Colorimetric Determination of Thallium PAULA. SHAW,California State Division of Fish and Game, San Francisco, Calif.
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and fill the colorimeter wedge with H E i n c r e a s e d usage of A colorimetric method for the quantitative the iodine s t a n d a r d o b t a i n e d . thallium in recent years, determination of thallium in toxicological mateCalibrate the wedge by oxidizparticularly as a rodentiing 4-, 8-, and 12-cc. portions of rial, poison bait, or thallium salts, and utilizing cide, has resulted in numerous t h a l l i u m solution with 50 cc. of the Hellige wedge type colorimeter, is described. bromine, adding 5 cc. of otassium instances requiring the determiiodide and extracting witi 20 cc. of The analysis of samples containing 10 to 75 mg. nation of small amounts of thalcarbon disulfide. Place these solulium in toxicological material. of thallium per kg. can be made on 10- to 20-gram tions as prepared in the colorimeter The gravimetric and volumetric trough, match with the standard, samples and completed in 2 to 3 hours, within and note the readings. On millimethods in general use are cuman accuracy of 3 to 5 per cent. The analysis may meter graph paper plot the readbersome and time consuming, ings against milligrams of thallium be shortened for thallium-coated grain and be require relatively large samples represented by each cubic centicompleted in approximately 30 minutes. Details to obtain a weighable precipitate meter of solvent. Further points or appreciable titration, and in should be determined if the graph of procedure, preparation of standard, and calidoes not form a straight line. most i n s t a n c e s are not highly bration of wedge are given. The method has been accurate as applied to toxicoIogifound satisfactory in the presence of copper, lead, Figure 1 s h o w s a t y p i c a l cal material. As an example, a arsenic, mercury, molybdenum, and tungsten, graph, the reading for zero thalstudy of the iodide method inlium content falling a t 97, and but not in the presence of chromates. Illustrative dicated that, by conducting the final washing of the precipitate results on tissues, urine, and thallium-coated each division below this point being equivalent to 0.00173 mg. with a s a t u r a t e d solution of grain are included. of thallium per cc. of solvent: thallous iodide, the results could be brought within an accuracy 0.168 (thallium content for zero reading) of *0.2-mg. of thallium. 0; this basis, and desiring the = 0.00173 97 (reading for zero thallium content) analysis as a whole to be accurate within * 5 per cent, it Blank tests should be made on the bromine solution to dewould be necessary on material of approximately 25 mg. per kg. to use a sample weighing 160 grams, the oxidation and com- termine the minimum time required for removing the excess, as continued boiling may produce low results. The hydropletion of the analysis requiring not less than 1to 1.5 days. The colorimetric method developed and here described chloric acid tends to prevent reduction of thallic chloride in requires 10- to 20-gram samples for material ranging from 10 to boiling solution and also increases the efficiency of the iodine 75 mg. per kg.and is accurate to *3 to 5 per cent, and the total extraction with carbon disulfide. Under the conditions specitime required is approximately 2 hours. On samples con- fied, approximately 96 per cent of the theoretical amount of taining less than 10 mg. per kg., somewhat larger errors are to iodine is extracted, but the loss does not influence the accuracy .20 be expected. of the method, since thallium OUTLINEOF METHOD determinations are made under Organic matter is first destroyed by the Fresenius-v Babo the same conditions as the caliprocess, following which thallic chloride is extracted from the bration. The purpose of the ‘I2 filtrate with ether. Organic matter in the ether residue is de- sodiumphosphatein the oxidiz- o8 stroyed with nitric and sulfuric acids, the nitrites resulting ing solution is to minimize the from this treatment being decomposed by evaporating the ionization of ferric salts in the a diluted acid solution to dryness after the addition of excess samples analyzed and has no ammonium chloride. Thallous chloride contained in the significance in the standardi- ,o residue is oxidized with a bromine solution, the excess being zation other than to maintain FIGURE 1. CALIBRATION removed by boiling. Potassium iodide is added and iodine similar extracting conditions. CURVE A volumetric method in which liberated as shown in the equation: thallium is oxidized with broTlC13 2KI = TlCl 2KC1 21 mine, and the influence of ferric ion eliminated by phosphate, The liberated iodine is extracted with a measured volume of has recently been published by Fridli (2). Owing to evapocarbon disulfide, and the color intensity matched against a ration (even in a glass-stoppered wedge) and the action of standard contained in the wedge of Hellige Universal color- light, the standard should be discarded and a fresh one prepared after 24 to 48 hours. imeter. By proper adjustment between the weight of sample used and the volume of extracting solvent, the standard will apply PREPARATION OF STANDARD AND CALIBRATION OF WEDGE to samples of any thallium content. For example, assuming PROCEDURE. From a c. P. thallium salt, pJepare a standard solution containing 0.2 gram of thallium per liter. Measure 16 a sample of approximately 2 mg. per kg. on which it is desired cc. (3.2 mg.) into a 150-200 cc. narrow-necked flask and add 50 that the colorimeter will give a reading of approximately 10 cc. of bromine solution, prepared by adding 100 cc. of concen- divisions, we have: trated hydrochloric acid and 100 grams of secondary sodium 0.00173 X 1000 X 10 X cc. = mg. per kg. phosphate to 900 cc. of bromine water. Boil vigorously for 3 weight of sample, grams minutes while holding the flask with a clamp and rotating in a free flame. Cool, transfer to a 125-cc. separatory funnel, and adjust Solving for the required sample per cubic centimeter of solthe volume to 60 cc. Add 5 cc. of potassium iodide solution (2 grams per liter), and 20 cc. of carbon disulfide. Stopper the vent, we obtain 8.65 grams, or, for a 25-gram sample, we would funnel and shake for 15 to 30 seconds, allow the layers to separate, use 3 cc. of extracting solvent. J~
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+
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ANALYTICAL EDITION
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As a second example, assume the sample to be coated grain of approximately one per cent; it is desired that the colorimeter will give a reading of say 50 divisions, and we have: 0.00173 X 50 X 100 X cc. = 1000 X weight of sample
per cent
Solving for the required sample per cubic centimeter of solvent, we obtain 0.00865, or, for 20 cc. of solvent, we would use a sample weighing 0.173 gram. The volume of bromine solution and potassium iodide should also be adjusted so that approximately constant conditions exist between the water phase and solvent.
PRELIMINARY TREATMENT OF SAMPLES For toxicological material the weighed and finely PROCEDURE. divided sample is reduced to a fluid mass with 1 t o 1 hydrochloric acid, brought to the boiling point on a water bath, and oxidized by successive additions of potassium chlorate in the usual manner. The cooled solution is filtered and washed to remove undecomposed fatty particles, and evaporated until a slight darkening is noted. Cool, transfer to B separator funnel and add sufficient strong chlorine water to discharge tile darkening and to leave considerable free chlorine in solution. Extract with two 50-cc. portions of ether for 1 t o 2 minutes each, allow the layers t o separate, and evaporate the ether portion in a narrow-necked flask. To the residue add 15 cc. of water, a few drops of hydrochloric acid, and 2 cc. of ,concentrated sulfuric acid. Insert a short-stemmed funnel in the neck of the flask, place on a hot plate, and evaporate to fumes of sulfur trioxide. Retain on the hot plate and at short intervals add fuming or concentrated nitric acid, a drop at a time through the funnel, until oxidation is complete and a colorless or light yellow solution remains. Cool, add 30 cc. of ammonium chloride solution (150 grams per liter), and evaporate to dryness while rotating in a free flame to prevent spattering. The analysis is completed by bromine oxidation, addition of potassium iodide, extraction, and color comparison as previously outlined. The entire procedure may be completed in 2 or 3 hours. Thallium-coated grain does not require the chlorine oxidation or ether extraction unless treating a sample larger than 0.3 gram. The weighed sample is dissolved in fuming nitric acid containing 2 cc. of sulfuric acid, and evaporated to fumes of sulfur trioxide. Complete destruction of organic matter and the remainder of the analysis is carried out as above indicated. Determinations made in this manner can be completed in approximately 30 minutes. Direct oxidation with nitric acid is satisfactory for urine samples sufficiently high in thallium to permit analysis on 5 cc. or less. If this is not the case, the complete determination should be used. Roughly, the direct method should not be used on urine containing less than 25 mg. of thallium per liter, or on grain containing less than 0.04 per cent of thallium. Following the filtration from fat, some evaporation should occur, even though the volume is small, to promote a clean separation of the layers when extracting with ether. Excess chlorine is required during the extraction to maintain thallium in the thallic state, thallous salts being insoluble in ether. In the absence of free chlorine, thallium is reduced by the organic matter undecomposed by the preliminary treatment. Ether extraction of thallium was first suggested by Noyes, Bray, and Spear (4) for its qualitative detection, and has been found an effective method for its complete extraction; this procedure separates the thallium from many inorganic constituents and most of the undestroyed organic matter. Although ferric iron is also extracted by ether, no interference results from this element, owing t o the later addition of phosphate which minimizes ionization of ferric salts. The procedure outlined for complete destruction of organic matter in the ether residue was utilized by Baldeschwieler (1) in lead determinations on ethyl gasoline, and has proved very satisfactory. Other less drastic methods did not give as rapid or effective results. The reaction by this method is violent, but practically no mechanical loss occurs with a funnel
Vol. 5 , No. 2
inserted in the neck of the flask. A preliminary evaporation with water and a little hydrochloric acid tends to give a less violent reaction than occurs if sulfuric and nitric acids are added directly to the residue. A few drops of fuming nitric acid are usually sufficient to complete oxidation; however, if a large sample has been treated, more may be required, and additional sulfuric acid may be necessary to maintain a fluid condition. The method employed for destruction of nitrites by evaporation to dryness in the presence of ammonium chloride was recently reported by Nelson, Levine, and Buchanan (3). Sufficient ammonium chloride should be present to react with all the free sulfuric acid, 15 cc. of 15 per cent solution being required for each cubic centimeter of sulfuric acid. While ammonium salts are present in the analysis and not in the standardization, they were found to have no appreciable effect on the extraction coefficient. The hydrochloric acid, potassium iodide, and volume of the final solution should bear approximately the same ratio to the volume of carbon disulfide solvent as that maintained for the calibration of the wedge. SUMMARY OF EXPERIMENTAL DATA RELATION BETWEEN THEORETICAL IODINE LIBERATED AND AMOUNT EXTRACTED. The method outlined for preparation of the standard and calibration of the wedge resulted in a straight-line graph indicating consistent results for both large and small quantities of thallium when extraction conditions were held approximately constant. The method used does not determine, however, whether the actual amount of iodine extracted is identical with the theoretical quantity of iodine that should be liberated from the known quantity of thallium. To check this point, the wedge+wasfilled with a standard containing a known quantity of iodine in carbon disulfide and calibrated with dilutions of the same solution with carbon disulfide. Aliquots of a standard thallium solution were also used to calibrate the iodine-filled wedge, and from these data it was determined that the iodine value obtained from thallium was 96 per cent of the theoretical value. To determine whether the low iodine value was due to incomplete oxidation and ionization of thallic iodide or to incomplete extraction, a standard aqueous solution of iodine was prepared, and aliquots of this were extracted with carbon disulfide after adjustment to the same volume and concentration of acid and potassium iodide. The extracted iodine when measured by the colorimeter was found to be 97 per cent of the value indicated by arsenious oxide standardization of the aqueous solution. Thus, within experimental limits of error, the low iodine value derived from thallium was shown to be due primarily to extraction loss. EXTRACTION CHANGES WITH VARIATION OF WATERPHASE AND SOLVENT.Experiments in which the carbon disulfide extractions were made in the presence of less hydrochloric acid and more potassium iodide gave results from 5 to 14 per cent below the actual values, these figures applying to onetenth of the suggested acid content and to two to four times the usual amount of potassium iodide. At the usual acid content of 5 cc. per 60 cc. of water phase, additional amounts of potassium iodide caused only minor decreases in the percentage of iodine extracted. Extractions made with the usual volume and composition of water phase, but with larger and smaller volumes of solvent, caused errors averaging - 1.3 per cent with 5 cc. of solvent, and averaging +2.3 per cent with 40 cc. of solvent. As these errors are not large, it is evident that the ratio between volume of water and solvent need be adjusted only roughly to insure consistent results. As 5 cc. of potassium iodide are sufficient to react with approximately 6 mg. of thallium, it is evident (assuming constant ratios are maintained) that the
March 15.1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
95
limiting factor is the upper limit of the standard rather than average being 0.834. These results indicate the variation the amount of potassium iodide present. that may be expected from the analysis of single kernels owing ANALYSISOF C. P. THALLIUM SALTS. The method devel- to unequal distribution of the thallium. A 3-gram sample of oped is essentially for samples of low thallium content, but is the same material (approximately seventy-five kernels) was satisfactory and extremely rapid for the assay of high per- pulverized and thoroughly mixed. Two analyses from this centage salts where an accuracy greater than *2 per cent is sample gave values of 0.79 and 0.84 per cent, the average not required. Analysis of the e. P. acetate, chloride, nitrate, being 0.815. Three blank tests run on strychnine-coated and carbonate gave values varying from the theoretical thal- barley did not liberate a measurable quantity of iodine in any lium percentage by 0.13 to 1.76 per cent. At the other ex- case. treme, analyses of small samples containing 0.04 to 0.1 mg. A dog was given thallium sulfate by capsule, equivalent to gave values in error by 3 to 5 per cent. 25 mg. of thallium per kg. of body weight. The animal was INTERFERENCE BY OTHER METALS. Analyses were conplaced in a metabolism cage, and the total urine for each day ducted on aliquots containing 0.5 mg. of thallium to which collected. Triple analyses on the samples for the first two were added 5 mg. of another metal in the form of a soluble days show the checks obtained: first day, 24.4 * 0.4 mg.; salt. These tests were made on copper, lead, iron, arsenic, second day, 13.9 * 0.3 mg. Blank tests made on normal mercury, tungsten, and molybdenum, the complete analysis urine gave zero values. being used exclusive of the preliminary oxidation with potasThe following data are illustrative of results obtained' on sium chlorate. The values obtained were in all cases within tissues from thallium-poisoned game birds on which a com0.01 to 0.02 mg. of the true value, indicating no appreciable plete report will appear elsewhere. The values shown are interference by the metals tested. Attempts to assay thal- on heart muscle from thallium-poisoned geese : lium chromate by the colorimetric method were not successTIME TIME THALLIUMUNTIL THALLIUMTHALLIUMUNTIL THALLIUM ful, however. No method was found to eliminate satisfacDOSAQE DEATH FOUND DOsAQE DEATH FOUND torily the chromate interference. Mo./ko. Daw Mob. Mg./kg. Days Mg./kg. PREPARED SAMPLES AND BLANKS. A number of blank tests 1 33.2 32 40 8 20.0 28 2 25.3 20 13 10.1 were made on 20-gram samples of beef heart and liver, the iodine values obtained ranging from 0.01 to 0.02 mg. of thalLITERATURE CITED lium. Prepared samples containing 0.5 mg. of thallium per 20 grams of meat were carried through the complete analysis (1) Baldeschwieler, E . L., IND.ENG.CHEM.,Anal. Ed., 4,101 (1932). (2) Fridli, R., Deut. 2. ges. gericht. Med., 15, 478 (1930). with errors of 1 to 5 per cent. G. H., Levine, Max, and Buchanan, J. H., IND.ENG. ILLUSTRATIVE RESULTSON GRAIN,URINE,AND TISSUES. (3) Nelson, CHEM.,Anal. Ed., 4,56 (1932). Thallium-coated wheat, prepared on the ratio of one pound (4) Noyes, A. A., Bray, W. C., and Spear, E . B., J. Am. Chem. SOC., 30, 515 (Procedure 65a), 517 (Procedure 65d) (1908). of thallium sulfate to 100 pounds of wheat, and thus containing 0.81 per cent of metallic thallium, was used for analysis. RECEIVED September 1, 1932. These experiments were carried out with Five analyses on individual kernels made by direct nitric the codperation of the Hooper Foundation for Medical Research, San Franacid oxidation gave values from 0.605 to 1.11 per cent, the cisco, Calif.
Microdetermination of Calcium in Sea Water PAUL L. KIRKAND ERIKG. MOBERG Division of Biochemistry, University of California Medical School, Berkeley, Calif., and Scripps Institution of Oceanography, La Jolla, Calif.
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OR many investigations in oceanography and marine
biology information concerning the calcium content of sea water is required. Previous workers have determined calcium in sea water by precipitating with oxalate, igniting, and weighing as the oxide. A summary of the results obtained is given by Thompson and Wright (C), who also determined the concentration of calcium in water from the Puget Sound and the Gulf of Alaska. They found that in these regions calcium bears a constant ratio to the chloride, and computations made from the data of other investigators indicated that this is the case also in other parts of the sea. It is especially noteworthy that 77 samples collected by the Challenger Expedition from various parts of the world and analyzed by Dittmar (1) gave an average calcium-chloride ratio but slightly higher than that obtained by Thompson and Wright. It thus appears that for most purposes the calcium content of normal sea water can be calculated with sufficient accuracy from the chlorinity or from some other easily determined component or property of the water directly related to the chlorinity. However, there is often need for determining calcium in connection with experimental studies
in which sea water is used and in investigating water from localities where calcium salts may be dissolved or precipitated. For many such investigations, which usually call for numerous analyses, the standard gravimetric method is too time-consuming and requires larger samples than are often available. For that reason the applicability to seawater analysis of the microcalcium method described by Kirk and Schmidt (8) was studied and it was found to give satisfactory results after certain modifications were made. Because of these modifications and because of the necessity for close attention to certain details, a rather detailed description of the technic finally adopted is given in this paper. Nearly all the chemical constituents of sea water vary with depth and this is true also of a number of factors which affect the solubility of calcium salts. By several workers calcium has been determined in water from various depths of the sea, but there is no record of a detailed study of its vertical distribution in any locality. After perfecting the analytical method, such a study was consequently made and the results, which also indicate the order of accuracy of the method, are included in this paper.
