I N D U S T R I A L A N D E'N G I N E E R I N G C H E M I S T R Y
PO4 Table 111. Temp.,
c.
Typical Reproducibility Data
Medium Mineral Oila Cleaning efficiency Standard index deviation 56 53
Sulfurized F a t t y Oil Baseb Cleaning efficiency Standard index deviation 80 86 85 81 83
25 25 23 55 24 53 24 55 26 56 85 a Mineral oil of high viscosity index. Viscosity 470 sec. per 100' F. S.U.V. Av. weight 0.283 gram. b Sulfurized fatty oil in toluene (1 t o 9). Av. weight 0.038 gram. Temperature between 23' and 27' C. Cleaner, 3% sodium orthosilicate plus 0.15% sodium keryl benzene sulfonate (40%). Conditions, 5 minutes, 10 r.p.m., 60' C.
Variations in the rinse-water temperature were found to be not very important. I n the procedure a fairly long rinsing time is provided a t a fairly high temperature. Under these conditions it was found unnecessary to dip the panels in dilute acid, prior to the evaluation, t o avoid "false water film continuity" (1) due to the presence of some of the surface-active agent. The main reason for eliminating the acid rinse was that rusting of the panel developed after this rinse and tended to obscure the patterns of oilcovered areas that were being sketched. EVALUATION ASD REPRODUCIBILITY. While the spraying of the panel with water is not extremely critical, care should be exercised to prevent its becoming drenched with a large excess of water. Two or three fairly slow passes with a fine spray of water appear to be optimum. It is also desirable to avoid having the
Vol. 18, No. 3
water under very high pressure or the spray source close to the panel. One possible source of a subjective error lies in the sketching of the pattern of oil-covered areas disclosed by the condensation of the spray of water. Comparison of the values obtained with three different operators, on a number of occasions, indicated that this error was rather small, being less than 2%. For operators who might have difficulty in this evaluation, it is possible to provide assistance in the form of a viewing screen divided inro 100 squares or some similar arrangement. Some reproducibility data, obtained on different days over a period of several months, are listed in Table 111. The values for cleaning index fall well within the range to be anticipated from the magnitude of the standard deviation. Appreciation is expressed to Lt. Col. C. H. Greenall, officer-incharge, Maj. W. W. Culbertson, research officer, C. C. Fawcett, associate director, and E. R. Rechel, chief of the Chemical Research Section of Frankford Arsenal Laboratory, as well as the Ordnance Department, for permission to publish this paper. Special thanks are due J. W. Mitchell for his helpful review of the paper. LITERATURE CITED
(1) Harris, J. C., A.S.T.M. B'ull., 136, 39 (1945). (2) Morgan, O., and Lankler, J. G., IND. ENG.CHEM.,34, 1158 (1942). (3) Morgan, O., and Lankler, J. G., IND.ENG.C H ~ MANAL. ., ED.,14, 725 (1942). PRESENTED a t the spring meeting of the Philadelphia Section and the MeetSOCIETY, Division of Analytical and ing-in-Print of the AMERICAXCHEMICAL Micro Chemistry, 1945.
Fluorometric Attachment for the Beckman Spectrophotometer MARY H. FLETCHER, CHARLES E. WHITE', AND MILTON S. SHEFTEL' Eastern Experiment Station, Bureau of Mines, College Park, Md.
A fluorometric attachment for the Beckman spectrophotometer for use in the measurement of fluorescence in solutions consists of a light-tight cell compartment equipped with suitable Filters and a lamp housing. It uses the receiving and amplifying systems of the Beckman instrument. General Electric B-H-4 mercury lamp is light source. Lamp emission is controlled b y Sola constant-voltage transformer No. 30,852 and b y proper ventilation of lamp housing.
M
EASUREMENT of the fluorescence of solutions as an analytical procedure has been confined primarily to the field of vitamin chemistry, and for this reason, most commercial fluorometers have been designed for use with the brilliantly fluorescing solutions encountered in this field. For weakly fluorescing solutions, such as those encountered in the determination of beryllium @), the commercial instruments a t hand proved to be insufficiently sensitive for an accurate measurement. Since a Beckman spectrophotometer was available, it was decided to adapt it for use with these solutions. The receiving and amplifying system of the Beckman instrument ( I ) possessed the desired characteristics with respect to sensitivity and range, and consequently it could be used with a minimum of change. All that was needed to make it operative was the addition of a source of ultraviolet light and a compartment for holding the optical cell and filters. An attachment which consisted of a light-tight cell compartment and a ventilated lamp housing was built from sheet brass. The interior of the cell compartment was painted with a nonfluorescent flat black paint. The principal parts are shown in Figures 1 and 2. The original cell compartment was removed from the Beckman instrument and replaced by the attachment, the cell compartment of which was bolted to the original photo1 3
Address, University of Maryland, College Park, Md. Present address, Goring Products Co., Kenilworth, N. J.
tube housing. The arrangement is shown in Figure 1, in whlch 1 is the lamp housing, 2 the cell compartment, 3 the phototube housing, 4 the Beckman spectrophotometer, 5 the ventilating fan, and 6 the ventilating louvers. The ventilating louvers occupy two of the outer adjacent sides and the top of the lamp housing section. An opening is provided on the third side to permit a connection with the fan. Figure 2 is a plan view (covers removed) of the fluorometric attachment and shows the relative positions of the various parts of the instrument. The light source, a General Electric B-H-4 mercury lamp, was chosen because previous experience had shown i t to be generally satisfactory. Another possible light source, the hydrogen discharge tube furnished with the Beckman instrument, was tried on the beryllium-quinizarin solutions and proved unsatisfactory because of the very low intensity of the exciting wave lengths. On t h other hand, the B-H-4 lamp because of its strong emission a t 3660 A. is an excellent light source and provides an intense radiation of the proper wave lengths for an efficient excitation of fluorescence in solutions of the type under consideration. The emission of the mercury lamp is influenced by the voltage and ambient temperature of the lamp; therefore, t o ensure constant emission, both voltage and temperature regulation on the lamp were found necessary. For the former, a Sola constantvoltage transformer No. 30,852 specifically designed for use with the H-4 lamp was employed. For the latter, an Eastman darkroom ventilating fan, Model A, was used.
Table
Input Voltage 110 120 130 Spread, 20 volts
I.
Stability
Reading for 22.4 Micrograms of B e 0 in 25 M1. of Solution 98.0 101.4 103.8 5 . 8 scale divisions
Reading for 11.2 lllcrograms of B e 0 in 25 M1. of Solution 46.8 48.0 50.0 3 . 2 scale divisions
ANALYTICAL EDITION
March, 1946
205
per volt. For the weaker solution, the difference of 3.2 scale divisions corresponds to 0.90 1. Lamp housing, Ruorometric attachment microgram of beryllium oxide, 2. Cell compartment Ruorometric attachment 3. Phototube compabnent, Beckman spectrophotometer which is 8.1% of the amount 4. Beckman spectrophotometer 5. Ventilating fan present, or an error of 0.4% per 6. Ventilating louvers volt. These figures are given merely to show the performance of the setup under extreme conditions and do not represent the results obtained in normal operation. There was no measurable lag between voltage change and change in reading. Proper ventilation of the lamp housing provides satisfactory control for the lamp temperature, and equilibrium is generi INCHES ally reached after a half-hour warm-up period. In all fluorometers certain problems of light filtration exist. Visible light should be excluded from the cell compartment, and ultraviolet light should bd exThe stability of the instrument accompanying large changes cluded from the phototube, yet the fluorescent light must pass in input voltage is illustrated by Table I. These data were obfreely to the phototube. tained by varying the input voltage to the Sola transformer by I n the present case the combination of filters chosen (Corning means of an autotransformer connected to the line, and noting Nos. 5874 and 3486), together with the blue sensitive phototube, the change in the phototube response to two of the berylliumhave the characteristics necessary t o permit measurement of the fluorescence. The primary filter (Corning 5874) eliminates all quinizarin standards. light lying between 4100 and 7000 A. from the exciting radiation; I n the case of the stronger solution, a difference of 5.8 scale diviand the secondary filte? (Corning 3486) absorbs all light of a wave sions resulted from a change of 20 volts. This change would length less tha; 5000 A. but has a high transmission in the region correspond to 0.81 microgram of beryllium oxide (value obtained 5700 to 6400 A. The phototube is insensitive to light with a from working curve, micrograms of Be0 versus Beckman scale readwave length greater than 7000 A. Hence, since the fluorescent ing), which is 3.6% of the amount measured. or an error of 0.1870 radiation is the only light transmitted which affects tXe phototube, it alone is measured. The attachment herein described was designed for a particular purpofe, the measurement of a weak fluorescence of 5700 to 6400 A. I n this case, the optical glass cell used to contain the solutions was a 31-mm. cube, inside measurement, with a wall I L L I thickness of 1 mm. Cells of this type may be purchased from a& Pyrocell Manufacturing Co., 207 East 84th St., Xew York 28, N. Y. Figure 1.
-
Photometric Instrument
I
Comparative data on the performance of the instrument are given elsewhere (3). It can be adapted for use in the measurement of other wave lengths and stronger fluorescence by changing the sensitivity setting of the Beckman instrument, by the proper selection of filters, by varying the size of the aperture in the brass diaphram, and by the use of other light sources. The attachment should prove useful to any laboratory that has a Beckman spectrophotometer in its possession.
Scole
0
2
4
ACKNOWLEDGMENTS
The study reported in this paper was under the general direction of J. B. Zadra, chief, College Park Division, Metallurgical Branch, U. S. Bureau of Mines. The writers are indebted to Alton Gabriel and Morris Slavin for assistance in the writing of this paper, to Rudolf Kudlich and his men in the shop for the construction of the attachment, to John P. Wintermoyer and Rebecca Bland for the drawings, and to Stephen L. Windes for assistance with the electrical units. LITERATURE CITED
Figure 2. 1.
P.
Fluorometric Attachment
Lamp housing a. Louvers b . E-H-4 mercury lamp c. Filter for absorbing visible light Cell com artment d . Figer for absorbing ultraviolet light e. Brass diaphraem * f. Optical cell 8 . Guide for optical cell
3. Phototube housing h . Phototube 4. Beckman spectrophotometer 5. Fan 6. Electrical cables
(1) C a w , H. H., and Beckman, -4. O., J . Optical SOC.A m . , 31, 682-9
(1941). ( 2 ) Fletcher, M. H., White, C. E., and Sheftel, M. S., IND.ENQ. CHEM., h . 4 ~ ED., . 18, 179 (1946). (3) Ibzd., Table 11. PLBLIBHED by permission of the Director, Bureau of S h e s , U S . Depsrtment of the Interior.
