870
A N A I. Y T I C A L C H E M IS T R Y
which is begun exactly on the next minute, and so on, until the series have all been started. At exactly 30 minutes from the of the first flask is removed and its contents are auickly washed into a 50-m]. volumetric flask containing 1 ml: of glacial acetic acid. The second s a m ~ l eis removed exactly 1 minute after the first, and SO on, until'all samples are
in Figure 5 , shows no interference in this range. Aluminum, at this pHi shows turbidity>as indicated in the figure. Shapiro (3) compared visually the green color in basic solutions., usintz- standards alone with unknowns. His total volume was about 3 m], and his oubservations were taken after 5 to 6 ~ ~ ~ ~ a ~ ~ s k ~ h , ' , " , e l , ~ ~ f ~minutes ~ ~ ofh development. a ~ ~ ~ ~NO~ limits ~ nof ~accuracy ~ ~ were ~ ~ mentioned. ~ t ~ ~ ~ f ~ Although his results indicate less interference than has been obtheir densities are determined. served in the present experiments, the comparisons are considered satisfactory. RESULTS AND DISCUSSIOY -4s recommended by Shapiro, a procedure in which known Figure 1 shows data for three different times of development. copper solutions (controls) are run simultaneously with unThe slopes of the lines are closely proportional to the time of knowns is also considered best in the present technique. F'ariadevelopment within the range, 16 to 60 minutes. However, 2tion in optical density from one run to another for solutions conhour development gave erratic data. taining no copper could not be entirely avoided, but the use of The effect of varying the concentration of resorcinol is shown simultaneous controls gave satisfactory results. In such a case, in Figure 2. At a concentration of 1 nil. of 5% resorcinol, and accurate control of the temperature may not be so important, above 0.4 microgram of copper, the data are no longer linear. and so a thermostat may not be required. From the data given Below 0.3 microgram of copper, however, one single experiment here, it is estimated that, in the range 0 to 1.0 microgram of copgave the data of Figure 3. per in 25 nil. of solution, the accuracy is 10.05 microgram of The interference of silver is shown in Figure 4. One-half copper in 25 ml. of solution. microgram of copper was added to all samples, and the silver was varied. From Figure 1, for the determination of copper, the LITERATURE CITED deviation from the mean (for 15-minute development) is about (1) Henrich, F., Sitzber. phgsik.-nzed. S o z i e f a f . Erlangen, 71, 199-202 0.02 in density. Therefore, up to 2 micrograms of silver might (1939). be tolerated in the determination of 0.5 microgram of copper. ( 2 ) Lavoye, M., J . pharm. Belg., 3,889-90 (1921). In like manner, in Figure 5 , the data for iron show increased (3) Shapiro, M . Ya., Zhur. Anal. Khim., 4, 199-200 (1949). density sufficient to cause interference at 50 micrograms and (4) Triebs, W., Ber., 63B, 2423-8 (1930). (5) K a r e , A. H., Chemist and Druggist. 123, 282 (1935). higher concentrations under these conditions. Aluminum, (6) JYePt, P. Ifr., ANAL. C H E Y . , 23, 176-80 (1951). magnesium, and tin show inhibition of autoxidation, the effect decreasing in the order named. Lead, mercury, calcium, and RECEIVED for review Iiovember 1 4 , 1951. Accepted February 7 , 1952. zinc have no effect in the range studied. Cadmium, not shown Communication N o . 1462, Kodak Research Laboratories.
Fusion Method for Microscopic Identification of Inorganic Ions PHILIP W. WEST AND LAWREYCE GRAKATELLI Louisiana State Cniversity, Baton Rouge, La.
This investigation was initiated in order to determine whether the fusion of inorganic salts with 8-quinolinol could be employed for the detection of the inorganic ions in these salts. By fusing inorganic salts with 8-quinolinol on a microscope hot stage, the following ions may be identified by studying the color, morphology, and certain optical properties of the addition and chelate salts thus formed: nitrate, chloride, sulfate, copper, zinc, uranyl, calcium, chromium, and magnesiuni. Bubble formation
M
ICROSCOPIC fusion methods for the characterization and identification of organic compounds have been extensively studied by Kofler and Kofler ( 3 ) . They employ as criteria of identification the micro melting point of the compound, the eutectic temperature of the compound with each of two test substances, and the temperature a t which the refractive index of the fused compound matches that of a glass powder of known refractive index. More than 1000 organic compounds are rharaterized by the authors in this manner ( 9 ) . Grabar and McCrone ( 2 )have extended the field of microscopic inorganic fusion analysis by constructing hot stages which may be operated to temperatures of 500' and lo00 '. Feigl and Baumfeld ( 1 ) have fused 8-quinolinol (&hydroxy-
occurring in the temperature range 100" to 110" C. is indicative of the presence of w-ater of crystallization in the inorganic salt. The technique described here is of special interest because in many cases i t permits the simultaneous identification of cation, anion, and water of crystallization in a given inorganic salt. The melting point of the inorganic salt examined need not be approached before characteristic crystals of the chelate or addition products are formed.
quinoline, oxine) with various inorganic salts in microcrucibles and studied the colors thus produced. They noted that, with the exception of ferric and vanadium salts, the melts obtained were colored yellow or yellow-orange. With ferric salts a dark green color was formed; with vanadium salts, a black-brown color. They recommend their method for the detection of small quantities of ferric oxide and vanadium pentoxide in the presence of greater quantities of other basic or acidic metal oxides. The present investigation was initiated in order to study further the reaction of inorganic salts with fused 8-quinolinol. From the work of Feigl and Baumfeld ( 1 ) it was realized that, if conditions could be brought about so that the chelate salts in the fused 8-quinolinol were made to crystallize in the melt, microscopic ex-
V O L U M E 2 4 , NO. S, M A Y 1 9 5 2
871
reagent and dispersion medium, the following anions and cations from certain inorganic salts: nitrate, ohloride, sulfate, copper, zinc, uranyl, calcium, chromium, and magnesium.
A
APPARATUS AND REAGENT
The amaratus employed in this investipation consisted of B pol~"zin'gmicroscop~ a~ hot ~ stage. Any microscope may be employed, but with a polarizing microscope not only color and morphology but also some of the ontical Dronerties of the crystals may be studied. Such oDtical Gopertlees i s profile angle,'extinctioh angle, sign of elongition, and pleochroism may be useful in serving to characterize further the crystals obtained. Unfortunately, the crystals cannot readily be isolated from the 8-auinolinol matrix, and such properties as optic axial angle, op........
Figure 1.
up to 350". Merok reagent grade 8-quinolinol was employed both as reagent and dispersing medium.
8-vuinolinol-IYitric Acid
EXPERIMENTAL
amination of the color and morphology of these erystds mould serve to identify them. The fusion micro method described in this paper has been aPplied to a large number of inorganic salts. The results a t present are such as to enable one to identify readily, with 8-quinolinol a8
Table I. Salt
Cu(N0&3H10 Cu(CiOi0di. H.0 CuSOc5Hz0 CUSO. CUO CUCl, CUCl CuBr CUI CuNCS CUlO
A very small fragment of the inorganic salt is pulverized an 8 microscope half-slide. The pulveriaed salt is covered with gquinolinol, so that the area between slide and cuver is filled when the reagent melts. Concentration ratios of salt to reagent in the range 1to 50 to 1t o 100 are used. The prepared slide is placed on the hot stage of the microscope and by means of the rheostat the temperature of the hot stage and preparation is raised a t a rate of about 5" to 10" per minute. The preparation is examined microscopically as Identifioation of Ions in Inorganic Salts M,F,,n C,.? Zn++ CI- soI-the temperature rises and, after the rheostat is turned off, as the temperature decreases. .. 114.5+ .. .. . . . . Effectively, only temperatures up to itbout 200" . . . . .. .. 115 + .. . . . . ++ may he employed with 8-quinalinol as reagent. -4H.O 110 + .. 200 + .. . . . . At 120" to 130" the reagent begins to volatilize .. . . . . d.1026 .. readily; the preparation diminishes in 8-quino498 .. .. .. .. linol content and one is compelled to replace the $22 .. 004 .. . . . . .. volatilized reagent if high'temperatures (130" to .. . . . . 605 ++ ... ... .. 200") are to be employedfor an extended time. . . . . .. 1084 .. I235 .. . . . . .. In order to avoid excess volatilization of the .. . . . . + reagent when high temperatures are necessary for Tr.39 .. + 36.4 .. + .. .. + the reaction one may proceed in the followins ... + . . . . manner: Prehezt the hot stage to 150" to 200 , + .. .. + .. 262 + place the preparation on the hot stage, and allow .. . . . . .. 236 .. + .. . . . . .. i t to react for 15 to 30 seconds. Remove the 18on .. + -co2 300 .. + .. . . . . .. preparation and cool i t rapidly on a cooling block. -2HxO 100 .. .. + . . . . .. Cool the hot stage helow 130" and examine the 60.2 .. .. + . . . . .. .. .. preparation. ... .. .. +
ZnS04.7HsO Zn(NOi)..6H*O zinc uranyl aoetPrte Z"C1. Zn(CsHa04s.2H.O ZnO Z"CO1 UO*(C,HxOd2. ZHIO UOs (NOd>.6H>O NalUOd HNOa (oonod.soln.) HCI (conod. soln.) HiSO. (eonoil. soln.) Meltingwint dstafrom
+ ++ ++
+
+
... ...
...
.. .. ..
.. ..
..
..
..
+. .
+. .
. . . .
.. ..
.. +
The photomicrographs accompltnying this paper were made on hot preparations a t temperatures above 75" (the melting point of &quinolinol) in order to avoid crystdlizslcion of the reagent. The refractive indexes of the crystals obtained m.erestudied relative to t h e refractive index of the melt and RE represented in the diagrams aecompanying the photomicrographs by slow and fast rays. Where bath indexes of refraction, of the common views shown, are higher t h m the melt (at ahout 85"), the slow and fast rays were deduced from the sign of elongation of the crystals and the difference in contrast of the cry&& in the two extinction positions. Pleochroic COlOIB are indicated in the diagrams relative to the respective vibration axes.
..
RESULTS
+
Lange (4).
Table 11. Identification of Ions in Inorganic Salts Salt
Ca0 CaC, Ca(OHh C~(C~HIO)~.H~O CSF. CaCO, CaSO1.2HnO
h1.P.. C.* 2572 2300 -Ha0580 d. 1336
825
-1.5HaO 12s 772 76; 42.7
CaCls CsBra Ca(NO8)..4HaO Cr(NOi)r.SHsO 36.5 ... CrC1, .... Cr*(SO.)a.rH.O C ~ ( S O . ) I . K I S O ~ . ~ ~ H " O 89 Cr(0H)COs ... crrot 1990 Mg NOda.6HzO 100 d.116-8 MgS0..7H%O MgAi,.eH,O -6HzO 150 Mg(CIO& d.251 MgCOi d.350 M - ~ ~ ( C ~ H ~ O Z ) S . ~ H ~ d. O
nfpo a
2800
MeltingpointdatafromLsnge(4).
Ca+* C r * i *
++ +
..
..
.. ..
..
,
. . . . . . . .
. . . . . . . .
..
..
..
. . . . . . . .
.. .. ..
.. ..
+. . . . .. + .. +. . . . . .
..
++ +
..
.. .. ..
..
-
.. .. .. .. ..
..
.. ..
+-
.. .. ....
M z * + N O % - CI.. . . . .
+++ +..
.. ..
..
..
.. ..
..
.. .. ..
.. .. ..
-
+ ++ ~
..
-
. . . .
. . . . . . . . ..
+
+
SO.--
..
..
.. ..
.. .. ..
.. .. ..
..
+ .. .. ..
.. .. ,. . . . .
+.
. . . .
..
. . . . . . . .
.. ..
. .
The fusion of inorganic salts with Squinolinol and the microscopical examination of the reaction products obtained sllow for the detect,ion of nitrate, chloride, sulfate, copper, zinc, uranyl, calcium, chromium, and magnesium ions in certain inorganic salts. Tables I and I1 list
872
ANALYTICAL CHEMISTRY
the salts in which the cation and/or anion of each salt was detected. Table I11 lists certain salts of which only the reactions of the anions were studied.
~
Table 111. Identification of Anions ia Inorganic Salts
.
Figure 2.
Melting point data from Lange (4)
8-Qoinolinol Hydrochloride
Nitrate. The nitrate radical of certain inorganic saltlts can be detected by the formation of colorless lamellar crystals of rhombic form (Figure 1). These crystals show a profile angle of 51" symmetric extinction, and a positive sign of elongation. Crystals of 8-quinolinol-nitric acid am observed to form in the melt UBUallybetweentemperaturesof 75'to80Dand todissolvein thefused reagent a t about 85' to 90 '. Chloride. The chloride radical is detected by the formation of colorless crystals of tabular habit (Figure 2). Crystals of 8quinolinol hydrochloride exhibit oblique extinction (14') and a profile angle of 137*. The crystals are observed to form usually between 75" and 80' and to dissolve in the melt at about
Figure 4. 8-Quinolinol-Sulfuric Acid Fused in Fused 8-Quinolinol
ally past 150"), yellow liquid areas are noted in the I3-quinolinol melt (Fiigure 4). A8 the temperature of the . prenarsti on is cooled . slowly on the hot stage, the yellow areas are observe11 to crystallise as feathery aggregates (Figure 5) until the whole! of the yellow areas are solidified. Copper. COPPER(II). Copper(I1) salts react wi t h fused 8quinolinol to form crystals of four different sppearanoes. A t 85' to 95' green crystals of the forms shown in Figures 6 and 7 appear. Both crystals are pleochroic. The indenes of refraction of both crystals arc greater than that of the melt a t 85". The index of the fast ray (Figure 7) approaches that of the melt a t about 65'. At higher temperatures (about 135') crystals shown in Figures 8
d
organic salts ion of three y BE formed ts of a circle:
135' colorless X-shaped crystals are also formed (Rgure 3) When the temperature of the preparation is raised further (mu-
-. - "a-yurnoiiaoi-~uiiurlo _. . " . * . ~. e. ,i axn rigwe a. 1.
Commencement of Crystallization
V O L U M E 24, NO. 5, M A Y 1 9 5 2
-
a13
_""__
CIyStdE (Figure 13) exhibiting oblique extinction ( 8 7 . Both indexes of refraction are greater than that of the melt at 354 Another View generally observed is shown in Figure 14. Calcium. Caldum salts react with fused 8-quinolinol t o yield crystals of various appearances. The oxide, carbide, hydroxide, and acetate salts of calcium form, a t about 170", small, light yellow rodlike crystals (Figure 15). The chloride, bromide, and nitrate react t o form prismetio crystals (Figure 16) exhibiting symmetrical extinction and more generally lamellar crystals (Figure 17). The lamellar crystals usually appear gray when vieuwd between crossed Nicols. They exhibit parallel extinction, a positive sign of elongation, and a profile angle of 669
light green
Figure
Figure 7.
Copper(11) Oxinate
and 9 may be obtained. The crystals in Figure 8 have a tabular habit, are pleochroic, and exhibit parallel extinction and a profile angle of 125.5'. The crystals represented in Figure 9 are yellow in color and lamellar in habit, and exhihit parallel extinction, a positive sign of elongation, and a profile angle of 60". COPPER(I). All the cuprous salts listed in Table I, when fused with 8-quinolinol, yield crystals, recognized under the microscope, of copper(I1) oxinate (Figures 6 to 9). In addition to the formation of crystals of copper(I1) oxinate, the cuprous halides yield also oraugeyellow crystals, each of charsckristic appearance and typical of the respective halides. Crystals obtained with cuprous chloride are shown in Figure 10. At about 140" an opaque stippled precipitate farms. If the stippled effect is attributed to the presence of metallic copper, the following reaction is indicated
8.
Lopper(l1) Oxinate
Calcium fluoride, calcium carbonate, and calcium sulfate dihydrate do not react to form crystals of calcium oxinate. Chromium(II1). Chromium(II1) salts react with fuaed 8quinolinol, usually in the temperature range 90' to 110q to form small brown-red, rodlike crystals (Figure 18). The crystals cxhibit parallel extinction and show a positive sign of elongation. With the exception of basic chromium carbonate and chromium trioxide, all the chromium salts listed in Table I1 form crystals of chromium oxinate Magnesium. Of the magnesium Salts listed in Table 11, only the carbonate, acetate, and oxide yield crystals of maguesmn oxinate. Crystals of magnesium oxinate form a t ahout 180". They are yellow-green in color and prismatic in hahit (Figwe 19). The crystals show a profile angle of 84",oblique extinction (30"). and a negative sign of elongation.
Table IV.
Temperature of Rubble Formation in
Nonhgdrated Salts
Salt
Temo..
" C.
+ cu
2CU+ ----f cu++
snd explains the oxidation of copper(1) to copper(I1). The crystals obtained with cuprous chloride are orange in color and pleochroic. They exhibit parallel extinction, a negative sign of elongation, and a profile angle of 74.59 Zinc. Zinc salts react with fused 8-quinolinol to form yellow lathlike crystals (Figure ll),whioh exhibit parallel extinction and positive elongation. They form between 8 5 O and 100" and dissolve in the fused 8-qninolinol at about 140'. Uranyl. Uranyl salts react with fused &quinolinol to yield, usually at about SO", orangered pleochroic crystals (Figure 12). These crystals dissolve in the melt a t about 120" and reappear, upon lowering the temperature of the preparation, 8.8 prismatic
Bubble Formation. During these investigations it was noted that msuy of the salts which were fused with 8-quinolinol evolved gaa buhbles. These buhbles formed on the surface of the incompletely dissolved salt and escaped from the preparation by migrating t o the edge of the cover glass. This phenomenon was demonstrated by 36 salts containing water of crystallization. With the exception of three of these hydrated salts, all evolved gap bubbles between the temperature range of about 100' to 110". Calcium acetate dihydrate evolved bubbles at
ANALYTICAL
874
CHEMISTRY
about E O " , stannous chloride dihydrate a t about 130",and stannic chlorate pentahydrate a t about 85". Table IT' contains a list of nonhpdrated salts with which the formtion of gas bubbles was also demonstrated and the temperature range a t which gas evolution occurred. In most cases, gas evolution occurs a t temperatures very different than in the temperature range 100"to 110". DISCUSSION
The method of qualitative analysis described here is unique in that in many oases both the cation and anion of a. given inorganic salt may he detected simultaneously. It is apparent that &quinolinol acts, in these reactions, both as an addition compound and as a chelating agent; a i t h certain minerd acid anions an mid salt is formed, whereas with certain cations, metal
Figure 11. Zinc Orinate
orange
Figure 12. Uranyl Oxinate Figure 9.
Copper (11) Orinate
orang.
1
colorless \%SO
Figure 10. Crystals Obtained hy Reaction of Cuprous Chloride with 8-Quinolinol
Often, the fused reagcnt reacts almost immediately with the inorganic salt in such a manner that the inorganic salt is encrusted by the metal oxinate formed. This initial reaction prevents the unreacted portions of the salt from reacting further with the reagent and characteristic crystds may not he observed until the preparation is heated to such a temperature that the oxinate encrusting the salt dissolves and dlows new salt to he exposed to the aotion of the reagent. In certain eases a gradual temperature rise to 150"to 200'may fail to demonstrate the formation of the expected addition or chelate salts. However, if the preparation is cooled gradually or suddenly to solidification, these orystals may be observed after the crystallized preparation is reheated. This probably is an indication of a supersaturation phenomenon. This investigation demonstrates that the melting point of the inorganic salt need not he approached before a reaction will occur. This is proved by the reactions (at temperatures below 200") with the oxides of copper, zinc, calcium, and magnesium rhose melting points lie above 1000". These reactions are probably topochemical in nature, as explained by FBigl and Baum-
oxinates result. A typical reaction may be exemplified by the following equation: OH
OH HSOa
,O--Cu/,
I CU(NO3)*
+4
+2
Of the various anions examined, only nitrate, chloride, and mlfate reacted with the reagent to form crystals charaoteristic of these anions. The experience to date indicates that, in general, there are three conditions under which typical crystal formation is likely to be observed: In many cases, typical crystals are observed soon after the 8quinolinol has melted.
Figure 13. Uranyl Oxinate c0l0rl~~
arc 8-quinolinol-nitric acid
875
slt~of other ions which Bere found to react with 8quinolinol
