Preparing Extruded Specimens for X-Ray Diffraction Analysis L. J. E. HOFER AND W. C. PEEBLES, O f i c e of Synthetic Liquid FuelsJ Bureau of Mines, Bruceton, Pa., AND P. G. GUEST, Fuels and Explosives Division, Bureau of Mines, Pittsburgh, Pa.
-RAY powder diff raction analysis has many features that X qualify it as a method for microanalysis of organic com6, 6) pounds in the solid state. The extruded binderless (2,
specimen probably represents the best type of specimen for microanalytical work because of its minuteness ( 2 to 3 mg.) and absence of foreign materials. The disadvantages of other types of specimen are: ( a ) excessive size [wedge specimen ( I ) , McLachlan specimen (7), the flat specimens used in Geiger counter spectrometry, etc.]; ( h ) contamination of the specimen so that it must be repurified for further use [specimens mounted on fibers with adhesive (S), specimens extruded with binder ( S ) , specimens mounted on a stage with adhesive (67, etc.];(c) and the presence of foreign materials which contribute to the background scattering [specimens in little tubes (3)of cellophane, nylon, or glass, or coated on fibers 1. This last difficulty is particularly important for organic specimens whose scattering power is not much greater than the containing tubes and supporting fibers. There are several objections to the use of extruded binderless specimens in microanalysis. Although the specimen is very small, a relatively large amount of sample is required to fill the extrusion tube by the usual “scoop and tamp” technique. It is hard to prepare a sample that is mechanically strong. Extrusion of samples a t high pressures is said to lead to preferred orientation of crystallites. Morse (8)has designed a loader which apparently was intended to cope with some of these difficulties. Unfortunately, specimens produced in this way are mechanically weak and insecurely anchored. Moreover, the use of adhesive for anchoring the specimen tends to contaminate the specimen so that it cannot be used subsequently without repurification. Morse also mentions that high extrusion pressures tend to cause preferred orientation in the specimen. . The present authors have been unable to substantiate this claim, although they have used pressures up to -40,000 pounds per square inch. I n all cases (naphthalene was especially troublesome), preferred orientation could be completely avoided by grinding the sample to a small enough particle size. Specimens of 59 aromatic hydrocarbons ( 4 ) whose diffraction patterns are soon to be published, could he prepared so that no preferred orientation was evident.
the thickness of the funnel block and the length of the specimen tube should be such that the specimen. tube projects out of the funnel block even when it has made contact with the neck. The apparatus, with the evception of the alignment pins and the studs, is made of brass. It is now used routinely in the a u t h o d laboratory. This apparatus has been used only with organic compounds for which there are noncorrosive organic solvents. Inorganic samples present R difficult cleaning problem. Although the apparatus shown is very convenient, a much simpler form, consisting of funnel block and anvil block clamped together with external clamps, can be used. ACKNOWLEDGMENT
The authors wish to express their indebtedness to J. Schulta and W. L. Fauth, Instrument Shop Unit, Research and Development Branch, Office of Synthetic Liquid Fuels, Bureau of Mines, Bruceton. Pa. LITERATURE CITED
(1) Ballard. J. W., Oshrey, H. I., and Schrenk, H. H., Bur. Minea, Rept. Inrest. 3520 (June 1940)
PROCEDURE
The details of the eyuiqment are shown in Figure 1.
produced in this way contain no binder and are sufficiently ru ged t o permit mounting in typical Debye-Schemer cameras. !‘he neck prevents the specimen tube from being pulled out of the loading device during tamping. The anvil rod acts as a spacer and serves to keep the specimen tube against the neck. By using anvil rods of different lengths, specimen tubes of different lengths can be accommodated. The relation between
Sectton A A
Loading Device for Preparing Extruded Samples for X-Ray Diffraction Analysis
Figure 1.
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V O L U M E 2 2 , N O . 9, S E P T E M B E R 1 9 5 0 (2) Barrett, C. S.,“Structure of Metals,” P. 118, New York, McGraw-Hill Book Co., 1943. (3) Bunn, C. W..“Chemical Crystallography,” p. 110, London, Oxford University Press, 1946. (4) Hofer, L. J. E., and Peebles, W. C., “X-Ray DiffractionPatternsof Solid Aromatic Hydrocarbons.” to be published in ANAL.CHEY.
1219 ( 5 ) Levin, I., and Ott. E., 2. Krist., 85,305 (1933). ( 6 ) McKinley, J. B., Nirkels, J. E., and Sidhu, S. S.,IND.ENO.
CHEM..AN.AI..ED., 16,304 (1944). (7) McLachlan, D., Jr., U.S.Patent 2,317,329(April 20,1943). ( 8 ) ”orse, J‘ K‘! op‘iea’ A m ’ t l6, 360 (1928). RECEIVED November 30, 1949
Interference of Methyl Anthranilate in Estimations of Parathion R. C. BLINN AND F. A. GUNTHER University of California Citrus Experiment Station. Riaerside. Calif. I T H the initial application of the insecticidal material wO,O-diethyl 0-pnitrophenyl thiophosphatc (parathion) to agricultural products h m coincided the introduction of a method for the quantitative estimation of its residues upon these products (1). The basis of this very sensitive method is the quantitative r e d u d o n of the nitro to the amino group, which is then diazotized and coupled with N-1-naphthylethylenediamineto give an intense magenta color (“dyed” parathion). However, Gunther and Blinn (S),Norris ( 4 ) , and Edwards ( 2 ) have reported that aniline and some of its analogs afford essentially the same magenta color by this procedure. This suggested that methyl anthranilate, reported by Power and Chestnut ( 5 )to be found in grapes and by Small (6) t o be found in citrus fruits, might int.erfere wit.h the determination of parathion residues on and in these products, particularly as the ,methyl anthranilate content may vary with both the age and the variety of the fruit. The present report deals with the spectral study of “dyed” methyl anthranilate. DISCUSSION
After being carefully purified, methyl anthranilate hydrochloride was subjected t o the exact dyeing procedure used for parathion estimations ( 1 ) ; the resulting int,ense magenta color was visually very similar to that produced by parathion. The absorption characteristics, determined on a Beckman spectrophotometer Model DU, in the visible range are compared with those given by dyed technical parathion in Figure 1. The molar extinction co6fficients were based UFO? the concentratioris of the undyed materials. Although the spectral characteristics of the two dyed compounds differ slightly, i t can be seen that methyl anthranilate would interfere seriously in a determination for parathion by the above-mentioned procedure. The maxima are separated only by 8 mp, but they differ in molecular extinction coefficient by about 800 units (2%). Maximum color development is achieved by methyl anthranilate well within the 10-minute period specified for parathion. The presence of methyl anthranilate in a “strip” solution can be demonstrated, even though intermixed with parathion, by the use of the dyeing procedure ( 1 ) without the preceding reduction step. Howevdr, any interference caused by methyl anthranilate can largely be removed from the strip solution by modifying a procedure originally reported by Gunthcr and Ulinn (3). T o illustrate, 100-ml. portions of benzene were each fortified with 81 micrograms of methyl anthranilate, then washed one, two, or three time.: with 25 ml. of 10% hydrochloric acid solution. After evaporation of the benzene in the usual mariner, the dyeing procedure was applied. If was found that one hydrochloric acid wash removed 60.5% of the methyl anthranilate present. With two and three washes with the dilute acid, there was left no detectable amount of methyl anthranilate in the benzene.
It is therefore suggested that strip solutions, in which methyl anthranilate is suspected, be washed at least twice with dilute hydrochloric acid.
It was incidentally noticed that the color characteristics of dyed methyl anthranilate behaved according to Beer’s law within the range of 18 to 360 micrograms of parent material. This
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