2516
Anal. Chem. 1986, 58, 2516-2523
should provide a useful supplement to the NBS Certificate of Analysis. Registry No. Ag, 7440-22-4;Al, 7429-90-5; As, 7440-38-2; Br2, 7726-95-6; Ca, 7440-70-2; Cd, 7440-43-9; Clp, 7782-50-5; Co, 7440-48-4; Cr, 7440-47-3; Cs, 7440-46-2; Cu, 7440-50-8; Fe, 7439-89-6; Hg, 7439-97-6; 12, 7553-56-2; K, 7440-09-7; Mg, 743995-4; Mn, 7439-96-5; Mo, 7439-98-1; Na, 1440-23-5;Rb, 7440-17-7; Sb, 7440-36-0;Se, 7782-49-2; Sn, 7440-31-5;Zn, 7440-66-6.
-
(6) U.S. National Bureau of Standards, Certificate of Analysis Standard Reference Material 1549, Non-Fat Milk Powder, July 29, 1985. (7) Byrne, A. R.; Dermelj, M.; Kosta, L.; Tusek-Znidaric, M. “Radiochemical Neutron Actlvation Analysis in Standardization of Trace Elements in Biological Reference Materials at the Nanogram Level”; presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, The Netherlands, August 1963. (8) US. Natlonal Bureau of Standards, Certificate of Analysis - Standard Reference Material 1577, Bovine Liver, June 14, 1977. (9) Gladney, E. S.;Burns, C. E.; Perrin, D. R.; Roelandts, I . ; Gills, T. E. NBS Spec. Publ. ( U . S . )1984, 260-288.
LITERATURE CITED Dybczynski. R.; Veglia, A,; Suschny, 0. “Report on the Intercomparison Run A-1 1 for the Determlnation of Inorganic Constituents of Milk Powder”; 1980; IAEA Report RL/68. Greenberg, R. R. Anal. Chem. 1979, 51, 2004-2006. De Soete, D.: Gijbels, R.; Hoste, J. Neutron Activation Ana/ysjs ; WileyIntersclence: London, 1972; pp 490-496. Gallorlnl, M.; Greenberg, R. R.; Gills, T. E. Anal. Chern. 1978, 50, 1479- 1481, Greenberg. R. R. Anal. Chern. 1980, 52,676-679.
March 13, 1986. Accepted May 21, Certain commercial equipment, instruments, or materials are identified in this paper in order to adequately specify the experimental procedures. Such identification does not irpply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. RECEIVED for review
Nonelectric Gas Chromatograph with Direct Optical-to-Pneumatic and Pneumatic-to-Optical Conversion for Transmission and Control Raymond Amino,* Charles Caffert, and E. L. Lewis The Foxboro Company, Corporate Research, Foxboro, Massachusetts 02035
A nonelectrlc pneumatically powered process stream chromatograph Is described that Is controlled vla an optical fiber link from a remote location and that also transmits a chromatogram as a frequency modulated optlcal signal to the remote locatton where It Is transduced and decoded to produce the commonly observed chromatographic record. The detector/transmHter, conslstkrg of an orlfice/capillary primary sensor In comblnatlon with a resonant hobw beam/optlcal transducer, has a minhnum detectable quantity of 25 ppm and a dynamlc range of 2.5 X lo4 and operates on an optical source power of 50 pW. The opticactopneunatk transducer, whkh Is at the chromatograph end of the control Ink, utlllzes the photoacoustlc effect produced by 0.70 mW of optical power and fleurlc technology to amplify pressure to sufflclent power levels to do useful work, such as sequence a multlplexer, Inject a sample, etc.
A nonelectric pneumatic based process stream gas chromatographic analyzer was described in the literature some time ago (1-3). The design was directed toward those process control applications that could be satisfied by highly reliable measurements of one or two components at concentrations exceeding 0.5 mol %. As such, it was a true composition transmitter capable of being located in hostile or hazardous process environments, generating continuous pneumatic trend signals proportional to the concentration of the selected process stream components. As a stand-alone “smart” transmitter, however, no provisions were made to enable one to, in effect, “tune” the device from a remote location. In terms of chromatography, the “tuning” might involve changing the peak selection parameters, changing gain settings, transmitting the chromatogram 0003-2700/88/0358-2516$01.50/0
for total analysis by a computer situated elsewhere, putting the unit on standby, injecting standard, etc. Assuming that the remote location is too distant for accurate transmission in the pneumatic domain, the aforementioned tasks require, a t the instrument in the field, (1)pneumaticsignal to transmission-signal conversion in order to transmit information from the device to the remote location and (2) control-signal to pneumatic-signal conversion in order to act upon control signals transmitted from the remote location to the device. Again, recalling the restraints imposed upon the design by the hazardous environment where the device is to be located, all domain conversions must preclude any that might lead to an explosion in the presence of gases such as hydrogen, acetylene, ethylene oxide, etc. (that is, presuming one wishes to avoid explosion-proof housings and the like). This paper reports the results of our research using optical transmission and direct pneumatic conversion schemes to satisfy the above described requirements and to access the large dynamic range and parts-per-million sensitivity of the orifice/ capillary detector system. Although the conversion schemes are demonstrated using the Pneumatic Composition Transmitter as a vehicle, we believe they have much more general application in the field of process and laboratory instrumentation.
EXPERIMENTAL SECTION Conversion of Pneumatic Detector Signal to a Frequency-Modulated Light Signal. The pneumatic chromatographic detector has been described previously ( 2 ) . Briefly, its output is the differential pressure signal that is developed across an 0.05 mm orifice/capilIary combination which is then amplified to span the 20.7-103.4 kPa (gauge pressure) range. In the optical version of this detector, the line carrying the signal to the on-board pneumatic logic and signal processor is teed and also connected to a resonant element pneumatic to light transducer 0 1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 12, OCTOBER 1986
2517
n IMPULSE NOZZLE
Flgure 1. Hollow beam construction details.
0 fROMCOL
~
0
FLOW COMPENSATING
-
ORIFICE
for transmission to a remote location. Hollow B e a m Resonant Element. Resonant element tech-
nology has been developed in these laboratoriesover several years. The resonant structure may take on many forms but in this case it is a hollow beam pneumatically driven to vibrate at its resonant frequency. An exploded view of the hollow beam is shown in Figure 1. It is made from Nispan C, which is an alloy whose modulus remains constant as temperature is changed. The skin is diffusion bonded (Cr/Ag at 10.3 X lo4 Wa, 676 O C for 4 h) to the 0.0635 mm thick skeleton and the beam is then mounted to a fiiture that positions it in space and also provides an inlet port for the input pressure that is being measured. There are a number of ways to excite the hollow beam to vibrate at its resonant frequency. In view of the design restraints, and also the availability of instrument air, it was decided to power it with air. Thus, the hollow beam was excited to its resonant frequency by a special type of nozzle, which will be described in the following section. The resonant frequency, f,, of the beam is given by the relationship
where k characterizes the stiffness of the beam and m,its mass. The stiffnessin turn is related to the internal pressure of the beam through its moment of inertia. The hollow beam described above was designed to have a resonant frequency between 600 and lo00 Hz a t gauge pressures of 0-138 kPa gauge pressure. The chromatographic pressure signal from the detector is fed into this beam. The resulting change in the “stiffness” of the hollow beam as its internal pressure changes causes a change in its resonant frequency which is sensed by a fiber-opticprobe. This frequency-modulatedsignal is transmitted to its destination where it is finally converted to a chromatographic signal in the electrical domain. The complete system is depicted schematically in Figure 2. Power Nozzle for the Resonant Element. The nozzle used to power the hollow beam has been designated as an ”impulse nozzle” by its inventor (4). I t is shown in Figure 3 attached to the fixture used to position it close to the beam and to supply it with air. Its operation relies on the relationships of the times necessary for the nozzle volume to fill and empty and the frequency range at which the beam vibrates. The nozzle exit hole (0.254mm) is larger than the nozzle entry hole (0.178 mm) so that when this hole is not blocked, the nozzle volume, 2.09 X cm3, can be emptied quickly. However, when the exit passageway is impeded so that the exit flow is throttled (as the beam approaches), pressure increases sharply within the nozzle volume and this force is imparted to the beam. Oscillation is sustained provided that the orifice/volume time constant is less than one-quarter the period of the natural fundamental frequency of the beam. Oscillations are initiated by the white noise energy of the jet; however, once started, the oscillation is sustained by the mech-
Flgure 2. Schematic outline of complete pneumatichptical detection, conversion, transmission, and decoding system: PS, LED source and photodetector; F-V, frequency to analog voltage conversion circuit. Dotted lines enclose the modification made to the existing orificekapiliary detector system.
NI O I O m m T l l l C I
Flgure 3. Impulse nozzle construction details.
anism discussed above. The main advantage to this type of nozzle is that it concentrates the total energy available in the air stream and releases it at the appropriate time. It approximates a clock escapement in that it applies a short-duration pneumatic pulse at the proper time to sustain oscillation. In order to meet these requirements using 4-5 psig input pressure to a 0.178 mm diameter orifice requires a sphere diameter of less than 1.58 mm. The nozzle was made by first machining a sphere of 1.58 mm diameter at the end of an aluminum mandrel. This sphere (still attached to the mandrel) was then nickel plated (0.10 mm thick). It was then cut from the mandrel and the aluminum dissolved .with sodium hydroxide (access of NaOH was through the hole (0.65 mm diameter) where the sphere had been attached). The hollow nickel sphere was cemented (at the 0.65 mm hole) to the 0.178 mm orifice held in the inlet fixture and the 0.254 mm exit hole was then drilled from the opposite side. F i b e r Optic Transmission. The fiber optic displacement sensor assembly, No. ABD-50, was purchased from AETNA Telecommunications Laboratories, Westborough, MA. It consists of a packaged light emitting diode (LED) emitter and photodetector coupled through a form of beam splitter to a 100 bm diameter optical fiber. The peak wavelength of the EMITTER is quoted at 820 nm and typically the optical power coupled into the fiber is 50 pW. The detector responsivity at 850 nm is quoted at 0.55 A/W with a response time of less than 2 ns. The end of the optical fiber is positioned close to the vibrating beam. As the beam moves toward and away from the fiber, more or less light is reflected back into the fiber creating a modulated light signal on top of the dc component of the light continuously reflected from the beam. This modulated light signal is transmitted to the remote location where it is diverted by the beam splitter to a photodetector. The ac component of the photodetector output is amplified and converted to an analog signal by a frequency to voltage converter. This analog signal represents the recovered pneumatic chromatographic signal converted to the electrical domain. The electrical circuit used for driving the LED and receiving the return signal is shown in Figure 4. It consists basically of three sections, a constant current driver for the LED source, a transistor-transistor logic (TTL)control circuit to allow on/off
2518
ANALYTICAL CHEMISTRY, VOL. 58, NO. 12, OCTOBER 1986
Figure 4. Transmission link LED driver and receiver circuit. -15 V
t15 V
INPUT
* 10 K
---I+ .1 uF
Figure 5. Schematic of frequency to voltage converter.
computer control, and a receiver amplifier section that converts the photodiode current to a voltage for presentation to the frequency to voltage converter, which is shown in Figure 5 . Since the information contained in the light signal is contained in only a small fraction of the total light component received at the photodetector, it is necessary to design the frequency/voltage converter with a very stable auto zero circuit for subtracting the dc component from the signal. The heart of this auto zero circuit is the clock, serial counters, and digital to analog (D/A)converter.
Switching to the “zero” mode enables the clock (CD4047).The three serial up/down converters (CD4029)are connected as a rippled counter in a binary counter mode, depending on the sign of the difference voltage between the outputs of the D/Aconverter and the frequency to voltage (F/V) converter (which appears at the output of amplifier 1). Amplifier 4 generates either 0 or 15 V on the up-down (U/D) line to the counters. On a positive clock transition, a high on this line will command an up count and a low on this line, a down count. The results are transferred to the
ANALYTICAL CHEMISTRY, VOL. 58, NO. 12, OCTOBER 1986
digital input of the D/A converter. The final voltage will oscillate between one LSB as the autocircuit hunts for balance. In the ‘‘run- switch position this memorized base line voltage is applied constantly to amplifier 1and subtracted from the F/V converter output. Manual dc offset as well as adjustable gain are provided through amplifier 2 and the final output circuit acts as a low pass filter. Conversion of Light to Pneumatic Power. The direct conversion of light to a pneumatic signal (without involving the electrical domain) was first reported by Bell (5),Tyndall (6),and Rontgen (7) and forms the basis of present day photoacoustic spectroscopy. The basic theory behind the process is quite simple in concept. It involves the absorption of light by a sample with subsequent excitation of a fraction of the ground-state molecules to higher energy levels, the generation of heat by the nonradiative component of the relaxation process in the localized region of the exciting light beam, and finally the generation of a pressure wave that is propagated away from the heat source. If the exciting light is modulated, the resulting periodic variation in temperature causes a periodic variation in the pressure wave and this acoustic disturbance is detected by a suitable sensor such as a sensitive microphone. The problem presented in the work reported herein is somewhat more complex. We require not only a conversion but a conversion that can supply enough power so as to complete the assigned control task. I t is necessary to transform a 0.75-mW or less transmitted optical signal to a 20.7-103.4 kPa (gauge) power signal. One method to accomplish the above conversion might be to use a photodiode as a receiver. The resulting electrical signal would then be converted to a usable current/voltage signal to drive a solenoid or actuating device. The latter actuating device may, in fact, be an electrical/pneumatic converter since most valve positioners are pneumatically operated. In the absence of considerations that might argue to the contrary, however, a direct conversion of the light energy to pneumatic power appeared to us to be the most efficient way of achieving the objective. The method we adopted was to amplify the original acoustic disturbance fluidically. This amplified pressure signal was then used to activate a pneumatic power amplifier which supplied the final control signal. That the small pressure variations produced by a modulated light source can be sufficiently amplified by a block of self-staged laminar proportional amplifiers (LPA’s) has been reported by Gurney (8) in a Harry Diamond Laboratory (HDL) internal document. This author used a 20-mW, 632-nm, HeNe laser as the light source, three stages of amplification, a rectifier, and finaly a diaphragm amplifier as the power stage. The only similarity between the work reported here and in thii previous report is that we have used the same basic fleuric amplifier design as utilized by this author. Besides operating on 1/20 of the power, however, our final system is different and is based on the use of a phenomena not heretofore reported. Laminar Proportional Amplifiers. The no-moving-part or “fleuric” amplifier used in this work is of a class of fleuric amplifiers called beam deflection proportional amplifiers, or simply laminar proportional amplifiers (LPA’s). They should not be confused with the more commonly known Coanda wall attachment fluidic devices that have been investigated as sample injection valves for chromatography ($16) although one of these workers (15) has demonstrated that LPA’s can also be used as an injection valve. The wall attachment fluidic amplifiers constitute a class of bistable full output, ON/OFF digital fluidic elements while the former device, the LPA, produces an output proportional to the magnitude of the input signal. Thus, a number of LPA’s can be staged to accept a very small input and produce a much larger output. It is this ability of the LPA to amplify extremely small pneumatic signals that were utilized in this work. A complete description of the design theory of fluidic components may be found elsewhere (17)and only a brief explanation of LPA operation is offered here. A basic beam deflection amplifier is illustrated in Figure 6. Normally, it is of two-dimensional construction. The planform shown in Figure 6 is enclosed from above and below with cover plates. The power jet nozzle is thus a rectangular slit. The height of this slit divided by its width, b,, is called the aspect ratio, u. Relatively high-energy fluid is
2519
4k 0 . 5 0 b .
cx
OUTPUT
iKv
CONTROL PORT
CONTROL PORT
SUPPLY
HDL MODEL 3.1.1.8
Flgure 6. Silhouette of a laminar proportional amplifier.
b
d
c
f
Flgure 7. Silhouettes of varlous functional elements used in the construction of Reuric devices: (a)resistor, (b) LPA, (c) bkxk one hole, (d) exhaust, (e) exhaust, (f) vent. supplied to this nozzle. The emerging power jet can be deflected by low-energy fluid directed into the interaction region from the so-called control nozzles positioned on each side of the jet. A difference in momentum forces between the two control jets will cause the power jet to flow more into one output port than the other and lead to a difference in pressure between the two output porta. The output pressure difference divided by the control port pressure difference is a measure of the amplifier gain. Pressure gains for single elements commonly range from 5 to 10 when unloaded but commonly drop to 3-4 when loaded. Fluidic Circuit Construction. The fleuric circuits used in this research were constructed from planar 3.3 cm X 3.3 cm square laminates photochemically milled from 0.010 mm, 455 stainless steel with 9.254, 0.50 and 0.381 mm orifice sizes in the LPA laminate. (Similar laminates are now commercially available from TriTec, Inc., Columbia, MD.) Each laminate had a particular functional purpose: LPA, vent, resistor, capacitor, etc. Examples of some representative patterns are shown in Figure 7. The individual laminates were arranged in a vertical stack, between two end plates (5 cm x 5 cm X 1cm) containing input and output fittings and the two restrictors to which the right and left vents were tied. Alignment was made with two steel pins, which were also mounted to the end plates. The stack was held together by four bolts extending through the four corners of the end plates but not through the LPA laminates as illustrated in Figure 8. An exploded view of a typical single-stage LPA is shown in Figure 9 and the critical design parameters for the complete eight-stage unit is shown in Figure 10. The standard amplifier hole format was that adopted by HDL and is designated as a C-format. A complete description of this fabricating procedure is given by Garrett Pneumatic Systems Division, Phoenix, AZ, in a report prepared for HDL (18).
2520
ANALYTICAL CHEMISTRY, VOL. 58. NO. 12. OCTOBER 1986
I
I
II
Iil
TO DIAPHRAGM AMPLIFIER Ps
-
6 1 1 Pa 0
b,
(I
b,
(I
bs
j I
I
~ L
o
=
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08 0.254 mm
-
= 0.8 0.254 mm
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0.8 0.254 mm
.
b, = 0254 mm
z
l
A
I
-
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_I
Flgure I O . Schematic dhgram of the eight-stage LPA amplifier showing crklcal design parameters.
Flgure 9. Exploded vlew of a typical singbstage LPA OR A SlMPLE ONOFF SWITC"
Photoacoustic Stage. The essential elements of the primary photo to acoustic conversion system are shown in Figure 11. The light source was a pigtail-LED operated at 80 mA. The optical power measured at the exit end of a 1-m fiber was 1.04 mW (880 nm). The complete optical assembly consisting of light emitting diode, step index fiber, and 1.8 mm diameter collimating lens was purchased from Nippon Sheet Glasa Co., L t , NSG America, Inc., Clark, NJ, Catalog No. OPCV-ZOH-CWII,200/250 fim diameter, NA = 0.50. The LED was modulated "ON", "OFF" a t 625 Hz with the circuit shown in Figure 12. A Plexiglas cover plate transparent to this light was used to provide a window for the light beam into the control port cavity of the LPA. The back cover plate was coated with earbon black and acted as the light absorbing target from which the acoustic disturbance was generated. An
Flgure 11. Schematlc of complete opticallpneumatk control link.
exploded view of this stage is shown in Figure 13. LPA Amplifier Stages and Final Diaphragm Amplifier Driver. The acoustic disturbance generated by the modulated light entering the control cavity of the photoacoustic amplifier moves the power jet of the LPA in phase and thus generates a varying pressure signal a t the output ports of the device. Since the prime mover (light) is "on" or 'of?, the resulting output signal is biased at some dc level. The output of this first stage is coupled (19)to seven other stages of amplification as shown in Figure 10. The varying outputs of each stage are biased at higher de levels as the biased output of each stage acts as the input to the next stage. Thus, the system also acts as a dc amplifier. What is not
ANALYTICAL CHEMISTRY. VOL. 58. NO. 12. OCTOBER 1986 -15 Y
2521
TP
FREOAOJUST
- MODULATED LED DRIVER
Figure 12. Schematlc 01 the control link LED drlverlmodulator clrcun.
Fbwe 13. Exploded view of the photoacoustic stage.
ohvious. though, is the large increaee in the dc amplification level at certain fixed frequencies which was discovered in these lahoratories. This phenomena has not yet heen fully characterized and will therefore not he discussed further a t this time. Experiments are in progress to determine its origin and these results will he reported at a future date. It is the optimized dc component of the output signal that was used in this research. A t an optimum modulation frequency of 625 Hz,gating the modulated LED sources fully Ion" or "off' drives the output stage from a slightly negative pressure to 2.49 kPa gauge pressure. This output stage is coupled to a diaphragm amplifier (Air Logic Division, Racine, WI). The operation of this amplifier is depicted in Figure 14 along with an example of its typical input/output characteristics. The diaphragm amplifier supplies the required 138 kPa (gauge) power pressure signal when activated. Note that this is a very sensitive high-gain device (switchingon a pressure difference of less than 0.249 kPa gauge pressure) hut that, in the current setup, it is not being operated close to its switching pressure. The LPA output stage maintains the diaphragm amplifier input a t a slight negative pressure and drives it to 2.49 kPa gauge pressure in the 'on" condition. This design leads to stable operation, which is quite insensitive to temperature variation, acoustic shoeks, and so on. The output of the diaphragm amplifier, in the simplest configuration of the instrument, is fed directly to the pneumatic actuator of a spring returned inject/hackflush valve. The inject/hackflush command is, in this case, controlled from the remote location.
Multiplexer. It is ohvious that for those situations where a greater number of control tasks must he accomplished with the single control link, the output of the diaphragm amplifier must be multiplexed. A simple mechanical multiplexer, which has been tested for this purpose, is shown in Figure 15. The pneumatic powered impulse motor (Foxhoro Part M0146NB. GOl09GL) is stepped hy pulses from the diaphragm amplifier and connects the 138 kPa gauge pressure signal to the selected control site via a wafer type selector switch (W0601/1P-l2T, Scanivalve Corp., San Diego, CAI. The position signal for the selector switch is generated by feeding hack the 138 kPa signal through a series of resistors80 that each position generates a unique pressure. Thii signal is then fed hack to the hollow beam so that it appears as a dc offset in the transmitted signal which is unique to the position of the selector switch. The position signal is only present when a control signal is active on the control link and thus does not interfere with the chromatographic signal. The specific actions that are indicated refer to particular options available in the commercial version of the pneumatic chromatograph in which the multiplexer was tested. Control and Peak Processor Intelligence. The remote location control of the analysis cycle or multiplexer was accomplished by computer control of the modulated LED on/off cycle with an Apple I1 Plus microeomputer equipped with a data acquisition and control interface (ISAAC 91A, Cyborg Corp., Newton, MA). The optically transmitted chromatogram was converted to an analog voltage by frequency to voltage converter already described (see Figure 5 ) and was further processed by the computer system and/or plotted directly on an analog reorder.
RESULTS Control System. It was found that a minimum of 70 mW of power was required at the exit end of the fiber for the current version of the LPA switch to operate reliably. At the commonly observed 3 dB/km power loss in multimode fiber transmission, the present fiber output will be 73.5 mW a t 1 km. Thus, for transmission distances of greater than 1 km, a higher powered LED must be substituted for the one described herein. Detector System. T h e typical pressure vs. frequency response for the nozzle powered hollow beam system over the normally useful range of the pneumatic amplifier (20.7-103.4 kPa gauge pressure) was found to he constant at &0.7% of the maximum value of the range setting (i.e., &0.72 kPa a t
2522
ANALYTICAL CHEMISTRY, VOL. 58, NO. 12, OCTOBER 1986 TO SAMPLE VALVE DRIVER
FROM LPA
7
AIR SUPPLY 20 osia
INPUT ON
t
100-
OUTPUT ON
80-
W
LT 2
60-
v)
W v)
a Q
OUTPUT OFF SUPPLY VACUUM
INPUT OFF
2
Q
40-
Q
2
m U
0 + 20-
z
W
B W
n
0-
-20-
-40TYPICAL INPUT-OUTPUT CHARACTERISTICS
Flgure 14. Schematic illustration of the diaphragm amplifier and typical transfer curves for two models. CHROMO SIGNAL
SELECTOR POSITION SIGNAL
HOLLOW BEAM
1 1
, R4
R5 0
-.-,e.
Re 4 CYCLE
-
PROGRAM
-
UPDATE
I
I
n
II
Figure 15. Schematic illustration of a simple mechanical multiplexer.
the maximum range of 103.4 kPa gauge pressure). The reproducibility, on the other hand, was found to be f0.021 kPa, as was the linearity of the beam when it was mechanically plucked and the frequency of vibration determined from the ring down spectrum. The discrepancy between these results was found in the actual shape of the pressure vs. frequency curve when the beam is powered by the nozzle. The curve can be slightly curved up or down depending on whether the equilibrium position of the beam approaches or retreats from the nozzle as pressure is increased. It can be computer fitted if greater accuracy is desired. The correlation coefficient for a second order polynomial fitted to the raw data is 0.9999. Chromatographic System. A typical chromatogram record obtained a t the remote location is shown in Figure 16. The 0.1 % reproducibility of chromatographic peaks, which was obtained, was consistent with what was expected from the results of static pressure experiments. The noise level of the system on a pressure basis was found to be k0.04 kPa. The relationship of this value and the
0
1
2
TIME IMINI
Figure 16. Typical chromatograms obtained with the optkal/pneumatlc detector-transmitter: I,transmitted and decodeti chromatogram, 1.O mL sample = 1.5% methane (A), 3% ethane (B), 2 % propane (C), 2% propylene (D), 2% isobutane (E); 11, chromatogram generated at the output of the orificekapillary detector system; 111, noise level at remote station end of transmission line. I t is equivalent to 40 ppm propane.
minimum aetectame quantity (ivwq)or sample component depends on the gain setting of the pneumatic amplifier. A pneumatic amplifier gain setting such that 100% methane sample eluting from a column operated at 34.5 mL/min of helium gives a full scale 103.4 kPa signal results in a MDQ of 80 ppm of propane in the detector. This MDQ is reduced
Anal. Chem. 1986, 58,2523-2527
to 25 ppm a t the full gain of the pneumatic amplifier albeit a t the expense of the original dynamic range of 2.5 X lo4. The base line sensitivity of the pneumatic amplifier, when its gain is set so that 100% methane sample yields a full scale deflection, is 0.117 kPa/OC and 0.110 kPa/(mL/min) of flow. The insensitivity of the base line to these two parameters ensures a live zero which can always be software compensated a t the remote, peak processing end of the system.
CONCLUSIONS A sensitive optical version of a nonelectric, multicomponent, pneumatic-powered chromatograph suitable for process control applications has been described. The demonstrated insensitivity of the field-mounted package to temperature, pressure, flow, and electromagnetic interference while the system maintains its parts-per-million detectability argues for a consideration of this technology for the design of instruments to be located in hostile environments.
ACKNOWLEDGMENT The authors gratefully acknowledge the contributions of Bent Norlund and Bill Sherwood for their electronic designs and Bill Cloyd for his machining skills.
LITERATURE CITED (1) Annino, R.; Curren, J., Jr.; Kallnowskl, R.; Karas, E.;Linqulst, R.; Prescott. R., J. Chromafcgr. 1976. 126, 301. (2) Annino, R.; Voyksner, R. J. J. Chromatcgr. 1977, 142, 131.
2523
(3) Annino, R. CHEMTECH 1961. 482. (4) Bodge. P., unpubllshed work. (5) Bell, A. 0. Phibs. Mag. 1881. 7 1 , 510. (6) Tyndail, J. Roc. R . Soc. London 1881, 31, 307. (7) Rontgen, W. C. Phibs. Mag. 1881 1 7 , 308. (8) Gurney, John D. Photo-Nuidlc Interfaces; preliminary report; Harry Diamond Laboratories: Adelphi, MD, 1982. (9) Wade, R. L.; Cram, S. P. Anal. Chem. 1972, 44, 131. (10) Cram. S. P.; Chesler, S. N. J . Chromatogr. 1974. 99, 267. (11) Gaspar. G.; Arpino, P.; Guichon, G. J. Chromatcgr. Sci. 1977, 15, 256. (12) Gaspar, G.; Annino, R.; Vidai-Madjar, C.; Guiochon, G. Anal. Chem. 1978, 5 0 , 1512. (13) Annlno. R.; Gonnord, M.-F.; Guiochon. G. Anal. Chem. 1979, 5 1 , 379. (14) Annino, R.; Leone, J. J. Chromatogr. Sci. 1982, 20, 19. (15) Annino, R. "The Application of Fleurlc Devlces in Gas Chromatographic Instrumentation." I n "Advances in Chromatography;" Giddings, Grushka, Cams. Brown, Eds.; Marcel Dekker: New York. 1987; Vol. 28. (16) Schutjes, C. P. M.; Cramers, C. A.; Vidai-Madjar, C.; Guiochon G. J. Chromatcgr. 1983, 279, 269. (17) Kirshner. J. M.; Katz, S. Design Theory of Nuidic Componenfs; Academic Press: New York, 1975. (18) Eycon, M. F., Jr.; Schaffer, D. J. "Design Guide for Laminar Flow Fluidic Amplifiers and Sensors"; Report HDL-CR-82-288-1, April 27, 1982. (19) Manion, F. M.; Neurics: 33 ., Design and Staging of Laminar Proportional Amplifiers; Harry Diamond Laboratories: Washington, DC, 1972; AD-751, 181.
RECEIVED for review March 4,1986. Accepted June 9,1986. Presented in part a t The Pittsburgh Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, Atlantic City, NJ, March 10-14, 1986.
Multipoint Kinetic Method for the Immunochemical Quantitation of Isoenzymes Developed and Evaluated with Creatine Kinase Inhibition as a Model System William E. Weiser and Harry L. Pardue*
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
Thls paper descrlbes the development and evaluatlon of a new kinetlc approach for immunoassay procedures. I n particular, lt descrlbes a new approach for the slmultaneous quantltatlon of Isoenzymes that Interact dlfferently wlth antlbodies. The proposed approach Is evaluated by uslng the muscle (M) and braln (B) wbunlts of the Isoenzymes of creatine klnase (CK, EC 2.7.3.2) as a model system. The approach Is based on the selectlve lnhlbltlon of one of the subunlts (e.g., M) by an antibody and the use of nonllnear least-squares data processing to compute the M and B subuntt actMtles from the thne-dependent response curve. For several concentratlons of the two Isoenzymes In the range of diagnostk slgnlficance, leastaquares flts of computed ( y ) vs. expected ( x ) values yielded equatlons of y = 0 . 9 8 ~ (9.3 X and y = 1 . 0 4 ~ (3.6 X loJ) for the MM and BB Isoenzymes, respectively.
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Because antibodies offer high degrees of selectivity for a variety of species, they are useful as analytical reagents. The most common immunoassay procedures involve measurements made after antigen/antibody reactions have approached e q u i l i b r i u ~ .Although these equilibrium-based procedures have proven effective, they do not represent the only option 0003-2700/88/0358-2523$01.50/0
and it is probable that kinetic. -ssed procedures could offer complementary capabilities as has been the case with more traditional types of reactions. A few studies that involve measurements during the kinetic phases of antigen/antibody reactions have been reported (e.g., ref 1-3), but these studies only begin to exploit the capabilities of kinetic-based immunoassays. To date no one has reported the use of multipoint kinetic data to resolve two or more components simultaneously. The primary purpose of this study was to develop and evaluate a new kinetic approach for the simultaneous quantitation of isoenzymes that interact differently with antibodies. Quantitation of the muscle (M) and brain (B) subunits of the creatine kinase (CK) isoenzymes is used as a model to evaluate the new approach. The basic premises on which the study was based were that the antibody used would be completely selective for one subunit (M or B),the kinetic behavior of the inhibition reaction could be controlled to follow some welldefined kinetic order, and the percent inhibition of the affected subunit would be reproducible and independent of concentration. Assuming conditions could be established to satisfy these criteria, then the plan was to make multipoint measurements during the inhibition process and to use curvefitting methods to compute the initial (uninhibited) activity of each subunit. In addition to serving as a model for the 0 1986 American Chemical Society
