Measuring and testing – Gas analysis – Gas chromatography
Reexamination Certificate
1999-02-19
2001-03-27
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Gas chromatography
C356S315000, C356S417000, C436S122000, C436S123000, C436S119000, C436S172000, C436S171000, C422S089000, C422S091000
Reexamination Certificate
active
06205841
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a gas chromatograph with a flame photometric detector (FPD). More specifically, this invention relates to the gas chromatograph with the FPD which detects, in just one analysis, plural components included in a sample, each component having a different light-emitting wavelength.
Various types of detectors of the gas chromatograph are made practicable. The FPD, one of these detectors, is a detector for selectively detecting a sulfur compound and a phosphorus compound. Therefore, the FPD is used for various purposes, such as for an analysis of offensive odor elements like hydrogen sulfide, methyl mercaptun and the like, the detection of a very small quantity of sulfur included in chemicals, an analysis of residual pesticide, an analysis of biochemical elements, and the like.
FIG.3
is a schematic diagram of a detection cell of a typical FPD. A sample gas tube
10
connected to a column outlet of a gas chromatograph, a hydrogen supply tube
11
, and an air (or oxygen) supply tube
12
are connected to a nozzle
13
having a gas spouting outlet
14
directed upward. A transparent crystal cylinder
15
is placed around the nozzle
13
. The whole of the crystal cylinder
15
is covered with a heat insulation block
16
made of metal. A heater and temperature sensor, not shown in the Figure, are embedded in or attached to the heat insulation block
16
. According to a known feedback control of the heater using temperature information, the heat insulation block
16
is kept at a designated temperature. A designated part of the heat insulation block
16
is bored to define a detection window
17
. A wavelength filter
19
is placed through a cooling fin
18
outside the detection window
17
. Further outside the wavelength filter
19
, a photomultiplier tube
20
as a detector is placed. The wavelength filter
19
is designed to transmit only the light with the target wavelength corresponding to the target sample component.
An operation principle of the above mentioned FPD is as follows. Carrier gas such as nitrogen gas supplied through the sample gas tube
10
, hydrogen gas supplied through the hydrogen supply tube
11
, and air supplied through the air supply tube
12
are mixed at the tip of the nozzle
13
, then a hydrogen flame
21
is formed by combustion of this mixture. For example, when a sample component flowing out of the gas chromatograph column is introduced into the flame, it is combusted and the light having the target wavelength corresponding to the sample component is emitted. Especially, a reducing flame of peroxide emits the light with wavelengths of 394 &mgr;m and 526 &mgr;m through combustion of a sulfur compound and a phosphorus compound, respectively. The light emitted from a combustion part
22
for the sample component in the hydrogen flame
21
passes the transparent crystal cylinder
15
and reaches the wavelength filter
19
. Only the light with the target wavelength selectively passes through the wavelength filter
19
and reaches the photomultiplier tube
20
. By these steps, component detection with very high selectivity becomes possible. The crystal cylinder
15
is used for protecting the wavelength filter
19
from tarnishing over from steam or soot and the like produced by the hydrogen flame
21
.
As mentioned above, in the FPD, the light of the target wavelength which is different depending on material of the target component such as phosphorus, sulfur, and tin is emitted. In the FPD, shown in
FIG.3
, the wavelength filter
19
has to be changed depending on each different target component in order to detect the different target components. Therefore, in this single filter type of FPD, it is impossible to detect, in one analysis, both a sulfur compound and a phosphorus compound which are separated in a column to exit from the column at different times. On the other hand, there is another type of FPD which has two different wavelength filters transmitting the light of the target wavelengths corresponding to two components, respectively, and two photomultiplier tubes detecting the light transmitted by the wavelength filters, respectively. In this dual filters type of FPD, a phosphorus compound and sulfur compound, which are separated in the column to exit at different times, are combusted in a hydrogen flame. The light with each of the target wavelengths corresponding to phosphorous and sulfur compounds emitted from the flame is selectively transmitted through a respective one of each of the wavelength filters, and each transmitted light is detected by a respective one of each of photomultiplier tubes.
In the FPD, shown in
FIG.3
, when a mixture rate of hydrogen gas and air changes, the size of the hydrogen flame
21
changes and also the temperature distribution in the flame changes. Since each mechanism for emission of light in sulfur, phosphorus, and tin, is different from the others, each mixture rate of hydrogen gas and air for maximizing a light amount emitted by combustion is also different depending on each component combusted. Therefore, it is desirable to set a proper flow amount of hydrogen and air supplied to the nozzle
13
depending on the target component in order to obtain a large amount of light and to enhance the detection. In the single filter type of FPD, shown in
FIG.3
, the most suitable combustion can be realized by changing the wavelength filter into a proper wavelength filter for the target component and resetting proper flow amounts of hydrogen gas and air depending on the target component.
On the other hand, when plural components are measured in one analysis (one sample injection) with the dual filters type of FPD, each flow amount of hydrogen gas and air is set so that a mixture rate of them becomes intermediate among the optimum mixture rates of those target components. In this case, since the combustion of the components is not optimum and each amount of light emitted is not maximum, the detection for each of the target components is not good.
SUMMARY OF THE INVENTION
This invention is achieved to solve the above problems. An object of this invention is to provide a gas chromatograph with a FPD which makes it possible to improve its detection by carrying out the optimum combustion for every target component in a hydrogen flame when plural components are measured in one analysis.
This invention is a gas chromatograph, with a flame photometric detector having a hydrogen flame formed by combusting a mixture of hydrogen and oxygen, a sample tube for introducing a sample to said flame, at least two different wavelength filters transmitting only the light with the target wavelengths corresponding two target components, respectively, at least two optical detectors detecting said light transmitted through said filters, respectively, a chromatographic column connected to the sample tube, in which each of the components included in the sample are separated, a hydrogen gas tube supplying said flame photometric detector with the hydrogen, a oxygen gas tube supplying said flame photometric detector with the oxygen, a first mass flow controller controlling a flow rate of said hydrogen, a second mass flow controller controlling a flow rate of said oxygen, and control means for controlling said first mass flow controller or/and second mass flow controller to change a mixture rate of the hydrogen gas and the oxygen timewise so that components introduced into said flame combusts most suitably, respectively.
When plural components in the sample are predetermined, the time when each of the components comes out of the column, which is called retention time, is predictable. Flow amounts of hydrogen gas and air or oxygen are set to the control means to be the most suitable mixture rate of them for combustion of the mixture, that is, for detection of each component. Each predicted the retention time when each component comes out is also set to the control means. Through the analysis, the control means controls the first and second flow controller based on the mixture rates and the predicte
Armstrong, Westerman Hattori, McLeland & Naughton
Miller Rose M.
Shimadzu Corporation
Williams Hezron
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