The chief advantages of this automatic change-over system over mechanically operated stopcocks are simplicity, low cost, ease of operation, and, above all, versatility. Up to 20 steps may be made within one column run. Gradients may be used along with linear steps. This system has several possible uses in routine amino acid separations and various other column procedures where solution changes are required. ACKNOWLEDGMENT
Figure 3. Schematic diagram of automatic device for changing solutions in column chromatography
relay, connected by a patch cord to a double pole-double throw on-off ratchet relay (Series IR-RC-100-115 G R ratchet relay, Guardian Electric hlanufacturing Co.). This on-off ratchet relay, which also can be operated manually by a momentary contact mitch, STT'-4,12volt on-off relay combination (Series 200, Guardian Electric llanufacturing Co.), autoniatically shuts off the pump, fraction collector, etc. The on-off ratchet should not be actuated nianually when the ratchet is on the off position at the end of a run. The stepping relay must be reset first or the 110-volt on-off ratchet mill energize and ulti-
mately burn out the coil on the associated 12-volt relay. I n practice, the glass valve system is filled in reverse order, using a technique similar to that of Hamilton and Anderson ( 2 ) . After filling, the stepper relay is manually placed in the number 1 solenoid valve position. The changes can be followed visually by white, high resistance lights (18-volt) on the front panel. To start the pump and fraction collector, the on-off relay is actuated manually, STV-2. As the collection table rotates, the appropriately placed glass stops actuate the stepping relay, resulting in the required solution changes.
The authors thank Paul Hamilton, Alfred I. du Pont Institute, Wilmington, Del., for helpful discussion and P. V. Avizonis for suggesting the use of glass valves. LITERATURE CITED
(1) Ellis, S., Simpson, J., J . Bid. Chem.
220,939 (1956).
(2) Hamilton, P. B., Anderson, R. X., ANAL.CHEM.3, 1504-12 (1959).
(3) McClendon, J. H., Kreisher, J. H., Pror. IXth Intpmational Botanical _... Congress, Montreal, Canada, Aug. 1929, 1959, Vol. 11, Bbstracts, p. 239. (4) Peterson, E. A., Sober, H. A., J . Am. Chem. Sac. 78, 751 (1956). (5) Rhodes, bI. B., Parvis, R. A , Feeny, R. E., J . Biol. Chem. 230, 399-408 (1958). PUBLISHED as Miscellaneous Paper S o . 354, with the approyal of the Director of the Delaware Agricultural Experiment Station. ~
~
Heated Cell for Quantitative Infrared Spectrophotometry Frederic J. Linnig and James
E. Stewart,'
cell for quantitative infrared studies is shown in a diagrammatic cross~sectiona~ view. ~t employs cell windows inch in diameter and is designed for use with Perkin-Elmer or Beckman equipment. Modification may make it applicable to other instruments. The rectangular front and back plates, I and A , are made of l/d-inch stainless steel stock, with a circular hole and flare, G, sufficient to accommodate the cone of infrared rays from the source housing. A is flanged along the sides to allow for insertion into the ways of the instrument. The heating units, B. are made of aluminum for easy machining, and contain circular spaces, L , in which the heating coils are placed. The roil cavities are covered by thin aluminum plates, M , attached to the aluminum blocks by small screws. The heating coils are identical in reAHEATED
1 Present address, Beckman Instruments Inc., Fullerton, Calif.
National Bureau of Standards, Washington 25, D. C.
sistance and are made of glass-insulated resistance wire that is in turn insulated from the aluminum cavity on all sides by glass paper held in place with sodium
P
silicate. The coil wires emerge through two holes, K , in each of the heating units. The four stainless steel posts, c, may be friction-mounted in -4 and are provided with holes a t the other end threaded to accommodate an 8-32 screw. The lead sparers, AT, about 0.1 mm. thick, are cut as shown in the front view of the cell proper. .4 nell, 0, is drilled in the inner sides of the cell window, F . The heaters, the cell windows, and spacer are mounted on posts C as shown and a circular Phosphor bronze spring, E, is placed over the outer heating unit. I is held in place with four 8-32 Allen-head cap screws, D. The Phosphor bronze spring should be made so that it will provide a constant adequate tension on the whole assembly TT ithout the screws being completely tightened. It will also prevent the assembly from becoming loose when used, and thus help to maintain constancy of cell thickness. The length of the coils may be varied to suit individual temperature requirements, and if the resistance in both coils VOL. 32, NO. 7, JUNE 1960
891
is the same, they may be wired in parallel as well as series. The lower end of plate I is a convenient place t o mount a socket for making the electrical connections. Teflon or additional glass insulation should be used on the wires between the coils and plug connections. I n the present case about 7 or 8 feet of Constantan wire taken from S o . 28 glass-covered thermocouple wire was used in each heating unit. The units were wired in parallel, and the heated cell was plugged into a Variac, nhich was in turn connected to the secondary of a 10-volt 8-ampere filament transformer. This arrangement gave a temperature of 120' C. a t a maximum Variac setting of 130. Over-all temperature variability without special control devices was about 4" C. during about 100 minutes. To reduce the temperature drop when the cell is put into the instrument, the ways were insulated from the instrument proper by Bakelite. I n this iTay reduction in temperature on insertion into the ways was limited to less than 3" C. in the region near 70" C. The temperature
could be raised from 40' C. t o 110" C. in about one hour. For certain purposes this performance could be improved with a revision of the heating circuit and special devices for controlling temperature] but for most purposes i t was found adequate. This cell has been used mostly between 70" and 90" C. Richards and Thompson [Trans. Faraday SOC.41, 183 (1945)l discuss the use of a heated cell a t temperatures up t o 200" C. The temperature of the cell may be measured by attaching a thermocouple to one of the heating units. This point may be calibrated with respect to the sample by inserting the flattened end of another thermocouple between the cell windows a t the well. Temperature variations over the section of the cell exposed to the infrared beam should ordinarily cancel out in much quantitative work; in some studies they may become important. The mounted cell, heated to the desired temperature, is loaded with the hot liquid sample; after measurement
the cell is cleaned and dried without demounting] using an appropriate solvent and a n air stream. As a safeguard] the thickness of the cell should be checked occasionally using interference patterns. Limitations imposed on this simple procedure by the use of highly elevated temperatures have not been studied. This heated cell has been used in a quantitative method for oil and stabilizer in oil-extended SBR synthetic rubber in which the semisolid extract of the sample to be analyzed must be heated before analysis to form a homogeneous liquid. A cell of this type has been used in quantitatively comparing transmittances of highly viscous and semisolid fractions of high molecular w i g h t oils [Linnig, F. J., Stewart, J. E., J . Research Natl. Bur. Standards 5 9 , 27 (1957); RP 27711. WORK performed as part of a research project sponsored by the Federal Facilities Corp., Office of Synthetic Rubber, in tonnection with the Government Synthetic Rubber Program.
Simple Thermostatic Device for the Beckman DU Spectrophotometer Harold J. Martin' and George Gorin, Department of Chemistry, Oklahoma State University, Stillwater, Okla. HE absorption spectra of many Tchemical systems are significantly altered by temperature changes. For the spectrophotometric analysis of these systems some means of temperature control is desirable, and such control is necessary for studies of reaction rate. An apparatus is described that can be constructed a t low cost and M ill provide temperature control of 10.5' C. in the range from 20" to 50' C . for cells in the Beckman DU spectrophotometer.
The parts that must be qpecially made are a cell compartment cover and two hollow metal cell. shaped like the IO-mm. rectangular cells commonly used in the spectrophotometer. The cover is milled from a 1 X 1.1 X 5 inch block of aluminum and fits the cell conipartment in place of the standard cover. The hollow metal cells. each 0.5 X 0.5 X 1.5 inches, are made from t n o pieces of brass soldered at the seams. The water inlet and outlet of each cell are made of copper tubing, 3'16 inch in outer diameter, and soldered into the top of each cell; the inlet tube evtends through to the bottom of the cell. Water connections to the cells are made through holes in the cowr with thin-walled black rubber tubing inch in outer diameter. Care should he taken in making these connection. t o Present address, Connors State -4gricultural College, Warner, Okla. 892
ANALYTICAL CHEMISTRY
forestall the possibility of a connection's coming loose inside the instrument. The tubing must fit tightly in the holes through the cover, so light will not enter; a simple check can be made n-ith a flashlight with the phototube shutter open. Finally, the tubes must have enough slack so the cells can be moved in and out of the light path. The metal cells are placed in locations 1 and 4 of the standard Beckman cell holder; locations 2 and 3 are used for the blank and sample cells. The temperature in the blank or sample cell is determined by inserting one junction of a thermocouple through the compartment cover into either cell. The junction has flexible leads and is clipped to one side of the cell to avoid interference with the light beam. The cover, the tn-o cells, and the thermocouple junction are assembled as shown diagrammatically in Figure 1. The temperature in the cell compartment is regulated and maintained by circulating water from a constant temperature reservoir through the metal cells. The exchange of heat is not sufficiently efficient to establish temperature equilibrium between the sample cells and the reservoir. which must therefore be maintained several degrees above or below the temperature desired, if this is substantially different from the normal operating temperature of the instrument. Little or no regulation can be achieved by varying the rate of flow of nater through the cells.
hC_i
Figure 1.
Cell compartment unit 1. 2.
3.
Cover Cell Thermel
The constant temperature reservoir can be of conventional type. The reservoir used in this work was a 4-liter Deaar flask, with an immersion heater placed inside it. Water was circulated from the reservoir to the metal cells to a cooling coil or a bypass tube and back into the reservoir by means of a small centrifugal pump (Eastern Engineering Co.. S e w Haven, Conn., Model B-I)] run a t 60 volts. The cooling coil was made from a 12-foot length of ','r-inch copper tubing. The flow of water through the cooling coil could be regulated by diverting part of the flow through the bypass and the temperature i n the reservoir could thus be maintained below room temperature.
