Automatic sampler

In a direct injection type automatic sampler, a sampling needle having a liquid sample collected from a sample vessel by using suction force of a pump is inserted into an injection port. Then, a flow path-switching valve is rotated to switch a flow path to make a flow of mobile phase liquid pass through a loop to thereby introduce the collected sample into a column. The injection port is directly incorporated in the flow path-switching valve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic sampler, for example, an automatic sampler for introducing each sample into a liquid chromatograph automatically.

2. Description of the Related Art

FIG. 3shows flow paths as important parts of a related-art automatic sampler for liquid chromatograph.

InFIG. 3, an automatic sampler has a 6-port 2-position flow path-switching rotary valve1which has six ports arranged at regular intervals, and two path positions for connecting every adjacent two of the six ports to each other. When the flow path-switching valve1is rotated, one of the two path positions is moved to the other to switch flow paths.

Sample vessels3each containing a liquid sample to be analyzed are arranged on a rack31. A sampling needle5sucks in and collects the liquid sample from selected one of the sample vessels3. The sampling needle5is connected to a pump2through both a looped flexible conduit pipe (hereinafter referred to as “loop”)6and the flow path-switching valve1, so that the pump2gives suction force to the sampling needle5. After the sampling needle5driven by a not-shown automatic drive mechanism sucks in the liquid sample in the position (sampling position) represented by the broken line inFIG. 3, the sampling needle5moves to the position (injection position) represented by the solid line inFIG. 3. In the injection position, the sampling needle5is inserted into an injection port4. After the insertion, the sampling needle5is kept liquid-tight in the injection port4.

A mobile phase liquid for the liquid chromatograph passes through the flow path-switching valve1from a liquid feed pump91via a mobile phase liquid feed flow path7and further flows into a column92via a column upstream side flow path8.

The automatic sampler further has a rinse mechanism10which includes another valve (low-pressure valve)11, and a rinse port12. The rinse mechanism10plays the important role of rinsing the sample liquid from the sampling needle5, etc. prior to analysis of a next sample to prevent contamination caused by the previous sample. The detailed description of the rinse mechanism10will be omitted because it is not directly related to the description of the present invention.

Introduction of each sample by the automatic sampler is performed in the following sequence.

(1) In the condition that the path of the flow path-switching valve1represented by the solid line inFIG. 3is validated while the sampling needle5is located in the sampling position, the sampling needle5is dipped into the sample vessel3and the pump2is actuated so that a predetermined amount of the liquid sample is sucked in and collected. The collected liquid sample is mainly retained in the loop6.

(2) The sampling needle5is moved to the injection position and inserted into the injection port4.

(3) When the flow path-switching valve1is rotated by 60 degrees so that the path represented by the broken line inFIG. 3is validated, the mobile phase liquid fed by the liquid feed pump91flows into the column92via the mobile phase liquid feed flow path7, the loop6, the sampling needle5, the injection port4having the sampling needle5inserted therein, a pipe41and the column upstream side flow path8successively. As a result, the liquid sample mainly retained in the loop6is carried to the column92and analyzed.

(4) The flow path-switching valve1is rotated back and rinsing (which will be not described in detail) is performed by the rinse mechanism10to prepare for collection of the next sample. Then, the automatic sampler stands by for collection of the next sample.

The automatic sampler shown inFIG. 3is called “direct injection type automatic sampler” because the sample sucked in and collected by the sampling needle5can be directly introduced into the column92. In the related-art direct injection type automatic sampler, the injection port4and the flow path-switching valve1are disposed separately and connected to each other by the pipe41. As described above, because the liquid sample must pass through the pipe41, the inner volume of the pipe41forms dead volume. Hence, there is a drawback that the sample peak is spread. In addition, if there are piping joints in the path through which the sample passes, there is generally possibility that the sample may remain in fine gaps at the piping joints so that cross contamination occurs easily. Therefore, the number of piping joints needs to be reduced as extremely as possible.

SUMMARY OF THE INVENTION

The present invention is developed in consideration of the problems associated with the related art. An object of the present invention is to provide an automatic sampler in which both the inner volume of a path through which a sample passes and the number of piping joints are reduced as extremely as possible.

To solve the problems, an automatic sampler according to the present invention comprises an injection port and a flow path-switching valve wherein the injection port and the flow path-switching valve to be connected thereto are connected to each other directly without interposition of any pipe. That is, the automatic sampler according to the present invention is a direct injection type automatic sampler having an injection port and a flow path-switching valve integrated with the injection port.

Hence, the number of piping joints in the path through which the sample passes is reduced while dead volume is reduced, so that cross contamination is reduced.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is shown inFIG. 1.FIG. 1shows flow paths as important parts of a direct injection type automatic sampler according to the present invention. The embodiment shown inFIG. 1is substantially the same as the related-art example shown inFIG. 3except that the injection port4is directly connected to the flow path-switching valve1. The operating sequence in this embodiment is the same as that in the related-art example. Constituent parts the same in function as those inFIG. 3are referred to by numerals the same as those inFIG. 3for the sake of omission of duplicated description.

FIG. 2is a view showing an example of specific structure of the flow path-switching valve1to which the injection port4inFIG. 1is connected directly. The flow path-switching valve1, the injection port4and the sampling needle5inserted into the injection port4are shown inFIG. 2.

The flow path-switching valve1has a packing13, a stator14, a rotor15, a spring16, a body17and a shaft18. The stator14is attached to an inner side of the body17of the flow path-switching valve1through the packing13. The rotor15is fixed to the shaft18. The rotor15frictionally rotates relative to the stator14while the stator14and the rotor15are pressed against each other by the spring16.

The injection port4is provided vertically in a top portion of an upper surface (rear surface viewed from the shaft18side) of the flow path-switching valve1. Another port111is disposed around the injection port4. Flow paths piercing the packing13and the stator14and led to a frictional surface19of the rotor15are provided so as to extend from the ports4and111respectively.

Paths for connecting adjacent ports of the flow path-switching valve1as shown inFIG. 3or1are formed as three circular arc-like grooves in the frictional surface19of the rotor15. Hence, because paths connected to the ports respectively are made to communicate with one another by the three grooves, the flow paths can be switched by rotation of the shaft18.

The stator14is made of a rigid material such as ceramics. The rotor15is made of an elastic material such as a polyimide resin. In addition, frictional surfaces of the stator14and the rotor15are smoothened. Hence, the stator14and the rotor15adhere closely to each other, so that they are kept liquid-tight.

The injection port4has a needle seal43provided with a through-hole in its center, and a nut42for pressing the needle seal43. The nut42and the needle seal43may be formed integrally with the same resin material. When the sampling needle5is inserted into the injection port4, a tapered portion at a tip of the sampling needle5is fitted into the center hole of the needle seal43. Hence, the sampling needle5can be connected to the injection port4without liquid leakage. Because the center hole of the needle seal43is directly connected to the frictional surface by the path piercing both the packing13and the stator14, dead volume is very small and the liquid sample can reach the column at the shortest distance from the sampling needle5by the flow path-switching function.

Incidentally, the loop6in the above description need not be always formed like a loop if it can be provided as a conduit pipe having an inner volume of not smaller than the amount of the collected sample. AlthoughFIG. 1which is a view of flow paths andFIG. 2which is a view of the structure of the flow path-switching valve show an embodiment of the present invention, the present invention is not limited thereto.

Further, the automatic sampler according to the present invention is not limited to the automatic sampler for liquid chromatograph as above stated. It may be an automatic sampler for gas chromatograph, etc.

As described above in detail, the automatic sampler according to the present invention comprises the injection port and the flow path-switching valve wherein the injection port and the flow path-switching valve are connected to each other directly without interposition of any pipe. Hence, the following effects are brought about. That is, the dead volume of the flow path between the injection port and the flow path-switching valve is reduced, so that the volume of delay caused by the gradient of the flow path is reduced; the analyzing time is reduced; and the sample peak is prevented from being spread. In addition, because the pipe is omitted, the number of piping joints can be reduced. Hence, cross contamination caused by the sample remaining in fine gaps at piping joints can be reduced.