a t a concentration of 2 nanograms (about 6 gpmoles) would be visible (about 5 mm. high on the most sensitive galvanometer). A GC peak height of 1 mm. would correspond to approximately 0.6 nanogram. A GC peak of 56 mm. was obtained from 28 nanograms of standard methyl undecanoate (retention time, 14.5 minutes). Because a 1mm. peak is visible, it follows that 0.5 nanogram or 2.5 pgmoles can be detected. I t is possible to make the total ion current detecting unit a t least 10 times more sensitive, but routine operation of the combination instrument a t this setting was unsatisfactory. This combination mass spectrometer-
gas chromatograph can detect as little as 0.5 nanogram of a substance, provide a molecular ion peak at a concentration of 2 nanograms, and provide an interpretable mass spectrum from 20 nanograms. These values are typical for methyl esters of fatty acids such as methyl undecanoate or methyl docosanoate. LITERATURE CITED
( I ) Gohlke, R. S., ANAL. CHEM. 34, 1332 (1962). ( 2 ) Mason, M. E., Eager, M. E., Waller, G. R., Zbid., 36, 587 (1964). ( 3 ) McFadden. W. H.. Teranishi. R..
( 4 ) McFadden,
W. H., Teranishi, R., Block, D. R., Day, J. C., J . Food Sci. 28, 316 (1963). ( 5 ) Ryhage, R., ANAL. CHEM.36, 759 (1964). ( 6 ) Widmer, H., Gaumann, T., H e l . Chim. Acta 25, 2175 (1962). R. RYHAGE
s. WrKsTROM
G. R. W A L L E R ~
Laboratory for Mass Spectrometry Karolinska Institutet Stockholm 60, Sweden This author is indebted to Oklahoma State University, Stillwater, Okla., for granting him leave of absence, and to the Xational Institutes of Health, Bethesda, Md., for a fellowship.
Molybdenum(V)-Th iocya na te Co m plex Extracted into Chloroform from an analysis of infrared spectra. SIR: The reduction of acidic solutions Recently, Allen et al. ( I ) examined of molybdate by stannous chloride in the several salts containing the oxyhalide presence of thiocyanate has been used ions, [pVloOX4]- and [ M O O X ~ ] -and ~, as the basis for the spectrophotometric deduced that the latter is an octahedral determination of molybdenum. Bemonomer. cause this reaction is kinetically and Aryl “onium” ions, including tetramechanistically complex, careful regulaphenylarsonium, tetraphenylphostion of the many variables in the phonium, and quaternary ammonium system is required to achieve analytical ions, have been useful both in the reproducibility. One representative extraction of inorganic anions into procedure i s that of Crouthamel and water immiscible polar solvents ( 4 ) and Johnson (5) involving an aqueousin the precipitation of anionic coordinaacetone solution for the reduction tion complexes ( I S ) . I n these applicamedium. Another approach was used tions the union between the complex by Wilson and McFarland ( I d ) in ion and the “onium” cation is an aswhich the thiocyanate complex of the sociated ion pair in the nonaqueous reduced molybdenum is extracted into solvent and an ionic bond in the solid chloroform in the presence of a quater( I f , IS). For the present study, nary ammonium thiocyanate. Altriphenylsulfonium bromide was used to though the thiocyanate complex meaextract and precipitate oxypentathiosured in these procedures contains cyanatomolybdate(V) ion from acidic molybdenum in the + 5 oxidation state, media, as shown by the net reaction in the exact identity of the colored species Equation 1 . is uncertain. Perrin (9) concluded that uncharged MoO(SCN)~is formed in [MOOC16]--2 5 SCNaqueous-acetone. I t is the purpose of this communication to report the isola2 (Ce“)aS+ --* tion of oxypentathiocyanatomolybdate [ ( C B H ~ ~[MoO(SCN)s SI~ It (V) ion from a chloroform extract. 5 c1- (1) Solid molybdenum(V) chloride is dimeric with an octahedral arrangement The solution of oxypentachloromolybof the chlorine atoms about the molybdate(V) ion was obtained by dissolving denum, and a similar structure has been molybdenum(V) chloride in dilute hyassigned by Mitchell and Williams (8) to pyridinium salts of [ M O O ~ ( S C N ) ~ ] - ~drochloric acid.
+
Table 1.
436
Element
Exptl. %
C H M0
52.0 3.20 11.15
ANALYTICAL CHEMISTRY
+
Elemental Analysis
52.9 3.26 10.35
35.6 2.49 15.8
EXPERIMENTAL
The absorption spectrum of the thiocyanate complex of molybdenum(V) was determined with a Beckman Model DU spectrophotometer. Reagents and Solutions. Triphenylsulfonium bromide was prepared by the Grignard reaction reported by Potratz and Rosen (IO). The melting point of the product was 285-6’ C., after recrystallization from acetone. A 0.01M solution wm made in water. Molybdenum pentachloride was synthesized by the direct union reaction analogous to that for tungsten(1V) chloride ( 7 ) . Manipulations of this compound were made in a dry nitrogen atmosphere. A 0,05M stock solution of molybdenum(V) was made by dissolving MoC16 in 3.1.1 HC1. Preparation of Bis(triphenylsu1fonium)Oxypentathiocyana t omolybdat e (V). An aqueous solution containing 0.24 mmole of the stock molybdenum(V) and 8 mmole of ammonium thiocyanate in a final volume of 80 to 100 ml. was allowed to stand in a separatory funnel for 30 minutes. A 0.24 mmole portion of the triphenylsulfonium bromide solution was added, and the mixture was immediately extracted with successive 50-ml. volumes of reagent grade chloroform until no red color appeared in the chloroform phase. The combined extracts were dried over calcium sulfate, and this solution was slowly concentrated a t room temperature in a vacuum desiccator with gentle suction from a water aspirator. When crystals began to form, the chloroform solution was cooled in an ice bath and the solid was filtered with suction. The crude product was recrystallized from chloroform to give a final yield of 9.3y0.The dark red solid had a melting range of 161-2” C. and an absorption band at 466-7 mp in chloroform. Results from elemental analysis by micro methods are summarized in Table I.
RESULTS AND DISCUSSION
The addition of triphenylsulfonium ion to the acidic reaction mixture containing XZo(V) and thiocyanate yields a deep red amorphous precipitate in the absence of chloroform. Since the identity of the chloroform-soluble species was the principal concern in this work, isolation of the water-insoluble product was not attempted. When the chloro-complex of Mo(V) in 3M hydrochloric acid was treated directly with the triphenylsulfonium bromide, no precipitation occurred. A trial preparation of tris(tetraphenylarsonium) hexathiocyanatoferrate (111) was undertaken as a model for synthesis of the corresponding hlo(V) compound. Finely divided crystals mere obtained from a water solution of the reactants; however, analyses for C, H, As, and Fe differed by more than 57, from the theoretical values. The visible and near ultraviolet spectrum for chloroform extracts of the reaction mixture contained a sharp absorption peak a t 315 mp, indicating tetraphenylarsonium thiocyanate was present, The same band was found in the chloroform extract of the aqueous mixture of N o ( V ) , S C S - , and tetraphenylarsonium ion ( 6 ) . I t was concluded that tetraphenylarsonium ion is not suitable for the precipitation of anionic thiocyanate complexes without coprecipitation.
The results in Table I indicate that [ M O O ( S C N ) ~is] -extracted ~ into chloroform when a large organic cation is present. I n the earlier application of the method of continuous variations to the molybdenum-thiocyanate system the measurement of the maximum absorbance in the chloroform phase corresponding to a given ratio in the aqueous phase (6) does not necessarily give a correct value for the M o : S C K ratio in the extract. Although the distribution ratio for the complex was not determined, it is likely that the 1 : 6 ratio for hlo :SCX obtained earlier reflects a displacement of the maximum in the continuous variations plot toward a higher ratio because of incomplete extraction of the complex. Babko ( 2 ) found evidence for a hIo:SCN ratio of 1: 5 in solutions of reduced molybdate containing high concentrations of thiocyanate, but he assumed this represented an uncharged species. It is clear that one of the pentavalent molybdenum thiocyanate complexes is anionic. Haight ( 5 ) assigned a dimeric structure in Equation 2 for the Mo(V) species formed by the Sn(I1) reduction of molybdate in 3.M hydrochloric acid. Mo(1V)
+ Mo(V1)
+
[Mo(V)]* (2)
The 2 : l stoichiometry of the onium ion-molybdenum complex above does not distinguish between a monomeric or dimeric structure for the oxypenta-
thiocyanatomolybdate(V); however, Wilson and McFarland (12) obtained a distribution ratio in chloroform indicating a 1: 1 association of a quaternary ammonium ion with Mo(V) a t very low concentrations of the complex. LITERATURE CITED
( 1 ) Allen, E., et al., J . Chem. SOC.1963, 4649. (2) Babko, A., J . Gen. Chem. (C‘.S.S.R.) 17, 642 (1947). ( 3 ) Crouthamel, C., Johnson, C., ANAL. CHEM.26, 1284 (1954). ( 4 ) Diamond, R., Tuck, D., “Progress In Inorganic Chemistry,” Vol. 2, p. 139, Interscience, New York, 1960. (5) Haight, G. P., J . Inorg. .Yucl. Chem. 24. 663 11962). ( 6 ) Kolling, 0. W., Trans. Kansas Acad. Sci. 58, 430 (1955). ( 7 ) Lietzke, M., Holt, ll., “Inorganic Syntheses,” Vol. 3, p. 165, AIcGrawHill, Yew York, 1950.
(8) Mitchell, P., Williams, R., J . Chem. Soe. 1962, 4570. (9) Perrin, D., J . A m . Chem. SOC.80, 3540
11958). (10) Po’tratz, H., Rosen, J., A N A L CHEM.21, 1276 (1949). (11) Sheldon, J., Tyree, S., J . A m . Chem. SOC.80, 2117 (1958). 112) Wilson, A , . McFarland, 0.. AKAL. CHEM.36.’ 2488 119641. (13) Zaslow, B., kundle, R., J . Phys. Chem. 61, 490 (1957).
ORLAND W. KOLLINC Department of Chemistry Southwestern College Winfield, Kan. 67156
Spectrophotometric Determination of Calcium in Uranium Using Glyoxal Bis-(2-Hydroxyanil) SIR: Glyoxal bis-(2-hydroxyanil) (hereafter glyoxal) is a specific reagent for spot test detection of calcium ( 1 ) . The spectrophotometric determination of calcium using this reagent was applied by Williams and Wilson (3) for solutions of calcium in the presence of common cations including magnesium, strontium, and iron. Nuclear pure ammonium diuranate and uranium oxides (cos, EOn, and c308) have been analysed in our laboratory for their calcium content with this reagent, after the separation of the uranium with hydrogen peroxide precipitation ( a ) ,tributyl phosphate (TBP) extraction in nitric acid, or retention of the uranyl sulfate complex on an anionic ion exchange resin(su1fate form). EXPERIMENTAL
Apparatus. Measurements were made with a Hilger spectrophotometer (Hilger 8: Watts, Ltd., London), using 1-cm. matched, square cells. Conical glass centrifuge tubes (12
cm. of height and 12-ml. capacity, with glass stopper) were used for the color extraction. Reagents. Glyoxal (E. hlerck Ag. Darmstadt). Make a 0.4yo w./v. solution of glyoxal in ethyl alcohol. Prepare this solution fresh daily. Prepare a color developing solution by dissolving 10.0 grams of sodium hydroxide and 0.5 gram of sodium carbonate in 100 ml. of water. Ion exchange column. Transfer 5 ml. of Kalcite SAR (30-50 mesh) anionic ion exchange resin to a glass tube (8-mm. i. d.) column and condition the resin by passing 25 ml. of 1-11 HzS04 and wash with 50 ml. of water. Procedure. SEPARATION OF URANJU.M.
Precipitation of Uranium by H y drogen Peroxide. Use uranyl nitrate solution prepared by dissolving the samples (17308j, U02, Cos, or ammonium diuranate calcinated to r 3 0 8 ) with minimum amount of 6J1 HxO3 and dilute to desired volume with water. The optimum p H of the final solution is 1-3. Pipet 2 to 10 ml. of uranyl nitrate
containing 100 to 500 mg. of r308 (2 to 14 pg. of calcium) into a centrifuge tube, add 1 ml. of 30% hydrogen peroxide, mix thoroughly with a glas:, rod and keep in the refrigerator for 20 minutes. Centrifuge and pour the supernatant through a R h a t m a n 41 filter (previously washed with water), recovering the filtrate directly into a platinum crucible (to avoid calcium from glass). Add 2-3 drops of 30% hydrogen peroxide to the centrifuge tube and make the volume 5-7 ml. with demineralized water, mix the precipitate thoroughly with a glass rod and centrifuge again. Collect the second sup,ernate using the same filter. Evaporate the filtrate to 3-5 nil. on a hot plate, transfer to a 25-m1. volumetric flask and make uli to the mark with water. I‘se aliquots of this solution for the determination of calcium. Extraction of Uranium with Tributyl Phosphate. To 2 ml. of uranyl nitrate solution (100 mg. of V308), add 5 ml. of 6.11 H?;Os and extract 5 times with 1 nil. of 20y0 TBP in CCl,, and finally wash the aqueous phabe twice with 2 ml. of VOL. 37, NO. 3, MARCH 1965
437
