thiourea in the solution t o avoid the reverse reaction between thiourea and gold(II1) which produced the gold(1) thiourea species. Oxidation of thiourea in acidic solution t o give sulfate ion required the action of a vigorous oxidant in a boiling solution (9). Aqua regia (3 parts concentrated hydrochloric acid to 1 part concentrated nitric acid) proved to be effective for this dual purpose. The higher the concentration of thiourea in the solution, the more aqua regia had to be added to ensure that the gold remained in the gold(II1) form; this relationship had to be determined empirically. The quantity of concentrated aqua regia required t o oxidize the thiourea in 10 ml of 0.1M sulfuric acid solution in shown in Figure 1 . The destruction of the thiourea was marked by a n effervescence in the solution (distinct from boiling) and the evolution of nitrous fumes; at higher concentrations of thiourea, this effervescence became very vigorous. A slight cloudiness in the liquor was usually the result of the addition of insufficient aqua regia; this shortfall was made good before proceeding further. The key to the success of this procedure was the complete destruction of the thiourea before the solvent extraction. This procedure was tested by preparing a stock solution of gold(II1) in chloride medium. Aliquots of this solution were analyzed by extracting the gold directly into diisobutyl ketone containing Aliquat 336, and the results compared with those obtained after aliquots of the gold stock solution had been made up to various thiourea concentrations. The results are shown in Table I. By varying the volume ratio of aqueous to organic phases between 1 :1 to 100: 1, gold(II1) chloride concentrations between 2.5 X to 5 x 10WM (50 to 0.01 mg l.-*) were determined by extraction into diisobutyl ketone containing Aliquat 336 and atomic absorption spectrometry (IO). Provided the thiourea concentration of the liquor to be analyzed
Table I, Results Obtained from the Determination of Gold in Solutions Containing as Much as 0.5M Thiourea Molar concn of Molar concn of Volume ratio used gold as determined thiourea of in solvent extraction by A.A. spectromaqueous sample (aqueous/organic) etry ( X 106) 1:l 1:l
NIL 10-3 10-3 10-2 10-2
3
x
3
x
2 5
x 10-1 x lo-'
IO-'
NIL
3
x
3
x
2
x
10-3
10-3 10-9 10-2 10-1 10-1
1:l 1:l 1:l 1:I 1:l 1:1 IO: 1 10:1 10: 1 10: 1 IO: 1 10: 1 IO: 1
42, 42 42, 42 42, 42 43,43 43,43 43,43 42, 42 41, 42 4.2,4 . 2 4.3,4.3 4.3,4.3 4 . 3 ,4 . 2 4.3,4.3 4.3,4.3 4.0, 4 . 2
was 50.1M, the volume of aqua regia added was too small to decrease the sensitivity of the technique. When the thiourea concentration was >O.IM, a limit was imposed upon the method by the large volumes of sample solution which had to be treated with aqua regia; when the thiourea concentration was as large as 0.5M, it was still possible to determine accurately gold concentrations of about 10-8M. ACKNOWLEDGMENT
We thank Miss L. M. D. Jones and Mrs. H. S. Stenton who were responsible for some of the experimentation. RECEIVED for review March 31, 1971. Accepted June 2, 1971. Permission to publish this manuscript was granted by the Chamber of Mines of South Africa.
(9) P. C. Gupta,Z. Alia/. Cliem., 196,412(1963). (10)T. Groenewald, ANAL. CHEM. 41, 1012 (1969).
Direct Analysis of Metal Halides by Electron Impact Mass Spectrometry Kozo Matsumoto, Nobutoshi Kiba, and Tsugio Takeuchi Department of Synthetic Chemistry, Faculty of Engineering, Nagoya Uniuersity, Nagoya, Japan
SERIOUS PROBLEMS occur in the analysis of metals by conventional (electron impact) mass spectrometry, mainly because of the severely restricted volatility of metal compounds. T o overcome these problems, some specific reactions between metal or metal compounds and chelating agents to form volatile metal chelates have been studied and been successfully applied to mass spectrometry (1-5). The resulting mass spectra, however, are generally fairly complex because of the (1) S . Sasaki, Y . Itagaki, T. Kurokawa, and K. Nakanishi, B ~ / / . Chem. SOC.Japan, 40, 76 (1967). (2) R . B. King, J . Amer. Cliern. SOC.,90, 1412 (1968). (3) Ibid.,p 1417. (4) Ibid.,p 1492. (5) M. J. Lacey, C. G. MacDonald, and J. S . Shanno, Org. Mass Spectnrm, 1, 115 (1968).
fragmentation of the chelate compounds, such as the fluorinated P-diketone complex of metals ( 6 4 , etc. This paper describes the direct analysis of metal halides by conventional mass spectrometry. This method can provide very simple and sensitive mass spectra of metal halides without any troublesome sample treatment. EXPERIMENTAL
Mass spectra of metal halides were obtained using a Nihondenshi JMS-OISG double focusing mass spectrometer (6) B. R. Kowalski, T. L. Isenhour, and R. E. Sievers, ANAL. CHEM., 41,998 (1969). (7) J. L. Booker, T. L. Isenhour, and R. E. Sievers, ibid.,p 1705. (8) 13. Belcher, J. R. Majer, R. Perry, and W. I. Stephen, A n d . Chim. Acra, 45, 305 (1969).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
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I
-c 0 Figure 1. Mass spectrum of bismuth iodide
I,'
100
I50
cdt
w 9
3
"ye
Figure 3. Mass spectrum of zinc chloride Sample temperature: 220 "C
Sample temperature: 160 "C
I+
50
ai+
0
f
I
YI
Figure 3. Mass spectrum of cadmium iodide Sample temperature: 280
xi'
Figure 4. Mass spectrum of cadmium bromide
"C
Sample temperature: 300 "C
SlCG Figure 5. Mass spectrum of stannous chloride
AI.
Id1 I I
I,
3-d 11
,
,
lll!JI,,
,
, ,111;
,
operating at a resolution of 5000 (collector slit: 50 k ; main slit: 30 p ) , a n ionizing voltage of 75 eV, and a n accelerating potential of 6 kV. The sample of metal halide was deposited in a glass capillary, 1-mm i.d. (one end of which was flamesealed from its alcohol solution by use of a microsyringe). After drying in a n air oven at 50 "C, the capillary was directly introduced into the ionizing chamber, whose temperature was maintained constant between 160 and 300 "C. Quantitative measurements were carried out by using the integrated ion current method proposed by Jenkins and Majer (9). RESULTS AND DISCUSSION
Figures 1-5 show the mass spectra of five metal halides, such as Birr, Cd12,ZnC12,CdBr?, and SnCL The mass spectrum of BiIa is very simple, because the natural abundance of both ZoQBiand 12'1 is 100%. The other spectra show more complex multiples because of the associated
,
.XI: +LI.l+-
Sample temperature: 190 "C
natural isotopes of the elements. Each cluster of the multiplets provides good information about the composition of the metal compounds when the mass number, interval, and relative abundance of each peak are taken into consideration together. From the spectrum of SnCh (first grade reagent), we can see two additional clusters of SnCW and SnC14+, which presents unambiguous evidence supporting the contamination of SnCI4in the reagent. By this method, less than 10-10 gram of Cd12can easily be detected. Further study of ultimate detection limit of each metal halide and the utility of this method for trace analysis and for other metal compounds besides the halides is now currently in progress. ACKNOWLEDGMENT
The authors thank Dr. S. Tsuge of Nagoya University for several helpful discussions.
.-
(9) A. E. Jenkins and J. R. Majer, Tuluntu, 14, 777 (1967).
1692
RECEIVED for review April 2,1971. Accepted June 4,1971.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 12, OCTOBER 1971
