This invention relates to a gas CHROMATOGRAPH for analyzing elements in a sample by introducing the sample into a chromatographic column through a sample introduction part and separating the elements through the column.
In an analysis of a sample by a gas chromatograph, the sample is injected into a sample introduction part with carrier gas also introduced therein. The sample joins with the carrier gas at the sample introduction part and is carried by the carrier gas into a chromatographic column. The sample is separated into its respective elements by interaction between a liquid, with which the inside surface of the column is lined, and the carrier gas. Differences among distribution coefficients of the elements cause this separation. Each of the elements exiting the column is introduced into a detection part connected to the outlet of the column, resulting in a chromatogram.
FIG. 1 is a schematic diagram of a typical gas chromatograph. A sample introduction part 1 evaporates a liquid sample injected therein. The sample introduction part 1 also introduces the carrier gas therein. The sample is delivered by the carrier gas into a chromatographic column 2 which is connected to the sample introduction part 1. A chromatographic column 2 separates the sample into its respective elements. A thermostatic chamber 3 controls temperature of the chromatographic column 2. A detection part 4 detects each element of the sample coming out of the chromatographic column 2. A carrier gas cylinder 5 supplies the carrier gas for the sample introduction part 1 through a carrier gas flow path 5a. A flow control valve 6 is placed in the carrier gas flow path 5a and controls a flow rate of the carrier gas. A split flow path 7 is connected to the sample introduction part 1 and exhausts part of the sample and the carrier gas. A filter 8 is placed in the split flow path 7 and prevents a needle valve 9 and split flow path 7 from becoming clogged. The needle valve 9 following the filter 8 is placed in the split flow path 7.
The sample introduced into the sample introduction part 1 is carried into the chromatographic column 2 by the carrier gas which is supplied by the carrier gas cylinder 5. The flow rate of the carrier gas is controlled by the flow control valve 6. The sample is separated in its respective elements through the chromatographic column 2. Each element of the sample coming out of the chromatographic column 2 is detected by the detection part 4.
Since only a small amount of sample can be introduced into the chromatographic column 2, almost all the sample and carrier gas are exhausted through the split flow path 7. The ratio of the amount of the sample exhausted through the split flow path 7 to the amount of the sample introduced into the chromatographic column 2 is called a split ratio. The split ratio is determined by the ratio of a flow path resistance of the chromatographic column 2 to that of the needle valve 9.
In the gas chromatograph, shown in FIG. 1, when the filter 8 is clogged, unnecessary pressure corresponding to a flow in the split flow path 7 is generated by the filter 8 even though the needle valve 9 may be left fully open. In such a case, it becomes difficult to set a pressure in the sample introduction part 1 properly low, and is therefore difficult to set the sample flow rate in the column 2 low. Therefore, each element in the sample does not separate suddenly from the other elements resulting in poor detection of the elements in the sample. To avoid such poor detection, an operator must often take the filter 8 off the split flow path 7 and observe whether the filter 8 is clogged to determine whether the filter 8 needs to be changed.
An object of the invention is to solve the above problems. Another object of this invention is to provide a gas chromatograph which can inform operators of a filter in a split flow path being clogged without taking the filter off the split flow path. Another object of this invention is to provide a gas chromatograph which can inform operators of the extent to which a filter is clogged without taking the filter off the split flow path. Another object of this invention is to provide a gas chromatograph which can instruct an operator to exchange a clogged filter without taking the filter off the split flow path.
A gas chromatograph analyzes elements in a sample by introducing the sample into a chromatographic column through a sample introduction part and separating the elements through the column, having a pressure measuring means for measuring a pressure in the introduction part, a flow control means, placed in a carrier gas flow path supplying a carrier gas into the introduction part, for controlling a flow rate of the carrier gas, a flow measuring means, placed in the carrier gas flow path, for measuring the flow rate of the carrier gas, a split flow path, connected to the sample introduction part, exhausting part of the carrier gas and the sample from the sample introduction part, a filter, placed in the split flow path, protecting the split flow path from being clogged, an exhaust valve, placed in the split flow path and following the filter, adjusting a flow rate in the split flow path, a monitor screen displaying information related to the filter, a controller calculating a flow path resistance of the filter based on a flow path resistance of the column, a pressure measured by the pressure measuring means in the exhaust valve opening, and a flow rate measured by the flow measuring means in the exhaust valve opening, the controller controlling the monitor screen to display information, by which necessity of exchange of the filter can be determined, based on the filter resistance.
The controller can obtain the column resistance xe2x80x9crxe2x80x9d based on the following formula by using temperature of the column (t), inside diameter of the column (D),length of the column (L), pressure at the inlet of the column (P1), the pressure of the atmosphere (PA), viscosity (U) in the column, and a proportional coefficient (K1).
In the following sentence, pressure is described in the gauge pressure scale, and temperature is described in the Celsius temperature scale.
r=P1/F0
F0=K1xc3x97(((D2)/L)xc3x97(D2)xc3x97(P1+2xc3x97PA)xc3x97P1)/(Uxc3x97(273+t))
The controller may also obtain the column resistance xe2x80x9crxe2x80x9d from the following formula, where xe2x80x9cfxe2x80x9d is a slow rate measured by the flow measuring means when the exhaust valve is closed and P is a pressure measured by the pressure means when the exhaust valve is closed.
r=P/f
The controller may calculate the filter resistance from a following formula based on the column resistance xe2x80x9crxe2x80x9d, a pressure xe2x80x9cPxe2x80x9d measured by the pressure measuring means in the exhaust valve opening, and a flow rate xe2x80x9cFxe2x80x9d measured by the flow measuring means in the exhaust valve opening.
R=rxc3x97P/(rxc3x97Fxe2x88x92P)
The controller compares the filter resistance to a preset resistance corresponding to a state in which the filter is clogged, and when the filter resistance becomes greater than the preset resistance, the controller indicates that the filter should be exchanged (e.g., on a monitor).
The pressure measuring means may be a pressure sensor sending an output thereof to the controller. The flow control means may be a flow control valve controlled by the controller. The flow measuring means may be a flow sensor sending an output thereof to the controller. The exhaust valve may be controlled by the controller. In this structure, the controller controls the exhaust valve to open, then reads outputs of the pressure sensor, and the flow sensor, and calculates the filter resistance.
The pressure measuring means may be a pressure gauge. The flow control means may be a flow valve. The flow measuring means may be a flowmeter. In such a case, pressures in the sample introduction part and a flow rate of the carrier gas are input into controller by an operator who reads them through the pressure gauge and flowmeter.
A buzzer 21 may be used instead of the monitor screen displaying information about necessity of exchange of the filter on the monitor screen. The controller makes the buzzer 21 sound when the controller finds necessity of exchange of the filter is determined based on the filter resistance.
A light 20 maybe used instead of the monitor screen displaying information about necessity of exchanging of the filter on the monitor screen. The controller makes the light 20 turn on when the controller determine it is necessary to exchange the filter based on the filter resistance.
The gas chromatograph mentioned above makes it possible to notify an operator of the extent to which the filter in a split flow path is stuffed without taking the filter off the split flow path. It is also possible to instruct an operator to exchange the filter in the split flow path. Therefore, this invention makes it possible to avoid carrying out the analysis with a clogged filter, that is, to avoid carrying out the analysis under a wrong split ratio.