US3858435A

US3858435A - Gas chromatograph

Info

Publication number: US3858435A
Application number: US338287A
Authority: US
Inventors: Mario R Stevens
Original assignee: California Institute of Technology CalTech
Current assignee: California Institute of Technology CalTech
Priority date: 1973-03-05
Filing date: 1973-03-05
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07

Abstract

A compact, efficient, portable gas chromatograph system is disclosed in which the gas chromatographic column is disposed in a closed loop with an electrolytic hydrogen generator-separator. The output from the column containing the bands of analyzable materials dispersed in hydrogen carrier gas is passed through the tubular anode of the generator-separator. The hydrogen passes through the wall of the anode, across the electrolyte through the wall of the cathode and is collected and returned by way of the sample inlet to the inlet to the column. The analyzable material remaining stalled within the anode tube is swept into the detector by an auxiliary electrolytic hydrogen generator. A pressure transducer downstream from the anode develops an increased voltage signal in response to pressure drop which is applied to the controller for the auxiliary hydrogen generator to maintain a constant flow of hydrogen carrier gas within the closed loop circuit while also maintaining a flow of hydrogen sweep gas to the detector.

Description

VOLTAGE Jan. 7, 1975 GAS CHROMATOGRAIPH [57] ABSTRACT [75] Inventor: Mario R. Stevens, Glendora, Calif. A compact, ffi i t portable gas chromatograph [73] Assignee: California Institute of Technology, tem dlsfllosed in Whlch the gas Chromatographic v Pasadena C lif umn is disposed in a closed loop with an electrolytic hydrogen generatonseparator. The output from the [22] Filed: Mar. 5, 197.3 column containing the bands of analyzable materials 211 App] 33 237 dispersed in hydrogen carrier gas is passed through the tubular anode of the generator-separator. The hydrogen passes through the wall of the anode, across the [52] 23/232 C, 23/254 electrolyte through the wall of the cathode and is col 55/158 lected and returned by way of the sample inlet to the [51] lllit. Cl. Gllln 31/08 inlet to the Column The analyzable material rel-aim [58] Flew of Search 73/231 27 R; 55/16 ing stalled within the anode tube :is swept into the de- 55/197; 23/232 254 R1 254 255 tector by an auxiliary electrolytic hydrogen generator. 255 E? 48/61 A pressure transducer downstream from the anode develops an increased voltage signal in response to pres- [56] References Cited sure drop which is applied to the controller for the UNITED STATES PA EN S auxiliary hydrogen generator to maintain a constant 3,400,650 9/1968 Burg 23/281 x flow of y g Carrier g within the closed 1001) 3,468,781 9/1969 Lucero 1 55/16 X circuit while also maintaining a flow of hydrogen 3,589,171 6/1971 Haley v 73/231 sweep gas to the detector. 3,690,835 9/1972 Lovelock 1 1 1 73/231 X r 3,701,632 10/1972 Lovelock 4. 73/27 R X Primary ExaminerRichard C. Queisser 15 Claims 6 Drawing figures Assistant Examiner-Stephen A. Kreitman Attorney, Agent, or FirmMarvin E. Jacobs CONTROLLER Patented Jan. 7, 1975 3 Sheets-Sheet 1 VOLTAGE CONTROLLER POWER SUPPLY T0 AUXILIARY GEN FIG. 4

atnted Jan. 7, 1975 3 Sheets-Sheet 2 FIG.

FIG.

atented Jan. 7, 1975 3,858,435

5 Sheets-Sheet 5 N :K V

HEAT INJECT ON SAMPLE 4 /CO\ TIME, min

FIG. 5

AIR

ORIGIN OF THE INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 83-568 (72 Stat. 435; 42 USC 2457).

, BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas chromatographic system, methods of analysis and more particu larly to a compact, efficient and reliable hydrogen carrier gas gas-chromatographic system.

2. History of the Prior Art Analysis of complex samples of matter is greatly facilitated by gasifying the sample and then passing it in gasified form through a device suchas a gas chromato- 0 graph which separates the components of the sample into sequential bands of analyzable components. In a gas chromatograph or other separation apparatus, gas or vapor sample to be analyzed is transported through the various functional parts of the apparatus by a stream of inert carrier gas. While this procedure facilitates automation of analysis, it does however introduce other problems.

Thus, sample constituents present in minute quantities are so greatly diluted by the much larger quantity of carrier gas necessary for operation of the chromato graph column that they may be difficult or impossible to detect. Furthermore, the pressure and flow rate of the effluent emerging from the chromatograph may exceed the capability of a detector such as a mass spectrometer or an ionization cross-section detector. Moreover, many detectors, such as gas density balance, thermal conductivity or ionization cross-section, are concentration dependent and variation in flow rate or excessive dilution of the sample in the carrier gas affects both precision and accuracy of analysis.

Various approaches to interfacing a gas chromatograph to a detector have been suggested, such as scaling down the dimensions of the chromatograph to suit the needs of the detector, interfacing the chromatograph and the detector with a capillary column or by the use of various plastic membranes or a fritted glass surface to separate carrier gas before introduction of the effluent into the detector. None of these approaches have been entirely satisfactory.

A much improved technique utilizing a heated palladium film as a selective hydrogen transfer device is disclosed in U.S. Pat. Nos. 3,638,396, 3,638,397 and 3,589,] 7 l. Optionally a steady flow of a second carrier gas impermeable to the palladium film such as helium can be introduced into the transfer device to sweep the sample into the detector. However, these systems require the use of auxiliary gas cylinders and associated valving to supply and meter the flow of carrier gas.

A substantial simplification was provided by the electrolytic hydrogen generator-separator disclosed in US. Pat. Nos. 3,690,835 and 3,701,632 in which the hydrogen carrier gas generation function was combined with the gas separation function in a single device. However, it was found difficult to operate the generatorseparator with a residual uniform flow to sweep the sample into the detector. Furthermore, loss of hydrogen from the system upset stoichiometry of the electrolytic cell and after sustained periods of operation, metal loss occurred leading to perforation of the electrodes of the generator-separator cell.

SUMMARY OF THE INVENTION The gas chromatographic system of the invention is completely self-contained and portable and is selfsustaining except for the requirement of small additions of water (5l5 cc/day). The system is highly versatile and exhibits high reliability and accuracy. The present lower limit of detection is of the order of 1-10 ppm of materials such as ethane. The system does not require an external heavy source of pressurized carrier gas.

Unlike previously reported gas chromatographs, the present system is capable of universal analytical appli cation and at the same time is completely independent of any external source of carrier gas supply or power. The portable gas chromatograph of the invention will find use in the on-site surveillance and monitoring of atmospheric pollution, confined atmospheres in mine shafts, plants or buildings and stationary sources, such as industrial smoke and stack emissions.

The chromatographic system of the invention generally comprises a continuous hydrogen carrier gas circuit including a gas chromatographic column and an electrolytic hydrogen gas generator-separator device. The output from an auxiliary hydrogen generator is introduced into the circuit upstream. from the generatorseparator device and a sample inlet is disposed upstream from the column. A detector disposed down stream from the device senses the components of the dispersed sample and vents the dispersed sample. A pressure sensing means senses the pressure downstream from the generator-separator device and develops a signal which is utilized to control the output of the auxiliary hydrogen generator.

These and many other features and attendant advantages of the invention will become readily apparent and the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagrammatic view of the gas chromatographic analysis system of the invention;

FIG. 2 is a cross-sectional view of the generatorseparator;

FIG. 3 is a cross-sectional view of the auxiliary hydrogen generator;

FIG. 4 is a schematic of the controller for the auxiliary hydrogen generator;

FIG. 5 is a chromatogram of a simulated Martian atmosphere; and

FIG. 6 is a chromatogram of an air mixture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The system as shown in FIG. 1 generally comprises a gas chromatographic .column 12, an electrolytic generator-separator device 14, an auxiliary electrolytic hydrogen generator 16 and a detector 18, such as an ionization cross-section detector. The column 12 and the generator-separator 14 form part of a continuous, closed circuit 10. The circuit 10 also includes a pressure gauge 20 and an inlet assembly 241. The inlet assembly, disposed just upstream of the inlet 26 to the column 12, includes an injection port 28 and a collection port 30 secured to

different segments

32, 34 of the assembly. The

ports

28, 30 can be isolated from each other and from the circuit by means of three-

way walves

36, 38.

The generator-separator 14 includes an anode 40 having an open inlet end 42 and an open outlet end 44. The cathode 46 has a closed end 48 disposed within the body 50 of the electrolyte and an open outlet end 52. The electrolyte 50 is contained in a housing 45 which may be externally heated by a coil 47 powered by a variable power source, not shown. The output from the column outlet 54 combines with the output from the outlet 56 from the auxiliary generator 16 atjunction 58 and is swept into the inlet 42 to the anode. The outlet 56 is isolated from the inlet by means of

check valves

57, 59.

A major portion of the hydrogen carrier gas transfers through the wall of the anode 40 across the electrolyte 50 and through the wall of the cathode 46, collects therein, and returns through the circuit 10, sample assembly 24 to the inlet 26 to the column 12. The sample dispersed in the remaining hydrogen leaves the generator-separator device 14 through the anode outlet 44 and passes through the flow restrictor 60' into the detector 18.

A pressure transducer 62 placed across restrictor 60 senses the change of pressure in the anode 40 and develops a control signal which is applied to the voltage controller 64 for the auxiliary hydrogen generator 16. The voltage controller 64 controls the auxiliary generator 16 to provide a steady flow of sweep gas through the anode 40 and compensate for any variation in the hydrogen transfer through the anode 40, i.e., the variation in generator-separator performance due to the presence of eluted gas components in the anode.

The auxiliary hydrogen generator is employed in the chromatographic circuit for the following reasons. The hydrogen generator-separator is the carrier gas source and absorber (sink) for the chromatographic circuit, as indicated by the arrows. As the carrier gas (carrying a sample of gas from the column) flows from the column into the hydrogen generator-separator, greater than 99.96 percent of the hydrogen is removed from the circuit at the anode.

Residual hydrogen pressures of approximately 10 to torr have been experimentally noted at the ancan be transferred through the anode wall under the balanced operating conditions of the hydrogen generator-separator. It does not, therefore, permeate through the anode wall, but instead mixes with non-hydrogen components as they proceed to the detector.

When the main carrier stream, containing nonhydrogen components, enters the anode, the amount of hydrogen transferred at the anode wall decreases. This decrease will cause variations to occur in the hydrogen carrier gas flow rate if it is not compensated for. The anode will attempt to maintain the constant transfer rate by utilizing hydrogen normally associated with the auxiliary carrier gas stream. In so doing, the pressure in the line, downstream of the anode, will fall. This pressure decrease is sensed by the pressure transducer whose increased output signal will immediately cause more voltage to be applied to the auxiliary hydrogen generator. The additional hydrogen generated enters the system and will in effect maintain the constant flow of hydrogen within the closed-loop circuit, while also maintaining a flow of hydrogen to the detector.

The need for a separate detector may be obviated should advantage be taken of the variation in the anode behavior when a non-hydrogen component is in the gas stream within it. This behavior is manifested in terms of a current variation as disclosed in Pat. No. 3,701,632. Amplification of this signal will let the anode serve as an excellent chromatographic detector. The intensity of the signal will be proportional to the concentration of the non-hydrogen components as well as its chemical affinity for palladium. Calibration must be done carefully.

While ambient air will be separated from samples by the chromatographic column, all the oxygen is quantitatively converted to water in the anode, requiring good temperature control at the detector to prevent condensation of this water. Also, certain unsaturates eluting from the column will undergo hydrogenation at the anode leading to a multiplicity of signals at the detector. Thus, in the calibration for unsaturated compounds this problem should be realized.

The portable, self-contained gas .chromatograph has been successfully operated continuously for a period of ode. Under normal chromatographic operations,,only

the sample gases would remain in the anode. These gases would stagnate there, except for diffusion and residual directional momentum, and would not be able to reach the detector. This is avoided by using a small quantity of an auxiliary carrier gas, in this case also hydrogen, to flush these non-hydrogen components out of the anode to the detector.

When the GC is being prepared for use, the carrier gas flow is first adjusted for no-sample conditions. Electric energy is applied to the hydrogen generatorseparator so that there is a gas flow circulating within the closed-loop circuit. The output of the pressure transducer which senses the pressure drop through the flow restrictor, is adjusted to provide sufficient voltage to the auxiliary hydrogen generator to produce from 0.1 cc to 1 cc hydrogen flow per minute, as required by a particular analysis. This additional hydrogen is led into the closed-loop circuit through a check valve at that junction. This hydrogen is in excess of that which 4 months. Maintenance was minimaLthe addition of small amounts of water (5-15 cc/day) to the auxiliary hydrogen generator daily accounting for virtually all of the maintenance. The system is completely portable, using a power pack consisting of two l2-volt batteries and one 6-volt battery. The device has a volume of less than 1 cubic foot and weighs less than 40 pounds, including a 20-pound power pack. It is independent of all external sources of supply.

FIG. 2 illustrates a suitable form of the electrolytic generator-separator. The carrier gas is hydrogen of high purity and the electrodes are formed of a material impermeable to all gases below a certain temperature and selectively permeable to hydrogen when. heated to a temperature above about C. Palladium and its alloys are remarkably permeable to hydrogen as long as heated to a temperature above about 100C to C.

Pure palladium when subject to temperature cycling in the presence of hydrogen, suffers mechanical distortions. However, an alloy of palladium containing 10 to 30 percent silver, preferably about 25 percent silver, is as permeable to hydrogen and is mechanically stable. Other palladium alloys, for example, palladiumrhodium alloys may confer more resistance to corro sion to the films and extend the useful life of the generator-separator. The palladium tube maybe provided in various configurations and lengths of tubing may be connected in parallel to provide increased surface area with less flow resistance. Membranes or tubes can also be formed from a base structural material such as a porous ceramic coated with a thin, continuous film of palladium or a suitable hydrogen permeable palladium alloy. The hydrogen flux for a given hydrogen pressure difference through a thin film of palladium or alloy is dependent on tube geometry, wall thickness and wall temperature.

To maintain the palladium film at a temperature at which it is permeable to hydrogen the cell may be heated by various means such as by disposing it in an oven or by heating the device electrically. For example, the heating coil 47 may be utilized to raise the

electrodes

40 and 46 and the electrolyte 50 to a temperature above 200C. Though it is desirable to maintain the resistance of the electrodes and electrolyte as low as possible for the purposes of electrical power efficiency, the electrolytic cell may in some configurations provide a sufficient internal impedance to produce the desired heating on passage of current through the electrodes and electrolyte. In other configurations, the heat supplied by operation of the electrolytic cell contributes to the heat received to maintain the films at the desired temperature. Thus, the electrolysis'current supplied by the electrolysis power and controller unit, not shown, may also be utilized to provide a portion of the necessary heating.

The electrolyte is a material capableof transporting an ionic species of the carrier gas from one electrode to the other, is inert with respect to the electrodes, is

stable at the temperature of operation and is capable of regenerating the carrier gas by electrolytic association or disassociation as is required. The electrolyte may be an acid, basic or salt material and is preferably an inorganic metal hydroxide.

The most suitable materials for use in the invention are the Group 1 metal hydroxides such'as sodium hydroxide, potassium hydroxide, or lithium hydroxide. The hydroxides should be utilized in a hydrated form, preferably contain 10 to 35 percent water of hydration since this both lowers the power requirement and the temperature at which the electrolyte becomes molten. Improved operation of the cell occurs when at least 10 to 25 percent of the lighter weight lithium hydroxide is mixed with sodium or potassium hydroxide, preferably the latter. Commercial potassium hydroxide containing 25 percent water melts at 275C. The addition of 10 percent lithium hydroxide to this electrolyte further lowers the temperature at which the electrolyte becomes molten to about 200C.

The fused electrolyte utilized must be very pure to provide continuous, trouble-free operation. The initial supply of hydrogen carrier gas should also be pure to avoid analytical error. It is important to maintain the temperature of the anode tube above the critical diffusion temperature so that a sufficient supply of hydrogen is maintained in the electrolyte at all times. It is also desirable that the tube be activated prior to assembling the cell and is preferable thatmetals other than palladium silver or gold not be present in the cell.

Referring now in detail to FIG. 2, the illustrated generator-separator 14 includes a flanged housing 70 enclosed by a cap 72, secured by bolts. not shown. The

interior cell recess 74 is surfaced with an insulator liner 76, suitably formed of Teflon (polytetrafluoroethylene). The cap 72 is fitted with three feedthrough ports which electrically isolate the anode inlet 42, anode outlet 44 and cathode outlet 52 while providing a positive seal for the cell contents. An annular disc 80, suitably formed of Pd/Ag, contains ports which sealingly receive and support the anode inlet 42 and anode outlet 44. A cap liner 78 insulates the cap 72 from the disc 80, and a cathode liner sleeve 81 insulates the disc from the cathode 46.

In an illustrated embodiment, both electrode assemblies are fabricated from palladium/silver alloy tubing. The center electrode 46 is the cathode. It is a tightly wound spiral, 0.67 meters in length, closed at the bot tom end. The spiral consists of 12 loops, each loop pro- 7 viding 1 cm of cathode surface area. The anode assembly is positioned so as to surround the cathode in the form of a loosely wound spiral approximately 2 meters in length. The anode 40 is open at both ends. Gas enters the anode from the chromatographic column and leaves the other anode on its way to the detector.

Both electrodes are immersed in an electrolyte. The cell is operated at 200C to 250C. Higher temperatures are avoided to prevent failure of the cell liner. Under such operating conditions, the pressure within the cell body is only slightly above atmospheric and arises mainly from the expansion of the trapped air plus the vapor pressure of water.

There is no complete understanding or description of the process by which a palladium alloy electrode permits the transfer of hydrogen through its wall. In practice the hydrogen transfer is governed by the tempera ture of the electrolyte, the applied potential, the electrode thickness, and the hydrogen concentration gradi-- ent. Nevertheless, the cell reaction may be considered as follows:

The forward reaction occurs at the cathode, where hydrogen is transported from the electrolytic side of the hollow electrode to the inside wall of the electrode. The reverse reaction takes place at the anode where gaseous hydrogen is transferred through the electrode wall into the electrolyte. Hydrogen flows from the cathode through the GC column and is removed from the gas stream at the anode. It is noted that the electrolytic reaction does not include the formation of oxygen. This is the main reason why' the cell body pressure is only slightly above ambient when the cell is operating. While the flow of hydrogen follows directly from Fara= days Laws of Electrolysis, the actual operation efficiency of the cell is cathode limited.

Maximum efficiency is attained when the cathode current density is 0.1,amp/cm of cathode surface area. For the system shown, then, the optimum hydrogen flow is 8.4 ml/min at a maximum operating current of 1.2 amps. Generation of this quantity of hydrogen is accomplished at 0.2 V or less. Thus, the maximum power of 0.24 watts required is far less than that associated with the direct electrolysis of water (1.86 watts) for an equal amount of hydrogen.

FIG. 3 illustrates the construction of a second electrolytic cell, designated the auxiliary hydrogen generator 16. The cell body 90, suitably formed of nickel, which serves as the anode, is a hollow cylinder. It is threaded at the top to accept a cell cap 92 fitted with a hydrogen outlet line 94 and an oxygen vent 96. Internally, the hydrogen outlet is connected to the cathode assembly 98 which consists of a palladium/silver tube 100 in the form of a tightly wound helix held in place at the bottom of the cell body by means of a Teflon spacer 102. The top part of the cathode tube is attached by a gold-platinum tube 104 to the hydrogen outlet line 94. The line 94 is insulated by means of an epoxy seal 106 at the cell cap. The cathode assembly is immersed within an electrolyte 108, suitably a 10 percent KOH aqueous solution.

The controller for the auxiliary hydrogen generator is illustrated in FIG. 4. The controller 200 includes a first amplifier 202 receiving the signal from the transducer 62. A second amplifier having a variable resistor 204 input for the pressure set further amplifies the signal and applies the signal to the power supply 206 for the auxiliary hydrogen generator. With no sample in the gas chromatograph and with the main hydrogen carrier gas flow circulating within the closed loop circuit, the output of the pressure transducer which senses the pressure downstream of the anode, but upstream of the flow restrictor is adjusted by means of variable resistor input 204 to provide sufficient voltage to the auxiliary generator to produce from 0.1 to 1.0 cc hydrogen flow per minute as required by the particular analysis.

When non-hydrogen components enter the anode, the decrease in hydrogen transfer causes variations to occur in the hydrogen carrier gas flow rate if it is not compensated for. The anode will attempt to maintain the constant transfer rate by utilizing hydrogen normally associated with the auxiliary carrier gas stream. In so doing, the pressure in the line, downstream of the anode, will fall. This pressure decrease is sensed by the pressure transducer whose increased output signal will immediately cause more voltage to be applied to the auxiliary hydrogen generator. Additional hydrogen which is generated enters the system and will in effect maintain the constant flow of hydrogen within the closed-loop circuit while also maintaining a flow of hydrogen to the detector. The power requirements for the unit will vary, but will not exceed 10 W. Maximum operation efficiency is achieved when the system is operated at 80C. The heater will require an additional 10 W.

The chromatographic system utilizes chromatographic column of conventional design and characteristics. In the illustrated embodiment, the chromatographic assembly included 0.16 cm i.d. tubular columns (packed or open type) of variable length excluding heating elements, thermocouples, and electrical connections. Each assembly is an independent unit. A

typical unit measures 15 cm X 2.54 cm o.d. Maximum power required to heat the unit is 30 W, with 10 W normally used.

EXAMPLE I A simulated Martian atmosphere comprising a mixture of the minor component (0.1) gases shown in FIG. 5 dispersed in a matrix of CO was analyzed.

The column was 1.2 meters long, 0.16 cm i.d. stainless steel packed with molecular sieve 5A. The column was temperature programmed, ambient to 200C, with the first four peaks eluting under ambient temperature conditions. A heating rate of 33C/min was then applied, with a maximum temperature of 220C being achieved within 7 minutes. The total run was completed in 12 minutes.

EXAMPLE 2 An analysis of a three-component gas in air was conducted in the system of the invention utilizing a 1 meter long stainlesssteel column having a 0.16 cm i.d. packed with Parapak R & Q in series, each 0.5 meter long. The hydrogen flow through the closed-loop was 3.5 cc/min and through the detector was 2.8 cc/min. The column was maintained at ambient-temperature.

FIG. 6 is a chromatogram of the'three-component gas mixture in air. The three minor components made up 33 percent of the sample volume. In this case the auxiliary carrier gas flow was almost equal to that of the main carrier gas flow. The minor component chromatographic peak intensity may be enchanced by sim ply reducing the auxiliary carrier gas flow relative to the main carrier gas flowrate.

The portable self-contained gas chromatograph has been developed and successfully operated continuously for a period of four months. Maintenance was minimal, the addition of small amounts of water (5-15 cc/day) to the auxiliary hydrogen generator daily accounting for virtually all of the maintenance.

The system is completely portable, using a power pack consisting of two 12-volt batteries and one 6-volt battery comprising a total of 9.07 kg. It is independent of all external sources of supply. It should be of value in air pollution studies, study of confined atmospheres, as in mine shafts, on stream studies of industrial smoke and stack exhaust. Utilizing the simulated Martian atmosphere, it was determined that the sensitivity limits of the system are in the range of l-l0 ppm for C 11 It is to be understood that only preferred embodiments of the invention have been described and that numerous'substitutions, modifications and alterations are all permissible without departing from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

l. An analysis system comprising:

- a closed hydrogen circuit including a gas chromatographic column and an electrolytic hydrogen carrier gas generator-separator including a selectively hydrogen permeable anode electrode and cathode electrode, the inlet to the column being connected to the hydrogen carrier gas output from said cathode and the outlet from said column being connected to a first inlet end of said anode;

sample inlet means connected to said circuit upstream of said column inlet;

an auxiliary electrolytic hydrogen generator having a sweep gas hydrogen output connected to the first end of said anode;

detector means connected to the second end of said anode for receiving and analyzing a dispersion of samples in said sweep gas;

pressure detector means for sensing the pressure of the second outlet end of said anode and developing an electrical signal indicative thereof; and

electrical controller means receiving said signal for controlling the output of said auxiliary generator.

2. An analysis system according to claim 1 in which said controller means includes a first output element for providing a substantially constant control signal for providing a minimum constant flow rate of hydrogen sweep gas in excess of the amount of gas permeating through the anode of the generator-separator.

3. An analysis system according to claim 2 in which said pressure detector means includes a transducer for developing an electrical signal inversely proportional to said pressure change and said controller includes a second control element for developing a control signal for changing the flow rate of said auxiliary generator above said minimum rate in response to changes in the hydrogen flow rate change through said anode.

4. An analysis system according to claim 1 in which said detector means is an ionization cross-section detector.

5. An analysis system according to claim l in which said auxiliary generator is an electrolytic cell for the electrolytic decomposition of water into hydrogen and oxygen.

6. A system according to claim 5 in which said auxiliary hydrogen generator includes a palladium-silver electrode selectively permeable to hydrogen.

7; An analysis system according to claim 1 in which the electrodes of said generator-separator comprise palladium and said electrodes are immersed in a fused body of aqueous alkali electrolyte.

8. An analysis system according to claim 7 in which said electrodes comprise an alloy of palladium and silver.

9. An analysis system according to claim 7 in which said cathode is a tubular element having a closed end immersed in said electrolyte, and an open output end extending therefrom, said anode is a tubular element surrounding said cathode having an open inlet end and an open outlet end extending from said electrolyte whereby a dispersion of sample in hydrogen carrier gas enters said anode, the hydrogen permeates through the wall of the anode tube, across the electrolyte through the wall of the cathode and recycles through the cathode output to the inlet of the column, and the sweep gas from the auxiliary generator sweeps the sample from the outlet end of the anode into the detector means.

10. A method of analyzing a vaporous sample comill prising the steps of:

circulating hydrogen carrier gas through a continuous circuit including a gas chromatographic column and an electrolytic hydrogen generatorseparator including a selectively hydrogen permeable anode electrode and a selectively hydrogen permeable cathode electrode containing an electrolyte capable of transferring hydrogen between said electrodes;

introducing a vaporous sample into the circuit immediately before said column; electrolytically generating a flow of hydrogen sweep gas in excess of the amount of hydrogen carrier gas in said circuit transferable through said anode across said electrolyte and through said cathode;

introducing said sweep gas into the circuit at the inlet to said anode;

removing a dispersion of sample in sweep gas from the circuit;

analyzing said dispersion;

sensing the rate of separation of hydrogen gas through said anode and developing a signal indicative thereof; and

controlling the amount of hydrogen sweep gas introduced in the circuit in response to said signal.

11. A method according to claim 10 in which the sensing step comprises developing an electrical control signal indicative of the pressure of the gas leaving the anode and applying said signal to control the output of an auxiliary hydrogen generator.

12. A method according to claim 11 in which the output from the column is delivered to the anode, substantially all of the hydrogen carrier gas is transferred through the anode, across the electrolyte and through the cathode and recycled to the inlet end of the column, and the sweep gas is introduced into the inlet end of the anode and sweeps the sample into a detector for analyzing the dispersion of samples in said sweep gas.

13. A method according to claim 11 in which the electrodes in the generator-separator comprise a hydrogen permeable alloy of palladium and are immersed in an electrolyte capable of transferring hydrogen between the electrodes under the conditions of operation of the generator-separator.

14. A method according to claim 12 in which the.

generator-separator separates 99.96 percent of the hydrogen carrier gas in said circuit.

15. A method according to claim 14 in which the sweep gas flow rate is at a rate between 0.01 to 1.0 ml

per minute of hydrogen.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION" Patent Ne. 3,858,435 Dated aanuaivmlsfis Invent fl Mario R. Stevens It is certified that error' appears-in theabove-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 1, after "0.1" insert line2'5,

change "'en'chanced" to --enhanced--. Column 10, line 49-, change "0.01" to --0.l--. V

Signed and sealed this 4th day 'of March 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer V and Trademarks FORM PO-105O (10- u scoMM-Dc suave-pee "v5. GQVERNMENT PRNf|HG OFFICE .959 0-365-33

Claims

1. An analysis system comprising: a closed hydrogen circuit including a gas chromatographic column and an electrolytic hydrogen carrier gas generator-separator including a selectively hydrogen permeable anode electrode and cathode electrode, the inlet to the column being connected to the hydrogen carrier gas output from said cathode and the outlet from said column being connected to a first inlet end of said anode; sample inlet means connected to said circuit upstream of said column inlet; an auxiliary electrolytic hydrogen generator having a sweep gas hydrogen output connected to the first end of said anode; detector means connected to the second end of said anode for receiving and analyzing a dispersion of samples in said sweep gas; pressure detector means for sensing the pressure of the second outlet end of said anode and developing an electrical signal indicative thereof; and electrical controller means receiving said signal for controlling the output of said auxiliary generator.

5. An analysis system according to claim 1 in which said auxiliary generator is an electrolytic cell for the electrolytic decomposition of water into hydrogen and oxygen.

7. An analysis system according to claim 1 in which the electrodes of said generator-separator comprise palladium and said electrodes are immersed in a fused body of aqueous alkali electrolyte.

10. A method of analyzing a vaporous sample comprising the steps of: circulating hydrogen carrier gas through a continuous circuit including a gas chromatographic column and an electrolytic hydrogen generator-separator including a selectively hydrogen permeable anode electrode and a selectively hydrogen permeable cathode electrode containing an electrolyte capable of transferring hydrogen between said electrodes; introDucing a vaporous sample into the circuit immediately before said column; electrolytically generating a flow of hydrogen sweep gas in excess of the amount of hydrogen carrier gas in said circuit transferable through said anode across said electrolyte and through said cathode; introducing said sweep gas into the circuit at the inlet to said anode; removing a dispersion of sample in sweep gas from the circuit; analyzing said dispersion; sensing the rate of separation of hydrogen gas through said anode and developing a signal indicative thereof; and controlling the amount of hydrogen sweep gas introduced in the circuit in response to said signal.

14. A method according to claim 12 in which the generator-separator separates 99.96 percent of the hydrogen carrier gas in said circuit.

15. A method according to claim 14 in which the sweep gas flow rate is at a rate between 0.01 to 1.0 ml per minute of hydrogen.