Liquid analyzing apparatus

In a liquid chromatographic analyzer apparatus, there is possibility that a flow cell is damaged when a flow passage is blocked and the inner pressure is increased. In order to prevent damage to the apparatus, liquid is prevented from leaking inside the apparatus. The liquid is discharged externally through a liquid discharging tube. A spring member is provided between the flow cell and the seal in a tube connecting portion to allow liquid to leak when the pressure is increased. Further, a light-proof tube for blocking light is connected to the flow cell to allow the leaked liquid to flow through the light-proof tube.

BACKGROUND OF THE INVENTION 
The present invention relates to a liquid analyzing apparatus having a 
liquid analyzing flow cell such as a liquid chromatographic analyzer and a 
flow injection analyzer. 
A common liquid chromatographic analyzer is constructed such that a liquid 
or a sample to be used for analysis is pumped using a pump having a high 
delivery pressure because a column of the liquid chromatographic analyzer 
has a large flow resistance. 
A flow cell is connected in the downstream of the column to measure the 
separated sample. 
However, there are some cases where the delivery pressure becomes so high 
due to change in various conditions that the column and the flow cell or 
the flow passage between them might be damaged. 
In order to solve the disadvantage, an invention is disclosed in Japanese 
Patent Application Laid-Open No.6-160271 (1994). In Japanese Patent 
Application Laid-Open No.6-160271 (1994), a bypass flow passage having a 
flow control valve is provided in parallel to the flow passage connected 
to the flow cell. The pressure applied to the flow cell is then removed by 
controlling the flow control valve based on a value indicated a pressure 
gauge detector detecting the pressure from a liquid delivery means. 
However, in a liquid chromatographic analyzer having a small liquid flow 
rate, the volume of the liquid flow passage between the column and the 
flow cell should be made small such that the delivered liquid to the 
liquid flow cell does not remain to suppress diffusion of the sample. 
Therefore, it is impossible to connect a protecting means against the 
occurrence of abnormal pressures such as a pressure gauge or a safety 
valve, as described in Japanese Patent Application Laid-Open No.6-160271, 
which increases the volume the flow passage. 
That is, a means for detecting abnormality cannot be installed and the 
pressure increase due to the occurrence of abnormal pressure cannot be 
detected even when abnormal pressures occur. Therefore, there has been a 
problem in prevention which cause the flow cell or the tube to become 
damaged. 
SUMMARY OF THE INVENTION 
The present invention is to solve the above problems and to provide a 
liquid analyzing apparatus having a protecting means against the 
occurrence of abnormal pressures without increasing the volume of a flow 
passage. 
A liquid analyzing apparatus comprising a liquid supplying passage, a 
liquid discharging passage, and a liquid flow passage. The liquid flow 
passage is formed by providing a liquid analyzing flow cell between the 
liquid supplying passage and the liquid discharging passage. A pressure 
release port is provided in the liquid flow passage which releases 
pressure from the liquid supplying passage with a pressing force exceeding 
a certain value determined by a maximum pressure applied by the liquid 
flow cell to the flow cell, the liquid supplying passage or the liquid 
discharging passage. 
The liquid supplying passage or the liquid discharging passage is 
constructed in a two-layer structure, having an end portion of an outer 
layer is constructed to be liquid-proofed and end portion of an inner 
layer pushed to the flow cell using a spring member or the like. 
Further, the outer layer of the liquid discharging passage is formed of a 
light-proof material. 
Since a seal structure using the spring member is provided in a connecting 
mechanism between the flow cell and a tube or flow passage the liquid 
flowing in the flow passage is discharged from the connecting portion when 
the pressure is increased above an allowable value, therefore, it is 
possible to prevent the pressure from excessively increasing. 
The tube is formed in a double tube structure. The tube in the outer layer 
is also connected to an outer wall of the flow cell to allow the 
discharged liquid to flow between the tube in the center and the tube in 
the outer side. By this construction, the discharged liquid can be 
conducted outside the analyzing apparatus together with the liquid flowing 
in the center tube. 
In that case, by forming the tube in the outer side with a light-proof 
material, the light-proof function for the tube in the center can be 
obtained at the same time, and the number of tubes extending from the 
apparatus can be decreased. 
In a liquid analyzing apparatus, in order to protect against damage to the 
flow cell or the tubes when the fluid flow resistance of the fluid flow 
passage is abnormally increased by the blockage of the fluid flow passage, 
a protection mechanism against the abnormal pressure can be utilized 
without increasing the volume of the fluid flow passage. 
Even if liquid is discharged outside the flow cell while operating the 
protective function during an abnormal pressure, the liquid can be 
discharged outside the analyzing apparatus without internal leakage. 
In an analyzing apparatus using light, it is necessary to block light from 
entering externally the apparatus. The tubes extending outside from the 
apparatus can be made light-proof, and the number of tubes can be 
minimized.

DETAILED DESCRIPTION 
Initially, description will be made on an embodiment of an apparatus for 
performing absorptiometric analysis of liquid to which the present 
invention is applied. 
FIG. 1 is a view showing the construction of a cell unit 1 in accordance 
with the present invention. In an absorbance detector in liquid 
chromatographic apparatus, cell unit 1 is mounted in a spectroscope 20 as 
shown in FIG. 2, and has a function of conducting liquid flowing out from 
a tube 10 outside spectroscope 20 into the spectroscope 20 and allowing 
the liquid to flow a given distance in a light path. 
In FIG. 2, light emitted from a lamp 22 is gathered by a light-gathering 
mirror 21, and scattered into individual wavelengths by a diffraction 
grating 24 after passing through a slit 23. Then a part of the light 
enters into a light receiving element 26 to be directly converted into an 
electric signal. After passing through cell unit 1, the other light enters 
into a light receiving element 25 to be converted into an electric signal. 
By obtaining the ratio of the two electric signals, the light absorptivity 
of liquid flowing through the inside of a fluid flow cell in cell unit 1 
is measured. 
As is described above, in liquid chromatographic apparatus, it is necessary 
to conduct liquid existing externally into spectroscope 20 to be measured. 
Therefore, it is possible that liquid flows into cell unit 1 of 
spectroscope 20 through a liquid flow passage. 
Since the liquid flows out to a waste liquid bottle (drain) outside 
spectroscope 20 through an outlet tube 10 after completion the light 
absorptivity measurement in cell unit 1, it is possible that light enters 
through a side of the flow passage. 
Since the quantity of light is measured in spectroscope 20, external light 
must be prevented from entering spectroscope 20. Therefore, a light-proof 
tube 9 covers outlet tube 10 preventing external light from entering the 
spectroscope 20 through outlet tube 10 or a gap between outlet tube 10 and 
a packing 12. Further, by forming tubing in a two-layer structure (i.e. 
light-proof tube 9 and outlet tube 10), and consequently decreasing the 
number of tubes, the possibility of conducting external light to flow cell 
30 is decreased. This contributes to decreasing the measurement error due 
to external light entering flow cell 30. 
Although the two-layer structure, which is one of the characteristics of 
the present invention, is employed only in the outlet tube 10, it may also 
be employed in an inlet tube 2. 
A light-proof tube 3 is constructed so that a seal member is tightened to 
the cell unit 1 using a screw 4 to prevent the liquid from leaking. 
Similarly, light-proof tube 9 is also constructed so that a seal member 6 
is tightened to cell unit 1 using a screw 8 to prevent the liquid from 
leaking. 
However, the outlet tube 10 contained in light-proof tube 9 is connected to 
flow cell 30 contained in the cell unit 1 through a spring 7 and seal 
member 6. 
FIG. 3 is an enlarged view of the flow cell 30 explaining the connections. 
Flow cell 30 is closed with window plates 31 and 32 to form a light path. 
Flow cell 30 is mounted in a holder 37 and fixed to fixing plates 39 and 
40 through a seals 35 and 38. 
Light-proof tube 3 is tightly fixed to flow cell 30 with screw through a 
liquid-proof washer 34. 
Screw 8 connecting light-proof tube 9 to cell 30 is connected to holder 37. 
An end portion of outlet tube 10 located in light-proof tube 9 is pushed 
towards flow cell 30 through washer 36 with spring 7 attached to screw 8 
(hereinafter, this pushed portion is referred to as "seal portion 6"). 
Outlet tube 10 is tightly fixed to flow cell 30 with screw 8 through washer 
36. Therefore, liquid flowing through inlet tube 2 does not leak through 
the light path in the cell but flows to the outlet tube 10. 
Incident light 27 to cell until passes through the light path in flow cell 
30 and goes out as an emitted light 28. 
With the construction, when the pressure in flow cell 30 is abnormally 
increased, a gap is formed between seal portion 6 and flow cell 30 to leak 
the liquid, and consequently the cell unit 1 and tubes 2 and 10 are 
prevented from damage. 
Light-proof tube 9 is connected to screw 8, and the leaked liquid, 
therefore, flows between light-proof tube 9 and outlet tube 10. The leaked 
liquid is conducted outside the spectroscope 20 without leaking into 
spectroscope 20. Since the outlet tube 10 is commonly connected to the 
waste liquid bottle (drain), the leaked liquid can be conducted to the 
waste liquid bottle (drain) by extending the light-proof tube 9 beyond 
outlet tube 10 without installing another tube. Since the leaked liquid 
does not leak into spectroscope 20 when liquid is leaked, degradation or 
fouling due to the leaked liquid does not occur in the optical system. 
FIG. 4 is an enlarged view of the vicinity of the seal portion 6. 
When internal pressure of the flow passage is increased due to any 
abnormality, spring 7 is contracted and liquid leaks from the liquid flow 
passage between the cell holder 37 and seal portion 6 as shown in the 
figure. Since light-proof tube 9 is connected to screw 8, liquid 42 leaked 
around spring 7 flows between the light-proof tube 9 and outlet tube 10. 
The space between light-proof tube 9 and outlet tube 10, to be called the 
second waste liquid passage, may be provided by using the two-layer tube 
structure as in the above embodiment, but may be also provided by 
arranging a new tube in addition to the existing waste liquid passages. As 
a detailed example, the connection portion of flow cell 30 and the new 
tube is constructed in the same manner as the above embodiment with the 
two-layer tube branched in a middle portion forming an inner layer space 
and an outer layer space. With this construction, by looking through which 
waste liquid passage of the two the waste liquid flows out, it is possible 
to judge whether an abnormal pressure is applied to the flow cell or not. 
Further, with this construction, liquid 42 does not spill in the connecting 
portion of the flow cell 30 and the tubing where the liquid 42 is apt to 
leak by nature. 
Although the above embodiment according to the present invention is applied 
to an absorbance detector, the same effects can be attained by applying 
the present invention to an fluorescent detector or a luminescent 
detector. Further, the same effects can be also attained by applying the 
present invention to an electric conductivity detector. 
FIG. 5 shows a flow cell 53 in an electric conductivity detector to which 
the present invention is applied. 
Liquid enters flow cell 53 through a light-proof tube 50, and the liquid 
after its electric conductivity is measured is directed to an outlet tube 
62. The outlet tube 62 is tightly pushed to a cell body 54 with a spring 
60. When the inner pressure of flow cell 53 is increased by any reason, 
the liquid is discharged through the tightly attached portion. 
Since the outlet tube 62 is covered with a tube 63 and connected to a screw 
61, leaked liquid flows between tube 62 and tube 63 to goes outside and 
does not leak inside the apparatus. 
Further, as shown in FIG. 6, two tubes in the inlet and in the outlet are 
formed in a double tube structure to use the passage between the center 
tube and the outer tube as a waste liquid flow passage, and both of the 
waste liquid flow passages are connected through a cell holder 65. With 
this construction, by allowing cleaning liquid 66 to flow from one end of 
the waste liquid flow passage, the cleaning liquid cleans the cell flow 
and the connecting portion and then flows outside. Therefore, the waste 
liquid flow passage and a spring mechanism can be cleaned from the outside 
without disassembling the cell flow. 
FIG. 7 is a view showing a detecting means for detecting whether liquid 
flows between the light-proof tube and the inlet tube or between the 
light-prof tube and the outlet tube. 
In the embodiments described above, when pressure exceeding a certain 
pressure value is applied to the flow cell, the liquid is leaked between 
the light-proof tube and the inlet tube or the outlet tube in order to 
release the pressure exceeding the certain pressure value. 
The embodiments according to the present invention described above are 
constructed in such that the leaked liquid does not spill over the 
measuring apparatus even if leakage of the liquid is large. In a case 
where the leakage of the liquid is extremely large, it is necessary to 
confirm the cause such as abnormality in the tube or blockage of the flow 
passage. However, in the above embodiment where the waste liquid flow tube 
has the two-layer structure, it is difficult to judge from which tube the 
liquid leaking, the inner or the outer because of using the light-proof 
tube. 
The construction shown in FIG. 7 is to solve the problem. Conductive 
connectors 104, 105 connected to an electrode 100 and an electrode 101 
respectively are arranged in the waste liquid flow passage 103 between 
light-proof tube 9 and outlet tube 10 through an insulator plate 102. A 
resistivity measuring means, not shown, is connected between the 
electrodes 100 and 101. 
When liquid flows in the waste liquid flow passage in this structure, that 
is, when pressure is released to the second flow passage of the waste 
liquid flow passage in order to protect the flow cell, the electrodes 100 
and 101 are conducted by the flowing waste liquid to react to the 
resistivity measuring means connected. With this reaction, it is possible 
to confirm the presence or absence of the waste liquid flow. 
In a liquid chromatographic analyzer, liquid is pumped at several tens MPa 
because of using a column. However, the flow passage and the cell in the 
downstream of the column are generally constructed using materials not 
requiring pressure resistivity since the flow passage in the downstream of 
the column is in a low pressure. When an abnormal condition occurs in the 
downstream of the column, damage in the cell or the piping tubes cannot be 
avoided. However, according to the present invention, it is possible to 
prevent the damage since the construction can prevent pressure increase at 
occurrence of an abnormal condition. Further, in a conventional apparatus, 
when damage occurs in the flow passage, the inside of the spectroscope is 
fouled with the leaked liquid and the apparatus sometimes becomes out of 
use or is degraded in its performance. In the present invention, the 
leaked liquid can be easily conducted to a waste liquid bottle without 
leaking inside the spectroscope. 
When the tube is broken, the liquid does not leak outside since the tube is 
formed in double tube structure. Therefore, the reliability is improved. 
Further, since these effects can be attained by not providing additional 
tubes, the construction can be made simple. 
When leakage occurs, it is required to disassemble and clean the apparatus 
since the liquid is apt to crystalize at this leakage position. In the 
present invention, since the cleaning can be easily performed by merely 
allowing the cleaning liquid to flow through the waste liquid flowing 
passage, the maintenance can be easily performed.