Spectrophotometric Determination of Nickel in Calcium Metal -
Using 1,2 Cyclohexaned ioned w x ime RAYMOND C. FERGUSON
AND CHARLES V.
In the course of searching for a method that would be satisfactory for the routine determination of nickel in calcium metal containing more than trace amounts of iron, the possibility of using the uic&oximes was investigated. The reactions of 1,2cyclohexanedionedioxime (nioxime) and l,2-cycloheptanedionedioxime (heptoxime) with nickel in the presence of an oxidizing agent in alkaline solution are similar to the reaction of dimethylglyoxime in that, in each case, unstable, reddish-brown colors
A
PPROXIMATELY 125 papers published since 1900 have dealt with the colorimetric, photometric, or spectrophotometric determination of nickel. Hydrogen sulfide (IO),potassium thiocarbonate (IS), and ammonia (4)aIp inorganic reagents which have been proposed. Organic reagents have proved to be more sensitive, and the majority of the colorimetric methods suggested for the determination of nickel were based on its reactions with such compounds Various authors have investigated the sodium salt of diethyl-dithiocarbamate ( d ) , potassium dithiooxalate (7), 8-hydroxyquinoline (18), triethanolamine ( I I ) , forand 3-nitrososalicyclic acid (20). maldoxime (8), The most widely used reagents for nickel have been the vzcdioximes-i.e., compounds containing the group -C(=NOH)C(=SOH)--, which reacts selectively with nickel and other transition group metals. The gravimetric procedures involving these reagents are well known ( 6 ) ,and recently Voter and Banks have discussed the use of some water-soluble dioximes ( 2 4 ) Colorimetric procedures employing the vzc-dioximes are also widely used. The American Society for Testing Materials procedure employs a-furildioxime ; the nickel complex is formed in aqueous solution and is extracted into o-dichlorobenzene for the colorimetric comparison or measurement (3). The reaction of nickel with dimethylglyoxime in the presence of powerful oxidizing agents in strongly basic solutions has been studied and used widely since its value as a means of quantitatively determining nickel was pointed out by Rollet ( 2 2 ) . While the intensely colored (reddish-brown) complex is potentially an txxcellent colorimetric form, its instability and the drastic conditions for its formation are disadvantageous. Although over sixty published papers have discussed Rollet’s method and recent spectrophotometric investigations have suggested improvements (9, 17), the exact nature of the reaction is still unknown. Consequently, the method is largely empirical, and a closely standardized procedure must be used (9). A similar reaction with afurildioxime has been reported, but the complex was too unstable for quantitative work (16). Johnson and Simmons (12) recently reported the same type of reaction for nioxime ( l12-cyclohexanedionedioxime). They preferred to stabilize the nickelous nioxime (Bomplex with gum arabic, however; and they used the latter torin for a photometric method of determination. Because the vic-dioximes offered a number of good possibilities, a11 examination of the colorimetric properties of their nickel complexes was undertaken. APPARATUS
Constant wavelength measurements of the solutions were made with a Beckman quartz photoelectric spectrophotometer, 448
BANKS, Iowa State College, .4mes, Iowa
are produced having absorption spectra which are very similar. However, the red inner complex compound of nickel(I1) with 1,2-cyclohexanedionedioxime can be stabilized with gum arabic, is insensitive to pH changes, absorbs most strongly at 550 mfi, and conforms to Beer’s law. The applicability of this method to the spectrophotometric determination of nickel has been established. The effects of diverse ions are discussed and the method is applied to the determination of nickel in calcium metal.
Xodel DU. The wave-length studies were made with a Cary automatic recording photoelectric spectrophotometer, Model 12. Matched sets of 5.000-em. and 1.000-cm. Corex cells were used for the solutions and blanks. Corrections for slight differences in the transmittancies of the cells were made whenever necessary. The pH measurements were made with Beckman Model H-2 and Model >I pH meters. REAGEVTS
Bromine water, saturated. Calcium chloride solution. A solution of the reagenbgrade silt was treated with nioxime and activated charcoal to remove traces of iron and nickel. Diammonium citrate solution, 20%. Dimethylglyoxime solution, 1% ’ in 95% ethyl alcohol. Gum arabic solution, 10%. Heptoxime (1,2-~ycloheptanedionedioxime,Hach ChenucaJ Co., Ames, Iowa) solution, 0.47%. Nickel solution. A stock solution was prepared from Alond nickel dissolved in a ua regia. Appropriate dilutions were used as the standard nick3 solutions for the preparation of calibration curves. Nioxime (l,%cyclohexanedionediosime) solution, 0.8%. Reagentgrade chemicals were used throughout the work. Further urification was carried out whenever necessary. The acids a n 8 bases used were the c . P. grade ordinarily used in the analytical laboratory. COLQR REACTIONS
Preliminary experiments with the reaction of nickel with dimethylglyoxime, using bromine water as the oxidizing agent, confirmed the reported instability of the oxidized complex Typical absorption spectra obtained for the complexes which develop in ammoniacal solutions (pH 11.3) are given in Figure l Curves 1 and 2 were obtained 10 and 60 minutes after mixing, respectively. Sets of curves obtained a t 10-minute intervals were nearly idcntjcal to those previously reported in the literatup ( 1 4 , 17, 19). iittempts to improve the stability of the oxidized complex were not uniformly successful. The addition of sodium hydroxide, as recommended by Makepeace and Craft ( 1 4 ) , increased the rate of fading. Makepeace and Craft attributed this behavior to impurities in the reagents, and recommended special precautions for the preparation of the solutions to be used. More recent papere, notably that of Furnian and McDuffie (9), have suggested further modifications which reportedly produce more stable products. Investigation of these reactions is to be treated in later work. B ~ c a u wheptovime and nioxime (34)have certain advantages over dimethylglyoximc, it was of interest to study their reactions with nickel in the presence of oxidizing agents. Both heptoxime and nioxime produced reddish-brown complexes nearly identical
V O L U M E 23, NO. 3, M A R C H 1 9 5 1
449
to the dimethylglyoxime complest~s. When they 1wxtec.i with nickel in the presence of bromine water and ammonium hydroxide, the thrrr vicdioxinies p r o d u c d ahsorption spectra which wcw very nearly suprrimposable throughout, the visible range. Rei'tiust' thr heptosime antl uiosinie roinpleses were also unstahle irtidcr thfw conditions, thc i i ~ wrrl:igc.iit,s :tpprared to prodwc, n o t iitpro\vrnt'nt i n Kollet's mctho~l.
X and 4 of Figure 2. The suspensions containcd 1 and 4 ml. ot gum arabic solution, respectively, and were at p H 9. The at)qorbancies of these solutions continued to incrraqe until thcy leached the value obtained for solution 1. The results in basic solutions weir: mole variable, undoubtedly because of the retardation of color development. The optimum pII range was from pII 4 to 6, although the complex roulrt
2. c
1.5
-c" = 1.0 \
0
0
* C
Q ? I
n U
0.5
0.0
350 I
1
400 , -- 4
Iq'igure 1.
d!L 450
500 Wavelength, 550 mp
600
650
7
4bsorption Spectra of Nickel Dioxinie Solutions
I 5 4 Y 01 nickel per 100 ml. (:ary instrument, using 5.0-om. cells 1. 2. Oxidized dimethylglyoyime rmmplex at 10 and 60 minutes, respectively
3. 4.
( ) I I the other hand, the for.ni;ttion o f nickelous niosinict in t,he 1)1esvncc'of gum arabic, according t o thc procedure of Johnson and Simmons (12), produced u highly cdoird, stable sul;pcnsion*. I his red complex was the form whvtcd for further spcctrophotoiiietric inwstigat,ion.
loped satiufactorily froni pH 3 to 10. The (solor development in acidic solutions was essentially complete in 1 hour. 1,oiiger periods n-rw net:estzary for suspensions prepared undttr I)itsic conditions. Calibration Data. Th(s optimum range of' concentrations wt~s obtained directly from Figure 3, in which the percentage transmittancv was plotted a e a function of the logarithm of concerttration. This method is similar to that suggested by Ringboni ( 2 1 ) , in which percentagt absorptancy was plotted against tht' logarithm of concentration. 111 this t,ype of plot, the range of maximum accuracy falls between 20 and 60% transmittancy . Thus, the optimum range wafi 2 to 7 microgranis of nickel p e r milliliter when 1.000-cni. cells were used, or 0.5 to 1.4 micrograni,u per inilliliter in 5.o~-(.lIl. cells. The relative accuracy at :L particular concentration can br determined from thp slope of the. curve (2'1 ). Conforniity to h e r ' s law was confirnied by applyiug the statirtical twatment recominended hy RIandel(f6). The at)sorbancit%.+ of duplicatr rets of suspcrisions, ranging from 0.1 to 1.4 niicros of riickel per niillilitei,, w s r c determined :It 550 nip. Thl, squaws line, total varial)ility, experimental error, and dtbpartun. from linearity w e i ~calculated. The variance ratio, F = 1.41 Kith n, = 12 and n2 = 14, proved to be much smaller than the value given by the F-table (25),in which F (5%) = 2.53; therefore, there was no significant departure from linearity in thr range studied.
r ,
COLORIMETRIC PROPERTIES 0 I.' YICKELOUS NlOXliM E
Absorption Spectrum. A pronounced niaximuiii in the absorption spectra of the suspcnsiotis 1 curve 3, Figure 1) occurred at 550 nip. The wave length of the inaximum was confirmed for H. range of concentrations of nickol. using both the Cwy and t h e I3ecknian spectrophotoniet The reagents did not ahsort) appi'c'uiat>ly iii the visihlr rtlgion, HS is shown by curve .2 of Figure I . I':scess niosinie had no i~fraton the color intensity. 10 nil. ( ~ fthe reagent protfucirig I ht: same intensity a$ 1 ml. bility. Although gum arabic stabilized the coloretl zystcni, ('urves ' reagent retarded the ratti ut' color development. I antl 2 of Figure 2 show the uhiiorhancy at 550 mp as a function of tinir for suspensions containing, ttspectively, 1 and 4 nil. of 10% gum arabic solution in a 10O-inl. final volume. The rolut i o i l s w r e a t p H 5. The atMJ~ballCi~S of both suspenRiaJns he(.:mica identical within 24 hours, :tnd they remained corist:tnt for :tt least a week. Effect of pH. The retardation of color developmelit was niuch more pronounced in basic wlutions, a3 indicated by curves
Nickel nioxime, stabilized with gum arabic at 10 and 60 minute* 1 ml. each ofO.8% nioxime and 10% gum arnhic colutions diluted to 100 ml.
450
ANALYTICAL CHEMISTRY 0.18
0.16
0.14
>
0.12
Q
0
0.10 % 0
c 0 n
5
0.08
n
a
0.06
0.04
0.02
I
0.00 t
I 2
I
I
I
4
lime, Figure 2.
1 6
I
I 8
I
I
I
IO
hours
Stability of Nickelous Nioxime Suspensions
154 y of nickel per 100 ml. Beckman instrument, using 1.0-om. cells. solution: 1,3. 1 ml.
The least squares line and the experimental points were plotted in Figure 4. The standard deviation of (5) absorbancy for a single analysis was 0.0049. “Confidence limits” at the 99% level were calculated from this standard deviation and Student’s t-table (28). Interferences. The Cary instrument was used to determine the effect of diverse ions on the absorbancies in the region of 550 mp. Those ions which produced absorbancies outside of the confidence limits were treated as interferences. Anions which did not interfere when present in concentrations 1000 times the nickel concentration were the acetate, arsenite, borate, bromate, bromide, carbonate, chlorate, chloride, citrate, dichromate, ferricyanide, fluoride, iodide, mandelate, molybdate, nitrate, nitrite, perchlorate, phosphate, silicate, sulfate, thiocyanate, thiosulfate, tungstate, and vanadate ions. Ferrocyanide, cyanide, and ethylenediamine tetraacetate ions prevented the formation of the color. Potassium iodate produced results n hich were 10% low. Hexanitratocerate formed a precipitate at the p H of the determination. The oxalate ion produced a cloudiness in the presence of gum arabic. The permanganate ion absorbed appreciably a t 550 mw and had to be absent. The cations which did not interfere when the ratio of the ion to nickel was 1000 to 1 were the ammonium, sodium, potassium, beryllium, magnesium, calcium, strontium, barium, lanthanum, hydroxylammonium, manganous, zinc, cadmium, mercuric, aluminum, and plumbous ions. Several cations precipitated a t
Volume of 10% gum arabic
2,4. 1,Z. 3,4.
4 ml. pH 5 pH 9
the p H of the determination--e.g., titanium, zirconium, hafnium, vanadyl, ferric, stannous, and stannic. The colored chromic ion absorbed somewhat at 550 mp and could be present in a ratio of no more than 50 to 1. The ferrous, cobaltous, and cupric ions reacted with nioxime to produce highly colored complexes which interfered. Curve 3 of Figure 5 mas obtained for a solution of the ferrous nioxime complex formed under acidic conditions. The interference was minimized by oxidizing the iron to the ferric state and complexing it with diammonium citrate. The absorption spectrum of the citrate complex has been given as curve 4 of Figure 5 . Curves for nickelous nioxime (curve 1) and for Rollet’s complex (curve 2 ) have been included for comparison. The slight interference due t o ferric citrate can be further reduced by the use of a suitable blank. The ferric citrate complex was slowly decomposed and the iron was reduced by excess nioxime. Therefore, a moderate excess of citrate is desirable. If the absorbancy measurements are t o be made within an hour or two after mixing, 3 ml. of 20% diammonium citrate solution in 100 ml. of suspension are the upper limit permissible, as citrate has a retarding effect on the color development. High concentrations of electrolytes caused the results to be consistently low. This manifestation of the diverse ion effect was eliminated by preparing the calibration suspensions a t the ionic strength expected in the determinations.
V O L U M E 23, NO. 3, M A R C H 1 9 5 1
45 1
100
8C h 0
c
0
c
4 60 b
c
2
I-
5 40 c
c
0
:
a
20
0
5 Concentration Figure 3.
'0
of
Nickel
,
y
per
600
l00ml.
Calibration Curves for Niclielous Nioxime Suspensions
5-crn. cells, Beckman instrument 1.0-om. cells, calculated
A 10.0-cm. cells, calculated
0.E
Least
Squares
Line : A=0.004937c
+
0.007
0.E Q n
0 - 0.4 0,
0
0 z-$
0
e
s:
n
I
20 Figure 4.
I
I
40 60 Concentration of
Nickel,
80 ./ per
100 ml.
-
I
100
c
Least Squares Fit for Nickelous Nioxime Suspensions
Measured with Cary instrument, using 5.O-cm. cells.
Duplicates run o n separate dags
I 120
I*
452
ANALYTICAL CHEMISTRY Table I.
Nickel in Calcium Solutions"
Kickel Taken,
Iron Added.
7
Alg.
7
.. ..
31
15 31
" Each solution contained
Nickel Found. 14
Calcium solutions cont.ainiiig ktiown amounts of nickel ancl iroir were analyzed to check thc arcuracy of the method. T:hlt, I gives the rrsults obtained for a series of these solutions.
1.0 grain of calcium.
DETERMINATION OF NICKEL IN CALCIUM METAL
Abbey ( 1 ) has applied Rollet's method to t8hedetermination of t,races of nickel in high purity calcium and magnesium metals. He was able to makc t,he absorbancy measurements at 445 rnp because the iron concentration was so low that absorption k)y ferric: cit,rate was negligible. Because the amount of iron in the metal is often many times that found in Abbey's samples, t.he absorbancies should generally be measured a t ,530 mfi. Reference t o curves 1 and 2 of Figure 5 indicates that the absorbancy indvses a t thr lower peak of t,he oxidized complex and a t the nickelous nioxime peak are near]>-the same. Therefore, t,he loss in srnsitivity in changing to t,he newer method is small.
Figure 5. Volume of solution 100 ml.
Calibration Curve. Solutions containing 1 gram of calcium and known amounts of nickel were prepared by adding .thr standard nickel solution to appropriate volumes of the calcium chloride solution. These solutions, in 100-ml. volumetric flasks, were treated with 1 ml. of 20% diammonium citrate solution, 1 ml. of 10% gum arabic solution, and 1 ml. of 0.8% nioxime solution. The contents of the flat;ks were mixed after each addit.ion and after dilution to volume. -4 blank solution was prepared in t,he same manner, omittirig the nickel and the nioxime. I n 1 to 2 hours the absorbancy measurements were made in 5.000em. cells, a t 550 mp and :i 5 inp nominal band width. The C U I I centration range was 10 t.o I50 micrograms of nickel per 100 nil.
Recommended Procedure. Place 50 ml. of wakr iii a 400nil. beaker, and carefully add N. weighed sample of 2 grain. of small calcium particles. JVhrn the reaction i8 complete, atid 5 ml. of concentrated hydrochloric acid and 1 ml. of concent.rated nitric acid, and heat to dissolve the hydroxide and to oxidize any iron. Cool and add 2 ml. of 207, diammonium citrate, then adjust the solution to pH 4 to 6 with ammonium hydroxide. Rinse the snlution into a 100-ml. volumetric flask, dilute to the mark, and mix. Pipet 50 ml. of this dilution into another 100-nil. flask, retaining the remainder for the blank. Add 1 ml. of 10% gum arabic solution to each flask, arid mix well. Add 1 ml. of 0.8% nioxime solut,ion to the first aliquot only, dilut.e both solutions to the mark, and mix well, Xieasure the absorbancy of the colored aliquot against t'he blank after. an hour. The wve-length set,ting should he 550 mp.
Absorption Spectra of Complexes of Iron
Obtained with Cary instrument, using 5.0-cm. rcllr 1. Nickelous nioxime 154 y of nickel present
2. 3. 4.
Oxidized dimethylglyoxime complex at 10 minutes, 154 y of nickel present Ferrous nioxime, 500 y of iron Ferrir citrate, 2000 y of iron
V O L U M E 23, NO. 3, M A R C H 1 9 5 1 The range of nickel concentration chosen will depend upon the cell thickness to be used. The order of addition of the reagents is not critical, provided that the niosime is added last. DISCUSSION
The nickelous niosime method appears to have several advantages over the conventional dimcthylglyosime colorimetric procedure. The gum arabic suspensions are much more stable, although the maximum intensity ia not reached immediately. The drastic conditions of Rollet’s method cause most cations to precipitate, but the milder conditions of the new method permit the direct determination of nickel i n the presence of averal of these ions. Although comparison of curves 1 and 2 of Figure 5 viould indicate that Rollet’s method is much niore sensitive, the absorption of ferric citrate is usually so grrat that the smaller maximum at 530 nip is used instead of the intense irinximuni a t 443 mp. The absorbancy index of nickelous riiosinie a t 550 mp is of thr, s a ~ n e order as that of Rollet’s complex a t 530 mp. On this basis, the sensitivities of the two methods are comparable. The nickelous nioxiine method has the great advantage of simplicit,y. It, requires fcw prcliminary separations and eliminates the extractions required in some procedures. The accuracy and reproducibility are suffirient for the purpopes of trace analysis. LITERATURE CITED
(1) Abbey,
s., ANAL.CHBM.,20, 630
(1948).
Alexander, 0. R., Godar, E. M.,and Linde, S . J., ISIJ. KXG. CHEM.,ANAL.ED.,18, 206 (1946).
(2)
453 American Society for Testing Materials, Philadelphia, ‘’A.S. T.M.Methods of Chemical .4nalysis of Metals,” p. 161, 1943. Ayres, G . H., and Smith, F., IND. EX. CHEM.,ANAL.ED., 11, 365 (1939).
Brownlee, K. A., “Industrial Experimentation,” p. 59, Brooklyn, N. Y., Chemical Publishing Co., 1947. Diehl, H., “Applications of the Dioximes to Analytical C%emistry,” Columbus, Ohio, G . Frederick Smith Chemical Co., 1940.
Fairhall, L. T., J . I d . Hug., 8, 528 (1926). Fischer, J., and Cayard, M., 2. anal. Chem., 122, 251 (1941). Furman, N. H., and McDuffie, R., Atomic Energy Commission, Classified Report, AECM-4234 (1947). Jiirvinen, K. K., 2. Nahr. Genussm., 45, 183 (1923). Jaffe, E., Industria chimica, 9, 151 (1934). Johnson, W. C., and Simmons, M., Analyst, 71, 554 (1946). Lindt, V., 2. anal. Chem.. 53, 165 (1914). Makepeace, G. R., and Craft, C. H., IND.E m . CHEX.,. ~ N A I . . ED., 16, 375 (1944). Mandel, J., J. Chem. Education, 26, 534 (1949). hfitchell, .4. M., “Spectrophotometric Study of ColorinietJ.ic Methods for the Determination of Nickel.“ 11,s. thesis. Purdue University, 1945. Mitchell, A. M.,and Mellon, M. G.,ISD. ERG.CHEar., A N \ L ED., 17, 380 (1945). . Lloeller, T., Ihid., 15, 346 (1943). Murray, W. M.,Jr., and -4shley, 9. E. Q., Ibid., 10, 1 (1938). Perry, M. H., and Serfass, E. J., ANAL.CHEM.,22, 565 (1950). Ringbom, A , 2. anal. Chem., 115, 332 (1938). h l l e t , A. P., Compt. T a d . , 183, 212 (1926). Snedecor, G. W., “Statistical Methods,” 3rd ed., pp. 5 5 . 184, Ames, Iowa, Iowa State College Press, 1940. Voter, R. C., and Banks, C. V.,. ~ N . \ L .CHCM.,21, 1320 (1949). RECEIVED July 31, 1950. Contribution No. 114 from the Institute for Atomic Research and Department of Chemistry. Iowa State College, Ames, Iowa. W o r k performed in the Ames Laboratory of the Atomic Energy Commission.
Spectrophotometric Determination of Cerium(W) A. I. MEDhLI-4 A N D B. J . BYRNE Brookhasen National Laboratory, Upton, Long Island, IV. Y It was desired to study the behavior of solutinns of cerium at as low concentrations as could be conveniently determined. It appeared likely that the sensitivity of an existing colorimetric method, based on the yellow color of ceriurii(IV),could be improved by working in the ultraviolet. Cerium(1V) was found to show an absorption maximum at approximately 320 mp, with a molar extinction coefficient of -5.58 X IO8, in 1 N sulfuric acid. t photometric sensiti\it>
T
HE fanii1i:ir yellow color ot tile ceric iou in acid mrdiuni has
been made the basis for i~ colorirnetric procedure, in which cerous ion is oxidized with persulfate ill boiling 1 N sulfuric acid with silver ion as a catalyst (8). If the intensity of the yellow color is determined visually, the sensitivity is approximately 10 micrograms of cerium per square centimeter, while the photometric sensitivity with a blue filter is 0.5 microgram (8). .I spectrojihotomotric study in the vi6it)Ie range (2’) has established that the ahsorption of ceric sulfate illcreases continuously up to 480 mp (t.he lower limit of the study), so that as pointed out by Sandell ( S ) , increased sensitivity would be expected to result from use of monochromatic violet light. Since completion of the present, xvork, Freedman and Hurne ( 1 ) have shown that the maxirniini ahsorption occurs in the neighborhood of 315 I ~ I P , and have reported on work in which cerium was oxidized by a modification of the procedure of Sandell, and measurements were made a t 315 mp.
of 0.025 microgram can thus be realized. In the determination of cerium by oxidation with persulfate, it is important not to take too large an amount of persulfate or of ammonium ion, because both residual persulfate, and nitrate ion formed by oxidation of ammonium ion, absorb appreciably at 320 nip. 4 spectrophotometric procedure for the deterniination of traces of ceriii~iiimproves sensitivity twentyfold oter the pre+iouscolorimetric procedure.
ABSORWION SPECTRUM OF CERIC ION
The absorption spectrum of a solution of ceric sulfate (1.92 X 10-5 V) in 1 N sulfuric acid, obtained with a Cary recording spectrophotometer (10.0-cm. cell), is shown in Figure 1. T h r maximum, which is fairly broad, occurs a t approximately 320 mp. The rnolar extinction coefficient is 5.58 X IO3, permit,t,ing a photometric sensitivity of 0.025 microptam of cerium. The effect of v i d strength on the location and height of the ma?;iniuni is slight,, over the range 0.1 to 6 .V sulfuric acid. DEVELOPMENT O F PROCEDURE
I t was first attempted to determine cerium according to the procedure of Sandell (8), with the modification that the absorption was measured a t 320 mp, using a Beckman DU spectrophotometer with a 1-cm. silica cell. In this procedure, 10 ml. of solution are made 1 N in sulfuric acid, and 0.2 gram of ammonium
