run a t a slightly faster gas flow of 140 ml. per minute. When interferences make the results of the conventional methods ambiguous, the proposed method can be of confirmatory value. Quantitative measurements can be made with creams ( I ) . Instances where the particular vehicle does not lend itself to any of these approaches, perhaps, could be subjected to a prior separation ( 6 ) . There is no doubt that the electron capture detector, being extremely sensitive to electronegative materials, such as those containing halogen, would be
exceedingly more sensitive and specific for the bisphenols. This field has not been investigated. LITERATURE CITED
(1) Bahjat, K., J . Pharm. Sci. 5 2 , 1006 (1963). (2) Bravo, R., Hernhdez, F., J . Chromatog. 7 , 60 (1962). (3) Clements, J. E., Newberger, S. H., J . Assoc. Ofic. Agr. Chemists 37, 190 (1954). (4) Derry, P. D., Holden, M., Newberger, S. H.. Proc. Sci. Sect. Toilet Goods Assoc.'36, 25 (1961). ( 5 ) Johnson, C. A,, Savidge, R. A., J . Pharm. Pharmacol. 10, Supp. 171T (1958).
(6) Johnston, V. D., Porcaro, P. J., ANAL. CHEM. 36. . ~ _ _ 124 ~( 1 964). ~ . (7) Jungermann, E., Beck, E. C., J . Am. Oil Chemists' SOC.38, 5 13 (1961). ( 8 ) Klinae. K.. Seifen43ele-Fette- Wachse Feb. 4 and 18 (1959). 85, 61,-87) , 19) Aar. , , Larso n. H. L.. J . Assoc. Offic. * Chemists'28, 301 11951). (10) Lord, J. W., McAdams, J. A., Jones, E. B., Soap Perjumery Cosmetacs 26, 783 (1953). I
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Sindar Corp. A4nalyticalLaboratory Delawanna, K.J.
PETERJ. PORCARO
RECEIVEDfor review March 9, 1964. Accepted April 27, 1964.
Determination of Ferrous Oxide in Ferrites SIR: In many ferrites the magnetic properties are fixed by the ratio of ferrous and ferric ions. Hence, both valency states must be determined before the ferrite composition can be related to the magnetic measurements. There is very little information in the literature on determination of ferrous iron in ferrites. Analysis for ferrous and ferric iron is simple in solution and if a solid sample can be dissolved in hydrochloric acid under an inert atmosphere, determination is not difficult. However, many ferrites do not dissolve in hydrochloric acid so that methods must be developed. This report describes a method of decomposing ferrites with phosphoric acid in the presence of a known amount of phosphatocerate a t a temperature of approximately 200" C. for 15 to 30 minutes. The excess phosphatocerate is then back titrated with a standard ferrous sulfate solution using ferroin as indicator. The determination takes 1 hour and several samples may be run simultaneously.
FERROUS h t M O N I U Y SULFATE SOLU-
phenanthroline indicator solution, and back titrate the excess phosphatocerate with 0.02A' ferrous ammonium sulfate ammonium sulfate hexahydrate in IN solution. The end point is from light sulfuric acid and standardized. blue FERROUS ~,~~-PHENANTHR INOLIN E to orange yellow. Run a blank along with the sample. DICATOR, 0.01M, available from The G. Frederick Smith Chemical Co. Procedure. A finely powdered DISCUSSION A N D RESULTS sample (100-mesh) of 30 to 100 mg. is h mixture of hydrofluoric acid and decomposed with a mixture of 3 ml. of dichromate has been used for determin0.1,V phosphatocerate solution and 10 ml. of 85% phosphoric acid (sp. ing ferrous oxide in rocks and silicates gr. 1.7) in a dry 100-ml. beaker on a ( 4 ) , a mixture of phosphoric acid and hot plate (heated a t 280' to 300' C.). sulfuric acid containing vanadium T h e decomposition requires from 15 pentoxide has been used for determining to 30 minutes depending on the nature ferrous oxide in chromite (S), and a and size of sample. After decomposimixture of phosphoric acid and sulfuric tion, cool a while, pour into a 400-ml. acid containing ceric sulfate has been beaker containing approximately 100 used for determining ferrous oxide in ml. of water, 10 ml. of concentrated chromite ( 2 ) . It was found that fersulfuric acid, and 1 drop of ferrous 1,lO-
TION,0.02N. Prepared from ferrous
EXPERIMENTAL
P H 0 S PH A T 0 C ER ATE Reagents. SOLUTIOK,0.1N. H e a t a t 280" to 300' C. on a hot plate 5.4286 grams of primary standard grade ceric ammonium nitrate (available from The G. Frederick Smith Chemical Co., Columbus, Ohio', i r i a drv 100-ml beaker with 10 ml. of 85% phosphoric acid until no nitric acid fumes are evolved (30 minutes are usually sufficient,). Cool somewhat and transfer to a 100-ml. volumetric flask. Rinse with 10 ml. of 8570,phosphoric acid and some water, then rinse with 20 ml. of concentrated sulfuric acid and water. Cool, make to volume. and mix well. The solution should be clear. If the presence of sulfuric acid is objectionable, rime with 20 nil. of 857, phosphoric acid in place of sulfuric acid.
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ANALYTICAL CHEMISTRY
0.1
MINUTE Figure 1 .
Effect of time on titer of oxidant solution
Mixture o f IO ml. o f 65% phosphoric acid and 2 or 3 ml. o f 0.1 N phosphatocerate solution contoining 20 ml. o f 65% phosphoric ocid and 20 ml. o f concentrated sulfuric acid p e r 100 ml. volume 8. Mixture of IO ml. of 65% phosphorjc acid and 2 or 3 ml. of 0.1 N phosphatocerate solution containing 4 0 ml. o f 65% phosphoric acid p e r 100 ml. volume C. Mixture of IO ml. of 65% phosphoric acid and 2 or 3 ml. o f 0.1 N dichromate solution in w a t e r The hot p l a t e was heated a t 290' to 300' C. A.
rites could not be deconiposed by hydrofluoric acid and dichromate. The vanadium pentoxide procedure is more complicatcd than our method, also the vanadate ion is unstablr, in the phosphoric-sulfuric acid mixture at tempcratiircs aliove 200” C. This results in a high and inconsi$tent blank. The procedure employing a mixture of phosIlhoric acid and sulfuric acid containing ceric sulfate recommended for chromite requires heating at, 290” to 300” C. for 90 niinutw. It seems that the proposed proc~etiurc~employing phosphoric acid and phosphatocerate is very simple, rapid, and has very lorn blank (Figure 1). When ceric ammonium nitrate is heated with phosphoric acid, nitric acid is formcd.
The above r e a h o n takes place smoothly. giving a lemon yellow phosphatoccmte solution in phosphoric acid. Presuniably it could be prepared by rcwting freshly 1)rtqm-d ceric hydroxide with phosphoric acid, since sulfatocerate can be prepared from ceric hydroxide anti sulfuric acid ( 6 ) . The t,erin sulfatowrate hiis been used in place of ceric Frilfat’e because the complex ion C C ( S O ~ )forms. ~ - ~ Phosphoric acid is a good coniplexing agent, which indicates the existence of the Ce(P04)n-2 ion, and phosphatoccrate \roultl be an appropriate name. Phosphatocerate in pho>phoric acid is easily hydrolyzed or pol~-rnerizc~l when acidity of the solution is insufficient. -10.1.V phosphatocwate solution containing 40 nil. of 85‘h ~ihosphoric acid per 100 nil. volume \vas stable for several hours. but it polynierized overnight to a cream yellow jellylike >ribstance. (Polymer-ization do(+ not occur during digehtion because the phoh~ihatoceratesolution is dilute and is more .ioluble at high teniperaturcs.) The 0.1A‘ phosphatocerate solution I)rq)ared containing 20 inl, of 85Tc pho~phoric w i d and 20 nil. of conc.cwti.atd iulfuric acid in 100-ml volunicb. h o w v c r , \vas stable for at 1 a \ t s(xver:d months. ‘The prcwnce of a hrn:ill a m w n t of ::ulfiiric acid has no adverne rffcct on the decomposition of niost of tlir, frrritcs. In the case of the ierritw containing barium oxide, the prrstmcnc’ of hulfiiric acid n-odd he ohjcvtionahlt~. I n fact, the nickel ferrite, ivhich cannot be decomposed by hydro(-hloric :wid can be decomposed with ~iliosphoric,acid or ciilfiiric acid alow. A alrition trnil)t~atrireof 200” C. ih mandatory: evidently a ])roton a t t w k oil tho strongly bonded oxygen U ( T I I ~ ~ only at highcr temperature.. ‘Thm>fow, ~ i n yacid having a boiling point aliovc~200’ C. n-oiiltl be able to tlecomposc the nickel ferrites; this
Table
I.
Determination of Ferrous Iron in Ferrites
Compound Ferrous ammonium sulfate hexahydrate Zinc germanium ferrite Nickel ferrite
Sample weight 0 100 mniole 0 200 mmole 44 ,55 mg 55 60 mg.
Ferrous iron Present Found 0 100 mmole 0 200 Inmole
11 165cn
0 099 mmole 0 198 rnniole 11 0370
11 0 7 5
46.42 mg. 28.39 mg. 2 5 , 5 5 mg.
a The result R-as obtained by decomposition of the finely powdered sample with hydrochloric acid under carbon dioxide atmosphere and titration with permanganate.
may also explain the ineffectiveness of the low boiling point acids, such as hydrochloric acid and hydrofluoric acid, in decomposing these ferrites. Reichen and Fahey (4)discuwed the blank problem in t,he decomposition of rocks with hydrofluoric acid and dichromate. Dichromate is a very stable oxidizing agent in aqueous solution at room temperature; however, it is unstable in concentrated acids at high temperatures above 200” C. The results of effect of time on the blank are shown in Figure 1. m’hen phosphoric acid is boiled, possibly phosphorus acid is produced but, with phosphatocerate in phosphoric acid heating for 30 minutes, the blanks are srnall and constant. By heating sulfuric acid. depending on temperature, sulfur dioxide and sulfur trioxide are produced. Therefore, when the solution contains sulfuric acid, it should not be fumed. I t is important to carry out a blank along with the sample under the same conditions. Table I shows the re,?ults obt,ained by the proposed method compared with known amounts of ferrous ammonium sulfate crystals. and with the results of ferrites which are easily decomposed by hydrochloric acid in an inert atmosphere and tit,rated with potassium permanganate. Since the nickel ferrite was not attacked by hydrochloric acid, no value could be obtained by other methods. The ferrous oxide content values shown in Table I are reproducible. The total nickel and iron were determined by the complrxometric titration and total iron was determined photonietrically ivith (ethylenedinitri1o)tetraacetic acid (EDTA\)and hydrogen 1)eroxide ( I ) ; nickel was obtained by difference or by direct EDTA\ titratmion at pH above 12 using 2,2’,2”-nitrilotriethanol as a masking agent for ferric iron and murexide as indicator. I t was found that the nickel ferrite contained ,5i.20y0total iron and 1 6 . 0 6 ~ o nickel by w i g h t . Based on the ohtained ferrous iron value, 8.707,, the composition can be calculated a:: 0.636 KiOp,0.364 FeO, and Fen03. That the
total amount of S i 0 and FeO in moles is one half of Fez03 is often expected based on its magnetic properties (j). In conclusion. the proposed method for determining ferrous iron in ferrites offers advant>agesof simplicity. rapidity, and satisfactory accuracy. The relative prror was found t,o be *I or 2yo or better depending upon t’hesize of sample taken and the time required for decomposition of t,he sample. I-nder most’ conditions, the sample can be analyzed within 1 hour and many samples can be handled simultaneously. The method can also be used to find out the amount of titanoil. and titanic ions presmt in the spinel Mg2Ti04. By analogy it should be possible to determine mixed valencies in compounds such as manganic oxide by decomposing the sample under an inert atmosphere using phosphoric acid containing ferrous iron or other reducing agent. S o interference was encountered for the ordinary ferrit’es. However, the method cannot be applied to the determination of FeO in the presence of another oxidizing agent, such as manganic oxide. S o method is known which can analyze a solid-state mixture of Fe203,FeO, and 31n203. LITERATURE CITED
(1) Cheng, K. L., Lott, P. F., A s . 4 ~ . CHEM.28,462 (1956). ( 2 ) Chwani, S . , Sci. Culture 22, 398 (1957). ( 3 ) Xagaoka, T., Yamazaki, S., Japan Analust 3.408 f 1954). ( 4 ) Reiixhen, L. ~ E . Fahey, , J. J., U . S . Geol. Sui-z‘. Bull. 1144-B (1962). ( 5 ) Sniit, J., tVijn, H. P. J., “Ferrites,” p. 270, JViley, S e w York, 1959. ( 6 ) Smith, G. F., “Cerate Oxidimetry,” The G. Frederick Smith Chemical Co., Columbus, Ohio, 1942.
RCA Laboratories Princeton, S . J.
K. L. CHENG
RECEIVEDfor review 1Iarrh 11, 1964. Accepted April 23, 1964 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 15th Conference, 1LInrc.h 2-6, 1964 VOL. 36, NO. 8, JULY 1964
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