difficult; however, a simple technique may be applied to determine the moleaverage sulfur rank. The spectrum of the pure disulfide is initially recorded, and the center of gravity of the alpha multiplet is determined from the in& gral. The series of multiplets of the polysulfide mixture is assigned to respective sulfur ranks (diagrammed in Figure 1). A plot of the multiplet centers of gravity u8. sulfur rank is drawn. The value of the mole-average
sulfur rank can be obtained directly from the plot, after the position of the integral half-height of the complete alpha-carbon multiplet is measured. The upper limit of values obtained by this technique is dependent upon the ability to resolve and assign one rank higher than the average rank of the mixture. The technique is otherwise unaffected by the presence of highrank polysulfides which cannot be resolved.
LITERATURE CITED
(1) Grant, D., Van Wazer, J. R., J. Am. cha. so,. 86, 3012 (1964). (2) Reid, E. E., “Organic Chemistry of Bivalent Sulfur,” Vol. III, Chap. 7,
(3)Chemical Vineyard, Publ. B. Co., J , erg, Newchm. York,J1, 1960. 601 (1966). D. J. MARTIN R. H. PEARCE
Stauffer Chemical co Eastern %semch ceAter Dobbs Ferry, N. Y. 10522
Niobium Dissolution by Hydrofluoric Acid and Potassium Iodate Prior to Nitrogen Determination SIR: This report presents a rapid method for the dissolution of niobium, niobium alloys, and iron alloys in preparation for determining their nitrogen content. A solvent which contains both a complexing agent and an oxidizing agent is necessary for the dissolution of niobium and its alloys (2). Niobium is readily dissolved by a mixture of hydrofluoric acid and nitric acid. However, the presence of nitric acid prohibits its use when a nitrogen determination is desired. Solvent mixtures of hydrofluoric acidhydrogen peroxide, sulfuric acid, sulfuric acid-hydrogen peroxide, and sulfuric acid-potassium sulfate have been used to dissolve niobium prior to nitrogen determinations but these systems involve iong dissolution times as compared to the hydrofluoric acid-nitric acid system ( 1 , s ) . We have found that fusion of niobium with pyrosulfate or its dissolution in perchloric acid results in a low nitrogen recovery probably due to a too vigorous oxidation reaction. This communication describes a solvent system which combines Pydrofluoric acid and potassium iodate to attain a rapid dissolution of niobium and its alloys without interference with the subsequent nitrogen determination. EXPERIMENTAL
Reagent Purification.
POTASSIUM
IODATE. T o 225 grams of KIOa dissolved in 1000 ml. of water, add 5 ml. of NaOH (3Oy0). Boil carefully for 20 minutes. Withdraw a few milliliters of the solution and add it t o 2 ml. of Nessler’s reagent. If the Nessler’s reagent turns yellow, ammonia is still present in the KIOa solution. Continue boiling the KIO, solution and testing with Nessler’s reagent until the test is negative. As the volume of water decreases K I 0 3 will precipitate. Decant the solution into a second beaker and continue boiling. By further boiling and decanting separate aa much of the purified KIOs as possible. Wash the KIOa with a small amount of water
and dry at 110’ C. overnight. in a sealed bottle.
Store
SODIUM HYDROXIDE (30%). Dissolve 900 grams of NaOH in 3000 ml. of water. Evaporate to 2OOO ml. to remove ammonia, filter through a glass wool plug into a 3-liter polyethylene bottle, and dilute to 3000 ml. Procedure. Samples (0.3 gram) are weighed t o the nearest milligram and transferred to 100-ml. platinumclad dishes. Six milliliters of hydrofluoric acid (24%) are added, followed by 1 gram of the purified potassium iodate. The reaction, which is initiated by heating, is carried out in a hood to dispel fluorine and iodine fumes. If the reaction becomes too vigorous, the heating is stopped. Samples will usually be dissolved in a few minutes, but in stubborn cases a little more hydrofluoric acid and potassium iodate may be added. The solution is diluted with water (ca. 25 ml.) and transferred to a steam distillation unit. Twenty-five milliliters of NaOH (3ooj,) are added and the basic solution
Table 1.
RESULTS AND DISCUSSION
Potassium chlorate and sodium and potassium periodates were tested as possible oxidizing agents for niobium and iron alloys. I n all cases while the reaction was vigorous and the samples dissolved rapidly, nitrogen recovery was low when compared to a sulfuric acid dissolution. The lower oxidation potential of the iodate ion led to its investigation for use as an oxidant. Potassium iodate was chosen in preference to its sodium analog because of the greater solubility of the potassium salt. The time required for dissolution of niobium-zirconium alloy by the hydrofluoric-iodate reaction compared with other commonly used acid solvents is
Effect of Particle Size and Solvent System on Time of Dissolution and Nitrogen Determination of Niobium-Zirconium Alloy
Pa fiic1e size Coarse powder
:EiTC/-?;der Small chip Large chip Large chip
Table .II.
is distilled. Ammonia in the distillate may be determined by any convenient method.
Solvent HF-Hz0 HF-KIOa Ha04 HF-KIOS HzSOrHz0z HF-KIOr
Time, min. 30 10 120 10
180 10
N found, p.p.m. 155, 144 145, 145 115, 130 120, 130 440, 420 430, 415, 400
Comparison of Nitrogen Results for Iron Alloys between Different Dissolution Methods
Iron alloy Cast iron 18Cr, 8Ni 3Si 8M0, 8C0, 4Cr, 2V, 1.5W
Ha04 method 89 390, 430 39, 41
175, 170
Nitrogen, p.p.m. HF-KIOI method 85, 84, 85 460, 395, 480 48, 47, 50 170, 165, 195
VOL 38, NO. 1 1 , OCTOBER 1966
1605
shown in Table I. Three different lots of this alloy were tested, and the nitrogen results are shown. It is also shown that sample particle size had no significant effect on the time of dissolution by the hydrofluoric-iodate method but with the other methods tested a smaller particle size resulted in a shorter dissolution time. Table I1 compares the amount of nitrogen found in several iron alloys employing two methods of dissolution. The sulfuric acid method is that of Hague, Paulson, and Bright (4). The nitrogen in the distillate was determined by a colorimetric technique making use of Nessler’s reagent to develop the color. I n general, iron alloys were found to be more difficultly soluble than niobium alloys and some experimentation is
necessary to find the optimum ratio of hydrofluoric acid to potassium iodate required to speed their dissolution. Alloys of niobium and other refractory metals were found to be readily dissolved by this technique including alloys with zirconium, molybdenum, tantalum, titanium, tungsten, vanadium yttrium, boron, hafnium, aluminum, chromium, and cerium. Many of these metals themselves are dissolved by this technique but some exceptions have been found. Unalloyed tungsten and boron as well as the oxides of niobium, tantalum, and aluminum are not dissolved by this technique. The method described is rapid and will dissolve most niobium and iron alloys; and because smaller amounts of reagents are used, lower blank values are obtained.
LITERATURE CITED
(1) Ciaranello, J. R., Combs, K. E., “The Determination of Nitrogen in Niobium Alloys,” U. S: At. Energy Comm. KAPL-M-JRC-3, July 1960. (2) Gens, T. A., “The Chemistry of Niobiyfn in Processing of Nuclear Fuels, U. S. At. Energy Comm. ORNL 3242. (3) Gowar, G. W., Tretwo, E. F., “The Determination of Nitrogen in Niobium,” U. S. At. Energy Comm..WAPD-CTA(GLA)-203, April 1956. (4) Hague, J. L., Pauison, R. A., Bright, H. A., J. Res. Natl. Bur. Std. 43, 201 (1949). RAYMOND J. JAW OR OW SKI^ Pratt & Whitney Aircraft, CANEL Middletown, Conn. WORKsupported by the Atomic Energy Commissionunder Contract AT(30-1)2789. Present address, General Telephone and Electronics Laboratories, Bayside, N. Y.
Gas-Liquid Chromatography of Ferrocene Derivatives SIR: Ferrocene and its derivatives have normally been identified and characterized by use of their infrared spectra, melting points, boiling points, and elemental analysis. In addition, paper chromatography and thin layer chromatography have been used (1, 4 ) . I n most instances the purification of these derivatives has involved high vacuum distillation, sublimation, recrystallization, and/or elution on an alumina or silica chromatographic column ( 3 ) . The research reported here resulted from our need for a more rapid and accurate method for the separation, identification, and purification of ferrocene derivatives from some of the mixtures we encountered. One mixture of particular interest was that resulting from the reaction of ferrocene with acetyl chloride in the presence of aluminum chloride. This reaction has been investigated quite extensively (3) and has been shown to produce a mixture of acetylferrocene, 1,l ’aiacetylferrocene, 1,2diacetylferrocene, and other tarry products, the relative amounts of each depending upon the molar ratio of reactants used. The method most frequently used for analysis of mixtures of this type involves depositing the mixture on an alumina or silica column and then eluting with a suitable solvent. Although the formation of light-catalyzed decomposition products of these ferrocene derivatives while on the alumina or silica column can be curtailed by wrapping the column, it has been pointed out more recently by Nesmeyanov and coworkers (2) that a number of ferrocene derivatives readily undergo oxidation, disproportionation, and condensation re1606
0
ANALYTICAL CHEMISTRY
I
1
I
0
5 RETENTION TIME (MIN.)
IO
Figure 1 . Separation of ferrocene (A), acetylferrocene (B), and 1,l ’-diacetylferrocene (C) by gas chromatography Column of stainless steel, 5-feet X ‘/*-inch 0.d. containing 5% w./w. SE-30 on 60- to 80-mesh Chromosorb W. Helium Aow rate of 30 ml. per minute. Temperature: column 175’ C.; detector 200’ C.; injection port 195’ C.
actions on both alumina and silica columns even in the absence of light. In order to circumvent Some of the disadvantages encountered in the above methods of separation and analysis, a n investigation into the use of the more rapid and accurate method of gasliquid chromatography was made. We report here the successful application of gas chromatography to a number of ferrocene derivatives. By this technique mixtures of ferrocene derivatives may be rapidly separated and identified, or a single ferrocene derivative may be checked for purity. EXPERIMENTAL
Chemicals. The compounds used in this study were synthesized by standard literature methods. For comparison purposes, samples of each
compound were obtained from commercial sources (Peninsular ChemResearch, Inc., Research Organic Chemical Co., Arapahoe Chemicals, Apparatus. ~~~~~~~~h model 1520-13 chromatograph equipped with thermal conductivity and flame ionization detectors and a Sargent SR 1 millivolt range recorder with disc integrator were used in this study. Of the several chromatographic columns studied, the one most Successful was made of stainless steel (5 feet by. l/ginch 0.d.) packed with 5y0 by weight of ~~~~~~l ~ l ~ ~ ~- 3 0 ~ (methyl silicone gum rubber) on 60/80 mesh Chromosorb W. The column was preconditioned a t 250’ C. for 72 hours prior to use. Operating Conditions. The compounds to be investigated were dissolved either in benzene, carbon tet-
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