Gas separation: processes – With control responsive to sensed condition – Gas flow rate sensed
Reexamination Certificate
2000-03-21
2001-09-25
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
With control responsive to sensed condition
Gas flow rate sensed
C095S056000, C095S082000, C095S127000
Reexamination Certificate
active
06293995
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for use in analytical instrumentation for the detection of an analyte in a carrier fluid, and in particular to analytical instrumentation having a closed-loop system for storage and reuse of hydrogen carrier gas.
BACKGROUND OF THE INVENTION
A simplified schematic view of a conventional chromatograph
100
is shown in FIG.
1
. The illustrated chromatograph
100
is representative of a Hewlett-Packard 6890 Gas Chromatograph. Analytical instruments such as the gas chromatograph
100
are known for use in determining the chemical composition of a sample which is typically injected at an inlet
112
into a carrier gas stream provided by a carrier gas source
111
through a manifold
113
. A fluid mixture of the sample and the carrier gas is directed through a separation column
114
located within an oven
116
and exposed to a controlled temperature environment provided by a heater
118
. The separation column
114
includes a stationary phase coating on the interior of the column. The interaction of the constituent compounds in the sample with the stationary phase cause differing chemical compounds in the sample to travel through the separation column at different rates and to leave the separation column at different times. The presence of compounds in the column effluent gas is sensed by a detector
124
. A detector output signal is provided to a controller
126
and a computer
122
on signal lines
128
,
130
. The compound of interest is typically called an analyte.
A significant shortcoming in the conventional gas chromatograph is due to the loss of one or more gas streams that are typically vented to the atmosphere from the inlet
112
or the detector
124
. The majority of the composition of such streams is carrier gas; for example, if the inlet
112
is constructed as a split/splitless inlet, much of the carrier gas employed by the chromatograph
100
is vented away from the inlet
112
. Accordingly, a column with a 1 ml/min flow rate and a split ratio of 100:1 will vent 100 times the amount of gas actually required to carry a sample through the column
114
for an analysis. Six liters of carrier gas at inlet pressure are typically lost to the surrounding environment during one hour of analysis. However, if the carrier gas were to be conserved, such a volume of gas could easily supply a column flow for many more hours of continuous operation.
The high rate of consumption of carrier gas observed in the conventional apparatus is one of the major factors that have inhibited the development of portable instrumentation, and has also limited the deployment of most bench top (i.e., non-portable) chromatographs in underdeveloped areas of the world where cylinders of carrier gas are in short supply.
There thus exists a need for analytical instrumentation that employs a carrier gas storage system wherein, among other factors, the flow of the carrier fluid is conserved and reused to an extent satisfactory for most analytical applications.
SUMMARY OF THE INVENTION
The advantages of the invention are achieved in a preferred embodiment of an analytical instrument, preferably provided in the form of a chromatograph, wherein a closed loop carrier gas storage system receives the gas streams that would be otherwise be vented to the atmosphere in a conventional apparatus, filters the received gas streams in order to remove the residual impurities, and stores the filtered gas stream in a gas storage system, such that the stored gas may thereafter be reused.
The preferred embodiment includes an inlet for receiving a sample and a pressurized stream of carrier gas supplied from a carrier gas reservoir, and in response, providing a sample/fluid mixture and (in some embodiments that operate a split/splitless inlet) an inlet output stream in the form of a combination of a split flow and a purge flow; a separation column located in a temperature-controlled compartment for receiving the sample/fluid mixture and for providing a column effluent stream; a detector for receiving the column effluent stream and providing in response a detector output signal and a detector output stream; and a gas storage system for filtering and storing the received gas streams for subsequent reuse. The detector generates an output signal, whereby one or more characteristics of the effluent stream that are related to the analyte of interest may be represented by the output signal.
Certain embodiments may further include a control system including a computer for sensing the volumetric flow rate of the fluid mixture entering the column and for generating a respective flow rate signal and for sensing the column input pressure and generating a respective input pressure signal, and an electronic pneumatic controller including means for receiving the flow rate signal and input pressure signal, for controlling the valve so as to control the input pressure and the volumetric flow rate of the carrier fluid.
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Agilent Technologie,s Inc.
Spitzer Robert H.
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