counted in a 5- X 5-inch NaI (TI) well crystal connected to a 256-channel pulse height analyzer. The portion of the y spectrum between 0.20 and 0.50 m.e.v., which included the 0.22 and 0.28 photopeaks, was used to calculate the Np239 count rate. This count rate was corrected for the contribution made by the Zr95-Xb95. DISCUSSION
Table I is a summary of the eight determinations that were made to establish the relationship between NpZ39 counts and Am243 concentrations a t equilibrium (Np eq./Am). The figure in column 4 is referred to as an “apparent counting efficiency,” since it also includes the errors involved in separating the Np. The results of Table I were then applied to the analyses of sixteen sam-
ples from laboratory scale studies of proposed processes for actinide-lanthanide separation and americium-curium separation. Where the age or history of the sample was uncertain, two extractions were necessary. The first Np extract was discarded and new Np was allowed to “grow in” for a specified time, usually about twenty-four hours. The “in-grown” Np was then extracted, counted, and corrected to equilibrium. The amount of Am243in the samples was also determined by the mass spectrometric method. The average recovery of AmZ43, when analyzed by separating and measuring its NpZ39daughter activity, was 99.5y0 of the value obtained by the mass spectrometric method. The relative standard deviation of an individual determination was =t3.3%‘,.
ACKNOWLEDGMENT
The author gratefully acknowledges the assistance of B. L. Bussey of the Savannah River Plant who performed the mass spectrometric determinations of Am243. LITERATURE CITED
( 1 ) Banick, C. J., Carothers,
G. A , ,
Donaldson, W. T., ANAL. CHEY. 35,
1312 (1963). (2) Murray, B. B., c’. S . At. Energy Comm. Revt. DP-316.SeDtember 1958. ’ C ~ R IJ. L BAXICK
Savannah River Laboratory E. I. du Pont de Nemours & Co. Aiken, S. C. The information contained in this article was developed during the course of work under Contract AT(07-2)-1 with the
U. S. Atomic Energy Commission.
Mass Spectrometer Used as Detector and Analyzer for Effluent Emerging from Capillary Gas Liquid Chromatography Column Sir: One of us (6) recently described a combination mass spectrometergas chromatograph which employed two molecular separators coupled in series between the column and the inlet line of the mass spectrometer. With this technique, the sample-to-helium ratio is increased a t least 100 times, and good spectra were obtained from less than 1 pg. of material. This communication describes the extension of this combination instrument to capillary gas liquid chromatography columns. The increase in resolution normally obtained with capillary columns is extremely useful in analyzing mixtures of compounds having similar properties-Le. , the fatty acid esters, C I S , CIS:^, CIS:^, and C18:3. With this combination instrument, capillary or packed columns can be used without modification of the inlet system of the mass spectrometer. The time required to change from a packed column to a capillary column is less than 1/2 hour. Other differently designed combination instruments using capillary columns have been described (1, 3, 4, 6), but attention has been directed chiefly to the analysis of compounds with low molecular weight. EXPERIMENTAL
Apparatus. The arrangement used for connecting the capillary column to the mass spectrometer varies from that previously reported (6) in that only one molecular separator is used and that a part of the total ion current is collected on a plate in the analyzer tube rather than in the source. Continuous registration of the total ion current serves
** M
354 /
as the gas chromatographic record. The helium pressure at the sample inlet side was in most cases 1.0 kg. per sq. cm., giving a flow rate of about 0.5 ml. of He per minute. The operating temperatures were: ion source, 250” C.; injection port, 285’ C. The column was run either isothermally or programmed linearly. The temperature programmer was the same as that used karKer ( 5 ) . GLC Column. h 90-foot stainless steel capillary column, 0.01-inch i.d., 20% diethyleneglycolsuccinate (DEGS) (Applied Science Laboratories, State College, Pa.) supplied by M.E. Mason, Oklahoma State University, was used. Methyl undecanoate was obtained from Applied Science Laboratories. I t was equipped with a 7 :1 precolumn split device. Methyl esters were prepared from peanut oil by the method of Mason, Eager, and Waller (2). The samples were injected onto the GC column in 0.1 to 0.5 jd. of redistilled acetone. Temperatures above 170’ C. were avoided because of excessive bleeding. RESULTS A N D DISCUSSION
-
* . d Figure 1 . High mass end of mass spectrum of compound identified as docosonoate Galvanometers sensitivity ratios, 1 : 10: 100
Figure 1 shows the high mass end of the mass spectrum of docosanoate from the iniection of 10 fig. of peanut oil methyl esters. The peaks in the m/e 333 region are caused by column bleeding. This spectrum was recorded when the concentration was less than 0.2 pg. [calculation based on the average content of docosanoate in peanut oil @)], the retention time was 46 minutes, and the GC peak height was 32 mm. The most sensitive galvanometer deflection was 470 mm., which indicated that the molecular ion of a mass spectrum taken VOL. 37, NO. 3, MARCH 1965
435
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 or methyl methyl undecanoate 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. WALLER~
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 ) . In 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 [(CBH~~ [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)Oxypentathiocyanat 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.
