1302
ANALYTICAL CHEMISTRY
Nitrogen gas (and alkaline pyrogallol gas scrubbing train). Thymol blue, 0.5%. Electrodes and Other Equipment. A dropping mercury electrode assembly similar to that described by Seaman and Allen ( 5 ) is desirable. Any manual or recording polarogrsph may be used. Operating Potential, -0.6 volt us. S.C.E. Procedure. Add 0.5 ml. of concentrated acetate buffer and 4 drops of thymol blue t o an electrolysis cell. Pipet 50.0 ml. of the water sample into the cell and gently stir the mixture with the tip of the pipet. Place the electrolysis cell in the constant temperature bath to adjust the temperature of the sample. Adjust the dropping mercury electrode according to the procedure described by Seaman and Allen ( 5 ) . Measure current passing through the sample a t -0.6 volt LS. S.C.E. before and after deaeration with nitrogen gas. Calibration. To calibrate the instrument for dissolved oxygen, measure the current by the above procedure on distilled water. Add 3.0 ml. of the concentrated buffer to a standard B.O.D. bottle and fill the bottle with distilled water. Measure dissolved oxygen by the Winkler method. Calculate the calibration constant, K , from the ratio of the Rinkler dissolved oxygen to the difference in the current before and after deaeration vith nitrogen. Calculations. Calculate the dissolved oxygen in a water sample by multiplying the difference in the current, id, measured before and after deaeration by the calibration constant, k'.
D.0.
= KZd.
Precision and Accuracy. Determine the precision and accuracy of the method for every apparatus and electrode. Limitations. This procedure is limited to water samples containing less than about 5% sulfite waste in terms of the sulfite waste liquor used in this study. If previous knowledge or experience does not indicate a low sulfite waste concentration, it may be possible to establish the effective concentration of the waste by determining the iodine-consuming capacity of the water sample before and after alkaline treatment. Additional n-ork is needed to establish the validity of such a method. LITERATURE CITED
Busch, A. W., and Sawyer, C. N., ANAL.CHEM.,24, 1887 (1952). Kolthoff, I. AI., and Lingane, J. J., "Polarography," New York, Interscience Publishers, 1941. AIeites, L., and Meites, T., J . Am. Chem. Soc., 73, 177 (1951). Rand, hl. C., and Heukelekian, H., Sewage arid I n d . T a s t e s , 23, 1141 (1951).
Seaman, W., and Allen, W., Ibid., 22, 912 (1950). Strassner, J. E., and Delahay, P., J . A m . Chtni. SOC.,74, 6232 (1952). RECEIVED for reriew November 23, 1953. .Iccepted 3Iay 7, 1954. Presented before the Division of Water, Sewage. and Sanitation Chemistry at the 124th Meeting of the SE ERIC AN C H E M I C A L SOCIETY, Chicago, Ill.
Polarographic Determination of Tungsten in Rocks LAURA E. REICHEN U. 5.
Geological Survey, Washington,
D. C
This work was undertaken to develop a simpler and faster method than the classical gravimetric procedure for the determination of tungsten in rocks and ores. A new polarographic wave of tungsten is obtained in a supporting electrolyte of dilute hydrochloric acid containing tartrate ion. This permits the determination of tungsten both rapidly and accurately. No precipitation of the tungsten is necessary, and only the iron need be separated from the tungsten. The accuracy is within the limits of a polarographic procedure; comparison of polarographic and gravimetric results is given. The method reduces appreciably the amount of time ordinarily consumed in determination of tungsten.
W
H E N tungsten is determined on rocks and ore concentrates, the classical gravimetric methods are usually eniployed. Tungsten is precipitated as tungstic acid after an acid attack to put the sample in solution, and the tungstic acid is ignited to the oxide. The impure oxide is then dissolved and corrected for contamination by silica, iron, and molybdenum. Analyses for trace amounts of tungsten in rocks have been made colorimetrically by measuring the color produced by the stannous chloride-thiocyanate reaction ( 5 ) . Lingane and Small (3)investigated the polarography of tungsten in hydrochloric acid media. I n 431 hydrochloric acid +6 tungsten (VI) undergoes stepmise reduction to the (V) and the (111) state. The first diffusion current start5 from zero applied electromotive force, and the half-wave potential of the second wave is 0.66 volt zs. saturated calomel electrode. Kolthoff and Parry ( 2 )reported a kinetic polarographic wave of tungsten in the presence of hydrogen peroxide, but it is not a linear function of the tungsten concentration. Stackelberg et al. ( 4 ) determined tungsten in eteel polarographically by precipitating the tungsten as the acid, igniting the acid to the oxide, dissolving the oxide in potassium hydioiide, and running the polarogram in about 9-11 hydrochloric acid with the half-wave potential a t -0.60 volt cs.
S.C.E.
In the proposed method the sample is fused with sodium carbonate, leached with water, and filtered; tartrate is added, and the solution is acidified with hydrochloric acid. The polarogram is run in dilute hydrochloric acid and the per cent of tungsten is calculated from the diffusion current constant obtained on standard tungsten solutions. EXPERINENTAL DATA
Apparatus. Polarograms were recorded with a Rutherford Polaro-analyzer. All measurements were made a t 25' C. 4 modified H-cell with an external saturated calomel electrode was used. Reagents. Reagent grade chemicals were used. The tungstic oxide that was added t o the samples was prepared from sodium tungstate. Sodium tartrate, 1M. Cinnamic acid, 5wo in alcohol. This solution should not be more than 5 days old. This soluStandard tungsten solution, about 1.0 X lO-*.V. tion was made from sodium tungstate and standardized gravimetrically ( 1 ) . CHAR4CTERISTICS OF POLiROGRIPHIC WAVE
Initially a solution of 831 hydrochloric acid was used as the supporting electrolyte for tungsten (5). HonTever, a difference was observed in the number of microamperes produced by a millimole of tungsten between the tungsten in some of the samples and the tungsten in the standard solutions. From the ratio of these differences it was clear that in the 8-11 hydrochloric acid, the tungsten in some of the samples formed polytungstates but that the tungsten in the standard solutions did not. It is, of course, necessary for the tungsten to be of the same molecular species-that is, the same number of atoms of tungsten in the ion or molecule containing the tungsten-in both the sample and the standard solution in order to calculate the per cent tungsten from the diffusion current. Therefore, tungsten was added to the samples both as a standard sodium tungstate solution and as tungstic oxide prior to the fusion so that the tungsten for the standard would be conditioned in the same manner as the tungsten in the sample. This did not solve the difficultv. The added tungsten
V O L U M E 26, NO. 8, A U G U S T 1 9 5 4 formed polytungstates (again the microamperes due t o a millimole of tungsten varied), but they were not the same polytungEtates as those formed by the tungsten in the sample. The polytungstate formed seemed to depend on the constituents of the sample, the chemical treatment of the sample, and the manner in which the tungsten was added to the sample. However, in a supporting electrolyte of 4.631 hydrochloric acid and 0.1Jf tartrate, the formation of polytungstates is prevented. Tungsten. in this solution, produces the same number of microamperes per millimole of tungsten, regardless of the constituents of the sample and regardless of whether the tungsten was that present in the sample or that added as standard t o an aliquot of the sample. The polarographic currentrvoitage curve obtained using a solution of 0.8mM tungsten in 4.631 hydrochloric acid and 0.1X sodium tartrate is shown in Figure 1. Tungsten is reduced stepwise, the half-wave potential of the first n-ave being - 0.35 volt and that of the second u v e -0.68 volt m. the S.C.E.
rn
w
1303 Table
I. Proportionality between Concentration of Tungsten and Diffusion Current 4.6.V HCl, 0.1M tartrate, r n 2 i 3 W = 1.20 mg.213 s c c . - l i 2 a t -0 78 volt us. 5 C . E . Diffusion Current Tungsten Concn., per Millimolar Concn., m.ll pa. 7.00 0.05 7.00 0.1 0.2 7.05 7.02 0.4 0.8 6.94 1.0 6.95 A v . = 6.99 C 0.05
Table 11. Effect of Hydrochloric Acid Concentration on Half-Wave Potential and Diffusion Current of Tungsten T.o.t n-. l
HCl, E”2, Volt llolarity (1st Wave) -0.57 1.4 2.8 -0.47 3.2 -0.43 3.7 -0.41 4.1 -0.39 4.6 -0.35 -0.33 5.1 5.6 Zero applied e.m f . Tungsten concentration 0 8 m M
E’/2, Volt (2nd Wave)
... -0.71 -0.69 -0.68 -0.68 -0.68 -0.68
Diffusion Current, pa a t -0 78 Volt 2.70 5.90 6.60 7.60 8.30 8.70 8.70
a W a
z 4
Determination of Tungsten. Transfer a suitable volume of the solution t o a polarographic cell and remove oxygen by passing nitrogen through the solution for about 5 minutes. Measure the diffusion current a t -0.78 volt us. S.C.E. Calculate the per cent tungsten in the sample from the diffusion-current constant or a standard curve for tungsten made from standard solutions of t’ungst,en in 4.6.11 hydrochloric acid and 0.1M tartrate.
0
a 0 I
RESULTS AND DISCUSSIOX
VOLTS
Figure 1. Polarogram of 0.8rn.W Tungsten in 4.6CI Hydrochloric -4cid and 0.1M Tartrate
The diffusion current is directly proportional t o the tungsten concentration in the range from 0.05 to 1.0 m M tungsten (Table I). Solutions more concentrated than 1.0 m M exceed the solubility of tungsten and precipitated before polarograms could be made. The accuracy is within the polarographic limit of 2%. The height of the second m v e is double that of the first wave. The diffusion-current constant for the second wave is 4.40, the value for m2I3t”6 being 1.59. B s the acidity decreases the diffusion current per millimole of tungsten decreases, and the half-a-ave potentials become more negative. The diffusion current shovm in Table I1 is the total diffusion current for both waves. In the weak acid (1.411)the dixharge of hydrogen precedes the second wave. The half-viave potential of the first xave is affected by a slight change in the acid concentration. However, no significant change in that of the second wave %\asnoted in the range from 3.7 to 5.111. PROCEDURE
Solution of Sample. Nix a 0.5-gram sample intimately with 5 grams of sodium carbonate and fuse in a crucible of a t least 25-
ml. capacity. When the rrucible is cool, add 20 ml. of water, cover the crucible, and leach overnight on the steam bath. Filter into a 50-ml. volumetric flask, washing with water as thoroughly as possible, make to volume, and shake thoroughly. Discaid the residue. Preparation of Polarographic Solution. Pipet a 10-ml. aliquot into a 50-ml. volumetric flask, and add 5 ml. of sodium tartrate solution and 0.1 ml. of thymol blue. Add concentrated hydrochloric acid dropwise until the first trace of pink appears in the solution. Add 20 ml. of concentrated hydrochloric acid with a serological pipet and cool t o room temperature. Add 0.25 ml. of cinnamic acid solution, swirling the contents of the flask immediately after the addition. Make t o volume and shake thoroughly.
The samples were selected a t random from samples submitted for tungsten analysis and were analyzed in duplicate. The results obtained by the polarographic procedure are in close agreement with the results from the gravimetric procedure. The average deviation of the two polarographic results was 0.57 mg., iThich is lvithin the limit.: of reproducibility of a polarographic method. The stability of the tungsten-tartrate solution depends on the acid concentration. The weaker the acid, the longer the tungsten remains in solution. Solutions made up in the morning were all usable a t the end of the working day. In the range from 3.7 t o 5.2121, tungsten had precipitated by the second morning; in the range from 2.S to 3.2121, tungsten had precipitated by the third morning; but in the 1.411fsolution no tungsten had precipitated. The effect of the tartrate is destroyed in 5.6-If acid. The curve produced by the tungsten-tartrate solution is not affected by the sodium carbonate in the solution In a solution to which potassium bisulfate and ammonium hydroxide have been added, the second n-ave has no satisfactory plateau and coincides Kith the discharge of hydrogen. However, in a solution to which potassium bisulfate and an escess of sodium carbonate have been added, the current-voltage curve of the tungsten-tartrate ion complex is not affected. Kitrate ion affects the curve and should not be present. -1current-voltage curve similar to the curve obtained with the tartrate solution is also produced by complexing the tungsten with Versene. However, the Versene-tungsten ion complex could not be used in the determination of tungsten because the complex begins to deteriorate almost immediately and produces a peculiar wave. 1-anadium, of cotirsc=, is also in the alkaline filtrate from the carbonate fusion. The half-xmve potentials of vanadium a t 0.0 and -0.80 volt vs. S.C.E. in 0.1.11 hydrochloric acid indicate that vanadium should not interfere in the measurement of the current voltage curve for tungsten. Actually, however, in the more concentrated acid solution, vanadium gives an ill-defined wave, ex-
ANALYTICAL CHEMISTRY
1304
indicator end point slightly, but it does not interfere with the determination of tungsten. Of the other elements that may be preJent in the filtrate from the carbonate fusion, attention need be given only to molybdenum. All the others either are not reduced in hydrochloric acid or their half-wave potentials are more negative than that of tungsten. Molybdenum, however, would necessitate a separation if its molar concentration greatly exceeded that of tungsten. The acid concentration must be carefully controlled so that the final acidity of samples and standard solutions is the same. The half-wave potential and particularly the height of the tungsten wave are sensitive to changes in the molarity.
Table 111. Comparison of Polarographic with Gravimetric Results Description of Sample 1. From edge of tailings pond 2 . Grab sample of mill heads, Idaho 3. From a tungsten mine, Alaska 4. From a tungsten mine, Alaska 5. Dredge concentrate of placer gravel Alaska 6. Dredge honcentrate of placer gravel, Alaska 7 . Dredge concentrate of placer gravel, Alaska
Tungsten, % Polarographic 1 2 Bv. 1.23 1.27 1.25 0.32 0.43 0.37
G ra vi. metric 1.25 0.40
3.25 5.97 3.20
3.06 5 . 80 3.37
3.15 5.88 3.28
3.11 5.30 3.40
0.32
0.32
0.32
0.30
1.00
0.96
0.98
0.96
ACKNOWLEDGMENT
The author wishes to acknowledge the helpful advice and suggestions of J. L. Hague, H. $. Bright, J. I. Hoffman, and J. K. Taylor, of the National Bureau of Standards, and D. R. Norton and J. J. Fahey, of the U.S. Geological Survey.
tending from zero applied electromotive force to -0.80 volt, which makes the measurement of tungsten impossible. Addition of cinnamic acid to the solution eliminates the current due to vanadium. Cinnamic acid has no effect on the wave of the tungsten and does not contribute any current to the system. Cinnamic acid is only slightly soluble in acid solution and precipitates copiously immediately when added to the acid, but this causes no difficulty. Several soluble complexing agents (cupferron, quinoline, and diphenylamine) for vanadium were tried, but the complexing agents themselves produced interfering waves. Most of the iron is removed by the filtration. However in many samples, some of the iron remains in the ferrous state after the carbonate fusion. Potassium nitrate added to the flux to oxidize all the iron to ferric later interfered with the tungsten current-voltage curve. Ferrous iron in the solution may obscure the
LITERATURE CITED
(1) Hillebrand, W.F., Lundell, G. E. F., Bright, H. A., and Hoffman, J. I., “Applied Inorganic Analysis,” pp. 683-93, New York, John Wiley & Sons, 1953. (2) Kolthoff, I. lf.,and Parry, E. P., J . Am. Chem. SOC.,73, 5315 (1951). (3) Lingane, J. J., and Small, L. A., Ihid.,71, 943 (1949). (4) Stackelberg, .\I. v., Klinger, P., Koch, W.,and Krath, E., Tech. Mitt. K r u p p , A . Forschungsber., 2, 59 (1939). (5) Ward. F. X., U . S. Geol. Surcey, Circ., 119, (1951).
RECEIVED for review October 31, 1953. Accepted May 13, 1954. Publication authorized b y the Director, U. S . Geological Survey.
Radioactivity Assay of Water and Industrial Wastes with Internal Proportional Counter LLOYD R. SETTER, ABRAHAM S. GOLDIN, and JOHN S. NADER Department of Health, Education, and Welfare, Robert
A method for determining low levels of nonvolatile radioactive contamination in water is proposed. The suspended and dissolved radioactivities are separated by filtration and evaporation. This permits counting both the alpha and beta radiation at levels less than the maximum permissible concentration of unknown isotopes in drinking water. When a 250-ml. sample of water containing about 50 ppc. per liter is prepared and counted for 30 minutes, the activity may be assayed with an accuracy (at the 95% confidence limit) of 10% for alpha and 20% for beta radiation. Levels as low as 10 ppc. per liter (beta) and 2 ppc. per liter (alpha) are detectable. Such sensitivity and accuracy are made possible by counting the dry solids spread over a large area and by using instruments with efficient counting characteristics.
A
METHOD for separately assaying the gross alpha and beta radioactivity of waters and industrial wastes is presented. Filtered or evaporated samples are counted with an internal proportional counter which is particularly applicable for assaying low levels in the order of 1 to 10 ppc. of alpha activity and 10 to 100 ppc. of beta activity per liter of water. This counter has the properties desirable for high efficiency counting. Graf et al. reported ( 7 ) that i t gives a counting rate as much as 7 to 11 times greater than that from an endwindow counter. Window and air absorption losses are eliminated because the sample is within the counting volume, and the
A.
r a f t Sanitary Engineering Center, Cincinnati,
Ohio
geometry of counting is 50%. Because some internal counters aill accept large ( 5 em. in diameter) dishes, the losses from selfabsorption for equal sample volumes are minimized. This is important for samples which have an appieciable (>200 p.p.m.) dry solids content. The counter aill count alpha activity in the presence of up to at least 500,000 counts per minute of beta activity without interference. Beta activity may be counted a t the higher beta operating voltage, provided the alpha activity is negligible or alpha interference is eliminated with an absorber. A detailed evaluation of the counting efficiency of the counter has been made (11). IN STRUM ENTATION
A commercially available internal proportional gas-floM- counting set was used, This counting set consisted of a Nuclear RIeasurements Corp., Indianapolis, Ind., PCC-10 converter plus a Suclear Instrument and Chemical Corp., Chicago, Ill. scaler, Model 161. A cross section of the counting chamber is shown in Figure 1. I t consists of a center wire assembly in a hemisphere-and-piston chamber. The chamber will accept dishes, 5 cm. in diameter by 1 cm. in depth, and may be readily taken apart for maintenance. One of the criteria of reproducibility and accuracy in counting is that a curve of count versus voltage (6) has a broad and flat plateau. The slope, length, and position of the plateau depend on the area of the source, and on the size and position of the center wire loop. To count samples of extended area, i t is
