Sample separator having impedance interface detector

The sample separator including a first suction nozzle, serving also as an electrode, for extracting one of first and second components each having an impedance different from each other, a second suction nozzle, serving also as an electrode, for extracting the other component, a nozzle driving member for ascending/descending the nozzles as one unit, and an interface detecting member for detecting an interface between two components. The interface detecting member further including an impedance detector for detecting an impedance between the two nozzles serving also as the electrodes, a storing section for storing a first threshold value to detect the first component, and an operation control member for comparing the first threshold value stored in the storing member with a detected value obtained by the impedance detector, and for controlling the nozzle driving member based on a result of the comparison.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a sample separating device, more 
specifically, a device for separating the components of a blood sample 
from each other. 
2. Description of the Related Art 
Generally, in the analysis of a blood sample, the blood sample is 
centrifuged, and the centrifuged components (blood plasma and blood cell, 
or serum and blood clot) are separately collected. A separating device of 
this type has an interface detector, and the interface between components 
adjacent to each other is detected by the interface detector. 
FIG. 7 shows the main portion of the separating device. The separating 
device includes a plasma suction nozzle 4 and a blood cell suction nozzle 
5, which are integrally set to a holder 6. Both nozzles 4 and 5 are 
connected to an impedance detector 7. The nozzles 4 and 5 are made of a 
conductive material, and serve also as electrodes. The nozzles are also 
connected to a suction driving source (not shown). The holder 6 is moved 
downward by a holder driving member (not shown). 
As the holder 6 descends, both nozzles 4 and 5 approach a test tube 1, and 
reach a blood sample 8 in the test tube 1. While the nozzles 4 and 5 are 
descending, the impedance between the nozzles 4 and 5 is detected by an 
impedance detector 7. When the output value from the impedance detector 7 
reaches a predetermined threshold value for the plasma detection, the 
holder 6 stops and a plasma component 2 is taken in from the plasma 
suction nozzle 4. 
After the suction of the plasma component, the descent of the nozzles 4 and 
5 is started once again. When the output value from the impedance detector 
7 reaches a predetermined threshold value for the blood cell detection, 
the holder 6 stops and a cell component 3 is taken in from the cell 
suction nozzle 5. 
For a simple explanation, the holder driving means for the holder 6 and the 
comparator are not shown in FIG. 7. 
FIG. 8 is a diagram showing a typical example of the relationship between a 
nozzle position and an output from the impedance detector 7. As the tip 
end of each of the nozzles 4 and 5 proceeds through the air, the plasma 
component, and the blood cell, the impedance significantly varies, as 
shown in the figure. The impedance is at the highest level when the tip 
ends of the nozzles 4 and 5 are both in the air, and is at the lowest 
level when in the plasma component 2. When the tips of the nozzles 4 and 5 
are located in the blood cell component 3, the impedance is somewhere 
between the two levels. In the figure, X and Y represent standard plasma 
impedance and blood cell impedance, respectively. 
Before the separation of the components, a threshold value, S.sub.1, for 
plasma detection and a threshold value, S.sub.2, for blood cell detection 
are determined. The value S.sub.1 is set lower than the value S.sub.2. The 
impedance having a value of S.sub.1 indicates that the plasma suction 
nozzle 4 has reached the plasma component 2. When this indication is 
detected, the plasma component 2 is taken in. The nozzles 4 and 5 further 
descend and when the impedance exceeds the value S.sub.2, which indicates 
that the blood cell suction nozzle 5 has reached the blood cell component 
3, the cell component 3 is taken in. 
It should be noted here that the variation of the impedance is not always 
constant for any type of blood samples, but each sample has its own 
variation characteristic of impedance. If the threshold values S.sub.1 and 
S.sub.2 are set at a constant for any blood samples regardless of the 
unique variation characteristic of each sample, it is difficult to 
accurately detect the interface between a plasma component 2 and a blood 
cell component 3. 
For example, when a detected blood cell impedance Y.sub.1 is much lower 
than a standard value (indicated by dot line 9a), and is even lower than 
the threshold value S.sub.2 for a blood cell components, the blood cell 
component 3 cannot be detected from the S.sub.2 value. 
As shown in FIG. 9, a blood cell component 3 having such a low impedance 
can be detected by setting the S.sub.2 value lower than Y.sub.1. However, 
in order to detect the plasma 2, the S.sub.1 value must be set even lower 
than S.sub.2. If the S.sub.1 value is simply set at a low level, S.sub.1 
may be lower than X.sub.1. Therefore, in the case where the detected 
plasma impedance X.sub.1 is much higher than the standard plasma impedance 
X (dot line 9b), the plasma component cannot be detected. 
In general, plasma suction nozzles 4 and 5, which are mass-produced, do not 
have exactly the same impedance, but the impedance varies from one to 
another. The impedance of each nozzle also varies with time (i.e. aging of 
nozzles). Other than the unique characteristic of each blood sample, the 
above factors cause an increase in the plasma impedance X.sub.1. 
The present invention has been proposed in consideration of the above 
drawbacks of the conventional technique, and the purpose of the invention 
is to provide a sample separator capable of accurately detecting the 
interface between components adjacent to each other regardless of the 
difference between samples in characteristics. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a sample separator 
comprising: a first suction nozzle, serving also as an electrode, for 
extracting one of first and second components each having an impedance 
different from each other; a second suction nozzle, serving also as an 
electrode, for extracting the other component; a nozzle driving member for 
ascending/descending the nozzles as one unit; and an interface detecting 
member for detecting an interface between two components; 
the interface detecting member further including an impedance detector for 
detecting an impedance between the two nozzles serving also as the 
electrodes, a storing section for storing a first threshold value to 
detect the first component, and an operation control member for comparing 
the first threshold value stored in the storing member with a detected 
value obtained by the impedance detector, and for controlling the nozzle 
driving member based on a result of the comparison. 
With the structure described above, the interface between two components 
can be accurately detected regardless of a variety of the characteristics 
of blood samples. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will now be described with reference 
to the accompanying drawings. Those elements of the embodiments which are 
similar to those of the prior art device will be designated by the same 
reference numerals. 
FIG. 1 shows the first embodiment of the present invention, and depicts a 
sample separator 101, and an interface detecting member 102 set in the 
sample separator. The sample separator 101 separately extracts two 
components (a plasma component 2 and a blood cell component 3) of a blood 
sample 8, which was centrifuged. The interface detecting member 102 
detects the interface between the plasma component 2 and the blood cell 
component 3. 
The sample separator 101 includes a pair of nozzles, a plasma suction 
nozzle 4 serving as a first suction nozzle, and a blood cell suction 
nozzle 5 serving as a second suction nozzle. The nozzles 4 and 5 have a 
hollow structure, and are fixed to a holder 6. The holder 6 is connected 
to a holder driving member 13, serving as a nozzle driving member, which 
is further connected to an operation control member 11 (described later). 
The holder driving member 13 moves the holder up or down, or stops in 
accordance with an instruction from the operation control member 11. 
The nozzles 4 and 5 both project vertically downward from the holder 6, and 
are arranged in parallel with each other. The distance between the nozzles 
4 and 5 is set such that they enter into a test tube 1 at the same time. 
Further, the tip ends 21 and 22 of the nozzles 4 and 5 are virtually level 
with each other. 
The nozzles 4 and 5 descends or ascends along with the holder 6 as one 
unit. As the holder descends, the nozzles 4 and 5 gradually enter into the 
test tube 1, and the tip ends 21 and 22 proceed through the air section 
23, the plasma component 2, to the blood cell component 3. The positions 
of the tip ends 21 and 22 are adjusted by the holder driving member 13. 
FIG. 1 shows a case where the tip ends of the nozzles 4 and 5 are located 
in the blood cell component 3. 
The nozzles 4 and 5 are connected to a negative pressure source 24, which 
is also connected to the operation control member 11. The negative 
pressure source 24 is driven in accordance with an instruction from the 
operation control member 11, and each of the nozzles 4 and 5 independently 
performs a suction operation as driven by the negative pressure source 24. 
Each of the nozzles 4 and 5 are made of a conductive material, and 
therefore serves also as an electrode. The nozzles 4 and 5 are connected 
to the impedance detector 7, which is set in the holder 6. The impedance 
detector 7 is connected to the operation control member 11 so as to detect 
an impedance between the nozzles 4 and 5, and output the result of the 
detection to the operation control member 11. 
As shown in FIG. 2, the operation control member 11 includes a CPU 25 and a 
comparison operation member 26. Connected to the operation control member 
11, connected are the impedance detector 7, the holder driving member 13, 
the negative pressure source 24, and a threshold value storing member 12 
serving as a memory. A value-setting member 27 is connected to the 
threshold value storing member 12. As the threshold value storing member 
12, general types of memories can be used. As the value-setting member 27, 
general types of keyboards, or the like, can be used. The operation 
control member 11 may include the threshold value storing member 12. 
In the threshold value storing member 12, a threshold value, S.sub.1, for 
plasma detection is stored by the value-setting member 27. A threshold 
value S.sub.1 is determined based on a standard plasma impedance X and a 
standard blood cell impedance Y shown in FIG. 3. More specifically, the 
value S.sub.1 is set sufficiently higher than the plasma impedance X, and 
slightly lower than the cell impedance Y. Further, the value S.sub.1 of 
the embodiment is sufficiently higher than the value S.sub.1 of the 
conventional device (shown in FIG. 8). 
A threshold value, S.sub.2, for blood cell detection determined based on 
the result of the detection by the impedance detector 7. More 
specifically, the operation control member 11 recognizes a plasma 
impedance X.sub.1 (minimum impedance) of a sample 8 from the output signal 
from the impedance detector 7, and determines a value S.sub.2 by adding a 
predetermined amount .delta. to the impedance X.sub.1. The addition value 
.delta. is small with respect to the difference between the plasma 
impedance X.sub.1 (detected value) and the blood cell impedance Y 
(reference value). Consequently, the value S.sub.2 is slightly higher than 
a detected plasma impedance X.sub.1. The value S.sub.2 varies in 
accordance with the plasma impedance X.sub.1 of a sample 8. An addition 
value .delta. is determined by use of the value-setting member 27. 
In the operation control member 11, the result of a detection by the 
impedance detector 7, a plasma detection threshold value S.sub.1, and a 
blood cell detection threshold value S.sub.2 are compared with each other. 
The operation control member 11 controls the holder drive member 13 and 
the negative pressure source 24 in accordance with the results of the 
comparison. 
The operation of the sample separating apparatus 101 having the 
above-described structure will be described. 
When an operation of the apparatus 101 is started, the holder drive member 
13 lowers the holder 6. At the same time, a detection signal from the 
impedance detector 7 is input to the operation control member 11, where 
the detection signal and the plasma detection threshold value S.sub.1 are 
compared with each other. 
The impedance decreases noticeably when the tip ends 21 and 22 of a pair of 
nozzles 4 and 5 are immersed in the plasma component 2. In FIG. 3, symbol 
A indicates the level of the tip ends of the nozzles when the impedance 
significantly drops, and the tip end level A is at the interface between 
the air component 23 and the plasma component 2. 
When the impedance decreases to S.sub.1 or lower, the holder drive member 
13 stops lowering the holder 6 in accordance with an instruction from the 
operation control member 11. After that, the negative pressure source 24 
is driven such that the plasma suction nozzle 4 starts to extract the 
plasma component 2. The minimum impedance at this point, that is, a plasma 
impedance X.sub.1, is stored in the threshold memory member 12 via the 
operation member 11. 
After extracting a predetermined amount of the plasma component 2, the 
holder drive member 13 once again lowers the holder 6. While the holder is 
descending, the impedance is continuously detected by the impedance 
detector 7. when the tip ends 21 and 22 of the nozzles 4 and 5 reach the 
blood cell component 3 (nozzle level B in FIG. 2), the impedance rapidly 
increases. When the impedance increases and gets a predetermined amount 
(.delta.) higher than the plasma impedance X.sub.1 previously stored, the 
operation control member 11 outputs an instruction to the holder drive 
member 13 so as to stop the holder 6. Then, the negative pressure source 
24 is driven such that the cell suction nozzle 5 starts to extract the 
blood cell component 3. The blood cell threshold value S.sub.2 is 
represented by (X.sub.1 +.delta.). 
The result of the detection obtained by the impedance detector 7 is 
influenced by the accuracy of impedance detector 7, the impedance of the 
each of the nozzles 4 and 5, which may vary from one another, and the 
like. The S.sub.1 and .delta. values that are optimum for detecting an 
interface should be determined in consideration of the above factors. 
In the sample separator 101 having the above described structure, a plasma 
detection threshold value S.sub.1 is determined based on a typical plasma 
impedance, and the threshold S.sub.1 is set considerably larger than the 
typical plasma impedance X. Thus, if the detected plasma impedance X 
increases due to the impedance of each of the nozzles 4 and 5 which may 
vary from one to another, and a characteristic change of each of the 
nozzles 4 and 5 with time, the plasma component 2 can be accurately 
detected. 
The blood cell detection threshold value S.sub.2 is set at (X.sub.1 
+.delta.) in accordance with the plasma impedance X detected each time. 
Consequently, the blood cell component 3 can be detected even if the blood 
cell impedance Y.sub.1 is significantly lower than a typical blood cell 
impedance Y. 
With the above-described arrangement, the interface between the plasma 
component 2 and the blood cell component 3 is accurately detected 
regardless of characteristic differences between blood samples. Even if 
the difference between the plasma impedance X.sub.1 and the blood cell 
impedance Y.sub.1 in a sample 8, is small, the interface therebetween can 
be detected. 
Regarding a blood sample centrifuged into a serum plasma component and a 
blood clot, the detection of the interface between the components can be 
carried out in a similar manner. 
The present invention can be modified into a variety of versions as long as 
the essence of the invention remains. 
FIG. 5 shows the main section of the second embodiment of the present 
invention. A great portion of this embodiment is common to the first 
embodiment, and therefore an apparatus similar to the first embodiment can 
be used. The common part is omitted from the figure. 
In this embodiment, a plasma detection threshold value S.sub.1 is 
determined based on an air impedance W. Before lowering of nozzles 4 and 
5, the impedance between the nozzles is detected, and the detected value 
is stored in a memory portion 12 as an air impedance W. 
In an operation control member 11, a value is obtained by subtracting a 
predetermined amount .delta.' from the air impedance W, and the value 
(W-.delta.') is recognized as a plasma detection threshold value S.sub.1. 
The value S.sub.1 is stored in the threshold memory portion 12, and 
compared with a value detected by the impedance detector 7. The 
subtraction value .delta.' is input to a threshold memory portion 12 along 
with the addition value .delta. by use of a value-setting member 27 before 
extraction of the plasma component 2. Thus, an optimum value .delta.' is 
determined in a similar way to S.sub.1 or .delta. of the first embodiment. 
Also in the second embodiment, the interface between the plasma component 2 
and the blood cell component 3 can be accurately detected regardless of 
the characteristic difference between blood samples 8. 
FIG. 6 shows the third embodiment of the present invention. In the first 
embodiment, the operation control member 11 includes electronic parts, in 
each of which circuits elements are integrated, such as CPU 25, memory 12, 
and the like, whereas in this embodiment, an operation control member 31 
is an electronic circuit in which comparators 32 and 33 are employed. The 
operation control member 31 includes the first and second comparators 32 
and 33, a negative peak-hold circuit 34, and an adder 35. Supplied the 
first comparator 32 are a reference voltage V, and an output signal from 
an impedance detector 7, whereas to the second comparator 33 are input a 
signal from the impedance detector 7, and an addition result from the 
adder 3. The adder 35 adds a predetermined value .delta. to a value held 
by the negative peak-hold circuit 34. 
The obtained output value from the impedance detector 7 varies as the 
holder 6 descends. The detected signal from the impedance detector 7 is 
input to the first comparator 32, and compared with the reference voltage 
V. The reference voltage V represents a plasma detection threshold value 
S.sub.1. when the detected signal decreases to the level of the reference 
voltage V or lower, a signal is output to the holder drive member 13 so as 
to stop the holder 6. Thus, extraction of the plasma component is started. 
The minimum impedance at this point is held by the negative peak-hold 
circuit 34 as a plasma impedance X.sub.1. 
After extracting a predetermined amount of the plasma component 2, the 
holder 6 is further lowered, and while the holder being lowered, the 
impedance between the nozzles 4 and 5 is continuously detected. The 
impedance values detected are successively input to the second comparator 
33 along with the addition results from the adder 35. The adder 35 adds a 
predetermined value .delta. to the plasma impedance X.sub.1, and the 
addition result (X.sub.1 +.delta.) is output to the negative input 
terminal of the second comparator 33. The second comparator 33 compares 
the result detected by the impedance detector 7 and the result (X.sub.1 
+.delta.) obtained by the adder 35. If an impedance value detected by the 
impedance detector 7 is (X.sub.1 +.delta.) or higher, the holder drive 
member 13 stops the holder 6, and extraction of the blood cell sample 3 is 
carried out. 
In this embodiment, the interface between the plasma component 2 and the 
blood cell component 3 is accurately detected regardless of the 
characteristic difference between blood samples as in the other 
embodiments described above. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, and representative devices shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.