Other Applications of Cerium(II1)EDTA. Because of the sharpness of the xylenol orange indicator end point in t h e E D T A titration of cerium(III), the proposed titrimetric procedure is useful for t h e determination of other metals such as bismuth, zirconium, and hafnium which form stable E D T A complexes. T h e end point is distinct and rareful p H control is unnecessary. Of course, t h e expected interference of most multivalent cations limits the applicability
of the titrimetric procedure. Nevertheless, it can be used advantageously for the standardization of various metal solutions such as cobalt and nickel and for the determination of metals following suitable separation. LITERATURE CITED
(1) “ASTM Methods for Chemical Analysis of Metals,” American Society for
Testing Materials, Philadelphia, 1956. ( 2 ) Fritz, J. S.,Hedrick, C. E., ANAL. CHEM.34, 1411 (1962). ( 3 ) Lundell, G. E. F., Hoffman, J. I.,
“Outlines of Methods of Chemical Analysis,” p. 96, Wiley, Sew York, 1938. (4) Meites, L., “Handbook of Analytical Chemistry,” McGraw-Hill, New York, 1963. STANLEY S. YAMAMURA Atomic Energy Division Phillips Petroleum Co. Idaho Falls, Idaho WORKdone under Contract AT( 10-1)-205 to Idaho Operations Office, U. S. Atomic Energy Commission. Presented a t the 147th Meet,ing, ACS, Philadelphia, Pa., April 5-10, 1964.
Column Extraction-Spectrophotometric Determination of Iron SIR: The adverse effects of diverse cations and anions limit the usefulness of available colorimetric methods for the determination of iron. I n the widely used 1,IO-phenanthroline procedure, for example, ions such as cit>rate,copper(II), mercury(II), nickel(II), phosphate, and zinc(I1) interfere even at very low concent,rations (3). Generally, two approaches are used to eliminate or minimize these interferences: separation of the iron prior to color development or t’he use of masking agents such as citrate, (ethy1enedinitrilo)tetracetic acid (EDTA), and tartrate ( 4 ) . Masking, though quite useful, is subject to some limitations. Because iron (111) itself is complexed by citrate, EDTA, and tartrate, the color development is lengthy because of the difficulty of reducing iron(II1) to iron(I1) in the presence of these cornplexing agents. Furthermore, a specific masking agent is not always applicable to all situations; thus, a variety of procedures is necessary for different samples ( 4 ) . Fritz and Hedrick ((1) recently described a reversed phase chromatographic procedure for .the separation of iron. In their procedure, an adaptation of the familiar ether extraction of iron (111) chloride from h:ydrochloric acid medium, the iron was extracted from a mobile 6 to 8 M hydrochloric acid phase into 2-octanone sorbed on an inert Haloport-F (a fluorocarbon polymer) column. The extracted iron and the 2-octanone solvent were eluted with methanol and ether, digested with nitric and perchloric acids, then determined titrimetrically with EDTA or spectrophotometrically with ?.,lo-phenanthroline. We have developed modifications of the above procedure both for macro and micro levels of iron. This paper describes the modified method for the determination of micro amounts of iron. After the iron-2-octan.one is stripped from t,he column, the irlon is determined in situ with 1,lo-phenanthroline, thus eliminating the time-’consuming acid
digestion. Comprehensive data, supplementing the Fritz and Hedrick paper ( I ) , are presented on the effect of various diverse ions. I n the macro procedure, the iron is stripped with acetone, then determined directly without digestion by a newly developed complexometric procedure using cerium(II1)-EDTA. Details of this procedure are described in a separate paper (6). EXPERIMENTAL
Apparatus and Reagents. T h e ion exchange columns were 7.2-mm. i.d. x 15 cm. with a 25-ml. reservoir, a Teflon-plugged stopcock, and a glass wool plug to support the column packing. All absorbance measurements were made in a 1-cm. cell with a Cary Model 14 spectrophotometer. Practical grade 2-octanone and reagent grade pyridine (Eastman Organic Chemicals) were used without purification. An iron stock solution, 5.00 mg. per ml., was prepared by dissolving spectrographic grade iron in aqua regia and fuming with perchloric acid. The iron(II1) solution was standardized by a direct E D T A replacement titration procedure with cerium-EDTA (6), and a working solution was obtained by diluting the stock solution 100-fold. Fluoropak (Wilkens Instrument and Research, Inc., Walnut Creek, Calif.) was screened through a 70-mesh sieve t o remove the fines and used without further treatment. A 0 1M aqueous solution of hydroquinone and a 0.03M solution of 1,lO-phenanthroline in 2-propanol also mere prepared. The hydroquinone solution IS relatively unstable and a new solution should be prepared when significant discoloration appears.
Procedure.
PREPARATION O F 2-
reservoir, then transfer a small portion of the treated Fluoropak to the reservoir, Using a 5- or 6-mm. diameter glass stirring rod, slurry the Fluoropak with the 7 X hydrochloric acid. Open the stopcock and, as the acid drains, gently tamp the Fluoropak to form a uniform bed 5 inches high. Avoid excessive pressure which results in solvent “bleeding” and an undesirably slow flow rate. Do not allow the column to drain dry. SEPARATION ANI) DETERMINATION OF IRON. Pipet an aliquot of the sample solution containing 5 to 100 pg. of iron(II1) into the column reservoir. Adjust the hydrochloric acid concentration to 7 f 1JI with concentrated hydrochloric acid. With dilute samples where volumes greater than 10 ml. must be taken, pipet the sample into a beaker, adjust the acidity, then transfer quantitatively in small portions to the column. Pass the sample through the column a t the rate of 3 to 5 ml. per minute. Wash with 20 to 30 ml. of 7 M hydrochloric acid added in approximately 5-ml. increments. Drain the excess wash solution until the acid level is a t the top of the Fluoropak bed. Strip the 2-octanone-iron(III) chloride solution with 15 to 18 ml. of 2-propanol into a 25-ml. volumetric flask containing 0.5 ml. of 0.1Jf hydroquinone. Add 2 rnl. of 0.03X 1,lO-phenanthroline, mix, then add 3 ml. of pyridine. Cool to room temperature and dilute to volume with 2-propanol. After 15 minutes, read the absorbance at 507 mp. against a reagent blank processed simultaneously with the samples. The iron(I1)-1, 10-phenanthroline complex is stable for several hours. The absorbance is linear with concentration over the range 5 to 100 pg. of iron. RESULTS A N D D I S C U S S I O N
OCTANONE - SATURATED FLUOROPAK Choice of Support. Both HaloA N D EXTRACTION COLUMN. Drench port-F (1) and Fluoropak were evalu200 t o 400 ml. of the screened ated. Fluoropak was selected because Fluoropak with 2-octanone. Remove it does not lump together under slight the excess solvent by suction filtration pressure as does Haloport-F. Fluorowith a Buchner funnel. Draw air pak can be reused indefinitely with through the Fluoropak for 10 t o 15 appropriate washing with acetone and, minutes. Store in a large-mouth if necessary, dilute nitric acid. screw-cap bottle. Column Extraction of Iron. T h e Pour approximately 10 ml. of 7-M column extraction of iron(II1) is hydrochloric acid into the column VOL. 36, NO. 9, A U G U S T 1964
1861
Table
I. Reliability of Spectrophotometric Procedure and Extraction-Spectrophotometric Measurement Procedure.
Procedure Spectrophotometric measurement without colunin separation Spectrophotometric measurement with column separation a
b
Rel. std. dev.,
detn.b
Average absorbance
14
0 447
0.56
20
0.446
0 74
KO.
of
70
The iron level was maintained at 54.60 pg. Data were collected over a period of 6 weeks; the number of rejects were zero.
quantitative from 7 i l M hydrochloric acid medium (Table I ) . This was confirmed by Fe-59 tracer studies. Presaturation of the 7 M hydrochloric acid solution with 2-octanone as ruggested by Fritz and Hedrick was unnecessary. In fact, n i t h a 2-octanone-saturated 7 J I hydrochloric acid solution, low recoveries of iron have been experienced ( 6 ) . Determination of Iron. I n the recommended procedure, the iron(I1)-
Table
II.
Effect of Diverse Ions
Diverse ion to Resultsb iron Iron Ion molar found, Diff., w added ratioa pg. /O BilIII) 5000 54.9 tO.55 + O . 18 5000 54.7 cd(11j 54.9 +0.55 Ce(II1) 5000 55.2 +l.lO 5000 Cr(II1) fO.OO 5000 54.6 CUlII) COiII) 5000 54.3 -0,55 HelII) j000 54.6 fO.OO 54 6 fO 00 hG(VI)c 1000 54 6 fO 00 Si(I1) 5000 54 9 +O 55 Th( IY) 5000 54 2 -0 73 U(1’I) 5000 54 6 f 0 00 VlIT)c 2500 -0.36 1000 54.4 Zr( 11:) 54.0 -1.10 Zn(I1) 5000 54.0 -1.10 2500 Citrate 54.3 -0,55 Oxalate 2500 +0.55 5000 54.9 Phosphate 55.0 -0.73 Tartrate 2500 a Iron level was maintained at 54.60 pg. b Average of duplicate determinations. c 3 to 5 drops of 30%, hydrogen peroxide were admitted to column reservoir at start of acid wash.
Results of the Analysis of NBS Standard Samples Resultsa XBS Rel. stated Iron std. value, found, dev Sample yG iron c” 5% NB8-157b 0 053 0 0534 0 9 YBS-16Jc 0 34 0 330 17 Six determinations were made on each sample. b hlajor components are copper (72”,), nicakel ( lSco), and zinc ( l o r & ) . c hIajor components are copper ( 2 9 5 ) , nickel (6Gr,), and manganese (2%).
Table 111.
Q
1862
ANALYTICAL CHEMISTRY
1,lO-phenanthroline complex is developed directly in the aater-2propanol-2-octanone column effluent. The color development is rapid and the sensitivity is slightly greater than in aqueous medium. In the 2-propanol medium, a molar absorptivity of 11,400 is obtained compared to a reported value of 11,100 in aqueous medium (4). Hydroquinone is used as t.he reductant rat,her t,han the more commonly used hydroxylamine hydrochloride. Hydroxylamine rea& with 2-octanone t’o form the oxime. Effects of Diverse Ions. The effects of common ions on the combined column e x t r d o n - 1 ,IO-phenanthroline spectrophotometric measurement procedure were investigated by analyzing synthetic sample mixt,ures containing known amounts of iron and high concentrations of selected cations and anions. Generally, cations were added as t,he chloride salt, dissolved in 7M hydrochloric acid. Molybdenum was admitted as ammonium molybdate. The complexing anions-citrate, fluoride, oxalate, phosphate, and tartratewere added as 7M hydrochloric acid solutions of the respective acids. As shown in Table 11, Ri(III), Cd (II), Ce(III), Cr(III), Cu(II), Co(II), Hg(II), Ki(II), Th(IV), U(VI), and Zn(I1) a t a 5OOO:l diverse ion t’o iron molar ratio, V(IT’) a t a 2500: 1 ratio, and h.Io(VI), Ti(IV), and Zr(1V) a t a 1000: 1 ratio are without effect. hlo(V1) which is coextractcd partially with iron was coml’lexed with hydrogen peroxide. V(IV), also coextract,ed!was eluted during the 7M hydrochloric acid wash with a few drops of 307, hydrogen peroxide. The com1)lexing anions--citrate, oxalate, and tart,rate at’2500: 1 anion to iron molar rat,io and phosphate a t a 5000:l ratio-do not interfere. Fluoride at a 5000:l ratio gave high erratic results because of the introduction of iron from t,he borosilicate glass column through etching. Though not verified by actual studies, no fluoride int,erference is expect,ed if columns of polyethylene or Teflon are used. Pot,entially interfering elements are gallium, gold, and thallium which coextract quantitatively and antimony, arsenic, germanium, iridium, and tel-
lurium which partially coextract (2). Of the latter group, antimony, arsenic, germanium, and tin can be volatilized completely from sulfuric acid with a 3: 1 hydrochloric-hydrobromic acid mixture (6). The remaining elements-gallium, iridium, gold, tellurium, and thalliumare uncommon, and are encountered only infrequently and at low concentrations. A special study was made of the effects of gallium, gold, tellurium, and thallium on the determination of iron with 1,lO-phenanthroline. Gallium did not interfere a t a 100:l molar ratio, but did interfere a t 200: 1. Gold a t 50: 1 did not interfere; however, because gold absorbs a t the working wavelength of 507 mp, a sample blank without chromogent is necessary. Tellurium interferes even a t a 10:1 ratio. With chloride masking, thallium a t 500: 1 did not interfere. Reliability. The reliability of the modified spectrophotometric procedure and the combined column extraction-spectrophotometric measurement procedure is shown in Tables I and 111. Based on 14 replicate determinations a t the 54.60-pg. iron level with the modified 1,lO-phenanthroline procedure, the relative standard deviation was 0.56%. For the extraction-spectrophotometric measurement procedure, the relative standard deviation based on 20 determinations a t the same iron level was 0.74%. The results of the analyses of two Kational Bureau of Standards samples are given in Table 111. Suggested Applications. Because of the high tolerance for diverse ions, the proposed procedure is suggested for the determination of iron in substances such as reagent grade chemicals where the diverse ion to iron ratio is unusually high. For greater sensitivity, 4,7 - diphenj-1- 1 , l O - phena n t hroline (bathophenant hroline) can be used advantageously. LITERATURE CITED
(1) Fritz, J. S., Hedrick, C. E., ANAL.
CHEM.34, 1411 (1962). (2) Lundell, G. E. F., Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” p. 96, Wiley, Sew York, 1938. (3) Sandell, E. B., “Colorimetric Determination of Traces of Metal,’’ 3rd ed., p. 523, Interscience, Sew York, 1959. (4) Tydra, F., Kopanica, M., Chemist Analyst 5 2 , 88 (1963). ( 5 ) Yamamura, S. S.,ASAL. CHEM.36, 1858 (1964). ~ I A R V EA.UW.4DE STANLEY S.YAMAMURA Atomic Energy Division Phillips Petroleum Co. Idaho Falls, Idaho WORKdone under Contract AT( 10-1)-205 to Idaho Operations Office, I?.S.Atomic Energy Commission. Presented at the 147th Meeting, ACS, Philadelphia, Pa., April 5-10, 1964.
