( 3 ) rlzini, S., Riddiford, A. C., unpub-
lished data. (3) Frumkin, A. N., Academy of Sciences of the U.S.S.R., Moscow,. private communication, 1961. (4) Frumkin, A. N., Tedoradse, G., 2. Elektrochent. 6 2 , 251 (1958). (5) Galus, Z., Olson, C., Lee, H. Y., Adams, R. N., AXAL. CHEM. 34, 164 (1962). ( 6 ) Gregory, D. P., Riddiford, A. C., J . Chenf. SOC.1956, 3756.
( 7 ) Gregory, D. P., Riddiford, A. C., J . Electrochem. SOC.107, 950 (1960). (8) Hogge, E. A., Kraichman, M. B., J . Am. Chem. SOC.76, 1431 (1954). (9) Kraichman, M. B., Hogge, E. A., J . Phys. Chem. 59,986 (1955). (10) Levich, V. G., Acta Physicochim. U.R.S.S. 17, 257 (1942). (11) Newson, J. D., Riddiford, A. C., J . Electrochem. SOC.108, 695 (1961). (12) Siver, Yu. G., Kabanov, B. N., Zh. Fiz. Khim. 22, 53 (1948).
(13) Vielstich, W.,Jahn, D., 2. Elektrochem. 64,43 (1960). RECEIVEDfor review April 5, 1962. Accepted May 2, 1962. SHAUKAT AZIM~ A. C. RIDDIFORD Dept. of Chemistry University of Southampton Southampton, England Deceased, January 1962.
Direct Flame-Photometric Analysis of Powdered Materials SIR: During the entire past century of spectrochemical analysis there has been interest in devising means of reproducibly feeding an untreated solid sample into a flame. With the coming of photoelectric photometry and the development of reproducible atomizers for handling solutions, the poorer precision of the known methods of directly handling undissolved solids has been more conspicuous. Xevertheless, the obvious great advant:tqe of being able to 1 lispcme with all preliminary chemical treatment--n.hich usunlly accounts for moFt of the time consumed in a flame analysis-would have been expected to stimulate 3, search for better methods of analyzing untrcated polvdered samples. Earlier methods of introducing a solid material directly into a flame were rcvien-ed by JIavrodinc,anu and Boiteus 1 ~ 5 ) .The sparking method of l l o n yoisin snd Jlavrodineanu (6') was more precise ( = t 5 7 , ) than the others, but i t \ v u limited to conductors and demanded internal standardization. Garman ( 3 ) patented a method of feeding powdered material to a Beckman atomizerburner, operated upside-down-the powder being carried from a shaking box with the fuel gas. It is perhaps a little surprising t h a t the paper by Cullum and Thomas ( 1 ) attracted hardly any attention from the point of view of powder handling. T o be sure, this rras incidental to their method. T o determine sulfate, they precipitated barium sulfate, centrifuged i t out, and suspended i t in a starch solution (to impede settling), which was then fed direct'ly to the flame photometer for determination of the barium. Evidently they did not favor this artificr, for in their later paper ( 2 ) they recommended dissolving the barium sulfate in EDT-4. solution instead. Aictually, the direct spraying of a suspension of a powdered sample in a moderately viscous medium into a n atomizer-burner flame is capable of giving high precision and sensitivity. -4sample to be suspended, if not already
in powder form, requires only preliminary grinding and mising in known ratio with the suspending medium. KOother treatment is needed.
To show the possibilities of this method, a sample of soil was taken at random and ground in a mortar under A
4c3
420
630-A-
44C
DEC
,
.=
55c
5CC
ccn
I
7
- 3
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Nore e y t t
Figure 1.
400
-u
Soil slurry in isopropanol-
glycerol Sheathed oxyhydrogen Slit 0.02 mm. Wavelength scale axis is zera of intensity
isopropanol. When i t seemed reasonably fine, an equal volume of glycerol was added and it was sprayed with a No. 4060 (large-bore) Beckman atomizer-burner with sheath (4); both oxyhydrogen and oxyacetylene were used. The spectrum obtained nit11 oxyhydrogen is shown in Figure 1. It )vas recorded with a Beckman D U spectrophotometer with wavelength drive, energy recording attachment, and Bristol 0.4-secondJ 10-mv. stripchart recorder. A 1P28 and a Farnsworth 1 6 P l l I photomultiplier xere used belor and above 600 mp, respectively. The atomizer sprayed steadily aiid uniformly. After 2 hours no fouling whatever could be seen under a microscope; after all, there is virtually no dissolved material, and the solid particles move freely through the capillary tube. Only when an oversized particle happened along did the atomizer clog; such particles could be dislodged by a quick reverse-flush, and clogging could be avoided entirely by allowing a few seconds for large particles to settle between stirring the sample and applying it to the atomizer. In practice, of course, adequately fine grinding would be essential. The principal emissions of sodium potassium, and calcium were extremely intense and far off scale (Figure 1). The lines of lithium and rubidium were strong, but no cesium was detectable (at least down to 1% of the rubidium content). Some of the weaker red CaO bands and the infrared sodium doublet, as well as weaker sodium lines in the visible, appeared. The strontium line was fairly bright, and the manganese line )\as strong enough for full analytical precision. The iron spectrum was fully developed, but no nickel could be seen. The green blgO bands were weak; the ultraviolet MgOI-I bands could be noticed under the forest of iron lines. The aluminum line 3962 -4. and the blue A10 bands were weak but unmistakable; the aluminum was measurable with a precision of 10% I n VOL 34, NO. 8, JULY 1962
1025
sheathed oxyacetylene, the calcium ion lines 3934 and 3968 1.were as intense as the 5540 CaOH band. I n rich (incandescent) Oxyacetylene, the magnesium line 2852 A. gave a net reading equal to one-third the background. As for precision, readings could be reproduced within 1%, provided the slurry was stirred before reading. Even after settling for many minutes, as during a spectral scan, the intensities dropped very little. Thus, a scan repeated without stirring showed an intensity loss of 5% for manganese and strontium, 12% for iron, 15 to 2070 for aluminum, 10% for rubidium, and less than 1% for sodium and potassium The different behavior of the elements may be due to the heterogeneous nature of the sample and the different composition of particles of different sizes, and perhaps the different volatilities of the elements from particles of a given size. Also, some sodium and potassium may have passed into true solution. It is obvious that a n undissolved, suspended material develops a full,
intense spectrum in the flame, even revealing certain trace elements. The slowly spraying, combustible organic suspending medium helps to keep the flame temperature high enough for efficient vaporization and escitation. Much higher solids contents can be handled in suspension than in solution without difficulty from incrustation a t the atomizer tip. Reproducibility seems to be comparable n i t h that available with dissolved samples, and it is an order of magnitude better than that of earlier polTder methods. There has been no opportunity in our laboratories for further study of this method of powder sprayin%. Prohlcms calling for attention include the effects of particle-size distribution on sensitivity and reproducihility, the choice of medium, the consequences of partial solubility of the sample, the action of interferences under these novel conditions, the preparation and nature of standards, and the possibility of determining minor constituents n ithout separations or difficult elements (alu-
minum, silicon) by proper choice of flame conditions. This method of introducing solid sample into a spectrochemical source should be equally applicable to atomicabsorption spectrometry, spark-in-spray and arc-in-spray techniques, and plasma-jet spectrometry. LITERATURE CITED
(1) Cullum,
D. C., Thomas, D. B., '4nalyst 84, 113-6 (1959). ( 2 ) Ibtd., 85, 688-9 (1960). (3) Garman, V. F., U. S. Patent 2,836,097 (Mav 1958). ( 4 ) Gilbert, P. T., Jr., Analyzer (Beckman Instruments, Inc.) 2 , No. 4, 3-6
(Oct. 1961). ( 5 ) Mavrodineanu, R., Boiteux, H., "L'analyse spectrale quantitative par la flammp," p. 65, Masson, Paris, 1954. (6) kfonvoisin, J., Mavrodineanu, R., Specfrochim. Acta 4, 396-9 (1951). PAUL T. GILBERT, JR. Beckman Instruments, Inc. Fullerton, Calif.
RECEIVEDfor review April 2 , 1962. Accepted hpril 30, 1962.
Comparison of Theoretical and Experimental Efficiencies in Glass Bead Gas Chromatography Columns SIR: Recent developments in the theory of chromatography have led to the suggestion that the performance of packed columns might be quantitatively predicted in terms of theoretical expressions and experimental data acquired in nonchromatographic experiments (a). Such a breakthrough would be of great practical significance in the search for new support materials and the characterization of known supports. Results are given beiow which verify the theoretical predictions regarding glass bead columns. These preliminary results are given here because this is, to the authors' knowledge, the first time in which column plate height has been successfully predicted using nonchromatographic experimental rate data. Even in the case of cxpillniy columns the rate data have been obtained from empirical formulas nith a possible error f:ictor of 4, and the calculated values are fiom 1.75 to 7 times too small ( I , 7 ) . AIthough the present e-qerimental results m e a t this time far less refined than those obtained on capillary columns, the agreement is better. Thus on a column with 0.25Yc liquid phase, n hich i q a good 1)ractical as ne11 as theoretical 1026
ANALYTICAL CHEMISTRY
value, the average theoretical result is too small only by a factor of 1.3. The predicted variation of plate height with particle size is in excellent agreement with experiment, and the variation with liquid loading is in satisfactory agreement. The experimental work \vas done using 2-meter '/,-inch copper columns packed with borosilicate glass beads of 0.540- and 0.976-mm. average diameter. The stationary phase, tri-otolyl phosphate (TOTP), \vas used in amounts ranging from approximately 0.1 to l . O ~ , . After preparing and packing in the standard manner, the columns nere conditioned a t 12.5' C. for 10 hours. Helium \vas used as the principal carrier gas, and all measurements xere made a t 50' C. The plate height was calculated using the peak nidth a t half height. The liquid diffusion coefficients n ere found by applying a thin layer of solute onto a column of TOTP contained in a glass capillary held a t 50" C. The concentration profile wab evaluated by extracting samples directly from the capillary using a syringe and injecting them onto a chromatographic column in which T O T P iyas the stationary phase. A more detailed description of
the experimental procedure will be reported later. The results discussed here refer to the high velocity (nonequilibrium controlled) plate heights which are of the great'est theoretical interest. The C term was obtained as the slope of the Hv vs. v2 plot ( H = plate height, v = flow velocity). As the results were nearly identical whether He or X2 was used for the carrier gas, i t was assumed that the liquid phase term, Ce, could be employed (to a first approximation) in place of the over-all term, C. The generalized nonequilibrium theory of chromat'ography (3, 4)has been used to formulate (2, 5) the Ce term for glass bead columns st' low liquid loads (
