ANALYTICAL EDITION
NOVEMBER 15, 1935
tensity, had been treated with iron oxide $nd is higher in oxygen. An oxygen line appears a t 2478.5 A.,.and increases the intensity of the carbon line from which it is not separated. The oxygen lines a t 2445.5 and 2433.6 A. also show an increase in intensity as compared with higher carbon samples. The aperiodic spark is therefore capable of detecting concentrational variations in oxygen content, but these variations must be much greater than those normally experienced in steels. A sample of iron containing less than 0.005 per cent of carbon and low oxygen was made available. This sample was of high purity, and had been treated with wet hydrogen a t 1495” C. for 61 hours. It probably contained about 0.001 per cent of carbon. Using the aperiodic spark, this sample was compared with a sample of steel containing 0.1 per cent of carbon. The carbon lines in the two samples are of equal intensity.
Conclusions Although the aperiodic spark detects gross changes in oxygen content, it apparently does not have potential enough t o bring out either small or large variations in carbon content. T h e problem of the spectrographic analysis of nonmetallics in metals may be solvable by using excitation which will ionize a high percentage of the metal atoms. Means of more intense excitation than the aperiodic spark are available in the exploded wire ( I ) , the vacuum spark (9))and electric furnace arc (7,8)methods.
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Aclrnowledgmen ts This work was made possible by a grant given by the National Smelting Co., Cleveland, Ohio, and was carried out on this company’s spectrographic equipment. The following companies donated analyzed steel samples: The Cleveland Twist Drill Co.; Newburgh Works, American Steel and Wire Co.; and the Illinois Steel Co. Low-carbon samples were obtained from the PJaval Research Laboratory and the Carnegie Institute of Technology.
Literature Cited (I) Anderson, Astrophys. J.,51, 37 (1920). (2) Baly, E. C . C., “Spectroscopy,” 3rd ed., Vol. 11, p. 124, London, Longmans Green and Co., 1927. (3) Fowler, A,, Proc. Roy. Soc., A105,299 (1924). (4) Gerlach and Schweitaer, “Foundations and Methods of Chemical Analysis by the Emission Spectrum,” London, Adam Hilger, 1932. (5) Kayser, H., “Tabella der Hauptlinien der Linienspektra aller Elemente,” Berlin, Julius Springer, 1926. (6) Kayser and Konen, “Handbuch der Spectroscopie.” Vol. 8. Part 1. I). 274. LeiDzia S. Hirzel. 1933. (7) Kink Astrophyi. i;37, 119 (1913). (8) King,lbid., 38,315 (1913). (9) Scheibe, G., and Neuhiiusser, A,, 2. angew. Chem., 41, 1218 (1928). (10) Twyman and Fitch, J. Iron Steel Inst., 88,289 (1930). (11) Twyman, F., and Simeon, F., Trans. Optical Xoc., 31, 169 (1930). RECEIVED March 24,1934.
Spectrographic Microdetermination of Zinc Preliminary Note LEWIS H. ROGERS, Florida Agricultural Experiment Station, Gainesville, Fla.
I
NTEREST of biologists in the physiological effects of small amounts of zinc on plants and animals has prompted a study of the applicability of spectrography to the quantitative determination of this element. For the spectrographic detection of zinc, various workers have used three lines in the zinc spectrq-namely, those occurring a t 4810.534, 3345.0, and 2138.5 A. Early in this investigation, it was found that zinc was not detected in many of the samples which were examined when only the first two of these lines were used, because they are not sufficiently sensitive to give an observable density on the photographicoplate with very small concentrations of zinc. The 2138.5 A. zinc line, however, proved t o be quite sensitive. Since calcium and strontium are common constituents of plant materials, a spectrograpb with good dispersion is neceoszinc line from the 4811.86 9. sary to separate the 4810.534 4. strontium line, and the 3345.0 A. zinc line from the 3344.49 A. calcium line. For the 2138.5 b. zinc line to register on the photographic plate, it is necessary to sensitize it in some manner. A plate sensitized by spreading ordinary mineral oil over the emulsion is satisfactory, but the Elastman spectroscopic plate, Type 111-0,with ultraviolet sensitization is more convenient. Of the various methods of quantitative spectrum analysis, i t was decided to follow that of Nitchie and Standen (b), substituting a nonrecording _microphotometer for the recording instrument used by them. Procedure A base, free of zinc, and approximating a representative plant ash, was synthesized as follows (after first running a
qualitative spectrographic analysis on the ingredients to insure absence of zinc): three grams of H3P04,3.5 grams of Na2C03,5 grams of MgClz.6H20, 10 grams of CaS04.2H20, and 32 grams of K2C03were dissolved in water where possible, then evaporated while stirring, to insure homogeneity. After drying, the mixture was thoroughly pulverized. It mas decided to use tellurium as the “internal standard” of the pethod, since a sensitive line of tellurium occurs a t 2143.0 A. Accordingly, 5 grams of H2Te04.2H20 were dissolved in 1 liter of water, filtered, and added to all samples and standards in the proportion of 1 ml. of solution to 1 gram of sample. For a stock zinc solution, 0.8797 grain of ZnS04.7H20vias dissolved in 1 liter of water. Five milliliters of this solution were added to 1 gram of the synthetic ash, plus 1 ml. of the tellurium solution, dried, then thoroughly pulverized and mixed to give a standard containing 0.1 per cent of zinc. Other mixtures, qrepared by adding 5 ml. of the proper dilution of the stock zinc solution and 1 ml. of the tellurium solution to 1-gram portions of synthetic ash, gave standards containing 0.05, 0.01, and 0.005 per cent of zinc. Each standard was spectrographed in quintuplicate under the following conditions : About 20 mg. of the standard were placed in the lower (positive) electrode of Acheson graphite rod 0.63 cm. (0.25 inch) in diameter and 3.8 cm. (1.5 inches) long, bored to a depth of 0.32 cm. (0.125 inch) with 0.436-cm. (0.172-inch) drill, and burned t o completion with an arc drawing 9 amperes and a direct current line voltage of 125. A quartz Leiss spectrograph which disperses the spectrum from 2100 to 8000 A. on one 22.5-cm. (9inch) plate was used. 9 rotating sector wheel with adjustable aperture was inserted between the arc and the slit of the spectrograph to reduce the exposure 75 per cent.
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since i t has never appeared in any spectrogram of any sample, the possibility of an iron interference has been neglected. The study of this interference and the development of a method to permit allowance for the presence of iron is to be undertaken (probably using the ratio of intensities between the 2132.011 A. iron line and the 2143.0 A. tellurium line).
affi
Accuracy 0
-N Y
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yo01 Y
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1
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The large deviation from the mean of the last analysis in Table I is due either to lack of homogeneity of the sample or to the use of the extreme end of the calibration curve. The maximum deviation from the mean in most cases is less than one part in five. Handling all samples and standards in solution will probably reduce this deviation. Further study of the method is proposed to determine probable error. The influence (if any) of synthetic ashes of different composition is also to be studied. TABLEI.
FIGURE 1. CALIBRATION CURVE The spectrograms were photometered on a Bausch & Lomb density comparator. The ratios of the densities of the 2138.5 A. zinc line and the 2143.0 b. tellurium line for the various standards thus determined were averaged and plotted on semi-logarithmic coordinate paper with the result shown in Figure 1. PREPARATION OF SAMPLES.In preparing the plant samples for analysis, they were first dried, and then ashed a t less than 450” C. in platinum, a t which temperature, according to Thompson (S),zinc is not volatilized. Tellurium solution was added to the ash, then it was dried, pulverized, mixed thoroughly, and spectrographed in quintuplicate under the same conditions as given for the standards. TIMEFOR ANALYSIS. Neglecting the time required for ashing the samples, adding tellurium solution, drying, and homogenizing, 2 hours are ample for making ten spectrograms-i. e., two samples in quintuplicate-developing, fixing, washing, and drying the plate, and an additional 1.5 hours are sufficient for photometering and conversion of the ratios to percentages.
Limits of Method The upper limit of the method is not 0.1 per cent although at about 1 per cent the 2138.5 A. zinc line begins reversing; hence for percentages greater than this, other lines would have to be used, probably that line occurring a t 4810.534 A. The lower limit is not necessarily 0.005 per cent, for assuming that the calibration relation holds below this concentration,extrapolation of the calibration curve would indicate sensitivity to about 0.002 per cent.
Interference When appreciable iron is present in the sample, an iron line may occur at 2138.587 A., which wzuld be unresolved by most spectrographs from the 2138.5 A. zinc line and thus lead to erroneous results. Preliminary tests indicate that from 0.5 to 1 per cent of iron is required to give an observable density of this iron line on the photographic plate. Burns and Walters (1) assign an intensity of three to this iron line, and to another iron line a t 2132.011 A. they assign an intensity of four. In this work, therefore, the plates were @ways examined for the presence of the iron line at 2132.011 A., and
QUINTUPLICATE ANALYSESOF SEVERAL SAMPLEB Ratio 0.471 0.438 0.415 0.415 0.451
Per Cent 0.0078 0.0070 0.0065 0.0065 0.0073 Av. 0.0070 0.0008 0,019 0.019 0.017 0.016 0.019 Av. 0.018 & 0.002 0.10 0.07 0.11 0.10 0.08 Av. 0.09 & 0.02
*
0.73 0.73 0.71 0.69 0.73 1.22 1.12 1.24 1.22 1.16
Summary A quantitative spectrographic method for determining zinc in plant material when present in concentrations between 0.1 and 0.005 per cent, employing tellurium as an internal standard, has been studied. Iron interferes with the determination when present in concentrations of about 1 per cent, and a procedure for making allowance for this interference is suggested. The maximum deviation of the analyses from the mean in most cases is less than one part in five. Further study of the method is proposed to determine the probable error and influence of other factors on the procedure. Literature Cited (1) Burns, K., and Walters, F. M., Pub. Allegheny Observatory Univ. P?hbuTgh, 6 , No. 11, 159-211, especially 180 (1929). (2) Nitchie, C. C., and Standen, a. W., IND.ENQ.CHEM.,Anal. Ed., 4, 182-5 (1932). (3) Thompson, P. K., J.Ind. Hug., 7, 358-70 (1925).
RECEIVEDJune 7, 1935. Based upon a part of a Master of Science thesis submitted to the graduate council of the Unwersity of Florida, Auguat, 1934, which waa carried out under the direction of R. C. Williamson, University of Florida, and L. W. Caddum, Florida Agricultural Experiment Station.
Correction In the article on “Constituents of Pyrethrum Flowers” by Haller and Acree [IND.ENG.CHEM.,Anal. Ed., 7,343 (1935)l an error was made in citing the page in the first of the literature references given. The correct reference is Butt, C. A,, J. IND.
ENG.CHEM.,7, 130 (1915).
