line leading from the conversion system to the inlet system of the spectrometer, in order to ensure adequate sample pressure in the inlet system. Table I1 shows pressures observed in our viscous inlet conversion system when various amounts of NH4+-Nwere converted to Nz. Manufacturers of the viscous inlet systems recommend crimping the dual capillaries of the inlet system to provide matched flows at 100 mm Hg pressure in the inlet system, and thus restricting the NZflow to the mass spectrometer so it can still be operated a t maximum sensitivity. Table I1 shows that in order to generate 100 mm Hg pressure of N2,the sample vial must contain 3 mg of NH4+-N. There is the alternative of crimping the capillaries when the inlet system is set a t lower pressures. Capillaries crimped at lower pressures provide greater Nz flow rates to the detector and still permit the mass spectrometer to be operated at maximum sensitivity. On our inlet system, we elected to crimp the capillaries at 35 mm Hg, and thus, we routinely try to
prepare our N samples so that the sample vials contain at least 1 mg NH4+-N.
LITERATURE CITED ( 1 ) R. Fiedler and G. Proksch, Anal. Chim. Acta, 78, 1-62 (1975). (2) D Rittenberg in "Preparation and Measurement of Isotopic Tracers", A. 0. C. Nier and S.P. Reimann, Ed., J. W. Edwards, Ann Arbor, Mich. 1948, pp
31-42.
(3) J. M. Bremner in "Methods of Soil Analysis", C. A . Black, Ed., American Society of Agronomy,Madison, Wis., 1965, pp 1256-1286. (4) J. M. Bremner, H. H. Cheng, and A. P. Edwards in "The Use of Isotopes in Soil Organic Matter Studies", Report of FAO/IAEA Technical Meeting in cooperation with the International Soil Science Society (Brunswick-Volkenrode),Pergamon Press, New York, N.Y., 1963, pp 429-442. (5) P. J. Ross and A. E. Martin, Analysf, (London), 95, 817 (1970).
RECEIVEDfor review March 18, 1976. Accepted December 13,1976. Reference to a company or product name does not imply approval or recommendation by the USDA.
Breakdown of Alkaline Complex Cyanide by Ion-Exchange lrith Gilath Soreq Nuclear Research Centre, Yavne, Israel
The term complex cyanide refers here to complexes formed from cyanides of alkali metals combined with cyanides of heavy or transition metals. In these compounds, the cyanide is part of the complex anion (i.e., Me11(CN)42-)and cannot be determined directly. The classical method for the determination of cyanide from complexes is based on its release from an acidified solution as cyanhydric acid and distillation into an alkaline solution ( 1 ) . The Serfass reflux and tartaric acid distillation procedures are most widely used. The apparatus and the methods are described in detail in the Standard Methods (1).The reflux procedure is somewhat more complicated than the tartaric acid distillation but is preferable since it results in a higher recovery of the cyanide. In the distillation of the stable cornpiexed salts, the release of hydrogen cyanide and absorption in alkaline solution is not always complete and depends on the heating rate of the distillation, carrier velocity, and alkaline absorption facilities. A few hours of distillation may be required to break down some stable complex cyanides by both methods (2). A new, quick and reliable method was developed by us for complex cyanide breakdown for application in the plating
Table I. Composition of Complex Cyanide Solutions
Free CN-, Complex K2Zn(CNh KzCd(CN)4 K~CU(CN)~ KAg(CN)e
Complexed CN-, gll.
Total CN-,
gll. 0.59 1.5 1.5 7.39
44.25 41.50 20 11.64
44.84 43.00 21.50 19.03
gll.
industry. The cyanide anion is absorbed on a strong anionexchange column and released by elution with sulfuric acid. The strong base characteristics of the anion exchanger permit the absorption and exchange of anions of weak acids. In the hydroxyl cycle, the strong anion exchanger shows remarkable salt-splitting properties. As compared with the time-consuming acid distillation of the cyanides ( I ) , this procedure is rapid and easy to perform.
EXPERIMENTAL Preparation of Ion-Exchange Column. About 5 g of dry Amberlite IRA-400 (Fluka) 20-50 mesh resin in hydroxyl form was swollen with distilled water and transferred to a burette. The burette was filled to a height which corresponded to seven times the diameter of the column. Preparation of Simple and Complex Cyanides. Simple cyanides were prepared by dissolving KCN or NaCN in distilled water and determining the concentration by argentometric titration. The cyanide complexes were prepared in solution by accurately weighing simple insoluble cyanides and dissolving them in known concentrations of NaCN or KCN solutions. The compositions of the concentrated complex cyanide solutions tested by us are summarized in Table I. Absorption of Cyanides. A 2-ml sample (containing up to 100 mg CN-/sample) of the cyanide solution and a few milliliters of distilled water were filtered through the resin bed a t the rate of 1drop/s. The resin was then washed with 15 ml of distilled water. Elution. The cyanide was released by two consecutive acid elutions: 15 m12 N HzS04 and 15 m14.5 N HzS04. The first acid elution was performed quickly to avoid the formation and escape of HCN bubbles. The second acid wash was performed slowly, to complete the removal of the cyanide from the resin. After the two acid elutions, the resin was washed with 15 ml of distilled water. The acid effluents and the water were delivered to the bottom of a magnetically stirred beaker, containing 80 ml of 2 N NaOH.
Table 11. Material Balance of Cyanide Filtered through Ion Exchangers
Complex
KzCd(CN14 KzZn(CN)4 K~CU(CN)~ KAg(CN)z 516
Total cyanide in sample,
Cyanide eluted in first wash,
Cyanide eluted in second acid
Total cyanide recovered,
mg
mg
wash, mg
mg
29.38 34.12 52.60 95.16
13.44 10.92 11.91 8.74
42.82 45.04 64.51 103.90
43 45 64.5 105
ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
Analysis. The total cyanide content of the sample was determined in the alkaline solution by AgN03 titration. For low cyanide concentration, Le., 0.1-1 mg/l, the colorimetric method using chloramin T and pyridine-pyrazolone was employed (3). Regeneration. The resin was regenerated with -8% NHlOH solution and washed with 15 ml of distilled water.
RESULTS AND DISCUSSION The cyanide absorption capacity of the strongly basic resin was first checked with KCN solutions in the concentration range of 5-40 gfl. The resin in the burette was found to absorb about 200 mg of cyanide per sample and completely absorbed the cyanide contained in 2-ml samples of concentrated solutions. The complex cyanides were treated in the same way as the simple cyanides and there, too, a cyanide-free filtrate was obtained. The efficiency of the complex cyanide breakdown and the recovery of cyanide was checked by material balance.
Some typical results are summarized in Table 11,where it can be seen that the recovery of cyanide is complete. A third acid wash may be used to ensure complete elution of cyanides, but care must be taken that the solution in the beaker where the acid effluents are collected is sufficiently alkaline. The complex cyanide breakdown and the recovery of free cyanide take no more than 20 min. The resin is regenerated by NH40H instead ef NaOH to prevent the formation of insoluble metal hydroxides.
LITERATURE CITED (1) "Standard Methods for the Examination of Water, Sewage and Industrial Wastes", Tenth ed., Amer. Publ. Health Assoc. Inc., 1955. (2) F. J. Ludzack et at., Anal. Chem., 26, 1784 (1954). (3) J. Epstein, Anal. Chem., 19, 272 (1947).
RECEIVEDfor review June 14,1976. Accepted November 10, 1976.
Autoradiography of Californium-252 Wire Neutron Sources Burton Tiffany," K. W. MacMurdo, and R. H. Gaddy Savannah River Laboratory, E. 1. du Pont de Nemours and Company, Aiken, S.C. 2980 1
Californium-252 is an intense neutron source and gamma emitter having many medical and industrial applications ( I 1. The sources are often fabricated in the form of a wire, and a piece of the wire is encapsulated in a metal sheath. For some applications, such as the neutron irradiation of tumors, the uniformity of distribution of 252Cfin the wire must be known. This paper describes a technique for measuring the distribution of 252Cfby placing a source on a photographic plate sensitive to gamma radiation to produce an autoradiograph and then reading the radiograph with an automated densitometer.
EXPERIMENTAL Apparatus. A Digital Equipment Corporation PDP-8/1 computer with two Dectape transports and 8K words of core memory was interfaced to a Grant microphotometer, Series 800. The photomultiplier tube was interfaced to a 10-bit analog-to-digital converter. The microphotometer was equipped with computer-controlled SLO-SYN driving motors to move the densitometer stage in the 3c and y directions. The autoradiographs were recorded on 2 X 10 inch Kodak Spectrum Analysis No. 1photoplates. Plate Preparation. The glass photoplate was encased in an opaque plastic sleeve that was backed with a 2 X 10 inch wood board for strength. Gamma-radiation absorbers such as 10- to 30-mil-thick sheet stainless steel or 10-mil-thick sheet tantalum were added in front of the emulsion on the photoplate to slow the exposure rate for strong sources. The photoplate was packaged in a darkroom. Procedure. The photoplate package was placed on top of the zizCf wire with the emulsion facing the wire for a period of time determined by the estimated concentration of 252Cfper unit length of wire, the thickness and type of encapsulation, and the thickness and type of radiation absorber in the photoplate package. After exposure, the photoplate was removed from the package without radioactive contamination and developed in Kodak D-19 Developer. After fixing and drying, the photoplate was positioned to give a lengthwise traverse on the densitometer glass stage. The autoradiographic image was generally about 3 mm wide and often not straight. Figure 1A shows an autoradiograph of a wire which is 140 mm long and contains 50 pg z5zCfper 25 mm. The densitometer optics were set to give a resolution a t the emulsion of 1pm in the width and 1 mm in the height. The length of the image was measured in millimeters and used as input information to the computer. The autoradiogaph was manually centered on the minimum transmittance point a t one end of the image and thereafter was automatically centered by the computer-controlled y-stepping motor. The percent
difference in the transmittance value used in the y -centering search routine was set a t the start of the evaluation to give accurate centering with minimal y-centering movement of the stage. The photomultiplier output was set to give 100%transmittance for a background region of the photoplate. Readings were generally taken a t 0.1-mm intervals and averaged for 5 to 10 of these values to give a regional value. The length of the image is limited to 204 mm with the present computer program.
RESULTS AND DISCUSSION Autoradiographs were initially interpreted manually on a densitometer with minimum transmittance values recorded every 3 mm (the estimated resolution of the technique). Kodak Spectrum Analysis No. 1 photoplates produced a satisfactory image. The transmittances were averaged and the percent differences were calculated. Because this was a very time-consuming task, photoplate image interpretation appeared to be an ideal application of computerized densitometry. A computer program was written to automate the readings of transmittance values and to convert transmittance to absorbance, which is directly proportional to the concentration
A
al
L a , '
a
P o s i t i o n Along Autoradiograph
Figure 1. 252Cf autoradiograph and distribution profile (A) Autoradiograph of a 252Cfwire. (B) Plot of the percent difference of the absorbance from the average absorbance along the autoradiograph ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
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