Spectrophotometric Determination of Iron in Ethylene Amines with Phenyl-Zpyridyl Ketoxime E.
R. SIMONSEN Research and Development Department, Union Carbide Corp., Chemicals Division, Tarrytown,
ROBERT CHERNIN' and
b Ferrous ion form!; a bluish-purple complex with phenyl-2-pyridyl ketoxime, in aqueous ethylene amine solutions, which is extractable into an isoamyl alcohol-ethanol mixture. Factors affecting the analytical use of this reaction have been investigated. The complex shows three absorption maxima at 588, 509, and 405 mp. The molar absorptivities clt 588 mp are of the order of lo4. A Beer's law study showed a linear relationship from 10 to 2 0 0 pg. of iron per 25 ml. of final solution over an absclrbance range of 0.075 to 1.52. The composition of this colored complex. is 2 moles of reagent to 1 of iron and indicates a neutral species. The tolerance to a number of diverse i c m has been established and a procedure for the determination of small amounts of iron in ethylene amines has been developed.
T
considerable interest in the relationship of iron content to color and color build-up in various commercial ethylene amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. The uses of these ethylene amines have become somewhat more sophisticated t h m were the initial uses, and in some cases the presence of small amounts of soluble iron can be a critical factor. The need for a reliable method to determine iron concentration in the p.p.m. range, where the iron may be complexed with the amine, appeared necessary. Such a method could be used by customers to monitor iron content since contamination most often arises through improper storage and handling of these materials. Highly satisfactory reagents are known for iron in nexral solutions (1). For example, 4,7-diphenyl-l,lO-phenanthroline and 2,4,6-tripyridyl-s-triazine are of such extraordinxy sensitivity as to make possible the determination of iron in the p.p.b. range. Phenyl-2pyridyl ketoxime is kss sensitive but has the advantage of reaction in and extraction from alkalir e solution. Trusell and Diehl (.a) have reported the use of phenyl-2-pyridyl ketoxime for the determination of small amounts HERE
HAS
BEEN
Deceased January 10, 1964.
of iron in strongly alkaline materials, such as the hydroxides of sodium, potassium, and lithium, and sodium carbonate. The intense red ferrous derivative was extracted from strongly alkaline solutions into isoamyl alcohol and the visible absorption spectrum exhibited a single band with a wavelength maximum a t 550 mp. The composition of the colored complex was found to be 3 moles of ketoxime for each atom of iron, indicating an anionic species. Since aqueous solutions of the ethylene amines are strongly alkaline (pH > 12), phenyl-2-pyridyl ketoxime was investigated as a reagent for the determination of small amounts of iron in such materials. EXPERIMENTAL
Reagents. STANDARD IRON SOLUThe standard used for measuring the recovery of the method and in preparing calibration curves was prepared by dissolving a weighed amount of iron wire in a minimum of hydrochloric acid and diluting with water t o a known volume. The standard for the precision study was prepared from a weighed amount of ferrous ammonium sulfate hexahydrate. REAGENTSOLUTION. Prepared by dissolving 2 grams of phenyl-2-pyridyl ketoxime in 1 liter of 0.1 AT hydrochloric acid. The reagent is available from the G. Frederick Smith Chemical Co., Columbus, Ohio, and should be checked for purity (melting point) prior to use. The desired melting point range is 150' to 152' C. If the melting point is low, reflux the material in the minimum amount of chloroform required to dissolve all of the solid. Cooling the solution will cause the syn-form of the oxime to crystallize. Filter and recrystallize the product from ethanol with a little Korite. REDUCINGAGEST SOLUTION, IRONFREE. Prepared by dissolving 10 grams of sodium hydrosulfite in 50 ml. of water and adding 25 ml. of 0.2% phenyl2-pyridyl ketoxime and 25 ml. of lOiM sodium hydroxide. Allow to stand for 10 to 15 minutes. Extract the iron complex with 10 ml. of an isoamyl alcohol-ethanol (15 :2) mixture. Pass the aqueous layer through Whatman #41 filter paper and collect. Prepare fresh each day. TIONS.
N. Y.
ETHYLENE AMINES,IRON-FREE. Prepared by distilling, under reduced pressure, commercial samples of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. These samples were tested and shown to be iron-free by the recommended procedure below. Apparatus. All absorbance measurements were made w-ith a Cary 14 spectrophotometer using matched silica cells of 1- and 5-cm. light paths, Procedure. Introduce a 10-ml. aliquot of the sample (or less if the iron content is suspected of being >20 p.p.m.) into a 50-ml. graduated mixing cylinder. Dilute to the 25-ml. mark with distilled water, mix thoroughly, and transfer the contents to a 100-ml. beaker. Add 2 ml. of the IO'% sodium hydrosulfite solution (iron-free) and allow t o stand for a few minutes. Add 5 ml. of 0.2% phenyl-2-pyridyl ketoxime solution and heat for 10 to 15 minutes in a hot water bath (80' to 100' C.). Cool the sample and transfer the contents t o a 125-ml. separatory funnel. Add 15 ml. of an isoamyl alcoholethanol mixture (15:2), shake vigorously, and allow the layers to separate. Draw off the aqueous layer and allow the alcohol layer to pass through Whatman #41 filter paper into a 25-ml. volumetric flask. Rinse the filter paper with isoamyl alcohol and dilute to the mark. Measure the absorbance a t 588 mp against pure isoamyl alcohol or a reagent blank and determine the iron content from a calibration curve which is prepared by adding known amounts of iron to a 10-ml. aliquot of the distilled iron-free ethylene amine and applying the above procedure. RESULTS
Absorbance Curves. Phenyl-2pyridyl ketoxime reacts with ferrous ion, in aqueous ethylene amine media, to form bluish-purple complexes. Sodium hydrosulfite serves to reduce any ferric ion to the ferrous state. In Figure 1 is shown the absorption spectrum of the ferrous complex (4.8 p.p.m. iron) formed in aqueous diethylenetriamine. Three wavelength maxima are noted a t 588,509, and 405 mp. The first is the major absorption band and the one with which quantitative measurements will be concerned. The reagent blank shows negligible absorbance. The absorbances of both samples were measured against isoamyl alcohol. VOL. 36, NO. 6, MAY 1964
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0.9 0.8 (A) 4.8 f i g . i r o n h l . extract
0.7
( 6 ) reagent blank
0.7 0.6 U u
4
'
0.5
t
0.4
0.3 0.2 I
0..O 400
440
480
I
I
520
550
I
I
600
640
0.1 680
Wovelength, m p
Figure 1. Absorption spectrum of ferrous complex formed in aqueous diethylenetriamine
The absorption spectra for the ferrous complexes formed in aqueous ethylenediamine, triethylenetetramine,and tetraethylenepentamine are identical with the spectrum in Figure 1. Rate of Color Formation and Stability. Studies revealed t h a t the bluish-purple ferrous complexes develop maximum intensity after heating in a water bath for 10 to 15 minutes. T o investigate the stability of the extracted complexes on standing the absorbances were measured a t intervals of 10 minutes, 20 minutes, 40 minutes, and 24 hours. There was
Table 1. Recovery Data in Ethylenediamine and Diethylenetriamine
Fe added, p.p.m.
0.5 1 .o 2.5 5.0 12.5 25.0
Fe, found, p.p.m.Ethylene- Diethylenediamine triamine 0.4 0.8 2.2 4.6 11.8 24.2
0.6 1 .o 2.2 4.8 12.0 24.6
Table II. Recovery Data in Triethylenetriamine and Tetraethylenepentamine
Fe found, p.p.m. Fe added, Triethylene- Tetraethylp.p.m. tetramine enepentamine
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ANALYTICAL CHEMISTRY
Moles ReugentNoles Metal
Figure 2. Mole-ratio method applied to ferrous complex formed in diethylenetriamine solution at 588 m b
no change in absorbance values over this period of time. Longer periods were not investigated. Conformity to Beer's Law. A Beer's law study showed a linear relationship from 10 to 200 p g . of iron per 25 ml. of final solution over an absorbance range of 0.075 to 1.52 for the various ethylene amines. The molar absorptivities ( E ) for the various ferrous complexes measured at A,,,=, = 588 mp were as follows: ethylenedidiethyleneamine, 10.50 X triamine, 9.61 X low3; triethyleneteand tetraethyltramine, 9.73 X enepentamine, 10.00 x 10-3. Limits of Detection. Employing 1-cm. cells, the method developed is capable of determining 0.5 pg. of iron per gram of amine. When 5-cm. cells are used the lower limit of detection is 0.1 pg. of iron per gram of amine. However, the observed increase in the absorbance of the blank is such that use of larger cells would be impracticable. Recovery Data. The results of the recovery evaluations are shown in Tables I and 11. It is seen t h a t the method gives acceptable results in all ranges tested with all four of the ethyleneamines. -4precision study was made using 1.00 p.p.m. iron in triethylenetetramine. The average iron content based on 15 determinations was 0.95 =t0.02 with the uncertainty expressed as the standard deviation. Effect of Diverse Ions. It has been reported (1) that phenyl-2 pyridyl ketoxime forms colored, water-soluble complexes with a number of the transition elements in neutral and alkaline solution. Most of the colored metal derivatives are reportedly extracted into chloroform or carbon tetrachloride,
but no mention is made of their extractability into isoamyl alcohol. In this study, solutions of Al+3, C U + ~ , "i+2, and Zn+2were prepared to determine the effect of these selected ions on the color reaction. These ions were added individually to iron-free and ironcontaining amines. The amount of iron was held constant a t 120 pg. Colors were developed and extracted in the usual manner. Extracts of the ironfree systems exhibited no absorption over the range investigated and with systems containing 120 fig, of iron the presence of as much as 1000 pg. of the above ions did not interfere with the determination of the iron. Nature of the Colored Complex. The empirical formula of the iron complex formed in diethylenetriamine was determined by the mole-ratio method introduced by Yoe and Jones (3). Figure 2 shows the result of applying the mole-ratio method to the metal complex a t 588 mp. The concentration of iron was held constant a t 8.57 X 10-6M. The data indicate that 2 moles of the reagent react with 1 mole of ferrous iron. DISCUSSION
The nature of the colored complex and the visible absorption pattern involved in this study (ethylene amine media) differ from the results of other workers (alkali hydroxide media). The bluish-purple complex formed in an ethylene amine solution and extracted into an isomyl alcohol-ethanol mixture exhibits three wavelength maxima a t 588, 509, and 405 mp. I n addition, a 2 : 1 mole ratio of ketoxime t o iron has been established. Trusell and Diehl
(2) found that the complex formed in alkali hydroxide medi t and extractable into isoamyl alcohol iii red in color and exhibits a $ingle abzorption peak a t 550 mp. The composition of this complex was found t3 be three molecules of oxime for each atom of iron when an excess of oxime was present. When the concentration of oxime was less than three times that of iroli, another species was apparently present.
where: M = E a , K, Li; the cation necessary for complete charge neutralization is readily available from the alkali hydroxide media empl3yed. In ethylene amine media the 2 : l complex that is formed is a neutral
entity. However, if the stereochemical arrangement is octahedral, two sites remain open for coordination. With a neutral 1,a-diamine species available, a complex of the following structure is possible:
The extraction step in the present procedure is of special significance since it was observed that only the colored complex is extracted and any extraneous color originally present in the amine is left behind in the aqueous phase. ACKNOWLEDGMENT
The authors express their sincere appreciation to J. F. Fisher, Union Carbide Corp., Chemicals Division, South Charleston, W. Va., for evaluating the phenyl-2-pyridyl ketoxime method us. other unpublished methods. where: R = IT, --CH2CH2KH2, etc. The specific ethylene amine medium in which the ferrous complex is formed does not affect the absorption characteristics to any great degree. This is evidenced by the identical visible absorption patterns obtained with three maxima a t 588, 509, and 405 mp. The molar absorptivities, a t the former wavelength, are all of the order of lo4.
LITERATURE CITED
(1) Diehl, H., Smith, G. F., “The Iron
Reagents” (Monograph), G. Frederick Smith Chemical Co., Columbus, Ohio, 1960.
( 2 ) -Trusell, F., Diehl, H., ANAL. CHEM. 31,
1978 (1959).
(3) Yoe, J. H., Jones, A. L., IND.ENO. CHEM.,ANAL.ED. 16, 111 (1944).
RECEIVED for review X’ovember 22, 1963. Accepted February 7, 1964.
Separation of Rare Earths from Other Metal Ions by Anion Exchange JAMES S. FRITZ and RICHARD G. GREENE Institute for Atomic Research and Department o f Chemistry, Iowa State University, Ames, Iowa
b Elements of the rare earth group are retained by a nitrate-form anion exchange column from dilute nitric acid solutions in water-isopropyl alcohol. Elution with ‘I .5M nitric acid in 85y0 isopropyl alcohol allows many less sorbable elements to be separated from the rare earths. The higher rare earths can be eluted from the column using lower percentages of isopropyl alcohol and separated from bismuth (Ill), lead(ll), and thorium(lV), which remain on the column.
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research ( I , 6, 6) has shown that the rare earths can be sorbed onto anion exchangers from nitric acid-alcohol systems. Korkisch and Tera (6) separated thorium from other metal ions using nitric acidmethanol as the medium, and from their data it appeared that the rare earths could be separai,ed from various other metal ions. Korkisch, Hazan, and Arrhenius in a rwent article (6) suggested, on the basi3 of distribution coefficients that the rare earths could be separated from some less sorbable elements using variouc, aqueous nitric acid-alcohol systems, REVIOUS
An anion exchange separat,ion of calcium and magnesium developed in our laboratory (3) uaing 0.5M nitric acid in a 90% isopropyl alcohol-lO~o aqueous solvent system led us to try B similar system for the separation of rare earths as a group from other metal ions. In the present study, rare earths have been separatd from other metal ions using Amberlyst XN-1002 resin and 1.5M nitric acid in 85% isopropyl alcohol as a sample and as an eluting medium. Up to 0.25 mmole of rare earths can be separated using a 1.2 x 12 cm. or 1.2 X 16 cm. column, and the method is selective for the rare earth group. EXPERIMENTAL
Apparatus. Conventional 12-mm. i.d. glass columns with coarse glass frits were used for the ion exchange separations. Resin. Amberlyst Xpi-1002 (Rohm and Haas Co.) anion exchange resin was used. It was ground to 60- to 100-mesh size for use in both the batch and column experiments. The resin was converted t o the nitrate form with nitric acid and then air-dried. Dowex 1-X8, 100- to 200-mesh, was also used in some comparison experiments.
For column experiments the airdried resin was soaked in the eluting solution prior to its addition of the column. The ion exchange column was also prepared by adding the resin to the column from an aqueous solution and then passing from 2 to 3 column volumes of the eluting solution through the column. Reagents. Stock solutions of the elements used were prepared 0.05M in metal ion, mostly from their nitrate salts in dilute nitric acid. Titanium(IV) and vanadium(1V) solutions were made up in sulfuric acid solution. Zirconium(1V) was used in a perchloric acid solution. The eluting solution was made up by adding concentrated nitric acid and water to the approximate amount of isopropyl alcohol needed and then diluting to the mark in a volumetric flask with isopropyl alcohol. Procedure. For the determination of batch distribution coefficients, aqueous solutions containing 0.1 mmole of metal ion were evaporated just barely to dryness in a 10-ml. beaker. Then 3 to 4 drops of dilute nitric acid were added to bring the residue into solution. This was then washed into a 50-ml. volumetric flask and diluted to volume with the medium of interest. The resulting VOL. 36, NO. 6, MAY 1964
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