Method and Apparatus for Fluid Sample Injection for Fluid Chromatography

1. Field of the Invention

The present invention relates to chromatographic analyzers. More specifically, the present invention is directed to a sample injection apparatus for a chromatographic analyzer.

2. Description of the Prior Art

The use of chromatographic analyzers for analyzing fluid samples, e.g., gas mixtures, is well-known in the art. A sample injection means is used for selectively injecting a sample of the gas to be analyzed into a carrier fluid stream to be carried to the chromatographic separating column. The purpose of the sample injector is two-fold, i.e., it must inject a sample into the carrier fluid stream and it must provide a means for predetermining the volume of the sample to be injected. The prior art sample injection devices have included mechanically operated syringes, e.g., U.S. Pat. Nos. 3,940,995 and 3,985,166, valves having internal storage loops, e.g., U.S. Pat. Nos. 3,787,026 and 3,975,946 and other complicated mechanical devices which have usually been unable to provide long term reliability in combination with a low manufacturing cost. Accordingly, it would be desirable to provide a sample injection apparatus capable of having extremely long operating life as well as a simple and inexpensive structure.

An object of the present invention is to provide an improved chromatographic sample injection apparatus.

In accomplishing this and other objects, there has been provided, in accordance with the present invention, a sample injection apparatus having an acoustic signal generator at one end of a closed chamber adjacent to a selectively controlled source of a carrier fluid supplying the interior volume of the chamber. A selectively controlled source of the sample to be analyzed is arranged to supply the sample at a point within the chamber aligned with the space between the nodes of the standing acoustic waves generated within the chamber by the acoustic signal generator.

A better understanding of the present invention may be had from the following detailed description is read in connection with the accompanying drawing, which the single FIGURE is an illustration of an example of a sample injection apparatus embodying the present invention.

Referring to the single FIGURE drawing in more detail, there is shown a diagrammatic illustration of a sample injection apparatus having a hollow-chamber in the form of a cylindrical tube 2 with an acoustic signal generator 4 located at one end thereof. An acoustic signal output device 6 driven by the single generator 4 is located within the hollow tube 2 at the aforesaid end thereof. The acoustic signal producing means 6 may be any suitable device such as a piezoelectric element capable of producing acoustic signals when suitably driven by an electrical signal, such devices being well-known in the art. Adjacent to the end of the tube having the acoustic signal output device 6 attached thereto is a first fluid inlet port 8. The term fluid as used herein refers to either a liquid or a gaseous fluid since the sample injection apparatus of the present invention is useable with either fluid medium. The inlet port 8 is connected to the output of an electrically controlled fluid valve 10. The inlet of the valve 10 is connected to a source of the carrier fluid 12.

At a suitable distance along the tube 2, as determined by the presence of the nodes of a standing wave within the tube 2, as discussed more fully hereinafter, is located at a second inlet port 14. A second selectively controlled fluid valve 16 has its output connected to the port 14 and its input connected to a fluid sample conduit 18 extending between the valve 16 and a source of a sample to be analyzed 20. A first fluid exhaust port 22 is connected to the conduit 18 between the valve 16 and the source 20. A fluid outlet port 24 is located in the wall of the tube 2 opposite to the second inlet port 14. A third selectively controlled fluid valve 26 has its input connected to the output port 24 and its output connected to a fluid exhaust conduit 28. The other end of the tube 2 is connected to the input of a chromatographic separating column 30, such devices being well-known in the art. A chromatographic detector 32 is connected to the output of the column 30. A timing and control means 34 is used to control the frequency and output energy level of the acoustic generator 4 and single producing means 6 and the selective operation of the fluid valves 10, 16 and 26.

In operation, the sample injection apparatus of the present invention is used to measure a sample volume and to inject, or transport, that volume of the sample to be analyzed to the chromatographic column 30. In order to determine the volume of the sample to be provided, the frequency of the acoustic generator is adjusted by the timing and control circuit 34 to produce a frequency output which is suitable for producing standing waves having nodes 36 separated by the desired spacing to produce the sample volume, e.g., a 150 Kilohertz frequency would product acoustic nodes 1 millimeter apart in air. Further, while the tube 2 is shown in an enlarged form for purposes of illustration, and actual tube may have an internal diameter of only several millimeters, e.g., 10 mm, and a commensurate length, e.g., 100 mm. The location of the sample injection port 14 and sample exit port 24 is predetermined to coincide with the location of the aforesaid sample volume determined by the position of the space between two adjacent nodes in the standing waves produced by the acoustic signal from the acoustic generator 4, i.e., an antinode.

During this initial phase of the operation of the injection apparatus, the valves 10, 16, and 24 are closed by the timing and control circuit 34. After the acoustic signal has been established within the column 2, the sample injection port control valve 16 and the sample exit port control valve 26 are opened by the timing and control circuit 34. This open state of the valves 16 and 26 allows the sample from the sample source 20 to flow through the fluid conduit 18 past the valve 16 into the inlet port 14. The sample continues across the space between the nodes of the standing waves in the hollow tube 2 into the exit port 24 and exits via the via exit valve 26 and the fluid exhaust conduit 28. After a predetermined period of time, the nodes and the volume therebetween having the sample flowing therethrough will be saturated by the sample. At this time, the valves 16 and 26 are closed by the timing and control circuit 34 to trap the sample of the sample fluid to be analyzed between the nodes within the column 2. Subsequently, the carrier gas control valve 10 is opened by the timing and control circuit 34. The carrier fluid from the carrier fluid source 12 is then allowed to enter the column 2 and to sweep the sample of the fluid to be analyzed which is present within the column 2 into the chromatographic column 30 for separating and into the chromatographic detector 32.

A further enhancement of operation during the transportation to the sample by the carrier gas 12 may be effected by the timing control circuit 34 to reduce the acoustic energy from the acoustic generator 4 and signal producing device 6 to prevent any possible interference with the transportation of the sample by the carrier fluid 12 into the chromatographic column 30. Thus, in this latter type of operation, the sonic energy would be elevated during the trapping phase of the sample between the standing wave nodes and subsequently reduced when the carrier gas is introduced into the column 2. In either type of operation, the sonic energy during the sample trapping phase should be high enough to prevent the sample fluid from migrating past the standing wave nodes within the column 2. Further, it should be noted that the size of the sample may be discretely vaired by varying the acoustic frequency by an adjustment of the acoustic generator 4 by the timing and control circuit 34. Additionally, a pressure sensor 38 may be mounted on the column 2 to project therethrough to sense the internal pressures representative of the nodes 36. An output signal from the sensor 38 would be applied to the control circuit 34 to effect a requisite frequency control of the acoustic generator 4 to ensure a proper location of the nodes 36 with respect to the ports 14 and 24.

Accordingly, it may be seen that there has been shown, in accordance with the present invention, an improved sample injection apparatus.