US3365951A - Sample injector for gas chromatographs - Google Patents

Sample injector for gas chromatographs Download PDF

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Publication number
US3365951A
US3365951A US447255A US44725565A US3365951A US 3365951 A US3365951 A US 3365951A US 447255 A US447255 A US 447255A US 44725565 A US44725565 A US 44725565A US 3365951 A US3365951 A US 3365951A
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US
United States
Prior art keywords
pressure
carrier gas
sample
reservoir
solenoid valve
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US447255A
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English (en)
Inventor
Jentzsch Dietrich
Schumann Wolfgang
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PE Manufacturing GmbH
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Bodenseewerk Perkin Elmer and Co GmbH
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/26—Conditioning of the fluid carrier; Flow patterns
    • G01N30/28—Control of physical parameters of the fluid carrier
    • G01N30/32—Control of physical parameters of the fluid carrier of pressure or speed
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/04—Preparation or injection of sample to be analysed
    • G01N30/16—Injection
    • G01N30/20—Injection using a sampling valve
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/04—Preparation or injection of sample to be analysed
    • G01N30/24—Automatic injection systems

Definitions

  • a system for repetitive injection of liquid samples into, for example, the inlet of a gas chromatograph includes a connection from the liquid sample reservoir to the chromatograph inlet, the conventional carrier gas supply connection to this inlet, and an optionally operable means for temporarily reducing the carrier gas pressure at the chromatograph inlet.
  • This optionally operable means includes a pressure-reducing restrictor or throttle between the carrier gas supply and the chromatograph inlet, and a normally open, but optionally closable by-pass valve, so that the restrictive throttle is normally by-passed or shunted.
  • Optional closing of this valve temporarily reduces the carrier gas pressureat the inlet, thereby causing a certain portion of the liquid sample in the reservoir (which is at full normal carrier gas pressure) to be pushed into the inlet of the chromatograph.
  • the liquid sample injection may be readily repeated at any desired time intervals.
  • This invention relates to a sample injector for gas chromatographs, particularly adapted to provide periodic injections of liquid samples to the chromatographic separating column.
  • the invention is especially suitable for use in so-called preparative chromatographic processes, in which the sample components are separated for the purpose of further analysis or other use thereof.
  • One form of existing apparatus for this purpose utilizes a sealed reservoir (holding the liquid sample), which is connected with a carrier gas line leading to the entrance of the separating column through a throttling or restrictive connection line, so that a pressure difference can be produced between the reservoir and the carrier gas line during desired predetermined periods of time.
  • a first carrier gas branch is maintained at a specific pressure (say, P by means of a pressure control; this first branch is connected to the entrance of the apparatus, for example, the sample evaporator or injection block of the gas chromatograph.
  • a second branch from the carrier gas source also contains a pressure control, which is adjusted to yield a somewhat higher pressure, P (i.e., P is larger than P
  • P i.e., P is larger than P
  • This second carrier gas branch is connected with the closed reservoir by means of a first solenoid valve.
  • This reservoir contains a supply of the liquid sample to be analyzed and is also connected with the first carrier gas branch by means of a capillary tube. Additionally, the reservoir is connected to the atmosphere through a venting tube containing a second solenoid valve.
  • both solenoid valves are initially closed. Pure carrier gas therefore flows through the first branch (at a pressure P to the gas chromatograph.
  • the first solenoid valve is opened for a short period of time. This causes the carrier gas to flow into the reservoir with the higher pressure P (i.e., the injection pressure) so that the pressure difference, F -P forces the liquid sample Patented Jan. 30, 1968 through the capillary into the entrance of the apparatus.
  • the first solenoid valve is closed.
  • the second solenoid valve is opened simultaneously with the closing of the first solenoid valve, so that the excess pressure in the reservoir is released through the second solenoid valve (usually through a throttling element, such as a throttle valve). In this manner the sample injection through the capillary tube is terminated relatively sharply. After the excess pressure in the reservoir has been released, the second solenoid valve is again closed; and the entire cycle may then be repeated.
  • sample injector just described is primarily utilized for preparative purposes (i.e., for separation of relatively large quantities of sample so as to allow subsequent use of the separated components). Therefore predetermined quantities of the sample are periodically injected into the gas chromatograph as long as there remains some sample in the reservoir.
  • This known arrangement suffers from the following drawbacks:
  • the primary object: of the invention is to avoid the just-mentioned disadvantages of the prior known arrangement.
  • this is accomplished by placing a pressure reducing throttle in the carrier gas line at a point before (i.e., more remote from) the gas chromatograph entrance than the connection of the sample reservoir.
  • This pressure reducing throttle is bridged or shunted by a by-pass line, which may be opened or closed (by means, for example, of a solenoid valve).
  • the by-pass line When the by-pass line is open, the full carrier gas pressure (say, P will be present at the entrance to the apparatus. This pressure will then be imparted to the closed reservoir through the connecting line thereto.
  • the carrier gas will flow back into the reservoir through this connecting line until the pressure in the reservoir has been balanced with the pressure in the carrier gas line (i.e., the gas in the reservoir above the surface of the sample will also be at pressure P If the by-pass line is then shut, a pressure drop will develop across the throttle. This will cause the pressure in the carrier gas line at the entrance of the apparatus to become less than pressure P This reduction in the pressure will cause the pressure in the reservoir (which is still P to be greater than the pressure in the carrier gas line at the entrance of the apparatus. Consequently liquid from the reservoir will be pushed by this excess pressure into the entrance of the apparatus. Whenever the by-pass line is again opened, the pressure drop in the throttle is immediately eliminated and the full pressure P will again prevail in the entire carrier gas line.
  • the solenoid valve for controlling the sample injection is in the carrier gas line exclusively. Therefore this solenoid valve cannot come into contact with either the sample liquid or vapors thereof, thereby obviating any possibility of the valve being attacked by potentially corrosive substances. Further, this solenoid valve is open during the major portion of the time that the apparatus is in operation (i.e., it is open except for the short time intervals during which the sample is being periodically injected). For this reason the solenoid valve is not being constantly strained by being biased to a closed position, as occurs in the prior art arrangement.
  • An additional advantage is that the reservoir is maintained in a closed condition continuously, and there is no need to release or exhaust the carrier gas contained therein into the atmosphere periodically.
  • the sole figure is a schematic representation of the sampling injector for a gas chromatograph.
  • carrier gas flows in the carrier gas line shown at the left-hand side of the drawing from a carrier gas source (not shown) through a fine pressure control, FPC, on its way to a gas chromatograph (not shown), situated beyond the arrow shown at the right-hand side of the drawing.
  • FPC fine pressure control
  • the carrier gas After the carrier gas has been adjusted by the fine pressure control, it passes through a pressure sensor 2, the purpose of which will be subsequently explained.
  • the gas then flows through a restrictor or throttle N
  • the by-pass channel or line 1 is arranged in parallel shunting arrangement to the throttle N so as to provide a possible alternate path for the gas around this throttle.
  • By-pass line 1 contains a solenoid valve M which may open and close the passage through by-pass channel 1.
  • the pressure of the carrier gas (in front of the throttle N may be measured by means of a manometer 3.
  • the sample liquid to be supplied to the gas chromatograph is accommodated in a reservoir 4,
  • a capillary tube K passes through the closure lid of reservoir 4, so as to be covered by the liquid sample.
  • the upper end of capillary tube K joins into the carrier gas stream (at 5) near the entrance to the gas chromatograph.
  • reservoir 4 there exists above the sample liquid a mixture of carrier gas and vapors of the various (volatile) liquid sample components.
  • An extremely highly resistant throttle valve N may be provided in a separate outlet from the reservoir, communicating with the atmosphere.
  • the purpose of this highly restrictive throttle N is to allow a very slow escape of gas under excess pressure caused by temperature variations.
  • the resistance of this valve may be adjusted in such a manner that, during the intervals when no sample is being injected, the carrier gas must enter vessel 4 through capillary K as individual bubbles at spaced intervals, in order to balance the pressure as previously mentioned. In this Way, an unintentional injection of the sample liquid is precluded.
  • the pressure in the carrier gas line decreases below its nominal value (P even though solenoid valve M is open. This may occur because of a leak in the carrier gas line or because of a reduction in pressure of the carrier gas source (i.e., the gas cylinder supplying the carrier is almost empty).
  • the reduction in pressure in the carrier gas line at 5 might cause an erroneous injection of sample liquid unless some provision is made to avoid this.
  • the pressure sensor 2 (which may be sensitive either to absolute or differential pressures) is provided at the side of the fine pressure control (FPC) remote from the carrier gas source. A drop in pressure, as determined by sensor 2, will cause an additional outlet from the reservoir 4 to be opened to the atmosphere.
  • a second solenoid valve M will open allowing an escape of much of the pressure in reservoir 4 through a throttle N which throttle is of relatively small resistance.
  • a further solenoid valve M may be closed at the same time.
  • an additional solenoid valve similar to valve M in the capillary tube or else supply an additional control of solenoid Valve M This additional means would cause the capillary tube K to be closed whenever the by-pass solenoid valve M is open. Therefore a sample injection could occur only when control solenoid valve M is closed.
  • Solenoid valve M may additionally be controlled by a mechanism (such as pressure sensor 2) in the carrier gas line, which mechanism would close the solenoid valve M (or another valve placed in capillary K) whenever the pressure from the carrier gas source dropped below a certain level (caused, for example, by a gas cylinder becoming empty, leaks in the various gas lines, or the like).
  • a mechanism such as pressure sensor 2 in the carrier gas line, which mechanism would close the solenoid valve M (or another valve placed in capillary K) whenever the pressure from the carrier gas source dropped below a certain level (caused, for example, by a gas cylinder becoming empty, leaks in the various gas lines, or the like).
  • the by-pass or control solenoid valve M may be energized (i.e., closed) periodically by any suitable control device, generating an electrical control signal.
  • a sample injection device particularly suitable for the periodic injection of liquid samples into a gas chromatograph, comprising:
  • a carrier gas line adapted to receive carrier gas from a source at a first point and to supply said carrier gas to the entrance of a gas chromatograph at a second point;
  • a closed, substantially gas-tight reservoir adapted to contain the liquid sample to be injected into the gas chromatograph
  • a pressure-reducing restrictive throttle means positioned in said carrier gas line between said first and said second points, whereby a pressure drop in said carrier gas line will occur when gas in flowing through said throttle means;
  • bypass line connected to said carrier gas line at opposite sides of said throttle means, so as to provide a shunting path for said carrier gas around said throttle;
  • valve means in said by-pass line, adapted to open and close said by-pass line;
  • valve means in said by-pass line will cause a pressure drop to be created at said junction point, thereby causing any liquid sample in said reservoir to be pushed through said tube to the point near the entrance of said gas chromatograph, thereby injecting a portion of said sample.
  • valve means in said by-pass line is a solenoid valve.
  • said relatively narrow connecting tube is a capillary.
  • a fine pressure control means is provided in said carrier gas line between said first point thereof and said throttle means.
  • an optionally openable venting outlet is provided for said reservoir
  • a pressure sensor means is positioned in said carrier gas line between said fine pressure control means and said throttle means,
  • said pressure sensor means being operatively connected to said venting outlet, so as to open the latter whenever the pressure in said carrier gas line at said sensor substantially decreases.
  • a shutofi valve is positioned in said narrow connection tube
  • a shutoff valve is provided in said narrow connection tube
  • control means are provided for closing said shutoff valve during the time that the value in said bypass line is open.
  • a shutoff valve is provided in said narrow connection tube
  • shutolf valve being operatively connected to said pressure sensor means so as to be closed thereby upon the occurrence of a substantial decrease in the carrier gas line pressure.
  • a constant vent including a very highly resistant restriction, is provided for said reservoir,

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Sampling And Sample Adjustment (AREA)
US447255A 1964-04-24 1965-04-12 Sample injector for gas chromatographs Expired - Lifetime US3365951A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DEB76492A DE1208523B (de) 1964-04-24 1964-04-24 Probengeber fuer Gaschromatographen

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US3365951A true US3365951A (en) 1968-01-30

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3475964A (en) * 1966-09-26 1969-11-04 W G Pye & Co Ltd Liquid injection device
US3887345A (en) * 1971-09-16 1975-06-03 Nasa Gas chromatograph injection system
US4038053A (en) * 1976-06-10 1977-07-26 The Perkin-Elmer Corporation Method and apparatus for introducing liquid samples into a gas chromatographic column
US4704141A (en) * 1985-06-20 1987-11-03 Siemens Aktiengesellschaft Apparatus for automatically transferring small quantities of liquid samples in gas chromatography
US4742716A (en) * 1985-11-07 1988-05-10 Bifok Ab Sample introduction system for nonsegmented continuous flow analysis
US4958295A (en) * 1986-05-21 1990-09-18 Hercules Incorporated Analyzing apparatus and method for analysis of liquid samples
US5074156A (en) * 1989-12-11 1991-12-24 Nikkiso Co., Ltd. Flow control mechanism for automatic pressure reducing equipment
US6286375B1 (en) * 1999-04-27 2001-09-11 The United States Of America As Represented By The Secretary Of The Air Force Apparatus for facilitating headspace sampling

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1673028B1 (de) * 1967-07-10 1972-11-16 Siemens Ag Dosiervorrichtung fuer vorzugsweise fluessige stoffe in der gaschromatographie

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3103807A (en) * 1960-07-08 1963-09-17 Phillips Petroleum Co Liquid sample injection in a chromatographic apparatus

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3103807A (en) * 1960-07-08 1963-09-17 Phillips Petroleum Co Liquid sample injection in a chromatographic apparatus

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3475964A (en) * 1966-09-26 1969-11-04 W G Pye & Co Ltd Liquid injection device
US3887345A (en) * 1971-09-16 1975-06-03 Nasa Gas chromatograph injection system
US4038053A (en) * 1976-06-10 1977-07-26 The Perkin-Elmer Corporation Method and apparatus for introducing liquid samples into a gas chromatographic column
US4704141A (en) * 1985-06-20 1987-11-03 Siemens Aktiengesellschaft Apparatus for automatically transferring small quantities of liquid samples in gas chromatography
US4742716A (en) * 1985-11-07 1988-05-10 Bifok Ab Sample introduction system for nonsegmented continuous flow analysis
US4958295A (en) * 1986-05-21 1990-09-18 Hercules Incorporated Analyzing apparatus and method for analysis of liquid samples
US5074156A (en) * 1989-12-11 1991-12-24 Nikkiso Co., Ltd. Flow control mechanism for automatic pressure reducing equipment
US6286375B1 (en) * 1999-04-27 2001-09-11 The United States Of America As Represented By The Secretary Of The Air Force Apparatus for facilitating headspace sampling

Also Published As

Publication number Publication date
DE1208523B (de) 1966-01-05

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