Gas separation: apparatus – Degasifying means for liquid – Heat exchanger to degasify
Reexamination Certificate
1999-07-16
2001-05-08
Walker, W. L. (Department: 1723)
Gas separation: apparatus
Degasifying means for liquid
Heat exchanger to degasify
C210S180000, C210S198200, C417S244000, C417S313000
Reexamination Certificate
active
06228153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a solvent delivery pump assembly which is used for high performance liquid chromatography (hereinafter called HPLC) systems. It removes air bubbles and gaseous components dissolved in eluent (solvent) which is separated and analyzed by the liquid chromatography, thereby allowing to make a fine and precise solvent delivery at a high speed required for HPLC.
2. Background Art
There is a tendency that HPLC used to separate components in a given sample is made more and more highly accurate. Usually in this type of HPLC, an eluent (solvent) drawn from a reservoir by a solvent delivery pump is delivered via a sample injection valve to a detecting section including a separation column. Detected signals are recorded or sent to a monitor screen. In high speed and high accuracy liquid chromatography systems (known as semi-micro HPLC and micro HPLC) which require high accuracy in delivering the eluent under a high pressure yet at a very small quantity, it is common to install such phase separator (gas/liquid separator) as an air trap or a degasser (degassing unit) on the inlet side of the solvent delivery pump in order to insure the stability of the pump.
The purpose of this type of degassing unit is to remove unnecessary gases (air and other gases) dissolved in the eluent. For example, when an electrode reduction reaction is measured, any oxygen dissolved in the eluent greatly influences its measured value. That is, the reduction reaction of the oxygen itself causes a big background current, thereby causing noises to be increased.
FIG. 5
is a block diagram of a system configuration of HPLC. An eluent
2
in a first reservoir
1
is drawn up by a pump
5
through a pipe
3
and degassed by a phase separator
4
. It is then delivered through a sample injection valve (auto sampler)
6
and a column
7
to a detector unit
8
. The eluent delivered from the detector unit
8
flows out to a second reservoir
10
as a waste eluent
9
. The reference arrow marks show the direction of the eluent delivery. Data detected by the detector unit
8
are transferred to a data processing unit
11
, wherein they are processed in a visual form or a computer processable data form to provide and store. The column
7
is accommodated in an isothermal oven
7
A to prevent the influence of external temperature. The pump
5
and the sample injection valve
6
are controlled by a system controller
12
. The phase separator
4
is installed before the pump
5
to insure the stable delivery of the eluent and the accurate analysis by removing gases dissolved in the eluent which is drawn up from the first reservoir
1
by the pump
5
.
As the other units and components consisting of this kind of high accuracy liquid chromatography system as well as the function of the whole system are well known so those explanations are omitted.
When the area of eluent delivery rate shifts from the range of 0.01-1.5 ml/min. for conventional HPLC systems to that of 1-300 &mgr;l/min. for semi-micro and micro HPLC systems, the issue of gases dissolved in eluent (so-called air trouble) which is presently a problem is much more serious in order to maintain the accuracy of eluent delivery.
This air trouble is caused by two kinds of air; one is the air contained as bubbles (so-called air bubbles) in the eluent and the other is the one dissolved in it.
Generally, the eluent is reserved in such a container as a reagent bottle (first reservoir
1
as shown in FIG.
5
). When it is drawn from the reservoir
1
directly by the pump, the reservoir and the pump are connected by a capillary tube
3
such as PTFE tube. Therefore, the eluent always passes through the capillary tube and is passed into the pump
5
. When operating the pump
5
, it is first checked whether or not there are air bubbles inside the capillary tube. If air bubbles are observed to be existing, they are removed from the tube by manual operation and then the eluent delivery is started. Even if no air bubble is recognized, problems may occur due to oxygen dissolved in the eluent in such a case that the eluent delivery needs to be stable over a long period of time in the area of the flow rates required for micro HPLC. The reason this may be so is because in the suction process of the eluent delivery pump the inside of the pump is in the state of reduced pressure, causing the dissolved oxygen in the eluent to become air bubbles which make the eluent delivery unstable.
For the above two problems, countermeasures are presently taken as explained in the following (1) and (2).
For air bubbles inside the capillary tube connected to the suction port of the pump, a small air bottle (air trap) is provided in front of the suction port, thereby separating the air bubbles and the liquid (eluent) so that the pump can draw the liquid component only.
FIG. 6
is a block diagram to explain a compositional example of the air trap. The eluent
2
in the reservoir
1
is drawn up through the capillary tube
3
by the delivery pump
5
(not shown in FIG.
6
). The air trap
4
A is installed in the capillary tube
31
before the pump
5
. The capillary tube
31
from the reservoir
1
is fed into the upper side of the hermetically sealed air bottle
4
A with its end opened, and the other capillary tube
41
connected to the pump
5
is connected to the bottom of the air bottle. If the eluent
2
containing air bubbles is transferred into the air trap
4
A, the air component (gas phase) and the liquid component (liquid phase) are separated to stay in the top and in the bottom of the air trap, respectively. The pump
5
draws only the liquid component from its bottom. The air trap
4
A is also provided with a capillary tube
32
and a valve
33
in its top to take the separated air component out of it. That means, when the pump
5
draws the eluent inside the air trap
4
A, the pressure in it is reduced. As the inside of the reservoir
1
is in the atmospheric pressure, the eluent
2
is sent through the capillary tubes
3
and
31
into the air trap
4
A. If air exists in the eluent, the components of air and liquid are separated and stored in the upper and lower portions of the air trap
4
A, respectively. Thus, the pump
5
is able to deliver the eluent alone without sucking the air. Air is gradually collected in the air trap
4
A as time goes by, which is removed suitably through the capillary tube
32
by opening the valve
33
.
For air bubbles existing inside the capillary tube connected to the suction port of the pump, a degassing unit (degasser) is installed prior to the suction port to separate the air component from the liquid (eluent) so that the pump can draw the liquid component only.
FIG. 7
is a block diagram to explain one construction example of the degasser. The eluent in the reservoir is drawn through the capillary tube
31
by the pump, and the degasser
4
B is installed in the capillary tube
31
prior to the pump
5
. The degassing module is composed of a number of tubes made of such gas permeable resin film as PTFE with multi-connectors
16
a
and
16
b
connected at their both ends. While the eluent passes through the tubes, gases dissolved in it are extracted to the vacuum chamber
13
, thereby avoiding the generation of air bubbles in the eluent delivery pump
5
during its suction process. However, mainly removed by this degasser is dissolved oxygen, and large air bubbles passing through the degasser. It apparently looks that the air trouble can be solved by using the air trap, but practically there are some points of problems that still are a cause for trouble.
The first problem is that it is not feasible to keep good conditions on the operation of HPLC system for continuous use over a long period of time.
When using the air trap, it is required to check an amount of air in the trap, which needs to be removed by manual operation if too much air is included. Under this kind of operational conditions, it is not possible to check all the time the amount of air which is gradually accumulated during the
Lackenbach Siegel
Micro Electronics Inc.
Sorkin David
Walker W. L.
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