930
ANALYTICAL CHEMISTRY
samples of milk. A comparison with the ethyl ether-petroleum ether-ethyl DDT Uncorrected, P.P.11. Corrected, P.P.M. % Recovery alcohol extraction method waa made by Added, Acetic acid Extraction Acetic acid Extraction Acetic acid Extraction extracting with ethyl etheri3kellysolve P.P.M. procedure procedure procedure procedure procedure Drocedure .. .. B as described by Carter ( I ) , 50 grams 0 (blank) 0.07 0.08 .. .. 0 (blank) 0.05 0.10 .. .. of milk to which had been added the 0.40 0.42 0.40 0:36 0:31 90 78 0 10 0.43 0.37 0.37 0.28 93 70 Rame amounts of D D T as above. The 1 00 1.00 1.01 0.93 0.92 93 92 99 91 acetic acid procedure, when applied to 1 00 1.05 1.00 0.99 0.91 2.00 1.93 1.90 1.87 1.81 94 91 milk containing as low as 0.40 p.p.m., 2 00 1.89 1.88 1.83 1.79 92 90 gave an easily discernible characteristic blue color. The blue color is obt.ainable in either procedure at 0.20 p.p.m., but DISCUSSION the accuracy is questionable. The results of these analyses are given in Table I. The method of extraction of the milk differs from the procedures Blank milk from the same sample will vary from 0.04 to 0.12 described by Schechter and Carter in that the solvent employed p.p.m., the results depending upon the amount of interfering (chloroform) is later used during the sulfuric acid extraction, substances left unremoved. Correcting for the higher blanks thereby eliminating the ethyl ether-petroleum ether-alcohol mixin the ethyl ether-petroleum ether-alcohol procedure resulted ture entirely and reducing by one third the over-all time conin low percentage recovery for the 0.40-p.p.In. sample. sumed. The results indicate that the acetic acid-potassium acetate With the amounts of reagents described in the acetic acidtreatment gives fully as good recovery as the longer ethyl etherchloroform procedure, emulsions which do not break in 2 minutes petroleum ether-ethyl alcohol extraction procedure. will be formed only rarely. If an emulsion is formed, the addition of 1 or 2 ml. of acetic acid will separate the chloroform LITERATURE CITED quickly. (1) Carter, R. H., IND. ENG.CHEM.,ASAL. ED.,19, 54 (1947). The chloroform solution is highly buffered, but the buffer is (2) Clifford, P. A., J . Assoc. Ofic.Agr. Chemists, 30, 3 3 7 4 9 (1947). removed along with some fat during the first sodium sulfate(3) Rlann, H. D., C. 8. Bur. Entomol. Plant Quarantine, Bull. ETsulfuric acid extraction. 268 (June 1949). The complete procedure, starting with the extraction of the (4) Scheehter, A I . S.,Pogorelskin, 11. A., and Haller, H. L., ISD. ESG.C H E MASAL. , ED.,19,51 (1947). milk sample, was tested by adding 0.0,20.0,50.0, and 100.0micrograms of pure 75-25 p,p'-o,p' D D T in duplicate to 50-gram R E C E I V El D u g u s t 22, 1950.
Table I.
DDT Recovered
Separation of Iron(ll1) from Aluminum H i R R Y TEICHER
AND
LOUIS GORDOK
Syracuse University, Syracuse, N . Y .
MALL quantities of iron are not easily separated from
S alunlinum prior to the gravimetric determination of aluminum. Employment of a cation exchanger for the simultaneous separation of iron( 111) and aluminum, followed by selective removal of the aluminum with sodium hydroxide, has been reported by Lur'e and Filippova ( 6 ) , although the data of Samuelson (8)indicate that this method results in sbme loss in iron. Separation by precipitation with cupferroii ( 4 ) leaves small amount@ of iron in solution. The ether extraction ( 1 ) of less than 1 mg. of iron is not easily accomplished. There are not sufficient quantitative data to appraise the chloroform extraction of either ferric 8-hydroxyquinolate ( 3 ) or ferric cupferronate ( 2 ) in the presence of aluminum. The use of the mprcury cathode often remlts in incomplete removal of iron ( 7 ) By the method described in this paper, iron(lI1) is removed as a negatively charged ferric thiocyanate complev ion on the anion ewhanger, -4mberlite IRB-400A. I t is necessary that this strongl) hnsic ion exchanger be converted to the chloride prior to its use. This method serves to separate 1 to 2 mg. of iron from up to 80 mg. of aluminum, so that the gravimetric determination of aluminum by precipitation as aluminum hydroxidr !e easily accomplished. The removal of iron in order to emplo\ colorimetric methods for trace quantities of aluminum is being investigated. MATERIALS USED
Ion Exchangers. Amberlite IRA-400 and Amberlite IRA400A wrre treated with 3 A' hydrovhloric acid and used to pre-
pare columns of ion exchange approximately 25 cm. in height and 1.3 cm. in diameter. Pure Aluminum Solution. Aluminum metal, containing 0.5% iron, w'as dissolved in hydrochloric acid. After removal of silica by filtration, ammonium thiocyanate was added in sufficient quantity to complex iron(III), the pH adjusted to 1.0, and the iron then removed by passage through a long column of the ion exchanger. The eluate was evaporated to dryness with aqua regia. This purified aluminum salt was used to prepare solutions which were gravimetrically standardized by precipitation of aluminum hydroxide. The precipitates of aluminurn oxide thus obtained were pure white, although analysis indicated 0.02% ferric oxide. Other Materials. Ferric chloride (low phosphorus), analytical reagent grade, was used to prepare solutions containing approximately 1 mg. of iron( 111) per milliliter. .4mmonium thiocyanate, reagent grade, was prepared as a 3 .VI solution. The potassium salt can be used with equal auccew. EXPERI.MENTAL
General Procedure. Except in a very few cases the ion exchanger, previously treated with 3 to 4 N hydrochloric acid to convert i t to the chloride, was rinsed with 50 ml. of 0.3 .\if ammonium thiocyanate, adjusted to pH 1.0 with hydrochloric acid, prior to the introduction of solutions containing iron(II1) and aluminum. The solutions passed through the ion evchangci were O.OOO4 to 0.0008 M in iron(II1) and 1.5 M in ammonium thiocyanate, contained varying amounts of aluminum, and were at p H 1. The presence of the ferric thiocyanate complex is indicated by its reddish color on the yellow ion exchanger. Aftei passage of the solution, the column was washed with several portions of 0.3 M ammonium thiocyanate. The aluminum in thfl eluate was then gravimetrically determined by a standard prd-
V O L U M E 2 3 , NO. 6, J U N E 1 9 5 1
931
cedure ( 5 ) . T h e column was easily regenerated with 3 to 4 Y hydrochloric acid, so that it could be used again. Effect of Thiocyanate Concentration. For solutions up to 0.0008 izI in iron(III), the concentration of ammonium thiocyanate should be 1.5 -If,although this may vary between 0.5 M and 2.0 M. Below 0.5 J f , some iron may pass through the column. The effect of ammonium thioc?-anate concentration above 2.0 Jf was not studied.
Talple I.
€‘low Rate
PROCEDURE FOR SEPARATION O F IROV
The solution from which iron is to be removed may contain up to 2 mg. of iron(II1) and up to 80 mg. of aluminum in a volume of about 25 ml. and it should be at approsimatrly pH 1. It ifeasible to separate larger quantities of iron with corrcspondingiy larger columns of ion euchanger, but difficulty in quantitative removal of aluminum may be encountered.
Effect of Flow Rate on Residual Iron Aluminum taken = 0 0782 gram I r o n taken = 1 0 mg. Final Iron Present Fe Found in A1 as Impurity
.W./Man.
Mg.
%lo 4-5
0.013 0 003.5 0.0014
1
Table 111. Determination of 4luminum after Kenlo\ al of Iron on Amherlite JR4-4004 No.
?4
Fe Taken
0.005
0.002
Table 11. Determination of Aluminum in Absence of Iron AI Found Difference Gram ‘VI g . fO. 1 10 0.0176 0.0177 0.0176 0.0175 -0.1 0.0782 0.0784 +o 2 46 0.0782 0.0783 +o. 1 Column washed 15 times with 10-ml. portions of 0.3 M NHiCPiS (pFI 1.0). Column washed 20 times with 10-ml. portioru of 0 . 3 .TI NHpCSS 41 Taken Gram
;:
AI Taken
A1 Found
a
Column Column Column Column
washed washed washed washed
DiRerpnce
.
Gram Gram Mg 2 0 0176 0 0175 -a 1 2 0 0176 0 0176 *o 0 2 0 0176 0 0177 +O 1 2 0.0176 0 0173 -0 3 1 0 0414 0 0412 -0 I 1 0 0414 0 0411 -0 3 1 0 0414 0 0414 10 0 1 0 0782 -0 ? 0 0780 1 0 0782 0 0781 -0 1 2 0 0782 0 0784 +o 2 2 0 0782 0 0782 *o 0 8 times u i t h 1C mi. of 0.3 A4 K C N S ( p H 1.0). 4 times with 10 ml. of 0.3 M K C N S ( p H 1.0) 15 times with 10 ml. of 0 3 M NHICKS (pH 1 01 20 times u i t h 10 ml. of 0.3 X SHaCNS (pH 1.01
MQ.
0.02
Effect of pH. At a pH of 1.0, satisfactory removal of iron is effected. While this valur may vary slightly in either direction. it should not be much higher, in order to prevent prrc-i .itation of ferric hydroxide and not much lower, else the ferric thiocyanate comples will be removed from the column. A I S hydrochloric acid solution will elute the ferric thiocyanate complex. The column was washed free of aluminum salts with 0.3 Jf ammonium thiocyanate adjusted to pH 1.0. At p11 2.0, some loss of aluminum was noted. At lev-er p H values than 1.0 it is probahlc that there will he removal of the i“c3rric thiocyanate complex.
NO.
of increased dimensions, but it might be difficult to wash out all aluminum salts.
Aniberlite IRA-40011 was treated with 3 to 4 .V hydrochloric acid t o convert it t o the chloride, and washed several times with distilled water. A column of suitable dimensions wa,
