Degassing unit

Details Degassing unit Degassing unit

2000-03-23

2001-11-20

Therkorn, Ernest G. (Department: 1723)

Liquid purification or separation

With means to add treating material

Chromatography

C210S656000, C210S188000

Reexamination Certificate

active

06319398

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a degassing unit, particularly that for high performance liquid chromatography, which makes it possible to perform a fast and precise eluent (solvent) delivery yet at a very small quantity by removing gaseous components dissolved in eluent (solvent) to be separated or analyzed with a liquid chromatograph.
2. Background Art
There is a tendency that high-speed (high-precision) liquid chromatography (hereinafter called HPLC) used to separate compounds in a given sample is made more and more highly accurate.
Usually in this type of HPLC, an eluent drawn from a reservoir by an eluent (solvent) delivery pump is delivered via a sample injection valve to a detection means including a separation column.
Shown in
FIG. 15
is a schematic diagram explaining the configuration of HPLC. An eluent
2
in a first reservoir
1
(an eluent containing vessel) is drawn up via a pipe
3
by a pump
5
and is degassed through a degassing unit
4
, and then is sent to a sample injection valve
6
(an auto sampler), to a column
7
and to a detector unit
8
. The eluent delivered from the detector unit
8
is thrown out as a waste eluent
10
to a second reservoir
9
. The 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 as required and is provided and stored in a visual form or a computer processable data form.
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 degassing unit
4
installed before the pump
5
insures a stable eluent delivery and an accurate analysis by removing gases dissolved in the eluent
2
which is drawn up from the first reservoir
1
by the pump
5
.
Other components consisting of this kind of high performance liquid chromatography and the functionality of the whole system are well known. So, explanations on these details are omitted here in this file.
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 the degassing unit
4
on the inlet side of the eluent delivery pump
5
in order to insure the eluent delivery stability of the eluent delivery pump
5
.
The purpose to install this type of degassing unit is to remove unnecessary gases dissolved in the eluent. The material used for degassing is a polytetra-fluoro-ethylene (PTFE) tube that is inactive to the eluent used yet good in eluent permeability. By flowing the eluent through this tube (hereinafter called PTFE tube or simply tube) and by reducing the pressure outside the tube, gaseous components dissolved in the eluent can be removed.
The stable micro eluent delivery is insured only because the eluent pump draws the eluent from which gaseous components are removed, and dispenses it.
Capillary electrophoresis chromatography (CEC) is a technology that is expected to be the next generation HPLC. This HPLC does not require an eluent delivery pump, but requires a degassing unit.
In the CEC type HPLC the eluent is transferred by the electro-osmosis flow that is generated by applying a high voltage to the column. When the high voltage is applied, the eluent is heated by joule heat, causing the temperature to rise. If oxygen (air) is dissolved in the eluent, bubbles are generated by this heat.
If bubbles are generated in the capillary column, no electric current is flown, thus making the separation impossible. The amount of eluent used in the CEC type HPLC is very small and is far smaller than that used in semi-micro HPLC. Consequently, a high-performance degassing unit that allows even smaller quantities is required.
FIG. 16
is a schematic cross section showing an example of a conventional degassing unit that uses a cylindrical capillary tube type degassing module. As explained in
FIG. 15
, the eluent in the first reservoir
1
is drawn via a pipe
31
by the eluent delivery pump
5
. The degassing unit
4
B is mounted on the pipe line
31
before the eluent delivery pump
5
.
In the case of the degassing unit
4
B a degassing module
16
is installed inside a vacuum chamber
13
, whose air is evacuated by a vacuum pump
15
, and the eluent delivery pump
5
is connected to an outlet pipe
41
of the vacuum chamber
13
.
The degassing module
16
consists of gas permeable films made of a number of polytetra-fluoro-ethylene (PTFE) capillary tubes, both ends of which are bundled by multi-connectors
16
a
and
16
b
. When the eluent passes through the PTFE tubes, gases dissolved in the eluent are extracted to the vacuum chamber
13
, thereby preventing gaseous bubbles from generating in the eluent delivery pump
5
while the pump
5
is drawing up the eluent.
If an attempt is made to change this degassing unit to that for micro quantity delivery, problems arise in both an internal volume of the degassing module and a structure of the module.
The internal volume of the degassing module has a standard capacity of 12ml. This volume is too large to apply to the semi-micro HPLC systems.
As the pump flow speed in semi-micro HPLC is 0.1 to 0.2 ml/min., it takes 60 to 120 minutes even in simple calculation for the eluent to pass through the degassing module. This is a considerably long time as the time of chromatographic analysis.
On the other hand, the structural problem of the degassing module is as follows. PTFE tubes, a typical degassing module material, are used in a bundle of 18 tubes with a length of 2.5 m. The eluent is distributed to each tube and flows through it.
As every tube is not the same in flow resistance, speeds for the eluent to pass through the tubes are different according to the tubes. Because of the differences of these flow speeds, the time required for the eluent to be replaced completely inside the degassing module is longer than such 60 to 120 minutes as previously mentioned.
In order to resolve such structural problem of the degassing module, I (inventor) propose the following degassing unit.
FIG. 17
shows a schematic diagram of a degassing module based on a thin film method. This figure is shown to explain another construction example of a conventional degassing unit.
FIG. 18
is a cross section view of
FIG. 17
taken along the line A—A in FIG.
17
.
100
in
FIG. 17
shows the degassing module that is a component of the degassing unit. This degassing module is accommodated in a vacuum chamber (closed console), but the illustration of the vacuum chamber is omitted here in this figure.
In
FIGS. 17 and 18
, this degassing module
100
is composed of two PTFE sheets
101
a
and
101
b
with a spacer
103
placed on their fringes as well as two stainless steel mesh sheets
102
a
and
102
b
put on the two PTFE sheets
101
a
and
101
b
, respectively. They are held by upper and lower holding frames
106
and
107
, and are fastened in one unit by tightening bolts
108
.
By means of this tightening, the fringes of the two PTFE sheets are closely contacted and form a hollow enclosure to create an internal space between them. The hollow enclosure is provided with an eluent feeding-in inlet
104
and an eluent feeding-out outlet
105
on one side (upper side of the figure) of the PTFE sheet (
101
a
).
The eluent feeding-in inlet
104
is equipped on one short side of the rectangular PTFE sheet
101
a and the outlet
105
on its other short side, respectively, thereby securing an eluent flowing pathway between the two ports which contributes to the degassing of the eluent.
The inlet
104
and the outlet
105
are composed each of a connector
109
and its fastening part
110
both of which are fitted to an opening created by getting through the PTFE sheet
101
a
and the stainless steel mesh sheet
102
a
. Preferably, the connector
109
should be made of PTFE resin, but any material may be u

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