thirds of that obtained using the manual method. Finally, although designed primarily for amino acid determinations by ion exchange chromatography, this type of equipment with but few niodifications could be adapted to carry out many time-consuming analytical determinations a t present requiring a considerable amount of manual labor. All that is required is a technique for introducing the analytical samples in sequence into the system, which then carries out the steps involved in the colorimetric or turbidimetric assay and records the results.
land in thc construction of this equipment, and by W. B. Hall, Division of Mathematical Statistics, C.S.I.R.O., Kith the experimental design and calculations involved in the standardizing procedure. Thanks are also due to Monica McShane, P. R. Ravenscroft and Steven Gardonyi for technical assistance. The authors particularly thank E. N. Paton, Paton Industries Pty., Ltd., Adelaide, South Australia, for his considerable help in the engineering development and construction of this and subsequent machines. LITERATURE CITED
(1) Edman, Pehr, Funk, Hans, Sjoquist, ACKNOWLEDGMENT
I t is a pleasure to acknorledge the assistance rendered by W, J. Suther-
John, Kgl. Fysiogruj. Sallskap. Lund
Forh. 26, KO.12, 121-4 (1956). (2) Gillespie, M. J., Simmonds, D. H.,
to be submitted to iiustraliun J. Bzol.
Sa.
(3) Hamilton, P. B., ANAL. C H m . 30, 914 (1958). (4) Moore, S., Spackman, D. H., Stein, W. H., Ibid., 30, 1185 (1958). (5) Moore, S., Stein, W. H., J . Bid. Chem. 192, 663 (1951). (6) Ibid., 211, 893, (1954). ( 7 ) Ibid., p. 9Oi.
(8) Rogers, G. E., Simmonds, D. H., Nature 182, 186 (1958). (9) Rosen, H., Arch. Biochem Biophys. 67, 10 (1957). (10) Simmonds, D. H., ~ A L CHEAI. . 30, 1043 (1958). (11) Simmonds, D. H., dust>alian J . Bid. Sci. 7 , 96 (1951). (12) Simmonds, D. H., Rowlands, R. J., ANAL. CHEN.32, 256 (1960). (13) Spackman, D. H., Moore, S.,Stein, W. H., Ibid., 30, 1190 (1958).
RECEIVEDfor review ilpril 2, 1959. Accepted October 14, 1959.
Photometer for Continuous Determination of Uranium in Radioactive Process Streams F.
A. SCOTT and R. D. DIERKS
Hanford labpratories Operation, General Electric Co., Richland, Wash.
b Uranyl nitrate concentrations in process streams can be monitored colorimetrically. However, commercial process stream photometers cannot easily b e applied to highly radioactive streams. The instrument described is a modified single-beam filter photometer. Because of a unique standardizing system, it is very stable, having a short-term variation of less than 1% and a calibration stability of 3%. The instrument has a remotely located sensing unit with the ruggedness and simplicity required for production plant applications. Its use in process stream monitoring can yield important process data and increase plant operating efficiency.
T
success of a n automated chemical process control system depends, in part, upon its ability to obtain a flow of up-to-the-minute information from key points in the chemical process. Because the most practical method of providing such information is by using continuous process stream analyzers (Z), instrument manufacturers have been adapting more and more laboratory equipment for continuous field service (4, 5 ) , giving the process control engineer a n ever-n idening field of instruments from which to build a control system. Hon-ever, in plants processing irHE
268
ANALYTICAL CHEMISTRY
radiated uranium, the usefulness of many of the early continuous analyzers was sometimes compromised by the hazards associated with radioactive solutions. Such things as large sample holdup, proximity of the sample to operating or maintenance personnel, or general complexity, all posed personnel radiation exposure problems that eliminated their use. As a result, a program to design and test an instrument for the determination of uranium in radioactive streams mas initiated a t the Hanford Laboratories. This paper rerorts the results of this program, which has paralleled similar programs a t other laboratories (3, 6). The Hanford Laboratories instrument is a filter-type photometer, similar to the conventional single-beam photonieter in that it employs a single light path and a single light intensity detector. However, by the alternate positioning of t n o filters in the transmitted beam, many of the desirable features of the more complex dual-beam photometers are obtained. Its operation is simple. Periodically, the intensity of the light source is automatically adjusted so that the apparent incident light on a sample solution is held constant, this being indicated by the intensity of the transmitted light beam a t 535 mp. The uranium concentration of the sample solution is then indicated directly by
the intensity of the transmitted light beam a t 420 mp. The problems of radiation exposure of operating and maintenance personnel have been minimized by three design features. First, the electronic equipment is separated from the sensing unit and is located outside radiation zones, facilitating routine maintenance. Second, the sensing unit is miniaturized, reducing the sample holdup, shielding requirements, and radiation levels in general. Finally, the sensing unit is kept simple, with a minimum number of easily replaceable parts, minimizing maintenance time in radiation zones. DESCRIPTION
OF
INSTRUMENT
The sensing unit (Figure 1) consists of a light source. a sample cell. t n o light filters, a phototube, and a filterpositioning air cylinder. Because the photometer monitors a continuously flowing sample stream and does not require periodic introduction of standardizing solutions, it is installed directly in the sample strenni n-ithout valving. A gasketed cover (not shown) protects the optics from dust and moisture and inadvertent dousings during n-ashdon-ns or decontamination operations. A bayonet-type, pilot light socket (Dialight Corp. of America, Yo. 91410931) housed in a slightly modified ( l l / l c inch 27NS-2B threads added) cable connector (American Phenolic Corp. No. AF3106.4-168) forms the light
Figure 2.
mol
Figure 1.
Uranium photometer filter assembly
Back
Uranium photometer sensing unit
source socket (Fieure 1). This desien facilitates raped Feplackment and reproducible positioning of the light source, a No. 44 miniature pilot lamp. This type of lamp was selected for its small size, long life, and adequate light output. The bulb is operated at about 6 volts when new; this voltage is gradually increased t o a maximum of about 7 as the lamp and the optics darken. Continuous operation of the instrument under simulated plant conditions indicates an average bulb life of about 2000 hours. The light source is uncollimated, sacrificing both signal streneth and bulb life for the simolified optical system. Figure 2 is an exploded view of the sensing unit and shows the phototube, the phototube-positioning socket, the assembly of the two filter systems, and the filter-positioning mechanism. The phototube, a Type 1P42, and suitable signal leads are potted with a high dielectric potting resin (Minnesota Mining and Manufacturing Co. Scotchcast)
Figure 3.
in a cable connector shell (American Phenolic Corp. No. 83-22SP) to facilitate replacement and reproducible positioning. Being almost completely encased in the resin, the phototube is a well insulated, rugged unit whose operation is not affected by handling, moisture, or mild abuse. Rapid phototube replacement has not proved t o be as important as lamp replacement, as no indications of changes in phototube response have been noted during more than three years of development and use of several instruments. The assembly of the two filtering systems is shown in Figure 2. A l/rincb thick 5113 band pass filter (Corning Glass Works) provides a band of light in the 420-mp region. An interferencetype filter (Bauseh & Lomb Optical Go.) peaking at 535 mp, a 3389 cutoff filter (Corning Glass Works), and a neutral density filter, all in series, provide nearly monochromatic light in the 535-mp r jgion. Figure 3 shows the relationshi]p between the absorption
Absorption spectra
Figure 4.
spectra of a typical uranyl nitrate sample and the two filtering systems. The 5113 band pass filter is commonly used with uranium filter photometers because its transmittance coincides closely with the uranyl ion absorption peak. If interfering materials in the sample exhibit absorntion oeaks near that of the
near 420 mp. I n the absorption spectrum of a typical sample solut,ion (Figure 3) the region beyond 530 mp is relatively free from absorption and can be used for standardization. The wave length used for standardization (535 mp) was chosen as close as practical t o the 420-mp region t o minimize errors due to differences in the spectral emission of the light source bulbs at their varying operating voltages. The harmonic passed hy the 535mp interference filter a t about 370 mp is absorbed by the 3389 cutoff filter. Without this filter, the apparent incident light intensity is slightly dependent on the uranium concentration of the sample. The nrutral density filter, a Diece of uniformly darkened photo-
Uranium photometer sample cell VOL. 32, NO. 2, FEBRUARY 1960
269
Table 1.
Concn. Grams Uranium/ Liter 450-300 140-0
n'eutral Density Filter,
~
Application Aqueous solutions
graphic film, is a light-balancing device, reducing the amount of light passed by the 535-mp filter, so the phototube receives approximately the same amount of light through either filter system when a uranium solution of midrange concentration is in the sample cell. In this manner the "read" and "standardize" phototitbe currents can be read without changing the range selector of the micromicroammeter. The absorbance of the neutral density filter is selected to fit the application of the instrument; typical values are shown in Table I.
Typical Instrument Applications
140-0
Window Spacing, Inch
Signal Strength, Amp. 3-10 X 10-'0 6-10 X 10-10' 3-10 X lo-'@'
0,050
0.050 0.075
Lamp AbVoltage sorbsnce 2.4
6
1.5 1.5
a
5
Organic solutions (kerosine-TBP) 110-40 0.260 3-10 X 10-10 5 a 5113 band pass filter replaced by interference filter peaking at 420 mp.
2.4
Y
7
0
0
0
0
0
0
- -. LD N w c
VI
I !
270
ANALYTICAL CHEMISTRY
I
The two position-indicating switches (Figures 1 and 2) or S3 and S4,Figure 5, are independently actuated by the filter holder and indicate on the programmer panel which filter is fully positioned in the optical path. The standardization system is also activated by Sa preventing standardization in the “read” filter position in the event of a failure of the filter moving system. The sample cell (Figure 4) has been designed as small as possible to minimize sample solution hold up. The viewing n indov-s are conically shaped pieces of radiation-resistant glas. (Bausch & Lomb Optical Co.. Boroeilicate Crown No. 2 ) and project into the sample chamber t o obtain the necessary close spacing of the indows without introducing an excessive pressure drop in the sampling system. This design also provides adequate passage for solids under and limited quantities of air bubbles over the viewing windows. The optical path length through the sample solution is chosen to suit the application of the instrument best; typical values are shown in Table I. The electronic components consist of a n amplifier, a recorder-controller, and a programmer. The output of the phototube, ranging from 10-9 to 10-10 ampere (Table I), is amplified with a micromicroammeter (Beckman Instruments, Inc., Model V), and is recorded on a strip chart recorder (MinneapolisHoneywell Regulator Co., Brown Electronic Recorder, Series 153x12). During periods of standardization a proportional control relay (MinneapolisHoneywell Regulator Co., Brown Electr0-Line Relay, Series 801C2), operating in conjunction a i t h the recorder, controls a scrvomotor driving a potentiometer, that in turn adjusts the light source operating voltage until the apparent incident light intensity reaches a predetermined value. The use of these commercially available units for the electronics of the instrument simplifies its maintenance. The programmer (Figure 5) consists of the phototube power supply, the light source circuit, the manual selector and the cycle timer, SZ. switch, SI, Two small electromagnetically shielded 45-volt batteries mounted on the programmer chassis make up the phototube’s 90-volt power supply. Because of the low current drain, the battery life is approximately equal t o the normal shelf life. The light source circuit consists of a constant voltage transformer, a 55-volt step-down autotransformer, a 150-ohni fixed resistor, a 0
50-ohm three-turn and a 25-ohm 10-turn potentiometer. The lamp circuit power can come directly from any 110-volt, BO-cycle alternating current supply n-hich is relatively free from large voltage fluctuations. Small short-term fluctuations of the line voltage supply are smoothed by the constant voltage transformer and the standardization system corrects for long-term voltage variations. The 55-volt stepdown transformer and 150-ohm fixed resistor are used in lieu of a simple 10-volt step-down transformer to linearize the relationship between the position of the servo-driven potentiometer and the source light output. The three-turn potentiometer is screwdriver-adjusted for coarse lamp voltage adjustment. The 10-turn potentiometer (Helipot Corp.) is adjusted, though a 4.5 to 1 speed reducer (Metron Instruments Co., Model 6A 9/2R), by the servomotor (Minneapolis-Honeywell Regulator Co., Brown Recorder Balancing Motor S o . 76750-3) for the automatic, fine control of the lamp voltage. The cycle tinier, S,, controls the sequence and frequencv of the standardization operation. &itch Sza controls the operation of the filter-positioning cylinder, thus controlling the “read” and “standardize” periods. SzB turns the light source off, providing a periodic “dark current” monitor of the phototube circuit, a valuable check on the validity of the photometer readings. Szc turns the vacuum-type sampling system off, draining the sample cell and sweeping away air bubbles that have become attached to the windows. The manual selector switch, SI,is a convenient device for overriding the cycle timer during troubleshooting periods. Although no operating manual has been m i t t e n for this instrument, manuals are available from the manufacturers for the conimcrcially available components (amplifier, proportional control relay, etc.). DISCUSSION
trate solutions containing from 300 to 450 grams of uranium per liter. For the first six months the sensing unit was installed in an air-lift assisted sampler system (1) that raised the Sample about 22 feet to the monitor. For this installation the sensing unit was fitted with a self-degassing sample cell (not shown) to remove the air-lift air from the solution prior to its passage through the viening chamber. For the remainder of the tests the sensing unit was installed in the sampler system of a 7000-gallon uranium storage tank, where the lift was only about 10 feet and the sampler was not complicated with airlift or sample-degassing problems. For this application the sample cell shown in Figure 4 !\as used. Design n eaknesses were expected only in the moving parts of the instrument-namely, the filter shifting mechanism, the motor-driven, potentiometer, the motor drive, and the motor controller. Because all of these parts are associated v, ith the standardization system, \\-ear on these parts was accelerated by standardizing the instrument every 15 minutes, roughly eight times more often than has been found necessary to maintain calibration stability. Although a number of circuit changes were made in the programmer during the testing period, none of the moving parts rvere replaced or showed signs of wear. The ability of the instrument to recover after prolonged operation under severely overranging conditions was inadrertently demonstrated several times it hile the air-lift assisted sampling system n a s being used. K i t h this sampling system it was difficult to maintain a continuously flowing sample stream and occasionally the instrument was operated without a sample flow, in some cases for periods of two days. With no sample flow the instrument monitored an empty sample cell, resulting in phototube currents several
A prototype of this instrument was tested on nonradioactive streams under plant conditions for approximately one year, the objectiws being to correct design weaknesses, to determine the limitations of the instrunient, and to observe the accuracy and stability of the system. The sensing unit tested was designed to monitor aqueouj uranyl ni-
I
I
I
Calibration C u r v e a f t e r 5 Months Operation Windows
-
10
Figure 6. Uranium photometer chart record
E
1
Clean Windows and Source L a m p Bulb Operat..,* a: 6 v
\\
3 300
I
I
I
dL 1 5 !d1n
P e r c e n t oi C h a r t
350 400 450 urmmum Concentratlo” C r a m . p e r Liter
I
-
Figure 7. Uranium photometercalibration curves showing calibration stability VOL. 32, NO. 2, FEBRUARY 1960
271
I
orders of magnitude greater than normal. Howvcr, with the return of the sample flow, the instrument operation returned to normal. Precision and stability observations were made during the second phase of the testing, when the sensing unit was installed in the storage tank sampler system. Transfers into and out of the storage tank were infrequent and the concentration of the tank contents remained very constant a t about 400 grams of uranium per liter. During one 18-hour period m hile the instrument was automatically standardized every 15 minutes, 72 separate measurments of the uranium concentration were recorded. (A portion of this record is shown in Figure 6.) During this period the mean chart rcading 1w.s 50.63 divisions (100 divisions full scale), corresponding to 403 grams of uranium per liter, and the standard deviation was 1.03 divisions, corresponding to 3 grams of uranium per liter, or about 1% of the indicated uranium concentration. The calibration stability of the instrument is a function of the standardization system. Essentially it is the ability of the system to correct for conditions that tend to change the apparent intensity of the incident light over a prolonged period of time-for example, fouling of the viewing windows or tungsten condensation on the source lamp bulb. The calibration stability of the instrument was determined by comparing the calibration curve obtained
after a prolonged period of operation with its original calibration curve. Figure 7 shows the two calibration curves, the solid curve being the original calibration and the broken curve being a calibration obtained after about 5 months of steady oFeration. During the first calibration the instrument had clean viewing windows and an undarkened light source that operated a t about 6 volts t o give the required signal strength. Only a small amount of cell windoTv fouling was observed during the second calibration, but considerable light bulb darkening had occurred, necessitating operation a t about 8 volts t o give the required signal strength. (The source light bulbs are normally replaced when the operating voltage reaches approximately 7 volts, but in this instance it was allowed to continue operating to observe the shift in the calibration curve that might accompany the higher-than-normal bulb operating voltages and excessive bulb darkening.) The mavimum calibration drift under normal operating conditions can be espected to be less than 3% (Figure 7 ) . The temperature sensitivity of the instrument has not been investigated thoroughly, as all of the applications of the photometer have been on room temperature sample streams. However, one sensing unit (window spacing 0.075 inch) shoived a difference of about 4% between the calibration curves obtained at 18’ and 43’ C., throughout the range 0 to 140 grams of uranium per liter.
For a given instrument reading the 43” C. calibration curve indicated a lower uranium concmtration than the 18’ C. calibration. Wliile the calibration shift is reversible, the shift resulting from a n increase in sampli. tpmperature is completed in 30 minutes or so, but the shift resulting from a corres1 onding decrease in sample temperature requires several hours to complete. The addition of a xvater-cooling system to cool the phototube and the sample cell block reduced the calibration shift to less than 2% for sample temperature changes between 18’ and 43” C. LITERATURE CITED
(1) Pierce, C. E., Ind. Eng. Chent. 48,
KO.3, 77A (1956).
(2) Pleasance, C. L., IS.4 Journal 5 , NO. 6, 39-42 ( 195S).,, (3) Prohaska, C. A., Flow Colorimeter
for Measuring Uranium Concentration in Process Streams,” U. S. Atomic Energy Comm., Rept. DP-229 (1957). (4)Savitzky, A., ANAL.CHEY.30, No. 3, 17A (1958). ( 5 ) Siggia, S., “Continuous Analysis of Chemical Process Systems,” Wiley, New York, 1959. ( 6 ) Stelzner, R. W.,Oak Ridge.Nationa1 Laboratory, private communication. RECEIVED for review June 8, 1959. Accepted November 2, 1959. Division of Analytical Chemistry, Beckman -4ward Symposium on Chemical Instrumentation Honoring Howard Cary, 135th Meeting, ACS, Boston, Mass., April 1959. Work performed under contract No. AT-(45-1)1350 for the U. S.Atomic Energy Commission.
Carbon-Hydrogen Determination by Gas Chromatography ALLEN A. DUSWALT’ and WARREN W. BRANDT Deportment o f Chemisfry, Purdue University, Iafayette, Ind.
A method developed for the determination o f carbon and hydrogen b y gas-solid chromatography has a precision to 0.5% absolute for carbon and 0.1% for hydrogen. The time for combustion, separation, and recording o f the chromatogram is 20 minutes. O n a continuous basis, a new sample may b e started every 10 minutes. Compounds containing oxygen, nitrogen, halogens, or sulfur may b e run directly without difficulty. Sample size i s on the order o f 2 to 6 mg. and might be considerably smaller with more sensitive equipment. The technique is simple and experimental manipulation is reduced to a minimum.
Present address, Hercules Powder Co., Wilmington, Del. 1
272
ANALYTICAL CHEMISTRY
HE Pregl method for combustion T a n a l p i s , generally considered to be the standard method for carbonhydrogen microdeterminations, has excellent accuracy and precision ( 2 ) . It is, however, somewhat lengthy and a fair amount of personal error may be introduced. By utilizing some of the advantages of gas chromatography (1), a method has been developed for carbon-hydrogen determination which reduces these disadvantages. The time of analysis has been improved to about 20 minutes for a single determination and to about 10 minutes each for a continuous series of analyses including the area measurement. The organic sample is burned in a dry, carbon dioxide-free oxygen stream. The resulting carbon dioxide and water
vapor are passed through a calcium carbide tube which converts the n-ater vapor to acetylene. The gases are passed through a liquid nitrogen freeze trap to concentrate the materials to be analyzed. The carbon dioxide and acetylene are then vaporized and swept into the chromatographic system by the helium carrier gas. Separation and detection occur in the column and thermal conductivity cell, respectively, resulting in a typical chromatogram with symmetrical peaks. The areas of the carbon dioxide peak and the acetylene peak are proportional to the weights of carbon and hydrogen, respectively, in the original compound. APPARATUS AND MATERIALS
Chromatographic.
A
4-filament
