ANALYTICAL EDITION
SEPTEMBER 15, 1935
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fate of the nitrogen after combustion was necessary. The hypothesis is advanced that the form in which the nitrogen appears after combustion is a function of the manner in which it is linked in the compound. It is suggested that, under the specific conditions of the combustion method used, all nitrogen compounds yield their nitrogen as nitric oxide and nitrogen, the ratio of these products, in case of amines and amides, being different from that obtained from nitriles, nitro-, and nitrogen-heterocyclic compounds. Experiments are now being carried out in order t o get further evidence in support of this hypothesis as well as to get some definite information as t o the mechanism by which lead peroxide absorbs oxides of nitrogen which are formed during the combustion of nitrogen-containing compounds.
(30) Lambris, G., Brennstpff-Chem., 6, 1-6 (1925); 8, 69-73, 89-93 (1927). (31) Lunde, G., Biochem. Z., 176, 157-64 (1926). (32) Meeker, E., and Wagner, E., IND.ENQ.CHEM.,Anal. Ed., 5, 396-8 (1933). (33) Merten, H., Mikrochemie, 6, 122-3 (1928). (34) Niederl, J. B., Z . anal. Chem., 89, 62 (1932). (35) Smith, R. C., and Howard, H. C., J . A m . Chem. Soc., 57, 512-16 (1935). (36) Stover, N., and Sandin, R., IND. ENG.CHEY., Anal. Ed., 3, 240-2 (1931). (37) Terres, E.,J. Gusbeleucht., 62, 173-7, 192-200 (1919). (38) Vetter, F., Mikrochemie, 10, 109-13 (1931). (39) Ibid., 10, 407-8 (1931). (40) Ibid., 12, 102-8 (1932). (41) Viebock, F., and Brecher, C., Bey., 63, 3207-10 (1930). (42) Winkler, L., 2. angew. Chem., 26, 231-2 (1913); 27, 630-2 (1914).
Summary
RECEIVED June 15, 1935. Presented before t h e Division of Physical and Inorganic Chemistry, Symposium on Recent Advances in Microchemicel Analysis, at the 80th Meeting of the American Chemical Society, New York, N. Y., April 22 t o 26, 1935.
The difficulties involved in the application of Pregl’s micromethods to the analysis of solid fuels are pointed out and the advantages of certain modifications, at present in use, are discussed. These modifications are necessitated by the unique physical and chemical characteristics of solid fuels which involve (1) their complex composition, (2) the low percentage of several of t h e constituents present, (3) the possibility of incomplete combustion of gaseous decomposition products, (4) the formation of highly combustion-resistant cokes, (5) their limited solubility in all solvents, and (6) the lack of a definite standard t o which analytical results can be compared. Still other modifications to existing methods are suggested, some of which are in process of investigation in the Coal Research Laboratory.
Titration of Fluorine in Biological Materials EUGENE W. SCOTT AND ALBERT L. HENNE Kettering Laboratory of Applied Physiology, University of Cincinnati, Cincinnati, Ohio
Literature Cited 411en, W., IND.ENQ.CHEM.,Anal. Ed., 3, 239-40 (1931). Baranov, A,, and Mott, R., Fuel, 3,31-4, 49-52 (1924). Beet, A. E., Iiid., 13, 343-5 (1934). Boetius, M., “Uber die Fehlerquellen bei der mikroanalytischen Bestimmung des Kohlen- und Wasserstoffes,” pp. 78-9, Berlin, Verlag Chemie, 1931. (5) Bornstein, E., and Petrick, A. J., Brennst0.f-Chem., 13, 41-5 (1932). (6) Bunte, H., and Schilling, E., J. Gusbeleucht., 30,707-15 (1887). (7) Carlile, J. H. G., J. Soc. Chem. Ind., 52,306T-8T (1933). (8) Clark, E. P., J. Assoc. Oficiul Agr. Chem., 15, 136-40 (1932). (9) Coombs, H., J . Soc. Chem. Ind., 53,311 (1934). (LO) Coufalik, F., Mitt. Kohlenforschungsinst. Prag, 3, 163-9 (1932). (11) Fieldner, A. C., and Taylor, C. A,, Bur. Mines, Tech. Paper 64 (1915). (12) Fleischer, H. C., “Die Stickstoffbestimmung in Kohle und Koks,” Sonderdruck aus dem Jahrbuch des Halleschen Verbandes fur die Erforschung der mitteldeutschen Bodenschntze und ihrer Verwertung, Erstes Heft, Halle (Saale), Wilhelm Knapp, 1919. (13) Foerster, F., Brennstof-Chem., 2, 33-4 (1921). (14) Friederich, A., “Die Praxis der quantitativen organischen Mikroanalyse,” pp. 75, Leipzig und Wien, Franz Deuticke, 1933. (15) Friederich, A., Ibid., pp. 20-53; iwikrochemie, 10, 329-54 (1931). (16) Friederich, A., 2. angew. Chem., 45, 476-8 (1932). (17) Friederich, A., and Watzlaweck, O., Z.anal. Chem., 89, 401-11 (1932). (18) Fritsche, W., Brennstof-Chem., 2, 365-7 (1921). (19) Funk, C., “Mikroanalyse nach der Micro-Dennstedt Methode,” Munchen, J. F. Bergmann, 1925. (20) Guillemet, R., Bull. soc. chim., 51,1611-15 (1932). (21) Haber, F., and Grinberg, A,, Z. anal. Chem., 36,557-67 (1897). (22) Herzig, J., and Faltis, F., Monatsh., 35,997-1020 (1914). (23) Hiinerbein, R., Brennstof-Chem., 4,337-8 (1923), (24) Iwamoto, K., Science Repts. Tohoku I m p . Univ., 17, 719-22 (1928). (25) Kirner, W. R., IXD. ENG.CHEM.,Anal. Ed., 5, 363-9 (1933). (26) Kirner, W. R., Ibid., 6, 358-63 (1934). (27) Kirner, W. R., unpublished paper. (28) Kopfer, F., 2. anal. Chem., 17, 1-53 (1878). (29) Kuhn, R., and Roth, H., Ber., 67, 1458 (1934). (1) (2) (3) (4)
F
LUORINE can be isolated from inorganic samples b y distillation as hydrofluosilicic acid ( 3 ) , and titrated in the distillate with cerium nitrate (1) in the presence of a mixed indicator (8). I n organic materials, the problem is somewhat complicated b y the necessity of ashing the samples without losing fluorine, and of obtaining the ash in such condition that the subsequent isolation and titration of the fluorine will not be interfered with. Fluorine in organic substances has been titrated before; a variety of elaborate and unreliable methods have been used and the results have always been inconsistent. As there are only minute amounts of fluorine in plant or animal tissues, the details of the chemical procedures become all-important. Therefore, standardized conditions for calcination, distillation, and titration are now presented, not on a basis of new principles but as simple and correct procedures which combine the desirable features of the various methods selected.
Preparation of the Samples The tissues obtained after necropsy are cleaned, washed, weighed, placed in individual containers, and kept in a refrigerator until ready for analysis. They are transferred to silica dishes, the containers are washed with hot water, the washings are transferred to the dish, and in the case of small samples, such as the heart, lungs, spleen, and kidneys, 50 to 100 cc. of a saturated solution of lime are added. To the large samples 2 to 15 grams of finely powdered calcium oxide are added, the amount depending on the size of the sample; to bones or teeth, no lime is added; to the liver of a guinea pig, 0.5 gram of lime is added; this is needed to prevent fusion on ashing, as well as loss of fluorine by volatilization. The samples are dried by keeping the dishes for several days on an electric heater at medium heat. The major part of fat-containing samples is burned by inserting s wick and igniting while on the hot plate. The dried samples are burned out in an electric muffle furnace at 600’ C. Teeth and bones require a higher temperature, 650’ to 700’ C. Liver samples fuse readily, unless a fairly large amount of lime has been added. Other samples do not fuse a t
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600" C., but in silica dishes may lose fluorine at a higher temperaTABLEI. ANALYSISOF PRECIPITATED CALCIUMFLUORIDE ture. The burning out is completed after 12 to 24 hours, exce t Fluorine found, mg. 3.54 2.80 2.44 in the case of teeth, which require 48 hours at 650" to 700" Fluorine calculated, mg. 3.46 2.87 2.48 After grinding in a mortar and weighing, the samples are ready for analysis. The large samples, such as bones, muscle, and reThe correction for blanks using thorium nitrate was estabmainders, are weighed before grinding. The actual weight of the ash is determined by subtracting the weight of the lime added lished b y the titration of sodium fluoride solutions without from the total weight. The ratio of the actual ash weight to the distillation, as shown in Table 11, and consequently a unitotal weight is used to calculate the amount of fluorine per gram of form 0'02-mg' correction 'was adopted. ash after determining the fluorine in the calcined sample. Ash samples weighing less than 1.5 grams are used in their entirety. OF A BLANK CORRECTIOX TABLE 11. ESTABLISHMENT
8.
Preaent, mg. 0 070 0 . 0 5 0 0 . 0 4 0 0 . 0 4 0 0 . 0 3 2 0 . 0 3 0 0 . 0 2 2 0 . 0 2 0 0 . 0 1 6 0 . 0 1 0 0 . 0 0 9 0.000 0.000 The long drying of the sample was Found,mg. 0 , 0 7 2 0 . 0 7 0 0 . 0 5 0 0 . 0 5 8 0 . 0 4 2 0 . 0 3 6 0 . 0 5 0 0 . 0 3 4 0 . 0 3 2 0 . 0 3 4 0 . 0 2 6 0.022 0.020 0 . 0 0 2 0.020 0 . 0 1 0 0 . 0 1 8 0 . 0 1 0 0.006 0 . 0 2 8 0 . 0 1 4 0 . 0 1 7 0 . 0 2 4 0 . 0 1 7 0.022 0.020 Difference necessary to avoid splatteringandlossof the sample when i.f,was placed in the The method itself was tested b y dividing the samples, mufle furnace. It was also found that samples containing measuring the fluorine content of one part, adding a known unoxidized carbon were difficult to distill and gave low reamount of calcium fluoride to the other, measuring its fluorine sults; consequently the ignition was carried out as completely content, and comparing the analytical results with computed as possible a t these temperatures. data. The results appear in Table 111. The ashed samples Isolation of the Fluorine used weighed from 1.0 to 1.5 grams. The ash is decomposed with perchloric acid and the fluorine is distilled off as hydrofluosilicic acid (3). The distillation apparatus consists of a 25-cc. round-bottomed flask with a neck 10 TABLE 111. ANALYSISOF ASHEDSAMPLESWITH ADDED cm. in length. A side arm is attached 4 cm. from the top of the FLUORINE neck, and is bent in an inverted U-shape to prevent contaminaFound Added Total Total in Ash as CaFz Calod. Found tion of the distillate by bumping. More elaborate trapping devices are inadvisable, because adsor tion causes fluorine deMQ. MQ. MQ. MQ. ficiencies. The side arm is connecte! by a ground joint to a Blood 0.55 3.43 3.98 3.99 small vertical condenser which delivers the distillate into a 125-cc. Erlenmeyer flask. The neck of the distilling flask carries a rubBone 0.12 3.65 3.77 3.70 ber stopper (which should be replaced after three operations), 0.29 4.72 5.01 4.93 fitted with a thermometer and the capillary stem (2 to 3 mm.) Liver 0 . 2 7 3 . 2 3 3 . 5 0 3 .58 of a dropping funnel. Both the thermometer and capillary extend to within 5 mm. of the flask bottom. The flask is mounted Muscle 0.14 5.01 5.15 5.12 over the 2-cm. hole of an asbestos pad and is heated by a micro0.14 4.77 4.91 4.90 0.24 2.97 3.21 3.16 burner. Fastened by small clamps to a single ringstand, this device makes a fairly compact unit. Oats 0.10 1.22 1.32 1.30 An accurately weighed sample of ash (1.0 to 1.5 grams) is 0.10 2.97 3.07 2.92 placed in the flask, with 3 cc. of water and several small pieces Teeth 0.14 1.12 1.26 1.26 of silicon carbide. The rubber stopper, condenser, and receiver 0.15 0.92 1.07 1.14 are attached. Enough water is placed in the receiver to permit 0.40 0.78 1.18 1.17 0.40 a 5-mm. immersion of the condenser tip during the first 5 minutes 0 78 1.18 1.01 of the distillation. Five cubic centimeters of 60 per cent perchloric acid are fed through the funnel. The heating is started and when the liquid temperature reaches 135" C., 50 to 75 CC. of Discussion water are slowly dropped from the funnel to compensate for the water distilling out, and to maintain the temperature at 135" The titration proposed b y Willard and Winter, using small C. (Small triangular grooves cut on opposite sides of the stopamounts of fluorine, was unsatisfactory in the authors' hands. cock of the dropping funnel improve the regulation of the water flow and hence the constancy of the temperature.) For small The above method gives a sharp end point and the results on amounts of fluorine, 50 cc. should be distilled; for larger amounts, solutions of known fluorine content (0.03 to 5.0 mg.) could be 75 cc. are needed. The distillation requires constant supervision duplicated with only small errors. It is inadvisable to allow the and takes from 45 to 90 minutes. The fluorine content of the lime used (Merck's reagent temperature to rise above 140" C. quality) was too slight t o affect the titration appreciably. Titration of the Fluorine The amount of lime in any of the ashed samples used was The condenser is detached and washed with a jet of water, never over 40 per cent of t h e total weight. Analysis of 10 which is added to the distillate. Several drops of 0.04 per cent grams of the lime gave a fluorine concentration of 0.0019 phenol red solution are added, and the liquid is neutralized with per cent. dilute sodium hydroxide, avoiding a large excess. The alkaline solution is boiled and re eatedly brought back to the apparent neutral point with 0.02 ??or 0.01 N perchloric acid. During this Summary neutralization, the volume is reduced to 5 to 10 cc. When the faint pink color is no longer restored by boiling (carbonate-free), A standard procedure has been given for ashing plant and the solution is cooled, transferred quantitatively to a 50-CC. animal tissues for the volatilization of the fluorine present by beaker, and boiled from about 25 cc. down to 2 to 3 CC. Two distillation with perchloric acid and for the titration of this drops of saturated alcoholic solution of methyl red and 10 drops of 0.04 per cent bromocresol green solution are added. (The fluorine with cerous nitrate or thorium nitrate. Amounts bromocresol green is weighed out exactly and neutralized with of fluorine as low as 0.02 mg. may be determined. standard sodium hydroxide to yield the monosodium salt. This prevents alteration of the neutrality of the solution when the indicator is added.) The liquor is titrated at 80" C. to the maximum Literature Cited red color with cerous nitrate solution (1 cc. 2 0.5 mg. of fluorine). When the amount of fluorine is less than 0.2 mg., thorium nitrate (1) Batchelder, George, and Meloche, V. W., J. Am. Chem. SOC.,53, solution (1 cc. 2 0.1 mg. of fluorine) may be substituted for the 2131-6 (1931). cerous nitrate, using the same mixed indicator. (2) Hubbard, D. M.,and Henne, A. L., Ibid., 56, 1078-80 (1934)..
Results Calcium fluoride was prepared and analyzed with the results shown in Table I.
(3) Willard, H . H., and Winter, 0.B., IND.ENQ.CHBM.,Anal. Ed.,. 5, 7-10 (1933). RECEIVED February 20, 1935.
