1484
ANALYTICAL CHEMISTRY
powder on the right side. I n the same experiment they were also able to compare the replica image with the direct transmission image. It is clear that without the replica image it would scarcely be possible to deduce the regular structure of the precipitate from the direct image alone. The shape in Figure 8, A , has some branches stemming from the V-axis. The branches have an almost uniform width of about 1 micron, or rather slightly Fidei at, the farther ends of the V-axis. This V-shaped precipitate is, in the authors' opinion, one side of an X-shaped axis, the branches appearing only within the acute angle of the V-axis, so that it also seems to belong to a cross-shaped type. Figure 9 shows precipitates from 0.0131 solution. They are similar to those in Figure 8, A , but not so large in size, and the mosaic blocks are not so clear. Figure 10 shows precipitates from O.OO5M solution. They have a butterfly shape, and the authors believe that they grow to an X-axis, with branches both inside and outside of the acute angle. Figure 11 shows the simplest type of precipitates obtained in this experiment. They are also similar to a cylindrical lens as are those in Figure 6, but they are not so large, and they are uniform in size. Were it not, for the replica method, one might suppose that these precipitates have rectangular and spindle shapes. But the work reported here confirmed that they have only one shape, and that the convex surface of the precipitate is not round like a lens. but is composed of four planes.
Mixed a t the boiling point, the size of the precipitates is proportional to the concentration throughout this experiment, and the velocity of growth is increased, so perfectly shaped precipitates can be seen even a t 0.1M. Independent of the mixing temperature, precipitates from higher concentrations have a complex crystal shape, and precipitates from 0.OOlM have the simplest shape and are small. Generally speaking, the large precipitate is easy to filter and the simply shaped precipitate is free from contamination. I n the case of barium sulfate, the larger precipitates have a complex shape and a large surface area. The size of the precipitate from 0.001.M solution a t the boiling point is small (about 2 microns) and its shape is the simplest, so the authors feel that these precipitates are the most free from contamination. The predominant shape of precipitates a t room temperature is a perpendicular cross shape (Figure 4), and that at the boiling point is an oblique cross shape. From this experiment it is clear that precipitates from a definite concentration have a definite characteristic shape, so one can deduce the conditions of the precipitation from the shape of the precipitates. It is obvious that the replica method is of value in the study of powdery substances, because the surface of the powder is shomn by the use of the replication, and no attention need be given to specimen change through electron bombardment.
DISCUSSION
(1) Fischer, R. B., ANAL.CHEM., 2 3 , 1667-71 (1951). Bull. Eng. Researchlnst. Kyoto Univ., 1, 37-43 (1952). (2) Nagari, S., (3) Okada, S., Kawane, ll.,and l l a g a r i , S., Mem. Fac. Eng. Kyoto C'n~t..13. 198-208 11951). (4) Okada, S. and l l a g a r i , S . , Bull. Eng. Research Inst. Kyoto Univ., 3, 59-63 (1953). (5) Suito, E., and Takiyama, K., Proc. J a p a n Acad., 28, 133-8 (1952). RECEIVED for review August 9, 1954. Accepted March 22, 1955.
In the case of the direct miying of both reagents a t room temperature. the size of the precipitates is smallest a t the highest conrentration (O.lM), and is largest a t medium concentration (0.01.11). Below O . O l M , the size of the precipitate is proportional to the concentration and the precipitate has a definite shnpc tlt.lwnding upon the concentration.
LITERATURE CITED
Flame Photometric Determination of Manganese WILLIAM A. DIPPEL'
and
C L A R K E. BRICKER
Department of Chemistry, Princeton University, Princeton,
A rapid method for the flame photometric determination of manganese in a variety of materials is described. The intensity of the emission of the manganese line at 403.3 mp is measured for this determination. Any enhancement or inhibition of this intensity by other ions present can be corrected by a standard addition technique. General background radiation in the vicinity of 403.3 mp can be detected from the intensity of the emission at 400 and 406 mp, respectively. Correction for such interference can be applied without any adverse effect to the standard addition procedure.
A
LTHOUGH several authors (8,5, 7-9) have reported that manganese can be determined by means of flame spectroscopy, the details of the procedures, in most cases, have not been reported, and the instruments used have been homemade adaptations of Lundegirdh's apparatus employing photographic recording of intensities. -411 of the previously reported methods have been concerned with the determination of manganese in organic matter or in minerals or rocks. After preliminary studies confirmed that several parts per million of manganese could be determined easily by flame photometry, a n investigation was undertaken in order to establish 1
Present address, E. I. du Pout de Semours & Co., Carney's Point, N. J.
N. 1. rapid procedures for the determination of this element in complex materials such as rocks and alloys. ris Kuemmel and Karl ( 5 ) have pointed out, the application of flame photometry in the metallurgical field has not been very widespread. I n addition to their paper on the determination of alkali and alkaline earth metals in cast iron, the only other metallurgical analyses employing flame photometry previously described are the determination of sodium and potassium in lithium metal ( d ) , the analysis of lithium in magnesium-lithium alloys (IO), the determination of traces of sodium in aluminum ( I ) , and the determination of indium in aluminum (6). This paper describes rapid procedures for the determination of manganese and presents simple techniques for reducing the errors in this determination caused by interference phenomena encountered with complex solutions containing a number of different chemical components present in the original samples or introduced by the dissolution procedure. APPARATUS
Measurements of emission intensities were made with a Beckman Model DU spectrophotometer equipped with a Model 4030 atomizer-burner employing an oxygen-acetylene mixture. The regular blue-sensitive phototube in the spectrophotometer was replaced by the Model 4300 photomultiplier accessory furnished bv the manufacturer. The manganese emission intensities were measured a t a wave length of 103.3 mp employing a slit width of 0.06 mm.
1485
V O L U M E 2 7 , NO. 9, S E P T E M B E R 1 9 5 5 Table I.
Results of Manganese Determinations
Sample NBS burned magnesite KO.104 KBS manganese bronze, 62G
NBS nickel-copper alloy, h-0. 162 Stainless steel F
llanganese. 70 Piesent Found 0.43
Error,
70
0.42"
-2.3
1 26 1.38 1.32
+2.3
AI..
2.28 2.45 2 . 36
+0.8G
Av.
1.68 1.67 1.68
-1.7
AT.
1.29
2.34
1 71
Stainless steel No. 8 Manganese ore N o . 134
Re1ati ve
0.76 42.3
0.76b 46.1
40.4 4v.
0.0
+2.1
43.2
Aluminum manganese No. 1 lL6 16.36 +A,,? Aluminum manganese No. 2 1.82 1.83b +O.: a Reported as manganese oxide. Values corrected for very large inliihition on eiiiission of manganese.
REAGENTS AVD STANDARDS
-111 chemicals used were of analytical reagent or C.P. grade. A standard manganese solution containing 1000 p.p.m. of manganese was prepared by dissolving 0.3957 gram of previously dried Baker's analyzed reagent grade manganese dioxide (less than 0.3% impurities) in concentrated hydrochloric acid. This solution was evaporated to dryness, and the residue was diluted with water to 250 ml. Suitable portions of the standard manganese solution were diluted with water so that solutions containing 50, 100, 150. and 200 p.p.m., respectively, were obtained. When the intensity of the emission a t 403.3 mp from each of these solutions was plotted against the concentration of manganese, a linear calibration curve was obtained. That is, if t'he sensitivity of the instrument was adjusted so that the solut'ion containing 200 p.p.m. of manganese gave :t reading of 100 on the per cent transmittance scale, the solution with only 50 p.p.m. of manganese shon-ed an emission of 25 on this same scale. Thus, the calibration curve for manganese is linear up to a t least 200 p.p.m. of manganese, as contrasted to a considerable number of metallic ions which do not give linear calibration curves over this same concentration range. The reproducibility of the individual readings for the calibration curve was usually within 3 ~ 0 . 5division on the per cent transmittance scale of the spectrophotometer. PROCEDURES
Elimination of Interferences. I n connection n-ith a broad program of study on flame photometric interferences, it was found that the emission from an 0.0018M manganese solution which contained either 0.1M phosphate or sulfate was reduced 25 and liY& respectively. On the other hand, the same concentration of chloride and perchlorate ions increased the emission intensitjof 0.0018.11 manganese 4 and lo%, respectively. Copper and zinc ions when present in amounts equivalent to the manganese concentration had no effect on the intensity of the emission a t 403.3 mp, but when these ions were present in larger amounts, as in a brass sample, a 5 to 10% decrease in the intensity of the manganese emission was observed. In addition to the int'erferences just mentioned, the effect of unresolved radiation has to he considered when determining the intensit,! of the manganese emission. This type of interference is simply :t consequence of the inability of the monochromator to distinguish betmen the manganese line a t 403.3 mp and the energy emitted by some other element present in the unknown solution. This unresolvable background emission commonly occurs as broad bands which result in a general increase in the background intensity. A simple but effective standard addition procedure was used to overcome the first type of interference. I n this method, intensity measurements are obtained on two solutions, one (solution A) containing an aliquot of the unknown solution and the other (solution B ) containing the same quantity of unknown solution plus a measured volume of the standard manganese solution.
The quantity of manganese in each of these solutions is then determined from their measured emission intensities and the standard calibration curve. Subtracting the quantity of manganese found in solution A from that found in solution B yields an amount of manganese equal to that added when there is no inhibition or enhancement. When one of these effect8 is present, however, the quantity of manganese found by subtraction is greater or less than that added. I n such cases, the true manganese content of solution -4is found by multiplying the observed manganese content by a factor which corrects for the interference. This factor is found by dividing the quantity of manganese added to solution B by the amount of manganese found by subtracting the observed manganese content of solution B from that of solution 11. The type of interference resulting from the presence of broad band emission can be eliminated by subtracting this background radiat,ion from the intensit!. measured a t the wave length of the analysis line. In the determination of manganese employing the spectral line at, 403.3 mfi) this was done by measuring the background intensity a t both 400 and 406 mp, where the sharp manganese line did not show any measurable emission. &leasurements are taken on both sides of the manganese line in order to establish the fact that there is no fine structure in t'he background in this region of the spectrum. If the background is found to be of equal intensity on either side of 403.3 mpLIit is assumed that the intensity level is constant within this narrow \vaw lcrigth interval, and that correction for this type of interference c:iii be made hy merely subtracting this background intensit,y from the intensity measured a t 403.3 mp. If, however, the intensities measured a t 400 and 406 nip are not equal, the average of t,liese two readings is taken as the background correction. This procedure assumes that the changr in hackground intensity within this narrorv wave length interval is linear, After correction has been made for the background in this manner, the st,andard addition procedure ran be u s d to correct for enhancement8 or inhibi t ion. Dissolution Procedures. ~\IINERALS. Lipproximately0.5-gram samples of the dried poTYderedmateria1 wereweighedintoplatinuni crucibles. I n the case of carbonate rocks, in order to prevent loss of sample by the evolution of carbon dioxide, the samples n-ere first covered with distilled water before perchloric acaicl was cautiously added. Sfter the evolution of carbon dioxide v a s complete, 5 ml. of perchloric acid and 5 ml. of hydrofluoric acid were added and the solution was evaporated to dryness. I n order to prevent bumping during this evaporation, the crucible \vas heated with a medium hot plate and an infrared lamp. The IYhite residue obtained by this treatment was dissolved in distilled xater and diluted to a final volume of 100 ml. For the determination of manganese, aliquots of this solution were talreii and diluted to contain less than 100 p.p.m. of manganese. ALLOYS. Brasses, bronzes, and alloys of nickel and copper were easily dissolved in concentrated nitric acid. I n e w h case, accurately weighed samples containing 0.2 to 1 gram of fine turni;gs were dissolved in 10 ml. of concentrated nitric acid. -1fter dissolution of the samples was complete. the solutions were evaporated to dryness and the residues dissolved in dilute hydrochloric acid. The solutions were then diluted to 100 ml. Aliquots were taken for analysis and diluted to contain less than 100 p.p.m. of manganese. A stainless steel sample was treated with dilute sulfuric acid (1 t o -I) and then warmed until solution was complete. .ifter the addition of 5 ml. of nitric acid, the solution was evaporated to a small volume. A heavy residue was formed which was difficult to redissolve. Consequently, prolonged heating and escessive evaporation were avoided in subsequent samples, and the solution containing a large excess of arid was diluted to 100 ml. with dist'illed water. Aliquots of this solution, diluted to c.ontain less than 100 p.p.m.. of manganese, were taken for analysis. The standard addition technique was successful in these cases even in t'he presence of a very high concentration of sulfate ion which normally behaves as a strong inhibitor. RESULTS .4ND DISCUSSION
The standard addition technique revealed no examplcs of enhancement of the manganese line in the analyses reported here. On the contrary, inhibition was found in every case except for the magnesite and manganese ore samples, with correction
1486
ANALYTICAL CHEMISTRY
factors varying from 1.25 to 2.38. Corrections for unresolved background emission were necessary with the magnesite, the stainless steels, and the mixture of aluminum and manganese containing a small amount of manganese. The background emission in the magnesite sample was attributed to the magnesium oxide band which has its maximum emission a t 383 mp. The quantity of magnesium in this material mas over 200 time^ the manganese content. The interfering background emission in the stainless steels was probably caused by iron which lias a series of emission lines in the vicinity of 400 mp or by iron oxide which produces a band spectrum in this region, I n the case of aluminum-manganese mixtures, the background emission is detectable only when the sample contains over 85% aluminum and is presumably due to a iveak band spectrum from aluminum oxide. The results of several determinations for manganese on six Tvidely differing materials are given in Table I. The accuracy found in these determinations is consistent with tha,t reported by other workers who have employed the flame photometric technique and is superior to that obtained by other emission spectrographic methods. Although this accuracy may he surpassed in absorptiometric or titrimetric methods for manganrsp.
the flame photometric method should he especially valuable where a simple, reasonably accurate, and rapid determination is required. After dissolution of the samples the time necessary to complete a duplicate analysis for manganese by the method suggested was never greater than 20 minutes. LITER4TURE CITED
Brewster, D., and Clanaen, C.. Iron &e, 166, S o . 18, 88 (1950). Cholnak, (J., and Hubhard. D. AI., ISD. EXG.C H m r . , ASAL.ED., 16, 728 (1944). Gri-gs, AI. d.,Johnstin, II., and Elledge, B. E., Ibid., 13, 99 (1941). Inman, W.R., Rogers, 1%. d.,and Fournier, J. A, har.. CHEY., 2 3 , 482 (1951). Kuernmel, D. F., and Karl. H. L., Ibid., 2 6 , 387 (1954). Meloche, 5'. IT., Ilamsay. .J. 13.. Mack, D. J., and Philip, T. V.. Ibid.,26, 1387 (1954). Mitchell. It. L.. J . Soc. C h e w I d . London. 55. 267 (1936) Xakai, T., h h i d a , It., and Hidaka, S., J . Chem. Soc. Japan: Pure Chem. Sect., 73, 19 (1952). Kamage. H., .Vature. 123, 601 (1929). Strange, E. E., ah-.
