Spectrophotometric Determination of Bismuth, Lead, and Thallium with Hydrochloric Acid CHARLES MERRITT, JR„ . M. HERSHENSON1, AND L. B. ROGERS Department of Chemistry and Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Mass.
Anal. Chem. 1953.25:572-577. Downloaded from pubs.acs.org by TULANE UNIV on 01/23/19. For personal use only.
The fact that halide complexes absorbed in the ultraviolet suggested that it should be possible to devise a simple sensitive procedure for the deterA mination of certain heavy metals in mixtures. comparison of the spectra for chloride, bromide, and iodide complexes of bismuth, lead, and thallium indicated that the separation of absorption maxima is greatest in chloride solutions with only a slight loss in sensitivity for each element compared
to that in iodide solutions. The effects of changes in concentration of acid and halide and the reproducihave been bility of the absorbancy measurements studied for bismuth, lead, and thallium and a prohas cedure for their simultaneous determination been worked out for concentrations of the order of 10 p.p.m. Several interferences have been evaluated. The spectra of other metal halide complexes will suggest the feasibility of other determinations.
A previous paper ($) the chloro complexes of certain of the
chloric acid has been extended to arsenic(III), copper(I), in-
INheavy metals have been shown to have characteristic absorp-
dium(III), iron(II), molybdenum(VI), selenium(IV), tin(II), titanium(III) and (IV), and tungsten(VI). The survey of
tion maxima in the ultraviolet region of the spectrum. Among these were lead and bismuth. Further studies have shown that thallium also exhibits an absorption maximum in the ultraviolet. The mutual interference of bismuth, lead, and thallium in the ordinary dithizone methods (f?) for the colorimetric determination of these elements and the difficulties of separating them conveniently have made it desirable to develop a new· procedure for their determination in the presence of one another.
Figure
1.
Absorption Spectra of
10
cadmium and mercury(II) has been extended to bromide and iodide solutions. REAGENTS
All solutions distilled water.
prepared from reagent grade chemicals and Standard 1000 p.p.m. stock solutions of the elements whose spectra were to be studied were prepared by dissolving the required weight of the compound in an appropriate solvent. The bismuth stock solution was prepared from bismuth oxide dissolved in a drop of 60% perchloric acid which was then diluted with water. The lead solution which was used in the chloride studies was an aqueous solution of lead chloride. For the bromide and iodide studies, solutions of lead bromide and lead iodide in 4 M sodium bromide and 4 M sodium iodide respectively were used. A stock solution of thallous chloride in water was used for all the thallium studies. The amount of chloride thus introduced when studying thallium diluted with strong bromide or iodide solutions was assumed to have a negligible effect. For the survey of spectra in hydrochloric acid, stock solutions were prepared from arsenous oxide, indium perchlorate, selenious were
P.P.M. Bis-
muth(III), Mercury(II), Lead(II), and Thallium (I) in
M Hydrochloric Acid
6
Thallium
——— ——
-
Mercury
——
-
-
-
Bismuth
The bromo and iodo complexes have also been studied to see if they offered greater advantages than the chloro complexes with respect to the intensity of maximum absorbancy and separation of the absorption maxima. The survey of the absorption spectra of elements in hydro-
Thallium(I)
in 4 M Sodium Bromide
——Thallium
Present address,
Mercury
—
—
i
Department of Chemistry, Wesleyan University,
Middletown, Conn.
-
572
-
-
-
Bismuth
VOLUME
2 5,
NO.
4,
573
1953
APRIL
acid, gallium oxide, titanic chloride, and titanous chloride by dissolution in concentrated hydrochloric acid, followed by dilution to 6 M. Tungstic and molybdic oxides were first dissolved in about 0.1 ml. of 6 M sodium hydroxide before being made up to 6 M in hydrochloric acid. For spectra in bromide and iodide, the stock solution of cadmium was prepared from cadmium oxide dissolved in a drop of perchloric acid and subsequently diluted with water; and the stock solutions of mercury were prepared from mercuric bromide and iodide dissolved" in 4 M sodium bromide and iodide, respectively. The stock solutions used in the study of interferences were of two kinds. For cations, 6 M hydrochloric acid solutions of the following chloride salts in a concentration of 10,000 p.p.m. were used: ferric, cupric, chromic, mercuric, plumbous, stannic, and antimonous. A solution of 1000 p.p.m. of thallous chloride in 6 M hydrochloric acid was the source of thallium. The 10,000 p.p.m. of vanadium solution was prepared from vanadium pentoxide first dissolved in 0.5 ml. of 6 M sodium hydroxide and then made up to 6 M in hydrochloric acid. For anions, 10,000 p.p.m. solutions of the following salts in water were used: sodium perchlorate, potassium nitrate, sodium phosphate, potassium sulfate, sodium oxalate, potassium tartrate, potassium iodide, and sodium bromide.
Figure 5. Absorption Spectra of 10 P.P.M. Lead(II) in Hydrochloric Acid of Various Concentrations --
----4M ----6 ---8 -----10
Figure 3. Absorption Spectra of
10
P.P.M. Bismuth(III), 4 M Sodium
Mercury(II), Lead(II), and Thallium(I) in Iodide
Thallium
——
—-
—
—
Mercury
-
—
—
·
·
-
Lead Bismuth
2M M M V/
All the solutions taken for spectrophotometric measurement prepared by diluting appropriate aliquots of the above stock solutions to give the desired final concentration of the constituents. Solutions of halides used for these dilutions were 12 M hydrochloric acid, 10 M lithium chloride, 7 M sodium bromide, and 6 M sodium iodide. The hydronium ion concentration was adjusted by the addition of perchloric acid. All spectra and quantitative measurements were made with a Beckman DU spectrophotometer using matched 1.00-cm. silica cells. were
EXPERIMENTAL
Figure 4. Absorption Spectra of 10 P.P.M. Bismuth(III) in Hydrochloric Acid of Various Concentrations -1M --3
M
---6
----10
M Af
All the spectra have been taken with respect to reference solutions of equivalent halide and hydronium ion concentrations. The spectra of 10 p.p.m. solutions of bismuth, plumbous, mercuric, and thallous ions have been studied in 6 M hydrochloric acid, 4 M sodium bromide, and 4 M sodium iodide. Typical behavior shows that the absorption maximum for each of the ions occurs at a longer wave length as the medium is changed from chloride to bromide to iodide. The spectra have been plotted in Figures 1 to 3 to show the separation of the absorption maxima in each of the halide media. Effect of Changes in Concentration of Hydronium and Halide Ions. A preliminary survey of the effect of hydrochloric acid concentration on the spectra of bismuth, lead, and thallium
ANALYTICAL
574
CHEMISTRY
concentration on the spectra were less pronounced, 6 M hydro(Figures 4 to 6) showed that the position and intensity of the chloric acid tvas chosen as the working medium. absorption maxima varied with the hydrochloric acid concentration. In order to evaluate separately the effect of hydronium Appropriate aliquots of the stock solutions of the elements were ion and halide ion, the respective spectra of bismuth, lead, and taken, to which were added from a pipet 50 ml. of concentrated thallium were taken in solutions having constant hydronium hydrochloric acid and the whole was diluted with water to 100 ml. in a volumetric flask. The absorbancy at the respective wave ion concentration but varying chloride or bromide concentrations. length of the absorbancy maximum for each of the elements was Other solutions having a constant halide concentration but varythen measured at constant slit width. These wave lengths were ing acidity were also studied. 245 mg for thallium, 271 mg for lead, and 327 mg for bismuth. The effect of acid on the bismuth peak at 327 mg in 6 M chloride was found to be negligible, since all concentrations of acid Reproducibility. A statistical study of the reproducibility of the absorbancy measurements was made on 20 samples each of from 1 M to 10 M gave identical spectra. bismuth and lead and on 13 samples of thallium. A sample was In 4 M bromide, no effect was observed on the bismuth peak taken each day on successive days. The experimental error at 376 mg due to changes in hydronium ion concentration up to 6 M, but the absorbancy of the maximum at 260 mg increased may be considered to include normal errors of manipulation such as those which occur from the use of different pipets and flasks. slightly as the acid concentration was varied between 1 and 4 M. No corrections were made for errors due to changes in the temLead and thallium in 6 M chloride solution showed only a small effect with acidity changes from 1 to 10 M, whereas in 4 M broperature of the room in which the solutions were prepared. mide an increase in absorbancy and a slight shift of the absorbSolutions of 10 p.p.m. of bismuth(III) from the same stock ancy maximum to longer wave solution showed, for 20 samples, an average absorbancy of 0.713, lengths was noted as the acidity was increased up to 4 M (Figure 7). Although the effect of changes in acid concentration on the spectra was very slight, the effect of halide concentration was appreciIn all cases, an inable. crease in halide concentration increased the intensity of absorbancy and shifted the maximum to longer wave lengths. In the case of bismuth, the spectra are no MILLIMICRONS longer effected as the concentration of halide is inFigure 6. Absorption Spectra of 10 P.P.M. Thallium(I) in Hydrochloric Acid of Various Concentrations creased above 4 M, but with -1 M lead, the absorbancy in—2 M creases and the wave length ----4 ----6 M is shifted as the halide concentration is continually increased. The changes in the spectra of bismuth, lead, and thallium with changing hydrochloric acid concentration as showm in Figures 4 to 6 may be attributed entirely to the effect of chloride. The effect of bromide at constant acidity on the spectra of bismuth and lead is shown in Figures 8 and 9. The behavior of thallium is again similar to that of lead. The effects of both acid and halide concentration are smaller in chloride solutions than in bromide solutions. Standardized Procedure. As a result of the studies of the spectra under varying conditions, a standardized procedure was evolved in order to evaluate the quan240 250 260 290 300 310 320 330 340 270 280 titative applications of these MILLIMICRONS spectra. Because the spectra Figure 7. Absorption Spectra of 10 P.P.M. Lead(II) in 4 M Sodium Bromide of bismuth, lead, and thalSolution at Various Acidities lium were most favorable in —' " " ' No acid --—I M HC104 chloride, and because the ---2 M HClOi effects of halide and acid -4 M HCIO4 —
----
—
VOLUME
2 5,
NO.
4,
APRIL
1953
575
MILLIMICRONS
Figure 8. Absorption Spectra of Ion Concentrations
P.P.M. Bismuth(III) in and 1 M Hydronium Ion
10
———0.1
M
---1.0
M
--—0.5 -
----
.
M
Vf -2.0 -4.0 Vi
a coefficient of variation ( ) of 3.23. concentration of 10 p.p.m., the average absorbancy was 0.546, the range, 0.530 to 0.590, and the coefficient of variation, 7.32. Thallium at a concentration of 20 p.p.m. showed an average absorbancy of 0.448, a range of 0.410 to 0.475, and a coefficient of variation of 11.8. The deviation from the mean may be expressed as follows: for bismuth, 0.7%; for lead, 1.8%; for thallium, 3.3%. a
range of 0.700 to 0.730, and
Similarly for lead(II), at
a
produce a 3% error were then calculated, and the final result was expressed in terms of the ratio of the concentration of interfering cation or anion to the concentration of the element to be determined. The results are summarized in Table I. In certain instances, a larger concentration of interfering substance does not cause a proportionately larger error. This has been observed in certain of the studies with thallium. The interferences of vanadium, mercury, chromium, tin, and oxalate produced errors which were proportional to the concentration of the interfering ion even for as great as a tenfold difference in conSolutions of Various Bromide Concentration centration. Lead, however, showed, for two separate determinations in which the total concentration differed by only twofold, that calculating back to a 3% error in absorbancy gave widely different lead-to-thallium weight ratios. The case of bromide was outstanding. For three determinations at different total concentrations, each differing tenfold from the other, the error was not proportional to the concentration nor was it always in the same direction. Elimination of Interference. Because a useful determination of bismuth, lead, or thallium would require either a prior separation of ferric or cupric ion or a treatment to eliminate the interferences, the effect of reducing to ferrous and cuprous ion was studied. Stannous and titanous chloride were found to reduce satisfactorily both ferric and cupric ion. Solutions of 10 p.p.m. of bismuth, 10 p.p.m. of lead, and 20 p.p.m. of thallium, respectively, were prepared according to the standardized procedure, together with 10 p.p.m. of ferric or cupric ion. Stannous or titanous chloride was also added to give a final concentration of
A series of absorbancy measurements taken over a period from a few minutes up to 48 hours after the solutions were prepared, beyond which no further measurements were made, and it showed no deviation greater than that shown in the reproducibility studies for the respective element. Effect of Temperature. No significant changes in absorbancy were observed for either bismuth, lead, or thallium over the range 0° to 30° C. This result is contrary to what one would expect; a cancellation of variations from two or more sources probably occurred. Calibration Curves and Optimum Range. The quantitative behavior of each of the elements was examined by preparing calibration curves. It was shown that all three followed Beer’s law over the range of concentrations studied. In order to find the optimum range for each element, the data were plotted as recommended by Ringbom(4). From the calibration curves thus obtained (Figure 10), the optimum ranges are seen to be 3 to 12 p.p.m. for bismuth, 4 to 10 p.p.m. for lead, and 8 to 40 p.p.m. for thallium. Effect of Diverse Ions. The interference of those cations whose spectra indicated possible interference was evaluated. The interference of anions which may commonly be encountered was also studied. The method of evaluation was to prepare solutions acFigure 9, Absorption Spectra of 10 P.P.M. Lead(II) in Solutions of Various cording to the standardized procedure but Bromide Ion Concentrations at Constant Acidity also containing an appropriate aliquot of ---0.1 M NaBr, 1 M HCIO. M NaBr, 1 M HCIO. ---0.5 the interfering constituent to produce an -1.0 M NaBr, 1 M HCIO. error The parts per ---2.0 M NaBr, 1 Vf HCIO. greater than 3%. ----4.0 M NaBr, 1 M HCIO. million of interfering constituent required to -----6.0 IIBr
Stability of Solutions.
was
-
.
ANALYTICAL
576
Table I.
Interferences in a Determination of Bismuth, Lead, Only One Is Present in 6 M Hydrochloric Acid Ion/Bi Weight
Cations Fe
Cu Sb
+ + + + + + + +
Ratio for 3% Error in Absorbancy 0.018 0.17
3.2 1.7 1.5
n&
l
1000 100 750 225 3350 690
BrBr~ Br~
µ
0.43
45 85
C4H406**
at 271
0.42
79.2
S04C104-
Change® in Absorbancy
0.053
>1000
P04s
e
i
>100
C2O4-
c
µ
108 630
Anions INO«-
b
at 327
Ratio for 3% Error in Absorbancy 0.030 0.035
0.86 0.94
Cr + + + Hg+++++ Bi Tl + Sn++++ Pb + + Pb + +
0
Ion/Pb Weight
Change® in Absorbancy
Ratio for 3% Error in Absorbancy 0.002 0.018 0.006 0.010 0.040 0.014 0.018
3.8
0ÍÓ45 0.45c 0.91d
6 3
0.05 0.50 d
=
d
«
Change® in Absorbancy at
245
j
1
>1000
18
4.2 e 104/
d d
9
Increase Decrease
Limit of solubility of PbCIz. Total concn., 100 p.p.m. Total concn., 50 p.p.m.
Total
concn
,
100 p.p.m.
/ Total concn., 1000 p.p.m. o Total concn., 10,000 p.p.m.
The solutions thus prepared were measured with reference solution of 100 p.p.m. of stannous or titanous chloride in 6 M hydrochloric acid at the appropriate wave length. The values for the absorbancy of 10 p.p.m. of bismuth in a solution containing either 10 p.p.m. of copper or iron and 100 p.p.m. of stannous chloride agreed, within the limits of error as shown by the reproducibility study, with the values obtained for solutions of bismuth alone in 6 M hydrochloric acid. Similarly, solutions of 10 p.p.m. of lead and 20 p.p.m. of thallium, containing 10 p.p.m. of iron and 100 p.p.m. of titanous chloride, were shown to give absorbancy values comparable to those containing no interferences. In the cases of lead and thallium, the interference of copper could not be eliminated because of the absorption characteristics of cuprous ion, which showed a maximum at 273 µ (Figure 11). Ferrous ion showed no appreciable absorption in the region 235 to 350 µ. The use of stannous chloride proved unsatisfactory at the wave lengths for the maxima of lead and thallium because the stannous solution itself showed a high absorbancy (Figure 11). Hydroxylamine hydrochloride and hydrazine dihydrochloride would not reduce cupric or ferric ion in 6 M hydrochloric acid. Analysis of Mixture. To show the feasibility of simultaneous determination of bismuth, lead, and thallium, sample mixtures of multicomponent analysis techwere analyzed by means nique (3). The absorbancy indexes were evaluated from measurements of the absorbancy at each of the three wave lengths using known concentrations and path lengths. (The absorbancy indexes given here are not molar extinction coefficients but, for convenience in calculation, are arbitrary constants relating absorbancy to the concentration in parts per million at the fixed path lengths for the cells and the slit widths used in the measurements.) These measurements gave the following for each of the elements: 100 p.p.m. respect to
a
ob
245 µ 271 µ 327 µ
i
0.0387 0.00167 0.0720
µ
bismuth, 10 p.p.m. of lead, and 20 p.p.m. of thallium. The following sets of mixtures were analyzed: lead-bismuth,
lead-thallium, bismuththallium, and lead-bismuthFrom the absorbthallium. measurements at the appropriate wave lengths and the absorbancy indexes previously determined, the concentrations of the elements in parts per million were calculated by means of simultaneous equations. Typical results of single determinations are summarized in Table II. All of the results for lead and thallium fell within the limits of the respective coefficients of variation established for solutions containing only one of the elements. One result for thallium, that for the threecomponent mixture, lay at 1.35 units from the known value. Eighteen per cent of the results on a normal curve of ancy
500
d
500
i
When
2 90
250 45 725 1500
d
Thallium
Ion/Tl Weight
1
d
or
CHEMISTRY
would fall outside this limit. Miscellaneous Spectra. The spectra for 10 p.p.m. concentrations of arsenic(III), copper(I), gallium(III), indium(III), iron(II), molybdenum(VI), selenium(IV), tin(II), titanium(III) and (IV), and tungsten(VI) have all been studied in 6 M hydrochloric acid solution. The spectra for copper, molybdenum, tin, and titanium are shown in Figure 11. The others showed no absorption. Cadmium(II) showed no appreciable absorbancy in 4 M sodium bromide. The spectrum of mercury(II) in 4 M sodium bromide and 4 M sodium bromide iodide has been shown in Figure 3. error
DISCUSSION
The proposed method for each of the elements is simple, convenient, and has a sensitivity comparable to the sensitivity of other common spectrophotometric or colorimetric methods (-5). The accuracy with which thallium can be determined in the presence of bismuth may be somewhat less owing to the uncertainty in evaluating the absorbancy index for bismuth at 245 µ. In the absence of interfering substances, the estimation of
an
0.00165 0.0547 0.00021
0.0242 0.00250 0.000008
Aliquots of the elements were taken as in the standardized procedure to give in each of the mixtures studied 10 p.p.m. of
Figure 10. Ringbom Plot of Calibration Data
O
Bismuth at 327 µ Lead at 271 µ Thallium at 245 mji
VOLUME
2 5,
NO.
4,
APRIL
577
1953
.
Miscellaneous
Absorption Spectra in Hydrochloric Acid
Figure 11.
6
M
--Ti(III), --Ti(IV), -Mo(VI),
10 p.p.m. 10 p.p.m. 10 p.p.m. —Sn(Il), 10 p.p.m. ——— Cu(i), 10 p.p.m. .
—
Table II. Mixture PbPb-Tl Bi-Tl Pb-Bi-Tl
-
ACKNOWLEDGMENT
Determination of Bismuth, Lead, and Thallium in Mixtures by Multicomponent Analysis As„
Assn
AS3S7
Bi, P.P.M.
Pb, P.P.M.
0.604 0.590
0.724
10.1
10.6
0; 490
0.725 0.718
10.1 10.0
1Ó '.2
0-,
895
0.840
0.622
tion of tin(II). Because the spectra of the dithizonates of these elements mutually interfere to a very great extent, it should be advantageous to re-extract into hydrochloric acid for quantitative determination. Interference from tin can readily by minimized by oxidation to tin(IV). The use of hydrochloric acid is superior to other halide media since it is a more common reagent, lower in cost, and the spectra are less critical with respect to halide or hydronium ion concentration. Better separation of the absorption maxima is obtained in chloride medium. Other halogen acids obtained commercially contain appreciable amounts of free halogen w'hich interfere seriously with the spectra, also, low' solubility of their salts prevents the use of highly concentrated solutions. In the case of iodide, when a solution of the salt is acidified even slightly, iodine is continually produced by air oxidation. Attempts to eliminate the interference of free halogen by means of thiosulfate or sulfite w'ere unsuccessful because of appreciable absorption in the ultraviolet. Furthermore, sulfite and sulfur are produced from thiosulfate by decomposition in acid solutions. Other miscellaneous spectra are reported which may suggest the feasibility of other determinations.
10.
1
P.P.M. 18.' 8
19.8 16.8
The authors are indebted to the Atomic Energy Commission for partial support of this study. LITERATURE CITED (1) Am. Soc. Testing Materials, Philadelphia, Pa., “Manual of Presentation of Data,” p. 15,1941. (2) DeSesa, M. A., and Rogers, L. B., Anal. Chim. Acta, 6, 534
(1952).
M. G., “Analytical Absorption Spectroscopy,” pp. 369ff, New York, John Wiley & Sons, 1950. (4) Ringbom, A., Z. anal. Chem., 115, 332-43, 402-12 (1939). (5) Rodden, C. J., “Analytical Chemistry of the Manhattan Project,” New' York, McGraw-Hill Book Co., 1950. (6) Sandell, E. B., “Colorimetric Determination of Traces of Metals.” 2nd ed., New York, Interscience Publishers, 1950. (3) Mellon,
lead, bismuth, and thallium can be performed without prior separation. If interfering substances are present, a preliminary separation from cyanide medium with dithizone would permit extraction as a group from all other substances with the excep-
Received for review September 30, 1952.
Accepted January 12,
] 953.
Determination of Particle Size Distributions by a Sedimentation Method JAMES S. SMITH1 AND RAN SEN GARDENIER, JR.2 Photo Products Department, E. I. du Pont de Nemours & Co., Inc., Towanda, Pa.
IMPORTANT property of a particulate material is its weight distribution as a function of some particle size parameter. If a material is such that substantially all of it, dispersed in a liquid, will settle in the field of gravity with velocities predicted by Stokes’ law' for spheres with diameters of 2 to 50 microns, a convenient function of the particle size and shape is to determine weight the “Stokes diameter.” It is common distributions as functions of the Stokes diameter by sedimentation according to two types of schemes, incremental and cumulative (10). The cumulative method described in this paper is useful and, it is believed, offers some advantages over similar procedures cited below. An alternative to Oden’s (8) tangential method of graphical computation is proposed. Kelly (2, 5) modified a scheme proposed by Wiegner (IS), in which the pressure exerted by a particle suspension above a l
1
2
Present address, Sylvania Electric Products Inc., Towanda, Pa. Present address, 331 Seventh Ave., Troy, N. V.
given point in a sedimentation column was balanced by a clear liquid in a capillary manometer attached at that point. Bv' inclining the capillary to an angle t? to the horizontal, he increased the sensitivity by the factor (sin t?)_1. This permitted the use of suspensions w'hose percentage of particles by volume was less than 1, assuring substantially free fall for the settling particles.
A number of refinements (7, 9, 11, 12) have been suggested. A thorough discussion of the disadvantages of the Kelly tube is given by Buncombe and Withrow (3). They have proposed an apparatus in which a Gaertner microscope is used to read a meniscus height in a vertical capillary side arm which re-enters the sedimentation tube above the suspension level. A large increase in sensitivity was gained by Goodhue and Smith (4). Their apparatus was in principle the same as that of Buncombe and Withrow' with the particle suspension covered by a less dense and immiscible liquid. The liquid-liquid interface in the side arm replaced the usual liquid-air interface.
