ANALYTICAL CHEMISTRY
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amounts up to 50 microgram. The density readings were 0.8 to 1.0 a t the upper limit. The curves for technical grades of sodium pentachlorophenate lie closer t o the curve for the pure material than would be expected, probably for the reason discussed for the methylene blue method. When 5-ml. samples of s n aqueous solution containing 25 micrograms each of technical sodium pentachloraphenate were analyzed, the following amounts were recovered: 23.6, 22.6, 24.0, 26.4, 22.4, 25.2, 24.2, and 27.0 micrograms. Precautions. The chloroform layer should be removed from the tubes within 30 minutes from the time of extraction because the color darkens on standing in contact with the aqueous phase; after removal the color remained stable for at least an hour, provided evaporation of the solvent was prevented. The water used
for the blank should be the same as that in the unknown solution; provision for this should be made when conducting field work and the samples are to he examined in the laboratory. Iuterfering ions, such as those found in hard water, and iron or copper may be dealt with by adding a small amount of sodium citrate to the sample as explained above undcr the methylene blue method. LITERATURE CITED
(1) Berry. E. G.. Nolan, M. O., and GonaBles, J. 0.. Pub. Health Rapt.. 65,939-50 (1950). (2) Nolan, M. 0.. and Berry, E. G.. Ihzd., €4,942-9 (1949). (3) Wallin, G. R..ANAL.CHEM..22, 1208-9 (1950). R E C E I VA ~ ~Dr i 4. l 1951
lsoquinoline in Chemical Microscopy HAROLD F. SCHAEFFER, Valparaiso University, Valparaiso, Ind. Although many heterocyclic nitrogen compounds, including quinoline, are usefill for the detection of various ions, no previous workers have reported on the miemchemical applications of isoquinoline. The investigation reported was carried out to determine the feasibility o f applying isoquinoline as a reagent in ohemioal microscopy. A procedure has been developed whereby isoquinolinium hydrochloride, in the presenoe of thiocyanate ion, can he employed for the microehemioal detection of zinc, cadmium, copper, and whalt, because each yields characteristic microcrystals with the reagent. One advantage of the prooedure is the ease with which cobalt and copper can he deteoted in the presence of each other and of nickel. Positive tests can be ohtained on a drop of solution, with the copper concentration as low as 1 part in 15,000 and the wbalt eoncentration as low as 1 part in 4000. For zinc the sensitivity approximates that of copper, but f o r oadmium it is only approximatelyone tenth as great.
A
LTHOUGH several ohemists (I*) have shown that quinoline m the presence of ammonium thiocyauste may serve m a reagent for the microchemical detection of certain cations, little attention has been given to the merits of isoquinoline and ammonium thiocyanate. Recently Spakowski and Freiser ( 4 )demonstrated that these reagents can he used for the quantitative precipitation of copper and zinc, hut they did not investigate the possibility of adapting the isoquinoline-rtmmonium thiocyanate combination to ohemical microscopy. It has now been found that the reagent oan be employed in the microchemical detection of several cations, because the resulting metallo-organic compounds separate in the form of characteristic microsoopic crystals.
PROCEDURE
In performing the test far vinc ion a small drop of the prepared reagent is caused to flow into a droplet of dilute test solution on a slide. In the presence of various aino salts, including the acetate, chloride, sulfate, and nitrate, characteristic crystals and clusters will separate (Figure 1). The composition of these crystals corresponds t o the formula Zn(CQH,N)x(CNS)2. With zinc acetate, for example, goad testa have been obtained on solutions containing 1 part of zinc in 15,000. Using a teat drop of 15 cu. mm. the reaction may detect the presence of 1microgram of Einc. The behavior of dilute solutions of ~ i n cchloride is approximately the same as that of the acetate, hut the presence of zinc nitrate appears to decreme the sensitivity. The temperature of the laboratory also influences the sensitivity of the tests, as very dilute solutions did not respond as well when the temperature was unusually high for a prolonged period. In the presence of cadmium acetate the isoquinoline-ammonium thiooyanate reagent causes the separation of characteristic orystals (Figure 2). Good tests have been ohtaiued with a oadmium ion concentration of 1 part per 1000, but at a dilution of 1 part in 5000 the test is not reliable. Because of the small dimensions of the crystals generally formed in the cadmium test, it is preferable to observe them through an &mm. objective instead of the more common 16-mm. lens. The test is much less
REAGENT
hydrochloride and 0.5 M-in reapeat t o thiocyanate. ‘As st this concentration part of the solute may eventually separate from solution, it is advisable to work with a frefih reagent prepared from two stable stock solutions. One of these is a 1 M solution of ammonium thioevrtnate. The other is a 0.4 M solution of iso~
~
0.2 .“m.
tiins.- The iioq$noline c&stks obtained by freezing the Eastman Xodek Ca. “practical” grade were found satisfsotory for the purpose.
Figure 1. Crystals Formed by Reaction of 1soquinolir.eAmmonium Thiocyanate Reagent with Zinc Chloride
V O L U M E 23, N O , 11, N O V E M B E R 1 9 5 1 sensitive when performed on solutions of cadmium nitrate or chloride. A very beautiful result is ohtained with solutions of cobalt compounds. Generally, very soon after the reagent is applied, a blue oil-like liquid begins to separate, especially along the edge of the preparation. Gradually deep blue crystals develop, the length of time required depending somewhat upon the eaneentrei tion of cobalt ion in the sample. The form of the crystals may
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under the conditions of the test. Unless the concentration is very low (less than 1 part in 2500), the green precipitate can be distinguished by the unaided eye. Under the microscope a pasibive test can he ohserved when the copper content is as low a8 1 part in 15,000, whether the salt he present as acetate, chloride, or sulfate. A very useful property of the isoquinoline-ammonium thiocyanate reagent is that it permits the detection of cobalt and copper in the presence of each other and in the presence of niokel. In spite of the sensitivity of the test for copper, the blue crystals which indicate the presenoe of cobalt have been obtained even when the test drop contained a considerable excess of copper. For example, when the reagent is added to a test drop containing 1 part of cobalt and 5 parts of copper per thousand, the result is the formation of a green precipitate which, to the unaided eye, resembles the precipitate obtained when cupric ion is the only cation present. Under the microscope, however, the observer will see the gradual separation of a light green liquid along the edges of the preparation, followed by a blue liquid. Eventually the deep blue crystals of the cohalt compound dcidop.
~
0.1 m,...
Figure 2. Typical Crystals Formed b y Reaction of Isoquinoline-Ammon i u m Thiocyanate Reagent with C a d m i u m Chloride vary in different cases, but this is no handicap; the blue color
itself is characteristic of cobalt (Figure 3). In cobalt chloride solutions satisfactory tests me obtained with a cobalt ion concentration as l o a as 1part in 4000. In the case of cobalt sulfate the concentration of metal ion may be as low as 1 part in 2000, but the orystals may not appear for 5 minutes. Dilute solutions of oohalt nitrate do not yield characteristic crystals readily. Thus with 1 part of cohdt in 500, the appearance of c:.yataIs may require 5 minutes, although the characteristic blue liquid separates promptly.
+0.1 , .,. Figure 4.
4
Pale Green Crystals
OEcssionelly reru1ting from intersotion Of isoqninolineammonium fhioeyanste reagent and nickcl chloride solution
TheZrelatively large, pale green crystals which are sometimes formed with nickel (Figure 4 ) me readily distinguished from the corresponding copper compound. The fact that nickel does not always yield crystals with the isoquinoline reagent does not constitute a serious disadvantage. After the reagent has been added to a te8t drop the preparation can easily be exposed to ammonia fumes by inverting the slide over an open bottle of ammonium hydroxide. Nickel is then detected by adding a drop of dimethylglyoxime solution. This test works very well even if the original drop has given positive teste for cupric and cobalt ions. INTERFERING IONS
0-1 "I,...
Figure 3. Deep Blue Crystals Developed when reagent oomhiner with cobelf chloride solution
The isoquinoline reagent Eerves as a very good test for cupric ion because of the prompt formation of a copious precipitate 'having a charaoteristio y e l h - g r e e n color. The crystals, which .appear to be very thin green leaves with a tendency to stand on .edge, are so small that the precipitate may resemble m amorphous mam. The green color, however, is sufficient indication of cupric ion; no other metal was found to yield a similar precipitate
Among the common metals which may interfere with the foregoing tests are silver, mercury, iron, bismuth, and antimony. In the presence of ferric ion the test for cadmium, zinc, nickel, or cobalt may be obscured by the formation of practically opaque cubic crystals and a red solution. However, if the iron is present in very small amounts (1 part in 10,000) the tests will not generally be obscured. LITERATURE CITED (1) Grapchenko, M. V.. and Shentzis, 0. G., J . Applied Chem.
(U.S.S.R.),Q. 544 (1936). (2) Korenman, I. M.,Mikrochemie, 9,223 (1931). (3) Martini. A,. Ibid.. 7, 30 (1929). (4) Spakowski. A. E.,and Freiser, H., ANAL.CEEX.,21,986 (1949). Rmcerv~oAugust 31, 1950.
