I AIDS FOR ANALYTICAL CHEMISTS Subdivision of Nonvolatile, Air- and Water-Sensitive Solids Sidney G. Gibbins Department of Chemistry, University of Victoria, Victoria, B. C., Canada
SUBDIVISION FOR ANALYTICALpurposes, etc., of large quantities of nonvolatile, air- and water-sensitive solids is accomplished by manipulation of the all-glass, grease-free apparatus shown in Figure 1. Absence of stopcocks permits prolonged operation with organic solvents. The apparatus is easily handmanipulated. The horizontal manifold, 14-mm o.d., is bent at 7 to avoid solute transfer to bulb 4. The fragile bulb sample tubes, 12-mm o.d., are approximately 14 cm long from the bulb to the constricted portion 8. Subsequently, a procedure, reference ( I ) , may be used to obtain weighed samples for analytical purposes. While possible in principle, the combining of these two procedures into one complex apparatus would likely be unmanageable. The bulk sample bulb A is sealed onto the sample subdivider B at 2. The apparatus is connected to a high vacuum line at the standard taper joint 3 and pumped down to less than mm Hg and flamed out. Additional solvent, if required, is condensed in bulb 4 (100 ml) by a cold bath ( I ) . After sealing off the apparatus at constriction 5 and breaking the fragile bulb 1 with a Teflon (Du Pont) coated bar magnet, an appropriate portion of the sample is transferred by solution and/or slurry manipulations to the fragile bulb sample tube 6. The constricted portion 8 of the tube is washed free of the solute by condensation of the solvent on the walls with, e.g. dry ice. After 6 and 4 are cooled to a temperature at which the solvent has negligible vapor pressure, 6 is sealed off. Freezing the solution in 6 should be avoided. The process is then repeated for each of the remaining tubes. (1) S. G. Gibbins, ANAL.CHEM., 43, 295 (1971).
1-5 cm
4
I 6
Figure 1. Sample subdivision apparatus
While failure of fragile bulb break seals is uncommon, it is good practice to flame out the end exposed to the atmosphere and seal it. This is accomplished by first necking the end down 10 and then collapsing the narrow orifice. Since region 9 is cooling during this process, the glass may suck in slightly. If bulb failure occurs, a minimal quantity of air is admitted. When the tube is to be used, the end is readily cracked off.
RECEIVED for review September 21, 1970. Accepted December 3,1970.
A Simple Spectrophotometer Scale Expander Emanuel P. Manche Division of Natural Sciences and Mathematics, York College of The City University of New York, Flushing, N . Y . 11365 SCALEEXPANDERS are useful in spectrophotometric work to expand a desired portion of a trace for better readability and identification of spectral details. Commercially available scale expanders are normally intended to be used with instruments which have a potentiometric output. The present paper describes a simple scale expander that is most useful with instruments that do not possess a potentiometric output to drive recorders. For this work a Perkin-Elmer Model 700 infrared spectrophotometer was used. This automatic recording doublebeam instrument features optical null. The trace is normally made with a pen linked to a servomotor which positions a linear optical attenuator in the reference beam to achieve null.
The recorder carriage is driven by the wavelength scan system with no provision for scale expansion. Construction Details. The scale expander consists of a few components which are readily obtainable in the laboratory, these being a mercury battery, a current adjusting pot in series with a slidewire, a switch, and a wiper contact. The electrical schematic is shown in Figure 1. Slidewire A-B was constructed by winding several hundred turns of 0.10-mm nichrome wire on a 4-mm diameter plastic rod, and then mounted on the scale support of the spectrophotometer. The wiper contact functioned best if made of a metal rod hinged on one side to the instrument pen. Also, provision had to be made to assure that the pen itself would not rotate ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
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LEAD FROM WIPER CONTACT
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STATIONARY PECTROPHOTOME T E R CALE SUPPORT
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POTENTIOME T R l C RECORDER WIPER CONTACT
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Figure 1. Electrical schematic for the scale expander. Variable resistor, R, is used to adjust the current through the slidewire
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Figure 2. Details of the wiper-slidewire assembly. The lead wire from the wiper contact was made into a large coil to minimize drag on the pen holder assembly. Points A and B correspond to those shown in Figure 1
FREOUENCY (cm-')
0
Figure 3. Upper trace is the spectrum of 0.05-mm polystyrene film as obtained from the spectrophotometer. Lower trace is the expanded spectrum obtained with the scale expander described here. Both traces were reduced on a 1 :1 scale
in the pen holder. Points A and B were tapped at the 0 and 100% transmittancy points, and the signal from the wiper contact and point B were fed into a Heath recorder. Figure 2 details the wiper-slidewire assembly. It should be noted that various wiper configurations were used, and the one pictured was the most satisfactory since it gave no noticeable drag on the pen assembly. Also, the lead going to the wiper was coiled so that there would be no undue force on the pen assembly. The potential drop across the slidewire was adjusted to approximately 100 mV and the output recorded on the 100mV range of the recorder. It was found convenient to use the recorder's variable sensitivity to position the vertical coordinates. The expansion on the horizontal axis was done
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ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
by carefully selecting the appropriate recorder chart speed. Results. An example illustrating the effect of the expander is shown in Figure 3. The upper trace represents the infrared spectrum of 0.05-mm polystyrene film taken on the spectrophotometer while the lower trace is the expanded form taken with a chart speed of 2 in./min. The trace is linear in wavenumber with a 2 : 1 scale change occurring at 2000 cm-1. If a complete trace is desired on the same scale, this can be achieved by halving the chart speed the moment the pen reaches the 2000 cm-l position.
RECEIVED for review October 8, 1970. Accepted December 15,1970.
