the input of the transistorized amplifier must be adjusted to zero after a warmup time of approximately 30 minutes. This adjustment is made by Rz with the feedback network in the balance mode and is independent of the stabilized amplifier balance adjustment. The stabilized amplifiers are balanced in the conventional manner (6). The amplifier was evaluated by constructing a coulometer which followed the basic design of Booman (1) and in which the vacuum tube power amplifiers were replaced with the transistorized units. The frequency response was determined by comparison with that of a similar coulometer which utilized vacuum tube amplifiers. The frequency responses were identical from 0 to 100 kilocycles. The least squares calibrations for the transistorized version showed a root mean square error of the full scale integrator of =tO,OlyG reading for both the anodic and the cathodic curves. A full scale integrator reading corresponded to 21.535 coulombs. il relative standard deviation of &O.O9yG ( n = 12) was deterniined for the titration of from 1 to 16
mg. of uranium, and a relative standard deviation of 0.09% ( n = 12) for the titration of NBS-13Ga potassium dichromate. Bias was absent in the titration of the uranium, while in the case of the potassium dichromate the recovery was 99.95%. Several versions of the transistor amplifier are possible, and less expensive transistors such as the 2x242 and the 2N32G may be utilized with some sacrifice in power capabilities and gain. Temperature compensation through the utilization of thermistors will result in improved stability. However, this feature was not considered necessary for the present application. Since the completion of this work, the K2X amplifiers have been discontinued by Philbrick and replaced by model K2Xa; also, a number of transistorized booster amplifiers have become available commercially. The K2Xa amplifier is essentially identical to the old model R2X but has a higher gain and is less tolerant of a capacitive load. I n some circuits where long cables are utilized between the coulometer and the titration cell, a
5GO-ohm, I/*-watt resistor must be incorporated between the output pin 6 of the K2Xa and the input to the transistorized amplifier. The incorporation of this resistor did not affect the performance of the instruments currently in use a t this laboratory. While commercial booster amplifiers are now available and may be preferred by some workers, no unit combining complementary symmetry operation n i t h high current output could be found in the literature. LITERATURE CITED
(1) Booman, G. L., ANAL.CHEV. 29, 213
(1957).
( 2 ) Connally, R. E., Scott, F. d.,U. S.
Atomic Energy Comm., Rept. HW65919 (1960). (3) Kelley, M. T., Jones, H. C., Fisher, D. J., ANAL.CHEM.31, 488 (1959). (4)Ibid., p. 956 (1959). ( 5 ) Philbrick, George -4., Researches, Inc., Boston 16, Mass., “GA4P/RElectronic Analog - ComDuters” (catalogdata eheets). ( 6 ) Stromatt, R . W., Connally, R . E., ANAL.CHEW33, 345 (1961). Work performed under contract hT(072)-1 with the U. S. Atomic Energy Commission.
Multiple-Column Gas Chromatograph Utilizing a Single Detector and Recorder Bernard
VERY
M.
Mitzner and Philip Gitoneas, International Flavors & Fragrances, Inc., Union Beach, N. J.
simple gas chromatographic
A apparatus makes possible the utiliza-
tion of a multiplicity of chromatographic columns of varying diameters in one instrument employing a single detector and recorder. One can easily proceed from one column to another by merely opening and closing a valve. -FROM
columns can all be maintained a t the same temperature or be used a t different temperatures. This system has been used for well over a year and found to be both useful and effective for analytical as well as preparative gas chromatography. A flow diagram is shown in Figure 1. The apparatus consists of four parts.
Columns. Several large diameter columns !%-ereinstalled in the instrument a t the same time ‘/4-inch and 3/16-inch columns were present. The larger columns may be used for trapping, and, by flipping a switch, the purity of the collected material can be monitored on one of the analytical columns. Approximately 2 to 3 minutes is required to switch from one column to another
GAS T A N K
-INJECTORS
----EXIT
No special parts are required and the
MANIFOLD
Figure 1. Flow diagram of five-column chromatograph
Inlet Manifold. The gas supply leading from the tank is split into the number of columns t h a t vie wish to employ. (For the present discussion, it is assumed t h a t five columns are required.) The inlet manifold consists of a l/r-inch “cross” a i t h extra fittings soldered in front and back to give a total of six “ports.” One port is connected to the gas line and the other five are connected to the valves. (We have found Hoke 1252 toggle valves ideally suited for this purpose.) Injectors. The tubing size leading from the valves is reduced to inch O.D. and connected to the injectors. The injectors can be simply constructed of a Swagelok 3 / 1 ~ X L/4 inch reducing union as shown in Figure 2. They are wrapped with Nichrome resistance wire and may be individually controlled via a Variac or joined either in series or parallel and controlled by a single Variac.
-
-SILICONE
L
I I B ’ s s TUBING SILVER SOLDERED I N HOLE DRILLED
REDUCINO
UNION
l N T o S I D E o F
Figure 3/1,j
X
2. ‘/4
l
l
SEPTUM
4
k
’
SWAGELOK NUT
3 1 6 ’ S S TUBINO FILLED WITH 5. WOOL
3/16
SWLGELOK N U T
Injector, constructed from inch Swagelok reducing
union VOL. 34,
NO. 4,
APRIL 1962
589
to obtain equilibrium. All columns are maintained a t the same temperature; however, one can easily construct individual ovens for the various columns if large temperature differentials are required. K h e n columns of different diameters are to be used, the proper reducing unions must be placed on the injector and the exit manifolds. Exit Manifold. The exit manifold is fashioned like the inlet manifold, except that a 1/8-inch cross is used to keep the internal volume as small as possible. Three inches of 1/8-inch tubing lead from the manifold to the ends of the various columns and are joined via the appropriate connectors. One line leading from the manifold goes directly to the detector. The principle of operation of the multiple-column apparatus depends upon the relatively small constrictions present in the short lengths of '/*-inch
tubing. The operation of the instrument can be explained as follows:
If tve consider five columns to be available, and we wish to use only column 1, the toggle valve of column 1 is opened. The carrier gas then goes through the inlet manifold, through valve 1, through injector 1, then through column 1, and finally to the exit manifold. There will be a rapid pressure build-up in all the remaining four columns, so that the flow of carrier gas will almost exclusively go directly to the detector. The 1/8-inch tubing cuts don-n any diffusion to the other columns. Comparisons of the separations obtainable in a conventional unit equipped with a single column and with a multicolumn system have indicated that there
is no loss of separating power due to the multiplicity of columns that are available. The quality of the separations that are obtained on a particular column when the multicolumn system is employed, is identical to that obtained when the same column is employed in a single-column chromatographic apparatus of conventional design, and operating under the same conditions. The system that has been described is extremely simple, and the fact that all the valves are a t room temperature makes them yirtually trouble-free. It is belie\-ed that many more than five columns can he used advantageously. -4 point will be reached, however, \There this method will not prove effectiveLe., the dead volume in the manifold becomes excessive, causing ill-defined peaks.
Adapter to Permit Scanning of Radiochromatograms Using a Simple End-Window Counting Setup W. D. Conway and E. J. Lethco, Environmental Cancer Section, National Cancer Institute, Bethesda 14, Md.
n o i v i n c scanning of paper strip chroniatograms to determine areas of radioactivity is more rapid than autoradiographic procedures, and unless spots separated by less than about 1 em. must be resolved, the sensitivities of both methods are comparable. The sensitivity of the autoradiographic procedure is proportional t o the length of exyosure, but radioactive areas which require exposure of 1 month to noscreen x-ray film can be detected by scanners using low background counters. The purchase of such scanners, however, may be limited by their high cost. 9 simple device is described here which permits manual scanning of chromatograms using the end-window counting apparatus usually employed for assaying samples plated on planchets. If a ratemeter and recorder are available, chromatograms may be scanned automatically. The adapter is designed to fit the space occupied by the shelf ordinarily used to hold planchets. The adapter is held in place by looping the free end of a small spring, one end of vhich is secured to the counter base, over a small hook on the underside of the adapter (Figure 2 ) . In positioning the adapter, the counter itself is not moved. Therefore, there is no danger of altering the counting geometry for planchet counting. The adapter described mas used with a Nuclear Chicago D-47 gas flow counter with a Micromil n-indom, mounted in a l4
590
ANALYTICAL CHEMISTRY
RIodel 3054 manual sample changer.
A similar device could be used ivith most setups for end-window counting. Scans of a chromatogram of certain metabolites tagged with CI4 are shown in Figure 1. The manual scan \vas made with the collimator set a t 1 em. by taking 2minute counts a t 1-em. .intervals along the chromatogram, using a Suclear Chicago Model 174 scaler. The automatic scan was obtained with the collimator set a t 1/4 inch, using a Kuclcar Chicago 1620BS ratemeter and an 300-
i
zoo
h ,001 L
ADAPTER AdiOMATlC
l
ACIAP-E9 203-
NANUA-
5CAh
Figure 1. Scans of chromatogram containing metabolites tagged with C14
R-lOOO-AIrecorder. The scanning rate \vas 12 inches per hour and the ratemeter time constant was 20. The hctigraph I1 6can \vas made using the Suclear Chicago Actigraph I1 radiochromatogram scanner with a l\Iicromil windorv. This system includes the above counter, ratemeter, and recorder and in addition a ClOOB strip feeder. Collimator, scanning rate, and time constant were the same as above. The scans obtained using the adapter and Actigraph I1 system are identical except for the slightly lower count rate obtained using the adapter. This difference in count rate is caused by the difference in the distances from the paper to the counter rvindom, which are 4 mm. in the Actigraph I1 and 7 mm. in our adapter counting system. This could be changed and the adapter should then give a n equally high count rate. To use the adapter for automatic scanning, a paper strip leader is attached to the Chromatogram and this leader is attached to a strip of recorder paper. Sf7ith certain recorders, such as the Yarian, this paper can be fed into the recorder and the scan recorded directly on it. -4s the paper is fed into the recorder, it pulls the chromatogram through the adapter. K i t h a Texas Instruments recorder or the Nuclear Chicago R-1000-.4 used here, the paper used for pulling the chromatogram must be passed over the top of the recorder and then over the chart drive sprocket so as to clear the pen.
