supplied by United States Gypsum, 101 S. Wacker Drive, Chicago, Ill.) as shown in Fig. 1. The hypo- dermic needle was inserted through the serum cap and connected either to a vacuum line or inert gas line by means of a three-way stopcock. The same device can also be used for repeated freezing and thawing i n vacuo. During evacuation of the samples, they may even be gently warmed with a jet of hot air from an electric blower. This setup does not permit surging, even if the solution temperatures are near their boiling ranges, because of the constriction imposed by the narrow hypodermic needle. The tightly capped samples remained under vacuum for several days. Improved resolution was judged by running the spectra several times.

The device described above was very efficient and easy to handle. I t can be used for routine analytical work. I t saves time and is inexpensive. We recommend this method in preference to chemical deoxygenation or to sealing off NMR tubes under vacuum.

Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U. S. Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.

1. L. M. Jackman and S. Sternhell, Applications of Nuclear Mag- netic Resonance Spectroscopy in Organic Chemistry (Pergamon, Oxford, 1969), 2nd ed., p. 36.

2. F. A. Bovey, Nuclear Magnetic Resonance Spectroscopy (Academic, New York, 1969), p. 45.

3. G. C. Brophy, O. N. Laing, and S. Sternhell, Chem. Ind. 22 (1968).

4. J. C. Metcalfe, A. S. V. Burgen, and O. Jardetzky, in Molecular Associations in Biology, edited by B. Pullman (Academic, New York, 1968), p. 287.

5. J. J. M. Rowe, J. Hinton, and K. L. Rowe, Chem. Rev. 70, 1 (1970).

6. F. A. L. Anet and A. J. R. Bourn, J. Amer. Chem. Soc. 87, 5250 (1965).

7. N. Mandava and E. L. Gooden, J. Agr. Food Chem. 18, 172 (1970).

8. S. Sternhell, Rev. Pure Appl. Chem. (Australia) 14, 15 (1964).

Modified Micro Sample Support for X-Ray Emission Spectrography

David A. Nickey and James O. Rice X-Ray Fluorescence Laboratory, Analytical Section, Research and Development, Sun Oil Company, Marcus Hook, Pennsylvania 19061 (Received 30 November 1970;~revision received 18 January 1971)

INDEX HEADINGS: Technique, spectroscopic; X-ray fluorescence.

When quantitatively analyzing small quantities of liquids or powders by x-ray fluorescence spectrometry, sample handling technique becomes extremely im- portant in achieving repeatable results. The fluores- cent intensity of the element being analyzed in the

9MM OD GLASS / S A M P L E TUBE

~_=~ 'A" / /WRAP 4 MIL ,_, I,, I . . . . . . ~ / MYLAR AROUND

;" I I t ; I ~ TEFLON _--'k",II Ik\l L I I ! I J SUPPORT J

~___~'A" "SECTION A-An

FIG. 1. Modified sample support.

sample is dependent upon element concentration, matrix composition, placement in the primary beam, and the penetration depth of the primary beam. For the usual quantitative applications, the specimen thickness must be greater than the "critical" pene- tration depth of the primary beam for reliable results. Where the quantity of sample is sufficient, con- ventional sample cups work well. However, where less than 1 ml of liquid or 1 g of solid is available for analysis, the quantity necessary to satisfy the above requirement may not be met.

An effective device for holding small samples has been designed for use with a Phillips Norelco Uni- versal vacuum spectrograph, and shows general applicability to any x-ray spectrograph employing inverted x-ray optics. This holder, shown in Fig. 1, consists of a reusable sample support made from a Teflon rod 1¼-in. diam by 1 in. in length with a g-in. hole drilled through the center. Teflon was chosen because it gave the lowest background count of materials tested, including aluminum, Bakelite, nylon, and Lucite; and because of its chemical inertness, should the sample "creep." The ends of the support are machined smooth and flat. The sample container consists of a small piece of standard 9-mm-o.d. glass tubing, 13 in. in length, fire polished on both ends, with a }-mil Mylar film window to provide a flat, smooth surface of x-ray excitation.

To prepare a specimen for measurement, the sample support is placed on a flat furface. A 2½ X 2½-in. piece of }-mil Mylar film is placed over the support covering the g-in. h01e. The Mylar film is then pushed through the hole with the glass sample tube and provides a snug fit between the sample tube and the support wall. The need for providing a retaining band for the Mylar film on the glass sample tube is thereby eliminated. The g-in. length of the glass sample tube extending above the support serves as a "handle" for inserting and removing the specimen from the spectro- graph sample cup. The sample to be analyzed is added to the sample tube until level with the top of the support (---0.7 ml), placed in the spectrograph sample chamber and analyzed.

Effects due to minor variations in the Teflon support, glass sample tube, Mylar film, or sample can be minimized by using the "spin" position of the x-ray unit, if it is so equipped.

Sample tube diameter and support composition can be varied for specific analytical applications.

APPLIED SPECTROSCOPY 383