T a b l e 11. on, Values for FelI1)-FelIII) Couple Peak
Anodic
Y?;o,
2.0 2.5 4.0 5.0 10.0
No. of runs
E,(2)
10
0.010
6 5 6 6
-
E,fl)," V
+ +
0.000 0.015 =t0.005 0.020 0.000 0.025 i 0 . 0 0 5 0.035 i 0 . 0 0 5
Mean S t d dev Cathodic
2.0 2.5 4.0 5.0
10 6 5 6
10.0
6
0.010 i 0.000 0.011 0.020 0.021 0.031
i 0.003 i 0.000
IO.003 : 4 0.003
Mean Std dev
0.89
0.78 0.89 0.82
"m
c
0.84 0.85 0.04 0.89 1.07 0.89 0.98 0.95 0.95 0.07
ILAverage f standard deviation for Fe(I1) concentrations of 0.6, 1.0, 2.0, 3.0, and 4.0 m M .
6
Scmn R.I.
mV/sec
Estimated standard rate constant for oxidation of Fe(ll) as a function of scan rate. Identical results are obtained with 0.6, 1 . O , 2.0, 3.0, and 4.0mM Fe(ll) except at 500 mV/sec which was obtained with 3 . 0 m M Fe( I I )
Figure 2,
At a scan rate of 20 mV/sec, the separation of anodic and cathodic peaks is too close to 60 mV to provide kinetic information about the electron transfer reaction. For scan rates greater than 20 mV/sec, the large A E , and the relationship of current function (e.g., ~ ! , / U I ; t~o) scan rate correspond to Case I1 of Nicholson and Shain (19), an irreversible charge transfer process. Using the NicholsonShain treatment, ana values were calculated from the shift in E,, a t two scan rates; results are shown in Table
11. Anodic coulometric analysis of Fe(I1) a t +0.70 V in DMF 0.1M in TEAP indicates the expected one electron oxidation (experimental n = 0.94). The value of N must be 0.85 f 0.04. The standard rate constant for this reaction can be estimated from measured AE, and tabulated 4 values (20) using the simplified expression (21) (19) R . S Nicholson and I . Shain, Ana/. Chem.. 36,706 (1964) (20) R . S Nicholson. Ana/. Chem., 37, 1351 (1965). (21) R . N . Adams. "Electrochemistry at Solid Electrodes," Marcel Dekker, New York. N Y . , 1969, pp 124-60.
$
N
28.8k,/v1'2
(1)
Estimated values of k , are shown in Figure 2. The agreement of k , values a t different concentrations and scan rates 1 50 mV/sec indicate t h a t AE, is independent of cy and dependent only on iL. From results at the faster scan rates, k , tends toward 4.7 x cm/sec. Behavior of Fe(II1). Cyclic voltammograms of Fe(II1) in DMF solution 0.1M in TEAP were obtained by first sweeping cathodically ( E , = +1.5 V) and then switching toward anodic potentials (Ex = -0.7 V). Under these conditions, the same data are obtained as for Fe(I1) (see Table I). Received for review March 28, 1973. Accepted January 17, 1974.
Separation and Determination of Tin by Liquid-Solid Chromatography James S. Fritz and Louise Goodkin Ames Laboratory-USAEC and Department of Chemistry. l o w a State University. Ames. Iowa 50070
Methods gravimetry absorption (6, 7) and
which have been used to determine tin include ( I ) , titrimetry ( I ) , polarography ( 2 , 3 ) , atomic spectroscopy ( 4 , 5 ) , visible spectrophotometry fluorometric techniques (8, 9). However, it is
(1) N . H Furman, E d . , "Standard Methods of Chemical Analysis." 6th ed., D . Van Nostrand Co., Inc., Princeton, N . J . , 1962, Vol. I . (2) A. M . Bond. T. A. O'Donnell. A. 8. Waugh. and R. J W McLaughiin,Ana/. Chem.. 42, 1168 (1970). (3) T. Mukoyama, T. Yarnane, N Kiba. and M. Tanaka, Anal Chim Acta. 61, 83 (1972) ( 4 ) J A Bowman, Ana/ Chim Acta. 42, 285 (1968). (5) B. Molden, I . Rubekka, M Mikkovsky. and M Huka, Anal. Chim. Acta 5 2 , 91 (1970) (6) R . M Dagnall. T. S. West, and P. Young, Anaiys: ( L o n d o n ) , 92, 27 (1967). (7) J D Smith. Anal. Chim. Acta. 57, 371 (1971).
often necessary to separate tin from interfering species prior to determination. The separation of tin from other materials has been effected by precipitation ( I ) , liquidliquid extraction (10, 1I ) , distillation (12), liquid-liquid chromatography (13), ion exchange chromatography ( 14(8) B. R . Chamberlain and R . J . Leech, Taianta. 14, 597 (1967) (9) T D Filer,Anal. Chem.. 43, 1753 (1971). (10) N . Jordanov, St. Mareva, and M . Koeva, Anal. Chim. Acfa. 59, 75 (1972) (11) H.Green, Metailurgia. 70, 143 (1964). (12) M Farnsworth and J. Pecola in "Treatise on Analytical Chemistry." I . M . Kolthoff and P. J. Elving, ed., Interscience, New York, N Y.. 1961, Part I1 Vol 3 (13) J S Fritz and G L Latwesen, Taianta. 14, 529 (1967) (14) K A Kraus and F Neison, ASTM Spec Tech Pub/ No. 195, American Society for Testing Materials Philadelphia, Pa , 1958 A N A L Y T I C A L C H E M I S T R Y , V O L . 46, N O . 7 , J U N E 1 9 7 4
959
~
a
MI C
R O V O LTM E TER AMPLF E9
I 1
1 I
Table I. Approximate V o l u m e D i s t r i b u t i o n Coefficients for M e t a l Ions on XAD-11 Eluent
A>
HELIUM TANU
_ _ _ _ - -I _ 1 _ 1
',',"?bTOR
i
SOLVENT RESERVOIR FOR F L U S H I N G G A S MINIFOLD
t
Metal ion
~
1
1
Cr(II1)
1
I
Bi (111) c u (11)
1
Au(II1) Fe(II1) Pb(I1) Hg(W Mo(V1) Sn ( I V ) Ti(1V) V ( W
1-1 TANK FOR
SCRUBBING CORROSIVE GASES
I
i
Figure 1. Schematic diagram of the liquid chromatograph
17), and gas chromatography (18).
The separation method reported here is based on selective sorption of tin(1V) by Rohm and Haas XAD-11, a macroporous, polyacrylate resin containing amide functional groups. Previously, another polyacrylate resin, XAD-7, was shown to sorb gold selectively (19, 20). Tin is detected spectrophotometrically a t 225 nm by allowing the eluate stream to pass through a flow-through cell mounted in a visible-UV spectrophotometer. The amount of tin is obtained from a linear calibration plot of peak height us. pg of tin. The method reported here has several advantages over most other separation methods for tin: 1) The resin is selective for tin under the conditions used. 2) Tin is eluted from the resin under mild conditions ( L e . , 0.1M hydrochloric acid), whereas in other methods, eluents such as 9N sulfuric acid or hydrochloric acid-hydrofluoric acid mixtures are used. 3) Because there is no liquid phase coated on the resin as in liquid-liquid chromatography, there is no phase-bleeding problem. 4) Tin is detected automatically. 5) The separation of tin from other metals is rapid (5 to 6 minutes).
EXPERIMENTAL Instrumentation. A schematic diagram of the liquid chromatograph is shown in Figure 1. The eluent delivery and spectrophotometric detection systems have been described previously (21). For J Dawson and R J Magee Mikrochim Acta 1958, 325 T Nozaki 0 Hiraiwa C Henmi and K Koshiba Buil Chem SOC Jap 42, 245 (1965) W Husainand M Gulabi Separ Sci 6, 737 (1971 S T Sie J P A Bleumer and G W A Rijnders Separ S o 3 , 165 (1968) J S Fritzand W G Millen Talanla 18, 323 (1971) J S Fritz and W G Millen U S Patent No 3736126, May 29 1973 M D Seymour and J S Fritz A n a / Chem 45, 1632 (1973) A N A L Y T I C A L CHEMISTRY, V O L
46, N O 7 , JUNE 1974
1MHC1
2MHC1
4M HCI
6M HCI
