Measuring and testing – Gas analysis – Gas chromatography
Reexamination Certificate
2001-06-01
2003-06-10
Kwok, Helen (Department: 2856)
Measuring and testing
Gas analysis
Gas chromatography
C073S023420, C210S198200, C095S089000, C422S089000
Reexamination Certificate
active
06575014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to micro-machined back-flush injectors for gas chromatography. The present invention also relates to methods for manufacturing and operating micro-machined back-flush injectors.
2. Description of the Related Art
FIG. 1
illustrates a back-flush injector
10
according to the related art. The injector
10
includes a carrier gas inlet
20
connected to a main carrier gas loop
30
that is terminated at a fore-flush valve
35
.
Off-shooting from the main carrier gas loop
30
is a reference column loop
40
that terminates at a reference column inlet
50
. Also, off-shooting from the main carrier gas loop
30
is a pre-column back-flush loop
60
that terminates at a back-flush valve
70
. A gas chromatography reference column (not shown) is positioned external to the injector
10
and operably connected to the reference column inlet
50
. The reference column, typically used in conjunction with a thermal conductivity detector (not shown), enhances the detector signal and the overall sensitivity of the gas chromatography system.
The back-flush valve
70
is connected to an analytical column inlet channel
80
and a pre-column outlet channel
85
. The analytical column inlet channel
80
leads to a gas chromatography analytical column (not shown) that is positioned externally to the injector
10
. The pre-column outlet channel
85
leads to a pre-column (not shown) that will be discussed below.
A sample inlet
90
is also illustrated in FIG.
1
. The sample inlet
90
is connected to an inlet channel
100
that, in turn, is connected to a sample valve
110
. The sample valve
110
connects the inlet channel
100
to a dead volume channel
120
that extends to an injection valve
130
.
One function of the injection valve
130
is to control flow between a pre-column inlet channel
135
, that connects to the pre-column discussed above, and a fixed sample loop
140
, that extends to the fore-flush valve
35
. The fore-flush valve
35
regulates flow between the main carrier gas loop
30
, the fixed sample loop
140
, and a sample chamber
150
. The back-flush valve
70
controls flow from the pre-column back-flush loop
60
into the analytical column inlet channel
80
and the pre-column outlet channel
85
. The functions of these valves will be elaborated upon further when the operation of the injector
10
is discussed.
The sample chamber
150
terminates at a sample chamber outlet
160
that itself is connected to a switch solenoid
170
, which is external to the injector
10
. The switch solenoid
170
can either be opened to a carrier gas pressure source
180
or a pump
190
that leads to a vent
200
. The pressure of gas in the carrier gas pressure source
180
is approximately the same as the pressure of the gas at the carrier gas inlet
20
. The carrier gas pressure source
180
, when allowed by the switch solenoid
170
to be connected to the sample chamber outlet
160
, delivers carrier gas into the injector
10
.
During gas chromatography analysis, a carrier gas at a regulated gas pressure is delivered by an outside source to the injector
10
through the gas carrier inlet
20
. This carrier gas fills the main carrier gas loop
30
, the reference column loop
40
and the pre-column back-flush loop
60
. Carrier gas from the same outside source is also delivered to the carrier gas pressure source
180
.
During operation, the injector
10
injects a gaseous sample to be analyzed via gas chromatography through the pre-column and analytical column discussed above. In order to properly inject the sample, the injector
10
uses five stages of operation. These stages include sampling, dwelling, sample compression, injection, and back-flushing.
During the operation of gas chromatograph and of the injector
10
, a carrier gas such as, but not limited to, helium, hydrogen and argon, is delivered into the injector
10
through the carrier gas inlet
20
and fills the main carrier gas loop
30
, the reference column loop
40
and the pre-column back-flush loop
60
. The fore-flush valve
35
does not allow the carrier gas to flow into the fixed sample loop
140
or the sample chamber
150
. The reference column inlet
50
allows some carrier gas to flow into the reference column. The carrier gas that enters the reference column does not return to the injector
10
.
The back-flush valve
70
is also normally open during the idling stage (before the sample is introduced into the injector
10
) and allows the carrier gas in the pre-column back-flush loop
60
to enter and fill the analytical column inlet channel
80
and the pre-column outlet channel
85
. However, whether the back-flush carrier gas can travel into the fixed sample loop
140
is dependent on the status of the injection valve
130
. When the injection valve
130
is open to the pre-column inlet channel
135
, the carrier gas can then be delivered to the fixed sample loop
140
and the sample chamber
150
. This flow is known as back-flushing.
The injector
10
can be set to allow back-flushing in the idling stage or can be set to not conduct back-flushing in order to reduce the consumption of the carrier gas. The carrier gas flow that passes through the analytical column inlet channel
80
proceeds to enter the analytical column, passes the detector (not shown), and does not return to the injector
10
.
During the sampling stage, the sample valve
110
is opened and the pump
190
starts. Alternately, the pump
190
can be started earlier and the sample valve
110
can be opened subsequently. As another alternative, if the sample stream has a positive pressure, use of the pump
190
may not be needed.
Regardless of the alternative chosen, an inflow of gaseous sample from the sample inlet
90
enters and fills the inlet channel
100
, passes through the sample valve
110
and fills the dead volume channel
120
. The injection valve
130
allows the sample to fill the fixed sample loop
140
but does not allow flow of the sample into the pre-column inlet channel
135
.
After the gaseous sample has moved through the fixed sample loop
140
, it does not enter into the main carrier gas loop
30
because the fore-flush valve
35
is closed to this path. The sample can only travel into the sample chamber
150
and exits the injector
10
via the sample chamber outlet
160
. Further, because the switch solenoid
170
is opened to the pump
190
during the sampling stage, the sample then travels through the pump
190
and exits the gas chromatographic instrument via the vent
200
.
After the sampling stage, the sample valve
110
closes and the pump
190
stops drawing the sample into the injector
10
. After approximately 100-500 milliseconds, the sample pressure in the fixed sample loop
140
and sample chamber
150
are set to be in equilibrium with the ambient pressure. This is known as the dwelling stage. Sample compression then follows.
During the compression stage, the switch solenoid
170
is actuated to open to the carrier gas pressure source
180
and a stream of carrier gas is delivered to the sample chamber
150
via the sample chamber outlet
160
. Since the carrier gas has a higher pressure than the sample which has been set to be at ambient pressure during the dwelling stage, the carrier gas compresses the sample toward the fore-flush valve
35
, the fixed sample loop
140
, the injection valve
130
, the dead volume channel
120
, and the sample valve
110
. Furthermore, during the compression stage, the fore-flush valve
35
does not allow the compressing sample to enter the main carrier gas loop
30
.
During the injection stage, the injection valve
130
allows flow of the sample into the pre-column inlet channel
135
. Also, the fore-flush valve
35
allows carrier gas from the carrier gas inlet
20
to travel from the main carrier gas loop
30
into the fixed sample loop
140
and sample chamber
150
. However, since carrier gas from the carrier gas pressure source
180
is still compressing the sample, the only dir
Lo Chi K.
Wang Tak K.
Agilent Technologie,s Inc.
Kwok Helen
Wiggins David J.
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