calibration curve obeying Beer's law was obtained. Processing Aqueous Samples. An aliquot of the neutral aqueous sample is introduced into a 100-ml. volumetric flask. Samples which are acidic or basic must be neutralized. The size of the aliquot depends upon the amount of acetaldehyde present. Trial and error may be necessary to find a volume of sample which will give a result falling on the calibration curve. To the flask are added 3.0 ml. of 20% (v./v.) morpholine solution, 2.5 ml. of 10% (v./v.) acetic acid solution, and 1.5 ml. of 2% (w./v.) freshly prepared sodium nitroprusside solution. The
sample is diluted to volume, mixed thoroughly, and allowed to stand for 3 hours. Per cent transmittance is determined as for the calibration standards. The concentration of acetaldehyde is then read from the calibration curve. Concentration in the sample can be determined by multiplying the parts per million of acetaldehyde in the diluted aliquot by lOO/V, where V is the volume of sample in the aliquot,. Interferences. Several other aldehydes have been reported as interfering in the spot test for acetaldehyde ( I ) . To check their interferences in the quantitative colorimetric procedure, various concentrations of these aldehydes were
added to samples containing 30 p.p.ni. acetaldehyde, and per cent transmittance data n-ere obtained. The results are shown in Table I. LITERATURE CITED
(1) Doeuvre, J., Bull. Soc. Chim. (France.) 39, 1102 (1926). (2) Feigl, F., "Spot Tests in Organic Analysis," 6th ed. p. 352, Elsevier, 1960.
(3) Lexin, L., Chem. Be?. 32,388 (1899). DONALD J. CLAXCY DAVIDE. KRAMM
Research Division V.R. Grace & Co. Clarlisvjlle, hld.
Adaptation of a Gas Chromatograph for Analysis of Radioactive Gas Samples A. D. Horton, A. S. Meyer, Jr., and J. L. Botts, Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.
gas chromaA tographicfour-column assembly which operates COMPACT
by remote control was constructed for the analysis of radioactive gas samples. The assembly consists of a heated castaluminum cubicle with a hIicarta faceplate, a detector oven with a thermal conductivity (TC) cell, a sheet-metal cabinet that supports the cubicle and four chromatographic columns, and a gas-sampling apparatus. The assembly was designed specifically for the anaIysis of the hydrolysis products of neutronirradiated thorium carbides and uranium carbides. These samples contain high levels of beta and gamma activity emitted from Krs5 and XeX33and cannot be analyzed safely without escellent ventilation and moderate shielding. The assembly may be used to analyze any sample that can be introduced in the vapor state. Operation of any column in the assembly requires the positioning of only two valves and one selector snitch. The assembly (Figure 1) is located in a shielded area and is operated primarily by means of the control section of a Burrell Kromo-Tog gas chromatograph. Cables of convenient lengths connect the assembly to the control section. The assembly may be placed a t any desired angle without loss of operating efficiency. This flexibility makes possible the more efficient utilization of an available shielded area. The overall dimensions, including the column guards but excluding the sampling manifold, are 11 x 11 x 60 inches. The remotely controlled assembly is equivalent to the corresponding components of the Kromo-Tog in every way except that sampling is slower and the component parts are less accessible. 1988
ANALYTICAL CHEMISTRY
The following items, available from Burrell Corp., Pittsburgh, Pa., were used in the construction of this assembly: columns, 2.5 ft. long by 0.5-em. i.d., wire-wound U-tubes, Cat. KO., 347-01-25; packing (used to obtain the
results shown in Table I), mediuniactivity silica gel, 30- to 60-mesh, modified n-ith 3 wt. % squalane; detector oven for RIodel K-2 Kromo-Tog; gas sampler, Cat. KO.347-3-0; column guards for Model K-2 Kromo-Tog;
,9
, , %.
"
/
THERMOCOUPLE I AND COLUMN H E A T E R SELECTOR)'
i,' \ ~ . w ~ yV
'
O ~ ~TOE D E T E ~ T C R
'THEFMCCCIIPLE
Figure 1.
CPBLE
Four-column gas chromatographic assembly
inlet connectors, for sample and for carrier, Cat. KO. 264-35; and column connectors, Cat. No. 344-8. Other commercially available equipment includes : therrial conductivity detector, RIodel KO. 9677-AEL with 8-K thermistors (Gowhlac Instrument Co., Madison, N. J.); 5-way valves, stainless steel with Teflon plugs (Conant Valve Co., hledford, hcass.). The following components were fabricated in the ORNL shops: cubicle, cast from Xo. 108 alumhum casting alloy; cabinet, U. S. standaid 18-gauge coldrolled sheet steel; fmeplate, 1/4 inch thick Micarta. The cubicle is 8 inches on each side; one side is open. The walls of the cubicle are 9/16 inch thick. Inside the cubicle, connecting lines are provided for the f l o ~of gas from the gas-sample inlet to a %way valve, from the 5-way valve to each column inlet, from each column outlet t o a second 5-way valve, and from this 5-way valve to the detector. In order to minimize dead volumes, these connwtions are made with l/le-inch 0.d. stainless steel tubing. The cubicle may be hwted by means of cartridge heaters inser ed into its base a t each corner. Electrical connections from the selector switch to each column heater and to each thermocouple and from the selector switch to the cable connectors are also 13cated inside the cubicle. The detectcr oven with the TC cell is mounted on the bottom of the cubicle. The door 01 the side of the sheet-metal cabinet Flrovides access to the carrier-gas connections of the TC detector and to the cwtridge heaters of the cubicle. A chromatographic column
Table 1.
Results of Analyses of Synthetic Gas Mixture
With unmodified Kromo-Tog Component" found, Std. dev., vol. 7c vol. 7* 25.15 0.10
Component present Ethane 11.88 Ethylene Propane 8.42 Butane 20.31 Butene-1 34.24 Average of four determinations.
is connected to each of the four vertical faces of the cubicle. The columns are held securely in place by Transite standoff insulators with latches. Guards provide insulation and protection for the columns. The valves and switch on the removable faceplate are operated by means of extension handles through the n-alls of a shadow shield or, if simple adaptors are provided, by means of a master-slave manipulator. The vacuum-gas sampling apparatus is designed for measuring and injecting samples a t pressures in the range from 10 mm. to 2 atmospheres absolute.
A synthetic mixture that contained most of the principal components obtained from the hydrolysis of the carbides of uranium and thorium was used to compare the operating efficiencies of the unmodified Kromo-Tog and the described assembly. The results of the analyses are shown in Table I. The
0.07 0.25 0.09
0.16
With remotely controlled assembly Component" found, Std. dev., vol. yo vol. % 25.65 11.35 8.51 PO 21 34.28
0.25 0.34 0.34 0.31 0.55
identities of the constituents of the mixture were known but not the amounts. *4Disc Integrator was used to measure the area under each elution peak. The area of the peak for each component ivas compared with that for a known volume of a C.P.grade standard gas. The results obtained by means of the described assembly are in good agreement m-ith those obtained by means of the unmodified Kromo-Tog. The loss of precision with the former is caused primarily by the difficulty in reading the shielded manometer. The results were normalized to eliminate the contribution of approximately 1% contamination by air that was introduced during sampling. The effect of radiation on column packings and on electrical components has not been studied fully. The radioactivity of the samples that have been analyzed to date has not exceeded a few microcuries of gamma radiation.
A Simple Cryoscope for Molecular Weight Determinations Using a Thermel Detector and Phenyl Ether as Solvent R. H. Campbell,' A.
E.
Bekebrede, and B. J. Gudzinowicz, Monsanto Research Corp., Boston laboratories, Everett 49, Mass.
was needed for determining the average molecular weight of dark colored polyphenyl mixtures taken from organic-moderated nuclear reactors. The color of these samples rendered impossible an accurai e or reproducible visual detection of either the freezing or the melting point. This problem was overcome by the design and fabrication of a cryoscopic molwxlar weight apparatus incorporating an automatic stirring device and a thermel for temperature measurement. Phenyl ether was used as solvent. Although the use oj' thermocouples to measure freezing po nts in molecular n-eight determinations is not new, this paper describes a 1m-cost, efficient,
A in. our laborator:;
N ANALYTICAL METHOD
Present Address: IvIonsanto Chemical
Co., Nitro, W. Va.
versatile molecular weight apparatus that can be readily assembled for use in any laboratory. EXPERIMENTAL
Apparatus. A schematic drawing of the thermocouple assembly and components is given in Figure 1. The potentiometer used for this investigation was a Model 2733 Rubicon instrument ( Minneapolis-Honeywell Reg. Co., Philadelphia 32, Pa.) containing a standard cell and reference galvanometer with a reported accuracy of 0.005 mv. A 30-inch) 4-junction therinel of 20 gauge iron-constantan thermocouple wire (A. S. Richards Co., Kewton Highlands, Mass.) was prepared according to Daniels et al. ( 2 ) . To prevent thermocouple short-circuiting, a Teflon spacer was placed 1 inch from the end of the thermel. With this arrangement, the thermel provided a senqitivity of
approximately 0.2 nil.. per degree centigrade. The automatic stirring assembly consisted of a belt-driven linear reciprocating stirring device (E. H. Sargent Co., Chicago, Ill.) driven by a 1/100 H.P., Type V-10, electric motor (Palo Laboratory Supplies, Inc., New York,
h-. Y.)
The cell was prepared by inserting a 20- x 150-mm. borosilicate glass test tube through a rubber stopper into a 40- x 100-mm. tube. This arrangement optimized the cooling rate. The solvent used in this method was phenyl ether (Matheson, Coleman and Bell, East Rutherford, K. J.). Procedure. The technique employed is very similar to the steadystate freezing point depresqion methods (I).
One end of the thermel is placed in a reference ice bath while the other is inserted into the cell containing 7 to 8 grams of weighed phenyl ether solvent, VOL. 35, NO. 12, NOVEMBER 1963
a
1989
