geometry varied; therefore, counting rates on successive runs are not comparable. The limits of error listed take into account all possible factors; the results in all probability were more accurate than these limits suggest. The peaks of plutonium-236 fell in the channels predicted from calibration data, and the proportions of high and low energy components agreed with the literature values (69% and 31 %) (4). Sample No. 7 had previously been assayed a t Savannah River Laboratory by a radiochemical method. [The plutonium was separated from uranium. After a three-week grow-in period for uranium-232 and uranium234 from plutonium-236 and plutonium-238, respectively, another uranium-plutonium separation was performed. The ratio of the uranium daughters after the second separation was determined by alpha pulse height analysis, and the relative amounts of plutonium-236 and plutonium-238 were calculated from this ratio and the known grow-in time (5).] The result (4) D. Strominger, J. M. Hollander, and G. T. Seaborg, Rev. Mod. Plzys., 30,823 (1958). (5) E. L. Albenesius, Savannah River Laboratory, private communication, January 30, 1967.
of this indirect determination was 1.26 ppm plutonium-236 Thus the simpler, quicker, direct method described herein gave results (1.31 ppm) which agreed closely with the independent determination by the indirect method.
(a with a n estimated accuracy of 10%.
ACKNOWLEDGMENT
The author acknowledges with gratitude the suggestion of G. Matlack, Los Alamos Scientific Laboratory, that the analyses could be made by alpha pulse height measurements, and the contribution of R. H. Lambek in the preparation of the slides used in the study.
RECEIVED! for review February 2, 1968. Accepted March 27, 1968. Mound Laboratory is operated by Monsanto Research Corp. for the U. S. Atomic Energy Commision under Contract No. AT-33-1-GEN-53. (6) M. G. Linn, Savannah River Laboratory, private communication, August 28, 1967.
Spectrophotometric Determination of Cyanide Ion with tris( 1,lO-Phenanthrol ine) Iron( II)-Triiodide Ion Association Reagent Jack L. Lambert and David J. Manzo Department of Chemistry, Kansas State Uniuersity, Manhattan, Kan.
THEPROCEDURE described here is presented as a useful, rapid method for the determination of small concentrations of free, uncomplexed cyanide ion in neutral solution in the absence of strong oxidizing or reducing agents. It is also presented as an example of a solid phase colorimetric reagent, consisting of an insoluble ion association compound, one of whose member ions reacts selectively with a species in solution and thereby releases the colored counter ion into solution. The very insoluble tris(1,lO-phenanthroline)iron(II) triiodide reacts rapidly with cyanide ion to release the red complex cation for spectrophotometric determination. Most ions found in the concentrations normally encountered in natural waters d o not interfere. Cyanide ion is usually determined colorimetrically by modifications of the Konig method (1, 2) developed by Aldridge (3, 4 ) and Epstein (5). The method of Aldridge involves the reaction of cyanogen bromide with a pyridine-benzidine mixture, while the Epstein method used the reaction of cyanogen and chloride with pyridine, l-phenyl-3-methyl-5-pyrazolone, bis-l-phenyl-3-methyl-5-pyrazolone.Other workers (6-9) (1) W. Konig, J . Prcrkt. Cliem., 69, 105 (1904). (2) W. Konig, 2.Agnew. Cliem., 69, 115 (1905). (3) W. N. Aldridge, Analyst (London), 69,262 (1944). (4) Ibid.,70, 474 (1945). (5) J. Epstein, ANAL.CHEM., 19,272 (1947). (6) . , G. V. L. M. Murtv and T . S . Viswanathan. Anal. Chim.Acta. 25, 293 (1961). (7) L. S. Bark and H. G. Hieson. Talarzta., 11., 621 (1964). . (8j A. Niwinski and H. DuGykowa, Przemysl Ferment. Rolny, 10, 352 (1966). (9) M . Simon, Tech. Eau (Brussels),239, 17 (1966). ,
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e
ANALYTICAL CHEMISTRY
have reported variations of these procedures, notably substituting barbituric acid in place of benzidine (6). Specific and highly sensitive fluorescent methods for cyanide ion have been reported by Guilbault and Kramer ( I O , 11), which involve the production of fluorescent compounds by the reaction of quinones and quinone derivatives with cyanide ion. Guilbault and Kramer (12) have also described a specific and extremely sensitive spectrophotometric method in which cyanide ion catalyzes the reduction of o-dinitrobenzene by p-ni trobenzaldehyde. Analytical use of an insoluble ion association compound as a colorimetric reagent has been reported previously at least one time. G. Bouilloux (13) proposed a method for silver ion in which methylene blue dye cation was released from the insoluble compound formed between methylene blue cation and tetraiodomercurate anion by the reaction of silver ion with the complex anion. EXPERIMENTAL
Reagent. Porous porcelain chips (30-60 mesh) served as a support for the reagent. Unglazed porcelain plates (Fisher Scientific Co. catalog No. 13-750) were ground and sieved to the desired size range, and repeatedly washed. Subsequent study has shown that more effective washing can be (10) G. G. Guilbault and D. N. Kramer, ANAL.CHEM., 37, 918 (1965). (11) Ibid., 1395. (12) Zbid.,38, 834 (1966). (13) G. Bouilloux, Bull. Soc. Chim., 7,184(1940).
accomplished with an ultrasonic cleaner. Deionized water was used throughout, and reagent grade chemicals were used in all preparations. A Bausch and Lomb Spectronic 20 colorimetric was used to obtain absorbance measurements. tris(1,lO-Phenanthroline)iron(II) was prepared by adding an excess of 1,lO-phenanthroline monohydrate to a saturated solution of ferrous ammonium sulfate hexahydrate. The undissolved 1,lo-phenanthroline was filtered off and the solution diluted with twice its original volume of water. Potassium triiodide solution was prepared by dissolving 33 grams of potassium iodide in 100 ml of water at 80 "C and adding 5.0 grams of iodine with stirring. Porcelain chips were soaked in the tris(1,lO-phenanthroline)iron(II) solution for 20 minutes, dried with suction on a Biichner funnel for 2 hours, and air dried for at least 5 hours. The chips were then treated with the potassium triiodide solution for 20 minutes and air dried for at least 5 hours. They were again treated with the tris(1,lO-phenanthro1ine)iron(I1) solution and filtered with suction as before, after which they were dried in air overnight and stored in a tightly sealed bottle. Batches of the reagent varied slightly, which would necessitate making a calibration curve for each batch. This variability and to some degree the small variability in response to cyanide ion is believed to be caused by variation in the nature of the support rather than in the reagent compound itself. Samples of the reagent stored in sealed bottles in diffuse daylight showed no changes in response or blank up to five weeks, and no changes up to seven weeks if washed prior to use. Storage in an equilibrium atmosphere of iodine vapor might extend the storage life of the reagent, as some loss of iodine because of volatility is suspected, but this possibility has not been investigated. Calibration Curve. Samples were prepared by diluting a 20.0-ppm solution prepared from a 500-ppm stock solution freshly prepared every three to four days. Twenty milliliters of sample solution was added to a 125-ml evaporating dish containing 0.3 g or 0.33 ml of reagent. The solution was allowed to stand for 20 minutes with frequent but not necessarily constant stirring, and the absorbance was determined at 514 mp. The calibration curve in Figure 1 shows the results of five determinations made at various concentrations of cyanide ion in the 0 to 8.0 ppm range. Above 8.0 ppm, the absorbance US. concentration curve begins to level off, probably because of insufficient available reagent. By use of twice the amount of reagent, the range can be extended to 20.0 p.p.m. of cyanide ion, but the blank is doubled. Study of Interferences. In the absence of cyanide ion, 500 ppm of the following ions produced an absorbance at 514 mp no greater than that obtained with deionized water: sodium, potassium, ammonium, calcium, iron(III), iodide, chloride, nitrate, carbonate, and sulfate. Fifty ppm of fluoride ion likewise had no effect on the blank. In the presence of 5.0 ppm of cyanide ion, 450 ppm of the following ions produced an absorbance at 514 mp equal to that obtained with 5.0 ppm of cyanide ion in deionized water: sodium, potassium, ammonium, calcium, iodide, chloride, and nitrate. Fifty ppm of fluoride ion did not interfere, but 10.0 ppm of iron(II1) interfered by removing cyanide ion by complexation.
o'6
0.5 0.4.
r
t
I
I
I
I
I
I
I
I
I
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
CONCENTRATION, ppm CN-
Figure 1. Calibration curve 0 Average I Range 0 Standard deviation DISCUSSION
As described, the reagent has limited applicability. It does have the advantages of simplicity, rapid response, and freedom from interference by a number of common ions. The effective concentration range could be extended by dilution of samples containing more than 10.0 ppm of cyanide ion, and concentration by distillation of samples containing less than 1.0 ppm. Porcelain is an aluminosilicate material having ion exchange properties, and thus the initial treatment with tris(1,lOphenanthroline)iron(II) cation saturates its exchange sites. The compound as prepared by the two subsequent treatments probably is a thin layer on the extensive surface on and within the porous porcelain. The mechanism of the reaction of the reagent with cyanide ion is not definitely known, but it is reasonable to assume that the triiodide ion is destroyed in the following manner
+
Fe(phen)3(13)2 CN-
-t
Fe(phen)02f
+ ICN + 21- + Is-
(1) The concept of release of a colored or fluorescent ion from an insoluble ion association compound by selective attack upon the other ion has not been extensively explored. Desirable improvements in this method would include greater insolubility of the reagent and a higher molar absorptivity for the released ion. Iron(I1) complex cations of ligands similar to 1,lO-phenanthroline or possibly cationic dyes that are nonreactive toward cyanide ion may yield improved reagents. RECEIVED for review March 13, 1968. Accepted April 15, 1968. Work supported by Federal Water Pollution Control Administration Research Grant Number WP-00326. Abstracted in part from the M.S. Thesis of David J. Manzo.
VOL 40, NO. 8, JULY 1968
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