ACKNOWLEDGMENT
Table II. Analysis of Standard Samples GraviProposed metric“ method Monazite (Tho2 %) (Tho2 %) NBS Standard 9.65 9.72 NBL-C-824
3.42
3.33
NBL-C-822 6.74 6.64 South African 5.85 5.90 Kava 6 . LO 6.01 Indian 10.00 9.88 Lindsay 5 . !34 6.00 a Analysis by the supplier except Lindsay monazite.
determined by the proposed method. The results are quite satisfactory as shown in Table 11. The time required for the determination of thorium in monazite sand is less than eight hours, including the time for the perchloric acid decomposition. This method is fairly rapid when compared with the usual gravimetric procedures.
The authors are grateful to the New Brunsivick Laboratory of the U. S. Atomic Energy Commission, Thorium Limited, England, and the Lindsay Chemical Division of the American Potash and Chemical Corp. for kindly supplying the samples of monazite. LITERATURE CITED
(1) Clinch, J., Simpson, E. A,, Analyst 82, 258 (1957). (2) Dyrssen, D., Svensk Kem. Tidskr. 65, 43 (1953). (3) Dyrssen, D., Dahlberg, V., Acta Chem. Scand. 7, 1186 (1953). (4) “Treatise on Analytical Chemistry,” I. &I.Kolthoff, P. J. Elving, eds., Part 2, Vol. 5 , p. 139, Interscience, 1961. ( 5 ) International Union of Pure and Ap-
plied Chemistry, “Spectrophotometric Data for Colorimetric Analxsis,” 1). 521, Butterworths, London, 1963.’ ( 6 ) Tsmail. A. M.. Harwood. H. F.. \ - I
Analyst 62,185 (1937). ( 7 ) Korenman, I. hl., Tumanov, A. A,, Sorokina, V. M.,Izv. Vysshikh Ucheb. Zavednii. Khim. i Tekhnol. 3, KO. 4, 580 (1960); C.A. 5 5 , 1163 (1961).
W.,Sprain, W.,Banks, C. V., ANAL.CHEM.25, 249 (1953). (9) Moeller, T., Ramaniah, bI. V., J . (8) Margerum, D.
Am. Chem. SOC.75, 3946 (1953). (10) Mukoyama, T., Hirano, S., Yagi, I., Katsurnata, S.,Kogyo Kagaku Azsshi ( J . Chem. SOC.Japan, Ind. Chem. Sect.), 64, 969 (1961). (11) Okura, T., Goto, K., Yotuyanagi, T., ANAL.CHEY.3 4 , 581 (1962). (12) Star$, J., Anal. Chim. Acta 28, 132 (1963). (13) Stine, C. R., Gordon, L., ANAL. CHEM.25, 1519 (1953). (14) Takeuchi, T., Ishii, D., Shijo, Y., Kogyo Kagaku Zasshi ( J . Chem. SOC. Japan, Ind. Chem. Sect.), 6 5 , 1956 (1962). (15) Tillu, &I. AI., Sthavale, V. T., Anal. Chim. Acta 1 1 , 62 (1954).
KATSUMI GO TO^ D. S. RUSSELL S. S. BERMAN
Division of Applied Chemistry National Research Council Ottawa 2, Ontario, Canada 1 Permanent address, Faculty of Engineering, Hokkaido University Sapporo, Japan.
High Resolution Mass Spectra of Compounds Separated by Ca piIla ry Co Iu m ns Use of a Plate Scan Technique SIR: The use of a high resolution mass spectrometer of the AlattauchHerzog type for combination with a gas chromatograph was described recently by Biemann and Watson (1, 6). They also discussed the special advantages of the high resolution technique. The authors connected packed columns to the mass spectrometer with a pressure reduction system, the use of which results in enrichment of the sample in the carrier gas by a factor of a t least 10. Many analytical problems require the high separation power of narrow capillary columns. We tried to determine whether a connection of such a column to a high resolution mass spectrometer would work successfully.
m-&--, Figure 1, ments
Plate
Interconnection of instru-
A. Mass spectrometer inlet system with calibration compound B. Capillary column C. Connection device MS. Mass spectrometer FID. Flame ionization detector TI. Total ionization signal
EXPERIMENTAL
Figure 1 shows the arrangement of the entire apparatus. The gas chromatograph (Perkin-Elmer F 20) was equipped with a 160-foot, 0.Ol-inch i.d. column, which gave a helium flow rate of 1-2 ml./minute with a pressure drop of about 20 p.s.i. The mass spectrometer (CEC 21-110) is of the hlattauchHermg type, offering the advantages of taking complete spectra on a photographic plate. Ion source temperature was 150’ C.; ionization current, 40 pa. By means of the normal inlet system a perfluorocompound was added to give calibration lines for accurate mass measurement. Because the original beam monitor amplifier was too slow to follow the variation of total ion current when a peak from the column passed the ion source, it was replaced by a faster one (Atlas DC 60). The beam monitor signal was written on a dual trace recorder together with the flame ionization detector signal. Fortunately the high pressure of helium in the ion source (between and torr) does not contribute much to the beam monitor signal because ions of m/e 4 are suppressed according to mass discrimination. For the connection of capillary columns to a mass spectrometer it is of great importance to maintain the gas chromatographic separation. Among the examples in the literature are some in which this requirement is met (24). For our work we preferred a sys-
tem (Figure 2) similar to that described by Brunnke et al. (8). It consists of a leak built by a glass capillary which is in connection with the inlet line of the mass spectrometer. The effective part of this capillary is of a length of about 1 cm., and the diameter is chosen to cause a flow rate of 0.5 ml./minute of helium into the ion source. One half of the column effluent is led onto this leak via a 50-cm.-long, coated steel capillary of 0.01-inch i.d. To get the maximum amount of flow from the gas chromatograph into the mass spectrometer, very careful adjustment is required in positioning the capillary exit of the gas chromatograph in respect to the glass leak entrance. This can be achieved by an arrangement of a spring and two screws (Figure 2). The optimal position was found by running the column with argon and adjusting the position of the capillary up to a maximum current of m/e 40. Because even with best adjustment small amounts of gas from outside of the connection region enter the mass Spring
I
u
-A
m ! r
Adi .
SA
Figure 2. device
1
Scavenge
GCS
Schematic of connection
VOL. 38, NO. 3, MARCH 1966
495
-ETHYL
PROPANOATE
PLATE SCAN O F PARTIALLY SEPARATED COMPONENTS
.t.
TIME
I
*BENZENE
FLUORO C O M P O U N D
FLUORO C O M P O U N D BENZENE ETHYL PROPANOATE
+ +
Figure 3.
spectrometer, a scavenge gas flow of helium around this region is provided to reduce air background and to protect the filament against high oxygen pressure. A connection between the gas chromatograph and mass spectrometer with an enrichment device of the kind described bv Watson and Biemann mav not be ve“ry useful when using narro; capillary columns for separation. With an effluent flow rate of 1-2 ml./minute of helium and a flow of 0.5 ml./minute into the mass spectrometer, the best enrichment obtainable is given by a factor within only 2 and 4, and i t is questionable whether such a system causes broadening of peaks with the result of lower resolution of the a p paratus. Recently Ryhage reported the connection of a capillary column to a mass spectrometer by means of a one-stage molecular seDarator (6). The influence of the system on separation in not given in this report. RESULTS AND DISCUSSION
With the connection system described above, peak widths of flame ionization detector and total ionization signal are the same for peaks emerging under conditions where 100,000 theoretical plates are calculated. It is possible, therefore, to take advantage of the good separation capabilities of a narrow capillary column. The total ionization signal is essential to make use of the separation power of the column because peaks a t the beginning of the chromato-
496
ANALYTICAL CHEMISTRY
Spectra of t h e effluent of the capillary column
gram pass in only a few seconds and demand a precise control of the time schedule for exposure time and movement of the plate from one trace to the next. The limitation of the combination of instruments with respect to the sensitivity of the mass spectrometer is characterized by the following example: With
[email protected] current, 0.3 Mg. of a substance (methylcyclopentane) is needed to get a spectrum on the photoplate with all stronger lines clearly visible. Figure 3 is a part of a plate with spectra obtained from the effluent of the capillary column. The lowest spectnun originates from a mixture containing benzene and ethyl propanoate. It corresponds to a peak which is unsymmetrical and is 1.5 times wider than it should be, indicating partial overlap of the two components. I n this special case the high resolution technique not only gives the elemental composition of the ions, but separates the two spectra, because the two compounds are of different elemental composition. But there is another possibilityfor additional information. That is to make a plate scan for looking at the variation of individual spectra in time. A plate scan is achieved by continuously moving the plate during emergence of a peak. This results in a variation of intensity for the whole spectrum, proportional to the partial pressure of the substance in the ion source.
The upper part of Figure 3 shows the results of a plate scan for the poorly separated peaks containing benzene and ethyl propanoate. The lines from benzene appear earlier than those of etbylpropanoate. By recognizing the center of density for an individual line, its origin can be determined. The result in Figure 3 is not optimal because the slit in the magnet gap, which defines the length of the lines on the plate, is 2 mm. wide. 4 new slit 1 or 0.5 mm. in width would have shown a better resolution in time axis during plate scan. The ordinary technique of taking a number of individual spectra through the peak by moving the plate stepwise appears impractical for peaks which pass in a few seconds. LITERATURE CITED
(1) Biemann, K., Watson, J. T., Maatah. Chem. 96,305 (1965). (2) Brunnhe, C., Jenckel L , Kronenberger, K., Z. Anal. &hem. 197, 42 (1963). (3) Dorsey, J. A Hunt, R. H., O’Neal, M. J., ANAL. %am. 35, 511 (1963). (4) Henneberg, D., Schomburg, G., “Gas Chromatography 1962,” p. 191, M. van Swaay, ed., Butterworths, London, 1963. (5) Ryhage, R., Wirkstrom, S., Wnller, G. R., ANAL.CHEM., 37, 435 (1965): (6) Watson, J. T., Biemann, K., lbid., 37, 844 (1965).
Dmma HENNEBER Max-Plnnck-Institut fur Kohlenforschung Mhlheim-Ruhr, West Germany
