Rapid Determination of Fluorine, Sulfur, Chlorine, and Bromine in Catalysts with an induction Furnace ANNE 1. CONRAD, JEAN K. EVANS, and V. FRANCES GAYLOR Chemical and Physical Research Division, The Sfandard Oil Co. (Ohio), 4440 Warrensville Center Rd., Cleveland 28, Ohio
FModifications of high temperature induction furnace methods have speeded the determination of many volatile elements normally determined by combustion. Fluorine is determined by volatilizing fluosilicic acid and titrating colorimetrically with thorium nitrate. Sulfur and chlorine are determined simultaneously by using a silver nitrate absorber between the furnace and the sulfur titrator. Sulfur and bromine are similarly determined using a carbon tetrachloride trap.
R
determination of the volatile constituents in catalysts is becoming increasingly important within the petroleum industry. Concentrations of catalyst pronioters and poisoners must frequently be determined rapidly to predict process controls. A search for faster procedures has resulted in neIv methods for several determinations. The fluorine content of catalysts can be determined by a basic fusion, foll o ~ e dby the steani distillation of fluosilicic acid (8,16, 28). and completed with a thorium nitrate titration. This niethod was originally published by K l l a r d ($6)and modified by others. Although the fusion methods give excellent results, they also introduce several salts which niust he removed before the final measurement. For this separation, steam distillation (36), ion exchange colunins ( I O , S i ) , and precipitation methods (5, 29) have been used, all of T$ hich are time-consuming. The present method permits the evolution of fluosilicic acid uncontaminated by the fusion elements remaining in the crucible. High temperature combustion methods permit the rapid evolution of fluosilicic acid if sufficient silicon is present during the fusion. Some catalysts hare this required silicon content. If not, sufficient pure silica gel is added to the crucible so that the final silicon-fluoride ratio is a t least 3 to 1 . Iron is the only accelerator used. The cvolved fumes pass through a heated tube to prevent condensation of evolved salts. Seventy-five milliliters of dilute sodium hydroxide solution (pH 9 to 9.5) are used in the absorber. Subsequent measurement of fluorine content depends on the concentration 422
APID
ANALYTICAL CHEMISTRY
range and the accuracy required. Although thorium nitrate titration is the most common, many different colorimetric methods are also suitable for measuring fluorine absorbed in hnsic solutions. Gravimetric procedures have also been used (19, 23, 27‘), as well as arid-base titrations (3, 7 , 12, 32), amperometric titrations (6.as),indirect polarography (SO), oscillometry (16)) radioactivity (23. %)< and nuclear magnetic resonance ( 3 2 ) The method selected utilizes a thorium nitrate titration u4ng the spectrophotometer to detect the end point (17’). The total t h e required for the induction burning and spectrophotometric titration is approximately 30 minutes, compared to 1.5 hours if steam distillation ic reyuired. Orginal methods for the drtermination of sulfur by induction furnace combustion do not provide for simultaneous determination of other elements (4, 9, 11. 21). Because chlorine defiiiitelv interfercs M ith the sulfur titration, these methods have qeverr limitations. I n 1954 Holler and Klinkenherg published an induction method for simultaneous determinations of carbon and sulfur ifc?), and Ckrhardt and Dvroff in 1956 for su1f;lr and phosphorus ( 2 4 ) . Deterniination of sulfur and chlorine in the same sample is often necessary in the petroleum industry. Because these elements have been determined after other methods of conihustion (1, 2. 33. 35), it seemed possible to apply such methods to the induction furnace procedure. The removal of chloride by absorption in a silver nitrate solution (.?3)was investigated. It was found that sulfur and chlorine could be quantitatively qeparated under the proper conditions. Chlorine was qiiantitativcly rrtained in the silver nitrate absorbrr and sulfur 17-as quantitatively tlelivercd to the iodine titrator. A 0.005S solution of silver nitrate was a n optimum Concentration. Sulfur is retained in the silver nitrate solution if high concentrations of this reagent are used; chlorine is not retained if the silver content is too low. High concentrations of chlorine can be held, I
however, by increasing the volume of the retaining solution. hIeasurement of the sulfur content follows the standard iodate titration, as published by the instrument suppliers ( 2 2 ) . Siihsequcnt measurement of the chloride content is performed amperometrically, titrating the ewe35 iilrer in the absorber solution n ith hTdrochloric acid. An indicating giaphite electrode mas used ( I S ) nith a potassium nitrate salt bridge and a calomel reference electrode. A rotating platinuni dectrode could also be used (20, 22). The simultaneous sulfur-chlorine determination can be completed in approximately 30 minutcs, in the concentration ranges of 0.1 to 23% sulfur, and 0.03 to 16% chlorine. Organic saniples can be analyzed in the same manner if the sample size is kept below 110 nig. The quantitative scparntion of sulfur and bromine is more coniplirated. Bromine will not be retained in a d v r r nitrate solution but n-ill be absorbed in an alcoholic- d v c r nitrate solution. H o n e w r , not all of the sulfur is evolved when alcohol iq prewit. Thus alcoholic silver nitrate in an absorber can be satisfactorily used for bromine detcimination, hut not for a sini~~ltaneoi~s sulfur-bromine method. Carbon tetrachloride can lie used to trap all of the bromine without retarding the sulfur. I n this case the nhsorbing solution should be iced during the burning period anrl the broniine EXtracted from the cold carbon tetrachloride solution lvith ice water. The bromine content can be determined b?. a thiosulfate titration. The niethod is applicable to both catalysts and engine deposit qaniples and a single sample can be analyzed in l r ~ s than 30 minutes. Repeatability 1s usually within + 2yGof the concmtrxtion. APPARATUS
Fluorine. High Tempeiature Induction Furnace. T h e Leco Xodel X-519 (Laboratory Equipment Corp.) was used, but other suitable models are available. Attachments required for this furnace include: a.
Hot finger supplied for combustion
of organic materials, Leco X-519-5
ti. Inlet-gas washing, drying, and control system, Leco 1150 c. Source of pressurized oxygen d. Inverted L-shaped glass extension 011 top of combustion tube and connected t o absorber e . Heating mantle for d, special model I'rom Brisco hlanufacturirig Co. f. Ceramic crucibles, Leco IH-10-855, mid porous covers Leco Y-519-8 g. Measuring scoop, Leco IH-13 h. Absorber or gas-washing bottle, Harsliaw 5 0 0 (Harshaw Scientific). Spectrophotometer equipped iyith titration assembly. The Beckman hIodel B was used with the Beckman titration assembly attached. Other models with adequate sensitivity and rc,solution a t 520 nip and equipped n i t h titration units are equally satisfactory. Sulfur-C hlorine. Induction furnace and attachment's as described. Sulfur titrator which utilizes the potassium iodate titration, similar to LWO nIodel400-1. Amperometric titrator, similar to the 11. H. Sargent &. Co. Anipot, Model S-29710,complete wit'h indicating elect'rode, wax-impregnated graphite rod (13); saturated caloniel reference electrode with potassium nitrate salt bridge; magnetic stirrer with Teflon stirring rod; and a 10-nil. buret graduated in 0.01 nil., with curved tip. Sulfur-Bromine. Induction furnace, with attachments a s described. Absorption tube with gas bubbler, 100-nil. capacity. Ice bath, to surround absorption tube. Sulfur titrator, as described. REAGENTS
Fluorine. Iron chip accelerator, available in pure form from Leco, No. 160 (needed also for t h e sulfur chloiide arid sulfur-bromine determinations). Silica gel, Davison Chemical Co., a(*tivated, 100 to 200 mesh, undesiccated. Triple distilled or deionized water, used for all reagents, dilutions, and washings. Standard fluorine solution, 0.075 gram of drird sodium fluoride in 100 ml. of water. The sodium fluoride is first heated to redness in a platinum crucible and cooled in a desiccator. One milli1itc.r of this solution contains 0.000339 gram of fluorine. Sodium hydroxide solution, diluted to p H 9 to 9.5. Hydrochloric acid solution, 0.1 and 0.2.Y. Standard thorium nitrate solution, 0.02S. A holution of 2.76 grams of thorium nitrate quadrihydrate in 1000 nil. of watcr and acidified with 0.4 nil. of coiicwtrated nitric acid iq later standardizcd. Buffer a t pH 3. Reagent grade monocliloroacetic acid (18.9 grams) is dissolwtl in 50 ml. of water and half of thiy solution is neutralized with sodium hydroxide to the phenolphthalein i m l point. Hoth halves are mixed and the solution is diluted to 100 ml.; thc resulting pH equals 3.0 =k 0.2. This buffcr deteriorates after 2 to 3 Iyeeks.
Sodium alizarin sulfonat'e indicator, 0.057, aqueous solution. Sulfur-Chlorine. Vanadium pentoside, purified, Fisher Scientific Co. RR Alundum, 90 mesh, refractor)grain, Korton Co. (used also for sulfurbromine determination), Silver nitrate, 0.005S. Hydrochloric acid, 0.1S and 1.5%. Gelatin solution, 1% in water, stabilized. Sitric acid, conccntratcd, specific: gravity 1.42. Starch solution, 17c in n-at'er, stabilized (also for sulfur-bromine dettmiinat'ion) . Potassium iodide-iodate solution, approximately 0.03.\- and 0.01.\- n-ith respect to potassium iodate. Five grams of potassium iodide are added to each solution. The reagent must be standardized by burning a known sulfur compound. Potassium nitrate solution, l.OA\-. Sulfur-Bromine. Carbon tetrachloride, C . P . Hydrochloric acid, 0.1S. Potassium iodate solution, 0.03 and 0 .o 1s. Sulfuric acid, 10%. Potassium iodide, 10%. Sodium thiosulfate solution, 0.01-Y. PROCEDURE
Fluorine. Grind t h e catalyst samples t'o powders and d r y 1 hour a t 110" C. i l d d 2 scoops of undesiccated silica gel t o a ceramic crucible a n d w i g h 0.1 t o 1.0 gram of the catalyst, into it. Add 2 additional scoops of silica gel or more if t h e expected fluorine content is high for a 3 t o 1 ratio of silicon t o fluorine and stir thoroughly with a glass rod. Add 1 or 2 scoops of iron chips and cover with a porous lid. Assemble the induction furnaw using the Vycor combustion tub? and hot finger. Bdjust the oxygcn flon- to 1 or 1.5 liter per minutc.. Preheat the exit tube from the furnace to the absorber to 300" to 350" C. n-ith the heating mantle. Add 7 5 nil. of dilute sodium hydroxide solution (pH 9 to 9.5) to the absorber. Connect the absorber to t'he heatcd exit tube. Preheat the hot finger and position the sample crucible. Follon the instruction manual for furnacc. operation. The combustion and flushing should be complete in about' 15 niinutcs. Shut off the furnace and remore the crucible and absorber. Rinse the absorber solution into a suitable volumetric flask and add 3 drops of sodium alizarin sulfonate indicator. Add 0.2.1- hydrochloric acid dropnise until the purple color changes to a dist'inct ycllon- ( p H 3 to 4.5). Dilute to volume. Assemble the spectrophotoniet,ric titration unit. On tlic Beckman B, use the red sensitive phototubr and make readings a t 520 mp with sensitivity a t 2 and slit width at 0.7 mm. Pipet into the positioned titration tube a suitable aliquot of thP sample solution, or the entire sample if the volume has been reduced. Add 0.3 nil. of the buffer solution and 10 drops of alizarin indi-
cator, and dilute to a visible height. _. l u r n on the stirrer and adjust its height and rate so that no air bubbles a r r fornircl. Place the tip of the microburet brlow the surface of t8he liquid in the tube. After tmhe absorbance becomes st'eady a t 0.00 with stirring, titrate v-it'li 0.02.Y t'horiuni nitrat'c. There must. IIV sufficient, time between additions of thc increments for complete mixing. Continue t,hc t,itrat,ion until the absorbance values attain a constant niaxinium value. Plot volume against absorbance. The end point is the int'ersection of thc increasing absorbance line with thcl maximum absorbance linr. Calculate the concciitration using the fluorine equivalent value of the thorium nitrate, obtained by etandardization. STAXD.4RDIZATIOTi. Prepalc sodium fluoride solutions of knov-n concentrations ranging from 0.5 to 2.0 nil. of the 0.075-gram standard. Titrat? each solution as described under Procedure and determine the averagr fluorine equivalent' for 1 nil. of thorium nitrate sdution. BLAXK.Burn in the induction furnacr a blank containing the same amounts of silica gel and iron as in the sample burning. Absorb the evohed gasc's in dilute sodium hydroxide solution ( p H 9 to 9.5) and titrate as described under Procedure. Corrwt all sample values for the blank concentration of fluorine, usually less than 0.2 nil.
Table I.
Fluorine Determinations
Theoretical and Experimental Value Fluorine, yo Sample Composition Theory Found K-1 1 Oyl,S a F in A1203 PtK-2
02.Co30r
0 45
0 5'3h'aFin 4i2-03 Pt0 2 Cos04
0 43 0 46
0 23
0 24
B. Comparison of Two RIetliods Fluorine, FusionInduction Catalyst distillation furnace 1 0 46 0 46 0 47 0 46 2 0 16 0 46 0 46 0 43 0 65 0 62 3 0 65 4 0 54 0 56 5 0 49 0 49 0 51 0 51 C. TJ pica1 Petroleum Catall sts Fluoiine Foiind, OL 1 0 35 0.36 2 0.19 0.22 3 0 21 0 22 4 0 32 6 fresh 0.89 5 used 1.20 6 experimental 0 22 0 24
VOL. 31, NO. 3, MARCH 1959
423
Sulfur-Chlorine. Grind and dry t h e catalyst samples as for t h e fluorine analysis. Add 2 scoops of vanadium pentoxide t o t h e ceramic crucible a n d weigh in t h e sample. Add 1 scoop of vanadium pentoxide, 1 of R R Alundum, and 1 or 2 of iron accelerator. Assemble t h e induction furnace as i n t h e fluorine method. Pipet 50 ml. of O.OO5N silver nitrate solution into the chlorine absorber. Adjust the p H to 1 with nitric acid. Be sure that the fritted-glass bubbler a r m of the absorber is connected to the heated exit tube from the furnace. Connect the exit tube of the absorber t o the sulfur titrator. Fill the sulfur absorber with 1.5% hydrochloric acid, Add 2 ml. of starch solution and sufficient potassium iodate reagent to produce a light blue. Choice of potassium iodate normality will depend upon the expected sulfur content. Zero the potassium iodate buret. Place the sample crucible in position and complete the combustion, following the instruction manual. Titrate the sulfur with standard potassiuni iodate as rapidly as i t is evolved, never letting the solution remain colorless for more than a few seconds. Purge the system thoroughly and calculate the sulfur content from
the potassium iodate titration, using the calibration factor for the reagent. Disconnect the chlorine absorber and rinse the solution into a titrating beaker or a volumetric flask if aliquots are to be titrated. Add 5 ml. of 1N potassium nitrate and 1 ml. of 1% gelatin. Place the titration beaker above the magnetic stirrer, add the Teflon-covered stirring rod, and control moderate stirring. Because the slope of the titration curve is governed by the rate of stirring, do not change during titration. Lower the graphite rod and one end of the potassium nitrate salt bridge to inch below the surface of the solution. Connect the other end of the salt bridge to the reference electrode. Titrate with 0 . W hydrochloric acid using an applied potential of 0.05 mv. The tip of the buret should be below the surface of the solution. Continue the titration using small increments until a constant microampcre reading is obtained. Plot milliliters us. microamperes. The end point is the intersection of the decreasing microampere line with the constant microampere line. STANDARDIZATION. A sulfur equivalent for the potassium iodate reagent must be determined experimentally by burning a compound of known sulfur content in the furnace; this eliminates
the need for a sulfur blank. A chlorine blank must be determined, however, and all quantitative results corrected for it. Sulfur-Bromine. Grind and d r y catalyst samples as in fluorine determination. Weigh t h e sample into a ceramic crucible. Add 1 scoop of R R Alundum and 1 or 2 of iron chips. Cover with a porous lid. Assemble t h e furnace as for sulfurchlorine determination. Preheat t h e mantle on t h e exit tube t o 300' C. ildd 70 ml. of carbon tetrachloride to the absorption tube and connect i t to the furnace exit tube and sulfur titrator. Place the absorption tube in an ice bath. Complete the combustion, titration, and calculation of the sulfur content as in the sulfur-chlorine method. Rinse the cold carbon tetrachloride solution into a 250-ml. glass-stoppered Erlenmeyer flask. Add 50 ml. of ice water and shake vigorously. Add 10 ml. of cold 10% sulfuric acid and 10 ml. of cold 10% potassium iodide solution. Shake vigorously. Titrate with 0.01.L' sodium thiosulfate solution to the colorless starch end point, shaking vigorously during the titration. Make a blank determination through the furnace and titration. Correct all d u e s for the blank concentration. RESULTS
Table II.
Simultaneous Determination of Sulfur and Chlorine in Standard Samples
Sample Type
Low s
A-0
c1
Low s Low c1 Low s Low C1 Low s High C1 High S Low c1 High S High C1 Table 111.
Sample Composition NBS la
+ KC1
NBS l a NBS 89
+ KC1
SBS la
+ KnSOa Na2S203+ KC1 NBS 89
+ +
Table IV.
0 37
0 24
0 35
6
0 12
0 05
0 12
0 051
5
020
9 7
022
99
4
4 77
0.036
4 66
0.035
3
15.69
15 57
22 92
5
of Sulfur and Chlorine in Organic Samples Experimental, % xo.
Theoretical] % S ci14.9 0 0 37 5
S 14.9 0
37 2
13 0 15 5
10 0
13 1 15.5
10.1 10.0
C1 0
9.8
Detns. 3 4 4
1
Simultaneous Sulfur-Bromine Determinations
Theoretical] % S Br
Known Blends Dibenzyl sulfide KBr CdOn KBr K&Oa KBr03
+
11.9
17.2
11.3
Engine Deposit
424
0 24
22 85
Simultaneous Determination
Sample Dibenz 1 sulfide Monoczloroacetic acid monochloroDibenzyl sulfide acetic acid Dibenzyl sulfide KCl
+ +
Theoretical, % Zxperimental Bv., % KO. S c1 S C1 Detns. 0.25 0 00 0 26 0 00 3
13.4 12.0
17.7
Found,
1
S 1.00 1.04
2
0.54 0.59
3
1.42 1.43
ANALYTICAL CHEMISTRY
Exptl., %
KO.
S
Br
11.3 17.7
13.8 12.0 18.1
11.4
yo Br 9.22 9.30 6.70
6.74
10.63 10.80
Detns. 3 3 2
Fluorine. Samples of knon n fluorine contents were prepared by quantitatively miving dried sodium fluoride with fluorine-free aluminum oxide. Small amounts of platinum and cobalt oxides \yere added, because these materials are frequently present in petroleum catalysts. The calculated concentrations of fluorine are compared in Table I, A, with experimental values. llaximum deviation was -0.02% a t the 0.2% concentration level. d series of typical samples nas analyzed by the induction-photometric method and results coniparcd to those obtained by carbonate fusion-steamdistillation methods, Table I. B. Average difference between the two methods n a s 0.013%. For information only. several types of petroleum catalysts were a150 analyzed by this method (Table I. C). These data shoiv that the method is applicable to most types of petroleum catalysts. Repeatability is *0.03%. Sulfur-Chlorine. To check the accuracy of t h e method, solid standard samples from the Sational Bureau of Standards were analyzed, as ne11 as quantitative blends of these materials with high purity potassium chloride, potassium sulfate, and sodium thiosulfate, prepared so t h a t both low and high concentrations of both elements could be measured (Table 11). Average differences between the theoretical and experimental values were 0.035% for sulfur and 0.07% for chlo-
rine, in the entire concentration range studied. Two organic. standards were also prepared froin dihenzyl sulfide, monocliloroacetic acid, and potassium chloride, and :tnalj-zecl quantitatively to check the acc*uracy of the experinient>al nicthod. .l(wptnhle recoveries were obtained in all cases (Tahle 111). I n addition to thc analysis of catalysts, t,he nirt,hod is applicable to engine deposits, big!) boiling oils. and organic chemicals. Sulfur-Bromine. Several purc' rompourids \!-we blended t o ohtnin aamplc,s of knon-n concentrations of both sulfur and bromine. Dibenzyl sulfide (Ehstnian Kodak Co.), and calcium and potassium sulfate were used a s t h e source of sulfur. Potassium bromide a n d bromate were t h e bromine standards. Mixtures of these materials were prepared quantitatively and analyzed by this method (Table
LITERATURE CITED
(1) Agazzi, E. J., Fredericke, E. M., Brooks, F. R., ASAL. CHEM.30, 1566
(1958).
( 2 ) Agazzi, E. J., Parks, T. II.>Brooks, F. R., Ibid., 23, 1011 (1951). 1 3 ) Baker. I3. B.. hlorrison. J. D.. Ibid.. 27, 1306 (1955)'. (4) Bennet, E. L., Zbid., 26, 426 (1954). ( 5 ) Brunner, A. J., Matson, F. R., IND. ENG.CHEM.,A ~ LED. . 19, 156 (1947). (6) Caston, C. R., Saylor, J. H., A s . 4 ~ .
IV\. The niethod has been applied to the analysis of catalysts and engine deposits (Tahle IV). I n the latter case, !vet chemical methods are extremely complicated and uncert,ain. Repeatability averaged +0.03% on sulfur a t the I .0% level and 10.07% on bromine a t the 5 t o 1075, level.
(20) Koltlioff, I. M., Harris, IT. E., ISD. ESG. CHEX., ANAL.ED.18, 161 (1946). (21) Laboratory Equipment Corp., Leco Method for Sulfhr Determination rom-
\
,
CHEII.24,1360 (1952).
( 7 ) Chilton, J. ll., Horton, A. D., Zbid.,
27,842 (1955).
(8) Chu, Chin-Chen, Schnfer, J. J., Ibid.,
27, 1429 (1955).
(9) Coller, 11.E., Leininger, R . K.: Zbid.,
27.949 11955). (10) 'Eger,' Chaini, 'I-arden, Asher, Ibid., 28,512 (1956). (11) Erickson, C., Petrol. Processing 9, 1087 (1954). (12) Frieir, H. E., Sippoldt, B. W., Olson, P. B., Weiblen, D. G., ANAL. C H E ~27,146 I. (1955). (13) Gaylor, V. F., Conrad, A. L., Landerl, J. H., Zbid., 29,224 (195i). (14) Gerhardt, P. B., Dyroff, G. V., Ibid., 28, 1726 (1956). (15'1 Grant. C. L.. Haendler. H. 11..Zbid.. 28.415 (i956). ' (16) 'Grimaldi, 'F. S., Ingram, Blanch, Cuttitta, Frank, Zbzd., 27, 918 (1955). (17) Gwirtsman, Joseph, Mavrodineanu, Radu, Coe, R. R., Ibid., 29, 887 (1957). (18) Holler, A. C., Klinkenberg, Rosemary, Zbid., 23, 1696 (1951). (19) Kaufman, Samuel, Zbid., 21, 582 (1949).
(24) Sicksic, S. W.,Fade!-, L.' L.,Zbid.,
30, (1958). (25) Onstott, E. I., Ellis, W. P., Ibid., 28,393 (1956). (26) Petron-, H. G., Xnsh, L. K.) Ibid., 22, 1274 (1950). (27) Popov, A. I., Iinudson: C.: E., Zhid., 26, 892 (1954). ( 2 8 ) Remmert, L. F., Parks, T. I).; Ibid., 25,450 (1953). (29) Shaw, IT. RI., I h i d . , 26, 1212 (1954). 130) Shoemaker. C. E.. I b i d . . 27. 552 (1955). (31) Slioolery, J. S . , Ibid., 26, 1400 (1954). (32) Sweetser, P. B.,Zbid., 28, 1766 (1956). (33) Teston, Rebecca, RIcKenri:i: F. E., Ibid., 19, 193 (194i). (34) Wayman, D. H., Ibid., 28, 865 (1956). ( 3 5 ) Thite, T. T., Penther, C. J., Tait, P. C.. Brooks. F. P.. Ibid.. 25. 1664 (i953j. (36) Willard, H. H., \Tinter, 0. B., I N D . ESG. CHEX., h A L . ED.5 , 7 (1953). I
,
RECEIVEDfor review June 26, 1958. Accepted October 30, 1958. Group session on Analytical Research, 23rd midyear meeting of The Division of Refining, Smerican Petroleum Institute, Los .kngeles, Calif, May 1958
Reduction of Thallium(lll) to Thallium(1) with Metallic Reductors R A M O N F. ROLF' and ELMER LElNlNGER Kedzie Chemical laboratory, Michigan State University, East laming, Mich.
,Reducing columns of metallic bismuth, cadmium, or silver may b e used to reduce thallium(lll) to thallium(1) in dilute sulfuric acid solution.
A
FOR A METHOD to determine total thallium in solutions containing both thallium(II1) and thallium(1) ions revealed little information on the use of metals for the reduction of thallium(II1) to thallium(1). The most commonly used reductant is sulfur dioxide, b u t the removal of the excess reducing agent is tedious. The use of a metallic reductor coupled with a titrimetric oxidation procedure should yield a rapid and desirable scheme for the determination of total thallium. For this reason the action of various metal SEARCH
1 Present address, Dow Chemical Co., Midland, hlich.
reductors toward thallium(II1) was investigated. ks the titrimetric oxidation with standard potassium bromate solution appears to be the most satisfactory oxidation method ( I ) , the potentiometric modification ( 2 ) was chosen to determine the thallium(1) in the reduced solutions. SOLUTIONS
Standard Thallium. d 54-gram quantity of thallium(1) nitrate (Fisher Scientific Co.) was dissolved in 900 ml. of 1N sodium hydroxide solution a n d treated with 350 ml. of 5.25y0 sodium hypochlorite solution (commercial Clorox). T h e thallium(II1) oxide precipitate was washed twice b y decantation, then was dissolyed in 220 ml. of concentrated sulfuric acid a n d diluted t o 4 liters. T h e final solution was approximately 1.8X in sulfuric acid.
Aliquot portions of the solution were reduced with sulfur dioxide; the excess sulfur dioxide was removed b y boiling and the total thallium was determined by the potentiometric bromate procedure ( 2 ) . The solution contained 0.01066 gram of thallium per ml. A direct titration with bromate, omitting the prior reduction with sulfur dioxide, showed that approximately 3.5% of the thallium was present as thallium(1). Potassium Bromate. Prepared from Mallinckrodt analytical reagent grade as 0.10005 (0.01667M). REDUCING COLUMNS
Borosilicate glass columns (G. Frederick Smith Chemical Co.) , commonly used for preparing silver reductors, were filled with the following metals to give a n 18- to 20-cm. depth of the metal after first placing a plug of glass wool in the bottom. Cadmium. Filings obtained from cadVOL. 31, NO. 3, MARCH 1959
* 425
