Table IV. Repeatability of Thiocyanate Procedure on Commercial NazHPOl
P.P.M. Fe 9 9 6 6 36 20 27 33 15
Assay ( 76 Na4P207) R u n 2 R u n 3 Av.
Run 1 0.010 0.229 0.031 0.021 0.050 0.046 0.018 0.036 0.081
0.019 0.017 0.230 0.230 0.031 0.035 0.021 0.024 0.057 0.064 0.056 0.046 0.018 0.018 0.043 0.046 0.088 0.084 Av. range ( R ) = 0.0062. Std. drv., s = 0.0037
0.015 0.230 0.032 0.022 0.057 0.049 0.018 0.041 0.084
little temperature fluctuation ( 3 ~ 0 . 5 C. ” per 24 hours), no constant temperature bath was used. Since there is a nearly linear relationship between temperature and absorbance, more precise temperature control ( j ~ O . 1O C.) should improve the repeatability somewhat (Table 11). All pyro values in Tables I11 and IV are corrected for iron and aluminum content and were spot-checked by paper
chromatography to verify the absence of other interfering species. Figure 1 shows the effect of orthophosphate on the thiocyanate-iron complex. Curve C (peak A = 475 mp) contains no phosphate and represents conditions normally recommended for the routine determination of iron. (For clarity, curve C is reduced by a factor of four.) Curve D (peak X=400 mp) represents the same conditions except that the solution contains 4% NaH2P04. Curve 1 of Figure 2 is a plot of absorbance us. per cent Na2HzPz07 a t 475 mp and is at the same conditions as curve D, Figure 1. These curves show the effect of applying the thiocyanate procedure directly without modification to the determination of pyrophosphate. The original absorbance peak is shifted from 475 (no phosphate) to 400 mp (with phosphate) and is reduced in intensity by about twentyfold. The sensitivity at 475 mp would be ca. 0.02% NadP207 per 0.001 absorbance unit. By properly adjusting the pH, the reagent and sample concentrations, and working at the correct wave length, the effects of orthophosphate can be
minimized (curves A , B, Figure 1) and the sensitivity increased to 0.002% Na4P207 per 0.001 absorbance unit (curves 2 to 5, Figure 2). Curves 2-5, Figure 2, also show the effects of two impurities, A1203 and Fe. These impurities react independently in the presence of one another, greatly facilitating the necessary corrections. LITERATURE CITED
(1) Chess, W. B., Bernhart, D. N., ANAL.CHEM.30,111 (1958). (2) Karl-Kroupa, E., Ibid., 28, 1091 (1956). (Also modifications thereof for
specific applications to trace analysis, private communications.) (3) Kobayashi, M., Tada, S., Shinagawa, M., J. Sei. Hiroshima Univ., Ser. A
21,27 (1957). (4) Maurice, J., BulE. SOC. chim. France 6,819 (1959). (5) Sandell, E. B., “Colorimetric Determination of Trace Metals,” p. 369, Interscience, New York, 1950. (6) Van Wazer. J. R.. Callis.’ C. F.. Chem. ‘ Revs. 58, 1011 (1958). (7) Wirth, H. E., IND. EKG. CHEM., ANAL.ED. 14,722 (1942).
RECEIVEDfor review April 6, 1960. Accepted July 15, 1960.
Determination of Bismuth as Bismuth Phosphate by Precipitation from Homogeneous Solution HARLEY H. ROSS and RICHARD B. HAHN Department o f Chemisfry, Wayne Sfafe Universify, Detroit, Mich. ,Metaphosphoric acid is used to precipitate bismuth as bismuth phosphate from homogeneous solution. The method is more rapid than standard methods, requires fewer manipulations, and has no critical separation steps. The metals usually alloyed with bismuth do not interfere, or they are easily separated. The range of bismuth which can be determined i s 1 to 250 mg., olthough larger amounts could probably be determined without changing the general method. The precipitaie obtained is dense, crystalline, and easy to collect and wash. The volume of the precipitate is estimated to be about ‘/a to ‘/w the size of the same amount of precipitate obtained in the conventional phosphate precipitation procedure. The method was compared with the standard method for the determination of bismuth in bismuth alloys. The results are in very close agreement.
oxybromide in acid solution (2). Phosphate methods are used frequently for the determination of bismuth (1, 8-6). The resulting bismuth phosphate precipitate is bulky and difficult to filter and wash. Many impurities are carried down in this precipitate. This work is concerned with the separation and precipitation of bismuth phosphate from homogeneous solution using metaphosphoric acid. This reagent hydrolyzes in acid solution forming orthophosphoric acid which precipitates bismuth phosphate. A similar procedure was developed for the precipitation of zirconium by Willard and Hahn (6). This paper discusses the general method, its useful range, interferences encountered, and a procedure for the determination of bismuth in bismuth alloys.
M
A standard bismuth nitra?e so!ution was prepared by dissolvkg 57.3 g r a m of reagent grade bismuth n,lr:itt: pentahydrate in 200 ml. of concentru ted nitric acid and diluting to 2 !iter> with distilled water. The solution \vas ,stTnd-
have been proposed for the determination of bismuth and for its separation from lead. Bismuth i s best separated from lead by the precipitation of bismutb oxychloride or 16%
ANY METHODS
ANALYTICAL CHEMISTRY
REAGENTS
ardized by precipitation and weighing as bismuth phosphate and by precipitation as the basic carbonate, weighed as BizOs, using the procedures given by Hillebrand and Lundell ( 2 ) . Solutions used for the studies of interferences were made by direct weight without standardization. A 10% metaphosphoric acid solution was freshly prepared each day by dissolving 20 grams of c . ~metaphosphoric . acid in 200 ml. of water which was acidified with 2 ml. of concentrated nitric acid. The solution was filtered before using. EXPERIMENTAL
A general procedure for the determination of bismuth was used throughout the course of the work except in the cases where only a single precipitation was required. Procedure. Weigh out a sample of the alloy which contains 100 to 200 ing. of bismiith. Add 15 to 20 mi. of concentrated nitric acid and, aftcr the reaction has ceased, warm and dLg& for about 15 minutes. Dilute with a n equal volume of distilied .vater and filter off a n y metastannic a:id through a Gooch crucible with ai? :isbestos miit. Wash the residue
with five 5-ml. portions of 1M nitric acid and combine these washings with t h e previous filtrate. Transfer t h e solution to a 400-ml. beaker. Add 1 to 1 ammonium hydroxide slowly, with constant stirring, until a turbidity is permanent; then add 10 ml. of concentrated nitric acid. A clear solution should result. If a turbidity remains, add concentrated nitric acid until the solution is clear. Add 25 ml. of 10% metaphosphoric acid solution and make to 300 ml. with distilled water. Place the beaker on a hot plate, cover with a watch glass, and heat just at the boiling point for 1 hour. During this period a dense coarse precipitate of bismuth phosphate forms and settles. Remove the beaker from the hot plate, let the solution cool, then decant the supernatant liquid through a No. 40 Whatman filter paper. Decant as little precipitate as possible, and leave the bulk of the precipitate in the beaker. Wash the filter paper with 100 ml. of IO'% ammonium nitrate solution. Discard these washings and reserve the filter paper and precipitate for a later filtration. Add 10 ml. of concentrated nitric acid to the precipitate remaining in the beaker and stir until the precipitate has dissolved completely. Add 25 ml. of 10% metaphosphoric solution, then dilute to 300 nil. with boiling water. Place the beaker on a hot plate and keep at the boiling point for 1 hour. At the end of this period a dense precipitate and a clear supernatant liquid should be obtained. Remove the beaker from the heat and let stand until cool, then filter through the same filter paper used previously. Transfer the precipitate completely to the filter paper using a l0y0 solution of ammonium nitrate as wash solution. Place the filter paper and precipitate in a tarred porcelain crucible, slowly burn off the paper, then ignite at red heat. Cool and weigh as bismuth phosphate. The theoretical factor, Bi/BiPOc = 0.68755, is used to calculate the weight of bismuth. Determination of Acid Concentration Range. It was determined t h a t the precipitation of bismuth phosphate is quantitative in solutions 0.3i" in nitric acid. T h e effect of other concentrations of nitric acid was studied. T h e above procedure was followed b u t a standard bismuth solution was used in place of a n alloy, a n d only a single precipitation was made. T h e results of these determinations are shown in Table I. The data presented in Table I show that no significant error is obtained using acid concentrations as high as 0.65N. This is in agreement with the earlier work of Blasdale and Parle ( 1 ) who found that acid concentrations as high as 0.4N could be tolerated in the conventional procedure. Determination of Range of Method. Experiments were undertaken to determine the useful range of t h e method. A procedure similar t o t h e
Table 1.
Determination of Acid Concentration Range
Normality "01
Weight of BiPOh Grama
0.15 0.25 0.37 0.50 0.65 0.75 1.00 1.50
0.1845 0.1844 0.1845 0.1843 0.1844 0.1839 0.1784 0.1437
a
0.1269 0.1269 0.1269 0.1269 0.1269 0.1269 0.1269 0.1269
0.1269 0.1268 0.1269 0.1267 0.1268 0.1264 0.1227
0.0984
-0.oO01
O.oo00 -0.0002 -0.0001 -0.0005 -0.0042
-0.0285
Av. of two determinations. Table II.
HPOa Added, Gram
a
Error,a Gram O.oo00
Bismuth, Gram Calcd. Taken
Determination of Range
Bismuth. Gram Calcd. Taken
Error,a
0.2535 0.1269 0.0255 0.0126 0.0051
-0.0003
BiPO,,a Gram
2.5 0.3687 1.2 0.1845 0.25 0.0371 0.25 0,0183 0.25 0.0074 0.25 0.0014 Av. of two determinations. Table 111.
Gram
0.2538 0.1269 0.0254 0.0127 0.0050 0.0010
0.009
O.oo00 +O.o001 -0.0001 +0.0001
-0.ooOO
Interferences in a Single Precipitation
Total volume of solution, 300 ml.; nitric acid concentration, 0.5N; 1.2 gram HPO, used Added Subst. Mg+:'
Zn c u +z Fe +2 Cd + 2 Pb +2
so,-=
Gram 0.10 0.10 0.10 0.10 0.10 0.10 0.10
c10.10 Av. of two determinations.
BiPO,; Gram
Bismuth, Gram Calcd. Taken
0.1845 0.1847 0.1846 0.1848 0.1854 0.1916
0.1269 0.1270 0.1270 0.1271 0.1275 0.1317
0.1269 O.ooo(! 0.1269 +0.0001 0.1269 +O.OOol 0.1269 +0.0002 0.1269 +O.o006 0.1269 + O . 0048 Erratic results were obtained with a single precipitation Results were excellent with a double precipitation
Table IV. Comparison of Single and Double Homogeneous Precipitation Procedures
Bismuth and Bismuth Lead Added, Found, Error, Trial Gram Gram Gram Single Homogeneous Precipitation 1 0.1269 Bi+3 0.1319 +0.0050 0.1OOo Pb+2 2 0.1269Bi+a 0.1315 +0.0046 0.1000 Pb+* Av. 0.1317 4-0.0048 Double Homogeneous Precipitation 1 0.1269Bi+a
0.1271
+0.0002
2 0.1269Bi+a '0.1271
+0.0002
0.1OOOPb+*
0.1OOOPb+* Av. 0.1271
Error,a Gram
+0.0002
previous one was used except t h a t the acid concentration w a s held constant at 0 . 5 N and varying amounts of t h e stdndard bismuth solution were added. The useful range of t.he method is 1 to 250 mg. of b i u t h (Table 11). Larger amounts were not studied be-
Table V. Analysis of a Prepared Alloy by Conventional and Homogeneous Precipitation Methods
BiPO,,. Gram
Bismuth Found, Error,a Gram Gram
Double homogeneous precipitation 0.1851 0.1273 +0.0004 Conventional precipitation 0.1848 0.1271 + O . OOo2 Av. of two determinations. 0
cause it was assumed that a sample could be reduced to this range. Determination of Interferences. I n a third series of experiments t h e interference of foreign ions was determined. Elements which were known t o form insoluble phosphates-zirconium, antimony, and tin-were not studied. The same general procedure wan used and the nitric acid concentration was kept at 0.5N. The extent VOL 32, NO. 12, NOVEMBER 1960
1691
Table VI. Analysis by Standard Method and by Homogeneous Precipitation Method
Homogeneous Method Wt. sample, % gram bismuth
Standard Method Wt.
sample, gram
Fusible Alloy 24 94 0 8963
24 90 0 9375 25 07 0 9264 Av. 24 97 Av yo dev = 0 1270
ANALYSIS OF A PREPARED ALLOY
%
bismiith
Wood’s Metal 0 5166 48 53 0 4926 0 4892 48 39 0 5188 0 4441 48 49 0 5010 Av. 48 47 .4v. % dev. = 0 083% 0 9948 1 0110 0 9847
using the single and double precipitation procedure. Table IV indicates that a double precipitation from homogeneous solution serves to separate bismuth completely from lead.
48 48 48 48
24 24 24 24
48 36 45 43
98
89 96 94
of the interferences is shown in Table 111. Since lead interfered significantly, a double precipitation procedure was developed to remove this interference. The lead contamination was studied
Since standard bismuth alloys were not available, a synthetic alloy was prepared by mixing standard solutions containing 0.1269 gram of bismuth and 0.1OOO gram each of lead, zinc, cadmium, magnesium, copper, and iron. A series of experiments was carried out on this alloy to determine the magnitude of the error which might be expected in an actual alloy analysis. The determinations were done by the conventional phosphate method, after separation of the bismuth as the oxychloride, and by double precipitation from homogeneous solution without a preliminary separation of lead. The results of these determinations are shown in Table V; in both cases the results for bismuth are slightly high. The values obtained by each method are essentially the same and within the range of experimental error.
ANALYSIS O F WOOD’S METAL AND A FUSIBLE BISMUTH ALLOY
The method was checked also by determining the I)ismuth in a sample of Wood’s metal and in a fusible hismuth alloy. The fusible alloy was composed of bismuth, lead, and tin, and Wood’s metal which contains cadmium in addition to the above elements. In these samples, the general procedure was followed exactly. The amount of bismuth in these alloys was also determined by the standard method. The results for both methods are shown in Table VI. LITERATURE CITED
( 1 ) Blasdale, W. C., Parle, W. C., I N D . ENG.CHEM., . 4 N A L . E D . 8, 352 (1936). ( 2 ) Hillebrand, W.F., Lundell, G. E. F., “Applied Inorganic Analysis,” Wiley, New Yark, 1929. (3) Schoeller, W. R., I,nml)ie, 1). A., d n a l y s t 6 2 , 533 (1937). ( 4 ) Schnvllcr, W.R., Wntt~rhoiise, 1,;. F., Ihad., 45, 435 (1920).
(5) Silverman, Louise, Shidelrr, l I a r y , ANAL.CHEM.26, 911 (1954j. (6) Willard, H. H., Hnhn, R. H., Zbid., 21,293 (1949). RECEIVED for review December 1, 195!+. Accepted June 13, 1060. Division of Analytical Chemistry, 134th meeting, .4CS, Chicago, Ill., September 1958.
Identification of Impurities in an Acid-Washed 1O Coke-Oven Benzene C. F. GLICK, A. J. MISKALIS, and THEODORE KESSLER Applied Research laboratory, United States Sfeel Corp., Monroeville, Pa.
b The impurities in a typical, conventionally acid-washed, 1 coke-oven benzene were identified by a combination of progressive fteezing, gas chromatographv, and mass spectrometry. These impurities were then determined quantitatively by mass spectrometric analyses of gas chromatographic fractions of the benzene. Eight hepiones, eight naphthenes, toluene, and thiophene were identified with certainty, and their concentrations were determined. A trimethylcyclopentane and an octane were identified tentatively, and their concentrations were estimated. The total concentration of all these impurities was 0.670 mole %, or 95.6% of the total 0.70 mole impurity determined cryoscopically. Seven of ihe heptanes and three of the naphthenes (dimethylcyclopenianes) had previously been only tentatively identified in coke1 ,trans-IL,cis-4-Trioven benzene. methylcyclopentane has been identified with certainty in coke-oven benzene for the first time. Eleven new
’
yo
1692
ANALYTICAL CHEMISTRY
products of the high-temperafure carbonization of bituminous coal have, therefore, been definitely established.
A
of the impurities in an acid-refined 1’ coke-ovcn benzene was required for the logical selection of methods for the purification of this product. Surprisingly little definitive information is available on the irnpurities. other than thiophene and carbon disulfide, in refined coke-oven benzene. Stinzendorfer (14) reported that naphthenes of the niethylcyclohexane type prevailed in a residual gasoline fraction obtained in the purification of European cokc-ovcn benzene. .\nderson and his associates (5, 6) have reported some of the saturated nonbenzenoid impurities present in cokeoven benzene. Kimura and Yasui (10) identified methylcyclohexane and 2,2,4trimethylpentane in the residue from the commercial chlorination of benzene. In this work, the components of virtually the entire impurity content of a KNOWLEDGE
conventionally acid-washed 1’ cokeoven benzene have been identified positively, and their concmtrations have been measured. APPARATUS A N D REAGENTS
A Perkin-Elmer Model l 5 4 B Fractometer, equipped with a precision temperature controller, was used for the gas chromatographic separations. Samples were introduced by Perkin-Elmer calibrated capillary pipets. The following columns were used: A 2Moot by 0.375-inch diameter copper tubing column of poly(propy1ene glycol) 2025 (Union Carbide Chemicals Co.) on 30- to 60-mesh Fisher column packing in the proportions 31 to 69. A 40-foot by 0.375inch diameter copprr tubing column of a mixturc of oand p-bcnzylbiphenyls on 30- to 60mesh Uurrcll inert carrier in the proportions 24 to 76. The mass spectromctric aiialyses were performed with a Consolidated Model 21-103C mass spectromrtcr. All of the pure compounds for calibration of the gas chromatograph and the mass spectrometer were rithpr standard
