ments of the amine under analysis permits the estimation of the molar quantity of aliphatic amines with a deviation of about 3 which compares favorably with other analytical procedures for amines (see Table I>. Amines which form borane complexes of low stability, such as aniline derivatives,
may be too easily alcoholized to permit analysis by this method(3-6). RECEIVED for review July 12, 1968. Accepted September 6, 1968.
Chemical Microscopy of 10-Methylacridiniumctaloride Reactions with Platinum Metals and Gold Harold F. Schaeffer Depurtment of Chemistry, Wesfmiizster College, Fulton, Mo. 65251
BY MEANS OF chemical microscopy it has previously been shown ( I ) that an acid solution of acridiniumchloride, without benefit of any other complexing agent, could serve as a desirable reagent for the detection or identification of certain platinum metals and gold when present in acid solutions of their chlorides. The purpose of this paper is to report on the relative efficiency of the derivative 1O-methylacridiniumchloride as a micro reagent for these same metals. EXPERIMENTAL
The reagent solution was a 0.2M solution of 10-methylacridiniumchloride in 1N HCl; this appeared to be near the limit of solubility of the compound at room temperature. Just as in the previous experiments with acridiniumchlo:Ide, test solutions of the respective precious metal ions were prepared by appropriate dilution of stock solutions of gold(III), platinum(IV), palladium@), iridium(III), rhodium(III), and ruthenium(II1); the stock solution of osmium, however, was based on potassium osmate. All stock solutions were in 1N HC1, and all dilutions thereof were made with the 1N acid. Individual tests under the microscope were carried out by allowing a 20-pl reagent drop to flow into a similar droplet of sample solution on a slide. Most observations were made through an 8-nim objective and a 1OX ocular. Tests were considered satisfactory if appropriate crystals separated within 2 minutes. RESULTS AND DISCUSSION
With an acidified osmate solution containing the equivalent of one part osmium in one or two thousand, the reagent caused a prompt separation of an abundance of bright yellow crystals (Figure 1). Many were in the form of plumulose, branched X's, and other aggregates. In plumules the barbs joined the shaft at an angle of approximately 45". By polarized light the crystals appeared faintly dichroic, ranging from a very pale yellow to a slightly deeper shade. As samples were made more dilute there was a decreasing tendency to form the more complex branched aggregates, which were displaced by small yellow prisms. Two principal forms of the latter were observed; one type appeared as parallelepipeds having an extinction angle of approximately 30", while another form resembled slender rods, pointed at both ends, and exhibiting parallel extinction. With an osmium content of only one part in 40,000, none of the plumulose aggregates separated. The reaction permitted the identification of osmium in samples containing as little as one part metal in 150,000, or 7 pprn. (1)
H.F. Schaeffer, Microchem. J.,
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9, 492 (1965).
Figure 1. Crystalline derivative obtained by reaction of 10-methylacridiniumchloride with solution containing osmate Using a 20-pl sample, this was equivalent to the identification of approximately 0.13 pg. For the purpose of merely detecting osmium, assuming the absence of interfering ions, the sensitivity of the reagent could be considered as 0.07 pg, because an adequate crystalline precipitate separated from solutions containing as little as one part osmium in 300,000. Because of the small dimensions of the crystals formed at high dilutions, a 4-mm objective should be employed. At high dilutions, the observations are also facilitated by the use of crossed polars. Solutions of gold(II1) chloride in HCl promptly reacted to form a yellow precipitate of very fine crystals (Figure 2). Even with a gold concentration of only one part in 50,000 a rather abundant precipitate appeared. In general, the crystals were so small that the use of a 4-mm objective was indicated. As a rule, crystals which appeared as elongated rectangles exhibited an extinction angle of 45", while those with pointed ends showed parallel extinction. Identification was possible with a gold concentration below one part in 200,000, or the equivalent of 5 pprn. Another metal for which the reagent showed a high sensitivity was platinum. The yellow precipitate contained small prisms occurring singly, or in the form of crosses, daggers, and some more complex aggregates (Figure 3); there were also occasional parallelepipeds. Many of the individual crystals exhibited parallel extinction, but angles of approximately 10" and 25" were also observed. Positive identifica-
n Figure 2. Crystals of derivative formed with gold
tion of platinum(1V) could be made at concentrations as low as one part in 200,000. At a concentration of one part metal in a few thousand, solutions of palladium(I1) chloride reacted to yield branched yellow aggregates (Figure 4). As opposed to somewhat similar crystals formed by osmium (see above), the barbs of the palladium derivative were perpendicular to the shaft. In addition to these aggregates there were also some smaller crystals in the form of thin parallelepipeds. In their most common orientation the latter crystals exhibited profile angles of approximately 60" and 120". Extinction occurred when a shorter edge was parallel with one of the crossed polars. At higher dilutions the plumulose aggregates constituted a smaller proportion of the precipitate; when the palladium concentration dropped to one part in 25,000 or 50,000 the aggregates no longer were formed. However, by viewing through crossed polars the individual crystals still permitted identification of palladium at a concentration of one part in 100,000. One distinguishing characteristic of the precipitate formed by iridium trichloride solutions was the orange color. The product contained branched aggregates (Figure 5) in which the branches were perpendicular to the central shaft. In addition to these aggregates there were also thin plates, which
Figure 3. Platinum derivative
Figure 4. Palladium derivative appeared as relatively long rectangles or laths. All of these thin plates exhibited parallel extinction. In some preparations a small proportion of the crystals were elongated hexagons, in which case extinction resulted when the long axis was parallel with the plane of polarization. As is frequently the case, there was a general tendency for the crystals to decrease in size as the sample concentration was lowered. Although a fair precipitate could be obtained with a n iridium concentration of one part in 20,000, for the purpose of identification a concentration of one part in 10,000 should be considered the lower limit. At this dilution the use of a 4-mm objective is recommended. With ruthenium(II1) the reagent yielded a precipitate having a reddish brown macro appearance; viewed through an 8-mm objective the crystals showed a deep-yellow to amber color. The preparations were best observed through crossed polars. The crystals were in the form of thin leaves or plates, frequently irregular in shape. In some specimens the surface took the form of an elongated rectangle, with or without terminal notches; in other instances the plates appeared as parallelograms, with profile angles of approximately 45
Figure 5. Iridium derivative VOL. 40, NO. 14, DECEMBER 1968
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Figure 6. Ruthenium derivative
Figure 7. Derivative obtained with cupric ion
and 135". There were also elongated hexagons (Figure 6). Generally, for all forms, extinction occurred with the long edge of a crystal parallel with the plane of polarization. Not infrequently some of the thin crystals were oriented in a plane perpendicular to the surface of the slide. Under favorable conditions ruthenium could be identified in samples containing as little as one part in 2000. Rhodium(II1) was the only member of the platinum group which failed to yield a crystalline product at the concentrations considered in this study. Even a 1 solution of RhCb (approximately 4.7 parts Rh per thousand) failed to yield a precipitate with the reagent under the conditions of the experiment. Under these circumstances it was of interest to find that samples in which the concentration of gold, platinum, palladium, or iridium represented as little as one part
Table I. Sensitivity of Meth ylacridiniumchloride Reagent. Maximum Metal dilution pg Identified identified 2.0 x 105 0.10 Au Pt 2.0 x 105 0.10 1 . 5 X IO6 0.13 os 1.0 x 105 0.20 Pd 2.0 x 104 1.00 Tr 2.0 x 103 10.00 Ru a
Temperature range was 22-23 "C.
TabIe 11. Comparison of Acridiniumchloride and Methylacridiniumchloride Reagents. Lower Limits of Identification (in terms of p g of metal per 2 0 4 sample) 10-MethylAcridiniumchloride acridiniumchloride Au
Pt os Pd
Ir RU a
0.67 0.80 1.00 1.33
1.33 ...
Temperature range was 22-23 "C.
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0.10 0.10
0.13 0.20 1.00 10.00
in 10,000, good tests for the respective metals were obtained even in the presence of more than 20 times as much rhodium; furthermore, the presence of a moderate rhodium concentration did not interfere with tests for ruthenium. Because copper may be a component of certain precious metal alloys, the efi'ect of the methylacridiniumchloride reagent was tried on a 0.25M solution of cupric chloride in 1N hydrochloric acid. Under the conditions of the experiment no precipitate resulted. However, very interesting crystals of a copper complex were obtained by adding a few fine particles of solid cupric chloride to a reagent drop (Figure 7). It was also of interest to find that, in mixtures, the presence of Cu(I1) ion caused no serious interference in the detection of gold, platinum, palladium, iridium, or osmium. To illustrate, when the concentration of any of the latter was equivalent to one part in 10,000, characteristic crystals separated upon addition of the reagent, even when the test sample contained 80 times as much cupric ion. CONCLUSION As a reagent for the identification of precious metals at low concentrations, the IO-methylacridiniumchloride showed its greatest sensitivity for gold(III), osmium(VI), and platinum (IV) for which the limits of identification were in the range of 0.07-0.13 pg, while rhodium(II1) yielded no precipitate at the concentrations studied (Table I). It was of interest to note that the presence of rhodium(II1) or copper(I1) did not interfere with the response of the other metals. Probably the most serious disadvantage of this reagent is the fact that it is not generally suited for identifying the precious metals in mixtures of each other. As shown in Table 11, compared with acridiniumchloride, the 10-methyl derivative has been found the more efficient precipitant of the precious metals. I n regard to the numerical data which have been cited in this paper, it is important to consider the fact that the crystalline complexes formed by both reagents are temperature-sensitive, so that in a very warm laboratory the minimum concentration to yield a satisfactory test is appreciably increased.
RECEIVED for review July 10,1968. Accepted August 28,1968. Work supported in part by a grant from The Research Corporation. Presented at the Southeastern Regional Meeting, Atlanta, November 1967.
