High Temperature Thermal Conductivity Cell Herman R. Felton and Adolph A. Buehler, Jackson Laboratory, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.
MEW, compact, and versatile high temperature thermal conductivity cell which may be of particular interest to workers in high temperature gas chromatography has been developed in this laboratory. Whereas the conventional cells are limited to about 300” C. for units containing thermistors (Victory Engineering Co., Catalog 1956) and to 250’ C. for filament-type cells (GowMac Instrument Co., Bull. H-TC7-56), this new cell performs satisfactorily above 400’ C. Model airplane “glow plugs” are used as sensing elements in the unit rather than thermistors or filaments. The most satisfactory plug found for general use was the Champion model VG-2. A typical design of a cell used for analysis of gases by thermal conductivity measurement is shown in Figure 1. Both elements are of the “diffusion” type. “Direct pass” cells have been made by pulling the &-irecoil out of the plug so that it may be placed directly in the gas stream and suitably modifying the holes drilled in the cell block. As one side of the mire heating coil is shorted to the body of the glow plug, the measuring bridge into which the plugs are incorporated is grounded a t this point. The circuit of such a bridge design is shown in Figure 2. Full wave rectified current is used as a heating source for the elements. A Variac may be used in the 110-volt alternating current line to control bridge current. Operation has been found both stable and sensitive a t 1.5 volts across the bridge. The higher the voltage, the greater the sensitivity. A 10-mv. re-
SIDE VIEW DRILLED AND
GLOW PLUG
1/8” HOLE
STEEL BLOCK D
END VIEW
Figure 2. plug cell
-11. R1,R2. R3. R, R. P , P. G, G .
Transformer 10 v o h , 4 amperes, CT Rectifier UICISIG (radio receptor) Electrolytic condenser 500 mmf. 50 volts Voltmeter (0-3 volts d.c.) Resistor, 47 7 Helipot 10-turn, 25 7 Jacks for recorder lead i Jacks for glow plug leads Champion glow plugs,
B.
Conductivity cell’block
2’. Figure 1. cell
Cross section of glow plug
corder 11-assatisfactory, although a millivoltmeter may be used directly. These units have been used both as detectors for gas chromatography and for gas analysis by thermal conductivity. Response time, sensitivity, shortterm drift, noise, and reproducibility were comparable to the characteristics of a conventional “hot wire” cell. The simplicity of design and circuitry makes for simple replacement and maintenance. A burned-out plug may be changed n-ith very little lost time and only slight zeroing adjustments are needed after the replacement. The parts cost of the entire unit, exclusive of the recorder, is less than $100.
Electrical circuit for glow
S. C.
VG-2
The great advantage of these units is in high temperature operation, where more conventional units fail. For example, gas chromatography units using this design have been operated a t 420’ C. The maximum operating temperature has not been determined. Further detailed work to evaluate the applications and limitations of the device is in progress.
Small-Volume Five-Centimeter Absorption Cell Gerald Goldberg, A. S. Meyer, Jr., and J. C. White, Oak Ridge National Laboratory, Oak Ridge, Tenn. SERIOUS limitation
to the use of ab-
A sorption cells with long light paths is
the large volume of solution required to fill them. Commercially available absorption cells with 5-em. light paths normally require about 15 ml. of solution. The total available volume of the chromogen in solution must be a t least 25 ml., if such cells are to be used. An absorption cell that would provide a maximum light path yet not restrict the volume of solution would have numerous applications in the anal-
ysis of radioactive solutions and in the case of a limited volume of solution for analysis. This work was undertaken to fabricate a cell that would (1) fit the cell carrier of the Beckman spectrophotometers, Models DU and B, (2) provide suitable reproducibility of measurement, (3) be inert to various acids and solvents, and (4) be easily filled, drained, and cleaned by the operator. The length of the light path was arbitrarily selected as 5 em. To use the cell in the cell carrier of the
Beckman spectrophotometers, the outside diameter of the cell must be equal to that of the 5-cm. glass cells. The minimum diameter is limited by the cross section of the light beam of the Beckman spectrophotometer. Therefore, the inside diameter is 0.391 inch and the capacity is approximately 4 ml. Because the cell must fit into a standard cell carrier and the spacing between the inner surfaces of the windows must be precisely reproducible, the structural material must be machinable to close tolerances and inert to the acids and solvents used in colorimetric analysis. VOL. 30, NO. 6, JUNE 1958
1163
A Teflon cell with interchangeable quartz windon-s fits these requirements, and can be used with samples containing hydrofluoric acid, if the quartz windows are replaced m-ith mindow made from Plexiglas. The machinability of Teflon is such that a tolerance of ~ t 0 . 0 0 2 inch is possible in machining the 1.968inch cefi path. The small funnels used as fillnorts are force-fitted into the spaces machined for them on the cell. The grooved area connecting the fillports is included to collect air bubbles that may form while the cell is being filled. The nindows are made of optical quartz inch thick. When the threaded plugs on either end of the cell are locked in place, a liquidtight seal is effected between the cell and the windows. The windows can be made of any transparent material n-hich is chemically resistant to the solution contained in the cell and is of uniform thickness. Specifications are given in Figure 1.
.'56 b-
1.968"i.002-?
I
T
X.70O"Dia. ThreadRelief
-.080'
2 4 N S Threads Decimal ,f , 0 0 5 ' ' Fractional,? Knurl--]
1
,
Threod Relief
TWO REQ'D.
Figure 1.
Absorption cell
PERFORMANCE
A set of cells n a s filled \vith acetone. and its absorbance was compared using a Model B spectrophotometer a t wave lengths from 300 to 500 mp. The maximum absorbance difference between the cells over this range was 0.010. I n checking the reproducibility of absorbance measurements, each cell was filled with an acidified aqueous solution of sodium dichromate and the absorbance measured a t 480 mp us. a water blank in a 5-cm. glass absorption cell. Average absorbance values of 0.418 =t 0.002 and 0.419 i~0.002 absorbance unit
were found for the two Teflon cells; of 0.420, when the solution \$-as nieasured in a glass cell. When the cells were emptied and refilled with water without prior rinsing, the absorbance of the resulting solution was only 0.016. This corresponds to a retention of 4% of the cell volume when the solution is drained. T o measure the difference in path lengths of the cells photometrically, each cell was filled with a dichromate solution of absorbance 1.13. The difference in absorbance when the cells
were compared by using one cell as a reference was 0.001 absorbance unit. This corresponds to a difference in optical path of 0.1%. No difficulty in aligning the cells in the light beam of the spectrophotometer slit was encountered. The cells filled and drained easily in all cases with no leakage. WORK carried out under Contract S o . W-7405-eng-26 at Oak Ridge National Laboratory, operated by Union Carbide Suclear Co., a division of Union Carbide Corp., for the htomic Energy Commission.
Urea Phosphate Reagent as a Specific Test for Heptoses on Paper Chromatograms Frank L. Greener Philip Morris, Inc., Richmond, Va.
ORK with paper chromatography of wcarbohydrates has established that urea phosphate reagent can be used as a test for heptoses. Urea phosphate is a recognized detecting agent for ketoses. It reacts with them to produce a characteristic bluegray color [Wise, C. s., Dimler, R. J..
Table 1.
1164
e
reagent for paper chromatograms of sugars, produced a bright pink color for an unknown compound. A variety of compounds were investigated to determine what class would react 13-ith the
Color of Carbohydrates Produced with Urea Phosphate
Compound Tested DbGlyceraldehy de LRhamnose D-Xylulose D-Ribulose D-Xylose D-Fructose Morbose &Glucose LGalactoheptulose D-Ibfannoheptulose Sedoheptulosan
Davis, H. A., Rist, C. E., AXAL.CHEM. 27, 33 (1955)l. Urea phosphate, used in the author's laboratory as a sprag
Color Tan Tan Blue-gray Blue-gray Tan Blue-gray Blue-gray Tan Brown Brown Brown
ANALYTICAL CHEMISTRY
Compound Tested n-a-Galaheptose D-p-Glucoheptose D-p-hf annoheptose o-GIycero-D-alloheptose Sucrose Maltose Raffinose Dulcitol 3-O-Rfethyl-~-glucose Xylitol D-Glucosamine
Color
Pink Pink Pink Pink Blue-gray Tan Blue-gray None Tan White Brown
reagent to give a similar pink color. The known aldoheptoses, glycero-alloheptose, mannoheptose, glucoheptose, and galaheptose, were among the compounds chroniatographed on filter paper. The papers were dipped in a solution of 1 gram of urea and 4.5 nil. of S5yO phosphoric acid in 48 nil. of watersaturated 1-butanol and heated at 105" C. for a few minutes. All these aldoheptoses gave the same distinctive pink color, which was not given by the other carbohydrates tested (Table I), These tests show that urea phosphate can be used on paper chromatograms as a specific chromogenic agent for detecting heptoses in a range of concentrations from approximately 20 to 100 y . ACKNOWLEDGMENT
The author wishes to thank H. G. Fletcher of the Sational Institutes of Health, Bethesda, ?\Id., for supplying the samples of known heptoses.
