this 1:tborntory girvt- vduc of 1.1 x 106 for t h o perchlorate formatioll coilstant of pnnphtholbcnzcin. With this vrilue the iridividual constants of thc other u c:ik b:ws niid indicators in T:ible 111 c:in be c:ilcuIntcd. Such constlints provide n convenient qu:mtitlltive nleaSIIrc of basicity dctcrIlijncd by forlnntion jVith rcfercncc noid. Roliablc constants mny be obtriined
quickly by thc modified Type I1 plot; sevcral points in the indicator ratio r:iiipc 0.5 to 1.5 will s d f h for such detrrniinitions. LITERATURE CITED
( 1 )of nodill, J. 1 5 , Ph.D. thegi% University \\‘isconsin, 1958.
( 2 ) Eictielbcrger, W. C., LsJIer, V. K., J . .I m. Chert. SOC.55, 3633 (1933).
(3 karnstein, H b c h i , Charlcs, ‘rakCW ANAL r t e hCrrest. c- R.1 28, lx6 (lo56). (4) HJlghes, H, K., et a/., [bid., 24, 1349 ( 1902). ( 5 ) Kolthoff, 1. hi., hiekenstein, s., J. Ani. Ckem. SOC.78, 1 (1SS6). (6) Rehm C. It:, Bodin, J. I., coiiriors, K. A,, kiguctii, Takeru, X S A L CHEM. 31, 483 (1959). RECEIVEDfor review August, 6, 1939. Accepted Novcmber 2, 1959.
It i L.
L. LEWIS
and W. A. STRAUB
A p p h d Research laboratory,
United
Stales Steel Corp., Monroeville, Pa.
A nisthod has been developed for the routine determination of large amounts of nickel and cobalt in complex high-alloy and stainless steels, Nickel is isolated from other elements by dimethylgiyoxime precipitation with or without a preliminary ion exchange separation, and cobalt is isolated by ion exchange. The separated metals are then determined by titrafian with fetfiylgnedinitrilo)tp?traaceticacid. The method has the advantage of speed, yet retains the accuracy of the commonly used methods far determining these elements.
HE conipiesity and thc number of high-alloy and stainless steels being produccd both commercially itnd experirnentttlly hnvc incrcswl as performance requirements have beconie more stringent. Demands for more rapid and reliable methods of chemical analysis for large amounts of nickel and cobalt in these steels have accompanied the increase. The dimethylglyoxime sepnration and gravimetric determination of nickel, although time-consuming, are still widely used. Several published methods for determining nickel in the dimethylglyosime prccipitnte include the direct titration of nickel with eyanide following the chemical dccomposition of the precipitate (4),and a redox titration based on the hydrosylamine liberated when the precipitate is hydrolyzed ( 1 ) . The first method is undesirable bccnuse of the toxicity of the cyanide reagent and the indistinctness of the end point. The other method is indirect and is subject to error if the precipitate is incompletely washed or incompletely hydrolyzed. The determination of large amounts of cobialt in steels has been complicated
I)y limitations i n mcthods for sepnrntion and dcterminntion. Intcrferenccs must be removed before the final precipitation of coLnlt with 1-nitroso-2-naphthol or the clcctrodeposition of cobalt ns the metal. In addition, whrn cobalt is ignitcld nnd n.sighccl as Co304,it will bo nonstoichiometric in composition unless ignited propcrly ( 4 ) ; and, in the clcctrolltic method, the cob:& mny not be depositcd completcly ( 2 ) . T h e , ferriryiriidv titrrition of cobalt in coniplcs stecls is not completely rcliablc vithout seprntions bccause of interfcrcnces from sonie co-alloying elements (4.). In recent years, both nickcl and cobatt have been titratcd successfully with (cthylcncdinitrilo)tctnacetic acid (EDTA) (8). Direct application of these titrations to the analysis of highalloy and stainless steels, however, is impossible because EDTA is nonspecific. A method was nceded for rapidly separating these elcments from each other and from other alloying elements prior to the EDTA titration. Diniethylglyosime, a specific reagent for nickel, was considered best for isolating nickel; however, no specific reagent is known for cobalt. A &isfactory method for isolating cobalt was not avsihble before the pioneering work of Kraus and Nelson (6). Their data indicate that cobalt could be separated from other elements in steels by adsorbing the sample on an anion exchange resin column and eluting selectively with hydrochloric acid. Analytical applications of :Inion exchange sepnrations in chloride media to heat-resistant nlloys nnd Alnico-type magnetic alloys have been reported (2, 5, 9). These procedures can be highly accurate, but they lack speed. A procedure has been developed that is based on isolating nickel and cobalt
(by dimcthylglyosime prccipitation and ion exchange separation, rcspectively) and then titrating them with EDTA. Large amounts of nickel and cobalt in high-alloy nnd st:iinlrss stecls with wide ranges in composition can be cletermined rapidly and reliably, and as accurately as by convcntiond nicthods. PREPARATION OF REAGENTS
ION ExcHANaE RESIN. Remove fiys
from Dowex I-X8 anion cschangc resin (J, T. Bnker Chemical Co.) by mising the resin as a n aqueous slurry and decanting three times. Remove traces of iron and aluminum remaining from the resin synthesis by washing alterrintely with concentrated hydrochloric acid and water until washings are colorless. For samples t h a t contain less than 0,3% copper, use 100- to W-mesh, and use 200- to 400-mesh for snmplcs with more than 0.37, coppcr. ION EXCHANGE COLUMIK.Obtain a column approximately 2 cm. in dinmeter and 18 cm. long, tapered at one end, and provided with a stopcock. Place a tuft of glass wool in the bottom of the column, add a slurry of cleaned resin, allow i t to settle, and add more resin until the packed bed. is about 14 cm. high. Cap the bed with a perforated ceramic disk from a Gooch crucible to prevent resin disturbance when the sample is added. Into the column insert a one-hole rubber stopper fitted with a funnel. Pretreat the column with 50 ml. of concentrated hydrochloric acid. Reagent-grade chemicals were used, unless otherwise noted. STLNDARD0,031ci EDTA. Dissolve 22.3 grams of disodium dihydrogen (ethylenedinitrilo)tetraacetic acid dihydrate in 2 litera of distilled water. Store in a polyethylene bottle. Standardize with standard 0.03M nickel solution at € 9I by using Eriochrome Black T ind!cator and manganese a8 a back-titrant (8). I n t h h and other
r
Sn (IV)
d
Zr
('N) Mo (VI 1
w
l
3
1 LOG
D, -1 FOR Li, Na, K , Rb, Cs, NH,, Be, Mg, Ca, Sr,Ba,Cr X , T i ( [ I l l , Ni, AI,Y, AND RARE EARTHS.
-2
I 0
Figure 1 .
I
,
2 4 6 0 IO 12 14 HYDROCHLORIC-ACID CONCENTRATION, MOLARITY
Log volume-distribution coeMcients of metoh anion exchange resin and hydrochloric acid
between
titrations in which nianganous ion is used, add 1 gram of ascorbic acid. To obtain sharp end oints, place a filament-type shaded lklb dircctly behind the titration solation, snd stir with a magnetic stirrer, STANDARD 0.03.11 ~ I A N O A N O CCrr1.oP RIDE. Dissolvc 5.9 grams of manganous chloride dihydrate i n 1 liter of distilled water and add 2 grnms of ascorbic acid to prevent oxidation during storuge. Stnntiwclize by titrating standard EDTA a t pH '3, by using Eriochronie Black T. Titrate from blue to red. STAXDARD 0.031kf XICKEL CHLORIDE. Dissolve 1.7607 grfims of spec-pure nickel metal (Johnson, Rfntthey &. Co., Ltd., So. 890) i n n minimum amount ol hydrochloric acid and dilute to 1 liter with distilled water. ERIOCHROMF, I ~ L A CT.K Triturate 0.2 grain with 50 g r m s of sodium chloride. PYROCATECIIOL I'IOLET. TritUrak 0.2 grani with 50 grams of sodium chloride. BUFFER,pH 9. Dilute 40 ml. of concentrnted ~ i i i n i ~ n i i ihydroxide m and 107 grams of nnimoniuni chloride to 1 liter with distillcd watcr. EXPERIMENTAL PROCEDURE
Ion Exchange Separation. Dissolve 0.2-gramsample in 15 ml. of 2 t o 1 hydrochloric wid-nitric acid. (Hydrofluoric acid may be added to samples difficult to dissolve. Sulfuric, phosphoric, and perchloric acids interfere in the ion exchange separation and must not be used,) bvaporatc the solution to dryness and bakc until fumeE of nitric acid are no longer evolved. Add 5 to 10 hi]. of concentrated hydrochloric acid t o the cooled residue to dissolve it, by heating if necessary. Disregard acid-insoluble silica, tungstic acid, and other acidinsolubles, After transferring the sample to the resin bed with a medicine 5
drop er, wash the sample beaker with smalr portions ot 9N hydrochloric acid, which are then added to the column. Limit flow rate in all separations to about 2 ml. per minute. Continue until the washings are colorless. If nickel is to be determined, collect the eluate obtained during sample addition with the nickel fraction. NICKEL, After transferring the sample quantitatively to the resin, elute the column with QN hydrochloric acid (50 to 75 ml.) until the diffuse green band containin the nickel, chromium, titanium, vanafiurn, and manganese is completely removed. Collect this fraction in a 400-ml. beaker and reserve it for the nickel determination. COBALT. If no copper is present, elute the blue cobalt band with 4N hydrochloric acid and collect it in a 400RII. beaker. When copper is present, elute the column with 7N hydrochloric acid (about 75 ml.) until the cobalt and copper bands overlap. Then elute the cobalt with 4.74 hydrochloric acid until the blue band is completely removed from the column. (Two yellow bands caused by iron and copper will remain on the column nfter removal of the cobalt.) While continuing with the nickel determinwtion, remove excess hydrochloric acid from the cobalt fraction by evaporation. EDTA Titration. NICKEL.Add 15 ml. of 50Oj, (w./v.) citric acid solution to the nickel fraction; then add concentrated ammonium hydroxide t o this fraction until the solution is slightly basic. (If the manganese concentration i s above lo%, use more citric acid.) After acidifying the sclution with 5 ml. of glacial acetic mid, add sufficient 1% alcoholic dimethylglyoxime to precipitate the nickel (0.4 ml.per mg. of nickel present, plus 5 ml, in excess). While stirring the solution, add concentrated ammonium hydroxide by drops until
precipitation bcgins, and then add 5 ml. in excess. Cool in an ice bath, filter on a medium retentive paper, snd wash with about 100 ml. of cool, distilIed water. Decompose the nickeldimethylglyoxime recipitate and wash it into the originay beaker by alternate washings with 1 to 1 hydrochloric acid and distilled wvater. Dissolve with alcohol any tcice of dimethylglyoxime remaining oti the paper and collect it to ensure thc recovery of sny occludcd nickel. Should a suspension of dimethylglyosime appear in the filtrate, add sufficient alcohol to dissolve it. JIeasurc about 25 nil. of standard EDTA into thc acidic solution; thcn carefully neutralize the solution (litmus paper) with 5% sodium hydroxide. I n order, add 15 rnl. of buffer, 1 gram of ascorbic acid, and 0.2 gram of Eriochrome Black T indicator mixture. Then titrate the solution, which will be a clear blue if excess EDTA has been added, with standard manganeee solution until the first permanent pink nppears. Should the titration be overrun, add a few milliliters of standard EDTA and again back-titrate with innngancse to the pink end point. COBALT.After evaporating the cobalt fraction to a few milliIiters, add about 100 ml. of distilled water, excess standard EDTA solution, and 1 gram of ascorbic acid. Neutralize the sohtion carefully with 5% sodium hydroside solution (litmus paper), after which add 10 nil. of buffer and 0.2 gram of Pyrocatechol Violet indicator mixture. Add standard niangnncse solution until the color changcs from red to pure blue, then add a few milliliters in excess. Now titrate the solution with standard EDTA until the last trace of blue disappears. (At the end point, continued addition of EDTA will cause no further change in the color.) This titration is reversible and can be checked by adding more manganese solution and again titrating with EDTA until the blue dissppears. Direct Nickel D e t e d n a t i o n without Ion Exchange Separation, When
nickel only is to b e determined, the ion exchange step can be eliminated and the nickel isolated directly with dimethyIglyoxime. After dissolving the sample, add 30 ml. of 50% citric acid solution, and make the solution slightly basic with ammonium hydroxide. If more than 1% cobalt is present, a d 15 ml. of concentrated ammonium hydroxide plus 5 grams of ammonium persulfate, and boil the solution for 5 minutes.) Then acidify with glacial acetic acid. Add sufficient 1% alcoholic dirnethylglyoxime to precipitate the nickel conipletely and complex the trivalent cobalt formed by the persulfate oxidation (0.4 ml. of 1% dimethylglyoxime mg. of nickel and cobalt present, p US 5 ml. in excess), Continue the precipitation, filtration, and titration of the nickel dimethylglyoxime as above. If the filter paper L discolored with a reddish brown precipitate after the
6
per
YOL 32, NO. 1, JANUARY 1960 e
97
nickel dinictli?l~l?osiriir~ previpit:i tc clissolves, repreci pi t :I t e t he 11ickei , DISCUSSION
Ion Exchange Separation. 'I'otnl sq):ir:itioii tirnc by ion esclinrige is miriiniixctl I)y using n 0.2-gr:irii snmplc nntl n rc:isoriribly coarse ion cschnnge rcsiri (100 to 200 nirsh). X timcconsiiiiiinl: step is cliniinatcd by not filtei ing off :iny tnnt:iluni, niobium, or tuiigetrri i c i i r l c i c d insoluble in the initiril hytlrot~hlniic :icitl dehydration of t h e s : i i ) ~ p I ~7~' 1~1 ~ si ~n ~ o l ~ I con~lc stituents iei!i:ii!i 011 the top of the rmin bed, 2nd CVLTI if seine should dissolvc tlwy would IN strongly adsorbed by thc rcsin :tnd not interfere. Bccnusc resin denning would be difficult bccausc of tlww insolublcs, it is more practiunl to tlisc:tr.d the rcsin after one run than to eIc:in it for rc-usc. (Alternntivcly, the :icid-iiisoliihlcs cnn be re-
1novr4 by filtrntion before the ion eschange separation, in which case the rcsin can be cleaned and rouscd.) Thc sample was introduccd to the resin in 9.4' rnther than 7 N Iiyirochloric acid to keep thc adsorbed nictnls in as narrow R zone as possible a t the top of the resin bed while the nickel fraction \vns clutcd. This allowd thc subsequcnt sep:rrations to be eflected on the short colunin. Cobalt will not separate compkteiy from copper unless precaution is tskcn in the elution sequence. In 7iv hydrochloric acid nnd nbovc, cobalt is adsorbed niorc strongly than coppcr. but below T N , lcss strongly. This is shown in Figure 1, which is a compi1:ition of original data from the publications of Kraus and Xclson ( 0 ) . Coppcr precedes cobalt during thc removal of nickel: chromium, wnndium, nisngancsc. and titanium with OS hydrochloric ncid. Subsequent elution of cobalt by
Table I.
Cobalt and Nickel Results on Standard Samples (Ion eschmge separation and EDTA titration) Sickel, % _ _ Cobalt,, ~70 Reported Found Diff. Reported Found 8 ' 46" 8.44 -0.02 .,. 42.90" 42.94 +0.04 20.65" 20:64 4l.?Uo 41,ti -0,03 20.25" 20.15
Sample
NBS 1533 KBS 167
SBS I68
NBS 1187
20.804 2 3 . 72 5.64 23.4
BCS 233
20.75 213.63
HCS 241/1 5,55 BCS 266 23.31 XIRS provisionnl certificate Yiduee.
-0.06 -0.09 -0.09 -0.06
Sample
co
40 20
20.21 11.16
-0.10 -KO5 -0.06
13.3
i3:i3
-0.17
,..
.
.
I
.
.
10 " C o 20 >in 1 cu 19 &In 15 Cr 15 Cr 0.3 Cu
NBS 121c XBS 121c NBS 1139 S B S 130
0.125 9.05 1.81 11.16 10.51 10.51 10.51 0.563
11.18 10.50 10 51 IO. 55 0.586
f0.001 -0.01 40.02 +0. 02 -0.01 0.00 +0.04 + O . 026
0 563
0.566
+Os W3
I
I
...
S B S 160a
...
DifT. io.010
0.135 0.1'20 9.04 1.83
0.125
>In 1
-0.01
20.26" 11.2%
Table II. Nickel Results on Standard Samples (Dimethylglyosime separation 311d EDTA titration) Constituent Nickel, % Added. % Reported Found
SBS 72d NBS 72d NBS 10ld NBS l l l h XBS 121h n'B5 121c
Dig.
14,14
+os 02
14.16
Table 111.
Partial Nominal Compositions of 9.tandard Samples (Per cent) National Bureau of Standards BritishlChemical Standard
60
Ni Mn Fe 6r
M O
w
Nb
Ta Si
cu AI
0
167 43 21 1.6 ?. 1 20 3.9 4.5 3.1 0.1 0.4 0.03 I
.
.
168 41
20 1,5 3.4
20 4.0 4 0 3 .O 1.0 0.8
0.04 .
I
.
ANALYTICAL CHEMl$fRY
153a
5.5
0.2 0.2 74 3.7 8.9 1.8
,.. ...
0.3 0.1
...
1187
233
21
20
24 11
2i
bl
1.3
22 3.4
2.4 1.3 .
.
I
0.9
... *
.
I
0,2
... 1 . .
... ...
I , .
0.6 6.1 7.0
?41/1
266
5.6 0.1
23 13
* . I
50
0.3 5.0 0.5 20
...
.
I
#
0.3 0.1 * a *
0,3
.*, *
,
I
1.2 ... 0.2
3.3
8.0
using 4N hydrochloric acid to scpamte it from coppcr would then be difficult becsusc the cobalt would h v e to overtake the copper and bc cluted nhend of it. A eolunin longer than about 14 cm. wouid be ncccssary, with a corresponding increase in separation time. Howcvcr, the two elemelits cnn be eluted to thc sanie section of the resin bed with 7X hydrochloric acid before the elution of cobalt with 4.4' hydrochloric ncid is continued, This proccdurc for separating cobalt from coppcr \vas sntisfactory with 100to 200-rnc~hrcsin fur samples containing RS much ns 0,3% copper. Snmplcs containing 5% copper wcre sepnrnted successfully on a 200- to 400-mesh resin column by this Snme clution sequence. For samples with 4% copper, Hibbs and Wilkins (3) used a longer column with thc 100- to 200-mcsh resin. They itlso hnvc reconimended the preliminary removal of copper as the sulfide, to ensure complete separation (9). By using the specified acid elutions and a resin of 200- to 400-mesh, however, scparations were obtained readily without resorting to suIfide precipitations. Fortunately, the progress of the coppercobalt separation can be followed by noting the progress of the zones, which are yellow and blue, respectively. The cobalt fractions and the acidinsoluble residues were analyzed spcctragraphicaIly to determine the purity of the cobalt fraction, and the amount of cobalt and nickel retained in the acidinsoluble residues, rcspcctively. Bolated cobalt fractions from National Bureau of Standards Nos. 153a, 167, 168, and 1187 were found to contain traces of silica and iron only. Analyses of the acid-insoluble materials showed that they contained only trace amounts of cobalt and nickel; this loss of cobalt and nickel was calculated to lower the results by only approximately 0.02%, which is within the precision of the methods. EDTA Titration. XICKEL,I n the nickel titration, adding exccss EDTA t o the acidified solution of the nickel dimethylglyoxime and then raising the pH t o 9 before back-titration preveiit the dimethylglyoxime precipitate from reforming, because the E D T A complex is more stable. Consequently, the dimethylglyoxime need not be decomposed chemically prior to titration. Up to 50 mg. of nickel (25% nickel in a 0.2-gram sample) can be titrated accurately Kith no interference from the dimethylglyoxime liborated from the diasolved precipitate. Larger amounts of nickel can be titrnted without decomposing the dimethylglyoxime, but the precision will decrease. COBALT.T h e method of determining cobalt by EDTA may well supplant the older chemical methods, Quantities of -5 to 100 mg. of cobalt were titrated
Kith a relative accuracy to 0.2%, and end points were sharp and reversible. Previously reported cobalt-EDTA methods were limited by the small quantity of cobalt that could be titrated, and by the irreversibility of the color end point (8). These limitations were overcome by using a back-titration method and manganese-Pyrocatechol Violet for indication of the end point, respectively. Iron must be removed from the asreceived, commercial-grade anion eschange resin; otherwise the cobalt fraction will contain enough iron to make the end point of the cobalt-EDTA titration indistinct. Direct Nickel Determination without Ion Exchange Separation. K h e n
nickel is separated directly b y dimethylglyoxime precipitation, a reddish browi precipitate of iron(II1)cobalt(I1) diniethylglyosime ( 7 ) may form and be retained Tvith the nickel dimethylglyoxirne if cobalt is not oxidized completely to the trivalent state by persulfate ( 5 ) . Upon subsequent solution of the nickel precipitate with hydrochloric acid, enough iron may be liberated from the slightly soluble ironcobalt complex to cause the nickelE D T A end point to be poor. When the discoloration of the filter paper s h o w the prc’sence of the reddish broirn precipitate, the nickel should be reprecipitated. The specified procedures for all E D T A titrations should be followed for precise titrations with stoichiometric end points For convenience in these nickel and cobalt titrations, the same reagents are used, except for indicators. The EDTA-manganese ratio was established as being the same for the two indicators. I n the cobalt titrations, accurate titra-
tions resulted only when excess E D T A was added, then excess manganese, folloived by E D T A to the end point. RESULTS
The results of the anaIyses of seven certified steels and cobalt-nickel alloys covering the range of metallurgical interest are listed in Table I. Each value for the “per cent found” is a n average of four or more determinations. The results tend to be slightly lo^, for no definite reason, but, in all but one case they fall within the range of values quoted on analysis certificates that w r e available. The precision of the method calculated as the standard deviation of a single determination was 0.05% for nickel and 0.08% for cobalt. The better precision of the nickel determination reflects the sharper end point obtained on the nickel titration. Table I1 contains results obtained on seven Sational Bureau of Standards steel samples in which nickel was determined by direct precipitation and titration (excluding a n ion exchange separation). The average error is 0.02%, and reveals no significant bias. The precision is comparable to that obtained when the ion exchange step is included in the procedure. T o test the applicability of this procedure to highalloy and stainless steels, several of these samples were modified with added elements. These additions caused no significant error in the nickel results. illthough the composition ranges of the certified steel samples analyzed do not duplicate those of many commercial and experimental steels, the niasimuni elemental compositions of these certified samples (Table 111) are generally
not exceeded in steel-making practice. Thus, the percentage compositions of the samples analyzed cover a range sufficiently wide to indicate that the procedure is applicable to a variety of high-alloy and stainless steels. ACKNOWLEDGMENl
The authors acknowledge the assistance of M. J. Nardozzi and the encouragement of L. M . Melnick throughout this work. LITERATURE CITED
(1) Furman, N. H., Flagg, J. F., IXD. ESG. CHEM.,ANAL.ED. 12, 738 (1940). (2) Hague, J. L., hlacxkowske, E. E., Bright, H. A., J. Research Natl. Bur. Standards 53,353 (1954). (3) Hibbs, C. E., Wilkins, D. H., Talanta 2, 16 (1959).
(4) Hillebrand, W. F., Lundell, G. E. F., Bright, H. .4.,Hoffman, J. I., “Applied Inorganic Analysis,” 2nd ed., Wiley, Sew York, 1953. (5) International Nickel Co., “Methods for Chemical Analysis of Nickel and High-Sickel Alloys,” 29 Bull. T-36 (1954). (6) Kraus, K. A., Nelson, F., “Anion Exchange Studies of the Fission Products,” Vol. VII, Proceedings of International Conference on Peaceful Uses of Atomic Energy, Geneva, 1955, Cnited Nations, New York, N. Y., 1956. (7) Welcher, F. J., “Organic Analytical Reagents,” Vol. 111, p. 184, Van Nostrand, Keiv York, 1957. (8) Welcher, F. J., “Analytical Uses of Ethj-lenediaminetetraacetic Acid,” Van Sostrand, Sew York, 1958. (9) Kilkins, D. H., Hibbs, C. E., Anal. Chznz. Acta 18,372 (1958). RECEIVEDfor review June 12, 1959. Accepted October 15, 1959. Division of Analytical Chemistry, 136th Meeting, ACS, Atlantic City, IT. J., September 1959.
Application of EDTA to Titrimetric Determination of Nickel in Nonferrous Alloys VERNON A. NELSON and LEWIS J. WRANGELL Research Laboratories, Allis-Chalmers Manufacturing Co., Milwaukee, Wis. F A method is described for the titrimetric determination of nickel in nonferrous alloys, using EDTA. Separation and purification of nickel are accomplished by double precipitation with dimethylglyoxime, thus eliminating the use of hydrogen sulfide for the removal of copper. Interferences caused by cobalt, iron, and tin are avoided. Cal Ver I is the indicator chosen. The method has been applied to a wide variety of nonferrous alloy standards containing from 0.1 6 to 66.3870
nickel. The 95% confidence limits for a single determination in the 0.16 to 0.60% range are +0.03%. In the 30.08 to 66.38% range they are
10.2 1 %.
I
laboratories, nickel in now ferrous alloys is usually determined titrimetrically. h gravimetric method is sometimes used. Each method has the disadvantage t h a t hydrogen sulfide is used (prior to N THESE
dimethylglyoxime precipitation of nickel) to remove copper which would otherwise interfere. The titrimetric method has the further disadvantage that the titrant (standard cyanide solution) requires frequent restandardization. It has been reported (1, I, 5, 6) that several metal ions, including nickel, have been successfully titrated with disodium dihydrogen (ethylenedinitri1o)tetraacetate (EDTA)-a stable solution. Furthermore, E D T A is reported (2) to VOL. 32, NO. 1, JANUARY 1960
99
