equivalent of resin. This suggests that organic acids are not being solubilized merely by amine salt formation, but that other factors such as adsorption or bonding of some type i: involved. Solubility of the acid -resin salt in the solvent used may limit the amount of acid which can be sihbilized. For oxalic, citric, and tartaric acids, the solubility limit in CS2 is approximately 0.5 mole of acid per eqiivalent of resin at room temperature. Somewhat more can be dissolved in CHCl,; beyond this point the acid-resin s d t tends to precipitate out. The5e limiting factors may reduce maximum acid concentration, particularly in a mixture, to a 2oint where only the stronger peaks m e analytically useful. Although for most acids a sufficient amount can lie solubilized, it is apparent that in any analysis the approximate total acid concentration of the unknown solution, as well as of the standard solutions, mLst be known in advance and an aliquoi chosen EO as to bring total acidity within a range that can be satisfactorily solubilized. Beer’s Law. ;ibsorbance 2’s. concentration was studied for hydrochloric, nitric, sulfuric, perchloric, tartaric, succinic, oxalic, lactic, citric,
cyanoacetic, pyruvic, a n d trichloroacetic acids. T h e inorganic acids showed no appreciable deviations from Beer’s lau u p to the maximum concentration which could be solubilized. This was not true for the organic acids. For these acids there was no significant deviation from Beer’s law up to a point where approximately 1 equivalent of acid was bound per equivalent of resin; beyond this point some acids showed marked deviations, depending on the wavelength of the absorption band being used for analytical measurements. For organic acids, where concentration exceeds one equivalent of acid per equiralent of resin, i t is important to establish the limits within which Beer’s law is applicable a t the wavelength of analytical measurement. Reaction with Halide Plates. Rock salt or other halide plates are not suitable for analysis of strong inorganic acids. T h e resin salts of these acids tend t o form a precipitate on the surface of t h e plate. This appears t o be a n ion exchange phenomenon in which halide ions from t h e plate go into solution and acid anions from the resin salt precipitate out. For the analysis of strong acids, Irtran glass cells were used. These were very satisfactory. I n the case of organic acids
no precipitation was observed and rock salt cells can be used. Results obtained in the analysis of several synthetic mixtures are shown in Table I. The accuracy of the results varies according to whether or not analytical conditions are favorable. Although the procedure cannot be applied to all possible mixtures, there are many combinations of acids which can be easily and accurately analyzed. The procedure, where applicable, may have definite advantages in both speed and accuracy over conventional chemical methods. LITERATURE CITED
( 1 ) Coleman, C. F., Brown, X. B., Moore, J. G., Crouse, D. J., Znd. Eng. Chem. 30, 1756 (1958).
(2) Dolinsky, Meyer, Stein, Charles, . 4 N A I . . CHEM. 34, 127 (1962). ( 3 ) Kunin, R., Angew. Chem. Intern. Edition, 1, 149 (1962). ( 4 ) Rohm & Haae Co., Technical Notes, hmberlite LA-1, August 1958. ( 5 ) Smith, E. L., Page, J. E., J . SOC. Chem. Ind. (London) 6 7 , 48 (1948). MEYERT ~ O L I S S K Y
CLIFTON H. WILSON Division of Color and Cosmetic Chemistry Food and Drug Administration Department of Health, Education, and Welfare Washington, D. C.
Determinatioln of Nickel in Hydrogenated Fats by Neutron ,Activation Analysis SIR: Neutron activation analysis has been used b y a number of investigators for the qumtitative determination of nickel in a variety of materials. Nickel was determined in fission products (5) and in titanium metal and its compounds (4). Kickel was also determined in aluminum metal ( 2 ) . in NBS aluminum-base alloys (3),and in tobacco (9). As an extention of these studies, nickel was determined with neutron activation analysis in fats of various origins, hydrogenated and nonhydrogenated. Simple irradiation techniques and selective radiochemical separations were used. EXPERIMENTAL
Nuclear Reaction. On irradiating fats with neutrons, the following nuclear reaction is (3f interest for nickel determinations (8). Ni6‘ (1.16%) ( n , ~XiG5 ) 2.57 hours; u =
1600 f 200 barns
Counting Techniques for NiBSNuclide. Standard beta counting techniques were usually employed (1, 3, 4 , 7 ) . Gamma counting at discrete energies (1.19, 1.11, 0.37) has also been
employed, or gross gamma has been similarly counted. Reagents. Twenty milligram samples of nickel turnings (JohnsonMatthey spectrographically pure) were weighed; then they were irradiated for 5 hours in a neutron flux of 3.8 X 10” neutrons per sq. cm. per second, dissolved by several drops of 500/, (v./v.) nitric acid, and diluted to 1 liter. Procedure for Hydrogenated Fats. EXPERIMENTAL METHOD. With the assumption t h a t some inorganic form of nickel is found in hydrogenated fats, a nickel extraction was made. T h e extraction mixture consisted of toluene and 20% nitric acid with the fat appearing in t h e toluene layer and t h e nickel nitrate in the aqueous layer. Toluene was chosen as the suitable organic solvent because of its low solubility in water (6). T o investigate the chemical yield of Ki with the toluene-nitric acid eltraction, a synthetic experiment (10) was carried out using W5radiotracer and precipitating ?Ti as Xi-DMG (dimethylglgoxime), which was then counted. Comparison of counting rates u i t h those of an experiment done without the extraction step showed that both chemical yields were the same, approaching 100%. Experiments also carried out with carbon tetrachloride and benzene gave practically the same chemical yields.
Preparation of Samples to De Irradiated. Two 20-mg. quantities of Johnson-Matthey spectrographically pure Ni turnings were weighed in two polythene snap-closure tubes (d = 8 mm., h = 15 mm.) t o serve as standards. .A 2- to 3-gram quantity of melted hydrogenated fat was put into a polythene snap-closure tube (d = 15 mm., h = 60 mm.), which was then sintered. I n the usual standard positions one of the small tubes containing the standard was attached to the left side of the big tube and a t the level of the hydrogenated fat and the other to the right side and lower part of the big tube. A l l three tubes were put into a water-proof polythene bag. Irradiation Conditions. The targets were irradiated for 5 hours in a neutron flux of 3.8 X 10” neutrons per sq. cm. per second in the “Democritus” sn imming pool nuclear reactor. *ANALYTICAL PROCTXXJR-E. Nickel I’ptake by Fktraction. After irradiation the tube containing the fat waq opened, the fat mas melted, and both nere weighed together. An aliquot of about I gram of the melted fat was poured into a separator!. funnel containing 20 ml. of toluene, 15 ml. of H 2 0 , 4 ml. of roncentrated HSOa, I ml. of Si carrier (10 ma. of Ni per ml.) and the tube was reweighed. Thg same procedure was repeated in triplicate for the VOL. 36, NO. 7, JUNE 1964
1385
remaining fat. The separatory funnel was shaken for 3 minutes. After the separation of the two phases the aqueous phase was collected. The tolueiie phase was rinsed with a 10-ml. aliquot of 20% nitric acid. The washings were added to the first layer extracted. Isolation of Xi by Precipitation, Extraction. Back-Extraction. The aaueous solution was neutralized by ammonia solution until a p H value of 9 was obtained. The following hold-back carriers were then added: 1 ml. of NaCl (10 mg. of K a per ml.), 1 ml. of (”4)s AS04 (10 ml. of As per ml.), and 5 ml. of 20% potassium sodium tartrate. Standard precipitation of Ni as Ni-DMG was performed, and the Xi-DMG was then extracted in chloroform. The chloroform layer was collected. Another extraction step was carried out in the same aqueous solution. The two chloroform extracts were combined and nickel was back-extracted from chloroform using 2 N HCl. Back-extraction of Xi with 2N HCl was once again repeated in the former chloroform quantity. The two aqueous layers were combined. Isolation of Ki by Precipitation, Dissolution, Reprecipitation. The aqueous solution was adjusted t o a p H value of 9 using ammonia solution. Standard precipitation of Ni as Ni-DMG was carried out in the presence of the hold-back carriers and tartrate. The Ni-DMG precipitate was rinsed using hot holdback carriers (Na+, C1-, h + 5 ) and hot water. The Ni-DMG precipitate was dissolved using hot 4N HCl. After dissolution, the filtered solution was neutralized by ammonia solution and brought t o a p H value of 9; then a standard reprecipitation of Ni as NiD M G was performed in the presence of the same hold-back carriers and tartrate. The precipitate was filtered (IO)using a preweighed No. 50 Whatman filter paper (d = 26 mm.). The precipitate was rinsed in the same manner as before. The filter paper with the precipitate was dried, counted, and weighed t o determine the chemical yield, which was about 95% on the average. As for the two standards, the nickel turnings were transferred into two beakers where 2-ml. aliquots of 50% nitric acid were added and then heated until dissolution of the turnings. The two nickel nitrate solutions were transferred into two 1-liter volumetric flasks. Aliquots of 100 pl., taken from each volumetric flask (sampling in triplicate), were subjected t o the same analytical steps mentioned before. Control of the Analytical Procedure. Before the analytical procedures mentioned above were fixed, the different steps were investigated taking into considerhtion on the one hand the gamma spectrum of the isolated precipitaton of Ni-DMG and on the other hand its half-life value serving as the criterion of its radiochemical purity. After the elimination of nickel from the hydrogenated product by the extraction process described, precipitation of nickel as Ni-DMG, filtration, dissolution by means of 4N HC1, and reprecipitation of 1386
ANALYTICAL CHEMISTRY
Table 1.
Concentrations of Nickel in Fats
Sample Hydrogenated olive oil Animal fat and hydrogenated olive oil Mixed fat ( h dro genated fisi oil, seed oil, etc.) Olive oil Milk butter
Nickel, p.p.m. Extrac- Hvdroltion ysis 0.249
0.266
0.054
0.052
5.6 0,017 0.019
5.2 0.019 0.018
drawal from the reactor, the isolated precipitate of Xia5 was qualitatively examined by scintillation counting. The energy spectrum showed no indication of y-emitting radionuclide. To show that nickel uptake from hydrogenated fat was complete by this extraction method, a comparison was made with fixed extraction uptake by the classical hydrolysis method. The nickel values obtained by the extraction method were compared with those nickel values obtained by the hydrolysis method. The results on both occasions were the same (Table I). RESULTS AND DISCUSSION
Ni were carried out, without the holdback carriers. Gamma-spectrum examination of the precipitate indicated clearly the presence of Na2* and Cl3*. Addition of hold-back carriers S a + and C1- t o the solution and precipitation of Ni didn’t give evidence of Na and C1 presence in the y-spectrum. Examination of the half life and its evaluation by the method of least squares gave the value 2‘1’2 = 3.6 h. Because of this, the chloroform extraction step was added which lowered the half life t o T1j2 = 3.3 h. Investigation of the remaining contaminant gave the value of !PI2 = 26 h. The probable contaminant was As76, the presence of which was certified by a gamma-spectrum analysis performed on the irradiated hydrogenated product under investigation. -4ddition of As04+3 as a hold-back carrier and rinsing of the Ki-DMG precipitate with hot solutions of hold-back carriers Na+, C1-, and hot HzO assured radiochemical purity of the isolated precipitate of Ni-DMG. Radioactivity Measurements. The Ni-DMG precipitate was transferred t o an aluminum tray having an internal diameter of 26 mm., and a Xia5j3-count was made using a Geiger counter connected anticoincidently. Identification and Control of the Radiochemical Purity of XiB5. T o identify Ni65 and t o be assured of its radiochemical purity, in the isolated precipitates of Xi-DMG originating from two sources-the standard and the hydrogenated product-the following steps were taken. Determination of the half life of the isolated radioelement was carried out by plotting a decay curve on semilog paper for the isolated precipitate of Ni-DMG in both the standard and the hydrogenated product. The half life was obtained from the slope of the straight line, which was calculated by the method of least squares. A value of 2.58 hours with a standard error of *O.l hour was found instead of 2.57 hours reported in the literature. Gamma spectrometric examination of the isolated radioisotope was used to determine whether or not there is any y-emitting contaminant in the precipitate of Si65 isolated from the analyzed sample. This serves as an additional indication of the radiochemical purity of the Ni66. Thus, 2.5 hours after with-
Quantitative nickel data for hydrogenated and for nonhydrogenated fats have been obtained using both extraction and hydrolysis. The data have been tabulated in Table I. This method utilizes radiochemical separations resulting in striking purity of the isolated precipitate. Primary extractions and isolations of nickel result in the elimination of the hydrolysis method of nickel determination which is tedious and a t times gives erratic results due to incomplete hydrolysis or incomplete separation of the two phases. Experimental values are reproducible within a relative error less than 12’%. The sensitivity of this method reaches the value of p.p.m. if a higher neutron flux is used. ACKNOWLEDGMENT
The author is indebted t o his collaborator, C. G. Vitogiannis, for his valuable assistance, and to A. G. Vassilaki for her laboratory help. Thanks are also due to James van Luick for revision of the text. LITERATURE CITED
(1) Batzel, R. E., Miller, D. R., Seaborg, G. I., Phys. Rev. 84,671 (1951). (2) Brooksbank, W. A., Jr., U. S. At. Energy Comm. Rept. ORNL-2266,
pp. 27-31 (1956). (3) Brooksbank, W. A., Jr., Leddicotte, G. W., Dean, J. A., ANAL.CHEM.30, 1785 (1958). (4) Brooksbank, W. A., Jr., Leddicotte, G. W., Reynolds, S. A . , Ibid., 28, 1033 i\ _ 19.56\ ” _ _
( 5 ) Bu&us, W. H., in U. S. At. Energy Comm. Rept. LA-1721, J. Kleinberg, ed., pp. Ni 1-7 (1954). (6) Chemical Rubber Publishing Co.,
“Handbook of Chemistry and Physics,”
43rd ed., pp. 828, 912, 918, 1961-62. (7) Johnson, J. E., Hall, N. F., J. Am. Chem. Soc. 70, 2344 (1948). (8) Kirby, L. J., “The Radiochemistry of
US. At. Energy Comm. NAS-NS 3051, 2, 28-38 (1961). (9) Oak Ridge National Laboratory Rept. ORNL-3243. 67 (1962). (10) Souliotis,’A. G., ANAL.CHEW36, 811 (1964). Nickel,”
Suclear Research Center “Democritus’’ Chemistry Department Athens, Greece
A. G. SOULIOTIS
