liter of an approximately 0.1% ether solution of the sample was then introduced into the syringe and left to react the appropriate time depending on the reagent used, as indicated in Table I. The sample was then injected into a gas-liquid chromatograph. Instruments. Two flame ioniaation chromatographs were used in our work: for the acids, a Pye Series 104 Model 4 and, for all the other compounds, a Perkin Elmer F11. I n the Pye machine where samples were injected straight into the column, a 0.25-inch 0.d. 4-fOOt glass column
was used. The packing was 5y0 isophthalic acid 5% Carbowax on acid washed Embacel (1). In the Perkin Elmer machine a glass tube was fitted into the injection port; the 0.25-inch 0.d. 2-meter copper tube was packed with LAC 2R-446 (10% diethylene glycol adipate linked with pentaerythritol on Embacel). These columns remain stable and useful for about 500 injections and are renewed when the retention time of standard samples begins to change. I n both cases nitrogen was used as carrier gas a t 7 5 ml. minute.
RESULTS
A summary of the results of analyses carried out in this laboratory is shown in Tables I and 11. LITERATURE CITED
(1) Clarke J. R. P.! Fredericks, K. M., J . Gas dhromatog. in press. ( 2 ) Hoff, J. E., Feit, E. D., ANSL. CHEM. 36, 1002 (1964).
K. M. FREDRICKS ROBERT TAYLOR Imperial Chemical Industries Ltd. Petrochemical & Polymer Laboratory Runcorn Heath Runcorn, Cheshire
A Simple Versatile Collection Programmer for Preparative Gas Chromatography Bruce H. Kennett, Commonwealth Scientific and Industrial Research Organization, Division of Food Preservation, P.O. Box 43, Ryde, N.S.W., Australia
for the automatic collection of material emerging from a preparative gas chromatograph may be considered to have two distinct parts. The function of one part is to govern the timing for changing the collection traps, and the other part is the actual trapchanging mechanism. Two methods in general use for automatically actuating the trap-changing mechanism utilize, respectively, either a switch fitted to the recorder and actuated by movement of the recorder pen, or mechanical or electronic timers preset to operate at the required times. Both methods have limitations, the first lacking flexibility when collecting components that are either not well resolved or are minor constituents in a complex mixture, while simple electronic or mechanical timers, though they may be programmed to any chosen pattern, are generally limited by the number of set points available on them. Examination of food volatiles in this laboratory involves the use of preparative gas chromatography to separate the complex mixtures into fractions which are then examined on high resolution columns. However, since the relative concentration of the coniponents in the volatiles from frozen peas was found to extend over a range of at least 10,000: 1 the recorder-actuated switch used to effect trap changing on an available Aerograph Autoprep ‘705 was not applicable, and the present programming system was therefore developed. The effectiveuse of the programmer is dependent on reasonable reproducibility of replicate chromatograms, and the Autoprep 705, whether isothermally QUIPMENT
1962
ANALYTICAL CHEMISTRY
Figure 1. 1. 2. 3. 4. 5. 6.
Tape drive
Sensing head (see Fig. 2) Tape Drive roller Pressure roller Fixed idler rollers Adjustable idler roller
operated or temperature-programmed, has given acceptable reproducibility. The programmer is operated by driving a continuous loop of punched tape around a set of rollers (Figure 1). The holes in the tape correspond to the injection and trap-changing points transcribed directly from a chromatogram of the material under investigation. When a punched hole corresponding to a trap-changing point passes through the sensing head (Figure 2), it actuates the trap-changing mechanism. Similarly the punched hole corresponding to the injection point either initiates injection of another sampIe, or, with gas chroma-
tographs having inbuilt automatic repetitive injection systems, causes the tape to pause until the next sample is injected. The drive roller 3 (see Figure 1) is machined to give tl tape speed identical with the recorder chart speed, and is attached to the shaft of a 10 r.p.h. motor. The pressure roller 4 is made from brass rod sleeved with soft rubber tubing, pressure being applied by a helical tension spring, Fixed idler rollers 5, together with an adjustable idler roller 6, allow the use of different lengths of tape; up to 3 meters can be accommodated in a space of 20 X 25 cm.
-
n
12 v
+ OCP 70
BCZ I 1
OCP70
BC211
MOTOR
(b)
Figure 2.
(C
1
(d 1
Sensing head
Reflector 2. light bulb 3. Cylindrical lens 4. Pressure plate 5. Tape 6. Injection hole 7. Trap-change holes 8. Slits 9. Locating and tape-guide pins 10. Phototransistors 1.
The sensing head (Figure 2) consists of a light source 2 (6.3-volt, 1.5-watt lamp) focused by 3, a cylindrical perspex lens 12 mm. in diameter, onto a pair S of slits, each 4 mm. X 1 mm. A phototransistor 10, type OCP70, is located below each slit. The program tape is produced by laying a strip of black paper 16 mm. wide along a test chromatogram of the material and marking the positions of the injection point and trap-changing points. Elongated holes 5 mm. X 1.5 mni. are punched on these marks, the hole for the injection point being punched near one side of the tape and those for the trap-changing points near the other (see Figure 3). After providing for a suitable length of tape beyond the last hole (see below), the ends of the tape are overlapped and joined. The tape is then fitted to the programmer, the slack being taken up by the adjustable idler roller. The tape is positioned in the sensing head so that light passes through the injection hole to the phototransistor. I n this position relay K3 turns off the drive motor and the programmer is ready to operate. (Figure 3a, d.) The cycle commences with the automatic injection of a sample by the gas chromatograph. The coil of relay K1 (Figure 3b) is wired in parallel with the chromatograph's sample injection solenoid, and, when the sample is injected, K1 is energized and the contacts K1/1 close (Figure 3e). The capacitor C1 discharges through the coil of relay K2, thus energizing this relay, and the relay is kept energized by means of the self-
RECORDER INPUT FROM G.C.
TO RECORDER 1.3 V
1M
6
0
(f) Figure 3. Programmer circuit Relays
K1: Coil voltage to suit G.C. sample introduction system K2: 185-ohm 1 2 volt Vorley Relay Type VP4CAB12 (Oliver Pel1 Ltd., Woolwich, London) K3, K4, K5: 185-ohm 12-volt Varley Relay Type VP2HD5ACAB12 2K2 denotes 2 2 0 0 Time delay: Belling Lee Type L422/1 C/A (Belling Lee, Enfield, Middlesex, England) switch TDS
latching contacts K 2 j l . Simultaneously the tape drive motor is turned on by contacts K2/3. After about one minute, a time delay switch (TDS) operated by contacts K2/2 de-energizes K2, but because during this period the injection hole has moved away from its slit the contacts K3/1 now take over and keep the drive motor running. Although, as occurs with the Autoprep 705, the sample-injection solenoid may remain energized for a considerable period after the sample has been injected, relay K2 will not be energized on the subsequent reclosure of the time delay switch, for the available voltage across its coil is limited by the 1KS resistor. Relay K2 can only be energized again after contacts K1/1 have opened and allowed C1 to recharge. As each punched hole corresponding to a trap-changing position passes its slit, relay K4 is de-energized and the contacts K4/1 close (Figure 3a, c ) , thus actuating the trap-changing mechanism. %'hen the injection hole again comes opposite its slit relay K3 is de-energized
and the drive motor stops, the tape remaining stationary until restarted by the next sample injection. The recorder is run continuously, each injection and trap change being automatically marked. The injection is marked when contacts K3/2 close and discharge capacitor C2 through the coil of relay K5, This energizes K5 for approximately 1 second, during which time contacts K5/1 open (Figure 3f) and the potential across the 100 0 resistor is fed into the recorder. The trap change is similar!y marked when contacts K4/2 discharge C3 through the coil of K5. The circuit shown in Figure 3 was designed to make use of the inbuilt automatic repetitive injection system of the Autoprep 705 and is applicable to other gas chromatographs similarly instrumented. For instruments not so equipped, the tape can be used to initiate the injection by a simple modification to the circuit. Relays K l and K2 are omitted, the tape drive motor is connected directly to the mains, and contacts K3/1 are used to operate the VOL. 38, NO. 13, DECEMBER 1966
1963
sample-injection solenoid. The period required for higher-boiling compounds to emerge or for cooling the oven after a temperature-programmed run can easily be provided by leaving a suitable length of blank tape after the last punched hole. To control the time cycle of a temperature-programmed oven, a third slit, phototransistor, and set of punched holes could be added. A further extension of the basic idea of this programmer is the provision of a
Thermometer
number of channels, each of which is connected to its own solenoid valve and associated trap. This would allow separated components to be directed to any chosen trap, an arrangement which would be valuable where only a few components are to be collected from a large volume of a mixture. Provided chromatograms are reproducible on a time basis, this programmer also has potential application t o liquid column chromatography especially in
conjunction with the highly sensitive liquid chromatography detectors recently developed. ACKNOWLEDGMENT
The author is indebted to E. Bourn for assistance in constructing the programmer. THIS programmer is the subject of Australian Patent Application No. 6389/ 66.
for Proton Magnetic Resonance Studies of Aqueous Solutions
D. N. Glew, H. D. Mak, J. S. Mclntyre, and N. S. Rath, Exploratory Research Laboratory, Dow Chemicalof Canada, Ltd., Sarnia, Ontario, Canada investigation of the proton Iof magnetic resonance chemical shifts aqueous nonelectrolytes between 0' N A RECENT
and 30' C. using a Varian Associates A-60 spectrometer equipped with a V6057 thermostat attachment, the full instrumental accuracy of k 0 . 3 Ha. could not be fully utilized due to sample temperature cycling, which led to systematic water proton chemical shift variations of k0.7 Hz. Further, the reconimended method ( I ) of sample temperature determination, by substitution of a methanol standard tube for that of the sample, was of uncertain accuracy due to the considerable time lapse of about 20 minutes between the measurements of the sample and that of its thermally equilibrated methanol thermometer substitute. To eliminate these uncertainties without resorting to instrumental modifications, it was required to develop a thermometer to be contained within the normal 5-mm. sample tube, which would provide a rapid and precise definition of the sample temperature in the coil region. To achieve this with convenience, it was decided that the thermometer temperature should be d 4 fined by proton magnetic resonance chemical shift differences of two signals
Table 1.
EXPERIMENTAL
The study of aqueous solutions required that the region 0 < 6 < 6.0 p.p.m. should be available for sample investigation, so that the thermometer signals had to be limited t o the region 6.0 < 6 < 8.3 pap.m. Study of numerous potential liquid mixtures showed that the ternary mixture 3 mole yo tetramethylsilane, 61 mole % m-chlorophenol with 36 mole % trifluoroacetic acid provided a suitable spectrum. In this mixture the m-chlorophenol aromatic protons furnish a complex multiplet signal which changes with temperature but which always contains a strongest sharp signal a t 6 = 6.86 p.p.ni. which moves little with temperature, while the trifluoroacetic acid exchanges rapidly with the phenolic protons t o give a single, sharp, temperature-sensitive peak which varies in the region 7.5 < 6 < 8.3 p.p.m. The temperature-sensitive phenolic peak is overlapped by the aromatic ring protons multiplet when no trifluoroacetic acid
Standard Errors of Methylene and Water Proton Magnetic Resonance Signals using Thermometer No. of
Mole % solute
observations
0 0.10 ethylene oxide 4 . 5 0 ethylene oxide 10.0 ethylene oxide 0.05 dioxane 10.0 dioxane 0 . 2 0 tetrahydrofuran 4 . 5 0 tetrahydrofuran
18 10 9
10.0 tetrahydrofuran Mean of data
1964
from an external standard, measured in the same scan as the sample signals. With such a thermometer it should then be possible to correct all chemical shifts to a standard sample temperature, thereby removing the parasitic effects of temperature fluctuations.
ANALYTICAL CHEMISTRY
Methylene signal error (Ha.)
Water signal error ( H a . )
0.288
0.300 0.274 0.441 0.399 0.342 0.266 0.292 0.344 0.304 0.326
7
14 8 17 13 8
...
is present. the composition given is particularly suitable for the temperature range - 10' t o $30" C. For use in higher temperature ranges, additional trifluoroacetic acid can be added to prevent overlapping of the aromatic multiplet by the phenolic acid peak a t the highest temperature. The thermometer sheath was axially symmetric and thin-walled as colddrawn from 6-mm. diameter borosilicate-glass tubing. It was filled with the liquid mixture via a fine capillary, then freeze-outgassed, and sealed a t its upper end. The final thermometer was a hemispherical bulb of 4.0-mm. diameter a t the bottom gently tapering to a 3.3-mm. diameter at a 6-mm. height, 2.7 mm. at 12 mm., 2.3 mm. at 18 nim., 2.0 mm. at 24 mm., becoming almost parallel at 1 mm. diameter at 100 mm. to the 170 mm. height of the seal. With this tapered thermometer, relative peak height changes of the sample and thermometer signals were readily made by vertical adjustment of the sample tube position. The thermometer locates itself accurately along the sample tube spinning axis by the close fit of the bulb at the bottom and by a centrally pierced Teflon disk surrounding it a t the top. RESULTS A N D DISCUSSION
The thermometer was calibrated using the instrument thermostat a t 14 temperatures between - 10' and +30' C. by the substitution method using a methanol standard ( I ) , which gave a standard error of k0.84' 6.on a single defined temperature. The thermometer accurately represented the calibration temperature t o C. by the linear expression.
t
= 87.961
- 1.0736
(VOH
- VA~H)
in which uOH and V A ~ Hare respectively the phenolic and the aromatic ring proton chemical shifts in Ha. The temperature sensitivity of the thermometer is 1.8 times greater than that of the methanol standard, so that with a
