ANALYTICAL EDITION
APRIL 15,1940
229
Zbid., 39, 775 (1918). Ibid., 50, 269 (1928). Ibid., 53/54, 312 (1929). Emich, F., A‘aturw. Rundschau. 25, 585 (1910). Emich, F., Oesterr. Chem.-Ztg., 13, 40 and 54 (1910). Emich, F., Physik. Z., 17, 454 (1916). (29) Emich, F., Science, 11, 443 (1900). (30) Emich, F., 2. anal. Chem., 32, 163 (1893). (31) Ibid., 54, 489 (1915). (32) Ibid., 56, 1 (1917). (33) Emich, F., and Donau, J., Monatsh., 28, 825 (1!>07). (34) Ibid., 30, 745 (1909). A,. Monatsh.. 43. 129 (1922). (35), Fuchs. (36) Gartner, E., Zbid., 41, 477 (1920). ’ (37) Goldschmidt, V., 2. anal. Chem., 16, 434, 449 (1877). (38) Gray, R. W., and Ramsay, Sir W.. Proc. Roy. SOC.(London), A84, 536 (1911); 86, 270 (1912). (39) Harand, J., Monatsh., 65, 153 (1935). (40) Klein, G., and Strebinger, R., “Fortschritte der Mikrochemie”, pp. 131-436, Leipzig and Vienna, F. Deuticke, 1928. (41) Krogh, A., Skand. Arch. Physiol., 20, 279 (19081. (42) Lanyar, F., and Zechner, L., Monatsh., 43, 405 (1922). (43) Mika, J., Kolloidchem. Beihefte, 23, 309 (1927). (44) Nernst, W., 2. Elektrochem., 9, 622 (1903). (45) Kernst, W., and Riesenfeld, E. H., Her., 36, 2086 (1903). (46) Pilch, F., Monatsh., 32, 21 (1911). (47) Schally, E., Ibid., 58, 399 (1931). (48) Schantl, E., Mikrochemie, 2, 174 (1924). (49) Schware-Bergkampf, E., 2. anal. Chem., 69, 321 (1926). (50) Staehler, A., Tiede, E., and Richter, F., “Handbuch der Arbeitsmethoden in der anornanischen Chemie”. Vol. 2. Part 2.
(23) Academy of Sciences in Vienna, and in 1928 he was elected a (24) full member. Honorary doctorates were given to him by (25) the University in Graz and the Technische Hochschule in (26) Aachen in 1925, and by his own Alma Mater in 1937. (27) (28) A. A. BENEDETTI-PICHLER
Literature Cited Abderhalden, E., “Handbuch der biologischen Arheitsmethoden”, Abt. I, Teil 3, pp. 45-324, Berlin and Vienna, Urban und Schwareenberg, 1921. Ibid., p. 111. Alber, H., 2. anal. Chem., 90, 87 (1932). Alber, H., and v. Renzenberg, Maria, Ibid., 86, 114 (1931). Bang, Ivar, Biochem. Z., 49, 19 (1913); 57, 300 (1913). Benedetti-Pichler, A., 2. anal. Chen., 70, 257 (1927). Brill, O., and Evans, C. de B., J. Chem. Soc., 93, 1442 (1908). Donau, J., Monatsh., 29, 333, 959 (1908). Ibid., 32, 31, 1115 (1911). Dutoit, P., J . chim. phys., 8, 12 (1909). Ebler, E., Ber., 43, 2613 (1910). Emich, F., Ann., 351, 426 (1907). Emich, F., Ber., 40, 1482 (1907). Ibid.,43, 10 (1910). Emich, F., Chem.-Ztg., 1911, No. 71; 1913, Nos. 143, 146, 147, 148; 1915, Nos. 126, 132. Emich, F., “Lehrbuch der Mikrochemie”, 1st ed., Wiesbaden, J. F. Bergmann, 1911. Emich, F., Mikrochemie, 2, 52, 193 (1924); 3, 60, 92 (1925). Emich, F., “Mikrochemisches Praktikum”, 1st ed., 1924, 2nd ed., 1931, Munich, J. F. Bergmann. Emich, F., Monatsh., 22, 670 (1901). Ibid., 23, 76 (1902). Ibid., 36, 407 (1915). Ibid., 38, 219 (1917).
~
pp. 655-882, Berlin, W-de Gruyter, 1925. (51) Ibid., p. 847. (52) Wiesenberger, E., Mikrochemie, 10, 10 (1931). (53) Zsigmondy, R., and Heyer, R., 2. anorg. allgem Chem., 68, 169 (1910).
Determination of Aluminum by Photometric Fluorescence Measurement CHARLES E. WHITE
AND
C. S. LOWE, University of blaryland, College Park, Md.
Aluminum may be determined quantitatively by photometric measurement of the intensity of fluorescent solutions produced by the aluminum-morin reaction. Intensity measurements may be made with the Pulfrich or a photoelectric photometer. The amount of morin and alcohol as well as the temperature and pH must be controlled.
the use of a source of ultraviolet radiation for producing the fluorescence, which may then be measured with either a visual or photoelectric photometer. Having determined a calibration curve, an analysis may be accomplished very quickly, the whole procedure being admirably suited to routine control of small amounts of aluminum. Experimental Details
A Hanovia quartz mercury vapor lamp was used as a source of ultraviolet radiation where the fluorescence was measured with the Pulfrich photometer. A purple filter, 5 mm. thick, was used with this to eliminate most of the visible radiation. Observations were made at right angles to the source of ultraviolet light. Cells 2.0 X 1.8 cm. were used, arranged so that the thickness peneT HAS been established by Feigl (2) that the intense green trated was the 1.8 dimension. Photoelectric measurements were made with an apparatus fluorescence produced in solutions containing aluminum as described by Hand (6) and improved by Levin (6). by addition of morin, first observed by Goppelsroeder (4, essentially A 5-cm. (2-inch) cubical ceU was used to contain the solution and makes possible the detection of as little as 0.0005 microgram a Wratten No. 8 yellow filter was placed between this and a Genof aluminum under ultraviolet light. Schantl (7) has preeral Electric photronic cell. The ammeter employed had 150 scale divisions in microamperes and the tenths listed in the tables sented evidence that this fluorescence effect is due to the forbelow are estimations. A fluorescein solution was used periodimation of a n aluminum salt of morin, Al(C~,Hs07)3,in cally in checking the constancy of the intensity of the light source. colloidal suspension. The results of further study of this reIt was found that fluctuations were not of an order to warrant making corrections. action indicate that it may be employed with a high degree of Standard aluminum solutions were prepared by dissolving accuracy in the quantitative estimation of aluminum a t conpotassium aluminum sulfate crystals in warm distilled water with centrations ranging from 0.1 to 1.2 mg. of aluminum per liter. addition of 2 ml. of 6 M acetic acid per liter to prevent hydrolysis. The range of usefulness may be extended to higher concentraIntermediate concentrations for calibration curves were obtained tions by dilution to within these limits. The method requires by dilution. Morin, the dyestuff principle of ’ustic wood, was
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
230
VOL. 12, NO. 4
PULFRICH READINGS AND MICROAMPS. VS. AL CONC.
I
FIGURE1. TYPICAL CALIBRATION CURVES
MG. AL PER 100 ML.
1 9 08
1
01
I
003
I
I
0 06
"
'
0 007
0 08
IO
Intensity values were also found t o vary with the temperature, low temperatures tending to produce higher readings. Table I11 shows this effect. The preparation of the calibration curves and the analyeis shouId be carried out at the same temperature.
I2
Procedure employed as a saturated solution of "fustic extract" in 95 per cent ethyl alcohol. This was made by placing 1.5 grams of fustic extract in contact with 1 liter of 95 per cent alcohol and filtering after thorough agitation.
Conditions for Maximum Fluorescence Intensity The intensity of fluorescence, in addition to varying with the concentration of aluminum, was found to increase to a maximum as the alcohol content was increased. Table I shows this effect.
TABLEI. EFFECTOF ALCOHOLo s FLUORESCENCE OF ALUMINUM IN MORIW E t h y l Alcohol, 95% MI. per 100 ml. of solutzon
Aluminum M g . per 200 ml. of solution
20 24 28 32 36 40
0.1
T.4BLE
0.1 0 1 0.1 0.1 0.1
11. EFFECTO F
VARYING
Morin
MI. per l!JO
ml. of solution 10 10 10 10 10 10
QCANTITIES OF
Fluorescence Xcroamperes
39.4 43.0 43.2 42.8 42.2 41.2
AIORIN O N
FLUORESCENCE
E t h y l Alcohol, 96% M1. per 100 ml. of solution
Aluminum Morin MQ.per 100 MI. per 100 ml. of solutzon ml. of solutton
I n order t o obtain reproducible results with the Pulfrich photometer, it is necessary to observe the following conditions: The source of the ultraviolet radiation must be placed in such a position relative to the photometer that equal intensities are obtained in the two fields when the same solution is placed in both cells. This adjustment must always be made before making observat,ions unless a permanent setup is available. The cells must be placed in the same relative position with regard to the prisms and to the source of ultraviolet radiation for each observation in reparing calibration curves. A satisfactory method of accomplisiing this i s to clamp to the stage of the photometer a piece of heavy cardboard, in which have been cut holes into which the cells fit tightly. Having once adjusted the height of the cells from the prisms, no change should be made in the setting during the course of a series of observations. The cells may be emptied by suction through a capillary glass tube and filled by a pipet without disturbin their position. However, this precaution is unnecessary if the cefls are handled carefully. They should be kept as clean as possible and free from fingerprints at all times. Care must be taken to use exactly the same amount of solution in both cells. I n preparing solutions for calibration purposes by diluting relatively concentrated aluminum solutions, most of the water was added before adding alcohol or alcoholic morin solution to avoid precipitation of aluminum by alcohol. After addition
Fluorescence Microamperes
34 32 28 26 24
On keeping the alcohol content constant and varying the amount of morin, a maximum brightness was noted where 28 ml. of alcohol and 12 ml. of morin solution were used. From the data of Table I1 it was concluded that maximum intensity would be obtained with a total alcohol content of 40 ml. per 100 ml. of solution-i. e., 30 ml. of pure alcohol and 10 mi. of saturated alcoholic morin solution-and that the morin content must be adjusted to the concentration of aluminum present, 10 mi. of the saturated solution being sufficient for 0.1 mg. of aluminum. I n carrying out a n analysis i t is therefore necessary to add enough morin to produce maximum intensity and a t the same time keep the alcohol content constant.
TABLE 111. EFFECTOF TEMPERATURE ox FLUORESCENCE OF ALUMINUM WITH MORIN c. Microamperes c. Microamperes 0
O
TABLEIT. ANALYSISO F
ALCMINUhf SOLUTIONS AT C.4LIBRATION DATA
Aluminum .Ilg per 100 ml. of solution
Morin Alcohol M1. per 100 ml. of solution
27"
c. FOR
FluorescencePulfrtch percentages Microamperes
C -
APRIL 15, 1940
ANALYTICAL EDITION
of morin, the solutions were allowed to stand 15 to 20 minutes before making measurements, in order that equilibrium conditions might be established. Table IV and Figure 1 show typical calibration data and curves for both visual and photoelectric photometers a t 27’ C. I n carrying out a n analysis of a solution of unknown aluminum content, morin is first added to a portion of the unknown until maximum intensity is reached. If the concentration is found to be beyond 0.12 mg. per 100 ml., the solution must be diluted to within the range 0.01 to 0.12 mg. per 100 ml. Alcohol and morin are then added in the amounts indicated above, the intensity of fluorescence is measured by either instrument, and the concentration is obtained from the calibration curves, taking into account the dilution factor. I n actual analysis the following procedure was followed :
A 25-ml. aliquot of the unknown was diluted to nearly 250 ml. and by means of acetic acid the pH was adjusted to 3.3. The dilution to 250 ml. was then completed. This step was followed in order to have the unknown at about the same pH as was used in obtaining the calibration curve. Five milliliters of this solution were placed in a 100-ml. graduated flask and after adding 20 ml. of water, 2 ml. of morin reagent, and 35 ml. of 95 per cent ethyl alcohol the volume was made to 100 ml. This was placed in the cell of the photoelectric apparatus and morin reagent added in 1-ml. portions until the microammeter reading reached a maximum and decreased. The successive microampere readings in this case were: 2 ml. of morin = 12, 3 ml. = 15, 4 ml. = 22, 5 ml. = 24, 6 ml. = 25, 7 ml. = 24. It was therefore concluded that 6 ml. was the proper quantity to use. Hence, 5 ml. of the solution were placed in a graduated flask, and 20 ml. of water, 6 ml. of morin, 34 ml. of alcohol, and xater to make 100 ml. were added. This was allowed to stand 15 minutes and the temperature adjusted to that of the calibrated curve. The readin this time was 35.2, which was above the usable portion of the cafibration curve; hence, another run was made using 2.5 ml. of the solution with 3 ml. of morin and 37 ml. of alcohol. This gave a reading of 19.2. Since this mas on the proper portion of the calibration curve, the concentration was calculated from this reading. The results of typical unknowns are given in Table V. TABLEV. NO.
1 2 3 4
RESULTS OF VNKKOWYNS
Aluminum Present
Aluminum
Found
Error
Mdml. 0.01
.Mg./mi.
0.0091
% 9.0
0.0048
0.0
0,019 0.004 0,0048
0.0185 0 0041
2.6 2.5
Discussion The determination by means of the Pulfrich photometer is just as accurate though not so convenient as b y the photoelectric apparatus. If the Pulfrich results are substituted in the modified Beer’s law equation as given by Danckwortt (1) a reasonable constant is obtained. This equation is an attempt to apply Beer’s law to the fluorescent situation and is stated as follows: F E = l o g A Fo - F
where
=
Kcd
E = extinction FO = Pulfrich reading of standard = 100% F = Pulfrich reading on unknown R = molecular extinction coefficient c = concentration in moles per liter d = thickness of cell in cm.
Using the data from Table IV the results obtained are tabulated in Table T’I. The intermediate values give a constancy that is quite in accord with ordinary fluorescing dye solutions and indicate that the curve is useful for quantitative determinations within this range.
231
The results with typical unknowns indicate that the usual error is around 3 per cent. Since the quantities involved in the determinations were from 4 to 10 micrograms per ml., i t is felt that these results are satisfactory.
Interfering Elements Since the basis of this determination is the colloid formed when aluminum reacts with the dye, it is subject to interference by materials which affect the colloid as well as those which combine with aluminum or the dye. Phosphates, arsenates, and fluorides decrease the fluorescence in all concentrations. Sulfates interfere if present to a greater extent than 9 mg. of sulfate ion in the final 100 ml. of solution. Chlorides and nitrates cause no difficulty. Of the metallic ions, beryllium,. gallium, indium, and the rare earths give a fluorescence similar to that of aluminum. Lead, zinc, and molybdenum will also fluoresce if the solution is not sufficiently acid with acetic acid. Silver destroys the fluorescence. Iron and chromium form black precipitates with morin and must be removed. Highly colored ions such as nickel, copper, and cobalt produce variations in the color shade. I n actual analysis these interfering agents are easily removed by the usual successive treatments with hydrogen sulfide, sodium peroxide, and ammonium hydroxide. A proper acidity is attained after removal of the interfering ions by neutralizing the solution to the phenolphthalein end point with 0.1 M sodium hydroxide or acetic acid and then adding 10 ml. of 0.1 M acetic acid in excess. TABLEVI. MOLECULAR EXTIKCTION COEFFICIENT Concn. of Aluminum
Mole/l. 0.37 X lo-’ 0.74 X 10-s
1.11 x 1.48 X 1.85 x 2.22 x 3.33 x 4.44 x
K
Pulfricb Readings
10.0 23.5
10-5
36.6
10-5 10-5 10-5
69 X 10’ 87 X 10’ 98 x 101 95 x 102
63.5
107 X 102 137 X 102
lo-‘
10-5
43.9 51.0 85.0
100.0
93
x
102
Comparison to Other Colorimetric Methods It is believed that the value of this method lies in the ability to determine very small concentrations of aluminum rapidly and with simple apparatus. It is more accurate a t lower concentrations than the ammonium aurintricarboxylate method which is reported to be most successfully used with amounts from 0.1 to 0.5 mg. (8). Alizarin S (8) is more sensitive than the morin, and hematoxylin (3)has the advantage of not being susceptible to fluorides. It was hoped that the Blue Black R reagent (9) which is specific for aluminum might serve as a quantitative reagent, but the difficulty of measuring the variation of intensity with a small change in Concentration has not been surmounted.
Literature Cited (1) Danckwortt, P. W., “Lumineszenze Analyse”, 3rd ed., pp. 1205 , Leipaig, hkademische Verlagsgesellschaft, 1934. (2) Feigl, F., “Qualitative Analyse mit Hilfe yon Tupfelreaktionen”, 3rd ed., p. 244, Berlin, Julius Springer, 1939. (3) Gadg and Naumank, Gas-u. T a s s e r f a c h , 81, 164 (1938). (4) Goppelsroeder, Fr., J . prakt. Chem., 101, 408 (1867). (5) Hand, B. D., IXD.EKG.CHEM.,Anal. E d . , 11, 306 (1939). (6) Levin, I., master’s thesis, University of Maryland, 1939. (7) Schantl, V. L., M i k r o c h e n i e , 2, 174 (1924). (8) Snell, F. D., “Colorimetric Methods of Analysis”, 2nd ed., Vol. 1. pp. 259-67, New York, D. Van Nostrand Co., 1936. (9) White, C. E., and Lowe, C. S..ISD. ESG.CHEM.,Anal. Ed., 9, 430 (1937). FRON t h e thesis of C. S. Lowe presented i n partial fulfillment of t h e requirementa for t h e degree of doctor of philosophy, 1939.
