in the latter case were obtained by exposing the granules to dimethyldichlorosilane vapors in a closed container for 2 weeks and then washing with methanol. Fatty acid ester analyses were made, using 9-foot, coiled copper columns, 1/4inch outside diameter, 0.03-inch wall thickness. The partitioning medium was 15% PVA by weight on Chromosorb R and Celite 545, respectively, and 0.25% PVA by weight on the glass microbeads. The helium flow rate for all experiments was adjusted to 83 ml. per minute measured at the column exit. The detector w'its of the thermal conductivity type, and the samples analyzed contained approximately 300 pg. of the mixed esters. The temperature of the column and detector was 205" C. for the Chromosorb R and Celite 545 columns. For the glass bead columns, several temperatures were used; results are reported for an operating temperature of 168" C. In Table I, the separation factors are the ratios of retention volumes compared to the retention volume of the C,; mnrgmic acid. The theoretical
plates were calculated in conventional manner by dividing the distance from the "air pip" to the peak in question, by the peak width a t the base, squaring this quantity, and multiplying by 16. Results, using treated Chromosorb R and Celite 545, mere uniformly good. The close check of the separation factors on these two PVA coated supports indicates that this treatment produced a reproducible, uniform, and similar surface on both materials. Microscopic observation of the coated granules showed marked difference in their surfaces, the granules of Celite 546 being more jagged in appearance than those of Chromosorb R. It may be that the differences in physical structure between these two materials are responsible for the difference in observed retention volumes. The use of glass microbeads as a support gave rapid results a t relatively low operating temperature; however, the peaks \\-ere too poorly resolved, under our operating conditions, t o make this column useful. If the glass microbead column is similar in performance to a capillary-type column, the poor resolu-
tion may be attributed to overloading. The glass microbead column may, therefore, be useful with ionization-type detectors, where smaller samples can be used, but unsuitable for use with thermal conductivity detectors. LITERATURE CITED
(1) Hishta, C., Messerly, J. P., Reschke, R. F., Abstracts of Papers, 137th Meeting, ACS, Cleveland, Ohio, April 1960, n. 29R r -
(2) Hishta, C., Messerly, J. P., Reschke,
R. F., Fredericks, D. H., Cooke, W. D., ANAL. CHEW 32,'880 (1960). (3) Homing, E. C., Moscatelli, E. A., Sweeley, C. C., Chem. and Ind. 1959, 751.
(4)Hornstein, I., Elliott, L. E., Crowe, P. F., Nature 184, 1710 (1959). (5) Howard, G. A., Martin, 8. J. P., Biochem. J . 46, 532 (1950). IRWIN HORXSTEIN
PATRICK F. CROWE Meat Laboratory Eastern Utilization Research and Development Division U. S. Department of Agriculture Beltsville, Md. MENTION of trade names in this paper is for identification and implies no endorse ment of the products.
Polarographic Determination of Iodine in Tellurium Metal SIR: Iodine-131 is produced by irradiation of tellurium metal. To analyze iodine-131, an accurate method is required for determination of the inactive iodine originally present in tellurium metal. The only method reported thus far is the one by Miles et al. ( 2 ) . Essentially, it consists of oxidation of iodine in tellurium and subsequent reduction and distillation. The distilled iodine is absorbed in alkali, extracted in carbon tetrachloride, and then estimated spectrophotometrically. However, a large sample (+25 grams) must be taken for analysis, as the final extract should contain a t least 5 pg. of iodine per ml. I t seemed, however, that the procedure for estimating iodine after distillation could be improved if the estimation were done polarographically. Smith and Taylor (4) showed that in the polarographic reduction of iodate very low amounts of iodine could be estimated by using potassium chloride and borax as supporting electrolyte. The procedure which follows was finally developed. APPARATUS AND REAGENTS
A Du-Bellay polarograph was used for recording polarograms. A single-stage distillation apparatus was used for distilling iodine. All the reagents used were of E. Merck R. G. quality. Iodine-free tellurium metal was prepared by first distilling iodine from the
metal and then following the procedure described by Scott (3). PROCEDURE
The distillation process was similar to one described by Miles et al. (2), except that a single-stage distillation apparatus was used and a constant stream of air was bubbled through the liquid during the distillation to sweep out all the iodine. One gram of tellurium metal was treated in a 1-liter flask with 3.55 grams of potassium dichromate and 80 ml. of dilute sulfuric acid (25 ml. of concentrated sulphuric acid plus 55 ml. of water) and was digested under reflux a t 80" C. for 1.5 hours. The flask was cooled, then attached to a Leibig condenser, the other end of which was dipped in 10 ml. of absorption solution (2 ml. of IN NaOH, 0.2 ml. of alkaline sodium bisulfite, and 8 ml. of water). Five mams of oxalic acid was added to the vdistillation flask and after the initial vigorous reaction the solution was heated to boiling to distill the iodine. A steady low stream of air was maintained during the distillation and was continued until a total volume of about 25 ml. of distillate was collected. The distillate was then concentrated to 2 ml., just acidified with dilute sulfuric acid (1 to 18), and cooled. Then 0.5 ml. of 10% (v./v.) hydrochloric acid and 1 drop of 10% solution of sodium nitrite were added. The liberated iodine was extracted with 5 ml. of carbon tetrachloride and was back-ex-
tracted into an aqueous phase containin 1 ml. of IN NaOH and 2 drops of lo& (w./v.) alkaline sodium bisulfite per 5 ml. of water. The aqueous phase, after separation, was just acidified with dilute sulfuric acid (1 to 18), 8 drops of a saturated solution of bromine water were added, and the solution was concentrated on a sand bath to a volume of 2 ml. It was then cooled, transferred to a 10-ml. volumetric flask, and made slightly alkaline with sodium hydroxide solution. One milliliter of 0.05M borax, 1 ml. of 1M potassium chloride, and 2 ml. of 0.1% gelatin were added and made up to the mark. The iodate in this solution was then determined polarographically. The potential range over which the polarograms were recorded was between -0.9 and -1.4 volts us. S.C.E. The half-wave potential was approximately -1.2 volts us. S.C.E. The polarographic cell was kept in a thermostat, the temperature of which was kept 0.1' C. by an elecconstant a t 30' tronically operated relay. Oxygen was removed by passing nitrogen through the solution in the polarographic cell for 15 minutes; 10 minutes was usually sufficient time to drive away all the oxygen. To standardize, different amounts of potassium iodate solution were placed in a 10-ml. flask, to which were added 1 ml. each of 0.5M sodium sulfate, 0.05M borax, liM potassium chloride, and 2 ml. of 0.1% gelatin. Standardization was also checked by taking iodide solution, oxidizing with bromine water, as described above, and then adding different constituents of the supporting
*
VOL. 33, NO. 2, FEBRUARY 1961
0
31 1
electrolyte and recording the polarogram. For standardization of the method, a sample of tellurium free from iodine was prepared by first distilling the iodine and then following the procedure described by Scott (3). Recoveries of iodine were tested by adding standard amounts of iodine to pure tellurium samples so prepared and following the procedure described above. The results are tabulated in Table I. RESULTS AND DISCUSSION
Smith and Taylor (4) reported that it was not possible to concentrate iodine solution after oxidation owing to the escape of iodine in hydrochloric acid used in the process of evaporation. It was, however, found possible to concentrate iodine solution after oxidation, if, as described in the present procedure, sulfuric acid were used, qrovided of course that the concentration did not reach the fuming stage.
Table I. Recovery of Iodine Iodine, pg. Added Found
10.0
9.75
Recovery, %
97.5
A polarogram could not be taken directly on the alkaline solution used for absorbing iodine in the distillation procedure, since the mechanical carryover of traces of chromium was a serious interference (1). Therefore, it was necessary to extract the iodine in carbon tetrachloride and then backextract it into the aqueous phase. As the iodine contents in most of the samples analyzed were low, the results could not be compared with the usual colorimetric method. One sample of
tellurium could, however, be analyzed by both methods owing to its slightly higher iodine content. The values obtained were 56.8 p.p.m. by the polarographic and 58 p.p.m. by the colorimetric method. LITERATURE CITED
(1) Lingane, J. J., Kolthoff, I. hf., Chem. SOC.62,852 (1940).
J. Am.
(2) Miles, B. J., Fletcher, C. W.,Faires, R. A., Payne, B. R., Hudswell, F.,
Atomic Energy Research Establ. (Gt.
Brit.)I/R 1038 (1952). (3) Scott, W. W., 'Wmdard Method of Chemical Analysis, Vol. I, p. 787, Van Nostrand, Yew York, 1939. (4) Smith, S. W.,Taylor, J K., ANAL. CHEM.29, 301 11957). V. T.ATHAVALE R. G. DHANESHWAR S. V. GULAVANE M. S. VARDE Analytical Division Atomic Energy Establishment Trombay Bombay, India
Assay of Barium Compounds by Precipitation of Barium Chromate from Homogeneous Solution SIR: There is a pressing need for a method for the assay of barium compounds. Because available methods are unsatisfactory, barium compounds are usually not assayed a t all or the assay is made by analyzing for the anion ( I ) . Firsching (2) and Gordon and Firsching (3) determined barium by precipitating barium chromate from homogeneous solution; Firsching used EDTA, while Gordon and Firsching used urea. In the method of Gordon and Firsching the pH was adjusted to 1.7 to 1.8, ammonium acetate, potassium dichromate, and urea were added, and the solution was heated a t 95 O to 98 O C. until the pH changed to 5.7. This took 2.5 hours or more. The present author has found that if 7 ml. of hydrochloric acid, or 6 ml. of perchloric acid and 2 ml. of hydrochloric acid, are present in 225 ml., and the solution is boiled until a precipitate appears (about 15 minutes) and then for an additional hour, there is no necessity for adjusting the pH exactly. The pH after the boiling period is 5.5 and it does not change on continued boiling. The technique has been applied to the assay of commercially important barium salts, using a 0.5-gram sample. If less than 3% strontium compound is present, only one precipitation of the barium chromate is necessary; if more than 3% strontium compound is present, the barium chromate is reprecipitated after dissolving it in nitric and perchloric acids and evaporating to fumes of perchloric acid. All the barium compounds 312
ANALYTICAL CHEMISTRY
analyzed in this laboratory contained less than 3% strontium compound. Interference from carbonate, peroxide, and sulfide was eliminated by boiling with acid, and interference from fluoride, organic anions, and silicon was eliminated by fuming with perchloric acid. Barium sulfate was fused with sodium carbonate, and the barium carbonate filtered off and dissolved by fuming with perchloric acid. The amounts of iron and other elements found in barium compounds did not interfere with the method. PROCEDURES
1. Barium Nitrate, Acetate, Chlorate, Chloride, Hydroxide, and Perchlorate. Transfer a 0.5000-gram sample to a 400-ml. beaker, add 225 ml. of water and 7 ml. of hydrochloric acid, and stir to dissolve. Heat to about 80" C. and add with stirring 10 ml. of ammonium acetate solution (400/,), 25 ml. of potassium dichromate solution (lo%), and 10 grams of urea. Cover with a watch glass, heat to boiling, boil moderately until a precipitate settles on the bottom of the beaker, and then continue boiling for 60 minutes more. Midway during this 60minute boiling period, wash down the cover lid with water and bring the volume to 225 to 250 ml. by adding hot water. At the end of the heating period, filter through a tared sinteredglass crucible of medium porosity, transfer the precipitate to the crucible with potassium dichromate wash solution [made by diluting 50 ml. of potassium dichromate solution (10%) to 1
liter with water], and finally wash the precipitate four times with water. Dry a t 120" C. for 1 hour, cool, and weigh as barium chromate. 2. Barium Carbonate and Chromate. Add 100 ml. of water and 7 ml. of hydrochloric acid, and boil for 10 minutes to dissolve the sample and drive off carbon dioxide. Dilute t o 225 ml., heat to 80' C., add the ammonium acetate, and proceed as in 1. 3. Barium Fluoride. Weigh the sample in a platinum dish. Add 40 ml. of mater, 10 ml. of hydrochloric acid, and 6 ml. of perchloric acid. Evaporate to fumes of perchloric acid, dilute to 225 ml., and add 2 ml. of hydrochloric acid. Heat to 80" C., add the ammonium acetate, and proceed as in 1. 4. Barium Oxalate and Other Organic Barium Salts. Add 25 ml. of nitric acid and 6 ml. of perchloric acid, and evaporate to fumes of perchloric acid. Dilute t o 225 ml. and add 2 ml. of hydrochloric acid. Heat to 80" C., add the ammonium acetate, and proceed as in 1. 5. Barium Oxide, Peroxide, and Sulfide. Add 50 ml. of water and 7 ml. of hydrochloric acid and boil for 12 minutes. Filter off any residue and wash with hot mater. Retain the precipitate and filtrate. Ignite the precipitate and fuse with 4 grams of sodium carbonate. Leach with 200 ml. of water a t 95" C. for 45 minutes, filter, and wash with hot 0.2y0 sodium carbonate solution. Discard the filtrate. Dissolve the precipitate in 10 ml. of hot hydrochloric acid (1 to 2) and wash with water. Make the filtrate so obtained just alkaline to
