Modifications of Beckman Aquameter to Improve Precision and Flexibility of Operation E. H. Unger and A. G. Herzog, Research and Development Laboratory, Socony Mobil Oil Co., Inc., Paulsboro, N. J.
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[ANAL. CHEW 24, 1126 (1952)l described an automatic dead-stop instrument for the titration of water with Karl Fischer reagent (Beckman illode1 KF-3 Aquameter). Several changes have been made in the reagent delivery system and the titration vessel to increase the versatility, rapidity, and accuracy with which the water content of a wide variety of samples may be determined. These additions and modifications are relatively easy and inexpensive. KO alterations have been made in the end point detection or indication system. REDIANI
MODIFICATIONS
Titration Vessel Drain. T o the bottom of the tall-form 300-ml. Berzelius beaker supplied with the instrument, an outlet tube with a stopcock was
sealed in a way t o permit complete drainage of the liquid in the beaker (Figure l ) , without removing the beaker from the titration assembly. A closed system is maintained a t all times, and the inevitable absorption of atmospheric water vapor that occurs when the titration assembly is opened is eliminated. Continuous Drying System. Modification of the titration assembly helps t o maintain a dry atmosphere within the system for reasonably long periods of time. The original unit contains an indicating tube and a drying bottle filled with a desiccant. 'By means of a rubber bulb, air is pumped through the drying bottle and into the top of the titration vessel. It generally requires 100 to 200 pump strokes to dry a new beaker. This manual air-drying system has been replaced with a continuous drying system (Figure 1). Kitrogen from a cylinder is passed through a dry-
U
Figure 1.
TO LEFT SIDE
sw-51
I
Modifications of Aquameter
TO RIGHT SIDE
I Isw-5
Figure 3. Modification of wiring diagram of Aquameter
v
ing tower (Harshaw Catalog No. H15130) filled with indicating Drierite, and through a Fischer and Porter Flowrator (tube 0.8-3.8) a t a rate of about 100 ml. per minute. The glass tubing through which the dry nitrogen flows is inserted through the rubber sealing diaphragm into the titration vessel. As the system is almost completely sealed, a slight positive pressure of dry nitrogen is maintained and atmospheric water vapor is prevented from entering. Maintenance of this dry atmosphere helps improve the precision of the end point, especially when a weaker reagent (described below) is used. Use of Two Concentrations of Reagent. I n dealing routinely with samples whose water content varies from a few parts per million to several per cent, it has been found convenient to have two different strengths of reagent available a t all times. Reagents equivalent to 3 and 0.5 mg. of water per nil. of reagent are used. The weaker reagent is prepared by diluting the 3 mg. per ml. reagent with an appropriate amount of dry methanol or methyl Cellosolve. The level of 0.5 mg. of nater per ml. of reagent is close to the lower limit a t which good instrument operation and acceptable repeatability were obtained. Additional Automatic Buret System. T o facilitate the use of the two reagents, the manually operated righthand buret has been replaced with an automatic buret identical to the present left-hand one. Another Potter & Brumfield No. SP1038-1 relay (Beckman KO. 7255) and arm rras mounted on a steel plate in such a way that the control arm' extended through the hole in the front right-hand side of the delivery unit housing cover (Figure 2). It was necessary to enlarge this hole slightly to permit free operation of the control arm. The plain glass delivery tip (Beckman No. 1851) was replaced IT ith a glass valve delivery tip (Beckman S o . 1850). Leads from the two relays were run through the back of the instrument to a double-pole double-throw sivitch mounted in a horizontal position on the front panel of the instrument
sw-5 RIGHT VALVE CONTROL RELAY
K3 S W - 5 DOUBLE POLE DOUBLE THROW SWITCH, TOGGLE, CENTER OFF
Figure 2.
Double valve controls VOL. 30, NO. 1, JANUARY 1958
157
(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.
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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
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-
Fluorescence Spectrum Attachment for Beckman
DU
Spectrophotometer
1. A. McCarter, Department of Biochemistry, Dalhousie University, Halifax,
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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.
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
