reaction between the fluoride ion and glass, the NMR tubes were coated with Araldite (Hysol Canada, Ltd.). Spectra were obtained using a Varian HA-60 spectrometer with frequency sweep and internal lock operating at 56.4 MHz. An external standard of CF,COOH was contained in a polyethylene capillary. Probe temperature was 32” i 1’C. DISCUSSION
Several methods can be used to determine H20-D20 mixtures. Gravimetric analysis can give results accurate to 0.01 deuterium. Optical spectrometry cannot be applied to this problem in a simple way because broad bands are observed. By calibration an accuracy of 5 % is a realistic limit for this method. Water and alcohol present special problems in determination of deuterium content by mass spectrometry. Exchange processes in the apparatus tend to falsify the results by introducing additional hydrogen. With special precaution, water can be analyzed directly with an accuracy of 0.3% (5, 6). Normally it is recommended to convert water to hydrogen gas before the determination. This method is accurate although errors may arise from the conversion. Integrated intensities in NMR (7) have been employed. Because only one component is observed, careful calibration is necessary and the accuracy is approximately 2 %. Measure(5) H. H. Krause and 0.H. Johnson, ANAL.CHEM., 25,130 (1953). (6) €3. W. Thomas, Zbid.,22, 1476 (1950). (7) J. A. Pople, W. G. Schneider, and H. J. Bernstein, High Resolu-
tion Nuclear Magnetic Resonance, McGraw-Hill, New York, 1959, p. 458.
ment of IH resonance signal amplitudes (8) has been used to determine H2O concentrations in heavy water. It is assumed in this method that the peak height is directly proportional to proton concentration, which is only strictly correct if there are no changes in the nuclear spin relaxation times. This method is capable of an accuracy of 0.1 %. The analysis involves a series of precise dilutions of the unknown mixture with small amounts of water. Extrapolation of the plot of signal amplitude against added HzO to zero signal gives the amount of HzO initially present. This method is more laborious and time-consuming than that presented in this paper. The method reported here is, in its present form, comparable in accuracy to most of the other techniques previously used. At higher magnetic fields, the observed ‘9F chemical shift will correspond to a larger number of Hz and, provided that the line width remains unchanged, the overall accuracy of the determination will be improved. An additional advantage of the proposed technique is the rapidity with which determinations of heavy water-water mixtures can be made once initial adjustments of ‘9FNMR spectrometer have been made. The method is, therefore, well suited to standard operation for repetitive analyses. The quantity of sample employed, approximately 0.5 mi, is sufficient to reduce errors which may arise from contamination by HzO during transfer operations to below the experimental accuracy. RECEIVED for review July 3, 1967. Accepted September 25, 1967. (8) “N.M.R. at Work,” No. 57, Varian Associates.
ination of Radioiron Using Benzene Sulfi nic Acid Richard €3. Hahn and Saadia Ibrihirn Allarnl Chemistry Department, Wayne State University, Detroit, Mich, 48202
INA RADIOCHEMICAL ANALYSIS, it is usually necessary to isolate the desired radionuclide and its added isotopic carrier in a pure, weighable form for counting. Many procedures for radioiron recommend the precipitation of ferric hydroxide followed by ignition to the oxide for weighing ( I ) . The filtration of ferric hydroxide is difficult and ignition to the oxide is time consuming. The following study was made to find a form in which iron might be precipitated and weighed directly. There are relatively few forms suitable for direct weighing of iron. Gilmore ( 2 ) recommends plating metallic iron on a platinum disk. This method was tried, but erratic recoveries were obtained owing to the partial oxidation of the iron by air prior to weighing. Oxine (8-hydroxyquinoline) precipitates insoluble Fe(CgHeON)3 from acetic acid-acetate buffered solutions. The iron(II1) oxinate is dried at 120” C Present address, Atomic Energy Laboratory, Cairo, Egypt, U.A.R. (1) J. M. Nielsen, “The Radiochemistry of Iron,” National Academy of Science, Nuclear Science Series NAS-NS-3017, Washington, D. C., 1960. (2) J. S. Gilmore, U.S.A.E.C.Rept. No. LA-1721 (1954).
1880
0
ANALYTICAL CHEMISTRY
for weighing (3). This compound is not very good for a radiochemical analysis because many other ions are precipitated by the reagent and the precipitate is bulky and therefore undesirable for counting purposes. Thomas ( 4 ) reported that benzene sulfinic acid reacts with iron(II1) salts to form a precipitate which is insoluble in dilute mineral acids. The compound is iron(II1) benzene sulfinate, Fe(C6H5SOs),and is stable at temperatures up to 130” C (5). Preliminary experiments showed that iron(II1) benzene sulfinate forms a dense precipitate which can be easily filtered, washed, dried, and weighed in a form which is suitable either for beta or gamma counting. EXPERIMENTAL
Apparatus. Beta activity was measured using, an end= window Geiger tube of the halogen quenched type and scaler. Gamma activity was measured using a 2 X 2-inch well type sodium iodide scintillation detector and scaler. (3) Frank Welcher, “Organic Analytical Reagents,” Van Nostrand, New York, 1947, Vol. I, p. 308. (4) J. Thomas,J. Chem. SOC.,95,342 (1909). (5) Frank Welcher, “Organic Analytical Reagents,” Van Nostrand, New York, 1947, Vol. IV, p. 202.
Reagents. The sodium salt of benzene sulfinic acid (Eastman Kodak No, 3785) was used. Four grams of the reagent are dissolved in 100 ml of distilled water. The iron carrier was prepared as follows. Dissolve 48 grams of chemically pure ferric chloride, FeC13 6Hn0, in 100 ml of 0.1M hydrochloric acid, then dilute to 1 liter with distilled water. This solution contains approximately 10 mg Fe(II1) per ml. It is standardized by taking a measured aliquot, reducing with stannous chloride followed by titration with standard potassium dichromate (6). Other reagents were prepared from reagent grade chemicals. Radioisotopes. These were purchased from the Isotopes Division of the Oak Ridge National Laboratory and were diluted with 0.1M hydrochloric acid to counting range. 65jFe-5gFetracer was used to study radiochemical recoveries and its activity was measured using a well-type sodium iodide scintillation detector. Beta activity of isotopes such as 9Y3r-90U were measured using a mica end-window Geiger tube and scaler. Procedure. Pipet a known volume (1.0-25.0 ml) of the solution to be analyzed into a 40-ml centrifuge tube. Add 2.0 ml of a standard ferric chloride solution, then adjust the acidity to approximately 0.1M in acid using ammonium hydroxide or hydrochloric acid as necessary. Heat the tube and contents to approximately 50” C in a water bath, add 15 ml of sodium benzene sulfinate reagent, stir thoroughly, then digest at 70” C for approximately 10 minutes. Remove the tube from the bath and let stand for approximately 15 minutes, then filter by suction onto a weighed filter paper disk in a filter ‘‘chimney’’ or Hirsch funnel. Wash with three 2-ml portions of 0.1M hydrochloric acid. Dry for 1 hour at 110” C, then weigh asiron(II1) benzenesulfinate. Transfer to a tube, then gamma count. Correct count for gravimetric recovery. The procedure was tested by taking known amounts of 56Fe-69Fetracer and carrying out the analysis. These results are summarized in Table I. A second series was run in which iron benzene sulfinate was filtered through filter paper, then ignited to ferric oxide for weighing and counting. The results of these analyses are given in Table 11. The above data show quantitative recoveries of both iron carrier and activity are attained when the iron(II1) benzene sulfinate precipitate is filtered through filter paper followed by ignition to the oxide. Slight losses of the carrier occur when the iron(II1) benzene sulfinate precipitate is weighed directly. These slight losses occur on filtering and transferring the precipitates from filter paper disks. When corrected for carrier losses, 100% of the added j5-59Fe activity is recovered. To test for interferences, known counts of other activities were added, the procedure was carried through, and the final iron benzene sulfinate precipitate counted. The following radionuclides caused no interference, the number of counts in the final precipitate being less than background A2 a: ?BAS, Iz4Sb, Il5Cd, W a , 51Cr, W o , 192Ir, g9Mo, 63Ni, IOeRu, 9oSr, 204 TI, and B6Zn. Serious interference was encountered
with 1d4Ce and 96Zr-g5NNb where greater than 90% of the activity was carried down on iron benzene sulfinate precipitate. The radioisotopes used in the above studies were either carrier free or of high specific activity; the one lowest specific activity was 90Mo which was 10 mCi per gram of Mo. Effect of Acid Concentration and Other Cations and Anions, Precipitation of iron benzene sulfinate was studied at various concentrations of hydrochloric acid. Quantitative recoveries of carrier were obtained in solution 0.001M-0.1OM. Increasingly lower recoveries were obtained as the acid concentration was increased. At 0.3M acid, 94 % of the iron carrier was recovered, while at l.0M acid only 65% was recovered. As the concentration of acid was lowered below O.lM, foreign activities such as lZ4Sbwere carried down on the iron benzene sulfinate. Optimum results were obtained in the range 0.05M to 2.OM acid. Aluminum, cerium, thorium, tin, titanium, uranium, and zirconium also are precipitated by benzene sulfinic acid (6), and therefore should be absent from the solution. The common anions, such as acetate, chloride, bromide, nitrate, and sulfate do not interfere. Strong oxidizing and reducing agents must be absent because they could oxidize the organic reagent or reduce iron(II1) to iron(I1) and thus interfere. Anions, such as fluoride, which complex iron(II1) likewise must be absent.
(6) “Scotts Standard Methods of Analysis,” N. H. Furman, Ed., 5th ed., Van Nostrand, New York, 1939, Vol. I, p. 473.
RECEIVED for review May 25, 1967. Accepted September 27, 1967.
Table I. Determination of Radioiron as Iron(II1) Benzene Sulfinate in Six Samples Carrier Activity Corrected Activity recovered,a observed, activity,b recovered, CPm cpm 94.67 30,690 32,419 100.02 95.64 31,000 32,413 100.00 94.77 30,720 32,416 100.01 99.95 32,395 32,412 99.99 94.74 31,680 32,411 99.99 99.44 32,231 32,414 100.00 a 19.50 mg Fe(II1) carrier added to each sample. 32,414 cpm 65Fe-59Feadded to each sample.
z
z
Table 11. Determination of Radioiron as Ferric Oxide in Six Samples Carrier Activity Corrected Activity recovered,a observed, activity,b recovered, CPm CPm 100.02 31,202 31,202 100.0 99.94 31,180 31,199 100.0 100.05 31,220 31,220 100.1 100.00 31,198 100.0 31,198 100.05 31,209 31,209 100.1 100.00 31,201 31,201 100.0 a 19.51 mg Fe(II1) carrier added to each sample. 31,200 cpm 55Fe-58Feadded to each sample.
z
z
VOL. 39, NO. 14, DECEMBER 1967
1881
