1240
ANALYTICAL CHEMISTRY
filtered to remove unreacted zinc, the filtrate is cooled to 10” to 20” C., and 3 to 5 d r o p of 0.1N sodium nitrite are added with shaking. If desired, a test with starch-iodide paper may be made while the nitrite is added to see if the solution absorbs nitrite. After shaking well, the solution is spotted on a piece of filter paper alongside a spot of R-salt solution. A color, usually reddish, forming where the spots meet, is an indication of coupling, and therefore that the original substance is very likely an aromatic nitro compound, or, much leas frequently, a reduction derivative of such a nitro compound, such as a nitroso, azo, azoxy, hydrazo, or similar substance.
Discussion. All mononitro compounds encountered have given a good positive test by this procedure. Polynitro compounds are reduced and consume nitrite, but often fail to give the typical coupling test because of side reactions during diazotization. The spot test on filter paper is more sensitive than the usual test wherein the diazonium solution is mixed with a solution of a coupling agent. The white background of the paper makes it possible to detect as little as a few milligrams of amine. The use of R-salt is preferred to a solution of %naphthol, which Is sometimes used because such a solution is stable for a long time and generally gives azo colors of greater intensity. R-salt is
the sodium salt of 2-naphthol-3,6-disulfonic acid, and couples, like %naphthol, in the 1- position. A good R-salt test solution contains about 2% R-salt in a solution which is 5% with respect to sodium carbonate. The same diazotization-coupling test can be applied to identify any primary aromatic amine with certainty. LITERATURE CITED
(1) Callan, T.,and Henderson, J. A. R., J. SOC.Chem. Ind. (London). 41T, 157-61 (1922). (2) Callan, T., Henderson, J. A. R., and Strafford, N., Ibid., 39T, 86-8 (1920). (3) Knecht, E.,and Hibbert, E., “New Reduction Methods in Volumetric Analysis,” 2nd ed., London, Longmans, Green and Co., 1928. (4) O’Keefe,K., and Averell, P. R., ANAL.CHEM., 23, 1167-9 (1951).
(5) Siggia, S., “Quantitative Organic Analysis via Functional Groups,” pp. 824,New York, John Wiley & Sons, 1949. (6) Ueno, S.,and Sekiguchi, H., J. Soc. Chem. Ind. Japan,37B, 23.56 (1934). (7) Vanderzee, C.F., and Edgell, W. F., ANAL.CHEM.,22,572(1950). RECJEIVED for review August 20, 1953. Accepted April 23, 1954
Ultraviolet Absorption Spectra of Some Inorganic Ions In Aqueous Solutions R.
P. BUCK, SAMANG SINGHADEJA’,
and L.
B. ROGERS
Department o i Chemistry and Laboratory for Nuclear Science, Massachusetts lnstitute o i Technology, Cambridge 39, Mass.
A
LTHOUGH ultraviolet measurements in the range 210 to 400 m r are universally accepted for characterization and analysis of organic compounds, few investigations (6) have been directed toward inorganic compounds until very recently. Little information of analytical value is available about simple or complex ion spectra in general, though some studies may be found in the reviews of Rosenbaum (9). For that reason, a systematic survey has been made of a number of common anions which might absorb in the ultraviolet either by themselves or in the form of complexes with metal cations: sulfate, thiosulfate, peroxydisulfate, sulfite, nitrate, nitrite, chlorate, perchlorate, bromate, iodate, metaperiodate, vanadate, tungstate, molybdate, cyanid?, cyanate, thiocyanate, borate, phosphate, phosphite, hypophosphite, and pyrophosphate. In addition, the organic ions, acetate, citrate, tartrate, and oxalate, were studied because they are frequently encountered in analytical procedures. After most of the anions had been found to have low general absorption without characteristic absorption maxima, spectra of 15 metal and metal-containing ions, a t a level of approximately 10 p.p.m., were determined in tartrate, citrate, pyrophosphate, phosphoric. acid, and cyanide media wherever possible: zinc( 11), cobalt(II), cadmium(II), mercury(II), copper(II), nickel(II), manganese(II), lead(II), thallium(I), silver(I), indium(III), gallium(III), iron(III), thorium(IV), and uranyl. Arsenite, molybdate, tungstate, and vanadate were investigated in phosphoric acid and pyrophosphate media. Sulfuric acid medium was not examined because it had already been studied by Bastian ( 2 ) ,while hydrochlorir acid has been examined in this laboratory ( 4 , 8).
in preparing solutions of the anions with the exceptions of p h o s phoric and boric acids and ammonium metavanadate. Approximately 0.1Jf stock solutions of the cations as perchlorates were usually prepared by twice evaporating the nitrate with excesa perchloric acid before diluting to volume. Stock solutions of thallium(1) and uranium(V1) were made from the acetates by gentle evaporation with perchloric acid on a hot plate. In these two cases. the acetate may not have been completely
I SODIUM NITRITE
U SODIUM NITRATE
IU
SODIUM THIOSULFATE SODIUM PERSULFATE Y POTASSIUM BROMATE p1 POTASSIUM IODATE YU SODIUM SULFITE WII POTASSIUM CHLORATE IX SODIUM SULFATE Lp
6-
REAGENTS AND SOLUTIONS
Reagent grade chemicals and distilled water were used throughout this investigation. Sodium or potassium salts were used 1 Present addresa, Department of Science, Vatana College, Bangkok, Thailand,
220
240
260
280
300
WAVE LENGTH, M r
Figure 1.
Ultraviolet Absorption Spectra of
Aqueous Solutions of Simple Inorganic Salts
1241
V O L U M E 26, NO. 7, J U L Y 1 9 5 4 I
wave lengths, the spectra for both molybdate and thiocyanate tended to flatten out near 220 mp and then continued to increase sharply in absorbance. Only nitrate, nitrite, vanadate, metaperiodate, and thiosulfate showed characteristic absorption maxima in the range studied. The nitrate peak was 302 mp, nitrite 351 mp. vanadate 266 mp, metaperiodate 222 mp, and thiosulfatr 215 mp (1). Nitrate and nitrite also had peaks below 210 mp, a t 198 mp and 208 mp, respectively, but these would be of limited analytical value because they occur in a region where many ions absorb. The spectra for vanadate (6) and periodate (3) were dependent upon pH, as reported by others. The spectra for vanadate were found to be the same whether the starting material was sodium orthovanadate or ammonium metavanadate.
BORIC ACID
U PHOSPHORIC ACID
E SODIUM TARTRATE Y POTASSIUM CITRATE
I U
m IY V VI VI W
SODIUM PERCHLORATE POTASSIUM PHOSPHITE SODIUM HYPOPHOSPHITE POTASSIUM CYANIDE POTASSIUM CYANATE SODIUM ACETATE SODIUM TUNGSTATE POTASSIUM PERIODATE
WAVE LENGTH, Mr
Figure 2. Ultraviolet Absorption Spectra of Aqueous Solutions of Simple Inorganic Salts
Tahle I.
Spectral Characteristics of Complexes IIaving Potential Analytical Value
Ion
i!g(II) I.e(III) I,'e(III) CUfII) Cu(I1) CU(I1) Xi(I1)FeiC?r)s---
hledium 2 . OM HiPOi 2 . OM HaPOi 0 . 0 1 M KIPzO; 0 . 0 1 M KiPz07 0 . 0 1 M sodium citrate 0 . 0 2 M KCh0 . 0 2 M KCN 0.02M KCX
Wave Length of Maximum Absorption, Figure mr 235 4 254 5 279 4 244 4 258 t;
238
ti
267 260 303
lj
Molar Absorptivity, Liter/Mole Cm 1 3 . 9 X 102 5 . 3 x 103 4 . 5 x lo* 5 . 1 x 103 3 . 2 x 103 12.8 x 11.7 x 1.9 x 2.3 x
2
103 103
103 103
2 20
240
260
WAVE LENGTH, M p
Figure 3. Ultraviolet Absorption Spectra of Aqueous Solutions of Simple Inorganic Salts
removed. Manganese(I1) was used directly in the form of the sulfate. JVith this exception, the solutions were roughly 0.01M in perchloric acid. APPARATV S
The surl-ey of absorption spectra of the anions was performed on a Cary recording spectrophotometer over the range 210 to 400 mp. The Cary spectrophotometer was operated a t maximum sensitivity and minimum slit widths. The absorption spectra of metal perchlorates in phosphoric acid, potassium pyrophosphate, sodium citrate, sodium tartrate, and potassium cyanide were determined using a Beckman DU spectrophotomrter and 1-cm. quartz cells. The Beckman was oper:Lted a t a constant slit width of 0.36 mm. in the range 220 to 320 mp. The slit was necessarily larger a t wave lengths below 220 mp. RESULTS
The spectra of a number of anions listed above were obtained using 0 . l M solutions wherever possible. Further dilutions were always made to permit measurement of the absorbances to 210 mp. These data are shown in Figures 1, 2, and 3. Solutions of sulfate, boric acid, perchlorate, phosphoric acid, phosphite, hypophosphite, and cyanide were transparent throughout the spectral range. On going toward shorter
"'1 A 06
I MERCURIC PERCHLORATE 5 26 x m PHOSPHORIC ACID 2Om
LL
02
O L 210
0
WAVE LENGTH, Mr
Figure 4.
Ultraviolet Absorption Spectra of Mercu,ric Perchlorate and Cupric Perchlorate
ANALYTICAL CHEMISTRY
1242
The remainder of the anions cut off a t 210 mp or below without producing peaks. The molar concentration of each, which was calculated to give an absorbance of 1.0 a t 210 mp, was: acetate, 2.2 X bromate, 8.6 X l o + ; chlorate, 4.8 X l o p 2 ; citrate, 2.0 X low3; cyanate, 3.2 X 10-2; cyanide, 1.4 X 10-1; iodate, molybdate, 1.0 X nitrate, 1.1 X 3.8 X nitrite, 1.9 X oxalate, 1.5 X 10-3; peroxydisulfate, 2.3 X pyrosphosphate, 2.8 X sulfite, 9.0 X tartrate, 2.4 X thiocyanate, 3.4 X thiosulfate, 2.7 X and tungstate, 3.5 X These calculated values sometimes depended, to some extent, upon the concentration of the ion that was examined.
mp, the absorption increased rapidly, but no maxima were observed before the limit of the instrument was reached. On the other hand, iron(II1) and uranium(V1) in the five media, molybdate, tungstate, and vanadate in phosphoric acid and pyrophosphate, copper(11) in pyrophospate, citrate, and tartrate and mercury( 11) in phosphoric acid were exceptions inasmuch a s these solutions had characteristic absorbances greater than 0.1 a t 230 mp. Bismuth(II1) in pyrophosphate and tartrate, lead(11)in citrate and tartrate, and manganese(I1) in pyrophosphate produced white suspensions. Manganese( 11) in citrate developed a yellow turbidity on standing. Oxalate complexes were not investigated because the intrinsic background absorption of the oxalate ion itself is large. Those curves having characteristic maxima are shown in Figures 4, 5, and 6 and the data for the peaks are summarized in Table I. The complex or complexes of iron(II1) and phosphoric acid have been known for many years, but the mercury( 11) complex was hitherto unreported. In contrast to iron(II1) perchlorate in 1.0X perchloric acid which showed an absorption maximum a t 239 mp with a molar absorptivity of 4.1 X l o 3 liter per mole cm., mercuric perchlorate in 1.OM perchloric acid was transparent a t 235 mp. The molar absorptivity a t the wave length of maximum absorption increased with decreasing phosphoric acid concentration: 14.0 X 103 in 0.1M phosFERRIC1 2PERCHLORATE 1 ~ 1 0M~ ~ phoric acid a t 236 mp, 13.9 X I O 3 in 2.0M phosphoric acid a t 235 mp, 11.6 X 103 in 7.OM phosphoric acid a t I PHOSPHORIC ACID 2 0 M 233 mp, and 9.1 X 103in 9.OM phosphoric acid a t 232 mp. n PERCHLORIC ACID I O M Variation of the molar absorptivity was less than 1% in m POTASSIUM PYROPHOSPHATE 001 M the range 0.5 to 3.OM phosphoric acid. In 0.5M phos01 I I I I I I 1 7 ! J phoric acid, the molar absorptivity determined from 12 220 240 260 280 303 320 samples containing varying amounts of mercuric perWAVE LENGTH, Mp chlorate was 13.9 X lo3 with a coefficient of variation Figure 5. Ultraviolet Absorption Spectra of Ferric Perchlorate of 1.6%. A Ringbom plot of the data for mercury i n d t cated that the optimum range of concentration was from 2 to 12 p.p.m. Absorption spectra of 15 metal and metal-containing ions a t Among the many common complex ions that were examined in concentrations of approximately 10 p.p.m. in the metal were this study, comparatively few were found to have characteristic absorption peaks. However, those with peaks were sufficiently determined in each of five media: 2.OM phosphoric acid, 0.01M potassium pyrophosphate, 0.01M sodium citrate, 0.01M sodium absorbant to be useful analytically and they suffered from few interferences. Inasmuch as very few elements absorb in phostartrate, and 0.02M potassium cyanide. phoric acid, potassium pyrophosphate, sodium citrate, sodium These solutions had absorbances, with respect to a water blank, of less than 0.1 a t 230 mp and a t longer wave lengths. Below 230 tartrate, and potassium cyanide, addition of these substances might be useful as means of eliminating interferences in spectrophotometric determinations arising from the presence I 1 of heavy metals.
oi
\
14
POTASSIUM CYANIDE 0020 M
I COPPER PERCHLORATE
12
1.12 x IO-‘M NICKEL SULFATE 9.3 x K S 5 M COBALT SULFATE 1.015 x M POTASSIUM FERRICYANIDE 1.43 x W q M CADMIUM PERCHLORATE 1.05 x 10-3M
10
Y
5 0.8
1 m
06
ACKNOWLEDGMENT
The authors are indebted to the Atomic Energy Commission for partial support. LITERATURE CITED
(1) Awtrey, A. D., and Connick, R. E., J . Am. Chem. Soe., 73, 1842 (1951). (2)
Bastian, R., Weberling, R., and Palilla, F., A N ~ LCHEM., . 25, 284 (1953).
Crouthamel, E. E., Meek, H. V., Martin, D. S., and Banks, C. V., J . Am. Chem. SOC.,71, 3031 (1949). (4) DeSesa, M. A,, and Rogers, L. B., Anal. Chim. Acta, 6, 534 (3)
04
(1952).
Jander, G., and Aden, T., 2. physik. Chem., A144,197 (1929). ( 6 ) Jones, H. C., and Anderson, J. -4.. “The Absorption Spectra of Solutions,” Washington, D. C., Carnegie Institution of Washington, 1909. (7) Lindquist, I., Acta Chem. Scand., 5, 568 (1951). ( 8 ) hlerritt, C., Jr., Hershenson, H. and Rogers, L. B., ANAL.CHEM.,25, 572 (1953). (9) Rosenbaum, E. J., Ibid., 23, 12 (1951); 24, 14 (1952); 26, (5)
02
220
240
260
280
3co
320
340
360
380
WAVE LENGTH, M p
Figure 6. Ultraviolet Absorption Spectra of Copper Perchlorate, Nickel Sulfate, Cobalt Sulfate, Potassium Ferricyanide, and Cadmium Perchlorate in Potassium Cyanide
20 (1954). RECEIVED for review November 25, 1953. Accepted April 23, 1954.
