(Figure 3). The leads from the left-hand relay were connected to the left-hand terminals of the switch, and the leads from the right-hand relay were connected to the right-hand terminals of the switch (Beckman Division, Beckman Instruments, Inc., "Operating and
High-Temperature Cell for Infrared Spectroscopy
Maintenance Instructions, Models KF-2 and KF-3 Aquameters," October 1950). The two leads from the two-prong Jones plug, P-1, were connected to the center terminals of the double-pole doublethrow switch. Thus, when the switch is thrown to the left, the left-hand buret is
operative, and when thrown to the right, the right-hand buret is operative. When one buret is filled with the strong Karl Fischer reagent and the other with the weak reagent, either solution may be added automatically by this simple switching arrangement.
EUD P L A T E TANER SCREllS END OLATE
Allen L. Olsen, Chemistry Division, U. S. Naval Ordnance Test Station, China Lake, Calif.
T
HIS laboratory recently had occasion to measure changes of absorption of isomerizable solids in potassium bromide pellets and transmission of energy of interference filters and singlecrj stal materials at elevated teniperatures. -4 cell has been described in nhich alkali halide disks containing infusible solids were heated to 130" C. (Longworth, R., Noran eta, H., Chemistry & Industry, 1955, 1470). The higher temperature desired for certain studies required a closed system and a cell was designed for use in the PerkinElmer Model 21 spectrophotometer.
A brass cylinder with machined recesses accommodates standard gas-cell sodium chloride windows a t either end. The specimen holder is removable and is fixed in position by appropriate guides and stops. The specimen, 1 inch in diameter, fits into the groove of the holder and is held in place by a threaded annular ring. The thermocouple well is located close to the specimen. All metal-to-metal joints are silver-soldered. The outer surface of the brass cylinder is wound with 18 feet of Nichrome wire, B. & S. 22, 1.055 ohms per foot, threaded through ceramic beads inch in out-
A V O CERAMIC BEADS WINDINGS
ASSEMBLY-% RETAINER SCREWS
Fluorescence Spectrum Attachment for Beckman
DU
Spectrophotometer
1. A. McCarter, Department of Biochemistry, Dalhousie University, Halifax,
T
Beckman DU spectrophotometer has been adapted for use as a spectrofluorometer (1, 3, 5-7). In this laboratory a simple attachment uses a standard hydrogen lamp backplate of the spectrophotometer. HE
A cuvette containing the fluorescent sample is mounted in the position normally occupied by the hydrogen lamp. Fluorescence is excited in the sample by illuminating it with filtered ultraviolet radiation through a hole in the backplate. The fluorescent sample thus becomes the light source for the spectrophotometer JThich, when equipped with the Beckman photomultiplier detector, 158
ANALYTICAL CHEMISTRY
peratures are achieved a t any given level in a relatively short time and when equilibrium is established, the scan is made. The temperature remains constant during the trace and probably is within 2" a t the 200" C. level. Measurements of the system with and without specimen holder in the cell showed no detectable difference in per cent transmittance. An upper limit of 300" C. has been achieved without apparent damage to the finish on the Perkin-Elmer instrument.
side diameter. A layer of Sauereisen cement No. 7 is applied over the windings and the entire unit is baked a t 400" C. for several hours. The temperature, measured by a Chromel-Alumel thermocouple and a Leeds & Northrup single range potentiometer indicator, is varied in the usual manner by use of a Variac. With the high-temperature cell in the sample beam and a 10-cm. gas cell in the reference beam, the spectrophotometer is adjusted to 100% transmittance without specimen in the holder. Tem-
N. S.,
Canada
permits the fluorescence spectra of very dilute solutions to be obtained. The lamp bracket assembly of the Beckman 3240 hydrogen lamp backplate as supplied by the manufacturer has a hole (5/g inch in diameter), situated in a central position between the lamp bracket clamps. To provide a channel through which exciting radiation can pass from the source to the cuvette containing the sample, a hole (9//16 inch in diameter) is cut through the backplate behind the lamp bracket. The centers of the two holes lie on the same axis (Figure 1). Selected glass test tubes, used as cuvettes, are placed in a hollow cylinder of hard rubber clamped on the lamp bracket. The side of the cylinder is cut
away between the clamps to expose the cuvette to the exciting light and to the condensing mirror of the backplate. Khen the backplate is attached to the lamp house of the spectrophotometer, access to the cuvette holder is gained by lifting the lid of the lamp house. A mercury arc lamp (General Electric AH-4), light filter, and shutter are mounted in a suitable housing firmly attached t o the backplate. Nearest the backplate is the light filter (Chance's glass OX-l,2 mm. thick, t o pass 3630 A., obtained from Chance Bros., Ltd., Smethwick, Birmingham, England). Spring clips hold the filter against the back of the shutter, which is interposed between the filter and the light source. Except when fluorescence intensity is
Figure 1. Fluorescence attachment
A . Cuvette holder clamped B.
C. D. E.
G.
being measured, the shutter is closed, to minimize photochemical decomposition of the sample. The optical arrangement is such that the angle betxeen the incident light upon the cuvette and the emergent light viewed by the condensing mirror is approximately 20”. Because the sample is viewed on the illuminated side, errors due to overlap of absorption and emission spectra are diminished ( 2 ) . However, in a cuvette of large diameter, concentration effects shift the position of maximum intensity of emitted light within the cuvette and may make it necessary to adjust the horizontal focus of the mirror. T o permit easy adjustment of the horizontal mirror focus after the instrument is assembled, a wheel (13/4 inches in diameter) with a knurled edge is attached to the end of the horizontal adjustment screw. Once the vertical focus of the mirror and position of the cuvette holder have been adjusted, it is rarely necessary to change them.
on lamp bracket of backplate Beckman Model 3240 hydrogen lamp backplate Horizontal focus screw Filter house with side cut away to show filter in place Shutter assembly displaced vertically from position between filter house and lamp house, F Supporting rods screwed into backplate
The modified backplate is attached to the lamp house of the spectrophotometer and the mercury arc lamp is turned on. A cuvette containing the sample is placed in the cuvette holder and the lid of the lamp house is replaced. The sensitivity control of the spectrophotometer is turned to maximum sensitivity (fully counterclockwise). The sensitivity switch of the photomultiplier attachment is turned to full. The slit is opened to 2 mm., or less if intensity of fluorescence permits. The wave length selector is rotated to the desired position and the transmittance is set a t zero. The selector switch is set at 1.0 or 0.1, depending on the intensity of the fluorescence. The shutter switch is opened, and the dark current control is adjusted to bring the galvanometer to zero. The shutter on the backplate attachment is then lifted to illuminate the sample. The intensity of the emitted light is read on the transmittance scale in arbitrary units. K h e n an emission spectrum has been obtained, the wave length selector may be set at a position of peak intensity and the mirror focus adjusted to achieve a
450
500 mJJ
Figure 2. Fluorescence spectrum of quinine sulfate
maximum reading on the transmittance scale. -4 solution of quinine sulfate containing 0.3 y per nil. in 0.1N sulfuric acid, a t 460 mp and slit n-idth of 2 mm., pare a reading of 52.9 =t 0.47 (standard deviation) on the transmittance scale in 10 measurements made by removing and replacing the cuvette. The rmission spectrum of fluorescence of quinine sulfate shown in Figure 2 was obtained by using a solution containing 0.06 y per ml. in 0 . 0 2 s sulfuric acid. The slit of the spectrophotometrr was set a t 2 mm. A modified tungsten lamp backplate has been described by Cardon, Alvord, Rand, and Hitchcock ( 4 ) . ACKNOWLEDGMENT
The author is indebted to the Kational Cancer Institute of Canada and the Dalhousie Medical Research Fund for grants. LITERATURE CITED
Beckman Instruments, Inc., Fullerton, Calif., Bull. 19 (1957);( Bowen, E. J., Wokes, F., Fluorescence of Solutions,” Longmans, Green Co., Toronto, 1953. Burdett, R. A., Jones, L. C., J. Opt. SOC.Amer. 37, 554 (1947). Cardon, S. Z., Alvord, E. T., Rand, H. J., Hitchcock, R., Brit. J Cancer 10, 485-96 (1956). Gornall, A. G., Kalant, H., ANAL. CHEN.27, 474 (1955). Huke, F. B., Heidel, R. H., Fassel, V. A., Ibid., 43, 400 (1953). Lauer, J. L., Rosenbaum, E. J., Ibid., 4 1, 450 (1951).
Glass Pens for Beckman Model DK-2 Spectrophotometer A. C. Arcus, Nutrition Research Department, Medical School, Dunedin, New Zealand
of spectra in different colors with the Beckman Model DK-2 recording spectrophotometer has been facilitated in this laboratory by the use of readily interchangeable glass pens requiring almost no attention. ECORDIKG
A capillary 2 em. long with a bore of about 0.05 em. is drawn out from the end of a n 8-cm. length of borosilicate glass tubing (external diameter, 0.3 em.; bore, 0.2 em.). The tube is then clamped vertically, capillary end downward, and the capillary flamed evenly with a
microburner held directly underneath (Figure l),until the bore has narrowed sufficiently near its upper end. The surplus capillary is cut off a t the narrow place and the tip of the pen is ground t o a point of the size wanted. The finished tip, which is thick walled and strong, should be about 1 em. long and have a bore narrowing t o about 0.006 cm. The correct bore is best gaged by comparing its size visually through a magnifying glass with that of a pen found t o work well. On the recorder the pens are pushed into a stout spring clip made from brass
strip (24-gage, 0.9 cm. wide), which is permanently and rigidly screwed onto the pen carrier, as shown in Figure 2. This arrangement ensures that the pen does not vibrate on the pen carrier and that the position of the pen point on the chart is accurately reproduced &-hen pens are changed. K i t h the five pens being used a t present in this laboratory, the points all fall on the chart within a circle of 0.025-em. radius, corresponding to a maximal variation of =kO.l% on the transmittance scale. The reproduciVOL. 30, NO. 1, JANUARY 1958
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