very little unsaturation. Table I1 lists comparative results by the 30minute Wijs method and by the acetylation procedure in which the end points were satisfactory. A sample of commercial diethylenetriamine, which had an apparent iodine value of about 40 by the 30-minute Wijs, gave a value of 0.6 with the acetylation procedure. Trifatty tertiary amines, besides interfering with the starch-iodine end point, gave high results in the rapid Wijs method and especially in the 30minute Wijs procedure. However, by limiting the sample size and employing acetic acid as a solvent, reasonable values and a satisfactory end point n-ere obtained with the rapid Wijs procedure. Table I11 lists comparative results obtained with the three different methods. High molecular weight quaternary ammonium chlorides also gave very poor end points in the 30-minute Wijs procedure. Their behavior was similar to that of the primary and secondary amines, and apparently for similar reasons. Sodium lauryl sulfate was used in the Wijs method to tie up the quaternary ammonium cation as the lauryl sulfate salt. This appears to prevent the formation of the quaternary-iodine complex which causes the obscure end points during the titration of iodine with thiosulfate. With the recommended sample sizes, the indicated
Table IV.
Iodine Values of Quaternary Ammonium Chlorides
Quaternary Ammonium Chloride Iodine Value Trimethylhexadecyl 0.2 Dimethyldidodecyl 0.1 Methyltrioctadecyl 0.2 Dimethyldihydrogenated tallow 2.7 5 . 4 (calcd. 5 . 9 ) + 3 . 7 % oleic acid 8 . 9 (calcd. 9 . 0 ) 7 . 1yo oleic acid 13.9 (calcd. 14.3) 13,377, oleic acid 2 5 . 3 (calcd. 24.6) $25.07, oleic acid Dimethyldihydrogenated tallow Sample 2 l.lG Sample 3 4.2b Sample 4 11.4~ Dimethyldisoya 57. I d Trimethyltallow 27.8 Quantitative hydrogenation with palladium catalyst gave iodine values of
++
1;
*
3;
52.
quantity of sodium lauryl sulfate was sufficient to give satisfactory end points with starch indicator. Similar results were obtained either by adding the sodium lauryl sulfate initially to the sample in the iodine monochloride or by adding it after the reaction just before the titration. Table IV gives iodine values obtained with various purified and commercial grade quaternary ammonium chlorides. The mixtures of quaternary chloride with oleic acid simulated various levels of unsaturation.
Analytical Services Department who carried out the analyses reported herein.
ACKNOWLEDGMENT
RECEIVEDfor review May 20, 1960. Accepted September 26, 1960. Paper No. 249 Journal Series, Central Research Laboratories, General Mills, Inc.
The author gratefully acknon-ledges the work of Eileen Smith of the
LITERATURE CITED
(1) Am. Oil Chemists’ Society, “Official and Tentative Methods,” 2nd ed., 1947-1959, E. M. Sallee, ed., Method NO. Cd 1-25. 1956. (2) Hoffman, H. D., Green, C. E., Oil & Soap 16, 236 (1939). (3) Nagakura, S., J. Am. Chem. SOC.80, 520 (1958). (4) Smirnov, 0. K., Bexhentseva, V. M., Zavodskaya Lab. 21, 414 (1955). (5) Zvejnieks, A., Svensk Kem. Tidskr. 66, 316 (1954).
Extraction of Zirconium with Di-n-butyl Phosphate and Direct Determination in the Organic Phase with 1-(2- Pyridy Ia z 0)- 2- na pht ho I Application to Fluoride Solutions R. F. ROLF The Dow Chemical Co., Midland, Mich.
b A sensitive and selective method for separation and determination of microgram quantities of zirconium in aluminum-magnesium alloys consists of dissolving the alloy in a mixture of mineral acids and fluoboric acid. Aluminum nitrate is used to complex the fluoride and the zirconium is quantitatively extracted with a solution of di-n-butyl phosphate in chloroform. The addition of an alcoholic solution of 1-(2-pyridylazo)-2-naphthol to the zirconium extract yields an intense red color. The system obeys Beer’s law over the concentration range of
10 to 65 fig. of zirconium per 25 ml. The molecular absorptivity is about 32,000. The extraction of zirconium by di-n-butyl phosphate was studied using zirconium-95 tracer. A study of the effect of diverse ions showed the method to b e highly selective. A standard magnesium alloy containing mischmetall was analyzed by the proposed method with an average This method offers precision to f2%, the advantage over existing literature methods that fluoride can b e used to ensure complete dissolution, but does not interfere in the determination.
S
on the solubility of zirconium in aluminum-magnesium alloys required determining microgram quantities of zirconium. Low concentrations of zirconium in aluminum-magnesium alloys are commonly determined by a spectrophotometric procedure employing sodium alizar in sulfonate (Alizarin Red S) as the chromogenic reagent. A more sensitive method was needed, since the amounts of zirconium were found to be below the range of the Alizarin Red S method (I?’). A number of reagents have been proposed for the spectrophotometric TUDIES
VOL. 33, NO. 1, JANUARY 1961
125
determination of zirconium (1, 3, 4, 8-10, 16,17-19). Submicrogram quan tities of airconium can be determined fluorimetrically (6). Zirconium may be separated from many interfering ions by solvent extraction procedures. Mixtures of monoand dibutylphosphoric acids in nbutyl ether ( l d ) , tri-n-butyl phosphate (7,14), 2-thenoyltrifluoroacetone (TTA) in xylene (I,??), and cupferron in a mixture of benzene and isoamyl alcohol (6) have been used to extract zirconium. Fluoride interferes in practically all of the reported methods for the separation or determination of microgram quantities of zirconium. It is reported that tri-n-butyl phosphate in chloroform extracts zirconium from solutions containing fluoride when a high concentration of aluminum nitrate is present (7). The possibility of extracting zirconium from an aqueous solution containing fluoride and determining zirconium in the extract warranted further investigation. This would afford a direct determination of total zirconium in aluminum-magnesium alloys and perhaps other alloys, since fluoride or fluoboric acid could be used to ensure complete dissolution of the zirconium. I t has been reported that it is impossible to remove fluoride completely from a solution containing aluminum by fuming with perchloric acid (9),
"i I
4
PROCEDURE
WAVE LENGTH, rn+
Figure 1. Absorbance of PAN-zirconium species A. 6.
PAN, chloroform blank PAN-zirconium, PAN blank
PAN may be established by a spectrophotometric titration with a standard copper solution ( 2 ) . DI- BUTYL PHOSPHATE (HDBP) ExTRACTION SOLUTION.In a 125-ml. separatory funnel, add 5 ml. of chloroform to 10 ml. of the commercial mixture (Eastman Kodak 5i70) of di-nbutyl phosphate (55%) and mono-nbutyl phosphate (45%). Extract four APPARATUS AND REAGENTS times with 15-ml. portions of distilled water. Add 1 drop of methyl orange, Absorption spectra were recorded neutralize with a 10% solution of with a Cary Model 11 spectrophotomsodium carbonate, and add 10 ml. in eter using 1-em. cells. All other abexcess. Extract for several minutes sorbance measurements were made with and discard the chloroform. Wash the a Beckman Model B spectrophotometer carbonate solution twice with 15-ml. using 1.0-cm. Cores cells. A Beckman portions of chloroform. Acidify the Model G pH meter was used for pH carbonate solution with concentrated measurements. An Atomic 20 channel nitric acid and add 5 ml. in excess. pulse height analyzer Model 520 Extract the acidified solution four times equipped with a 2 X l 3'4 inch NaI (Tl) with 10-ml. portions of chloroform. well-type crystal was used for counting Filter the combined chloroform exthe Zrg5. Reagent grade chemicals tracts through absorbent cotton into a were used as received unless otherwise 50-ml. volumetric flask and dilute to stated. volume. This solution contains apmCresol purple indicator, 0.1% proximately 4.00 grams of di-n-butyl aqueous solution. phosphate and 0.10 gram of mono-nFLUOBORIC ACID (4.3% by volume). butyl phosphate, as shown by potenDilute 10 ml. of 43% fluoboric acid to tiometric titration with 0.2N sodium 100 ml. ALUMIXUMNITRATE COMPLEXIXGI hydroxide (16). Dilute 10.0 ml. of this di-n-butyl phosphate-chloroform soluSOLUTIOX.Dissolve 1800 grams of tion to 100 ml. n-ith chloroform (0.8 Mallinckrodt aluminum nitrate nonagram per 100). Prepare the extracting hydrate in 920 ml. of water. Twenty solution by diluting 10 ml. of the (0.8 milliliters of this solution when diluted gram per 100 ml.) solution to 1 liter with 10 ml. of distilled water should with chloroform. Store in a stoppered have an apparent pH of 0.0 to 0.3. bottle to minimize evaporation of the If the pH of the diluted aluminum chloroform. nitrate is outside this range, adjust with STAXDARD ZIRCONIUhI STOCK SOLUconcentrated nitric acid or ammonium TION. Dissolve 35.3 grams of zirconyl hydroxide. chloride octahydrate in 330 ml. of 1 to 1 Methanol, conforming to ACS specihydrochloric acid and dilute to 1 liter. fications. Standardize the stock solution by the PAN SOLUTION (0.050~oweight per p-bromomandelic acid method (13). volume). Dissolve 0.100 gram of Prepare a working solution containing 1-(2-py;idylazo)-2-naphthol rEastman 10 pg. of zirconium per ml. by dilution Kodak No. 7192) in methanol, filter of the stock solution. through glass wool, and dilute t o 200 ZIRCOSIUMTRACER SOLUTION. Add ml. with methanol. The purity of the 126
ANALYTICAL CHEMISTRY
10 mg. of zirconium carrier to 100 microcuries of Zrg5-Nbs6. Separate the Zr95 from the NbQ5by a fluozirconate procedure (11). Dissolve the hydroxide from the fluozirconate procedure in 2 ml. of nitric acid and dilute to 10 ml. Add 3 ml. of nitric acid to a 3-ml. aliquot of the purified Zrg6and dilute to 100 ml. The diluted solution contains 15.1 pg. of zirconium per ml.
Preparation of Standard Curve. Place 0.00-, 1.00-, 2.00-, 3.00-, 4.00-, and 5.00-ml. aliquots of the dilute zirconium standard in 125ml. separatory funnels. Add 1 ml. of dilute fluoboric acid and 1 drop of m-cresol purple indicator. Neutralize to the red to yellow color change by adding 1 to 1 ammonium hydroxide and then dilute to 10 ml. Add 25 ml. of aluminum nitrate complexing solution. Add 10 ml. of HDBP extracting solution and extract for 30 seconds. Allow 5 minutes for the phases to separate. Filter the chloroform extract through absorbent cotton into a 25-ml. volumetric flask. Repeat the extraction, using 5 ml. of HDBP solution, and then wash the aqueous phase with 2 ml. of chloroform. -4dd 5.00 ml. of the PAN solution to the combined extracts. Add 2.0 ml. of pyridine, dilute to volume with chloroform, and mix. Carry a reagent blank through the entire procedure. After 1 hour, measure the absorbance of the standards a t 555 mp in 1.0-em. cells using the blank as a reference solution. The system obeys Beer's law for zirconium concentrations of 10 to 65 pg. per 25 ml. The molecular absorptivity is about 32,000. The absorption spectra of 32.3 pg. of zirconium in 25 ml. are shown in Figure 1. The general procedure consists of dissolving a weighed sample in dilute nitric, hydrochloric, or sulfuric acid. One or 2 ml. of fluoboric acid is added to ensure complete dissolution of the zirconium and the sample is diluted to an appropriate volume. An aliquot of 1 to 5 ml. containing from 10 to 65 pg, of zirconium is placed in a separatory funnel and carried through the procedure as outlined in preparation of the standard curve. The number of micrograms of zirconium in the aliquot are calculated from the standard curve. EXPERIMENTAL
Extraction Variables. The effects of acidity, H D B P concentration, fluoride concentration, time of extraction, and diverse anions were studied using the ZrQ5tracer solution. The tracer studies were carried out within 12 hours after the purification of the Zr96 in order to minimize interference from the grow-in of the Kbsadaughter.
EFFECT OF ACIDITY. One milliliter of dilute fluoboric acid was added to 2:ml. aliquots of the standard zirconium tracer solution. Each solution was neutralized to the red-yellow transition of the indicator. To establish the
~~
Table 1. Acid or base added after neutralization, ml. HKOs N&OH
1.5
...
Apparent pH of aqueouEi phase after extraction Zirconium extracted, 70
0.0 101
effect of acidity (over or under neutralization) known quantities of nitric acid or ammonium hydroxide were added to each sample. The solutions were diluted to 10.0 ml. and 25 ml. of the aluminum nitrate solution was added to each. Each solution was extracted for 2 minutes with 10.00 ml. of the 0.00038M HDBP extraction solution. Five minutes after extraction a 3.00-ml. aliquot of the organic phase was pipetted and counted for Zrg5. The results are shown in Table I. The per cent of zirconium extracted falls off rapidly as the apparent p H of the aqueous phase excceds 0.65. This decrease in extraction of zirconium is probably due to hydrolysis. In the absence of fluoborate and aluminum nitrate, zirconium was quantitatively extracted from solutions 1 to 10M in nitric acid. Aluminum nitrate appears t o function as a complexing agent for the fluoride.
Effect of Acidity on Extraction of Zirconium 1.0
*.. 0.0
102
0.6
0.4
0.2
...
...
...
...
...
...
...
...
0.1
0.2
0.3
0.4
0.0 103
0.0 102
0.0 103
0.0 101
0.20 97
0.65 90
1.20 4.4
1.35 1.3
Table 11. Effect of Diverse Ions on Extraction of Zirconium Ion Fluoride Sulfate Tartrate Oxalate Citrate Uranium Ion, mg./10 ml. 80 142 20 40 20 476 Zirconium extracted, 70 99 99 97 97 85 100
the extraction of zirconium, which varied from 10 to 200j0. This is probably due to partial hydrolysis of the zirconium during the neutralization step and subsequent incomplete extraction.
Table 111. Effect of Diverse Ions (32.3 p g , of zirconium added) Ion Zirconium Concn., Found, Ion Mg./lO hfl. pg. A1
COLOR DEVELOPMENT
An attempt to establish the nature of the absorbing species by the method of continuous variation was unsuccessful. Aliquots of zirconium containing 0.354 ,urnole were extracted as for preparation of the standard curve. These solutions were treated with increasing amounts of EFFECTSOF HDBP COXCENTRATIONPAN in a constant volume of methanol. Two milliliters of pyridine was added to AND EXTRACTION TIME, The effects of each sample before dilution t o 25 ml. HDBP concentration and extraction with chloroform. The results indicated time were studied by neutralizing 2.00that PAX must be present in a t least ml. aliquots of the Zrg5after 1 ml. of dilute fluoboric acid was added. The a 14-fold molar excess for full color solutions were then diluted to 10 ml. and development. 25 ml. of aluminum nitrate solution One-half to 1 ml. of pyridine is necesadded. Two-minute extractions were sary for full color development in 1 hour. made with 10.0 ml. of 0.00019, 0.00038, Increasing amounts of pyridine acceler0.00057, and 0.00076M HDBP solutions. ated the rate of color development and In each case, 100 =t2% of the zirconium gave a slight increase in the final abwas extracted. A similar group of sorbance. For a workable procedure, extractions was carried out using 10.0 ml. of 0.00038M HDBP while the 2 ml. of pyridine was used. In the extraction time was varied from 30 to absence of pyridine, about 70% of full 120 seconds. I n all cases, 100 2% color development was noted. Maxiof the zirconium was extracted. mum color developed in about 45 minEFFECTOF ANIONSON EXTRACTION utes and the absorbance remained OF ZIRCONIUM.Known amounts of constant for 24 hours. anions were added to 2.00-ml. aliquots of It was found that 5 minutes for phase the tracer solution and 1 ml. of dilute separation after each extraction gave fluoboric acid was added to each solureproducible results. However, when tion. After neutralization to the redyellow indicator change, 25 ml. of 30 minutes was allowed, the absorbance. aluminum nitrate was added. Each was consistently higher by about 3%. solution was then extracted for 30 In all further work, a 5-minute phase seconds with 10.0 ml. of 0.00038M separation was used. HDBP. Three-milliliter aliquots of the organic extract were counted for ZrgS. EFFECT OF DIVERSE IONS Uranyl nitrate was also added to study the effect of uranyl ion. When the To study the effect of diverse ions, effect of fluoride was studied, fluoboric known quantities of zirconium (32.30 acid was not added. fig.) were treated with known concenThe effects of diverse ions on the extrations of diverse ions and the zirconium was determined by the protraction of zirconium are listed in Table 11. posed method. The results are shown EFFECTSOF FLUORIDE. Extractions in Table 111. Uranium(V1) gave a carried out in the absence of fluoride or slight positive interference when presfluoboric acid gave erratic results for ent in a 30-fold excess. Iron(II1)
*
...
Mg Bi
UVI
400 200 200 20
0.40 1.00
G O ,-2
Citrate Tartrate
9.6 15.5 3.5 3.5 2.2 7.1 80 142 40
20 20
32.4 32.3 32.0 32.2
32.2 33.9
33.7 31.9 31.7 30.0 33.7 32.9 32.1 32.6 33 0 33.3 33.7
Added aa mischmetall.
* 50 mg. ascorbic acid added. c
20 mg. tartrate added.
gave a positive interference when present in a 90-fold excess. Reduction of iron(II1) to iron(I1) with ascorbic acid enables zirconium to be determined in the presence of a 500-fold excess of iron. The interference of chromium(V1) can be eliminated by reduction of chromium(V1) to chromium(II1) with sulfite. When bismuth was present, the aliquot was neutralized with ammonia until a slight precipitate of bismuthyl nitrate was noted. COMPARISON WITH ALIZARIN RED S METHOD
A standard magnesium alloy used for ASTM evaluation of Zirconium and rare earth methods was analyzed by VOL. 33, NO. 1, JANUARY 1961
127
Table IV.
Zirconium Found in Standard Magnesium Alloy“
Zirconium Found, yo Alizarin Red S Method Pan method, Total Insoluble total Lab. 1 0.28, 0.29 0.008, 0.008 0.313, 0.304, 0.300 Lab. 2 0.27, 0.29 0.015, 0.022 0.316 Lab. 3 0.29, 0.30 0.009 , 0.007 Dow 0.27, 0.28 0.007, 0.010 0.308 Av. 0.284 , Alloy, EK 30-824118, rare earths 3.73%.
the proposed method. Determinations were performed on separate samples. Since fluoride or fluoborate do not interfere, the total zirconium is determined with one measurement. Results of analysis by the proposed method and the alizarin method are shown in Table IV. When the Alizarin Red S method is used (I?‘), the alloy is dissolved in dilute hydrochloric acid and filtered. The soluble zirconium is determined in the filtrate. The insoluble zirconium on the filter is ashed and fused with potassium pyrosulfate. The fused melt is dissolved in hydrochloric acid and iron(II1) added. The zirconium is scavenged by precipitating iron(II1) with ammonium hydrordde. The precipitate is dissolved in dilute hydrochloric acid and the zirconium is determined using Alizarin Red s. The total zirconium is calculated as the sum of the soluble and insoluble zirconium. Considerable variation was noted in the determination of insoluble zirconium
by the alizarin method. A possible explanation may be the incomplete removal of insoluble zirconium by filtration.
A sample of the standard alloy was dissolved in dilute hydrochloric acid and filtered through a Millipore-HA filter (0.45-micron pore size). The filter paper was treated with glycerol and ashed and the residue dissolved in fluoboric and hydrochloric acids. Determination by the proposed method gave 0.01S70 insoluble zirconium. COMPARISON WITH RADIOCHEMICAL METHOD
An aluminum-magnesium-zirconium alloy was prepared using irradiated zirconium, and was analyzed by a radiochemical method and the proposed method. Both methods gave 32 p.p.m. The specific activity of the irradiated zirconium was determined from a radiochemical assay using a fluozirconate procedure and a chemical assay using the p-bromomandelic acid method (IS). The zirconium content of the alloy was
obtained by using the specific activity of the radiochemical assay of the alloy. LITERATURE CITED
(1) Banerjee, G., Anal. Chim. Acta 16,
62 (1957).
(2) Cheng, K. L., ANAL. CHEM.30, 1027
(1958). (3) Cheng, K. L., Talanta 2 , 61, 187 (1959). (4) Freund, Harry, Holbrook, W. F., ANAL.CHEM.30.462 (1958). (5) Fritz, J. S., Richard, M: J., Bystoff, A. S., Zbid., 29,577 (1957). (6) Geiger, R. A,, Sandell, E. B., Snal. Chzm. Acta 16,346 (1957). (7) Gill, H. H., Rolf, R. F., Armstrong, G. W., ANAL.CHEM.30, 1788 (1958). (8) Gopalakrishna, V., Raghava Rao, S . V., Anal. Chim. Acta 19, 161 (1958). (9) Grimaldi, F. S., White, C. E., ANAL. CHEM.25,1886 (1953). (10) Hahn, R., Johnson, J. L., Zbid., 29, 902 (1957). (11) Hume, D. N., “National Xuclear Energy Series,” Division IV, Vol. 9, Book 3, pp. 1499-503, McGraw-Hill, New York, 1951. (12) Moore, F. L., ANAL.CHEM.28, 997 (1956). (13) Papucci, R. A., Klingenberg, J. J., Zbid., 27,835 (1955). (14) Scadden, E. M., Ballou, N. E., Zbid., 25, 1602 (1953). (15) Silverman, L., Hawley, D. E., Zbid., 28,806 (1956). (16) Stewart, D. C., Crandall, H. W., J.Am. Chem. SOC.73, 1377 (1951). (17) Wengert, G. B., ANAL.CHEM.24, 1449 (1952). (18) Young, J. P., French, J. R., White, J. C., Zbid., 30,422 (1958). (19) Young, J. P., White, J. C., Talanta 1, 263 (1958). RECEIVEDfor review April 15, 1960. Accepted September 16, 1960. Part of work carried out under Dow-AEC Contract AT(l1-1)-768.
Simplified Determination of Strontium-90 Preferential Extraction of Yttrium with Tributyl Phosphate R. J. VELTEN and A. S. GOLDIN’ Radiochemical Analyses, Radiological Health Research Acfivifies, U. S. Department of Health, Education, and Welfare, Roberf A. raft Sanitary Engineering Center, Cincinnati 26, Ohio
b A simplified approximate method for the determination of strontium-90, particularly applicable for screening purposes, is based on the preferential extraction of yttrium-90 by tributyl phosphate from strong nitric acid solution. The radioactive interferences-namely, the rare earths and zirconium-niobium-and the effects of calcium and of phosphates are discussed. In many cases, where alkaline earth activities are relatively enriched, useful preliminary results may b e obtained in one day. These results may b e readily improved in a few 128
ANALYTICAL CHEMISTRY
additional days by correcting for impurities on the basis of decay measurements.
V
methods (a, 4 , 6, IS) have been utilized for the determination of low levels of the biologically important radionuclide strontium-90 in environmental samples. Basically these involve concentration, separation of strontium from interfering radioactive and inert materials, and finally separation and counting of the yttrium-90 daughter after waiting a suitable time for its formation from strontium-90. ARIOUS
Often, particularly for administration or control purposes, a more rapid determination of strontium-90 is required. Even if this determination does not give results of the highest accuracy, it may still be entirely satisfactory on a “go-no go” basis. Such a situation, for example, might occur in the event of accidental release of radioactive materials, resulting in a high gross activity level in a water supply. It has been reported (8-10, 12) that 1 Present address, National Lead Co., Inc., P. 0. Box 151, Winchester, Mass.
