V O L U M E 23, NO. 6, J U N E 1 9 5 1 run for varying periods of time, depending on the demand for a particular type of analysis with only a single oscillator. The melting furnace described by Guldner and Beach ( 2 ) was modified, although the important features of this chamber-ease of maintenance, visibility of interior, and simple cooling-have been retained. I n place of the borosilicate glass outer chamber, a clear quartz envelope was installed to give complete assurance that this part of the assembly will withstand the hot zone surrounding the crucibles in the inner quartz thimble. This quartz envelope was fitted with joints to connect it to the measuring system and to the sample loading arm. Rather than use costly graded seals at these points, Vycor joints, which can be sealed directly t o quartz, were utilized and these were waxed to the joints of the rest of the system. The large three-way stopcock, Sp(Figure l),connects the furnace area to either of the two measuring units. The most timeconsuming part of the analysis is the cycling, freezing, expanding, and measuring of constituent gases. Doubling this part of the equipment virtually doubles the output per day by the same personnel. The actual melting of the sample is a short procedure; consequently only one furnace is needed. In addition, only one set of vacuum pumps is used by which both measuring units are evacuated. With sach a setup, a complete analysis of about ten samples for hydrogen, oxygen, and nitrogen can be made in an 8-hour day. From the schematic diagram (Figure 1) it can be seen that each measuring unit consists of a high speed pump, PI and Pz,a 5liter volume, VI and VZ, a cold trap, TIand Tz,a copper oxide furnace, E1 and E,, and connecting stopcocks. Opening stopcock
929 810, which leads to the oil diffusion um , Pa, serves to maintam a vacuum on the furnace tube, F , wlen $9 is in the “off” position Stopcock 811serves to let air either into the furnace area alone or into the whole system. Thermocouple gage glass envelopes, G1, Gz,and GI, are located so that a continual pressure reading can be obtained in the furnace area and the measuring systems. With a little experience, the analyst can tell by the gage reading when gases are fully oxidized after cycling, when gases are a t equal pressures after coming to room temperature, etc. Final pressure readings are taken on the McLeod gages, ;MI and Mz, Ground-glass joints, J1,Jz, . . . . . . . . J1&, were located to enable one to assemble the apparatus with the greatest ease and the least amount of glassblowing. Another advantage of these lace tions is in the repair and cleaning of sections, which are easily removed from the system with no glassblowing necessary. The number and locations of these joints can be varied to suit individual needs. High vacuum stopcock grease such as Apiezon L was used on the stopcocks. Apiezon wax 1%’ was used on the ground-glass joints. With these suggestions, the authors believe that any laboratory can utilize this versatile vacuum fusion apparatus with the least outlay of space, time, and cost. The double measuring system alone cuts the cost of operation in half, while the use of groundglass joints and the recommended combustion chamber further reduce the cost of assembly and maintenance. LITERATURE CITED
(1) Alexander, L. E., Murray, W. M., Jr., and Ashlq, S. E. Q., ANAL.CHEW,19, 417-22 (1947). (2) Guldner, IT. G., and Beach, A. L.. Zbid., 22, 366 (1950). RECEIVED August 23, 1950.
Improved Procedure for Extraction of DDT in Milk H. D. MA” AND R. H. CARTER Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, Heltsoille, Md.
HE determination of D D T in milk by the colorimetric Tmethod described by Schechter et al. ( 4 ) is a lengthy process; it is advantageous to introduce every timesaving device possible. The procedure heretofore used in this laboratory in carrying out the method has included as the first step four successive treatments of the milk with ethyl alcohol, ethyl ether, and petroleum ether (Skellysolve B), to extract the butterfat as described by Carter (I). It is then necessary to remove the solvent from the extract by evaporation, after which the residue is taken up in chloroform for further treatment with sulfuric acid. Recently the observation wm made that the addition of glacial acetic acid to milk curdled it and caused the butterfat to rise to the top, and that the subsequent addition of a buffer salt prevented the formation of emulsions during extraction with chloroform. As a result, the procedure described herein has been developed, which eliminates the time-consuming extraction of the milk with ethyl alcohol, ethyl ether, and petroleum ether. REAGENTS
Acetic acid, glacial, C.P. Potassium acetate, C.P. Sodium Sulfate-Sulfuric Acid. Dissolve 100 grams of C.P. anhydrous sodium sulfate in 1 liter of C.P. concentrated sulfuric acid (specific gravitv 1.84) with the aid of heat. and cool to room temperature. Fuming Sulfuric Acid-Concentrated Sulfuric Acid. A mixture of equal volumes of fuming sulfuric acid (20 to 30% sulfur trioxide) and concentrated sulfuric acid (specific gravity 1.84). Sodium bicarbonate, 6%. Technical chloroform, redistilled. I
“
PROCEDURE
Shake 50 grams of milk, which has been thoroughly mixed before sampling, in a 500-ml. separatory funnel with 35 ml. of
glacial acetic acid until the butterfat rises to the top. Add 45 g r a m of potassium acetate (a 50-ml. beaker full) and shake well Now extract the solution with 150 ml. of redistilled chloroform. (A mechanical extraction apparatus is a time and labor saver in both this extraction and the sulfuric acid extractions to follow, 3. ) After the layers have separated, filter the chloroform solution through a plug of cotton held in a large glass Gooch crucible holder resting in the neck of another 500-ml. separatory funnel. Extract the sample with another 150-ml. portion of chloroform and filter into the same funnel as before. The chloroform in this funnel contains almost all the butterfat and the DDT, and it is analogous to the first funnel in the Schechter sulfuric acid procedure. Filter a third extraction with 150 m]. of chloroform through the same plug of cotton but into another 500-ml. separatory funnel. This funnel is similar to the second or lower funnel in the Schechter sulfuric acid method. To make the method more sensitive a slight modification has been made in the Schechter sulfuric acid procedure. Extract the chloroform solutions successively with ( 1 ) 75 ml. of sodium sulfate-sulfuric acid, ( 2 ) 75 ml. of sodium sulfate-sulfuric acid, i 3 ) 75 ml. of fuming sulfuric acid-concentrated sulfuric acid, (4) (5 ml. of fuming sulfuric acid-concentrated sulfuric acid, and (5) 75 ml. of sodium sulfate-sulfuric acid. Drain each acid wash (lower layer) from the first funnel into the second funnel and finally into a 1-liter Erlenmeyer flask to be discarded. After the extractions have been completed, combine the chloroform solutions in the upper funnel. Drain off any arid that settles out before the chloroform solution is filtered through a plug of cotton held in a large glass Gooch crucible holder resting in the neck of the cleaned lower funnel. (If the stopper is kept in the neck of the upper funnel during this filtration, the level of the liquid is regulated so that it requires no attention.) In the lower funnel wash the chloroform solution with e sodium bicarbonate solution and again filter through a plug of cotton into a 500-ml. Erlenmeyer flask with a standard-taper 24/40 joint. Wash the bicarbonate solution remaining in the funnel with two successive 30-ml portions of chloroform, which are also run through the plug of cotton into the Erlenmeyer flmk. Complete the analysis as described hy Scherhteret al., but use Clifford’s ( 8 )suggestion of heating the sample in a drying oven a t 100’ C. for 1 hour before developing the color.
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 pH 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-
