Separation from Fission Product Mixtures. Two 1-mg. samples of uranium-235 were irradiated with thermal neutrons at different times in the Materials Testing Reactor at Arco, Idaho. About 36 hours after removal from t h e reactor, t h e uranium was dissolved i n hot aqua regia, evaporated to near dryness with perchloric acid, and taken up in hydrochloric acid. Aliquots of the fission product solution were made 1N in HCl, and the molybdenum-99 was extracted with a-benzoin oxime. A standard gravimetric radiochemical determination for molybdenum also was run on similar aliquots. The procedure consisted of adding a known amount of carrier and prccipitating the molybdenum as the oxime several times and finally as lead molybdate. This was mounted on a planchet and counted in a beta-ray endwindow counter which had been crosscalibrated with the scintillation gammarag well instrument. K i t h the first sample, extractions were carried out at various times after irradiation to determine the interference by niobium-95 as its ratio to molybdenum-99 increased. For 10 days no significant amounts of niobium-95 could be detected, b u t thereafter i t ivas necessary to make the aqueous phase O.1N in hydrofluoric acid to reduce the niobium contamination. Considerable 74-minute niobium-97 was observed in the chloroform layer for the first fern days, but this activity decayed very rapidly. Table 111 gives a comparison of the
Table 111. Comparison of Solvent Extraction and Gravimetric Methods for Molybdenum-99
Davs aft&
Aqueous Phase 1 S HC1
1N HCl lAVHClO.1N H F
Fission/Ml. (1012) radi- Extrac- Graviation tion metric SAMPLE1 4 4 4 4
7.07 7.20 6.99 7.24
7.03 7.10 7.20 7.14
19 22
7 32" 7.29"
...
SAMPLE 2 3 14.4 3 3
14.4 14.5
18
14 9~
...
14.7 14.6 14.7
Gamma-ray spectrum showed contamination. a
iodine-131 was volatilized. However. the 19- and 22-day fractions in sample 1, and the 18-day fractions in sample 2 showed some iodine-131 contamination. This was due to the decay of the tellurium-131 parent remaining at the time of the iodine removal, and i t became more significant as the amount of molybdenum-99 decreased with time. This is further evidence that the iodine extraction should precede the molybdenum extraction. The fissions per milliliter for the two methods of determining molybdenum are within 2?4 of each other, and both show about the same precision. The initial treatment of the sample with perchloric acid had no effect on the recovery of the molybdenum. The remaining aqueous phase can then be used for the analysis of other fission radionuclides b y ion exchange procedures ( 5 , 6, 7 , 8). LITERATURE CITED
1131
molybdenum-99 extraction and gravimetric results in fissions per milliliter. The number of fissions was obtained b y multiplying the gamma counts per minute by a factor which had been obtained indirectly (9). The iodine extraction by carbon tetrachloride was not used for these samples since originally they were boiled with strong acid. It was assumed that most of the
(1) Allen, S. H., Hamilton, M. B., Anal. Chiin. Acta 7, 483 (1953). (2) Goldstein, G., Manning, D. L., Menis, 0.. ANAL.CHEY.30. 539 (1958). (3) Jefferv. P. C.. Anulvst 8 1 . 104 (1956). (4)Mae& W. J., Kussy, Id,E.,' Rein, J. E., ANAL.CIIEM. 33, 237 (1961). (5) Wish, L., Ibid., 31, 326 (1959). ( 6 ) Ibid., 32,920 (1960). ( 7 ) Ibid.. 33. 53 11961). (8j Ibid.; p. '1002: (9) Wish, L., Freiling, E. C., U. S. Saval
Radiological Defense Laboratory Report, USNRDL-TR-464,July 8, 1960.
RECEIVED for review December 11, 1961. Accepted March 9. 1962.
.
Determination of Tin and Molybdenum in Nuclear Reactor and Other Materials Extraction and Spectrophotometric Determination with 8-Quinolinol A. R. EBERLE and M. W. LERNER
U. S.
Atomic Energy Cornmission, New Brunswick laboratory, New Brunswick, N. 1.
b To eliminate the tedious and erratic distillation separation of tin, a new 8 quinolinol extraction spectrophotometric procedure was developed. Both tin and molybdenum are determined in uranium, beryllium, thorium, zirconium, steels, and other materials. The method involves the extraction of molybdenum from a sulfate solution in the absence of halide, followed b y the addition of halide and the extraction of tin. The molybdenum procedure can b e made
-
-
specific; tungsten interference in the tin procedure can b e readily elirninated. The procedure is rapid, accurate, and precise.
N
o
EXTIRELY satisfactory methods are available for the spectrophotometric determination of tin in uranium and other metals used in nuclear reactor technology. Because of the nonselectivity of the chromogenic reagents, a preliminary separation of
tin is required. For example, distillation of the bromide or chloride is frequently used (1, 9). This procedure, however, is troublesome and recovery of microgram amounts of tin is erratic (4). Ross and White (7) have recently described a procedure involving the extraction of tin from acidic chloridesulfate solutions with a cyclohexane solution of tris(2ethylhexyl) phosphine oxide and color development in ethyl alcohol dilutions of the organic phase with Pyrocatechol Violet. This proVOL. 34, NO. 6, M A Y 1962
* 627
cedure is satisfactory for many types of materials but i t appeared to be inadequate for certain samples, particularly uranium and zirconium materials low in tin. The other possible reagents, dithiol and phenylfluorone, are reviewed by Ross and White ( 7 ) and Sandell (9). I n the search for an efficient separation procedure that would lend itself to multiple determinations, 8-quinolinol (ouine), with which the final detcrmination could also be made, was investigated. Gentry and Sherrington ( 2 ) have reported that tin(1V) is quantitatively extracted with lyO oxine in chloroform over the p H range 2.5 to 3.5. Many other elements including copper, nickel, iron, molybdenum. and aluminum also give colored complexes co-extracting; uranium, thorium, and zirconium could also be expectcd to extract. Wyatt ( 1 2 ) found that somP separation from these elements is obtained by extracting a t a pH slight11 below 2.5, but the separation was described as being generally unsatisfactory. A diethyldithiocarbamatr srparation n-as necessary before the final determination with oxine. Ruf (8) investigated the application of osine to the detcrmination of tin and concluded that no satisfactory proccdure n a s possible. However, he reported a procedure for the detprmination of ~lemental Sn and SnlII) in stannic o\ide involving the use of 5,'I-dibrornooyine. Wakamatsu (10) used oyine for the detrrmination of tin after separating the tin on manganese dioxide precipitates and subsequent extraction with methyl isobutyl kctone. Motojima and Hashitani (6. 6 ) have studied the determination of molybdenum and niobium with ouine. I n the present investigation, tin is quantitatively extracted from solutions down to a p H of 0.7 by the use of fairly high concentrations of oxine. At this low pH, separation is made from most other elements. Molybdenum accompanies the tin, but since the extraction of tin requires the presence of halide, separation and determination of these two elements can be performed b y controlling the halide concentration. REAGENTS AND APPARATUS
Ammonium chloride, 47, and 20%, adjusted to p H 0.85 with hydrochloric acid. Oxine, 4.00/,, adjusted to p H 0.85 with sulfuric acid. Dilute sulfuric acid wash, p H 0.85. Standard tin(1V) solutions, 100 and 10 pg. per,ml. Dissolve 0.200 gram of tin metal in 10 ml. of hot concentrated sulfuric acid. Fume the solution strongly to expel sulfur dioxide. Add 30 ml. of sulfuric acid, cool the solution, and pour i t into 125 ml. of water. Rinse the dish, add the rinse to the solution, and dilute i t to volume in a 200-ml. volumetric flask. Transfer 100
628
ANALYTICAL CHEMISTRY
Analysis of Samples. The preparation of sample solutions and t h e necessary treatment of some of the solutions before extraction and measurement of tin and molybdenum are outlined in Table I. Detailed dissolution procedures for most of the sample types have been omitted. The tin in the final sample solutions will be tin(1V) because of the fuming steps necessary to remove either nitrate, chloride. or fluoride.
09 Mo
IO
20
30
40
50
4 % OXINE, m 1 / 1 0 0 m l
Figure 1 . Effect of oxine concentration on extraction of tin- and molybdenum-oxine complexes nil. of this solution to a 1-liter volumetric flask, add 300 ml. of 6 V sulfuric acid, and dilute to volume to obtain 100 pg. per ml. Dilute 10 ml. of this solution to 100 ml. with 3 M sulfuric acid to obtain 10 pg. per ml. Prepare this solution daily. (Alternatively, sodium stannate can be dissolved in dilute sodium hydroxide to provide a stable dilute standard solution.) Standard molybdenum(V1) solution, 100 and 10 pg. per ml. Dissolve 0.092 gram of (NH4)&o&.4HZ0 in water and dilute to 500 ml. Dilute 10 ml. of this solution to 100 ml. Spectrophotometer. Beckman Model DB with 1- and 4-cm. cells. p H Meter. Leeds & Northrup p H Indicator, Cat. 7664. PROCEDURE
Preparation of Standard Curves. Add 0 to 50 pg. of tin(1V) and 0 to 50 pg. of molybdenum(V1) to 60 ml. of the sulfuric acid wash solution. Add 25 ml. of 4.0% oxine solution and adjust the p H to 0.85 0.10 a t 25" C. with dilute sulfuric acid or ammonium hydroxide. Transfer the solution to a separatory funnel with no more than 15 ml. of sulfuric acid wash solution. Add 20.0 ml. of chloroform and equilibrate the mixture for 2 minutes. Drain the organic phase containing the molybdenum into another separatory funnel holding 50 ml. of the 4% ammonium chloride wash solution and equilibrate the mixture for 2 minutes. Filter the chloroform phase through a dry 11.5-cm. K h a t m a n KO. 41 filter paper. Measure the absorbance a t 385 mp in 4-cm. cells against chloroform as a reference. Wash the original aqueous phase with 10 ml. of chloroform. Discard the chloroform. Add 5.0 ml. of the 20% ammonium chloride solution to the aqueous phase and extract the tin for 2 minutes with 20.0 ml. of chloroform. R a s h and filter the chloroform phase as in the molybdenum extraction and measure the absorbance a t 385 mp against chloroform. For larger amounts, repeat the above with 50 to 500 pg. of tin and 50 to 400 pg, of molybdenum, and measure the absorbance in 1-cm. cells. The standard curves are rill linear.
*
EXPERIMENTAL
Effect of pH on Extraction of Tin and Molybdenum. Wyatt's (11) observation t h a t a p H below 2.5 may assist in the separation of tin from other metals extracting in acid solution prompted a study of the effect of pH on the extraction of tin when a large concentration of oxine v a s used. Aqueous solutions of 100 ml. containing 53 pg. of tin(IV), 23 nil. of 4.0% oxine, and 5 ml. of 20% ammonium chloride were adjusted to a definite p H between 0.35 and 1.60. The solutions were extracted \i-ith 20.0 ml. of chloroform. The absorbances were measured a t 385 nip in 4-em. cells against blanks prepared a t the corresponding pH. Tin extracts quantitatively from pH 0.68 to 1.60. Solutions containing 49 pg. of molybdenum and the same quantity of oxine were similarly extracted over the pH range 0.23 to 1.60. Molybdenum extracts quantitatively from pH 0.iO to 1.60. A p H of 0.85 = 0.10 was selectcd for the extraction of both tin and molybdenum. As shown in the srction on interferences, most elements do not interfere a t this pH and osinc concentration. Effect of Oxine Concentration on Extraction of Tin and Molybdenum. Solutions of 100 mi. containing 53 pg. of tin, 5 ml. of 20% ammonium chloride, and various quantities of 4.0YG oxine were adjusted to p H 0.85 =k 0.10 and extracted with 20.0 ml. of chloroform. The absorbances TTere measured in 4-cm. cells. For the molybdenum tests, the experiment was repeated without the addition of the ammonium chloride, Figure 1. The horizontal portions of both curves represent 1 0 0 ~ extraction. o Although the use of 15 ml. is apparently sufficient for the proposed procedure, 25 nil. was selected as giving a comfortable excess in the presence of large quantities of such ions as iron(II1). Effect of Halide Concentration on Extraction of Tin. T h e extraction of tin(1V) in the absence of halide at p H 1.00 and with the recommended oxine concentration was investigated. S o tin extracts in the absence of halide when the amount of tin present is 600 pg. or less per 100 ml. of solution. Beyond this point, tin begins to extract.
1
80
175
200
PH
Figure 2. Effect of pH and tin concentration on extraction of tin-oxine complex in the absence of halide
If it is aqsunied that the tin(1V) compie\ extracting has about the same absorbance as that extracting in the presence of halide, the amount extracting when 1600 pg. of tin is present is only about 12 pg. When 10 mg. of tin is present, about 35 pg. extracts; nhen 20 mg. is present. about 120 pg. ex-
Table I.
Sample u308
Steels Cu-Zn Base Alloys Zr Metal Be Metal Zircaloys Zircaloys
SamDle Weight, Determination Grams Sn and >lo 5 2
Sn ;\Io
ThOn
Sn and ?*lo
Stainless Steel (Containing Nb, Ta, and
&I0
IT')
Rn
4
3
I
tracts. Some hydrolysis may occur with these large quantities. Thus, the procedure has potential application even if large amounts of tin are present. A p H of 1.00 was used in this test instead of 0.85 to obtain a maximum value in the event a slight error is made in the p H adjustment. More tin extracts as the pH increases in the absence of halide as shown by Figure 2 which is plotted from data obtained n-ith 1-cm. cells. Figure 2 also shows that, with quantities of tin below 100 pg., little or no tin extracts a t p H 1.30. At this pH, tungstrn Pxtracts. The importance of this fact is discussed in the section on interferences. The optimum amount of chloride, bromide, or iodide for complete extraction of 50 pg. of tin(1V) in the proposed procedure is shown in Figure 3. The optical measurements were made in 4 c m . cells against chloroform as a reference and were corrected for the
1
"-
,----"-----
a 02
2
4
6
8
1
0
HALIDE, m e q / 100ml.
Figure 3. Effect of halide concentration on the extraction of tin-oxine complex
appropriate blanks. The horizontal portions of the curves represent 100% extraction. It can be seen that 3 meq. -106 mg.-of chloride ion is necessary per 100 ml. of solution. I n practice,
Pretreatment and Extraction Conditions for Various Samples
Solution Preparationa Dissolve sample and treat so that a definite volume of solution free of nitrate, chloride, or fluoride is obtained. Select an aliquot of about 50 ml. containing less than 500 p g . of Sn and 400 pg. of 310 and adjust pH to 0.85 zk 0.10. Add 25 ml. of 4.0y0oxine solution. Dissolve sample in HF-H,O,. Evaporate solution nearly t o dryness, and dissolve residue in 50 ml. of water plus 10 ml. of acid wash solution. Add 25 ml. of 4.070 oxide solution. Dissolve thorium oxide conveniently with hot 7oyOperchloric acid containing fluoride, 5 ml. of acid, and 12.5 mg. of NaF, respectively, per gram of oxide, under reflux. After dissolution, add 50 ml. of water, 0.5 gram of boric acid and 5 ml. of 20% ammonium chloride solution; adjust to pH 0.85 with dilute ammonium hydroxide. (The metal is treated similarly after ignition to oxide.) Add 25 ml. of 4.0y0 oxine solution. Prepare 100 ml. of solution as with U308,etc., but omitting the oxine addition. Select an aliquot of 50 ml. or less containing less than 400 pg. of hlo. Add 200 mg. of NaF. Add 25 nil. of 4.07' oxine solution.
Treatment Necessary before Extraction and Measurement as in Standard Curve Preparation" None
(With Zircaloy samples, discard M o extracts. ) None
Extract both Sn and Mo with two 20-ml. portions of chloroform. Evaporate chloroform to dryness. Fuse the residue with 3 grams of potassium persulfate. Dissolve melt in 50 ml. of dilute sulfuric acid wash solution a t pH 0.85. Add 25 ml. of 4.0% oxine solution.
None
Select from above an aliquot of 50 ml. or less containing less than 100 pg. of Sn. Omit the NaF addition. Add 25 ml. of 4.0% oxine solution.
Extract Mo and other elements with 20 ml. of chloroform; wash aqueous with 10 ml. of chloroform. Discard organic phases. Extract Sn and some Nb, Ta, and W with two 20-ml. portions of chloroform. Wash each extract with the same 50 nil. of 4% ammonium chloride wash solution. Combine extracts and evaporate to dryness. Fuse residue with 3 grams of potassium persulfate. Dissolve melt in 50 ml. of dilute sulfuric acid solution. Add 25 ml. of 4.0% oxine solution. Adjust pH to 1.20 to 1.30 with dilute ammonium hydroxide. Extract W with 20 ml. of chloroform. Wash solution with 10 ml. of chloroforni and discard organic phases. Add 5 ml. of 20% ammonium chloride solution, and adjust the pH to 0.85. Transfers and washing should be made, after the pH adjustment, with the dilute sulfuric acid wash solution to avoid pH changes. ~~
VOL. 34, NO. 6, MAY 1962
~~
629
w,
ug./100rnl.
Figure 4. Absorbances of the tin and molybdenum extracts due to tungsten A. B.
molybdenum procedure tin procedure following the molybdenum extraction WAVELENGTH, m y
1.0 gram is used to furnish a large excess. The order of increasing absorbance of the mixed complexes is C1- < Br- < I-. Fluoride seriously hinders the extraction, presumably because of the strength of the tin(1V) fluoride complex Composition of Complexes. Although i t mas assumed t h a t t h e molybdenum extracts as t h e normal oxinate, M O ~ ~ ( O X t h)e ~ dependence , of the tin extraction upon the presence of halide prompted a brief study of t h e tin complex. By extracting a large quantity of tin in t h e presence of chloride and washing out a n y excess chloride with a n oxine solution at pH 0.85, a chloroform solution was obtained containing the comple.; and no more than a small amount of free oxine. Suitable aliquots of this solution w r e analyzed: for tin by the proposed procedure; to determine the weight of the complex by evaporation and heating a t 105’ C.; and for chloride by evaporation, distillation of the chloride, and a Mohr titration. The results of duplicate tcsts showed that the probable composition of the complex is SnC12(ox)2. This formula is in agreement with a recently reported compound (3)suitable for the gravimetric determination of large quantities of tin. The usual spectrophotometric meth-
Figure 5. Absorption spectra of oxine, tin(lV)-oxine and molybdenum(V1)-oxine in chloroform extract
ods of determining the formula of colored complexes-Le., continuous variation, mole ratio, and slope ratio methods-were not attempted because a large excess of oxine is necessary for the formation and extraction of the complex at p H 0.85. A few tests were carried out b y the continuous variation and slope ratio methods with a chloroform solution of SnC14.5Hz0 and an equimolar solution of oxine in chloroform. Although the results were not conclusive, they suggested a 1 to 3 or 1 to 4 complex. Under these conditions, perhaps a mixture of the 1 to 2 and the “normal” 1 to 4 complex is produced. Interferences. Potentially interfering elements in both the tin and molybdenum procedures are tungsten, niobium, and tantalum. However, the molybdenum procedure is made specific in t h e presence of greater than 100 pg, each of tungsten, niobium, and tantalum, and over 600 p g . of tin, by the addition of fluoride. With less than 100 pg of niobium and tantalum and 600 pg. of tin, even the fluoride can be dispensed with since the tin will not extract, and the other two elements are
II.
Quantities of Elements Having No Effect on Tin and Molybdenum Determinations with Basic Procedure Quantity, X g . Element Quantity, hIg. Element Illg 3000.0 0.005 -4g
Table
A1
As+3, h s + 6
a
2000.0
0.5a 2000 0 0.05 0.025 0.005
Mn Xi Pb
8 5
46 0
0 47 Be 0 50 Sh, + 3 Sbf6 Bi 4000.0 Th Ca 10.0 Ti Cd 5000.0 u co 1 .o 0.5 45.0 V cu 1000.0 90.0 Zn Cr 2000 0 Zr 2000.0 Fe These ions were studied in separate testa by addition to standard Sn and Mo solutions.
630
ANALYTICAL CHEMISTRY
eliminated in the washing step. Tungsten, however, must be absent under these conditions. I n the absence of fluoride, greater than 100 pg. of either niobium or tantalum gives precipitates during the eytraction step and consequently makes phase separation increasingly difficult as the quantity of precipitate gets larger. Upon heating such samples with sulfuric acid to the point of fuming to remove the hydrochloric and nitric acids in the sample solution preparation, the insoluble earth acids separate with any silica. Filtration of the solution a t this point apparently leaves less than 100 pg. of both elements in solution, because the extraction is now satisfactory. When tin is to be determined, fluoride cannot be employed. In this case, only tungsten interferes. KOwashing method could be found to eliminate this interference. JJ‘ashing the chloroform phase with citric, tartaric, o d i c , or phthalic acid solutions, or (ethylenedinitrilo) tetraacetic acid (EDTA) solutions, in some instances removed the tungsten but a t the same time caused wine tin loss. The tolerance of tungsten wa. studied. The sequential tin and mol) bdenum procedures rvere used with a solution of 200 pg. of tungsten, Figure 4. Eutraction of tungsten, as shown by the absorbance a t 385 mp, occurs in both eutraction steps, but chiefly in the niolybdenum step. The absorbance a t 385 mp from a starting quantity of 200 p g . of tungsten is 0.025, equivalent to 1.5 pg. of tin. The relationship is linear. E o serious interference 1%-illoccur, therefore, if less than 25 pg. of tungsten is present. If a little more is present, a preliminary hydrogen sulfide separation of the tin with copper carrier is advisable. However, with large quantities of tungsten, Ivashing out the tungsten
from the sulfide precipitation becomes difficult. For the analysis of these high tungsten samples, a brief study was made of the oxine extraction of this element. With the proposed amount of oxine in 100 ml. of solution, u p to 500 pg. of tungsten is extracted completely from sulfate solution in the p H range of 1.20 to 1.40. Figure 2 shon-s that up to 100 pg. of tin(1V) is not extracted from sulfate solution at p H 1.30 or lower, although some extraction does occur with larger amounts of tin. Accordingly, i t is possible to separate 500 pg. of tungsten from 100 pg. or less of tin by first extracting the tungsten (and molybdenum) at p H 1.25. Tin may then be extracted after the addition of chloride. It should be noted that more free oxine extracts a t p H 1.25 than a t 0.85, and a n e n blank must be prepared a t this pH. The tungstenoxine complex has an absorption maximum a t 355 mp and shows no absorbance a t 420 mp. Tin in the presence of tungstcn could be measured a t 420 mp, but obviously a loss of sensitivity n ould occur. No other interfering elements were found. Table I1 lists the known noninterfering elements in the quantities tested. These quantities m-ere determined by the analysis of standard samples and, therefore, do not represent the maximum permissible amounts; undoubtedly most can be tolerated in much greater amounts. Contrary to the experience of K y a t t (11) n h o worked at p H 2.5 and with lower concentrations of oxine, large quantities of sulfate do not interfere in the proposed procedure. Nitrate in large quantities apparently interferes with the tin results. T h e presence of perchlorate should also be avoided except where it is used in the recommended procedures. When perchlorate is used, the tin extraction becomes unpredictable, and it is better to add chloride and extract both the tin and molybdenum prior to the separation extractions with and without the presence of halide. Whether the perchlorate ion itsclf or r d d u a l chloride resulting from the rt.duetion of perchlorate causes this behavior was not determined. Sample dissolution with perchloric acid must be carried out under reflux; otherwise, some tin is lost. Absorption Spectra. T h e absorption spectra shown in Figure 5 were obtained by carrying 300 pg. each of tin(1V) and molybdenum(V1) in the same solution through the procedure. Absorbances were measured in 1-cm. cr.lls against chloroform as a reference. The oxine spectrum shows the absorbance of the quantity extracting under tlie same conditions. The maximum absorbance of the tin complex occurs at 382 mp, Because the peak is flat, a wavelength of 385 mp is recommended
for convenience. The maximum of the molybdenum complex occurs a t 368 mp. Before i t was found that the 4% ammonium chloride solution a t p H 0.85 removed most of the ovine extracting along with the metal complexes, the resulting oxine absorbance compelled the use of a wavelength of 385 mp. Some data were obtained at this wavelength. When the ammonium chloride wash is used, the wavelength of 368 mp affords about a 16% increase in absorbance over that at 385 mp. Stability of Solutions of Oxine and Complexes. T h e dilute sulfuric acid solution of oxine is stable for a t least 4 weeks. The color of both the molybdenum and tin oxine complexes in chloroform is stable for at least 24 hours. Sensitivity of Tin and Molybdenum Procedures. T h e proposed tin procedure is very nearly as sensitive as the dithiol procedure (9) and somewhat less sensitive than the phenylfluorone (9) or Pyrocatechol Violet ( 7 ) procedures. The proposed molybdenum procedure is less sensitive than the dithiol (9) or thiocyanate (9) procedures. However, this apparent disadvantage is more than compensated by the greater
selectivity and simplicity of the proposed procedures. RESULTS
The data obtained with a wide variety of samples analyzed by the particular recommended procedure are shown in Table 111. Most of the values are single determinations. A precision study carried out by analyzing a Us08 standard sample is shown in Table IV. I n addition to the tin and molybdenum this sample contains the following impurities a t the approximate parts per million values: 500 each of aluminum, iron, zinc, phosphorus, potassium, and sodium; 250 of silicon; 100 each of magnesium, vanadium, chromium, and nickel; 50 each of manganese, lead, bismuth, and copper; 25 each of calcium, and lithium; 5 each of cadmium, silver, and boron. DISCUSSION
A brief study of the extraction of tin(I1) was made. Apparently i t does not extract; the trace of color developing upon extracting a tin(I1) solution in the absence of a reducing agent was
Determination of Tin and Molybdenum in Various Materials by Recommended Procedures Molybdenum, To Tin, % __ Present Found Material Analyzed Present Found 0.006 0,004 0.004 0.006 Ingot iron, NBS 55c 0.002 0.003 0.002 Bessemer steel, NBS 8g 0.003 0,036 0.036 0.013 0.013 B.O.H. steel, NBS 152 0.010 0.012 0.010 0.012 -4.O.H. steel, NBS 19e 0.013 0.013 0.017 0.017 A O.H. steel, NBS 20e 0,076 0.077 0.035 0.035 A.O.H. steel, NBS 21d 0.011 0.011 0.002 Electric steel, NBS 51a 0.002 0.008 0.007 0.008 0.007 Basic electric steel, NBS 65c 0,003 Nickel steel. NBS 33c 0.032 0.003 0.032 0.008 0.008 0.095 0.095 Cr-Ni (18-9)steel, NBS lOlc 0.0017 0.0015" 0.0004 Beryllium metal, NBS BF 0.0006a 0.0014 0.0003 0.0002b ... Zirconium, NBL E-8918 0.0095 0.0021b 0 .N23 ... Zirconium; NBL E-8919 1.42 1.43O 0.0004* 0.0004 Zircaloy, NBL E-7177 1.75 0.0004 Zircalov. NBL E-8920 1 .75" 0.0002b 1.29 1.27c Zirca1oj.i NBL G-3156 ... ... 1.41 1 .3gC Zircaloy, NBL G-3158 1.58 0.0029b 0.0029 1 . 5ge Zircaloy, NBL E-9830 0,0004 0.O004d 0.00004d 0.00004 AldS0i)s. 18Hz0 0.0004 0.00004 0 .0004d MgSOc .'nHzO 0 .00004d 0.95 0.97 ... Sheet brass, NBS 37d ... 0.64 0.63 ... Aluminum brass, NBS 164 ... 0.96 0.97 ... Silicon bronze, NBS 158 ... Zinc-base die casting alloy, 0.0050 0.005 NBS 94a 0.0050 0.0050~ 0.005Od 0.0050 Ua08,NBL 95-1 0.0020 0.0020d NBL 95-2 0.0020d 0.0020 0.0010 0 .OOlOd NBL 95-3 0 . OOlOd 0.0010 0.0005 NBL 95-4 0,0005 0.0005d 0 . 0005d 0.0002 0.0002d 0.0002 NBL 95-5 0 0002d 0.0001 ISBL 95-6 0.OOOld 0 .O O O l d 0.0001 0.0051 Thorium Oxide - 1 0.0050d 0,0048 0.0050d 0.0020 0.0020d -2 0,0019 0.0020d 0.0010 -3 0.0009 0 . OOlOd 0.OOlOd 0,0005 -4 0.0005d 0,0005 0 . 0005d 0.0002 0.0002d -5 0 I0002d 0.0002 0.0001 0 . OOOld -6 0 .O O O l d o.oO01 a Spectrochemical values. * Thiocyanate procedure values. c Volumetric values. d Quantity added.
Table 111.
VOL. 34, NO 6. M A Y 1962
631
Table IV. Replicate Analyses of Tentative U 3 0 8Standard Sample NBL 95
Parts Per RIilIion PresStandard enta Foundb deviation 50 49.7 0.95 Tin 50 49.8 0.56 Molybdenum a Quantity added. * Average of eight determinations. Determination
shown to be due to some tin(1V) in the solution. No special steps are necessary to ensure the correct oxidation state. With every type of sample analyzed, the dissolution and fuming steps result in complete conversion of any tin(I1) to tin(1V).
No study was made of possible hydrolysis of tin before the extraction could be made. I n the usual elapsed time of a t least 30 minutes between the final pH adjustment and the extraction, no evidence of hydrolysis was found in the analysis of samples. Both the tin and molybdenum osine complexes appear to form immediately, and the extraction coefficients for the chloroform-aqueous system appear to be large. The extractions are complete within 30 seconds despite the unfavorable organic to aqueous volume ratio used. LITERATURE CITED
M.,Pekola, J., ASAL. CHEM.26, 735 (1954).
(1) Farnsworth,
(2) Gentry, C. H. R., Sherrington, L. G., Analyst 75, 17 (1950). (3) Hamaguchi, H., Ikeda, N., Osawa, K., Bull. Chem. SOC.Japan 32, 656
(1959).
( 4 ) Menis, O., Manning, D. L., Ball, R.
G., U . S. Atomic Energy Comm. Rept.
ORNL-2111, August 1956. (5) Motojima, K., Hashitani, H., ANAL. CHEM.33, 48 (1961). (6) Motojima, K., Hashitani, H., Bunseki Kagaku 9, 151 (1960). (7) ROSS,W. J., White, J. C , h A L . CHEM. 33, 421, 424 (1961). (8) Ruf, E., 2. anal. C h p . 162, 9 (1958). (9) Sandell, E. B., Colorimetric Determination of Traces of Metals,” 3rd ed., Interscience, New York, 1959. (10) Wakamatsu, S., Bunseki Kogaku 9 , 858 (1960). (11) Wyatt, P. F., Analyst 80, 368 (1955). RECEIVED for review November 15, 1961. Accepted March 1, 1962.
Spectrophotometric Determination of Copper with Ethylenediamine E. A. TOMlC and J. L. BERNARD Explosives Departmenf, E. 1. du font de Nemours & Co., Wilmington 98, Del.
b The purpose of this study is to utilize the chelation of Cu by ethylenediamine (en) in a rapid and simple analytical method for the determination of copper. Copper(l1) reacts with ethylenediamine in aqueous solution to and (Cu form the blue (Cu chelates. The aqueous solutions of the chelates conform to Beer’s Law and are stable for several weeks. As described, the method is designed to determine copper in the concentration range of 20 to 1000 p.p.m. in solution when 1-cm. cells are used. It is particularly useful for the analysis of ores and alloys which contain several per cent copper.
+’
all metal ions, C U + is ~ probably the one for which the largest number of photometric determinations have been published. Most of these methods (12) are designed to determine copper in trace amounts. The determination of copper with HBr (3, 7 ) has been adopted widely for the determination of relatively large amounts of copper although molybdenum, vanadium, chromium, cobalt, gold, and platinum metals can interfere. The classic cupric ammonia method (6) and its modifications (10, 11, 1:) provide the means to measure copper concentrations in the range of 40 to 600 p.p.m. However, these methods suffer especially from dependence of color intensity on reagent MOSG
632
ANALYTICAL CHEMISTRY
concentration, volatility of reagent, and interference by foreign metal ions. Ethylenediamine (en) forms complexes with C U + of ~ comparable absorptivity. Therefore, substitution of en for ammonia as the reagent for Cu t2promised to overcome some of the disadvantages. EXPERIMENTAL
Apparatus. Absorption spectra were obtained with a Perkin-Elmer recording spectrophotometer, Model 4000A. Routine measurements were made in a Beckman, Model B spectrophotometer. One-centimeter cells were used in both instruments. Spectrographic metal analyses were obtained with a 3.4-meter Ebert Type (Jarrell--4sh Co.) emission spectrograph. Measurements of p H were made with a Beckman Model H2 pH meter equipped with a glass and reference electrode couple. Reagents. COPPER SOLUTIOSS. Stock solution was prepared b y dissolving 120 grams of cupric nitrate (trihydrate) in 500 ml. of mater containing 1 ml. of concentrated nitric acid. T h e solution, standardized b y electrolytic deposition, contained 61.70 mg. of Cu+*per ml. Standard copper solution containing 10 mg. of C U + per ~ ml. was prepared by diluting 81.04 ml. of the stock solution to 500 ml. A 0.5M cupric nitrate solution was prepared by diluting 51.5 ml. of the cupric nitrate stock solution to 100 ml. ETHYLENEDIAMINE REAGENT SOLUTION. An ethylenediamine solution-
en reagent solution-was prepared by diluting redistilled 98% ethylenediamine with an equal volume of water. Ethylenediamine solutions, 0.5iIf and 5M, were prepared b y diluting appropriate amounts of the redistilled 98y0 ethylenediamine with water. SOLUTIONSOF OTHER METAL IONS. Reagent grade nitrates of the following metals were dissolved in water with the aid of concentrated H?;Oa to give approximately 1M solutions of p H ‘v 1: Th4-4, Fef3, Crf3, Ti+*, Mn+2, Ca+2, Sn+21 UOz+2, Xif2, and Co+2. Reagent grade sodium salts of W04+, MOO^-^, VOs-, and Crz0,-2 were dissolved in water to give 1M solutions. These solutions were standardized by titration with EDTA or by conventional gravimetric analyses. Copper-Ethylenediamine
System.
T h e copper-ethylenediamine chelates were studied b y several authors by means of different techniques (4, 5, .9, l S ) , and the existence of the complexes (Cu en)fZJ (Cu enz)+2,and (Cu en3)+? with the respective formation constants of log kl = 10.75, log kz = 9.28, and log k3 = 0.90, was established. Figure 1 compares the absorption spectra of copper(I1) nitrate solutions which contain no ethylenediamine, the stoichiometric amount of ethylenediamine to form the (Cu enz)+2 complex, and a large excess of ethylenediamine. These spectra show the existence of two different complexes with absorption maxima a t 550 mfi and 610 m p , respectively. Job’s plots (8) a t these n-ave-
