1898
ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
LITERATURE CITED
IC
+I
(1) E. Desimoni, F. Paniccia, and P. G. Zambonin, J . Chem. SOC. Faraday Trans. 7 . 89. 2014 (19731. (2) E. Desimoni, F . Paniccia, L. Sabbatini, and P. G. Zambonin, J . Appl. Electrochem., 8, 445 (1976). (3) E. Desimoni, F. Paimisano, and P. G. Zambonin, J Electroanal. Chem., 84, 323 (1977). (4) E. Desimoni, B. Morelli, F. Palmisano, and P. G. Zambonin, Ann. Chim.. 67. 451 . . (1977). (5) E. Desimoni, F. Paniccia, and P. G. Zambonin, J. Phys. Chem.. 81, 1985 (1977). (6) E. Desimoni, F. Paniccia. L. Sabbatini, and P. G. Zarnbonin, "Proceedings of the 149th International Symposium Molten Salts," J. P. Pemsier, Ed., The Electrochemical Society Princeton, N.J., 1976. (7) P. G. Zambonin, V. L. Cardetta, and G. Signorile, J . Electroanal. Chem., 28, 237 (1970). (8) H. S. Swafford and P. G. McCormick, Anal. Chem., 37, 970 (1965). (9) P. G. Zambonin, Anal. Chem., 41, 868 (1969). (10) H. S. Johnston, L. Foering, Yu Shang Tao, and G. H. Messerly, J . Am. Chem. SOC., 73, 2319 (1951). (1 1) G. G. Bombi, R. Freddi, and M. Fiorani, Ann. Chim., 57, 759 (1966). (12) P. G. Zambonin, Anal. Chem., 44, 763 (1972). (13) G. H. J. Broers and M. Shenke, "Fuel Cells", Vol. 2 , G. J. Young, Ed., Reinhold, New York, N.Y., 1963, p 6. (14) A. D. S.Tantram, A. C. C. Tseung, and B. S.Harris, "Hydrocarbon Fuel Cell Technology", B. S. Baker, Ed., Academic Press, New York, N.Y., 1965, p 187. (15) W. M. Vogel and C. D. Iacovangelo, J . Nectrochem. Soc., 124, 1305 (1977).
2 Y
\
- -~
-
'8
POTE NT I A L
Figure 6. Cathanodic profile relevant to process 4 recorded in a melt containing [CO,*-] = 2.7 X mol kg-' and maintained under flux of a mixture of CO,, H, and H,O: pco, = pHz= 372 Torr and pHZO
= 15 Torr
respectively t o reactions 7 and 4) have similar values. T h e cathodic peak currents (better resolved than the anodic ones) were linearly related to the square root of the scan rate while the peak potentials remained practically constant for moderate scan rate variations (up to 200-500 mV/s).
Pure Melt + Carbonate + Water + Carbon Dioxide + Hydrogen. As expected on the basis of the experimental
-
,
RECEIVED for review March 30, 1978. Accepted July 25, 1978. Work carried out with the financial assistance of the Italian National Research Council (C.N.R. ROME).
results described in the previous paragraphs, a cathanodic profile was obtained when a mixture of wet hydrogen and C 0 2 was fluxed in a carbonate containing melt: see Figure 6.
Determination of Microgram Amounts of Tellurium in Steels by Atomic Absorption Spectrometry Michael Bedrossian The Armco Inc., Research & Technology, Middletown, Ohio 45043
This present atomic absorption procedure is applicable to a wide variety of steels. The high sensitivity allows the determination of 0.0002% tellurium.
A solvent extraction procedure has been developed for the determination of tellurium in all types of steel. After dissolution, the sample is extracted with trioctylphosphine oxide-methyl isobutyl ketone. The extract is then nebulized directly into the atomic absorption burner flame. This method requires 25 minutes and can determine as low as 2 parts per million level tellurium.
EXPERIMENTAL Apparatus. A Perkin-Elmer Model 503 Atomic Absorption Spectrophotometer, equipped with an air-acetylene, three-slot burner head and Perkin-Elmer tellurium hollow cathode lamp was used. Reagents. All chemicals used were ACS certified reagent grade quality. Standard tellurium of 100 rg/mL was prepared from the pure metal. Working solution of 25 rg/mL was prepared monthly by appropriate dilution of the stock solution in 1070 HC1 acid. Iodide reagent solution (30%)was prepared by dissolving 30 g of KI and 10 g of ascorbic acid in water containing 10 mL of HCl. This solution was prepared daily. Trioctylphosphine oxide-methyl isobutyl ketone (TOPO-MIBK) solution (570)was prepared by dissolving 12.5 g of TOP0 in MIBK in a 250-mL volumetric flask. Procedure. The desired sample size (0.1to 2.0 g) was dissolved in 25 mL of HC1 (1+ 1) and 5 drops of HF. After dissolution, 7 mL of HzOz(30%) were added dropwise; then the solution was digested over medium heat and cooled. Sufficient ascorbic acid (8 g) was added to change the dark yellow color to light yellow; then 15 mL of the iodide reagent were added and the sample solution was transferred to a 100-mL volumetric flask which had been marked at the 50-mL level. The volume was adjusted to 50 mL and 10.0 mL of the 5% TOPO-MIBK reagent were added. The extraction was made by shaking the solution for 1 min. Deionized water was added to raise the TOPO-MIBK layer to the top of the flask.
Since certain properties of iron and steel critically depend on the presence of trace amounts of tellurium, it is desirable to have a reliable analytical method for determining tellurium in steel below 100 ppm. The accurate determination of less than 50 ppm of tellurium is time consuming by classical methods (1-5), and difficult by direct instrumental techniques (6, 7). Concentration techniques are required to compensate for low sensitivities. Solvent extraction techniques, which have been used successfully to separate tellurium from many types of sample matrix (8-10) have been combined with both photometric and gravimetric measurements to determine tellurium. The above procedures require a preliminary separation of tellurium in order to remove interfering elements and they lack sensitivity. Atomic absorption methods have been used in several procedures for tellurium in steel (11-14). These methods are either insensitive, suffer from interference, or require elaborate separations. 0003-2700/78/0350-1898$01.OO/O
G
1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 13, NOVEMBER 1978
Table I . Effect of Hydrogen Peroxide on the Recovery of Tellurium % Te
sample A80 A81 A82
grade (stainless) type 18-8 type 18-8 type 18-8
present 0.0068 0.0189 0.105
recovered with without H,O, H,O, 0.0059 0.0066 0.0176 0,0190 0.0977 0.105
Standard calibration solutions were prepared from the working solution (25 pg/mL) by extracting 0.00, 25.00, 50.00, 75.00, and 100.00 pg of tellurium using the above procedure. The TOPO-MIBK extract was nebulized directly into the burner flame. The absorbance readings were made at the optimum instrumental settings, and the concentration of tellurium in the test solution was determined.
Table 11. Analyses of Armco Standards, SRM Standards, and Standard Reference Materials with Tellurium Added % Te recovered present sample grade A80 A81 A82 SRM SRM SRM SRM SRM SRM SRM
type 18-8 type 18-8 type 18-8 1261 1262 1263 1264 1175 365 25b
low alloy low alloy
low alloy low alloy cast iron carbon silicon
0.006 8 0.0 189
0.1.05 0.0 0 0 6
0.0064 0.0187 0.103 0.00057
O.ClO11
0.0011
0.0009 0.00 0 18 0.009 0.0013 0.00 5 0
0.00083 0.00014 0.009 0.001 3 0.0049
Table 111. Comparison of Methods %
RESULTS AND DISCUSSION Generally, most samples are dissolved in hydrochloric acid, hydrofluoric acid, and hydrogen peroxide, and extracted from a 5% (v/v) hydrochloric acid solution. Hydrogen peroxide oxidizes Te(I1) to Te(1V) for quantitative extraction. When Armco standards 80, 81, and 82 were analyzed using no hydrogen peroxide, lower tellurium values were obtained as shown in Table I. The dissolution of certain types of steels may require the use of a combination of acids. If hydrochloric and nitric acids are used, it is important t h a t any nitric present be removed; otherwise, the organic phase becomes dark and viscous, and low tellurium values are obtained. Formic acid completely decomposes the nitrate ion. The excess of formic acid is removed by evaporation with hydrochloric acid. T h e extraction of tellurium as TeI, complex with TOPO-MIBK is quantitative since phosphine oxides are more efficient metal extractants than ethers, alcohols, and ketones. As a result, the extraction need not be controlled as closely as does extraction with MIBK alone. Complete complexation of tellurium can be achieved by the addition of 0.6-7.5 g KI per 50 mL of solution. Small variations in the volume of the aqueous phase are not important. However, large variations will affect the final volume of the organic phase because of the solubility of the MIBK in the aqueous phase. A study was made on the effect of hydrochloric acid concentration on the MIBK extraction. Little or no effect was noted if the normality of hydrochloric acid is between 1.2 and 4.8. Above 4.8 N hydrochloric acid, the solubility of MIBK in the aqueous layer increased. Precise control of the equilibration time is not required because the extraction can be completed in a few seconds. The extracts are stable for several days. Occasionally, with some samples, an emulsion is formed in the organic phase due to partially hydrolyzed silicon. This emulsion can be broken by the addition of a few drops of hydrofluoric acid during extraction. Although antimony, bismuth, lead, and tin are quantitatively extracted (15),these elements are normally present at microgram levels and, therefore, do not interfere. Zinc is also partially extracted; however, it is not generally present in steels. Copper, if present, is extracted along with tellurium. I t was found that 0.2 mg of tellurium can be determined in the presence of as much as 75 mg of copper without interference. Any level of copper greater than 100 mg gives a precipitate of copper(1) iodide and low results are obtained. Iron(II1) must not be present in the sample solution when the extraction is performed, since it will also be extracted and the organic phase will be dark and viscous. Therefore, prior to the extraction, ascorbic acid is added to reduce iron(II1) to
1899
sample A80 A81 A82
grade type 18-8 type 18-8 type 18-8
Te
atomic absorption, TOPO-MIBK 0.0065 0.0191 0.1103
photometric 0.0068 0.0189 0.105
iron(I1). Various amounts of ascorbic acid in excess of the amount necessary to reduce the iron (up to 12 g) did not interfere with the extraction. The proposed TOPO-MIBK extractant is a useful solvent for several reasons. The extraction of tellurium is essentially complete, while less than 1% of aluminum, calcium, chromium, cobalt, iron(II), magnesium, manganese, molybdenum, nickel, niobium, titanium, vanadium, and zirconium is extracted. I t was confirmed that the 11% extracted causes no appreciable interference. iv1 the resulls indicate that tellurium can be determined by this method without interference, except from large amounts of copper and zinc. Results obtained on Armco standards, SRM standards, and standard reference materials with tellurium added are given in Table 11. A comparison between the TOPO-MIBK-atomic absorption procedure and the tellurium diethyldithiocarbamate-photometric procedure (16) for three steel samples is presented in Table 111.
LITERATURE C [TED T. Kuroha and S.Shibuya, BunsekiKagaku, 21, 1197-1201 (1972); Chsm. Abstr., 77, 172321m (1972). G. Fikp and G. Balogh, Banyasz. Kohasz. Lapok, Kohasz, 107 (2), 75-76 (1974); Chem. Abstr., 81, 32879 (1974). H. Goto and Y. Kakita, Jpn. Anal., 3, 299-304 (1954). S. Kaneschi and C. Gallazzi. Anal. Chim. Acta, 54, 461-467 (1971). E. Y . Zel'tser and N. N. Kuznetsova, T r . Vses. Nauchno-Issled. Inst. Nektromekh., 35, 167-171 (1971); C h e m Abstr., 77, 697412 (1972). M. It0 and K. Yanagihara, BunsekiKagaku, 22, 10-16 (1973); Chem. Abstr., 79, 26848p (1973). L. S. Kopanskaya and A. T. Russu, Ostsillograficheskaya Peremennotokovaya Polyarcgr., 109-118 (1971); Chem Abstr., 77, 121813r (1972). Y. Uzumsa, K. Hayashi, and S. Ito, Bull. (%em. SOC.Jpn., 36, 301-306 (1963); Chem. Abstr., 58, 13130h (1963). H. Goto, Y. Kakita, and T. Furukawa, Nippon Kakagu Zasshi, 79, 1513-1520 (1958). N. Iordanov, and Iv. Khavezov, Freseniue' Z.Anal. Chem., 248 (5-6), 296-298 (1969); Chem. Absfr., 72, 74353a (1970). W. D. Cobb. W. W. Foster. and T. S . Harrison, Analvst(London), 101 (1198), 39-43 (1976) W B Barnett and J D Kerker, At Absorpt Newsl , 13 (3), 56-60 (1974) G G Welcher, 0 H Krege, and J Y Marks, Anal Chsm , 4 6 , 1227-1231 (1974) M. V.'MarEec, K. Kinson, and C. B. Belcher, Anal. Chim. Acta, 41, 447-45 1 (1 968). K. E. Burke, Analyst(London), 97, 19-218 (1972). Sneii 8 Snell, Colorimetric Methods of Analysis, IIA, 678, 683 (1959).
RECEIVED for review March 10, 1978. Accepted August 16, 1978.
