1984
Anal. Chem. 1980,
52, 1984-1987
the analysis area rather than the field limiting aperture used in SAED. In SAED the field limiting aperture and the spherical aberation of the objective lens limit the minimum analysis diameter to 0.5-1 pm. In microdiffraction the beam diameter a t the sample defines the diffraction analysis diameter which can be as small as 40 nm.
ACKNOWLEDGMENT We wish to thank T. Huber of JEOL, USA, and J. Fahy of Philips Electronics Instruments for making the JEOL lOOCX and Philips EM400T instruments available for this work. We also gratefully acknowledge assistance with the experimental measurements by I. Piscopo of Philips and T. Yoshioka of JEOL.
LITERATURE CITED Figure 1. Microdiffraction pattern from a chrysotile fibril obtained in a JEOL lOOCX instrument at 100 kV
provide good SAED patterns were successively examined in the microdiffraction mode, and a positive pattern was obtained on each (see Figure 1). In another experiment 40 consecutive fibrils gave positive microdiffraction patterns. The patterns were stable and did not fade within the time required to establish diffraction conditions. In two experiments on pattern stability the pattern did not fade in 20 min. This is a significant improvement over SAED and will allow electron diffraction t o be effectively utilized in the routine analysis of chrysotile asbestos in water and air samples. In relatively clean water samples, such as tap water and many lakes, an accurate analysis should be possible by using the EPA interim method (5) with SAED replaced by microdiffraction. In relatively unclean waters, such as waste-water effluents and many river samples where a few fibers lead to a large concentration and the fibers may be compromised by coatings and other interfering materials, the identification should be based on morphology, the Mg/Si ratio determined by EDS and the microdiffraction pattern. When this approach is used in conjunction with a sample preparation technique where fiber losses are minimized (carbon-coated Nuclepore) ( 3 , 9),improved accuracy and interlaboratory reproducibility should be possible. Microdiffraction has been referred to as microbeam diffraction (17, 18), focused beam Riecke technique (19), or focused aperture microdiffraction (20). The image and diffraction patterns are formed in the normal manner, but the sample is illuminated with a fine beam of electrons. The fine parallel beam of electrons is formed by using a strongly excited first condenser lens and a small (typically 20 pm) second condenser aperture. The second condenser is focused to provide the minimum spot diameter. The diffraction pattern is formed on the back focal plane of the objective lens, magnified (intermediate lens), and projected (projection lens) as in conventional diffraction. Microdiffraction differs from SAED in t h a t the small second condenser aperture defines
"Asbestos, Ambient Water Quality Criteria". Criteria and Standards Division, Office of Water Planning and Standards, U.S. Environmental Protection Agency: Washington, DC, 1979;Document No. 297-917. Beaman, D. R.; Flle, D. M. Anal. Chem. 1978, 48, 101-110. Cook, P. M.; Rubin, I. 6.; Magglore, C. J.; Nicholson, W. J. Proceedings of Internatlonal Conference on Envronmental Senslng and Assessment; IEEE: Las Vegas. 1976;Sectlon 34-1. Mlllette, J. R. I n "Electron Microscopy of Microflbers"; Asher. I.M., McGtath, P. P., Eds.; Proceedings of the First FDA Office of Science, Summer Symposium, U.S. Government Prlntlng Office: Washington DC, 1976;pp 85-92. Anderson, C. H.; Long, J. M. "Interim Method for Determining Asbestos in Water"; US. Environmental Protection Agency: Washlngton E€, Jan 1980;EPA-600/4-80-005. Summary Report (111) of the Asbestos Methods Task Force, New Orleans, Chlorine Instttute Products Analysis and Speclflcations Committee, Analytical Procedures Subcommlttee, H. Bohmer, Chalrman. Feb 4,
1980. Mlllette, J. R.; Twyman, J. D.; Hansen, E. C.; Clark, P. J.; Pansing, M. F. I n "Scanning Electron Microscopy/l979/1"; Joharl, 0. Ed.; Scanning Electron Microscopy, Inc.: AMF O'Hare, IL, 1979,pp 579-586. Beaman, D. R.; Walker, H. J. NBS Spec. Pub/. ( U . S . )1078, No. 506,
249-269. Beaman, D. R.; Walker, H. J. I n "Electron Mlcroscopy of Microfibers"; Asher, I.M., McGrath, P. P., Eds.; Proceedings of the Flrst FDA Office of Science, Summer Symposium, U.S. Government Printing Offlce: Washlngton DC, 1976;pp 98-105. Arnplan, S. G. I n "Electron Microscopy of Microfibers"; Asher, I.M., McGrath, P. P., Eds.; Proceedlngs of the First FDA Office of Science, Summer Symposium; U S . Government Printing Office: Washington, DC, 1976,pp i2-27. Ross, M. I n "Electron Microscopy of Microfibers"; Asher, I.M., McGrath, P. P., Eds.; Proceedings of the First FDA Offlce of Sclence, Summer Svmooslum: U.S. Government Printing Office: Washlnaton. - DC. 1976, pi, 34-35. Biles, 6.; Emerson, T. R. Nature (London) 1966, 219,93-94. Samudra, A. V. I n "Scanning Electron Microscopy, 1977/1"; Joharl, O., Ed.; Scanning Electron Microscopy, Inc.: AMF O'Hare, IL, 1977, pp
-
385-392. Feldman, R . S. USEPA, Cincinnatl, OH, private communicatlon, 1979. Lee. R. J.; Lalb, J. S.; Fisher, R. M. NBS Spec. Pub/. ( U . S . )1978, No.
506,367-402. Beaman, D. R. I n "Environmental Pollutants"; Toribara, T. Y., Coleman, J. R., Dahneke, B. E.,Feldman, I., Eds., Plenum Press: New York, 1977, pp 255-294. Sherman, E. S.:Thomas, E. L. J . Mater. Sci. 1979, 14, 1109-1 113. JEOL News 1077, 15E (No. I), 14-24. Thompson, M. N. Phi/@s Nectfon Optics Bull. 1977, EM110, 31-39. Warren, J. B. I n "Introduction to Analytical Electron Microscopy"; Hren, Joy, D. C., Eds.; Plenum Press: New York, 1979, J. J., Goldstein, J. I., pp 369-385.
RECEIVED for review April 11, 1980. Accepted July 14,1980.
Recovery of Naphthalene during Evaporative Concentration Cecil E. Higgins" and Michael R. Guerin Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
The analysis of trace organics usually requires concentrating organic extracts to small volumes prior to instrumental analysis. The use of a concentration apparatus employing a nitrogen blanket and reduced pressure is desirable because 0003-2700/80/0352-1984$01 .OO/O
the inert atmosphere and low temperature inherent with the use of such a system helps to ensure stable composition. Unfortunately, diaromatic compounds such as the naphthalenes and biphenyls are frequently almost completely lost 0 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 12, OCTOBER 1980
Flgure 1.
1985
Kuderna-Danish (left)and inert atmosphere-reduced pressure concentration devices
during this concentration step. Even under carefully controlled conditions only 26 f 11% of the naphthalene is recovered (1). We have found t h a t Tenax, a frequently used sorbent for the collection of trace organics from air (2-11) or other media (2, 3, 11, 13), or other similarly used sorbents (5-7, 9, 10, 14. 15) placed either in or downstream of the evaporative con. centration flask can significantly improve the recovery of‘ two-ringed compounds. Recoveries with and without the USE‘ of sorbents are reported here, as well as the effects of solute concentration, purge time after solvent removal, and type of solvent used.
I ------c
VACUUM GLASS WOOL
