Table VIII. Determination of Magnesium in Various Water Samples
Source
Mg found, p.p.m. VolumetSpectroric~ photometric
37.8 Iowa State University (Tap) Ames, Iowa, 4.62 Municiual (Tap) Ames, Iowa 37.1 Municipal (Untreated)b Duluth, 2 86 Minn..
38.4, 38.0, 36.6, 3 i . 9 (Av. 37.7) 4.52, 4.53, 4 45, 4 48 (Av. 4 48) 37 0, 37.3, 37.0 (Av. 37.1) 2.73, 2.70, 2.85, (Av. 2.79)
a Calculated w difference between calcium plus magnesium and calcium only (2, 4 ) . b Analyzed for iron by method of Collins, Diehl, and Smith ( 1 ) and found to contain 6.7 p.p.m. Samples contained virtually no iron.
photometric calibration curves prepared at various concentrations of calcium are given in Figure 12. The effects of several ions on the determination of magnesium are summarized in Table 1711. The hydrosulfite reduction of iron was not satisfactory in the spectrophotometric procedure as it introduced considerable uncertainty in the p H . Application to Municipal Water Supplies. Several water samples were analyzed according t o the procedure above and by the conventional ethylenedianiinetetraacetate titration for comparison (4),The results are summarized in Table VIII. Because of superior sensitivity and less critical adjustment of conditions, the fluorometric procedure would be the one of choice. The spectrophotometric procedure can, however, be successfully applied to many situations if a fluorometer is not available. The analysis of natural or treated water as was described above is one illustration. It would be expected that either procedure could be adapted for
the analysis of numerous biological materials also. LITERATURE CITED
(1) Collins, P. F., Diehl, H., Smith, G. F., ANAL.CHEM.31, 1862 (1959). (2) Diehl, H., Ellingboe, J. L., Ibid., 28, 882 (19561. ( 3 ) Diehlj H., Ellingboe, J. L., Ibid., 32, 1120 (1960). (4) Diehl, H., Goets, C. A., Hach, C. C., J. Am. Water Works Assoc. 42, 40 (1950). ( 5 ) Ellingboe, J. L., Chelate Ring Derivatives of Azo Dyes, Ph.D. Thesis, Iowa State University of Science and Technology, Ames, Iowa, 1956. (6) Freeman, D. C., White, C. E., J. Org. Chem. 21, 379 (1956). (7) Olsen, R. L., Diehl, H., ANAL.CHEM. 35. 1142 (19631. (8) %’illstat&, R., Benz, M., Rer. Deut. Chem. Ges. 39, 3492 (1905). RECEIVED for review December 13, 1962. Accepted May 22, 1963. This work was supported by The Kational Science Foundation Grant NSF-G10012, and an E. I. du Pont de Semours and Co. Post Graduate Teaching Assistantship, held by Mr. Olsen, 1961-62.
Determination of Micro Amounts of Calcium in Potassium Chloride by Neutron Activation Analysis F. W. E. STRELOW’ and HEINRICH STARK lnsfifufe of Radiochemisfry, Technische Hochschule, Munich, Germany
b A method for the determination of microgram amounts of calcium in alkali halides using neutron activation analysis was developed and applied to the determination of calcium in a number of samples of potassium chloride The determination was done by measuring the activity of the scandium-49, daughter of calcium-49. Radiochemically pure scandium was separated from large quantities of other radioisotopes b y a procedure consisting of a hydroxide precipitation, a chromatographic ion exchange separation, a thenoyl trifluoroacetone complex extraction, and a final hydroxide precipitation. The separation procedure takes about 2 hours. About 0.5 pg. of calcium or more can b e determined with satisfactory accuracy. Ion exchange elution curves, decay curves for the separated scandium-49, and experimental data for the hydroxide precipitation and the liquid-liquid extraction steps are given.
T
HE s m s i T I v I w of the direct spectrographic determination of calcium in alkali halides is limited by interference from the large amount of alkali
11.54 *
ANALYTICAL CHEMISTRY
metals present. Preliminary separations are likely to introduce too much calcium when the total amount of calcium present is of the order of a few micrograms. ,4polarographic method for the determination of about 10 fig. t o 1 mg. of calcium in alkali halides has been described by Trnka (IO). Errors are claimed to be less than 10%. Some spectrophotometric methods for the determination of small amounts of calcium have been described (2, 5, 8, 11, 16). However, these are either not sufficiently sensitive or are disturbed by interference from other elements. .4nderson, Wiley, and Hendricks(1) have published some results on the determination of trace metals in potassium chloride and potassium bromide using neutron activation analysis. Nothing except the remark ‘‘less than 0.1 p.p.m.” is given about calcium. For the determination of calcium by neutron activation, either the Ca44 isotope (2.01y0 abundance and 0.67 barn cross section) or the Ca*3 isotope (0.16yo abundance and 1.1 barn cross section) can be employed. Some activation data are given in Table I. Because of the long half life of Ca”, high neutron doses are necessary for
the activation of Ca44. Generally, one would prefer low neutron doses and short time activation, a s has been pointed out by Meinke (‘7). But, the use of the short-lived Ca49 activity (8.8 minutes) would require automatic irradiation facilities and a very fast separation of calcium from the high alkali and halogen activities which would, by random coincidence, interfere with the radiometric determination of the calcium. Baumgartner (3) has already pointed out that the determination of calcium can be accomplished by making use of the 57-minute Sc49 daughter of Ca49. TVanke (14), and Kemp and Smales (6) have described procedures for the radiochemical separation of scandium from rocks and meteorites. These procedures are too time consuming for the separation of the relatively short-lived Sc49activity. It thus remained to devise and test a method for the separation of radiochemical, sufficiently-pure scandium with a separation time not exceeding 1 The first author was a guest worker from the South African Council for Scientific and Industrial Research, Pretoria, South Africa.
about 2 or 3 half iives. A procedure consisting of a coprecipitation of carrier-free scandium with hydrous ferric oxide, a cation exchange separation, a thenoyl trifluoroscetone extraction, and a precipitation as hydroxide with scandium carrier wtis investigated, applied to potassium, and was very satisfactory. EXPERIMENTAL
Reagents and .Apparatus. Scandium oxide, 99.95530 pure, and TTA were provided by Th. Schuchardt G M B H , Munich, Germany. Samarium oxide of 99.9% purity was provided by Rasmus and Co., Hamburg, Germany. Analytical grade reagents were used whenever possible. Hydroxide Precipitation. Coprecipitation with hydrous ferric oxide using ammonium hydroxide as a precipitant was used as a first step to separate scandium. from the large chloride and alkali activities. Precipitation of hydr0.m ferric oxide was carried out behind lead shielding in a precipitation beaker according to Schwartz-BergkampE (IS). This consisted of a flat-bottomed, closed, glass vessel of about 100-ml. capacity fitted with two side-arms (2 cm. wide and 2 to 3 em. long) a t opplisite positions a t the upper rim of the vessel. The side-arms made an angle of about 45 degrees with the vertical. One side-arm was fitted with a fused-in-sintered-glass filter of KO.4 porosity and 20-mm. diameter. This arm was drawn out into a narrow opening of about :I-mm. diameter so that a plastic tube could be attached. The other side-arm 'was fitted with a B 14 ground-glass cont!. Hydroxide precipitation is a standard procedure used in inost radiochemical rare earth separations. However, because scandium is amphoteric, forming a scandate anion ( I ; ? ) in strong alkalis and also capable of forming soluble hexamino scandiurr cations (22) in excess of ammonia, the chemical scandium yield using different conditions for precipitation was in,iestigated. To 40 ml. of about 0.02N hydrochloric acid were added :ibout 1 gram of ammonium chloride, 1 gram of potassium chloride, 10 drops of 0.1% bromocresol purple : n ethanol, 5.2 mg. of Fe(1II) as the chloride, 1 ml. of carrier-free scandium-46 activity (84 days' half life) and, in some cases, 4.1 mg. of scandium car:*ier as the chloride. One milliliter of the solution was then taken and kept for counting. The bulk solution was brought, to boiling and the insoluble hydroxides were precipitated by the addition of ammonium hydroxide. After boiling for 1 minute, the solution was filtered and 1 mI. of the filtrate was taken for counting in a sodium iodide crystal borehole counter. The results are presented in Table 11. They seem to indicate that, especially a t higher p€I value:;, better recoveries of scandium are azhieved when the scandium carrier is omitted. Furthermore, a precipitate consisting mainly of hydrous ferric oxidr! is more easy to filter and to wash than a precipitate
Table 1.
Activation Data"
Activity in mc. per gram Half life 10 min. 100 min. 10 days 153 days 0.69 x lo-* 0.69 x 10-2 1.0 1.56 8.8 min. 2.86 2.86 sc49 57 min. 0.98 x lo-' 1.85 2.86 ClJ7 c1a 42.3 37.3 min. 213 252 a 3 6 87 days 1.48 X lo-* s35 1.48 X lo-' 20.2 c1* P32 1.92 x 10-3 14.2 davs 1.92 .X. 10-2 2.2 K41 K42 12.5 h o b 1.04 10 112 Abstracted from (S). The activities refer t o a thermic neutron flux of 4 X 1012 neutrons per sq. cm. per second (cone side of Forschungsreactor Munchen, Germany) Irradiated isotope Product Ca" Ca46 Ca49 Ca48
Table 11. Fe( 1,II) carrier, mg. 5.2 5.2 5.2 5.2 5.2
s:
carrier, mg. 4.1 4.1
nil nil nil
Precipitation of Scandium Hydroxide Counts/min. Countsjmin. Final ml. before ml. in PH precipitation filtrate 8.5 7163 269 7.2 7163 39 7.2 7163 3.i 8.5 5840 18 9.5 5840 19
containing larger amounts of scandium. ;\s the recovery of scandium with hy-
drous ferric oxide carrier mas better than 99%, it was decided to add the scandium carrier only after the first hydroxide precipitation, but before the ion exchange separation. Ion Exchange Separation. Scandium was purified from residual alkali, halogen, and sulfate activities by cation exchange on a column. The large amount of P3* activity which originates from C135by (n, CY) reaction and quantitatively accompanies the scandium through the hydroxide precipitation is simultaneously separated. This is a great advantage as phosphate would partly accompany the scandium through the following thenoyl trifluoroacetone separation step. Cabell (4) has described a cation exchange method for the separation of calcium and scandium as occurring in neutron irradiation products. Yet his work is of a more qualitative and preparative character. He presents a curve for the distribution of scandium against hydrochloric acid concentration, but the distributions were determined for very small amounts of scandium. Considerably lower dibtribution coefficients have to be expected for milligram amounts of Ecandium than those given by Cabell (4). Cons?quently, scandium will appear earlier in the eluate when larger amounts are present. Therefore, elution curves for 4.1 mg. of scandium using 1.0, 1.5, 2.0, and 3.ON hydrochloric acid as eluent were prepared. Five grams of oven-dried (105" C.) Dowex 50x8, 100 to 200 mesh, resin in the hydrogen form were weighed out and slurried into a polyethylene column fitted with a sintered-glass filter plate of 1-cm. diameter and porosity No. 2 and drawn out to a tip a t the lower end. The resin column was 14.8 em. in length and 0.9 cm. in diameter. The resin was purified by passing 200
Per cent recovery 96.2 99.5 99.5 99.7 99.7
ml. of 5N hydrochloric acid through the column follon-ed by 50 ml. of water. Five milliliters of solution containing 4.1 mg. of scandium as the nitrate and 2 ml. of Sc46 activity were mixed and washed on to the column with 0.1N hydrochloric acid, and the scandium was then eluted a t a flow rate of about 1.0 ml. per minute using hydrochloric acid of the appropriate concentration. Fractions of the eluate were collected using a "Fractomat Y-2" automatic fractionator obtained from K. Haiss, Jungingen (Hohenzollern), and the yactivity of the Sc-4G of the fractions was counted using a 1.5' X 2' sodium iodide crystal borehole counter. The elution curves are given in Figure 1. From these curves i t was decided to elute the alkalis, sulfate, phosphate, and the halogens with liv hydrochloric acid. About 3N hydrochloric acid seemed to be the most favorable concentration for the elution of scandium. As a next step, the ion exchange elution curve of scandium and the radioactive isotopes from 1 gram of irradiated potassium chloride mere inyestigated. The column size was decreased to l .5 grams of dry resin, and the flow rate was increased to 3.5 ml. per minute. Column preparation and absorption of the sample were done as described above, but 0.5iV hydrochloric acid was used to wash the sample onto the resin. The alkalis and the anions were eluted with 1N hydrochloric acid and the scandium with 3147 acid. Portions of 20 drops were taken on large aluminium planchets a t 5-nil. intervals. The acid was neutralized with ammonia, the solution was dried under an infrared lamp, and the residue was counted using a 2 r-methane flow counter with a 0.8 nig. per sq. em. gold end-window. The experimental elution curve is presented in Figure 2. The curve indicates that the alkalis and anions can be quantitatively eluted VOL. 35, NO. 9, AUGUST 1963
e
1155
I
ml, eluate. Figure 1. Elution curves for scandium with hydrochloric acid of various concentrations as eluent Columns of Dowex 50x8, 100 to 200 mesh, resin. length 14.8 cm.; diameter 0.9 cm.; flow rate 1 .O ml. p e r minute 3.ON HCI 0-0-0 2.ON HCI X-X-X 1.5N HCl A-A-A 1 .ON HCI No Sc preseni in flrrt 400 ml.
from the column with about 100 ml. of 1N hydrochloric acid. The second small peak could be due either to calcium or to manganese or another divalent heavy metal cation of high neutron capture cross section which could be present in small traces in the potassium chloride. When a 1.5-gram resin column is used, more than 95% of the scandium is eluted by 60 ml. of 3N hydrochloric acid. Thereby the time required for the ion exchange separation of scandium with the absorption step included is reduced to about 50 to 60 minutes.
expect the same kind of behavior for the extraction into hexone. Samarium, because of i B large neutron capture cross section, is the rare earth most likely to interfere with the scandium determination. For this reason, the TTA extraction of samarium was also studied. Five milliliters of scandium carrier solution containing 4.1 mg. of scandium and 1 ml. of S C ' ~activity were pipetted
into a separation funnel. Measured amounts of 1N hydrochloric acid and distilled water were added to give a 50-ml. solution of the desired pH value. One milliliter of the solution was taken and kept for counting. Then 10 ml. of 0.2M TTA in hexone were added and the solution was shaken for 2 to 3 minutes. After the phases had separated, l ml. of each phase was pipetted out and counted. A similar procedure was applied for samarium, using Sm153 as radioactive tracer. The results are presented in Table 111. Further experiments indicated that the extraction of scandium is depressed by the presence of large amounts of ammonium chloride, while the presence of even a few milligrams of ferric iron seems to enhance the extraction of both scandium m d samarium considerably. From the results given in Table 111, it was decided to use extraction a t pH 2 for the separation of scandium. The TTA complexes of calcium, strontium, and barium are much less stable than those of the rare earths. Thus. these elements are not extracted a t pH values below 5 or 6. ANALYSIS OF IRRADIATED POTASSIUM CHLORIDE
As a result of the foregoing investigation, a method for the determination of microgram amounts of calcium in potassium chloride and other alkali halogenides was elaborated. This method was applied to the determination of calcium in potassium chloride of A.R. quality and a number of synthetic potassium chloride samples containing different amounts of c d cium.
15,000
Thenoyl Trifluoroacetone Extraction (TTA). Barium, strontium, and calcium are not quantitatively separated from scandium by the described ion exchange procedure. T o separate these elements and to further redurr other residual radiochemical impurities, a separation of scandium by extraction as TTA complex at a low p H value and back-extraction into 2 N hydrochloric acid was considered. Sheperd and Meinke (9) have compiled an excellent survey of pH dependent eytraction curves of the TTA complexes of metals into benzene. We preferred extraction into methyl-isobutyl-ketone (hexone) because it provides a faster and a smoother separation of the two phases. Furthermore, the distribution coefficients for scandium a t pH values between l and 2 seemed to be slightly higher when hexone was used. The curves of Sheperd and hleinke (9) show that the scandium complex of TTA is extracted into benzene a t a considerably lower pH value than tho-e of the other rare earths. This is explained by the considerably higher stability of the scandium TTA complex I t therefore seemed to be reasonable to 1 156
ANALYTICAL CHEMISTRY
sc+?+
!'olooo
1
Figure 2. Elution curve for irradiation products from 1 gram of irradiated potassium chloride after Fe(OH)s precipitation plus Sc46 tracer and 4.1 mg. of scandium as carrier Column of Dowex 5 0 x 8 , 100 to 200 mesh, resin. ml. per minute
length 4.7 cm.; diameter 0.9 cm.; flow rate 3.5
About 1 to 5 gramai of potassium chloride were weighed out accurately in a polyethylene bottle. A desired amount of standard crtlcium solution was measured out and added with a microsyringe. The sample wm irradiated for 1.5 to 2 hours a t a neutron 0ux of about 5 X 10" neutrons per sq. cm. It was left standing for about 45 minutes to reduce ihe high initial Cl@activity. Even aftor this time the activity was of the order of a few hundred millicuries of yradiation, and the sample had to be handled behind lead shielding. It was quantitatively transferred into the precipitation apparatus described above and the plastic bottle was washed out five to six times with small amounts of warm distilled water. Enough warm distilled water was added to bring the total volume to about 50 ml. Ten drops of 0.1% bromocresol purple in ethanol and 5 mg. of fe-ric iron carrier were added, and the solution was warmed to about 80" C on an electric hot-plate while it was xtirred magnetically. Hydrous ferric oxide was precipitated by the addition of 1 ml. of about 1N ammonium hydroxide, and the solution was kept a t about 80" C. for about 5 minutes. The precipitate was then separated by filtration through the sintered glass filter while the precipitation vessel was s owly inverted. Water-pump suction wa3 applied. The highly active filtrate wa3 collccted in a wash bottle covered by lead shielding. The precipitation vessel and precipitate were carefully washed five times with about 20-ml. portions of a warm solution containing 1% potassium chloride, 1% ammonium chloride, and 6 drops of concentrated ammonium hydroxide per
Time
Table 111.
Extraction of Sc and Sm with TTA into Hexone
pH of
aqueous phase before extraction
Sc counts/min.
nd.
Before extraction
After extraction
7648 7674 7613
6705 2026 460
1.o
1.6 2.0
Sm countsjmin. ml. Before After extraction extracticn
liter. Then the precipitation vessel was removed from the lead castle and the precipitate was dissolved by introducing a minimum amount of hot 2N hydrochloric acid through the sidearm with the sinter, while applying light suction a t the other one. The solution was transferred into a small beaker and the precipitation vessel was washed with slightly acidified distilled water. Two milliliters of scandium carrier solution containing 1.5 mg. of scandium and enough distilled water were added to reduce the total acid concentration to about 1N. The solution was rinsed onto a column of 1.5 grams of oven-dried (105" C.) D o m x 50x8, 100 to 200 mesh, resin in the hydrogen form with about 30 ml. of 1N hydrochloric acid. The column was about 4.7 cm. long and 0.9 cm. in diameter. Alkali metals and anions were eluted by passing 70 ml. of 1X acid containing 1% dihydrogen ammonium phosphate and 0.2% sodium chloride, followed by 50 ml. of 1N acid through the column a t a flow rate of 3.5 ml. per minute. Then the scandium was eluted with 60 to 70 ml. of 3N hydrochloric acid a t the same flow rate.
in hours.
Figure 3. Decay curves for Sc49 from KCI of A.R. grade purity and from standards containing 10 pg. of calc:ium KCI not corrected KCI corrected for impurity lmpuiity (5 to 6 hours half life) Stanclard 1 Stanclard 2
x-x-x 0-
0-
A-A-A
+-+-+ n-m-0
0
9987 8314 9411
9862 8149 9227
Apparent distribution coefh'icient SC Sm 0.70 13.7 77.8
0.06 0.10 0.11
The eluate was partly neutralized by the addition of solid potassium hydroxide and then finaily adjusted to a pH of 2 with concentrated ammonium hydroxide. The solution was transferred into a 150-ml. separating funnel and extracted with 20 ml. of 0.211.1TTA in hexone. The aqueous phase was separated and the hexone phase n as nashed three times vrith 20 ml. of a solution containing 1% potassium chloride and 0.01N hydrochloric acid. Scandium was then extracted from the hexone into a 2N hydrochloric acid using two 20-ml. portions. The acid extract n a s wa~med, 10 drops of 0.1% bromocresol purple in ethanol were added, and scandium hydroxide nas precipitated with concentrated ammonium hydroxide solution using 3 drops of excess. The solution was boiled for 1 to 2 minutes and the precipitate filtered onto an organic membrane filter of Pcm. diameter, using a funnel and applying water-pump suction. It PI as n ashed three times with warm 1% ammonium chloride solution contltining 6 drops of concentrated ammonium hydroxide per liter. Then it was sucked dry, mounted in a 4 c m . diameter planchet and counted in a 2 ir-methane flow counter n i t h a 0.8 mg. per sq. em. gold end-nindow. The counting was repeated after time intervals and the decay curve of the activity R as prepared to verify R hether it was pure S C ' ~ As a standard, 1 mi. of an aqueous solution containing 1.00 mg. of calcium was irradiated with the sample. After irradiation, the solution was diluted to 100-ml. volume, and 2 aliquots of 1 ml. each representing 10 fig. of calcium were taken. One and a half milligrams of scandium carrier Kere added, and the scandium was separated from the aliquots by extraction into TTA and back-extraction into 2N hydrochloric acid as described above. One gram of ammonium chloride and 10 drops of 0.1% bromocresol purple in ethanol mere added to the extract, and hydrous ferric oxide was precipitated from the hot solution with conrentrated ammonium hydrouide. 'The precipitate 'ii a$ separntcd and counted as dcwibed :djove for the sample. The numbers of counts \\ere plotted against time on VOL 35, NO. 9, AUGUST 1963
1157
Table IV. Resultsfor the Determination of Ca in Various Samples of Potassium Chloride
Ca expected, p.p.m.
Sample KCl, A.R. grade Riedel de Haen Not known KCl single crystal 0.86 p.p.m. Ca added 1.5 to 2.0 KC1, A.R. grade Not known Merck KCI 8.8 p.p.m. Ca 9.8 KCl 20.0 p.p.m. Ca 21.0 KCl 20.2 p.p.m. Ca 21.2 KCl 36.7 p.p.m. Ca 37.7
+ + + +
Time in hours. Figure 4. Decay curves for Sc49 from pure KCI containing 60.5 p.p.m. Ca and standards of 10 pg. of Ca KCI Standard 1 Standard 2
semilogarithmic paper. The curves were used to test the radiochemical purity of the precipitates. Decay curves for some samples and standards are presented in Figures 3 and 4. For the determination of percentage recovery, the hydroxide precipitates of the sample and the two standards were packed and sealed in thin polyethylene films and irradiated for 30 seconds a t a flux of 5 X neutrons per second per sq. cm. together with two standards of I-ml. solution each containing 1.5 mg. of scandium. The S C ‘ ~activity originating from Sc45by (n,y ) reaction was counted in a sodium iodide crystal borehole counter. From the results for percentage recovery and from the decay curves for the sample and the standards, the amount of calcium present in the original sample was calculated. Some results are presented in Table IV. DISCUSSION
The foregoing method offers the possibility for a reasonably accurate and reliable determination of microgram amounts of calcium in potassium chloride. The method can be used for determination in other alkali halides as well, and without doubt can be modified and used for the determination of calcium in other water-soluble compounds. The total time for the separation is about 2.5 to 3 hours, 45 minutes’ initial waiting time included. The counting takes only a few minutes, but has to be repeated a t 1158
ANALYTICAL CHEMISTRY
time intervals. The ion exchange separation does not only separate the alkalis and the anions, but also serves to separate copper and zinc, and to reduce the amount of manganese significantly. These are probable radiochemical contaminants because of their large neutron capture cross section (Cu, Mn) or their relatively high concentration (Zn). X small part of the manganese may remain on the column with the scandium, but this would be separated in the following TTA extraction step. It may be pointed out here that Cabell’s method to separate scandium and calcium with 1.5N hydrochloric acid as eluent would require fairly large exchange columns when milligrams of scandium are present and a quantitative separation is contemplated. This can be estimated from Figure 1. For the purpose in mind, 1N hydrochloric acid was the more useful eluent. Most of the ferric iron is also separated by the ion exchange step. A smaller part is extracted together with the scandium into hexone as a TTA complex, but it is not appreciably back-extracted into 2N hydrochloric acid and is thus separated. The only elements that would accompany scandium through the whole separation procedure are zirconium, thorium if present in larger amounts, and the heaviest rare earths. Xone of these are likely to be present in amountr that would interfere from the radiochemical point of view. The presence of scandium in the original
Ca found, p.p.m. 0.74
2.00 1.02
10.5
23.1 22.9 39.0
sample would lead to the formation of S C ~ ~This . has a half life of 84 days and can thus easily be recognized and corrected for on the decay curves. Figure3shows that even for low amounts of calcium a radiochemical, fairly pure Sc49 is the product of the separation. An impurity of about 10 to 20 counts per minute of an activity with a half life of 5 to 6 hours is present. Khen a correction for this activity is applied, the evaluation of the curves results in the theoretical half life of 57 minutes for S C ~ ~The . curves for larger amounts of Sc49 on Figure 4 show the correct half life, since such a small impurity, if present, would not be evident. About 0.5 pg. to 1 nig. of calcium can be determined. Larger samples than about 5 grams are inconvenient to handle because of the high chloride and potassium activity (see table for activation data). Thus, the limit of the determination is about 0.1 p.p.m. calcium in potassium chloride. It mould be different in other alkali halides, depending on the amount of activity induced. Systematic information about induced activities is given by Baumgartner (3). KO special ex. periments were conducted to investigate self-absorption or shielding effects during irradiation. However, the results in Table IV seem to indicate that up to sample amounts of about 5 grams selfabsorption or shielding effects are small and do not influence the analytical results significantly. ACKNOWLEDGMENT
The authors thank H. J. Born of the Radiochemical Institute of the T. H., Munich, for the use of the facilities a t the Institute of the atomic reactor
F. R. M. near Garching, and Bernd Bocklitz and the personnel of the reactor station, Garching, for their help with the experimentd work. LITERATURE CITED
(4) Cabell, M. J., At. Energy Res. Estab.
(G.Brit.) C/M-233 (1957).
(5) Gammon, N., Jr., Forbes, R. B., ANAL.CHEM.21, 1391 (1949). (6) Kemp, D. M., Smales, A. A., Anal. Chim. Acta 23, 410 (1960). (7) Meinke, W. W., ANAL.CHEM.31, 792
(1959).
(1) Anderson, S., Wili?y, J. S.,Hendricks, L. J., J. Chem. Physics 32,949 (1960). (2) Banerjee, D. K., Iludke, C. C., Miller, F. D., ANAL.CHEM.33,418 (1961). (3) Baumgktner, F., Kerntechnil 3, 356
(1961).
s., Penniall, R., Ibid., 27, 434 (1955). (9) . , SheDerd. E.. hleinke. W. W.. U. S . At. &.ergy Comrn. AE(U-3879) i1958). (10) Tmka, J., Che7n. Listy 151, 1378 (1957). (8) Natelson,
(11) Tyner, E. H., ANAL. CHEM. 20, 76 (1948). (12) Vickery, R. C.,J . Chem. Soc. 251, (1955). (13) Vpgel, A. I., “A Text-boo& of Quantitative Inorganic Analysis, 2nd ed., p. 827, Longmans, Green and Co. London. 1951. (I4) Naturforsch* 13a, 645 (1958). (15) Young, A , Sweet, T. R., Baker, B. B., A?iaL cHEDI, 27, 356 ( 1 ~ ~ 5 ~ ) . RECEIVEDfor review July 10, 1962. Accepted April 29, 1963. H‘j
’‘
2,3-Diaminonaphthalene as a Reagent for the Determination of Milligram to Submicrogram Amounts of Selenium PETER
F. LOTT,
PETER
CUKOR, GEORGE MORIBER,’ and JOSEPH SOLGA?
St. John’s University, Jamaica 32,
N. Y .
b Selenium is detemnined with 2,3diaminonaphthalene. The reagent permits the determintation of milligram amounts gravimetrically, microgram amounts spectrophcrtometrically, and submicrogram amourits fluorometrically. Masking agents are employed to increase the selectivity so that selenium can b e determined n the presence of tellurium, copper, zinc, aluminum, etc. Data are included on such reaction conditions as the effect of pH, foreign ions on the reaction, and solvent extraction.
T
HE DETERMIXATION of small amounts of selmium is of considerable biological interest since the investigations of Sc hwarz and Foltz (7) which showed that trace amounts of selenium are of nutritional benefit. Kolthoff and Elving (4) recently reviewed methods of selenium analysis. The determination of trace amounts of selenium generally is based either upon a reduction 0 ; splenium(1V) to (.lementa1 selenium 01 a measurement of the piaaselenol form’:d when selenium (IV) reacts with an aromatic o-diamine, particularly 3,3-diaminobenzidene. The use of this reagent has been recently reviewed ( 1 ) . The reagent is not specific; t o preve it the interference of foreign ions, procec ures incorporating masking agents or prior extraction of selenium with toluen1:-3,4-dithiol ( 2 , 8) have been developed. Procedures of
greater sensitivity are desired. Concurrent t o our work, Parker and Harvey ( 5 ) also investigated a series of aromatic o-diamines and similarly observed the greater sensitivity of 2.3diaminonaphthalene (DA4N)as a selenium reagent, but did not apply the reagent to the determination of selenium t o samples containing foreign ions. Gravimetrically, selenium is determined by reduction of selenium(1V) to the elemental state. To prevent the interference of many ions in this procedure, Schumann and Koelling (6) incorporated an ion exchange separation of cations prior t o the reduction of selenium. The use of an organic precipitant for the gravimetric determination of selenium has not been reported. Reported herein is a study on the determination of macro and micro amounts of selenium with DAN, in the presence of foreign ions. The reagent has been found suitable for the direct determination of milligram amount5 of selenium gravimetrically, while micro and submicrogram amounts of selenium are determined spectrophotometrically or fluorometrically, respectively. In addition to the use of masking agents to prevent foreign ion interferences, the separation of macro amounts of forpign cations by ion exchange has been incorporated into the determination of trace quantities of selenium. EXPERIMENTAL
Present address, Brooklyn Technical High School, Brooklyn, N. Y. 2 Present address, Geigg Chemical Co.,
Ardsley, N. Y.
Apparatus and Reagents. Optical nieasurements were performed with t h r following instruments: Beckman DU, I’erkin-Elmer Model 202, Bausch
and Lomb Spectronic 20 spectrophotometers, and as Aminco-Bowman Spectrofluorimeter. Aisolution of 2.3-diaminonaphthalene was prepared by dissolving 1.00 gram of 2,3-diaminonaphthalene (Aldrich Chemical Co.. Milwaukee, Wis.) in 1 liter of 0.10N HCI, using a magnetic stirrer . Standard selenium solution containing 5.00 mg. of selenium per ml. was prepared by dissolving 8.168 grams of selenous acid (H2Se03)in 1liter of water. The solution was standardized gravimetrically by precipitation of the selenium with hydroxylamine. Other solutions of selenium were prepared by appropriate dilution of this stock solution. Masking mixture-solution 0.1M in sodium fluoride, sodium oxalate, and EDTA. Procedures. Preliminary experiments indicated t h a t the reaction was greatly influenced b y acid concentration, temperature, t h e length of time employed for color development, and the presence of foreign ions. The conditions cited below should be followed for samples known to contain a diverse number of foreign ions. GRAVIMETRIC PROCEDURE. To a solution adjusted approximately t o p H 2, and containing from 10 t o 50 mg. of selenium, add 25 ml. of the masking agent mixture and 60 to 300 ml. of stock Dd4K solution. (Stoichiometrically, 1 mg. of selenium requires approximately 1 1111. of 0.1% U - i S solution; for complete precipitation a four- to six-fold excess of DdS is necessary.) Adjust the solution to p H 1.5-2.0 by adding either S a O H or HC1, using a p H meter. Allom- the mixture to stand 2l/? t o 3 hours a t room tcmperature. Filter tlie prrcipitate through a fineporo-ity sintered-gla\\ crucible, wash with 20 ml. of l . 5 S HC1 and 50 ml. of water (to remove all traces of HCl), VOL. 35, NO. 9, AUGUST 1963
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