Extraction of the 1,lO-Phenanthroline, 4,7-Diphenyl-l, 10-Phenanthroline, a nd 2,4,6-Tr ipyr idy I-sy m -Triaz ine Complexes of Iron(l1) into Propylene Carbonate Application to the Determination of Iron in Sea Water and Aluminum Alloy B. G . Stephens and H. A. Suddethl Department of Chemisrry, Wofford College, Spartanburg, S . C . 29301
IDEALLY A SOLVENT used t o extract a species from an aqueous phase should be colorless, more dense than water, nontoxic, immiscible, and have little tendency to form emulsions. During an investigation aimed a t increasing the sensitivity of the iron-phenanthroline method for the determination of sulfur dioxide ( I ) , it was observed that propylene carbonate (4methyl-I ,3-dioxolane-2-one) extracted the orange tris( 1,lOphenanthroline)iron(II) complex rapidly, completely, and neatly. A study was initiated t o evaluate propylene carbonate as an extractant. Propylene carbonate has recently been proposed as a solvent for electrochemistry and electron paramagnetic resonance spectrometry (2). Propylene carbonate is colorless, nonhygroscopic, noncorrosive, chemically stable, and practically odorless. It is essentially nontoxic in oral doses or by skin absorption. It is more dense than water and has a high dielectric constant (69 esu at 23" C). Propylene carbonate has been used as a solvent for polymers and plasticizers and a number of inorganic salts. One hundred grams of propylene carbonate will dissolve 8.3 grams of water at 25" C (3). The l,l0-phenanthroline (phen), 4,7-diphenyl-l ,IO-phenanthroline (bathophen), and 2,4,6-tripyridyl-sym-triazine (TPTZ) complexes of iron(I1) were chosen as models for a study of the extractability of ion association chelate systems into propylene carbonate. Chelates containing the ferroin group have been widely used for the determination of iron. Vydra and Kopanica have reviewed the many analytical applications of phen ( 4 ) . The F e ( ~ h e n ) ~ complex +? has been successfully extracted into nitrobenzene as the perchlorate (5) and into chloroform as the dioctyl sulfosuccinate (6) o r iodide (7). The molar absorptivity is 11,100 in water at 510 m p and is increased by 1 3 . 5 x in nitrobenzene (5). A monograph has recently appeared which describes various applications of bathophen and TPTZ to the determination of iron (8). The authors point out that the Fe(bathophen)3+2 complex can be extracted into Present address, Department of Chemistry and Geology, Clemson University, Clemson, S.C. (I) B. G. Stephens and Frederick Lindstrom, ANAL.CHEM.,36, 1308 (1964). (2) R. F. Nelson and R . N. Adams, J . Electround. Chem., 13, 184 (1967).
(3) Jefferson Chemical Co.. Houston, Texas, Promlerir Carbonate .. Techtiicul Bulletin ( 1960). (4) F. Vydra and M. Kopanica, Chemist-Atmlyst, 52, 88 (1963). (5) D. W. Margerum and C. V. Banks, ANAL.CHEM.,26, 200 .
I
(1954). (6) K. Sono, H. Watanabe, Y . Mitsukami, and T. Nakashima, Bwiseki Kagaku, 14,213 (1965). (7) F. Vydra and R. Pribil, Talco?m,3,72 (1959). (8) Harvey Diehl, G. Frederick Smth, Loren McBride, and Richard Cryberg, "The Iron Reagents: Bathophenanthroline, etc.," 2nd ed., The G. Frederick Smith Chemical Co., Columbus, Ohio, 1965. 1478
ANALYTICAL CHEMISTRY
nitrobenzene, isoamyl alcohol, n-amyl alcohol, n-hexyl alcohol, octyl alcohol, chloroform, trichloroethane, and isoamyl acetate. Molar absorptivities range from approximately 22,000 to about 23,000 in the various organic extractants. Collins et ul. (9) found that the Fe(TPTZ)2+2complex was extracted rapidly and completely into nitrobenzene when associated with iodide or perchlorate, nitrobenzene being the only solvent that would extract the complex. The molar absorptivity of the complex was 22,600 in water and 24,100 in nitrobenzene. Propylene carbonate extracts the F e ( b a t h ~ p h e n ) ~ +com* plex completely in the presence of any common anion. The Fe(phen)3+2 and Fe(TPTZ)2+2complexes are partially extracted in the presence of any common anion and completely in the presence of iodide or perchlorate. EXPERIMENTAL
Apparatus. Separatory funnels with Teflon plugs and plastic stoppers were used for the extractions. Glassware was soaked in hydrochloric acid overnight and then rinsed with deionized water after each use. A Beckman Model D U spectrophotometer was used for quantification measurements; a Perkin-Elmer Model 4000A spectrophotometer measurements. One-centimeter Corex was used for , ,A, cells and 0.5-inch square cuvettes were appropriately utilized. A Corning Model 10 pH meter with conventional electrodes was used for measurement of hydrogen ion. Reagents. Solutions of 0.005M phen and 0.001M bathophen were prepared in 50% ethanol. 0.001M TPTZ was prepared by dissolving the appropriate amount in a few drops of hydrochloric acid and diluting with water. Distilled water was passed through a monobed ion exchange column composed of Dowex 50W-X2 resin in the hydrogen form and Dowex 1-X1 resin in the hydroxide form. Ethanol was distilled in all-glass apparatus. Propylene carbonate was vacuum-distilled in all-glass apparatus. Stock 0.002M iron solution was prepared from ferrous ethylenediammonium sulfate tetrahydrate (G. Frederick Smith Chemical Co.); 0.00002M iron solution was prepared fresh daily from the stock solution. Five milliliters per liter of iron-free hydrochloric acid (G.F.S.) were added in each case. Three 10% aqueous solutions of hydroxylammonium hydrochloride were prepared and rendered iron-free by extracting iron(I1) with the appropriate chromogen into propylene carbonate. Ten per cent sodium acetate and 2 M acetic acid-sodium acetate solutions were rendered iron-free by adding hydroxylammoniurn hydrochloride, the appropriate chromogen, and extracting with propylene carbonate. The 1M solution of sodium perchlorate could not be rendered iron-free by extracting with propylene carbonate alone because the solvent had a very high solubility in the
(9) Peter F. Collins, Harvey Diehl, and G. Frederick Smith, ANAL. CHEM., 31, 1862 (1959).
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Table I. Maximum Wavelength, Molar Absorptivity, and Results of Analysis of Spectrophotometric Data by Ringborn Method for the Three Complexes of Iron in Propylene Carbonate error - Relative analysis ___ Reagent , , ,A E 1 % absolute photometric error 5 10 11,400 2 9 (0 18-0 60 pmole Iron) Phen 5 0 (0 10->I 00 pmole iron) 10 0 (0 037->1 00 pmole iron) Bathophen 533 22,200 2 8 (0 095-0 33 pmole iron) 5 0 (0 054-0 50 pmole Iron) 10 0 (0 020->O 50 pmole iron) TPTZ 593 22,100 2 9 (0 090-0 33 pmole iron) 5 0 (0 054 0 50 pmole iron) 10 0 (0 023->O 50 pmole Iron)
Figure 1. Effect of pH on extraction of the three complexes curve 2, Fe(phenh+*(left ordinate), and curve Curve 1,Fe(TPTZ)2+*, 3, Fe(bathophe&'2 (right ordinate) salt solution. The iron was extracted by adding hydroxylammonium hydrochloride, phen, or TPTZ, and extracting with propylene carbonate-chloroform mixtures. Sea water that had been stored for approximately 8 months in a polyethylene bottle was filtered through Whatman NO. 40 paper. Recommended Procedure. An aqueous solution of the sample (containing 0.05 to 1.O pmole of iron if phen was to be the chromogen, or 0.025 to 0.5 pmole of iron if bathophen or TPTZ was to be the chromogen) was placed in an appropriate separatory funnel. Three milliliters of 10 hydroxylammonium hydrochloride, 5 ml of chromogen solution, 5 ml of 1 M NaCIOl (except for bathophen), and 5 ml of buffer solution were added ( l o x sodium acetate for phen and bathophen; 2M acetic acid-sodium acetate for TPTZ). Enough propylene carbonate was added so as to give about 3 ml of extractate. This was conveniently accomplished by adding 15 ml of propylene carbonate for each 100 ml of solution and shaking for a few seconds, then adding 5-ml portions of the solvent and shaking until a second phase was noted. If the propylene carbonate (lower) phase was less than 3 ml, it was adjusted by the addition of a small amount of the solvent. The whole operation of saturating the aqueous phase with propylene carbonate routinely took about 1 minute. The funnel was shaken for about 1 minute and the phases were allowed to separate while swirling intermittently; the lower phase was drained into a 10-ml volumetric flask. The stopcock bore and funnel stem were rinsed with about 1 ml of solvent and extracted again with 2-ml and 1-ml portions of solvent, rinsing after each extraction. The extracts were made to volume with 95 ethanol (iron-free) and the absorbance was measured at the appropriate wavelength (Table I) in 1-cm cells. Calibration curves were conveniently prepared using standard ferrous ethylene diammoniumsulfate tetrahydrate solution. Determination of Iron in Sea Water and Aluminum Alloy. The recommended procedure was used t o determine iron in 200-ml aliquots of sea water which had been spiked with various amounts of standard iron solution. The amount of iron added was 0 to 5.6 pg; the chromogens used were TPTZ and bathophen. Iron was determined in NBS Standard Sample 85B wrought aluminum alloy. Approximate 0.1-gram portions were weighed into 100-ml volumetric flasks, dissolved in 0.75 ml of " 0 3 and 1.2 ml of HCI, and made t o volume with deionized water. Ten-milliliter aliquots were analyzed for iron using the recommended procedure and employing phen as the chromogen. A n equal number of analyses were performed wherein 2 ml of saturated EDTA solution were added prior to extraction (Table 11).
x
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Table 11. Determination of Iron in NBS Standard Sample 85B Aluminum Alloy via Extraction of the Fe(phen)3+2Complex
X Fe 0.237 0.238 0.234 Average 0.2360 NBS analyses, reported 0.24%, average 0.236 range 0.23-0.24%. a Identical results were obtained when saturated EDTA solution was added prior to extraction.
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Miscellaneous. , , ,A values for the three complexes in propylene carbonate were determined in the usual manner. The spectrophotometric data were analyzed by the method of least squares to determine molar absorptivities and by the method of Ringbom (IO, I I ) to determine optimum concentration ranges for the methods and to establish the concentration ranges within which the relative analysis errors per 1 absolute photometric error were 5 and 10% (Table I). The effect of hydrogen ion concentration on the methods was studied by employing the recommended procedure without buffer and varying the pH with 1 M HCl and 1 M NH3. Absorbances were measured at the appropriate wavelength with a Bausch & Lomb Spectronic 20 spectrophotometer (Figure 1). The solubility of propylene carbonate in water and 50:50 mixtures of water and saturated sodium chloride solution was determined by titrating 100 ml of liquid with propylene carbonate to the cloud point, while stirring vigorously with a magnetic stirring bar.
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RESULTS AND DISCUSSION
The determination of iron in the parts-per-billion range is readily accomplished via extraction of the TPTZ or bathophen complex into propylene carbonate. The average per cent error for the determination of iron in sea water with bathophen and TPTZ was 5 in the 5- to 27-ppb range. The Certificate of Analysis for the aluminum alloy showed that the alloy contained 3.99x copper, this being about 17 times the reported iron content. Because EDTA will not pull the ferrous ion away from the Fe(phen)3"2 complex, it was assumed that incorporation of EDTA would prevent the formation of the Cu(phen)2+1complex and hence its extraction into the propylene carbonate layer. Apparently, under the conditions of the experiment, the copper complex was not formed even in the absence of EDTA. The Cu(phen)*+' complex readily formed in solutions made alkaline with
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( I O ) A. Ringbom, Z . Alia/. Cliem., 115, 332 (1939). (11) G. H. Ayres, ANAL.CHEM., 21,652 (1949). VOL. 39, NO. 12, OCTOBER 1967
1479
aqueous ammonia and was rapidly extracted into propylene of the extractant can be decreased by the addition of certain carbonate. However the addition of EDTA prior to extracelectrolytes. Although three extractions were made in these studies, two tion destroyed the complex. would probably have done just as well, particularly for the The analyses described in this paper were performed to demonstrate that the three iron(I1) complexes could be readily more dilute iron solutions. In all experiments the extracts extracted into propylene carbonate from relatively complex were made to volume with 95 % ethanol. This was probably matrices and be determined spectrophotometrically. unnecessary as they were never cloudy. The A,, and E values shown in Table I are not significantly Propylene carbonate should completely replace nitrodifferent from those obtained in other solvents (5, 8). The benzene as an extractant for the three complexes, particularly shapes of the absorption spectra were also very similar t o the Fe(TPTZ)2+zcomplex. Its density should make it the those obtained in other solvents. Ringbom plots showed choice over the lighter-than-water alcohols for the extraction of the F e ( b a t h o ~ h e n ) ~ +complex. ~ A minor advantage that the three complexes obeyed Beer's law over the range arises because of the low vapor pressure of propylene carstudied. Under conditions of analysis similar to those embonate at room temperature: there is practically no presployed in the recommended procedure, the relative analysis sure build-up when it is shaken with an aqueous solution in a error over the optimum range is 0.6% with the reagents studied when employing spectrophotometers which have a separatory funnel. As is true when using other solvents which extract the three complexes, reagent solutions can be rendered 0.2% photometric error (Table I). iron-free by prior extraction, The p H range over which the complexes studied can be extracted is fairly wide. The range for the F e ( ~ h e n ) ~ + ~ The only disadvantage in using propylene carbonate as an extractant is that it is somewhat soluble in water; however, complex is at least 2 to 9, for the Fe(TPTZ)*'* complex 2.5 to 8, and for the Fe(bathophen)3c2complex 2.5 to 9. These aqueous solutions can be rapidly and predictably saturated with the solvent. ranges are as wide or slightly wider than those reported for the extraction of the complexes into other solvents (5, 8). Propylene carbonate solutions of the three complexes ACKNOWLEDGMENT showed no signs of deterioration over the period of the inThe authors thank Frederick Lindstrom of Clemson vestigation. Also there were n o indications that any of the University for obtaining the absorption spectra and J. C. complexes were precipitating from the solvent. Loftin and Dan W. Olds of Wofford College for technical The solubility of propylene carbonate at 24" C expressed assistance. A donation of propylene carbonate from the as milliliters per 100 ml of liquid was 21.2 in water and 10.4 in Jefferson Chemical Company, Houston, Texas is gratefully a 50:50 mixture of water and saturated sodium chloride acknowledged. solution. The solubility in saturated sodium chloride solution could not be determined accurately by the cloud-point RECEIVEDfor review April 17, 1967. Accepted July 20, method because salt crystals began to precipitate after 5.5 ml of 1967. propylene carbonate were added. Apparently the solubility
Radiochemical Method for Determination of Arsenic, Bromine, Mercury, Antimony, and Selenium in Neutron-Irradiated Biological Material Knut Samsahl' A B Atomenergi, Stockholm, Sweden
NEUTRON ACTIVATION ANALYSIS of trace elements forming volatile compounds may in many kinds of materials be simplified by introducing a distillation step. The distillate may then be analyzed by gamma-spectrometry, either directly or after further chemical separations. Detailed methods for the distillation and quantitative determination of groups of radionuclides in different kinds of neutron-irradiated industrial product have been developed by Gebauhr ( 1 , 2 ) and Ross (3). In the present paper a radiochemical method for the determination of As, Br, Hg, Sb, and Se in biological material is described. It is based on a procedure developed for the simulPresent address, Gesellschaft fur Strahlenforschung ni. b. H ., 8042 Neuherberg, Ingolstadter Landstr. 1, Munich, West Germany. (1) W. Gebauhr, Kerntechnik, 4(8), 323 (1962). (2) W. Gebauhr, Radiochirn. Actn, 4 (4), 191 (1965). (3) W. J. Ross, ANAL.CHEM., 36,1114 (1964).
1480
ANALYTICAL CHEMISTRY
taneous distillation as oxides or bromides of 12 trace elements from sulfuric acid solution ( 4 ) . EXPERIMENTAL
Apparatus. The distillation apparatus, shown in Figure 1, is made of borosilicate glass, and ungreased B 14, B 10, or spherical joints are usedas connections. The neck of the distillation flask, A , is surrounded by three turns of a coil with a n inner diameter of 5 mm. This coil, which reduces spray during the distillation, forms the direct connection to the receiver, B. Reagents for flask A are added to a small funnel, H , and then sucked in through a capillary tube which continues along the walls and ends near the bottom of the flask. The distillation flask is surrounded by a borosilicate glass tube in order to ensure sufficient isolation during the distillation. The flask is heated with hot air from a Bunsen burner. (4) K. Samsahl, Aktiebolaget Atornenergi, Stockholm, Sweden, Rept. AE-82 (1962).
