%
3 x 10-16 99%
ured by a microdensitometer. The results of the development process reported here should be discussed for each evaluation method. Each plate submitted to photometric evaluation is measured with a microdensitometer which records the density information in computer-compatible format. This information is used t o compute the characteristic curve for each plate (8). One of the outputs of the computer program consists of four parameters related to a power series expansion of the characteristic curve. During a six-month period using this developer, these parameters mere tabulated and averaged. The result is an average characteristic curve for the internal image developer. The same thing was applied to the D 19 developer and to the surface image developer. The resulting characteristic curves are shown in Figure 1. The slope of the characteristic curve is related to the contrast of the developed plate. For quantitative purposes, a steep slope is desirable since an error in determination of density results in a smaller error in calculated exposure. The slopes of these curves a t a density equal to 507, saturation are tabulated in Table 11. The reproducibility of the development process when studied in this manner would be measured by the amount of spread of the characteristic curve parameters from the average. It was found that the reproducibility of the internal image developer from plate to plate is considei ably better than that for either D 19 or the surface image developer. The relative mean deviation for all the characteristic curve parameters is tabulated in Table I1 for each developer. -4loxer value implies greater reproducibility. Background fog was measured setting the niicrodensitonieter to 10070 transmission with no plate in position. The background transmission due to D 19 was 787,, that due to the surface image developer was 83%, and that due to the internal image developer was 88%. The absolute sensitivity of a plate for each developer may be estimated from Figure 1. The absolute sensitivity of Ilford &I1 plates developed using the internal developer is greater than the sensitivity of the same plates developed using the surface image developer, but in less than the absolute sensitivity of the plates developed using D 19. +4more useful estimate of plate sensitivity may be obtained from the visual evaluation of a plate, since it is this evaluation which places the most stringent requirements on plate sensitivity. I n making a visual evaluation of a plate, it is customary to determine the plate sensitivity by finding the shortest possible exposure which will barely produce a visible image. Then, by comparing this to the exposure
.-.
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-
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.
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.
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-= m
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z
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10-1
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EXPOSURE 1x104 COULOHBS~
Figure I . veloperr
Average characteristic curves for three de-
necessary to produce a barely visible image for the impurity under analysis, it is possible to calculate the concentration of the impurity. Since the monitor system of the mass spectrograph varies in its sensitivity from instrument to instrument, absolute exposures cannot be reported. On the author's own instrument (BE1 MS7), a n exposure of 0.01 nanocoulomb was necessary with D 19 developer to produce a visible image of the lWW+lines. The 'TJisotope has a n abundance of 0.14qb, implying that lo-'' coulomb would he required to produce an image using D 19. The same value was observed using the surface image developer. With the internal image developer, a 0.003-nanocoulomb exposure was required to barely detect the ISOW+ line, implying an exposure of 3 x 10-16coulomh. It should be noted that these "barely detectahle images" depend on the fog in the neighborhood of the lines. With the surface image and internal image developers, a visual image could he reliably detected at a somewhat higher level of transmission than with D 19. The transmission of a barely visible image with respect to a neighboring clear area of the plate was 95 to 97% for plates developed in D 19, 98% for the surface image developer, and 99% for the internal image developer. Although the plates were exposed to different samples, Figure 2 shows some of the properties of the different developing processes. The first plate is developed in D 19 developer. The maximum exposure on this plate is 100 nanocoulombs. The second and third plates were developed using the surface image developer. The maximum exposure on these plates was 300 nanocoulombs. The fourth plate was developed using the internal image developer. Its maximum exposure was also 300 nanocoulombs. The last plate, which is from a different matrix material has a maximum exposure of 1000 nanocoulombs. I t is quite clear that the secondary fog on the last plate is comparable to the fog on the first plate.
.......
_p___.__
...
_ l _
Figure 2. Mass spectrograph plotes showing effects of different developers: top, D 19 max. exposure 100 ncoulombs; 2,3,surface developer, max. exposure 300 ncoulombs; 4, internol developer, max. exposure 300 ncoulombs; bottom, internal developer, max. exposure 1000 ncoulombr
Thus, taking the relative maximum exposures into consideration, the technique results in a reduction of secondary emission fog by at least a factor of 10. When one compares the microstructures of plates developed by these three processes, one can see that the grains produced by the surface image developer and by D 19 developer appear to he composed of a number of filaments clumped together while the grains developed by the internal image developer are quite.regular. One can speculate that the measurement of the density of the plate should be more meaningful in terms of the number of ions involved in the exposure when the density is cansed by regular opaque particles than when it is caused by clumps of filaments. DISCUSSION
Previous work (1) showed that a surface image developer is useful for reducing fog; the present results show that an internal image developer is useful for the same purpose. The explanation of this paradox probably lies in the characteristics of the D 19 developer. This developer, when used undiluted, is so energetic that any of several different developers would produce a substantial reduction in background fog on a Schumann-type plate.
Thus, the work with the surface developer, which was undertaken to find a developer which gave more reproducible results, showed a useful reduction in fog in addition to better. reproducibility. The present work was undertaken to reduce fog with a hypothesis regarding the location of the latent image responsible for most of the background and secondary emission fog. The work showed that the internal image developer results in a substantial reduction in fog, while also improving the reproducibility of the development process. Even more important, the present work shows that 20-k.v. positive ions are capable of producing a useful internal image. By designing a n emulsion in which the sensitivity to the internal image is enhanced, photographic plate manufacturers should be able to produce a superior mass spectrograph plate. One additional point remains to he commented upon. The ahsolute sensitivity of the internal image developer is less than that of the D 19, and yet the sensitivity of the mass spectrographic technique is improved. The reason for this is that the improvement is a result of improvement in signal-to-noise ratio rather than a n improvement in ahsolute sensitivity. Very little has been said in the literature regarding noise in the mass spectrograph technique. It would apVOL 38, NO. 4, APRIL 1966
e
635
pear that reduction in noise is just as important as improvement in absolute sensitivity. ACKNOWLEDGMENT
The author expresses his appreciation to J. R. Mitchell for many helpful suggestions and discussions.
LITERATURE CITED
(1) Kennicott, P. R., AXAL. CHEY. 37,
313 (1965).
(2) Kennicott, P. R.. 12th Annual Conference on Mass Spectrometry (1964).
Also available as General Electric Report RL 37660 (1964). (3) Kennicott, P. R., 13th Annual Conference on Mass Spectrometry (1965). (4) Stevens, G. W. W., “Fundamental
Mechanisms of Photographic Sensitivities,]’ Proceedings of a Symposium Held at the Universitv of Bristol in March, 1950, 3. W. J h h e l l , ed., p . 227, Butterworths, London, 1951. P. R. KEXXICOTT
General Electric Co. Research and Development Center Schenectady, S . Y.
Simple Technique for Rapid Analysis of Radioactive Gases by Liquid Scintillation Counting SIR: Radioactive nuclides in the gaseous phase are usually counted by internal gas ionization chambers, internal sample proportional counters, or Geiger counters (1, 4 ) . Koble gases have been counted by condensation on a liquid scintillator a t liquid nitrogen temperatures ( 3 ) . I n the case of H3 an alternate procedure is to convert the gas t o water by burning and to count the water in a liquid scintillator (4). For beta-gamma emitters a well scintillation crystal is satisfactory for relatively high concentrations (10-6 mole % or higher in the case of Krs5). Internal sample proportional and Geiger counting are absolute methods which can be used for low concentrations of activity; however, impurities in the gas and contamination (radioactive and nonradioactive) in the vacuum system and other equipment present serious problems, particularly xhere a large number of samples are measured (1, 2 ) . Ionization chambers with vibrating reed electrometers are less sensitive and less precise than internal gas counters. The conversion of the gas to water is time-consuming. Condensing the gas on a liquid scintillator is applicable to those gases which dissolve readily in aromatic hydrocarbons and freeze at liquid nitrogen temperatures. It is comparatively complex and time-consuming for routine quantitative assay. A simple method was devised for routinely counting gas samples by liquid scintillation without converting the gas to a liquid. The method is used extensively a t this laboratory in conjunction with the gaseous isotope sales program for determining H3 in He3, and KrS5 in xenon for the concentration range of 10-2 to 10-9 mole %. EXPERIMENTAL
Apparatus. Standard glass tapered joints and stopcocks are attached to hypodermic needles (Figure 1) through which gas samples can be expanded into 25-nil. polyethylene sample vials fitted with self-sealing rubber serum stoppers. A hypo636
ANALYTICAL CHEMISTRY
25ml. Polyethylene Vials
S e l f - S e a l i n g Rubber Serum Stopper Hypodermic Needles
Figure 1 .
Gas sampling system
dermic syringe with the plunger removed is used for adding scintillator solution to the vial. The counter is a Packard Tri-Carb scintillation spectrometer, Model 3003. Procedure. The sample gas is expanded into two evacuated sample vials simultaneously (Figure I ) , and a direct pressure measurement is read with a cathetometer. Pressures are limited t o 25 mm. or less. The stopcocks below the hypodermic needles are closed, and the vials are removed from t h e system. The self-sealing rubber serum stoppers prevent the escape of gas or the leakage of the atmosphere into the vials. The amount of sample in each vial is computed from the pressure and volume measurements. Scintillator solution (7 grams of PPO (2,5-diphenyloxazole) and 50 nig. of POPOP ( 1,4-bis [2- [ (5-phenyloxazolyl) ] benzene} made to 1 liter with toluene) is added to each vial through the hypodermic syringe (plunger removed and needle inserted through the rubber serum stopper) by equilibrating to
atmospheric pressure. This causes considerable agitation of the solution, thus trapping the gas in the solution. The needle is removed, sealing gas and solution in the vial. It is important t o count the samples soon after preparation because some of the trapped gas slowly escapes from the solution to the top of the vial where it is counted less efficiently, so that the counting rate decreases with time. The effect is more pronounced n-ith a soft beta emitter such as H3. The background is checked periodically by expanding He4 into the gas sampling system and into the counting vials through the hypodermic needles, then adding scintillator solution and counting. Efficiency. -In overall efficiency was determined by comparing samples standardized by internal sample Geiger counting ( I ) with liquid scintillation counting. The efficiency for H3 and KrSj was 21.8 and 92.57,, respectively. The absolute beta disintegration rate for liquid scintillation counting is determined by dividing the values obtained
