QualitativeA n dysis EDITOR'S NOTE: The papers following have been collected over a. period of months. Similar collections have appeared in previous August issues [J. CHEM.EDUC., 35,401 (19.58); 36,379 (1959); 37,407 (1960); 38,406 (1961); 39, 39.5 (1862); 40,413 (1963); 41, 435 (1964); 42,436 (1965); and 43,419 (1966)l. We esll to readers' attention the fact that often these represent the solution of problems given to freshrnsn students in qualitative analysis courses. We hope that publication in these pages can stimulate junt such activity.
Qualitative Analysis
N. S. Poonia Vikrom University Uiioin, India
with Paper Chromatography
Paper chromatography should aim a t producing practicable schemes of qualitative and quautitative analysis. Attempts at basic radical analysis have been made,' but no method in which the separation is accomplished in a single, simple operation has been reported. In this report a method of analysis is presented which is suitable for student work as well as being useful to the industrial chemist. A spot of the unknown mixture is subjected to radial development, and the circular chromatogram is divided into a desired number of segments. Different segments are used for the detection of different cations or group of cations. I n general, the cations have been resolved into the typical combinations and are detected by using a general or specific color reagent. When an ion cannot he separated from its group care must be taken to select a reagent with sufficient specificity. Masking and fractional precipitation are also used if required. The final characterization of ions is made by corroborating their R,values with the color they produce. A notable variation in the RJ values of some cations was noted when they were studied individually and in a mixture (Table 1). However, this will not matter if a reliable specific reagent can be found and if the predetermined R, changes are taken into account. The solvent system used was chloroform-acetoneisopentanol-HC1 (11 N) (1: 1:1:0.5 v/v), which is simTable 1.
ply a different composition of the same system previously r e p ~ r t e d . ~The cation mixture analyzed contained lead(II), silver(I), mercury (11), bismuth(III), cadmium(II), copper(II), cobalt(II), nickel(II), mauganese(II), zinc(II), iron(III), aluminum(III) or magnesium(II), beryllium(II), strontium(II), barium(II), thallium(I), zirconium(lV), thorium(IV), cerium(IV), uranyl(II), vanadyl(II), and molybdate. Sufficient concentrated nitric acid was added to prevent the h y drolysis of any of the salts. Table 2, which shows the R, values of the cations and the metal anions, should be helpful in showing the possibilities of analyzing other mixtures. The chromatogram, if needed, may be divided into more segments and additional color reagents incorporated into the scheme. The possibility of various tests on the same chromatogram and the better resolution of the multiconstituents in a minimum of space due to the compact circular zone on the chromatogram make this scheme superior to previous ones. POLLARD, F. H.,AND XCOMIE, J. F. H., "Chromatographic Methods of Inoreanic Andvsis!' Butterworths. London. 1953.
LEDERER, M., "&omatog&phio Reviews," ~lsevierpublishing Co., N.Y., 1961, p. 161. R. P., AND POONIA, N. S., Anal. Chcm., (a) BAATNAGAR, 34, 1325 (1962). (b) BHATNAGAR, R. P., AND POONIA, N. S., Anal. Chirn. Acla, 30,211 (1964). (c) POONIA, N . S., Indian J .
Chem., 4 , 511 (1966). (d) POONIA, N. S., J. CHEM.E D U C . , ~ ~ , 423 (1966).
The R, Values of the Ions Studied Individually and in Different Mixtures
Cu
Co
Ni
Zo
Mn
PM
Ae
Sr
Ba
Hs.
RJ"&IUB X 100 V U Tho
hln . A1
Ce
51 59 52 51 42 43
40 42 37 34 30 32
20 20 22 20 19 17
70
20 21 21 21
30 33 37 34 32 27
9
SM
0
80
22
64
30
100
0
84
48
80
29
17
20
7
Q 9 9 8
0 0 0 0
0 0 0 0
81 76 73 71
25 24 23
67 66 63
31 34 35
100 100 100
0 0
67 67
45 41
69 68
26
14
IS
6
81 83 80 78 76
16
14
FB
a When studied individuslly, s portion of the cstion wasleft at t h e point of spplication. h SM = Slight Movement.
21 Cd
Bi
MO Be
Remarks Studiedindir.idudly Mixture 1 Mixture 2 Mixture 3 Mixture 4 Mixture5
However, i n a mixtureit migrated.
Volume 44, Number 8, August 7967
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477
Table 2. RI value X 100
Ion Ferrous Ferric Molybdate Uranyl Vsnadyl Titanium Copper Cobalt Nickel Cadmium Arsenic Antimony Stannous Selenite S~lenate Tellurite Tellurate Zirconium Thorium
23 100 SO 64 22 27 51 40 20 85 94 96 100 96 60
95 SM
0
30
The R ~ V o l u e sof the Ions Studied Individually
Detection Reagent
Ion
Pot&ssium ferricyanide Potagsium ferroeymide
Plstinio Pslladous
Rub?hnic ?>id
Tuncstate Thhilous Plumbic Mercury
,.
Aurio
...,
Zino Manganese Chromium Barium Strontium Calcium Magnesium Beryllium Aiuminum Cerium
., ,, ., .,
Thmpnol
An ll-cm diameter Whatman No. 1 filter paper is spotted a t the center with the mixture and dried, and the contour of the spot is marked in pencil. A wick about 2 mm wide at its connecting point and 2-3 cm long is cut out of the disc. The development is carried out in the solvent, and the chromatogram is removed when the solvent front reaches the periphery (about 4 hr in this case). The solvent front is marked, and the disc is dried and divided into radial segments which are subjected to the cation detection reagents. The R,values for zones are also noted. In most cases the most suitable method to uniformly apply the reagent to the segment was to press it to a pad of 5 or 6 filter papers impregnated with an adequate, but not excess, amount of the reagent solution. Examination of segments Segment 1. Rubeanic acid (1.0%) is applied, and the paper exposed to strong ammonia vapors. Iron(II1) (black), cadmium, and mercury (greatly overlapping; initially both yellow but finally the interior portion of the zone becomes black on prolonged exposure to ammonia), copper (olive green), bismuth (black), cobalt (dull yellow), lead (black), nickel (violet), and silver (blackish brown) are noted in this sequence toward the center (see the figure). ,Ferric (block) Mercury & Cadmium (black 8 yellow, 0 respectively)
-Lead l ~ i '%Silver
Cupric (olive green! Bismuth (block) (dull vellow) (blackf c k e (violet) l (blackish brown)
ll.O~O1.
Segment 9. Potassium ferrocyanide (O.lyo) is applied.a From the periphery towards thecenter, iron(II1) (blue), molybdate (reddish brown), uranyl (brownish red), copper (chocolate), and vanadyl greenish-yellow are noted.
+ 478
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Journal o f Chemical Educafion
0 30 SO 9 48 70 20 0
Potassium iodide P ~ t ~iodide ~ and ~ iRubevic ~ , ~acid
16 17 29
Alisarin Aiumjnon
0 SM
Dithisone
Naoabeneidine
Sodium peroxide R~+~e~nio,aoid
20
0
.
Segment 1 of the chromatogrm showing t h e regions produced by rubeanic
acid
Detection Reagent
S t a n y u s chloride
Segment 3. Potassium iodide (1.0%) is sprayed onto this segment. Mercury (scarlet), copper (dull yellow due to the iodine), bismuth (brownish yellow), partly overlapping the iodine zone, lead (yellow), silver, (yellow), and thallium (yellow) are produced at first. However, the zones of mercury and bismuth disappear as more reagent is sprayed on. Thallium is further distinguished from the remaining cations and especially from silver, which has a R,value near it, by dipping the paper in 10Y0 hypo. Only thallium iodide persists, whereas the others disappear. Segment 4. It is dipped into 1:l ammonia to precipitate beryllium, magnesium, aluminum, and cerium as hydroxides and to deactivate ions such as silver, cobalt, nickel, copper, zinc, and cadmium as ammines. Aqueous aluminon (O.lyo) is applied after blotting the excess ammonia, and the paper is dried. A red color due to cerium appears in the region of the original spot; a bright red zone due to aluminum and/or adjoins it; and a red zone due to beryllium is noted at some distance from the others. Zirconium hydroxide adsorbs aluminon only insignificantly and does not interfere with cerium. Segment 5. Aqueous thoronol (0.1%) is applied. Bright red zones due to zirconium and thorium are noted. Any reddish zone produced in their absence disappears when the paper is dry. Segment 6. This segment is pressed onto a 1:4 ammonia pad to neutralize the acid in the solvent and then onto rodhisonic acid (0.1%). A red color is produced a t the point of application. The paper is treated with 0.5 N HCI. If the whole spot disappears then only strontium is present; if there is no change, only barium; if the color brightens, then both barium and strontium. Lead forms a bluish-red zone at some distance from the rest. Segment 7. First sodium hydroxide (2%) and then an acetic acid solution of benzidine (0.5y0) is applied. Only mnny:ineir is deterred n i n t,luc zonr j ~ ~ snutsitle t 1 1 1 tmint ~ of auolir~~riun of thr oricin:d .sirlirti(,i~. segment 8. Chloroformic solution of dithizone (0.1%) is sprayed onto the segment. Zinc is detected as a bright red zone. Other reddish zones towards the center are ignored.
Procedure
-5 -Cobalt
0
niamuth
..
,,
76 70 100
Silver
.,
SodFym d g d e ,, ,, ,'
.,
RI d u e X 100
"ee
+
+
reference (d) in footnote2.
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