metal was tactically assurried to be unity when the copper coverage was greater than about 10 monolayers. By use of 9.91 X 10-3M Cu(I1) in 0.1M NaC104, potential measurements were made with anodic and cathodic currents ranging from 35.0 to 1010 PA. The anodic and cathodic segments of plots of E US. log ([Cu2+] - i/kc,) were not continuous, as would be predicted from Equation 7, and neither segment was linear throughout the entire current range. Apparent linearity was observed for the points obtained with current values between 228 and 406 PA, yielding slopes of 0.53 and 0.34 for anodic and cathodic measurements, respectively. These values are in marked contrast to the value of 0.0296 predicted by Equation 7 for a reversible reaction. An additional experiment was performed in which stirred 1.OOM Cu(I1) perchlorate solution was electrolyzed at anodic and cathodic current densities low enough to ensure negligible concentration polarization. Pure copper wire electrodes with uniform areas were used. Plots of E us. log i yielded anodic and cathodic segments which became linear at an overvoltage of about 60 mV. This suggests that the rate-determining step in the reduction involves the transfer of the second electron, for which the following mechanism can be postulated: Cu(I1) Cu(1)
+ e+ e-
4
Cu(1) (fast)
4
Cu
(slow)
This mechanism would result in an inefficient plating process, because a portion of the Cu(1) would escape from the electrode surface by convective mass transfer. Additional studies are required to elucidate the kinetic parameters of the reaction. Mattsson and Bockris (3) conclude that the surface diffusion of adions is the rate-controlling step in thedeposition of copper from HzS04 medium at low current densities. Either this
explanation or the slow reduction of Cu(1) to Cuo could account for the low plating efficiency under convective conditions, In either case, the absence of stirring should enhance the plating efficiency significantly. This was tested by repeating several anodic stripping experiments under quiescent conditions, taking care not to exceed the chronopotentiometric transition time for Cu(I1). In each case, the value of overall efficiency exceeded 8 6 z . When an experiment under quiescent conditions (ec= 1400 microcoulombs) was repeated without pretreatment or oxidation of the platinum surface, the efficiency increased to 9 3 x , but did not increase further when the experiment was again repeated without pretreatment. This effect was reproducible and represents an increase of 100 microcoulombs in the amount of copper stripped. From physical measurement of the electrode area, we estimate that about 90 microcoulombs of copper are required to form a uniform monolayer on the RPE, assuming the electrode surface is smooth. This suggests the formation of a copper-platinum alloy. However, this effect appears to account for only a small fraction of each of the low efficiencies shown in Table I. Secondary waves which could be attributed to alloy oxidation were not observed during anodic or chemical stripping of the plated RPE. Thus, if an alloy is formed, it is apparently oxidized at the potential attained during the anodic step of the pretreatment. Further studies are in progress in an attempt to relate the observed efficiencies to experimental parameters and postulated mechanisms. RECEIVED for review July 31, 1967. Accepted October 30, 1967. Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for support of this research.
Gas Chromatographic Determination of 2,3=Butanediol in 1,2=Propanedio1 Using Tetrahydrox yethylethylenediamine as Stationary Phase B. A. Swinehart’ Wyandorte Chemicals Corp., Analytical Research Dept., Wyandotte, Mich. 48193
THE SEPARATION OF POLAR COMPOUNDS by gas chromatography has proved to be a generally troublesome problem. A typical example was presented by the need to determine trace quantities of 2,3-butanediol in 1,Zpropanediol. Phifer and Plummer ( I ) attacked this problem by choosing a partially deactivated solid support and by using water as the liquid phase and water vapor as the carrier gas. An alternative approach, as suggested by Smith and Johnson (2), is to choose Present address, Corning Glass Works, Sullivan Park, Corning N.Y. 14830 (1) L. H. Phifer and H. K. Plurnrner, Jr., ANAL.CHEM. 38, 1652 (1966). (2) E. D. Smith and J. L. Johnson, Zbid., 35, 1204 (1963).
a solid support which shows selective interaction with one of the components in a mixture. The systematic application of this technique to a variety of solid supports and liquid phases indicated that untreated Chromosorb W, regular, coated with tetrahydroxyethylethylenediamine (THEED) was a suitable combination for achieving the desired separation. Nadeau and Oaks (3) used a THEED column to separate ethylene and propylene glycols but they did not apply the procedure to other diols nor did they obtain sufficient sensitivity to determine parts-per-million quantities. This paper describes a method which has been applied generally to the separation of various diols and specifically to the determination of partsper-million quantities of 2,3-butanediol in 1,2-propanediol. (3) H. G. Nadeau and D. M. Oaks, Zbid., 32, 1760 (1960). VOL 40, NO. 2, FEBRUARY 1968
427
lLI l
C
a (L ir (L
C
c r I
10
20
30
40
MINUTES
I
I
15
Figure 1. Chromatogram of 1.5% of each glycol in water Col length, 1meter; col temp, 150' C; 2 4 sample A-Solvent B-Unidentified C-2,3-Butanediol D-l,2-Propanediol E-Ethylene glycol F-1,J-Butanediol G-l,3-Propanediol H-1,4-Butanediol
I
25
35
MINUTES
Figure 2. Chromatogram of 18 ppm 2,3-butanediol in 1,2propanediol Col length, 2 meters; col temp, 130' C; 3-pI sample A-Unidentified B-2,J-Butanediol C-l,2-Propanediol
EXPERIMENTAL Apparatus. An F & M Model 810-R12 gas chromatograph equipped with a hydrogen flame ionization detector was used in this study. The column was prepared from either a 1- or 2-meter length of l/c-inch 0.d. copper tubing. The solid support, 60/80 mesh Chromosorb W, regular (VarianAerograph), was coated with 10% THEED (Visco Products Co.). In view of the reported (4) beneficial effect of water, no special effort was made to dry the prepared packing. The column was conditioned for 1 hour at 150" C prior to use and was operated isothermally at 130" C or 150" C depending on the intended application. The injection port was operated at 180" C and the detector at 220" C. The flow rates of hydrogen and helium (carrier gas) were both set at 60 cc/minute. The recorder chart speed was 1/4-inch/ minute, and peak areas were measured manually using an Ott planimeter. RESULTS Calibration and Sample Analysis. For general qualitative work, the 1-meter column operated at 150" C gives separation as indicated in Figure 1. In order to determine parts-permillion quantities of 2,3-butanediol in 1,2-propanediol it is (4) D. M. Ottenstein, 7th Detroit Anachem Conference, October 1959.
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ANALYTICAL CHEMISTRY
necessary to use a 2-meter column at 130" C to obtain base line separation. Figure 2 shows the chromatogram for 18 ppm 2,3-butanediol in 1,2-propanediol. Quantitative results were checked in two ways. Chromatograms were obtained for as-received 1,2-propanediol and then again after addition of a known amount of 2,3-butanediol. The increase in area was related to the 2,3-butanediol content. A prepared standard of 2,3-butanediol in ethanol was used for direct area comparison, The two methods were in agreement to within 1 ppm at the 10-ppm level. The flame detector response was linear up to 115 ppm. Column Stability. Our observations on column stability have been similar to those of Nadeau and Oaks (3). As the column deteriorates the resolution decreases until it is no longer possible to separate 2,3-butanediol from 1,2-propanediol. This situation is readily apparent before becoming serious because the noise level increases noticeably. Column life is from two days to a week depending on the frequency of use. The column life can be extended by cooling to room temperature and decreasing the helium flow to a minimum when not in use. RECEIVED for review October 9, 1967. Accepted November 2,1967.
