and washings. This loss amounts t o 0.1 to 0.2 mg. for quantities of iron less than 100 mg. and rises as high as 0.5 mg. n i t h larger amounts. However, in terms of percentage error resulting from these losses, more accurate results w e obtained when the quantity of iron is greater than 100 mg. Extensive studies have been made
on the use of benzenephosphinic acid
for the separation of iron from other cations and the effect Of heavy common anions on recoveries of iron by the reagent (1). LITERATURE CITED
(1) Banks, J. E., Pennell, J. F., Skoog, D. .4..ASAL. CHEJI.29, 113 (1957).
( 2 ) Fortune, K.B., lIellon, hf. G., I?*.D. ENG. CHEM., ANAL. ED. 10, 60
(1938). (3) Michaelis, A., iinn. 181, 265 (1876). (4) Michaelis, A,, Ananoff, J., Ber. 7, 1688 (1874). ( 5 ) Victor Chemical Works, Chicago, Ill.. “New Victor Chemicals,” 1963. RECEIVED for review July 20, 1956. Accepted October 27, 1956.
Benzenephosphinic Acid as Analytical Reagent Separation of Ferric Iron from Certain Anions and Cations JAMES E. BANKS’, JOHN
F. PENNELL2, and
D. A. SKOOG
Department of Chemistry and Chemical Engineering, Stanford University, Sfanford, California
b Benzenephosphinic acid separates ferric iron satisfactorily from large excesses of manganese, nickel, cobalt, cadmium, magnesium, the alkaline earths, arsenic, phosphate, citrate, tartrate, oxalate, and chloride. The separations are comparable to or better than existing methods. The precipitate forms rapidly, is easily filtered and washed, and provides a satisfactory weighing form for the iron. Because of coprecipitation, iron cannot be separated satisfactorily from aluminum, chromium and vanadium. Other elements which form insoluble precipitates with benzenephosphinic acid include titanium, molybdenum, zirconium, cerium, uranium, tungsten, tin, bismuth, silver, and mercury.
F
BI~NZENEPHOSPHIKATE is a satisfactory weighing form for trivalent iron, and a procedure utilizing the formation of this compound can be carried out in acid solutions (1). Michaelis (Z)> in describing the properties of benzenepliosphinic acid, indicated tliat the heavy metal salts of blie acid irerc generally not soluble in water and that silver! mercurous, mercuric, and ferric ions formed insoluble precipitates from mineral acid solutions. KO other data are available in the literature regarding the solubility of the salts of benzenephosphinic acid, and it was not possible to judge how selective a reagent it would be for iron. Therefore, experiments were carried out to determine what other ions would affect the deterniination of iron, either by
ERRIC
Present address, O M S Box 173, Iiirtland Air Force Base, N. M. * Present address, Calavaras Cement Co., San Andreas, Calif.
precipitation with the reagent, by coprecipitation during formation of the precipitate, or by complex formation with the benzene phosphinate or ferric ions, REAGENTS AND SOLUTIONS
Benzenephosphinic Acid Solution. The method described previously (1) was used. Ferric Iron Solutions. These were prepared and standardized as described previously (1). Cation Solutions. Solutions of t h e various cations studied 11ere prepared by dissolving suitable quantities of t h e reagent glade salts in water. K h e r e necessary, sulfuric acid n as added t o preyent hydrolysis. I n most cases t h e chlorides, sulfates, or nitrates of t h e cations were used. Hon-ever. solutions of arsenic(II1) and arseniciV) were obtained from sodium metaarsenite and sodium metaarsenate, respectively; chroniium(J-I) from potassium chroniatr; vanadium
Table I.
(73 from aiiimonium metavanadate; molybdenum(V1) from ammonium molybdate; tungsten(V1) from sodium tungstate; and uranium(V1) from uranyl acetate dihydrate. The solution of vanadium(1V) was prepared b y reduction of a n acid solution of vanadium(\’) with sulfite, followed by boiling to remove the excess sulfur dioxide. The solutions of zirconium (117) and titanium(1V) mere prepared b y fusing the corresponding oxides with sodium pgrosulfate and dissolving t h e fluxes in 2N sulfuric acid. Anion Solutions. These were prepared b y dissolving suitable n eights of t h e reagent grade alkali metal or ammonium salts in water. Buffer Solution, pH 4. A solution approximately 0.75F in acetic acid and 0.12F in sodium acetate v a s prepared. T h e p H of this buffer v a s then adjusted b y additions of glacial acetic acid or sodium acetate such t h a t n hen diluted with 1 volume of water and 1 volume of 0.05F benzenephosphinic acid, a solution of pH 4.0 = 0.2 n a s obtained.
Qualitative Precipitation Tests with Benzenephosphinic Acid
Coinposition of Solutions 0 . 5 5 HzSOd
Ions Forming Precipitates Fe(III), Ce(IV), hIo(TI), U(VI), W(l-I), Ti(IV), %r(IS’)
O , l a l - HC10,
Fe(II), Fe(III), Bi(III), Sn(II), Sn(IV), Ag(I), Hg(II)
Acetate buffer, pH 4
Fe(II), Fe(III), Bi(III), Sn(II), Sn(IV), Hg(I1)
Ions XotlPrecipitating
Ca(II)a, Sr(II)Q, Ba(II)O, Mg(11),Cu(I1) Cd(II), Mn(II), Xi(II), Co(II), Cr(III), Cr(W), Al(III), V(IV), V(V), -4s(III), As(V). Ca(II), Sr(II), Ba(II), hTg(131, Cu(II), Cd(II), Nl(II), CO(11), Zn(II), Pb(II), Mn(II), Al(III), Cr(III), .4u(III). Ca(II), Sr(II), Ba(II), Mg(II), Cu(II), Cd(II), Ni(II), Co(11), Zn(II), Pb(II), Mn(II), ill(III),Cr(III), Au(II1).
Solutions 0.5-l’ in HCl.
VOL. 29, NO. 1 , JANUARY 1957
e
113
Table II. Separation of Iron from Metallic Ions b y Precipitation with Benzenephosphinic Acid
Table 111.
(Precipitation from 0.53- H#Or unless otherwise specified) Foreign Ion, Foreign Ion Mg. None
hk
...
635
63.5 63.3 63.3 63.3 63.3
63.5 63.2 - 0 . 3 63.3 -0.2
635"
63.5 63.2 63.2 63.8 63.5 63.3
Sr
635"
63.8 63.4 - 0 . 4 63.3 -0.5
Ba
635.
6 3 . 5 63.4 -0.4 63.4 -0.4
Ca
Mn(I1)
40
55 635
Cd
112 635
Ni( 11)
59 635
-0.3 -0.3 -0.3
+O.l
63.5 63.3 63.3 63.5 63.3 63.3
-0.2 -0.2
-0.1
-0.2
+0.1 -0.2 -0.2
-0.3 -0.2 0.0 -0.1 -0.1
-0.2 -0.2
635
63.5 63.1 -0.4 63.2 -0.3 63.5 63.3 -0.2 63.5 0.0
AE(111)
635
63.5 63.5 0.0 63.4 - 0 . 1
As( V)
635
63.5 63.0 -0.5 62.8 -0.7
Zn
635
63.5 64.2 f0.7 64.0 + 0 . 5
Co(11)
59
52
63.5 64.3 63.8 63.5 64.4 64.4
Cr( VI )
52
63.5 64.6 +1.1 64.8 $1.3
V( V)
49
63.5 64.2 1-0.7 64.3 +0.8
V( IV)
49
63.5 66.0 +2.5 64.5 $1.0
Cu(I1)
59 59b
63.5 62.4 61.4 63.5 59.2 59.9
27
63.6 66.8 +3.2 66.8 +3.2
Cr(II1)
A1
10
$0.8 $0.3 +0.9 +0.9
-1.1
-2.1 -4.3 -3.6
Precipitations from 0.5N HCl. b 1 0 0 ~ ' excess of precipitation agent used rather than 50% excess. a
1 14
ANALYTICAL CHEMISTRY
Taken 0'3 5
63 GS G'3 63 63
iYonea Caa SrQ Baa a
0 0 6%
635 635
5 5 3 3 5
63 8 63 8 63 8 G3 8
hIg.
Found 63 3 63 5 63 6 63 3
Calcd.
Found
0 0 0.2
... 0 2
64 1 64 4
63 4 63 4 63 4 63 4
0.0 0.0 0.0 0.0
...
