square root of the number of determinations. I t is realized that the 99% confidence limits would be somewhat lower for the results obtained from the solution calibration, since the average of four instead of three determinations was used. However, the slight difference was not significant in this investigation. In order to determine long-term accuracy, a freshly prepared standard was analyzed (sample 4, Table 11) using the solution calibration. The mean errors do not differ significantly from experimental error. The calibration was 5 months old a t the time of analysis. Also, in the time interval between calibration and analysis, a new filament had been installed in the source. I t is not unreasonable that the solution calibration gives results closer to the true values. This is so because the calibration data are obtained under conditions closer to those for actual analysis of unknowns. For example, the partial pressures obtained for the various compounds in the known mixture used for calibration are closer t o the partial pressures obtained from the known solutions used to check the method than is the approximately 100-micron pressure used for each compound during the pure compound calibration. Also, any interference errors ( 2 ) tend to cancel, since they are present during calibration as well as during analysis of unknowns. These effects could be investigated, but
they were beyond the scope of the present work. Errors Due to Hydrolysis. Because of the reactive nature of chlorosilanes with moisture, i t was necessary to determine the errors due to hydrolysis of samples submitted for analysis. It was found t h a t 1% by weight of water could cause errors of more than 10 relative 7,. However, leaving samples in uncapped bottles for 30 minutes caused no significant errors. This is much longer than the time needed to remove a sample for analysis. Any significant amount of hydrolysis can be detected by observing the polysiloxane peaks a t mass numbers 187, 207, and 281. The 281 peak, which is due to a fragment ion from the polysiloxane, is the most sensitive. Detecting the hydrogen chloride given off during hydrolysis is not satisfactory, since it might be lost from the sample because of its volatility. The HC1+ ion is frequently observed as background in the mass spectrometer. Pumpout Time after Analysis. The diphenyldichlorosilane has the lowest vapor pressure in the present system (b.p. 304’ C. a t 760 mm.). Two minutes after opening the reservoir to the pump the strongest peak a t mass number 154 was reduced to 0.2% of its original height. This is equivalent to 0.2 mole Yo diphenyldichlorosilane.
ACKNOWLEDGMENT
The author is grateful to A. S. Crouse, who obtained most of the experimental data for this n-ork. LITERATURE CITED
(1) Barnard,
G. P., “Modern Mass Spectrometry,” pp. 65-7, Institute of Physics, London, 1953. (2) Bernstein, R. B., Semelup, G. P., Arends, C. B., ANAL.CHEM.25, 139 (1953). (3) Beynon, J. H., “Mass Spectrometry
and Its Applications to Organic Chemistry,” p. 298, Elsevier, New York, 1960. (4) Brewer, S.D., unpublished work. (5) Dibeler, V. H., “Organic Analysis,” p. 418, Interscience, New York, 1956. (6) Dibeler, V. H., Reese, R. M., ANAL. CHEM.32,211 R (1960). (7) Grenoble, M . E., Launer, P. J., A p p l .
Spectroscopy 14,85 (1960). (8) Grubb, H. M., Ehrhardt, C. H., VanderHarr, R. W.,Moeller, W. H., ASTM Committee E-14 meeting, Los Angeles, Calif., 1959. (9) Mea!, R. K.,Lewis, F. M., “Silicones, pp. 107-10, Reinhold, New York, 1959. (10) Norton, F. J., unpublished work. (11) Taylor, R. C., Brown, R. A., Young, 14’. S.,Headington, C. E., ANAL.CHEM. 20,396 (1948). (12) Youden, W. J., “Statistical Methods for Chemists,” Wley, New York, 1957.
RECEIVEDfor review April 27, 1961. Accepted September 7, 1961. 8th Annual Meeting of ASTM Committee E-14 on Mass Spectrometry at Atlantic City, N. J., June 26 t o July 1, 1960.
Report on Recommended Specifications for Microchemical Apparatus Oxygen Combustion Flask Committee on Microchemical Apparatus, Division of Analytical Chemistry, American Chemical Society AL STEYERMARK, Chairman, Hoffmann-La Roche Inc., Nutley, N. J. H. K. ALBER, Arthur H. Thomas Co., Philadelphia, Pa.
V. A. ALUISE, Hercules Powder Co., Wilmington, Del.
E. W . D. HUFFMAN, Huffman Microanalytical Laboratories, Wheafridge, Colo. E. L. JOLLEY, Corning Glass Works, Corning, N. Y. J. A. KUCK, College of the City of New York, New York, N. Y., and American Cyanamid Co., Stamford, Conn. J. J. MORAN, Kimble Glass Co., Vineland, N. J. C. L. OGG, Eastern Utilization Research Branch, Agricultural Research Service, U. S. Department of Agriculture, Philadelphia, Pa. C. E. PIETRI, U. S. Atomic Energy Commission, New Brunswick, N. J.
I
ACCORDANCE with the practice followed in previous reports of the Committee on Microchemical Apparatus (1, 9, 4,these specifications are for pieces of apparatus that are either the most widely used in their respective fields of application or are an improvement over such apparatus according N
to tests made by members of this committee and cooperating chemists. In this report, specifications are recommended for the conventional apparatus used in connection with oxygen flask combustion procedures (7, 8). Types of apparatus employing electric ignition (2, 6, 6) are not included be-
cause of lack of experience with these forms. Figure 1 shows two sizes of borosilicate flasks-the 300- and 5Wml. sizes-and a glass stopper with platinum sample holder which is used with a flask of either size. Although oxygen flask combustion VOL. 33,
NO. 12, NOVEMBER 1961
1789
m
6 5 + 3 M M . O.D.
‘
I
I
r 0 E A D
WALL
1
2MM.
, 102 f 3 M M O D
1
500 M L
Figure 1.
has been proved to be generally Mfe, precautions such as the use of gloves, shields, etc., should be taken. LITERATURE CITED
(1) Chem. Eng. News 26,883 (1948). (2) Cheng, F. W., Smullin, C. F., Microchem. J . 4, 213 (1960).
Borosilicate flasks for oxygen combustion procedures
(3) Committee on MicrochemicalAppara-
tus, Division of Analytical Chemistry, ACS, ANAL. 26, 1186 (1954); 28, 112, 1993 (1956); 30, 1702 (1958); 32, 1045 (1960). (4) Committee for Standardization of Microchemical Apparatus, Division of Analytical Chemistry, ACS, Ibid., 21, 1283, 1555 (1949); 22, 1228 (1950); 23, 523, 1689 (1951).
(5) Juvet, R. S., Chiu, J., I&id., 32, 130 (1960). (6) A. J*, Deveraux, Ibd., 31, 1932 (1959). (7) SchCiniger, W,, MikTochim. Acta 1954, 74; 1955, 123; 1956,869. (8) Steyermark, A., “Quantitative Organic Microanalysis,” 2nd ed., p. 292, Academic Press, New York 1961. RECEIVED for review August 9, 1961. Accepted August 9, 1961.
Estimation of Microgram Amounts of Protein Using a Modified Ring Oven SIR: The ring-oven technique described by m7eisz (34) offers a rapid, simple means for concentrating and separating materials in small samples, so that conventional reactions may be employed for identification and quantitation (4, 6). The method has gained recognition for analyses of inorganic ions (6, 7 ) but does not seem to have been seriously applied to organic or biological materials. A modified apparatus and technique extend the ringoven concept to such materials. Fundamentally, the modified apparatus differs from the Weisz ring oven in that a strip rather than a circle of 1790
*
ANALYTICAL CHEMISTRY
filter paper is used, and the sample migrates in one direction along this strip to a pair of rectangular electrically heated aluminum blocks. Materials contained in the sample are thus deposited on the paper a t the heated edge of the blocks in a single, narrow straight line across the width of the strip. The apparatus might be termed a “line oven.” This modification improves the ability to concentrate materials from the sample. The ring oven concentrates a sample by causing it to migrate from a diffuse spot in the center of a circular filter paper to a thin, sharp ring a t the
heated evaporation zone. An aqueous sample of 2 5 4 . volume will make a diffuse spot about 21 111111. in diameter with an area of approximately 350 sq. mm. The dissolved materials in such a sample can quantitatively migrate to the evaporation zone and be deposited in a thin ring approximately 22 mm. in diameter and usually less than 0.5 mm. wide. Thus, the area on the paper occupied by the materials from the sample has been reduced from about 350 to approximately 35 sq. mm., a tenfold concentration. Ideal circwnstances may yield a ring of such width thac the sample is concentrated fifty-
