Determination of metallic iron, iron(II) oxide, and iron(III) oxide in a mixture

Short communicatrons

1483

R&r&-On d&It des methodes pour le dosage de 5-30 pg de tartrate seul et de 15-60 rg en la presence de citrate lusqu’a 6 mg, basees sur l’oxydatron par 3 moles ou 1 mole de perrodate respectrvement. On dose l’rodate forme spectrophotometrrquement a 350 nm a l’etat de trnodure apres rbctron avec l’rodure, l’exces de perrodate &ant drssrmule au moyen de molybdate. REFERENCES 1. 2. 3. 4. 5 6. 7 8 9 10. 11. 12. 13 14. 15. 16. 17. 18.

G. Nrsh and A Townshend, TuZanta, 1968, 15,1377. D. Burnel, Compt. Rend., 1965, 261,1982 G. Nrsh and A Townshend, Tafanta, 1968, 15,411 F. D. Snell, and C T Snell, Colorrmetrrc Methods of Analysu, 3rd Ed., Vol. III, pp 382-5 Van Nostrand, New York, 1953, R. F. Mrtton and W. A. Waters, Eds , Methods of Quantrtatzve Macro-analysis, p 326. Arnold, London, 1949 F P. Underhdl, F. I Peterman and A. G. Krause, J. Pharmacol., 1931,43, 351. K. Luthardt and R. Pohloudek-Fabmr, Pharm. ZentralhaBe, 1957,%, 453 H. Rebelem, Deut. Lebensm Rundschau, 1961,57, 36 J. R. Matchett, R. R. Legault, C. C. Nrmmo and G K Notter, Znd Eng. Chem., 1944, 36, 851. V. V. Andreev and E V. Panasyuk, Tr. Moldavsk Naudm. rssled Inst Pishchevol. Prom , 1964, No. 4, 62; Anal. Abstr., 1966, 13, 1330. A. K. Anderson, A. H Rouse and T. V Letonoff, Znd Eng Chem , Anal Ed , 1933,5, 19 J. Yashphe, Anal. Biochem., 1965,13, 345. E. A. Adelberg, Anal. Chem., 1953,25, 1553. T. Tsvetana, Tr. Vyssh. Inst. Narod. Stopanst. Varna, 1961, 1, 187 Anal Abstr , 1962,9, 4754. F. Gorskr, Bull. Intern. Acad Polon. Scz., Classe Ser. Math Nat., 1937A, 239. W. J. Kirsten and S. K. N&son, Anal Chum Acta, 1962, 27, 345 A. Berka and J. Zyka, Chem. Lzsty, 1958,52,930. E Schulek and L. Maros, Acta Chum Acad See Hung , 1959, 20,443. P. Fleury and G Bon-Bernatets, J Pharm Chrm , 1936, 23, 85.

Talanta, 1968, Vol

15, pp

1483 to 1486

Permmon

Press

Prtnted tn Northern Ireland

Determination of metallic iron, iron(I1) oxide, and iron(II1) oxide in a mixture (Recewed 17 Aprd 1968. Accepted 27 May 1968) literature records various methods for the determmatron of metalhc iron m presence of non(H) and rron(II1) oxrdes,ls* but grves less mformatron on a rapid, accurate, and dependable method for the determmatron of all the three together. Metallic iron has been determined uza reduction of a copper(I1) salts or mercury(I1) chloride4 m aqueous medmm followed by permanganate titration. Copper sulphate has also been suggested for the determmatron of metalhc Iron, but errors arise from the formatton of soluble copper(I) salts Is6 Habashy” suggested the use of mercury as a catalyst m the copper sulphate method. According to Weiss,’ use of larger quantrtres of mercury(I1) chlorrde to dissolve iron would favour the formatron of calomel, but the latter tends to occlude some of the Iron, causing low results. Morrrs* pointed out that recoveries of non are mcomplete with samples coarser than 65-mesh Aubry and Perrote prefer alcohohc mercury(H) chloride solutron and determine non m the filtrate by first oxrdrzmg rt with persulphate and then titrating with trtamum(II1). WakamatsulO titrated the rron(II1) m the filtrate with standard EDTA solutron at 40” with Trron as mdrcator ; mercury(I1) did not interfere. When the oxtdes are also to be determined, the residue after the mercury(H) chloride reactron has to be treated first to remove mercury(I) chloride and/or mercury. Aubry and Perrote suggest the use of alcohohc rodme solutron for this purpose, whereas Stognii I1 heats the dried precipitate m a stream of chlorme at 200-22” for an hour. Other methods for the determmatron of metalhc non include oxrdatron with non(II1) ,1p-14displacement of silver by iron m Ag(NH8)p(SCN)I,1S~1Bmeasurement of hydrogen evolved by reaction wrth an acrd,17s1*conversion mto uon(II) sulphrde by fusion with sulphur, followed by determination of the hydrogen sulphrde, I* reductron of lead chlorrde solutron,*O and reaction with bromine m ethanol a1 Except the last, these methods erther do not perrmt subsequent determmatron of iron oxides or are too lengthy and mvolved for precrse routme analysrs The bromine methoda’ depends on the selectrve drssolutron AVAILABLE

Short commumcattons

1484

of metallic iron. The oxide residue 1s analysed for iron(I1) and rron(II1) by the usual methods. The prmcrpal advantage of this approach is that the oxides are not contaminated by reaction products from the non dtssolutton. The present paper records a simple and reasonably accurate procedure for the determmatton of metallic iron and rron(I1) and (III) oxides EXPERIMENTAL Reagents

Iron powder and magnetite were prepared from reagent-grade uon(II1) ammomum sulphate. Hydrous rron(II1) oxide was precipitated, washed, dried and ignited to rron(III) oxides, whrch was reduced to metallic iron with dry hydrogen or to magnetite with moist hydrogen. Details will be published elsewhere. Synthetrc nuxtures containing known amounts of metallic iron and rron(II) and (III) oxides were prepared from the pure iron powder and magnetite. All chemicals used were of analyttcal reagent quality. Apparatus

The reaction vessel was a 500-ml glass-stoppered conical flask with a B24 lomt The stopper was made with an inlet and an outlet for carbon dioxide, and had a central caprllary tube ending m a porosity-3 smtered-glass disc; the capdlary was coaxial with the inlet tube and the smtered drsc was about 1 mm above the base of the flask. The capillary was connected to another 500-ml flask connected to a water pump through a trap. Procedure

Transfer an accurately weighed sample (ca. 200 m@ mto the 500-m] reaction flask wrthout Its stopper. Add 100 ml of freshly prepared 2 % bromine solutron m ethanol and strr magnetically for 60-90 mm to dissolve the metallic non. Put the stopper m place, connect the second flask and the trap, and start the filter pump. Wash the residue first wrth ethanol and then with water. Drsconnect the second flask which contains the filtrate and the washings. Add ammonium hydroxide to precrpltate the rron(II1) and then reprecrprtate It. Filter off the precrprtate, wash rt with 2% ammonium chloride solutton, dissolve rt m hydrochlorrc acrd(1 + I), add potassium iodide and titrate wrth O*lN sodmm thtosulphate Connect the flask containing the oxide resrdue to a carbon dioxide generator. Dissolve the oxides m hydrochlorrc acid m an inert atmosphere, heating rf necessary. Cool, adjust the acidity to 4-5N, and titrate the rron(I1) with 0 1N sodmm vanadate, using 10 drops of 0.2% N-phenylanthramhc acid mdtcator. Dilute the titrated solutron to brmg the acidity to 2N, and add a small quantity of sodium bicarbonate and an excess of potassium iodide. After 5 mm, titrate the liberated rodme wrth O*lN sodium throsulphate. The first tltratton gves the rron(I1) oxide, and the difference of the two tttrattons gives the uon(II1) oxide. RESULTS

AND

Typical results are given m Table I. Prehmmary did not affect the iron(I1) and (III) oxides TABLEI-DETERMINATION

experrments showed that the bromme solution

OF Fe, FeO, AND Fe,O, IN A MIXTURE

FeO, %

Fe, % Calculated

Found

154 194 28 8 29 1

152 19 6 28 3 28-6 34 2 43 5 46.5 57 3 62 9

34 6 43.6 47 4 57 0 63 0

DISCUSSION

Fe2% %

Calculated

Found

19 5 18 6 16 5 164 152 132 12 3 10 1 88

19 6 18 9 167 170 15.7 130 12 8 98 90

Calculated 64 2 61 1 54 0 53 7 49.5 42 6 39 6 324 218

Found 65 1 61 7 53 7 52 8 49 7 41 6 40 7 32 5 27 6

1485

Short cornmumcattons

Von Vogel*’ reduced rron(III) and titrated with permanganate (Ztmmermann-Remhardt procedure), but we found tt more convenient to use todometrrc tttratton, the mam advantage bemg avoidance of the reduction step. Generally, non(B) and (III) oxides are determined by drssolutron m hydrochlortc acid m a carbon dioxide atmosphere, followed by titration of tron(II), and determination of total oxide on a separate If sample. In the procedure described here only one sample IS reqmred for the entree analysts desired dtchromate can be used instead of vanadate as tttrant, but the ethanol must then be removed completely after the bromine reaction. Vanadate 1s preferred as the ethanol does not interfere. N-phenylanthramlc acid 1s used as mdtcator to avoid addition of phosphortc actd, whrch would interfere wtth the todometrrc titration. In the fnst expenments, the oxtdes of non after the bromine reactton were filtered off on a smteredglass crucible, but tt was found dtfficult m the dtssolutton step, to remove all the oxides from the filter. In the apparatus described here, the residue remains m the ortgmal flask; this system was found extremely convenient even when an inert atmosphere was to be mamtamed. The results for metallic non are satisfactory but the errors m the determination of the oxides are rather higher than those normally expected m quantitative analysts. However, the results are constdered satisfactory m view of the nature of the mixture and the stmphcity and rapidity of the determmatron. Acknowledgemen&--The in the work.

authors are grateful to Mr G. S. Chowdhury,

Director, for hts keen interest

Regronal Research Laboratory Bhubaneswar 4. India

B.R. T.P.

SANT PRASAD

Summa~-A procedure IS descrtbed for the esttmatton of metallic non, ferrous oxtde, and ferrrc oxtde when present together. The sample IS treated with bromine dtssolved m ethanol, and filtered. Iron m the filtrate IS titrated todometrrcally, and corresponds to the metallic non present in the mtxture. The oxide residue 1s dissolved m hydrochlortc acid under a carbon droxrde atmosphere. The trot@) formed, equtvalent to Fe0 present, IS titrated wtth a standard vanadate solutron, and the total non(II1) (=FeO + Fe,O,) in the titrated solution 1s then estimated rodometrtcally. Zusammenfassnng-Em Verfahren zur Besttmmung von metalhschem Bsen, Enen( und Ersen(III)oxrd nebenemander wtrd beschrteben Die Probe wird mrt emer athanolischen Bromlosung behandelt und filtnert Das Ersen tm Frltrat wtrd lodometnsch trtrtert und entsprrcht dem vorhandenen metalhschen Eisen. Der Oxnlruckstand wrrd unter Kohlendtoxid m Salzsaure gelost. Das gebrldete Ersen(II), das dem vorhandenen Fe0 entspricht, wird mtt emgestellter Vanadatlosung tttnert und dann das gesamte Etsen(II1) (entsprechend Fe0 + Fe,O,) m der austitrierten Losung Jodometnsch besttmmt. R&&--On d&&t une technique pour l’esttmatton du fer mbtalhque, de l’oxyde ferreux et de l’oxyde ferrtque lorsqu’ils sont presents ensemble. On traite l’echanttllon au brome dtssous en ethanol et filtre. Le fer du filtrat est tit& iodometrtquement, et correspond au fer metalhque present dans le melange. On dissout le restdu d’oxydes en actde chlorhydrtque sous atmosphere de gaz carbomque. Le fer(I1) forrne, Bqutvalant au Fe0 present, est trtre par une solutron Btalon de vanadate et le fer(II1) total (Fe0 + Fe,O,) dans la solutton t&&e est alors esttme todometrrquement. REFERENCES I. M. Kolthoff and R. Belcher, Volumetrzc Analysrs, Vol. III, pp. 85, 342 and 634 Intersctence, New York, 1957 G. Charlot and D. B&zier, Quantztatrve Inorgamc Ana[yszs, p 455 Wiley, New York, 1958. J. P. Rtott, Ind Eng. Chem., Anal. Ed., 1941, 13, 546. Wrhrer, Svenska Farm. Tm%kr, 1880, 225; cf E. Merck, Z. Anal Chem, 1902, 41, 710; G Frerrchs, Arch Pharm., 1908,246, 198. N I. Stognu and A. G Kntlenko, Zavodsk Lab, 1955,21, 254

1486

Short commumcattons

H. G. Habashy, Anal. Chem , 1961, 33,586 L. Wetss, Z. Anal Chem., 1934,98, 397 J P Moms, US. Bur. Mates. Rept. Invest., No 3824, 1945. J. Aubry and P. Perrot, Chrm. Anal, 1965,41,177. S. Wakamatsu, Tetsu To Hugune, 1961,47,612; Chem Abstr , 1962,56,79896 N I Stognii, Zavodsk. Lab., 1939,8, 391. A Christensen, Z. Anal. Chem., 1905,44, 535. A D. Horluck, Dansk. Tidsskr. Farm., 1926, 1,37; Chem. Abstr , 1927,21,215 B. Neumann and G. Meyer, Z. Anal. Chem., 1949. 129,229 F. Marion and J Aubry, Chrm. Anal, 1959,41,401. J. Aubry and F. Marion, Compt. Rend., 1952,235, 1509 N. St011 and A. Wagner, Rev. Tech. Luxembourg., 1961,53, 149. A Prksarv, H. Arro, and V. Vares, Tr. Tallmsk. Pohtekhn. Inst. Ser A, No 215, 1964, 137, Chem. Abstr., 1965,63,17134a. 19. A. T. Chemyt and K. V. Podoimkova, Zavodsk. Lab, 1950,16,1308 20. K L. Balabanoff, E. Schmtdt, and B. Seeger, Z. Anal. Chem , 1964,264, 107 21. H. U. von Vogel, Arch. Etsenhuttenw., 1949,20, 287. 6. 7. 8. 9. 10. 11. 12. 13 14. 15. 16. 17. 18.

Talanta, 1968, Vol

15, pp 1486 to 1488

Pergamon Press

Pnnted LIINorthern Ireland

Separation of rhenium, tungsten and molybdenum by thin-layer chromatography (Recetved 6 May 1968, Accepted 27 May 1968) THERE 1s little information avadable on the separation of rhenium, tungsten and molybdenum by thin-layer chromatography (TLC), although alloys of these elements have become technologcally important.’ Rt values for rhenium, tungsten and molybdenum have been recorded for systems of reversed-phase TLC with TBP* and hqmd-anion exchangers ,8 both in hydrochlonc acid media, but no separattons of the three elements were accomphshed m these systems. The present communication reports the evaluatton of a number of solvent systems for resolutton of the three elements on glass plates coated with slhca gel. The best separation was obtamed with methanol-3M hydrochloric actd (7: 3) and methanol-l M ammomum mtrate3M ammonia (14: 5: 1). EXPERIMENTAL A commercial sihca gel(Wako-Gel, B-O) was slurned with 10 % starch solution (3-l ml per g of gel), and spread 250 pm thick on 25 x 100 mm* glass plates wtth an applicator. The plates were air-dried, activated for 30 mm at 110” m an oven and finally stored m a desiccator over silica gel. The thm layer was spotted 15 mm from one end with one or two dabs (2-4 ~1) of the test solutton from a glass capillary, and dried under a heat lamp The plate was placed m a glass tank, 120 mm htgh and 50 mm m diameter, and allowed to stand for 30 mm to eqmhbrate with the tank atmosphere. Ascending development was carried out with the solvent systems listed m Table I, at a constant temperature of 25” unttl the solvent front had risen 65 mm This usually took 30-50 mm. After development the plate was dried and the postttons of the elements were located by spraying first with freshly prepared 0 1-O 2% toluene-3+dtthtol solutton m 0*25M sodium hydroxide and subsequently with cone hydrochlonc acid. Rhemum(VII), tungsten(V1) and molybdenum(V1) showed as yellowish green, blue and green spots, respectively. Drying under a heat lamp enhanced the mtensrty. DISCUSSION In all the solvent systems examined the mobthtles were m the order Re > MO > W. The low R, values for tungsten(VI) may be explained as due to the formatton of msoluble hydrated tungstlc aad. Increasmg the methanol concentration above 70% v/v usually resulted m marked streakmg of molybdenum(V1). Except for the ace& acid, formic acid, and sodium acetate systems, the differences m Rf value were large enough to permit separation of the three elements. Increase of the acid concentration beyond CM m th; 7.3 methanol:hydrochloric actd system gave poorer resolution of rhenmm(VII) and molybdenum(VI) When a mixture of the three elements is chromatographed the Rt values are usually a little lower than those obtained mdlvldually.