Spectrophotometric Determination of Tellurium as ‘the lodotellurite Complex RALPH A. JOHlVSON AND FRANCIS P. KW.4N University of Illinois, Urbana, 111.
law in the range 0.2 to 2 p.p.m. of tellurium. Errors from the side reaction involving iodine formation by air oxidation of iodide are avoided by using lowactinic glassware and by making readings soon after mixing the reagents. Bismuth also forms a colored iodo complex and must be removed. Selenite is reduced to colloidal selenium by the iodide. Ferric and cupric ions oxidize iodide and thus interfere. Convenient separations from each of these are described. Nitrate, sulfate, mercuric, cadmium, zinc, nickelous, and cobaltous ions do not interfere. The iodotellurite method is new, simple, and rapid. I t should find applications of interest in metallurgy, biological science, and industrial hygiene.
For the trace determination of tellurium, photometric methods involving formation of colloidal tellurium are most often described. These methods are naturally limited because variations in particle size, shape, and distribution can bring about marked variations in the absorption coefficient and deviations from Beer’s law. Because the iodotellurite complex is soluble and highly colored, it has been investigated as the basis of a new spectrophotometric method for tellurium. The iodotellurite complex shows absorption maxima at 335 and 285 mp. In mixtures of 0.15 N to 0.40 N hydrochloric acid and 0.25 M to 0.40 M potassium iodide, the absorption of the iodotellurite complex at 335 mg follows Beer’s
F
OR the trace determination of tellurium, photometric methods involving formation of colloidal tellurium metal are most often used (9-2-6).These methods are naturally limited, because variations in the colloidal size can bring about marked variations in the absorption coefficient and deviations from Beer‘s law. The soluble iodide complex of tellurium(IV), presumably Te16--, is highly colored and is suitable for the photometric determination of tellurium. A method using this comples is described and certain interferences and applications are discussed. IOWTELLURITE COMPLEX
The iodotellurite complex has a reddish yellor color. Its absorption spectrum is shown in Figure 1. There is absorption in the spectral region below 500 mp, Ehere maxima occur in the regions around 335 and 285 mp. The iodotellurite complex hydrolyzes readily if the acidity
Table I.
Effect of Hydrochloric Acid
(Each solution waa 0.4 M i n K I and contained 1 p.p.m. tellurium. Reference solutions of acidity corresponding closely t o t h a t of test solutions u-ere used throughout) % Transmittance -V HCI a t 335 mp Log IdI 74.7 0.05 0.126 56.0 0 10 0.252 49.0 0.15 0.310 47.9 0.20 0.318 47.6 0.25 0.322 47.9 0.40 0.318 44.4 0.60 0.352
Table 11.
JO WAVE LENOTU I N H l L L l M l C R O N B
Figure 1. Absorption Spectrum of Iodotellurite Complex in 0.4 M Potassium Iodide and 0.2 .Y Hydrochloric Acid
Effect of Iodide
(Each solution was 0.20 N in HC1 and contained 1 p.p.m. tellurium. Reference solutions of K I concentrations closely approximating t h a t of test solritions were used throughout) % Transmittance M XI a t 335 m p Log &/I
is not maintained sufficiently high. This effect is demonstrated by the data in Table I, where it is shown that the absorption of tellurium-iodide mixture falls off readily when the hydrochloric acid concentration is decreased below 0.15 N. The stability of the iodotellurite complex is also dependent upon the iodide concentration. .Is shown in Table 11, the iodide concentration should be maintained above 0.25 M for complete development of the iodotellurite color. 65 1
ANALYTICAL CHEMISTRY
652 Table 111.
Iodotellurite Calibration Curve
(Solutions contained 0.20 N hydrochloric acid and 0.40 M potassium iodide) Te Added, Yo Transmittance P.P.M. a t 335 m p Log IQ/I 100.0 0.0 0.000 87.4 0.2 0.058 0.3 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
’
76.1 71.6 62.0 55.0 47.2 42.1 37.0 33.5 29.9 26.9 22.8
0.118 0.145 0.207 0.260 0.326 0.376 0.432 0.475 0.524 0.570 0.642
APPARATUS
hlost of the absorption measurements were made on a Beckman Model DU spectrophotometer. The absorption spectrum was checked with a Carey recording spectrophotometer. Some photometric tests were also carried out with a Model 400A Lumetron photoelectric colorimeter, using the blue filter. This instrument was found to be satisfactory for application of the method described. For some experiments, low-actinic borosilicate glass volumetric flasks were used.
of the iodide. This may be accomplished successfully by working in artificial light, excluding all sunlight, or by using lowactinic glass volumetric flasks for the color development. Under either condition, the iodotellurite solutions show no significant change in transmittance on standing up to 20 minutes, after which time the slow intensification of color introduces significant errors. Possible errors in the test solutions arising from formation of iodine in this side reaction are largely compensated by use of a reference solution, or blank, containing all reagents and no t,ellurium. I t is advisable to prepare the stock iodide solution fresh and to preserve it in a cool dark place to minimize formation of iodine. Bismuth and Selenium. Bismuth forms an iodobismuthite complex which absorbs strongly in the same regions as the iodotellurite complex. However, the iodohismuthite may be formed a t an acidity and iodide concentration too low for formation of iodotellurite. The iodobismuthite is formed selectively at concentrations of acidity up to 0.06 -\-and of iodide up to 0.1 .If. The iodobismuthite may be separated from tellurite under these conditions by extracting the former with an amyl alcohol-ethyl w r t a t e misture. In acidic medium, selenite is reduced to the metal by iodide. Thp colloidal selenium and the iodine formed in the reduction
REAGENTS
Standard tellurium solution, 250 p.p.m. of tellurium, was prepared by dissolving 0.3357 gram of purified, crystalline KsTeBrb ( 1 ) in 250 ml. of 0.2 X hydrochloric acid. Potassium iodide, C.P.reagent, 2 M in distilled water. Hydrochloric acid, C.P. reagent, 2 S in distilled water. PROCEDURE
Place a sample containing 0.025 to 0.1 mg. of tellurium(1V) in a SO-ml. volumetric flask, dilute to about 30 ml., add 5 ml. of 2 N hydrochloric acid, and mix. Add with stirring 10 mL of 2 M potassium iodide (freshly prepared), dilute to the mark, and mix well. Read the per cent transmittance a t 335 mp within 20 minutes after adding the iodide. As a reference solution for ZO readings, use a blank prepared as above but without the tellurite. Carry out the operations after addition of the iodide without exposure to sunlight-Le., in artificial light or in low-actinic glassware.
Tahle 11’.
Separation of Bismuth and Selenium from Tellurium
(Each solution contained 0.100 mg. tellurium) Se Added, Te Found, Bi Added, Mg. Alg. Mg. 0.0 0.25 0.75 1.25 0.0 0.0 0.0 0.0 0.25 0.50 0.75 1.00
0.0 0.0 0.0 0 0 0.2s 0.75 1.50 2.50 0.25 0.50 0.75 1.00
0.100 0,099 0.100 0.101 0.102 0.102 0.098 0,102 0.100 0,098 0,099 0,098
RESULTS
The data for a calibration curve according to the above procedure are given in Table I11 and are plotted in Figure 2. Transmittance measurements were made a t 335 m p . At 285 mp, the transmittance measurements did not give good reproducibility. Data taken at 285 mp are also plotted in Figure 2. The transmittances a t 335 nip follow Beer’s law for concentrations up to 2 p.p.m. of tellurium (about 20% transmittance), but a t the higher concentrations tend to be a little high. Statistical treatment of the (log f o / l ) 0 s . concentration (p.p.m.) curve at 335 mp as a linear regression yields a regression coefficient of 0.322 (log units)/p.p.m. The standard deviation of ea:h reading from the regresion line is 0.0126 (deviations of log Io/I). ERRORS A S V INTERFERENCES
Oxygen-Iodide Side Reaction. In acid medium, dissolved oxygen reacts with iodide to form iodine, which absorbs in the regions in which measurements are made in the above method. To minimize this side reaction, the concentrations of hydrogen ion and iodide ion should be kept as low as posr?ible. Accordingly, in the recommended procedure, the acid is maintained a t 0.2 .V. The potassium iodide is held a t 0.4 M, which is somewhat above the minimum for apparently complete iodotellurite formation (see Table 11),because Beer’s law is not followed so closely at lower concentrations. The oxygen-iodide side reaction is photocatalyzed. Hence, the solutions should be protected from sunlight after the addition
P.P.M.
Figure 2.
TELLURIUM
Beer’s Law Curves
Solutions contained 0.4 .M potassium iodide and 0.2 ,V hy-drochloric acid
V O L U M E 23, NO. 4, A P R I L 1 9 5 1 interfere with the iodotellurite rnet’hod. Under the conditions described above for the separation of bismuth, the selenite is also reduced and the finely divided metallic selenium is ext,racted and suspended in the nonaqueous layer. Thus both selenium and bismuth may be removed in one step. If there is no bismuth to be removed, it is more efficient to extract the selenium wit,h chloroform than with the esteralcohol mixture. The iodohismuthite is not extracted with chloroform, however. For the determination of telluriuni when both bismuth and selenium are present, the following procedure is recommended.
To a 60-ml. separatory funnel add approximately 50 ml. of a solution containing 0.05 to 0.2 mg. of tellurium and either bismuth or selenium or both. Make the solution slightly acid (about 0.05 X hydrochloric acid) and add 2 ml. of 2 M potassium iodide. Allow to stand for 10 minutes. Extract with 5-ml. portions of amyl alcohol-ethyl acetate (3 to 1) until colorless. Transfer the aqueous layer to a 100-ml. volumetric flask. Add 20 ml. of 2 11.1 potassium iodide and 10 ml. of 2 -V hydrochloric acid, dilute to the mark, and read the per cent transmittance at 335 mp. Results of analyses carrird out by the above procedure are shown in Table IV. Iron and Copper. Both ferric and cupric ions oxidize iodide to iodine in acidic medium and thus interfere in the tellurium determination. Tellurium(1T’) may be separated from these ions by rpduction with stannous chloride to the metallic state and subsequent filtration. The tellurium may then be oxidized back to tellurite with nitric a d and determined by the iodotellurite method. To a niist,ure containing 0.05 to 2.0 mg. of telluriuni(1V) and irou and/or copper, add 2 ml. of 1 31 C.P. stannous chloride in 12 &Vhydrochloric acid. Let it stand for 10 minutes to assure complete reduction. Filter off the finely divided tellurium on asbestos with a suitable microfilter (the Kirk calcium-type microfilter, Microchemiral Sperialties Co., Berkeley, Calif., was successfully used in developing the method). Dissolve the met,allic tellurium by adding slowly 5 ml.of boiling vonceiitrated nitric acid to the filter. Collect the acid filtrate in a tuhe at the hottom of the filter, rinse the filter with three 3-ml. portions of 1 &Vnitric acid, and hoil the filtrate for 3 minutes to espel oxides of nitrogen. C‘ool and just nwtralizr to tlic ~~lic~iiolphthalein end point with
653 ammonium hydroxide. Transfer to a 50-ml. volumetric flask, add 10 ml. of 2 M potassium iodide and 5 ml. of 2 N hydrochloric acid, dilute to volume with distilled water, and read the per cent transmittance a t 335 mp. The effectiveness of this separation is shown in Table V. This method should be applicable to separation from a large number of other metals, including bismuth and arsenic.
Table V.
Separation of Tellurium from I r o n arid Copper
(In each case 0.05 m g . T e was taken. Separation was effected by the stannous chloride method and final determination made by the iodotelliirite method. Fe is added as FeCla and Cu as CIISOI) Fr Added. Cu Added. Te I:ound, XIK. >I& ME. 0.00
0.00
0 0500
0.00
1 .oo
0,0505 0.0510
1.00
0 00
0.0510 0.0500
1.00
1 00
0.0505 0.0.500
Other Ions. Ions that oxidized iodidt:, such as nitrite, chromate, and arsenate, should be avoided. Ions that form insoluble iodides, such as silver, lead, and niercurous, should also be absent. .ilthough they form stable iodide complexes, cadmium, mercuric. and zinc were found to be without, effect in concent,rations up to 500 p.p.m. Other ions tested and found to I)(, without effect are nickelous, cobaltous, nitrate, and sulfate. LlTERATURE CITED
Archibald, E. H., “Preparation of Pure Inorgaiiic Compounds,” New York, John Wiley & Sons. 1932.
Dehkio. R. H., ANAL.CHEM.,20, 488 (1948). Steinberg, H. H., Massari, S. C , Miner. A. C., and Rink. R., J . I d . Hug. Tozicol., 24, 183 (1943). (4) Volkov, S. T., Zauodskaya Lab., 5, 1429 (1936). ( 5 ) Zemel, V. K., Ibid., 5, 1433 (1936). RECLIVED October 9, 1950.
Estimation of Gold in Biological Materials S I M U E L NATELSOSl ~ Y D JOSEPtI L. Z U C K E R M W Jewish Hospital of Brooklyn, Rrooklyn, Y.Y . Gold compounds have been used in the treatment of arthritis. Two cases of gold poisoning during treatment have heen encountered by the authors. Because no method was available for the estimation of gold i n the minute amounts found in biological fluids and tissues, a method w-as devised by the authors. By this procedure 0.2 microgram of gold can be detected. The entire procedure can be
T
HE p u r p o ~of this inwstigation was to develop a method for thc. quantitative estimation of gold in biological fluids, tissues, and feces. Gold Compounds have been used for some time in the treatment of rhrumatoid arthritis (5, 8). 9 o t infrequently, t k c manifestations occur owing to such treatment. During t,he past year two patirnts have been admitted to this hospital suffering from exfoliative dermat,itis following therapy with gold salts. The use of such detoxifying agents as British .intiI,ewisit~has been suggested for thc treatment of t,his condition ( 5 ) . 1
Present address, Rockford 1Iemorial Hospital, Rockford, Ill.
carried out in one test tuhe. ‘The colorimetric reaction of p-diethylaminobenzal-rhodanine w-ith gold salts is employed. Results of tests on the blood, urine, and tissue of patients suffering from exfoliative dermatitis following treatment with gold salts are given. Thus, a method is abailable for following the gold levels in the blood and urine during treatment with gold detoxifying agents.
For effective evaluation of treatment with gold salts and the detoxification of gold in the body, a quantitative indication of gold levels in the blood, urine, and stool is necessary. Gold levels in tissue are also of interest for research and post-mortem studies. The available methods are not sensitive enough to determine gold in microgram and submicrogram quantities. For example, Block ( 1 ) reported a sensitivity in the range of 5 t o 30 microgranis in blood. Jamieson reported a sensitivity of 5 micrograms in urine (6). Consequently, the authors developed a nicthod of gold analysis of greater sensitivity.
