Fluidic Logic Sampling and Injection System for Gas Chromatography Robert L. Wade and Stuart P. Cram Department of Chemistry, Unioersity of Florida, Gainesuille, Fla. 32601 The design, development, and performance of a simple, rapid, and automated gas sampling and injection system for gas chromatography is described. Standard fluidic logic components are used to effect the sampling step and to control the variable sampling time. The switching speed and precision of the system are reported. Symmetrical injection peak profiles were obtained with peak widths as narrow as 9.5 msec. The shape and width of the injection peak profile depended on the logic element used for sampling, the timing and pressure levels of the control logic, the dead volume of the sampling system, and the back pressure of the chromatographic column. The system is unique in that it involves no moving parts, and can be configured for a large number of applications in analytical chemistry.
SAMPLING AND SAMPLE INJECTION have become vitally important in the experimental measurement of fundamental parameters, quantitative analyses, and automation in gas chromatography which use associated computer systems. Manual injection methods are almost untenable with the speed, high precision, and computation power available with digital data acquisition systems. Further, they cannot be justified in terms of the accuracy, timing, reproducibility, and potential for peak profile characterization studies. Although a wide diversity of sampling systems for gas chromatography have been reported (1-7), reviewed ( & ] I ) , patented (12-24), and manufactured commercially (25-28), very few are compatible with the precision and timing specifications of computerbased chromatographic systems. Present sampling systems may be classified as syringe (2935), ampoule (36-41), sliding seal valves (25, 42-47), rotary valves (27, 48-50), diaphragm seal valves (51-54,electrically activated hybrid-fluidic valves (55, 56) and those which are automated (34, 35, 57-65). Consequently, the chromatographer has methods of sampling gases (66, 67), liquids (68, 69), and solids (70-72), but all of these devices have inherent limitations and none of them operate as a n ideal sampling system. The injection peak profile is determined by the method of sampling, and the effect of the injection peak profile o n chromatographic peak shapes and column efficiency is well known (73-78). Guiochon (76) has studied the influence of injection time o n the efficiency of gas chromatographic columns and found that the injection time adds to thi: zone variance as the square of the standard deviation in the injection time. This effect must be considered for components with short retention times and in minimizing the band broadening of the chromatographic system. The band broadening contribution of a high precision gas sampling system was measured from moment analyses by Glenn and Cram (57) and they found that the sampling valve need not be a major contribution in a well-designed system. Cramers (79) described the effect o n resolution of injection band broadening by diffusion when a finite sample is injected in a finite time. Other work has shown that for gas sampling valves with switching times short relative to the time for the sample to be swept out of the sampling volume by the carrier
gas, a “nearly ideal plug injection” is obtained (73). Liquid injection with a syringe or sampling valve into a flash vaporizer in a time which is short relative t o the flow resistance time in the vaporizer gives nearly a plug injection which is degraded t o a Gaussian profile by diffusion. Oberholtzer and Rogers (80) measured the peak width, the valve actuation time, and the timing precision of three different types of automated sampling valves. Their results indicate that valves which had the most reproducible timing did not necessarily give the narrowest sample injection profile, and vice versa. They have also pointed out that once the variations of temperature and carrier gas flow rate have been minimized by proper thermostating and regulation that sample injection and retention time measurements remain as major factors that limit the precision and accuracy of chromatographic data. All previously described sampling valves have been necessarily constrained by their design limitations and mechanical inertia. A hybrid-fluidic valve (55, 56) has approached a n ideal peak injection profile with sampling bandwidths as narrow as 30 msec (57) compared to 340 msec or more for commercially available valves (80). In the faster valve, there is no sliding seal and the relative precision of the peak area and retention time is 50.275, but the speed is ultimately limited by the electromechanical solenoid and/or spring return. The ultimate in sampling speed can be achieved only when all mechanical movement is eliminated and only the molecular movement of the sample itself is involved. A fluidic logic system for chromatographic sampling and control of the sampling system has been developed here in order t o approach high speed, reproducible, automated sampling in a simple and inexpensive manner. Fluidic logic is a relatively new development as most of the publications have appeared since 1962 (81-90) and now a t least 18 commercial manufacturers offer fluidic logic components. Fluidic logic elements and devices have not appeared in the analytical chemistry literature to data. However, the first known application of fluidics in a n analytical experiment was reported by Cram and Wade (91)a t the 1971 Pittsburgh Conference. The application of fluidics to gas and liquid chromatography will be discussed here and the authors propose that they should also be useful as stream splitters, for column switching, switches for trapping column components or direct in-line switching to mass spectrometers and infrared spectrophotometers, gas phase separators for mass spectrometers, oscillators for fluid flow, modulators for switching between reference and unknown samples (as in emission o r absorption spectrometry), compensation for noise and base-line drift, for solution reaction rate studies, stop-flow kinetics experiments, and for complete experimental automation and control as is presently done with solid state electronics. These applications will be a natural’development in analytical chemistry because of the availability of fluidic logic gates, adders, diodes, capacitors, resistors, multivibrators, amplifiers, oscillators, counters, Schmitt triggers, shift registers, time-delay relays, high frequency pressure-to-electric switches, and integrated circuits.
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Figure 1. Schematic diagram of experimental system employed to measure injection peak profiles
02 A large number of engineering and control applications have been developed. For example, a fluidic velocity sensor (92), fluidic display systems (93), a pneumatic stepping motor (94), density measurements (951, and proportional control devices (96) have been reported. Alternating current circuit techniques have also been applied for frequency to analog conversion, frequency decoupling, and phase discrimination circuits using fluidic logic elements (97). The advantages over electronic and pneumatic devices of being simple, versatile, high speed, reliable, having no moving parts, long lifetimes, easy maintenance, low cost, high tolerance to vibration, hazardous environments, and temperature changes can result in improved accuracy and decreased downtime of any logical or control application ranging from hospital pressure pads to industrial machinery, and should very shortly include the analytical laboratory. EXPERIMENTAL The fluidic logic elements used in this study were obtained from Bowles Engineering Corp., Silver Spring, Md., and include a three input OR/NOR gate (Model B-202-A), a back pressure switch (two input OR/NOR key, Model B205-A), a four input flip-flop (Model B-201-A), amplifier valve (Model V-025-A), fluidic capacitor (Model A-003-A), panel indicator (Model M-501-A), and manifold mounting rack (Model B-200-A). The fluidic diodes were duckbill check valves (Model VA 3143, Vernay Laboratories). The experimental apparatus employed to measure the injection peak profiles is shown in Figure 1. Because of the high carrier gas velocities, a pressure transducer with a resonant frequency of 80 KHz (Model SP-64, Dynasciences Corp.) in a Wheatstone bridge circuit was employed. The
01
Figure 3. Cross-sectional view of the flow channels of a fluidic flip-flop output of the pressure transducer (0-10 mV) was connected to a voltage-to-current converter which has been described elsewhere (98). An output current of 0-20 mA was required to drive the fluid damped galvanometers (Heiland Series M-1000, Honeywell, Inc.) in the oscillographic recorder (Visicorder Model 1108, Honeywell, Inc.). The response time of this display system was limited to 1 msec by the time constant associated with the galvanometer. Elution peak profiles from both packed and capillary columns were studied by incorporating the fluidic sampling system into the digital data acquisition system shown in Figure 2 . A Varian Model 2100 gas chromatograph with a dual flame ionization detector was used for temperature control. The carrier gas flow control system was modified for higher precision flow control and has been described elsewhere (57). A low noise electrometer (Model 5044-100, Barber-Colman Co.) was used to drive both the servo recorder (Model 7101B, Hewlett-Packard) and the successive approximations ADC (Model A81 1, Digital Equipment Corp.). The computer system is based on a PDP-8/L (Digital Equipment Corp.) and its control, data acquisition, and display capabilities are the subject of another paper (99). Data acquisition rates were 1.0 and 0.2 KHz, depending on the sample pulse width. RESULTS AND DISCUSSION Basic Fluidic Operation. Fluidic logic components described in this work operate according to the Coanda effect (87) and take advantage of the wall-attachment principle. Figure 3 represents the flow channels of a basic fluidic flip-
Figure 2. Schematic diagram of chromatographic and data acquisition system used to measure elution peak profiles
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flop (FF) where the physical size of the FF is 2 X 11/2 X ”16 in. and the channel dimensions are 0.040 X 0.015 in. The supply gas from a well-filtered, well-regulated source enters the supply gas channel and flows into the power nozzle jet where turbulent flow is assured. Then the flowing stream enters the wall attachment area where a low pressure pocket is developed against the wall surface relative to the surrounding ambient pressure. Since the flip-flop is a bistable device the supply gas exits unbiased through either output channel 0 1 or 0 2 . The flowing stream will remain in this output channel (e.g., 0 1 ) until flow is stopped or until a control signal appears a t control channel C2. When the control pressure (-10-30z of the supply gas pressure, P,)is applied a t C2, the stream detaches itself from the wall surface and reattaches itself to the opposite surface in the wall attachment area. The supply gas is then output through channel 0 2 and remains in that state until a control signal is applied at C1 and C2 is cut-off. The switching time is nominally 1 msec. The fluidic elements discussed here were operated with fluid flows at Reynolds numbers, Ro,between 2,000 and 12,000 as given by (88)
[-p4 2(P8 - Pe)b2 ‘I2
Rb
=
where P, is the nozzle exit pressure, b is the nozzle exit width, p is the fluid density, and Y is the fluid kinematic viscosity. The supply pressure was nominally 1.25 psig with a flow rate of 5.1 l./min when measuring the performance characteristics of the logic system. It should be possible to operate with liquid flows as well if turbulent flow can be maintained and the supply pressure and nozzle exit widths are increased sufficiently to compensate for the higher densities and kinematic viscosities of liquids. Sampling Logic Configurations. Figure 4 represents an automated fluidic controlled gas sampling valve that employs only OR/NOR gates. The supply gas was’air or nitrogen and the sample in the vapor phase (methane in this study) was introduced as the supply gas at gate 3. Liquid samples are first vaporized in the exponential dilution flask (Figure 2) which is connected directly to P, of gate 3. The switch, S, is normally closed so that the supply gas is output through channel 0 2 of gate 1 when the system is in the nonsampling configuration. This output serves as the control signal on gates 2 and 3 so that their supply gas is vented through channel 0 1 in both cases. Channel 0 1 of gate 3 can be connected to the sample reservoir so that sample consumption is negligible. In this nonsampling mode, the carrier gas passes through duckbill check valve 1 and onto the chromatographic column. Check valve 2 prevents carrier gas from being aspirated up into gate 3 and allows high inlet pressures to be effected at the
head of the column. Check valve 1 also prevents compression waves from travelling down the carrier gas line, reduces the overall dead volume of the injection port, and sharpens the tailing edge of the injection profile by reducing the fall time. When the initiate switch is actuated, a fraction of the supply gas flow through gate 1 is diverted through the pneumatic resistor and switch in order to apply a control signal to C3 and cause the output to be switched to 0 1 . This switching action removes the control signal from C3 of gate 2 and C1 of gate 3. By cutting off control C1 on gate 3, the sample is then switched to output 0 2 . The positive sample pressure opens the duckbill check valve 2 and the sample enters the carrier gas stream. When control channel C3 on gate 2 is cut-off, the output is through 0 2 . After a time delay determined by the R C network, a control signal is applied to C3 of gate 3 which switches the sample output back to 01. The total effective dead volume which the sample sees in the sampling is less than 10 pl because of the small inside channel diameters. The sample size is determined by the concentration in the sample stream entering gate 3, the volumetric flow rate through the sample inlet, and the switching time of gate 3. The switching time is determined by the pneumatic R C time constant between gates 2 and 3 and is made up of a 10 cu in. buffer capacitor (C) and a n adjustable needle valve (R). The connecting tubing adds about 1 msec of delay per foot of tubing. It should also be noted that there is only one sample injected each time the control signal is applied by the initiate switch. Even if the switch is left open, only one sample is injected onto the column as the supply gas at gate 2 remains at outlet 0 2 which holds C3 on and holds the sampling gate in the nonsampling position. Therefore the sampling system
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lu - i ~u l Figure 7. Schematic diagram for back pressure switch, 2 OR/ NOR fluidic sampling and control system. P , is the supply gas
Figure 6. Timing and synchronization diagram for the 3 OR/ NOR gate system. P , is the supply gas will not go into oscillation and, more importantly, this makes the sampling time entirely independent of the method and timing of opening the actuating switch. Fluidics may be treated as the pneumatic analog of electronic logic devices and thus logic diagrams, truth tables, and Boolean algebra operations can be implemented. The logic diagram shown in Figure 5 illustrates how the fluid system in Figure 4 may be developed. Positive logic is used in Figure 5 and it is assumed that C3 on gate 1 is a logical “one” when switch S is open. Then the logic sequence or “truth table” can be implemented with OR/NOR gates. Table I clearly shows that after initiation, C3 of gate 3 remains a t logical “0” even though 0 2 of gate 2 is a t logical “one” because of the R C time delay when T RC
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o n the R C time constant unless the switch were closed prematurely such that At < 7 . This is highly unlikely since T will be seen to be on the order of a few milliseconds. An alternative logic system was designed and built, as shown in Figure 7, which incorporates a back pressure switch. Normally the supply gas is vented through C1 on the back pressure switch and the normally open switch. When S is closed a fraction of the supply gas is diverted back t o switch P , from outlet channel 0 2 to 0 1 and then the same logic sequence is triggered as before. Both configurations shown in Figures 4 and 6 worked satisfactorily, but there is one potential disadvantage in their design. When the output of gate 1 is switched to channel 0 1 , the pressure a t control channels C3 of gate 2 and C1 of gate 3 must drop to the return pressure, which is about 2 % of the supply pressure, before switching to output channels 0 2 will occur in these devices. It is much easier, faster, and more reproducible to generate a positive pressure switching action than to design a device to operate by decaying to a preset value. A flip-flop (FF) is used as the sampling element in the logic configuration shown in Figure 8. In the nonsampling position, S is open and the supply gas is directed out through channel 0 2 . This latches FF 2 to vent through 0 1 and holds C1 o n FF 3 off. When the switch is closed, the back pressure switch is switched t o outlet 0 1 which sets the outputs of FF’s 2 and 3 t o 0 2 . This positive switching action starts venting the sample onto the column and it will be held there until the end of the R C time constant applies a positive switching level a t C1 o n FF 3. Thus the pulse width and sample size can be predetermined by correctly choosing the time constant desired. Furthermore the pulse width can be calculated within 10% if the lengths of delay tubing between FF’s 2 and 3 and the back pressure switch and FF 3 are matched. One possible disadvantage of this system is the case where the back pressure switch remains at 0 1 too long. Then a n indeterminate state for FF 3 can exist when a control signal is applied a t both channels C1 and C2. This can be alleviated
ANALYTICAL CHEMISTRY, VOL. 44, NO. 1, JANUARY 1972
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Figure 8. Schematic diagram for back pressure switch, two flip-flop fluidic sampling and control system by placing a pneumatic resistance in the C2 line such that the control pressure a t C1 will override that a t C2 when both are on. Figure 9 illustrates a system which uses a feedback loop for control of the sample size and the width of the injection profile. Here sample switching is effected by closing S to apply a control signal a t C1 on FF 3. This control signal vents the sample onto the column through 0 1 and a fraction of the sample gas is split out of the gas stream a t 0 1 and diverted t o reset FF 2. The on-time of the sampling valve is then determined by the supply pressure, flow rate through line C, the length of connecting tubing, and the pneumatic time constant of the buffer capacitor and needle valve. This system has two distinct advantages over the one discussed in Figure 8. The reset function of FF 2 allows only one sample injection per initiate pulse and thus eliminates any chance of accidental sample injections during the chromatographic separation. Second, the possibility of a n indeterminate condition arising for the sampling FF in Figure 8 (when the back pressure switch remains in the state 01) is eliminated. In Figure 9, back pressure switch 1 will be switched back to outlet 0 1 when S is closed again, but FF 3 cannot be switched from 0 2 to 0 1 until C2 has been removed. The cessation of flow a t C2 of FF 3 will only occur when the reset switch is opened so that FF 2 is vented through outlet channel 0 1 . Perhaps the simplest fluidic sampling system is shown in Figure 10 which employs a fluidic monostable with a fixed cycle time of -25 msec. Under these conditions the sample size will be determined by the concentration in the supply gas and the flow rate through channel 02. Note that the supply gas must be the same as the carrier gas for sampling vaporized liquids in this configuration, and may indeed be the sample itself in the case of gas analysis. Although this sampling valve is simple and compact, the sampling time and control logic are invariant. Performance. In order for the sampling valve to operate reproducibly and reliably, the pressures and flow rates must be within the operating specifications of the fluidic device.
DETECTOR
READOUT
Figure 9. Schematic diagram of reset flip-flop fluidic controlled sampling system The fluidics in this study were typically operated a t 4.0 psig supply gas pressure. The carrier gas flow rate was 21.6 cc/min a t the column outlet. For a gated on-time of 10 msec the sample size of methane was calculated t o be 3.6 pl. If longer sampling times are desired, the inlet pressure us. switching time curve levels off with longer times and the fluidic device may trigger on pneumatic noise. This emphasizes the point for good flow regulation and the necessity of minimizing sample switching times. With a 5-10 msec switching time, a repro5 can be expected with these commercial ducibility of devices. The switching times should be decreased and the precision increased with the development of integrated fluidic circuits. With the pure fluidic sampling valve discussed here, there is no problem of sample bleed onto the column, such as en-
*
SAMPLE IYLET
ONE-SHOT MULTIVIBRATOR
IDETECTORHREADO Figure 10. Schematic diagram of fluidic monostable multivibrator sampling and control system
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Figure 12. Injection peak profile of back pressure switch, 2 OR/NOR gate system with 8 ft, 11 in. of delay line tubing
Figure 11. Injection peak profile obtained from the 3 OR/NOR gate system with 8 ft, 11 in. of delay line tubing countered with the electrically actuated hybrid-fluidic valves (55, 56). In order to obtain the maximum rejection ratio, Glenn and Cram (55) found it necessary to maintain the mixing
chamber time constant of the valve less than that of the diffusion coefficient of the sample gas. When the sample gas flow in the fluidic valve shown in Figure 9 is in outlet channel 0 2 the pressure in the injection port is much greater than that a t outlet channel 01. This effects a positive check valve closure (2) and with the aspirating effect of channel 01 assures that there is no measurable sample bleed onto the column. Evaluation. Figure 11 is the injection profile o n a millisecond time scale of methane with the 3 OR/NOR gate system shown in Figure 4. The total amount of connecting tubing for this system is equivalent to about a 9-msec delay in the network. The characteristics for the three different configurations of fluidic systems are given in Table 11. The 3 OR/NOR gate system is seen t o give the fastest rise time (measured as the time required t o go from 10 to 90% of the peak height), the narrowest peak width (usually measured as the width a t half-height), and generally the best precision of the three systems studied. These times do not represent optimum configurations and, therefore, not a lower limit of sampling speed. However it was felt that peak widths less than 10 msec wide with a reproducibility of less than onetenth of a per cent were so gratifying that a reconfiguration
really wasn’t necessary. The peak profile in Figure 11 is reasonably symmetrical and it is most significant to note that only a slight amount of exponential tailing exists. This is taken as a n indication that positive switching is occurring in the sampling gate and that the volume of any diffusion chambers that exist in the system are negligible. The back pressure switch (BPS), 2 OR/NOR gate valve profile is shown in Figure 12 and has a n effective delay time of 9 msec built into the system. This peak is likewise seen to have a narrow width a t half-height, 10.3 msec (Table 11), but the reproducibility is markedly decreased because of the tailing on the peak. This probably reflects the exponential characteristic of the switching action of the RC network in applying the control signal a t C3 to cut off gate 3. It should be noted that before every effort was made to reduce the dead volume of the injection port (and only a single diode was used) and tubing connections, that the rise time of this sampling configuration was 12.8 msec and the fall time was 12.3 msec. Thus, the peak shape is badly degraded to look like a square wave which has passed through a low pass filter with a time constant approaching the width of the square wave. Likewise, Table I1 giving values for the BPS, 2 FF system taken with only diode 2 installed gave a n exponential tail. However, despite this the reproducibility of injection was quite good. Thus minimum dead volumes and both diodes in the injection port are essential in order to generate well-behaved peaks.
Table 11. Performance and Reproducibility Data for Various Fluidic Sampling Systems
Peak height, cm. Base width, msec. Width at half-height, msec. Rise time, msec. Delay time, msec. Fall time, msec.
3 OR/NORa Re1 std Mean dev, % 10.2 0.53 4.3 20.2 0 9.6 4.1 3.5 1.8 ... 8.1 2.6
BPS, 2 OR/NOR5 Re1 std Mean dev, % 6.61 0.56 26.6 2.36 8.6 10.3 3.7 4.4 2.0 21 8.3 27
BPS, 2 OR/NORb Re1 std Mean dev, 7.6 3.0 9.9 69.0 63.9 11 6.7 4.8 1.6 7.8 4.2 13
Data taken with 9 ft of delay tubing in the sampling system. Data taken with 16.5 ft of delay tubing and the buffer capacitor in the sampling system. c Data taken with the buffer capacitor in the sampling system.
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Figure 13. Injection peak profile from back pressure switch, 2 OR/NOR gate system with fluidic capcitor and 16.5 in. of delay line tubing
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In order to demonstrate that fluidic sampling systems can generate well-defined pulse shapes for theoretical studies and high precision gas chromatography, and the effect of increasing the R C time constant to increase the sample size, a fluidic capacitor of 10 cu in. was added to the system with a n additional 16.5 in. of connecting tubing. A representative injection peak profile is shown in Figure 13 where the base width is 62.6 msec, the width a t half-height is 56.9 msec, the rise time is 4.9 msec, the delay time is 1.4 msec, and the fall time (from 90 to 10% of the peak height) is 3.8 msec. The slope of the leading edges is seen to be very sharp as the difference between the base width and the width at halfheight is only 5.7 msec and most of that can be accounted for on the back side of the peak. The noise on the plateau is attributed to flow instability and turbulence of the methane a t the outlet of the OR/NOR sampling gate, and could not be reduced with the particular venting design on these gates. Table I1 compares the mean values of the two BPS, 2 FF systems so that the effect of the R C time constant o n the performance of the sampling system can be seen. The results indicate that this is the least precise system and has the least positive switching action. The relative standard deviation of the sample width measurements were 11 times better for the profile in Figure 13 than in Figure 12 and can be attributed to the flattening of the pressure us. time curve and the uncertainty of reaching the same “turn-on” pressure at precisely the same time as the delay time is decreased. Generally, the shorter the delay time, the more reproducible is the timing of the device. Figure 14a was recorded as a column elution profile using the 3 OR/NOR gate design shown in Figure 8. The fluidic capacitor and 18.54 in. of Tygon tubing were used in the delay line and the column was a 12-ft X 0.023-in. stainless steel tube. One of the best measures of precision is the reproducibility of the peak area. For five samples run on the capillary column, the relative standard deviation was 2.70% with a coefficient of variation of 1.16%. This may be compared to the results on the packed column, shown in Figure 146, which gave a relative standard deviation of 7.16% and a coefficient of variation of 0.72 %. The peak profile in Figure 14a is very sharp considering the amount of diffusional broadening which occurs in the open tubular volume of the column. The tailing of the peak is serious and is due to the fact that the present “off the shelf” fluidic devices are built to operate within the *5% reproducibility at low pressures (1.25 psig) and high flow rates (4.2 l./min). When these are interfaced into a high pressure, low flow device like the injection port of a gas chromatograph, they may have to be operated out-
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Figure 14. Elution profile for the 3 OR/NOR gate fluidic logic system sampling methane onto (a) a 12-ft open tubular column, and (6) a 1 ft X lis in. packed column. The start of the two peaks are normalized to the same time to compare peak broadening side of their specifications. Consequently, switching becomes less positive and less reproducible. This problem is further illustrated in Figure 146 using the same logic for sampling and control on a 1-ft X lis-in. Teflon column packed with 5 SE-30 on 100/120 mesh AW-DMCS Chromosorb G . The pressure drop on this column is greater than the capillary column and higher inlet pressures were required on the fluidics. As new technology in fluidic devices is developed, devices with smaller power nozzles and higher pressures should be available. As long as turbulent flow is maintained, the wall attachment phenomenon will operate and it should be possible to design a fluidic sampling device that would operate at higher gas pressures. Liquid chromatography sampling would then also be feasible. CONCLUSIONS
The fluidic sampling system has been shown to provide an extremely fast sampling and injection system for gas chromatography, with a nearly ideal injection profile which is unobtainable by conventional sliding seal, diaphragm, or rotary seal valves. By virtue of its inherent digital design, it is readily amenable to complete automation. The sample size is dynamically and continuously variable so that there is no need to change sample loops, for example. When interfaced to SCOT or capillary columns, the fluidic sampler eliminates the necessity for a splitter and thereby gives representative sampling without fractionation. The device is exceptionally reliable, inexpensive, fast, and is not subject to noise or stray pickup. The problem of impedance mismatching between the fluidic elements and chromatographic columns has been overcome by using duck.bil1 check valves as diodes, although these diodes may ultimately limit the minimum sample size in volume and peak width. There is a pressure surge on the column caused by the injection of a sample into the carrier gas line, although this is generally true of any gas sampling valve. This signal is detrimental to flow sensitive detectors and fluctuations have even been noted on a flame ionization detector with this system. Presently, if liquid samples are to be studied, they must
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first be vaporized in a n exponential dilution flask. Condensation in a logic element would be detrimental to its operation. The sampling systems described in this paper represent a number of prototype designs assembled to study the feasibility of fluidics as sampling devices for gas chromatography. The ideal design would be a n integrated fluidic circuit which includes the timing, control, sampling, and interface logic. Work has been done on fluidic oscillators as chromatographic detectors (100, 101) and thus a new trend of miniaturized instruments which include the sampling valve, column, and detector in a single package may be on the horizon. New fluidic devices should also offer decreased response times [although fluidic devices have been reported which have switching times of 13 psec (96)J and dead volumes, operate at supply pressures of 15-100 psig, and be nonventing. LITERATURE CITED (1) T. Johns and B. Thompson, Abstracts Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1964, No. 63. (2) “Becker Application Notes,” 17 (83), Becker Delft N.V., Delft, Holland, June 1969. (3) R. Blomstrand and J. Gurtler, Acta Clzem. Scand., 18, 276 (1964). (4) D. A. Forss, M. L. Bazinet, and S . M. Swift, J . Gas Chromatogr., 2, 134(1964). ( 5 ) B. 0. Ayers, “Gas Chromatography,” V. J. Coates, H. J. Noebels, and I. S . Fagerson, Ed., Academic Press, New York, N.Y., 1958, p 93. (6) R. Kieselbach, ANAL.CHEM.,35, 1342 (1963). (7) E. S . Escher, I.S.A. Proc., 16, Part 11, Preprint No. 130-LA-61, 1961 Fall Instrument-Automation Conference and Exhibit, Los Angeles, Calif., Sept. 1961. (8) C. H. Hamilton, “Instrumentation in Gas Chromatography,” J. Krugers, Ed., Centrex Publishing Co., Eindhoven, 1968, p 33. (9) R. D. Condon and L. S . Ettre, “Instrumentation in Gas Chromatography,” J. Krugers, Ed., Centrex Publishing Co., Eindhoven, 1968, pp 87-109. (10) J. C. Cavagnol and W. R. Betker, “The Practice of Gas Chromatography,” L. S . Ettre and A. Zlatkis, Ed., Interscience, New York, N.Y., 1967, p 71. (11) D. W. Carle, “Gas Chromatography,” V. J. Coates, H. J. Noebels, and I. S . Fagerson, Ed., Academic Press, New York, N.Y., 1958, p 67. (12) C. R. Ferrin, U.S. Patent 3,306,111 (1967). (13) E. S . Watson and D. P. Bresky, U.S. Patent 2,757,541 (1956). (14) J. C. Lamkin, US. Patent 2,972,888 (1961). (15) E. R. Fenoke and J. H. McLaughlin, US. Patent 3,266,321 (1966). (16) H. G. Boettger, US. Patent 3,267,736 (1966). (17) W. F. Gerdes, U.S. Patent 3,435,661 (1969). (18) W. H. Topham, US.Patent 3,321,977 (1967). (19) D. Jentzsch and W. Schumann, US.Patent 3,365,951 (1968). (20) G. R. Harvey, Jr., U.S. Patent 3,368,385 (1968). (21) J. W. Todd and C. G. Courneya, U.S. Patent 3,393,557 (1968). (22) E. L. Szonntagh, U.S. Patent 3,386,472 (1968). (23) J. R. Rendina, U.S. Patent 3,318,154 (1967). (24) A. B. Broerman, U.S. Patent 3,111,849 (1963). (25) W. M. Crum, I.S.A. J . , 9,64(1962). (26) F. H. Harvey and W. J. Baker, Oil GasJ., 59, 147 (1961). (27) Carle Instrument Co., Fullerton, Calif., Bull. 2055 (1970). (28) “1970/71 Intehational Chromatography Guide,” J. Chromafogr. Sci., 8, G28 (1970). (29) M. Ellison, Analyst, 93, 264 (1968). (30) P. Pitt, Chromatographia,1,252 (1968). (31) R. J. Harris, Jr., US.Patent 3,355,950 (1967). (32) H. Abegg, J . Chromatogr., 9, 519 (1962). (33) M. Taramasso and A. Guerra, U.S. Patent 3,094,155 (1963). (34) Hewlett-Packard, Avondale, Pa., Automatic Sampling System Bull. (1970). (35) Hamilton Syringe Co., Whittier, Calif., Autosampler System Bull. (1970). (36) E. S . Khuhovskii and A. G. Sharonov, British Patent 1,042,652 (1964); Anal. Abstr., 14, No. 1788 (1967). 138
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(37) D. S . Berry, ANAL.CHEM.,39, 692 (1967). (38) R. A. Back, N. J. Friswell, J. C. Boden, and J. M. Parsons, J . Chrornatogr.Sci., 7, 708 (1969). (39) A. G. Nerheim, U.S. Patent 3,063,286 (1962). (40) A. G. Nerheim, U.S. Patent 3,119,252 (1964). (41) S . F. Micheletti, U.S. Patent 3,002,387 (1961). (42) G. S. Turner and R. Villalobos, “Gas Chromatography,” N. Brenner, J. E. Callen, and M. D. Weiss, Ed., Academic Press, New York, N.Y., 1962, p 363. (43) Tycam Engineering, Inc., Houston, Tex., 8-Port Valve Bull. (1965). (44) S. B. Spacklen, I.S.A. J . , 4, 514 (1957). (45) C. J. Penther and J. W. Hickling, Oil Gas J., 59, 130 (1961). (46) M. L. Marks and F. C. Calcaprina, US. Patent 3,000,218 (1961). (47) D. L. Peterson and G. W. Lundberg, ANAL.CHEM.,33, 652 (1961). (48) E. L. Szonntagh “Gas Chromatography,” L. Fowler, Ed., Academic Press, New York, N.Y., 1963, p 233. (49) G. L. Pratt and J. H. Purnell, ANAL.CHEM.,30, 1213 (1960). (50) C. J. Penther, Control Eng., 10, 78 (1963). (51) J. Hooimeijrt, S. Kwantes, and F. van de Craats, “Gas Chromatography,” - . . D. H. Desty, Ed., Butterworths, London, 1958, p 288. 152) W. H. Tooham. British Patent 1.111.443 (1968). (53j A. B. Broerman, U.S. Patent 3,387,496 (1968). ’ (54) Seiscor, Tulsa, Okla., Model VI11 Prod. Bull. (1970). (55) T. H. Glenn and S. P. Cram, J . Chromatogr. Sci., 8,46 (1970). (56) R. C. Palmer, Control Eng., 8, 121 (1961). (57) T. H. Glenn and S . P. Cram, ANAL.CHEM.,in press. (58) J. E. Oberholtzer, ibid., 39, 959 (1967). (59) F. G. McCarty, Amer. Lab., Oct. 1968, p 54. (60) P. J. Kipping and C. A. Savagein, “Seventh International Symposium on Gas Chromatography and Its Exploitation,” C.L.A. Harbourn and R. Stock, Ed., Institute of Petroleum, London, 1968, p 7. (61) Carle Instrument Co.. Fullerton. Calif.. Bull. 6607B (1970). (6i) R. W. Warren and S. J. Peperone, “Basic Principles, Fluid Amplification,” Vol. 1, Harry Diamond Laboratories, Washington, D.C., TR-1039, 1962. (63) D. Mennie, Elec. Design, 2, 32 (1970). (64) N. Sher, Instrum. Contr. Syst. 41, 81 (1968). (65) H. B. Horton, ibid., 39, 91 (1966). (66) N. P. Wong and D. P. Schwartz, J . Chromatogr. Sci., 7, 569 (1969). (67) D. J. McEwen, J . Chromatogr., 9: 266 (1962). (68) A. B. Broerman, U.S. Patent 3,103,807 (1963). (69) P. Jenkins, U.S. Patent 3,118,300 (1964). (70) R. M. Waters and D. D. Flanagan, J . Chromatogr., 35, 92 (1968). (71) K. Dorfner, Brennst.-Chem., 43, 110 (1962). (72) D. B. McComas and A. Goldfien, ANAL.CHEM.,35, 263 (1963). (73) J. C. Sternberg, “Advances in Chromatography,” Vol. 2, J. C. Giddinas and R. A. Keller, Ed., Marcel Dekker, New York, N.Y., 1966, 205. (74) J. W. Ashley, Jr., G. P. Hildebrand, and C. N. Reilley, ANAL. CHEM..36. 1369 (1964). (75) J. H. Purnell and D: T. Sawyer, ibid., p 668. (76) Georges Guiochon, ibid., 35, 399 (1963). (77) M. N. Myers and J. C. Giddings, ibid., 37, 1453 (1965). (78) C. N. Reilley, G. P. Hildebrand, and J. W. Ashley, Jr., ibid., 34,1198(1962). (79) C. A. Cramers, Third European Wilkens Gas Chromatography Symposium, Wilkens Instrument and Research AG, Basel, Switzerland, 1965. (80) J. E. Oberholtzer and L. B. Rogers, ANAL.CHEM.,41, 1234 (1969). (81) J. Young, Design Eng., 10, 26 (1964). (82) T. Sarpkaya and J. M. Kirschner, Proc. Third Cranfield Fluidics Conference, May 8-10, 1968, Paper nF3, p F37-48. (83) R. E. Olson, Fluidics Quarterly, 1, 85 (1967). (84) “Fluidic Manufacturers, Hydraulics and Pneumatics, 14th Annual Fluid Power Designers Guide,” 1970, p 106. (85) Fluid Logic, Instrum. Contr. Syst., 39, 93 (1966). (86) “Fluid Control Reference Book,” A. Krigman, Ed., Rimbach Publications, Philadelphia, Pa., 1969. (87) H. Coanda, French Patent 788,140 (Paris, France) 217, (1934). (88) D. I. McRee and J. A. Edwards, ASME (Amer. SOC.Mech. Eng.) Publ. No. 70-WAIFICS-5, New York, N. Y., 1970.
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(89) E. J. Kompass, Contr. Eng., 11,73 (1964). (90) K. Boardman, Corning Fluidics, Corning Glass Works, Corning, N.Y., private communication, 1971. (91) S. P. Cram and R. L. Wade, Abstracts 1971 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, Feb. 28-March 5 , 1971, No. 223. (92) J. W. Tanney, Instrum. Contr. Syst., 06, 3 (1969). (93) J. Van der Heyden, ibid., p 7. (94) W. S. Griffin and W. C. Cooley, ibid., p 19. (95) D. F. Folland, Instrum. Coritr. Syst., 41,537 (1968). (96) C. J. Miller, Electron. World, 79 (6), 23 (1967). (97) C. W. Woodson, Western Electronic Show and Convention, Los Angeles, Calif., Aug. 1968. (98) R. L. Wade, Ph.D. Dissertation, University of Florida, Gainesville, Fla., 1971. (99) S. P. Cram and J. E. Leitner, Abstracts 162nd National Meet-
ing, American Chemical Society, Washington, D.C., Sept. 1971, No. CHED 021. (100) D. E. Davis, ASME (Amer. SOC.Mech. Eng.) Publ. No. 70WAIFICS-7, New York, N.Y., 1970. (101) M. K. Testerman and P. C. McLeod, U.S. Patent 3,273,377 (1966). RECEIVED for review August 13, 1971. Accepted November 9, 1971. This work was presented in part by the authors a t the 22nd Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 4, 1971. The financial support of the National Science Foundation under Grant No. GP-14754 and a n American Chemical Society Division of Analytical Chemistry Fellowship sponsored by the Procter and Gamble Co. is gratefully acknowledged.
Identification and Estimation of Neutral Organic Contaminants in Potable Water A. K. Burnham, G . V. Calder, J. S. Fritz, G. A. Junk, H. J. Svec, and R. Willis Institute f o r A t o m i c Research and Department o f Chemistry, Iowa State University, Ames, Iowa 50010
A method has been developed for extracting trace organic contaminants from potable water using macroreticular resins. These resins extract weak organic acids and bases and neutral organic compounds quantitatively from water solutions at parts per billion to parts per million levels. The method has been tested with water from a well contaminated by organic compounds which produce an objectionable odor and taste in the water. The identification and quantitative analysis of the individual contaminants extracted from the well water were ascertained using a gas chromatograph-mass spectrometer combination and other spectrometric methods.
MINUTEQUANTITIES of organic contaminants can impart a disagreeable taste and odor t o water and the contaminants may be potentially toxic; however, data on the organic content of water and techniques for obtaining such data are rather limited (1-3). An adequate analytical method for determining trace organic compounds in water must satisfy two criteria. First, the identity and the relative amounts of the contaminants should not be altered by the extraction procedure used t o concentrate them. Second, an efficient scheme for analyzing mixtures of organic compounds must be employed, because even nominally pure water may contain a large number of organic substances in low concentration. The limitations of methods such as charcoal absorption and solvent extraction in fulfilling the first of these criteria are recognized (2, 4, 5). These methods usually require processing large volumes of water and meticulously purifying the sorbants and solvents. Furthermore, in the case of charcoal absorption, the contaminants sometimes react on (1) “Cleaning Our Environment, the Chemical Basis for Action,” The American Chemical Society, Washington, D.C., 1969, pp
152-155. (2) R. A. Baker and B. A. Malo, J. Sunit. Eng. Div., Amer. SOC. Cicil Eng., 93, 41 (1967). (3) J. B. Andelman, M. A. Shapiro, and T. C. Ruppel, Purdue Univ. Eng. Bull. Ext. Ser., 118,220 (1965). (4) J. Amer. Wurer Works Ass. 54, 223 (1962). (5) W. L. Lamar and D. F. Goerlitz, ibid., 55, 797 (1963).
the charcoal or cannot be removed from it. In solvent extraction, the distribution coefficient for the contaminants between water and an extracting solvent may be unfavorable, especially when trace amounts are involved. This report describes a procedure which involves quantitative sorption of trace organic compounds on a macroreticular resin bed, followed by selective desorption using appropriate eluents. This procedure has been used for extracting and separating a variety of model compounds from pure water in order t o test the scope and limitations. A modified procedure has been used for the extraction, separation, identification, and quantitative estimation of water from a contaminated well. Tentative identifications of the compounds in the well water were made with a gas chromatograph-mass spectrometer combination. The identifications of the major contaminants were confirmed by comparing gas chromatograph retention times and ultraviolet, infrared, proton magnetic resonance, and mass spectra with authentic samples. The quantitative analyses were based on ultraviolet spectrophotometry or gas chromatography. EXPERIMENTAL
Apparatus and Equipment. A 1.5-cm diameter glass column, approximately 15 cm long, was fitted with a female hose coupling. This column could be attached t o a pump outlet or water faucet for sampling large volumes of water. For some experiments, a 1.O-cm diameter conventional glass column was used. The column was filled t o height of 7.0 cm with 100-1 50 mesh Rohm & Haas XAD-2 or XAD-7 resin, obtained by grinding and sieving larger mesh resin. A small plug of glass wool was placed both above and below the resin bed. Neutral compounds isolated from water were separated by gas chromatography using a 1/8-in. 0.d. X 84-in. column at 200 “C,packed with 1 5 z Carbowax 20 M on Chromosorb P. A Perkin-Elmer 270 combination gas chromatographmass spectrograph was used for gas chromatographic separations in conjunction with mass spectrographic identification
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