Simultaneous Spectrophotometric Determination of Cobalt and Nickel with 8-QuinoIinoI A. J. MUKHEDKAR and N. V. DESHPANDE Department of Chemistry, University of Poona, Poona 7, India
b The cobalt-8-quinolinol complex absorbs at 365 and 700 mp, while the nickel-8-quinolinol complex absorbs only a t 365 mp in 1N HCI-acetone. This principle was used for the simultaneous estimation of cobalt and nickel. It is possible to extend the method to iron-cobalt and chromiumcobalt systems.
S
estimation of cobalt and nickel in excess of other metal radicals is well developed. Chilton (3) estimated cobalt and nickel simultaneously, using sodium diethyldithiocarbamate. Yoe and Jacobs (7) employed dithio-oxamide. Gustin and Sweet ( 5 ) used biureate. 4 s the metal chelates with these ligands absorb in the same wavelength region, simultaneous equations must be sohed t o get the concentrations of the components. Cobalt and nickel were estimated polarographically by using pyridine-pyridinium chloride as supporting electrolyte (6). In the present work 8-quinolinol in llY hydrochloric acid-acetone is used for the simultaneous estimation of cobalt and nickel. Absorption spectra of 8-quinolinol compleves of cobalt and nickel in 1.Y HCl acetone are given in Figure 1 (14.6 pg. of Co per ml.; 13.7 pg. of Xi per nil.). I n the literature S-quinolinol in carbon tetrachloride or chloroform is used for separation after adjustment of p H ; in these solvents the cobalt-8-quinolinol complex shows only one maximum a t 365 nip, I n the solvent used in the ['resent v-ork (1N HC1-acetone) the cobalt complex shows maxima at 365 and 700 mp, while the nickel complex s h o w only one maximum at 365 mp. CPARATE
nickel-8-quinolinol to be a monohydrate, Ki(C&ON)z,. HzO and the cobalt-8-quinolinol a dihydrate, Co(CQ&ON)~. 2Hz0. The solvent, 1N hydrochloric acid-acetone, was prepared by diluting 133.3 ml. of doubledistilled hydrochloric acid (7.5N) to 1 liter, using pure acetone,
Table I.
Molar Absorptivities 365 mp 700 m.u
3529 3228
EC.3 ENi
428.9
...
Table II. Analysis of Samples Using Sodium Diethyl Dithiocarbamate
ANALYTICAL PROCEDURE
Xi, pg. in Co. fig. in 10 ml. 10 ml. Sample Taken Found Taken Found
An aliquot of the sample containing about 30 t o 500 fig. of cobalt and nickel was taken in a 50-ml. centrifuge tube, and 5 ml. of p H 9.5 borax-sodium hydroxide buffer &ere added. Then 4% alcoholic 8-quinolinol was added in excess for complete precipitation of the complexes. The precipitate was digested on a water bath a t 60' for 30 minutes and centrifuged. Excess reagent was removed b y successive washings with p H 9.5 buffer. It was found t h a t the solubility of complexes in pH 9.5 buffer affects the spectrophotometric estimations negligibly. The precipitate was finally washed with distilled water, dried in an oven at l l O o , and dissolved in 1N hydrochloric acid-acetone, and the volume was made to 25 ml. in the measuring flask. ilb-
I I1 I11
2 5 . 0 25.23 23.24 23.15 50.09 50.69 23.24 22.96 74.98 90.35 23.24 19.50
sorption measurenients were done at 365 and 700 mp, using solvent as reference. RESULTS A N D DISCUSSION
Cobalt changcs spectra in the presence of excess of halide ions in aqueous medium, because of formation of halo complexes. I n acetone medium the
REAGENTS A N D APPARATUS
8-Quinolinol was crystallized from a 207, alcohol-water mixture and dried in vacuum [m.p. observed 73' ( I ) ] . Hydrochloric acid and acetone were lurified b y standard methods. Analytical grade cobalt sulfate and nickel sulfate were used (British Drug Houses). 8-Quinolinol complexes were precipitated a t p H 7.5 ( 2 ) . Excess reagent mas removed by washings with buffer of pH 9,5. Chemical analysis showed the
A
Figure 1.
,mp
-
Absorption spectra of 8-quinolinol complex in 1 N HCI-acetone 0 Cof2
0 Ni+* VOL. 3 5 , NO. 1, JANUARY 1 9 6 3
4
47
equilibrium shifts to halo complexes because of the low solvating power of acetone. Recently work similar t o our unpublished work regarding the equilibria of cobalt-halo complexes in acetone medium was reported ( 4 ) . Cobalt-8-quinolinol-halide complexes show maxima at 365 and 700 mp. The absorbance of the cobalt-8-quinolinol complex is a t a maximum when the acidity of the solvent is greater than 0.75N in HCl. Therefore all the solutions were prepared in 1N HClacetone. Beer’s law was studied b y using solid 8-quinolinol complexes; i t holds below 20 pg. per ml. of metal radical. The molar absorptivities are given in Table I. Beer’s law also holds good for mixtures of 8-quinolinol complexes of cobalt and nickel in the same concentration range. The accuracy of the experiment was kept constant b y using a 4-cm. path for absorbance measurements a t 700 mp. For the comparative analysis, samples of known composition (British Drug Houses, Analar) were used. The exact
Table 111.
Analysis of Samples Using 8-Quinolinol Co, Fg./lO ml. Ni, pg./lO ml.
Sample Taken Found Taken Found I 17.6 16.4 10.4 10.2 I1 44.0 44.5 10.4 10.2 I11 88.0 89.1 10.4 10.5 IV 105.6 106.5 10.4 10.2 V 132.0 133.7 10.4 10.3
concentrations of the stock solutions were determined with sodium diethyldithiocarbamate (3). From Table I1 it is obvious that Beer’s law does not hold good above 50 pg. of cobalt. The same stock solutions were used for the analysis using 8-quinolinol (Table 111). It will always be necessary to separate cobalt and nickel from the interfering radicals like iron and chromium, which form complexes in the same p H range. It is possible t o extend the present method to iron-cobalt and chromiumcobalt systems, as all these complexes
absorb at 365 mp while only cobalt also absorbs a t 700 mp. I n the present method, the solution of simultaneous equations are simplified, as only cobalt absorbs at 700 mp while the absorptivity of the nickel species is equal t o zero at 700 mp. ACKNOWLEDGMENT
Thanks are due to S. K. K. Jatkar for his interest in the work and for facilities given during the present work. LITERATURE CITED
(1) Am. Chem. Soc., “Reagent Chemicals,” p. 180, 1950.
(2) Berg, R., 2. anal. Chem. 76, 191 (1929). (3) Chilton, J. M., ANAL.CHEM.25, 1274 (1953). (4) Fine, D. A., J. Am. Chem. SOC.85, 1139 (1962). (5) Gustin, V. K., Sweet, T. R., ANAL. CHEW33,1942 (1961). (6) Lingane, J. J., Kerlinger, H., IND. ENG.CHEM.,ANAL.ED.13,77 (1941). (7) . , Yoe, J. H., Jacobs, W, D.. Anal. chim. Acta 20,‘332 (1959) RECEIVEDfor review March 29, 1962. Accepted September 21, 1962.
Determination of Trace Amounts of C& Acetylenes in Hydrocarbons. Hydration to Carbonyls and Determination by UItravio let Spectrophotometry of 2,4-Dinitrophenylhydrazones M. W. SCOGGINS and H. A. PRICE Phillips Petroleum Co., Bartlesville, Okla.
F A method is described for the deacetylenes with termination of C& both terminal and internal acetylenic bonds in concentrations as low as 5 parts per million. Total acetylenes are determined by catalytic hydration to carbonyls and conversion of the carbonyls to the corresponding 2,4-dinitrophenylhydrazones which are preferentially extracted and measured spectrophotometrically. All interferences tested except that of isoprene can b e eliminated. In the concentration range of 5 to 500 p.p.m., the 4 and 5 carbon atom acetylenes give an average recovery of 96%.
I
petrochemical processes, a knowledge of the amount of alkyne hydrocarbons in process streams is important. Alpha acetylenes are usually determined by adding a n excess N MANY
48
ANALYTICAL CHEMISTRY
of metallic ion and titrating either the acid formed in the reaction or the excess metallic ion. Dialkylacetylenes are rarely determined, especially if present in very low concentration, because suitable methods are not available. Wagner, Goldstein, and Peters ( 5 ) determined total Cd and CS acetylenes in liquid hydrocarbons by catalytic ketal formation followed by hydrolysis of the ketals in a hydrosylamine hydrochloride solution. The liberated hydrochloric acid was a measure of the acetylenes. This procedure is timeconsuming and not suitable for acetylene determinations in the parts per million range. Siggia (3) hydrated acetylenes t o carbonyls with a mercuric sulfatesulfuric acid catalyst and determined the carbonyl derivatives b y the hydroxylamine hydrochloride procedure. The method is accurate and free of inter-
ferences but is not suitable for microgram quantities of acetylenes. Toren and Heinrich (4) suggested the extraction of 2,4-dinitrophenylhydrazones with iso-octane as a possible general procedure for the separation and determination of carbonyl compounds. Lohman ( 1 ) determined several aldehydes and ketones by condensation with 2,4-dinitrophenylhydrazine, selective estraction of the 2,4-dinitrophenylhydrazone from excess reagent with hesane, and measurement of the absorbance of the solution at 340 mp. I n this procedure, acetylenes in cyclohexane solution are hydrated to carbonyls with a mercuric sulfatesulfuric acid catalyst. Mercuric ion is removed by addition of sodium chloride and the carbonyls are extracted with 2,4-dinitrophenylhydrazine (DNPH) in sulfuric acid solution. The carbonyl
