U.S. patent application number 11/260635 was filed with the patent office on 2007-05-03 for automatic sampler.
This patent application is currently assigned to SHIMADZU CORPORATION. Invention is credited to Yoshiaki Maeda.
Application Number | 20070095158 11/260635 |
Document ID | / |
Family ID | 37994567 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070095158 |
Kind Code |
A1 |
Maeda; Yoshiaki |
May 3, 2007 |
Automatic sampler
Abstract
An automatic sampler for automatically sampling liquid samples
to be introduced into apparatuses that analyze liquid samples, such
as liquid chromatographs, includes a needle with a tapered tip end
for suctioning and ejecting liquid, a mechanism for moving the
needle in the horizontal and vertical directions, and an injection
port having an insertion hole into which the tip end of the needle
can be inserted. The outer diameter of the tip end of the needle is
at least 0.1 mm and at most 0.6 mm. By reducing the needle-to-port
contact area, the automatic sampler facilitates high-sensitivity
and high-precision analyses by significantly reducing the amount of
cross-contamination, regardless of the type of samples.
Inventors: |
Maeda; Yoshiaki; (Kyoto-shi,
JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
1700 DIAGONAL RD
SUITE 310
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
SHIMADZU CORPORATION
Kyoto-shi
JP
|
Family ID: |
37994567 |
Appl. No.: |
11/260635 |
Filed: |
October 28, 2005 |
Current U.S.
Class: |
73/864 |
Current CPC
Class: |
G01N 35/1095 20130101;
G01N 30/24 20130101 |
Class at
Publication: |
073/864 |
International
Class: |
G01N 1/22 20060101
G01N001/22 |
Claims
1. An automatic sampler comprising: a container for storing a
liquid sample; a needle having a tapered portion with a tip end for
suctioning and ejecting the liquid sample, and a retention channel
for holding said liquid sample suctioned from said container via
said tip end, wherein an outer diameter of said tip end of said
needle is at least 0.1 mm and at most 0.6 mm; a mechanism for
moving said needle in a horizontal and a vertical direction; an
injection port for receiving said held liquid sample, wherein said
injection port has an insertion hole for insertably receiving said
tip end of said needle and said liquid sample ejected therefrom,
said insertion hole having a reduced contact area with an outer
surface of the tip end of the needle; and an analysis channel
connected to the injection port for receiving and analyzing said
liquid sample, wherein said moving mechanism is arranged such that
an insertion pressure applied when said tip end of said needle is
inserted into said injection port is 3 kg or less.
2. (canceled)
3. The automatic sampler according to claim 1, wherein said
insertion hole has an outer diameter greater than the outer
diameter of said tip end and less than an outer diameter of a
bottom of a tapered portion.
4. The automatic sampler according to claim 3, wherein said
injection port has a tapered receiving portion and a straight
portion extending from the receiving portion so that the tip end
contacts the straight portion.
5. The automatic sampler according to claim 4, wherein said outer
diameters of said tip end and said bottom are 0.4 mm and 1.2 mm,
respectively, and a contacting length between the needle and the
straight portion is about 0.45 mm.
6. The automatic sampler according to claim 5, wherein said
insertion hole has a diameter of 0.5 mm, and the insertion pressure
is about 2 kg.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to automatic samplers for
automatically sampling liquid samples to be introduced into
analytical apparatuses that analyze liquid samples, such as liquid
chromatographs.
[0002] In a liquid chromatograph, an automatic sampler is used in
order to automatically select numerous samples to be introduced to
columns. FIG. 3 is a schematic diagram showing the channel
structure of a conventional automatic sampler used in a liquid
chromatograph, as shown in Patent Reference 1.
[0003] In the automatic sampler 3, the injection valve
(high-pressure valve) 4 is a rotary six-port, two-position channel
switching valve having six ports 4a-4f. Through a switching
operation, two adjacent ports are selectively connected. In other
words, the combinations of the two-port connections indicated by
the solid or broken lines in FIG. 3 can be switched. The
low-pressure valve 5 is a rotary seven-port, six-position valve
having seven ports 5a-5g. The common port 5g, which is connected to
a measuring pump 6, can be coupled to any one of the other six
ports 5a-5f, which accordingly couples two predetermined adjacent
ports among ports 5a-5f. For example, when the common port 5g is
coupled to port 5b, ports 5a and 5f are coupled, as indicated by
solid lines in FIG. 3.
[0004] A column channel, which extends to column 2, is connected to
port 4b of the injection valve 4, and a mobile phase channel, which
is supplied with a mobile phase (solvent) by the liquid feeding
unit 1, is connected to port 4c. A sample loop 7 is connected to
port 4d, and also to port 4a via the needle 10 and the injection
port 9. Ports 4e and 4f are connected to ports 5b and 5c of the
low-pressure valve 5, respectively. A cleaning port 8 is connected
to port 5a of the low-pressure valve 5, port 5e is connected to the
measuring pump 6, and a cleaning solution is supplied to port 5d. A
small vial 11 containing a liquid sample is stored in a sample rack
12. The needle 10 is moved in horizontal and vertical directions
using a moving mechanism 13. The needle can be moved to locations
above the vial 11 and the cleaning port 8, and inserted into the
respective liquids contained therein.
[0005] The basic sequence of operations for introducing a liquid
sample in the apparatus described above will be explained. When the
liquid sample is collected, the injection valve 4 and the
low-pressure valve 5 are switched to the connected state indicated
by the solid lines in FIG. 3, and the needle 10 is moved to the
location above the vial 11 and inserted into the liquid sample (the
position indicated by reference numeral 10'). When the plunger of
the measuring pump 6 is pulled in this state, the liquid sample is
suctioned from the vial 11 through the mobile phase (or a cleaning
solution made of the same components) that fills the connecting
channel between the measuring pump 6 and the needle 10, and the
liquid sample is held within the sample loop 7. The amount of the
liquid sample collected is equivalent to the amount of suction
developed by the measuring pump 6.
[0006] After the sample is collected, the needle 10 is returned to
the position above the injection port 9 and connected to the
injection port 9. The injection valve 4 is switched to the
connected state indicated by the broken lines in FIG. 3. The mobile
phase supplied from the liquid feeding unit 1 is transmitted to the
column 2 via the sample loop 7, needle 10, and injection port 9. At
this point, the liquid sample, which has been held within the
sample loop 7, is fed to the column 2 along with the mobile phase.
The liquid is separated into components as it passes through the
column 2 to be sequentially detected by the detector, which is not
shown.
[0007] The needle 10 on which the liquid sample is deposited during
the suction is cleaned as follows. The injection valve 4 and the
low-pressure valve 5 are switched to the connected state indicated
by the solid lines in FIG. 4. The plunger of the measuring pump 6
is pulled to suction the cleaning solution into the syringe. When
the injection valve 4 and the low-pressure valve 5 are subsequently
switched to the connected state indicated by the broken lines in
FIG. 3, and the plunger is pressed to eject the cleaning solution
from the measuring pump 6, the cleaning solution is introduced to
fill the cleaning port 8, while discharging excess cleaning
solution from the discharge port of the cleaning port 8. The needle
10 is then moved to the location above the cleaning port 8, as
shown in FIG. 4, and dipped into the cleaning solution contained in
the cleaning port 8. Upon cleaning the needle 10 for a certain
period of time, the needle is returned to the injection port 9.
[0008] In the aforementioned automatic sampler 3, since the
cleaning of the needle 10 described above is always performed
between the introductions of one liquid sample and the next, the
likelihood of cross-contamination, wherein the previous sample is
mixed into the following sample, is reduced. However, even with
such cleaning steps, cross-contamination is not completely
eliminated. One reason for that is explained below.
[0009] FIG. 5 is an enlarged schematic longitudinal sectional view
of the section where the needle 10 comes in contact with the
injection port 9. The section indicated as "A" of the needle 10 is
straight, and the section indicated as "B" is tapered so that the
outer diameter thereof is continuously reduced towards its tip. The
sealing member 90 disposed in the injection port 9 is provided with
an insertion hole 90b with a wider funnel section 90a. To connect
the needle 10 to the injection port 9, the needle 10 is lowered so
that the tip end of the needle 10 is inserted into the insertion
hole 90b of the sealing member 90.
[0010] Since the inner diameter of the insertion hole 90b is larger
than the outer diameter of the tip end of the needle 10, the tip
end of the needle 10 begins entering the insertion hole 90b. Since
the tip section of the needle 10 is tapered, the outer surface of
the needle 10 comes in contact with the inner surface of the
insertion hole 90b when the needle 10 is lowered to a certain
position. The needle 10 is lowered by a predetermined level of
pressure; the needle 10 is pushed in while the pressure overcomes
the frictional force (including the resilience of the sealing
member 90) of the contact surface, but the lowering of the needle
10 ceases once the frictional force surpasses the pressure. In
other words, at this point, the outer surface of the needle 10 is
in tight contact with the inner surface of the insertion hole 90b,
thereby securing fluid-tightness.
[0011] When a liquid sample is suctioned from the vial 11, some of
the liquid sample is deposited on the outer part of the tip end of
the needle 10. The needle 10 is subsequently inserted into the
sealing member 90 of the injection port 9 as above, and thus the
liquid sample gets deposited on the section of the inner surface of
the insertion hole 90b of the sealing member 90 where the outer
surface of the tip of the needle 10 comes in contact. The liquid
sample adhering to the contact surface is not removed even when the
mobile phase is supplied from the needle 10 to the injection port
9, and thus remains even after the removal of the needle 10. When
the needle 10 is inserted into the insertion hole 90b of the
sealing member 90 in order to introduce the next liquid sample, the
previous liquid sample adhering to the inner surface of the
insertion hole 90b may be pushed by the needle 10 and mixed in the
channel.
[0012] Such cross-contamination described above often causes
problems, particularly in analyzing samples that are easily
adsorbed by the surface of a needle 10 made of metal, such as basic
compounds and lipid soluble substances.
[0013] Conventionally, for example, as in the automatic sampler
disclosed in Patent Reference 2, a vapor-deposit or coating of
precious metal is applied to the outer surface of the tip section
of the needle in order to make the chemical adsorption of samples
more difficult. Such a technique may be effective for samples that
adhere to the needle surface mainly through chemical adsorption,
such as basic compounds, but is not effective for samples that
adhere to the needle surface through causes other than chemical
adsorption, such as with lipid soluble substances.
Patent Reference 1: Japanese Laid-open Patent Publication No.
2002-277450
Patent Reference 2: Japanese Laid-open Patent Publication No.
2002-228668
[0014] In recent years, with increased levels of sensitivity and
precision of analytical apparatuses, even a trace amount of
cross-contamination such as that described above has begun to
greatly affect the results of analyses. Moreover, samples that are
subject to analysis have also diversified. A need exists for a
cross-contamination reduction measure that does not depend on the
type of samples.
[0015] An object of the present invention is to solve the
aforementioned problems associated with conventional sampling
devices. It is an object of the present invention, therefore, to
provide an automatic sampler that enables high-sensitivity and
high-precision analyses by significantly reducing the amount of
cross-contamination, regardless of the type of samples.
[0016] While in the aforementioned conventional approach, the
surface of a needle is designed so as to make adhesion of samples
more difficult, the present invention addresses the fact that the
amount of cross-contamination greatly depends on the contact area
between the outer surface of the needle tip and the inner surface
of the injection port's insertion hole. The present invention,
therefore, is based on reducing the amount of cross-contamination
by reducing the contact area.
[0017] Further objects and advantages of the invention will be
apparent from the following description of the invention and the
associated drawings.
SUMMARY OF THE INVENTION
[0018] The present invention achieves the aforementioned objects by
providing an automatic sampler that includes a needle with a
tapered tip end for suctioning and ejecting liquid, a mechanism for
moving the needle in the horizontal and vertical directions, and an
injection port having an insertion hole into which the tip end of
the needle can be inserted. The automatic sampler introduces a
liquid sample into an analysis channel by dipping the tip end of
the needle into a liquid sample stored in a container to suction
and hold the liquid sample in a retention channel via the needle,
and then inserting the tip end of the needle into the insertion
hole of the injection port to eject the liquid sample previously
retained. The outer diameter of the tip end of the needle is at
most 0.6 mm, and at least 0.1 mm.
[0019] Conventionally, the outer diameter of the tip end of a
conventional needle has been 0.65 mm or larger. In the automatic
sampler according to the present invention, however, the outer
diameter of the tip end of the needle is smaller, i.e., 0.6 mm at
most, and 0.1 mm at the least. Thus, the contact area between the
outer surface of the needle tip, which is inserted into the
injection port's insertion hole, and the inner surface of the
injection port's insertion hole is reduced. This reduces the
absolute amount of the liquid sample transferred from the outer
surface of the needle to the inner surface of the injection port's
insertion hole, i.e., the amount adhering to the inner surface,
when introducing the liquid sample via the injection port. As a
result, the amount of cross-contamination can be reduced relative
to that of a conventional automatic sampler.
[0020] For example, the automatic sampler of the present invention
employed in a liquid chromatograph prevents the peak derived from a
component in a previous sample from appearing in the chromatogram.
Even if the peak did appear to some extent, the peak intensity
would be reduced relative to that in a conventional sampler. This
increases the accuracy in calculating peak heights and peak areas
of object components, thereby improving the accuracy of analyses.
In addition, components found only in trace amounts, which have
been conventionally undetectable due to cross-contamination, can be
detected, thereby improving analysis sensitivity.
[0021] When the outer diameter of the needle tip is reduced,
however, its mechanical strength is also reduced, thereby rendering
the needle susceptible to buckling or the like during insertion. In
the automatic sampler in the present invention, therefore, it is
preferable to reduce the pressure applied during the insertion of
the needle into the injection port's insertion hole from the
conventional 4 kg, to 3 kg or less.
[0022] The aforementioned reduction in the contact area between the
outer surface of the needle tip and the inner surface of the
injection port's insertion hole also reduces the frictional force
experienced during the needle insertion. Thus, even when the
pressure is reduced, the needle can be pressed into the insertion
hole sufficiently deep enough to ensure fluid-tightness, thereby
preventing buckling or deformation of the needle.
[0023] By maintaining the same tapering angle of the tip section
itself as that of the conventional device, even when the outer
diameter of the needle tip is reduced, the resisting force
experienced during the insertion of the needle into the septum
remains the same as in the conventional device; the initial
penetration resistance is smaller in proportion to the reduced
outer diameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIGS. 1(a) and 1(b) are longitudinal sectional views
comparatively showing a section where a needle contacts an
injection port in, respectively, a conventional automatic sampler
(FIG. 1 (a)), and an automatic sampler according to one embodiment
of the present invention (FIG. 1(b)).
[0025] FIGS. 2(a) and 2(b) are charts for illustrating the effect
of reducing cross-contamination achieved by the automatic sampler
of the present invention.
[0026] FIG. 3 is a first schematic diagram showing the channel
structure of the conventional automatic sampler for a liquid
chromatograph.
[0027] FIG. 4 is a second schematic diagram showing the channel
structure of the conventional automatic sampler for a liquid
chromatograph.
[0028] FIG. 5 is an enlarged longitudinal sectional view of
connection sections of a needle and an injection port.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] In the following description, embodiments of the present
invention will be explained with reference to the associated
drawings.
[0030] In the following, an automatic sampler according to one
embodiment of the present invention will be explained with
reference to FIGS. 1(a) and 1(b). FIGS. 1(a) and 1(b) are
longitudinal sectional views showing the state where a needle 10 is
inserted into an insertion hole 90b of a sealing member 90 of an
injection port 9. FIG. 1(a) illustrates a conventional automatic
sampler, and FIG. 1(b) illustrates an automatic sampler according
to one embodiment of the present invention. In FIGS. 1(a) and 1(b),
the dimensions are expressed in millimeters (mm).
[0031] The needle 10 and the sealing member 9 used in the
conventional automatic sampler shown in FIG. 1(a) will be explained
first. The outer and inner diameters of the straight section of the
needle 10 indicated as "A" in FIG. 1(a) are 1.2 mm and 0.4 mm,
respectively. The outer and inner diameters at the tip of the
tapered section indicated as "B" are 0.65 mm and 0.26 mm,
respectively. Although the outer diameter in the tapered section is
gradually reduced towards the tip end, the inner diameter remains
straight. The inner diameter of the insertion hole 90b of the
sealing member 90 is 0.79 mm. When the needle 10 is inserted into
the insertion hole 90b of the sealing member 90, the needle 10 is
lowered vertically from above while applying a pressure of about 4
kg.
[0032] When inserted, the depth (i.e., length) of the contact area
between the outer surface of the tip end of the needle 10 and the
inner surface of the insertion hole 90b is, on average, from 0.4 mm
at the shortest to 0.63 mm at the longest.
[0033] The material used for the needle 10 is stainless steel, and
the material used for the sealing member 90 is a polyether ether
ketone resin, such as the resin sold under the registered trademark
PEEK. In this respect, the materials of the needle 10 and the
sealing member 90 are the same for the embodiment of the present
invention described below.
[0034] In the automatic sampler according to the present invention,
however, while the outer and inner diameters of the straight
section of the needle 10 indicated as "A" in FIG. 1(b) are 1.2 mm
and 0.4 mm, respectively, the outer and inner diameters at the tip
of the tapered section indicated as "B" are 0.4 mm and 0.2 mm,
respectively. Since the tapering angle of the tapered section is
the same as in the conventional device, the length of the tapered
section itself is longer, as is evident when FIGS. 1(a) and (b) are
compared.
[0035] In the present invention, the inner diameter of the
insertion hole 90b of the sealing member 90 is 0.5 mm in response
to the reduced outer diameter of the tip end of the needle 10.
Since the tip end of the needle 10 of the present invention is
narrower that that of a conventional tip, the mechanical strength
of the tip is less. Thus, in the present invention, the pressure
applied to lower the needle 10 into the insertion hole 90b of the
sealing member 90 is set to about 2 kg, or about one half that of
the conventional sampler pressure. If the pressure is reduced when
the outer diameter of the tip end of the needle 10 remains the
same, the insertion depth of the needle 10 would be insufficient.
In this embodiment, however, the frictional force between the
insertion hole 90b of the sealing member 90 and the needle 10 is
less, because the outer diameter of the needle 10 is smaller. Thus,
the reduced pressure can press the needle 10 deep enough to ensure
the fluid-tightness of the contact section.
[0036] According to the present invention, the length of the
contact area between the outer surface of the tip end of the needle
10 and the inner surface of the insertion hole 90b is, on average,
from 0.31 mm at the shortest to 0.45 mm at the longest.
[0037] As described above, since in this embodiment of the present
invention the outer diameter of the tip of the needle 10 is
reduced, and the inner diameter of the insertion hole 90b of the
injection port 9 is also reduced accordingly, the area where the
two come into contact when the needle 10 is inserted is therefore
smaller that that in a conventional apparatus. More specifically,
the contact area associated with the present invention is about one
half that of the conventional apparatus. Thus, the amount of a
liquid sample adhering to the contact area is reduced, and, as a
result, the amount of cross-contamination is reduced.
[0038] An example demonstrating the effect of cross-contamination
reduction according to the present invention will be explained
next. In this experiment, a sample made of strong basic
chlorhexidine hydrochloride (12 mg/10 mL) diluted in the same
solution as the mobile phase was analyzed in order to obtain the
peak area .alpha.. The mobile phase only (blank sample) was
consecutively analyzed in the same manner in order to calculate the
peak area .beta. of the peak appearing in the same retention time.
The amount of cross-contamination is expressed as the ratio of the
peak area .beta. to peak area .alpha..
[0039] FIG. 2(a) is the resultant chromatogram of the
aforementioned chlorhexidine hydrochloride solution, and FIG. 2(b)
is the resultant chromatogram of the blank sample. On these charts,
the graduations of the abscissas, which represent time, are the
same, while the graduations of the ordinates, which represent
intensity, are such that graduations in FIG. 2(b) are much smaller
in scale than those of FIG. 2(a). The peak area .alpha.
corresponding to chlorhexidine hydrochloride detected during the
analysis of the sample obtained from FIG. 2(a) was 41055552. The
peak area .beta. corresponding to chlorhexidine hydrochloride
detected during the analysis of the blank sample was 74712 for the
conventional automatic sampler as opposed to 14728 for the
automatic sampler of the present invention. The amounts of
cross-contamination calculated from these values were 0.182% for
the conventional automatic sampler and 0.036% for the automatic
sampler of the present invention. In other words, the amount of
cross-contamination in the automatic sampler of the present
invention is reduced to about 1/5 that of the conventional
automatic sampler.
[0040] The embodiment described above is merely one example of the
present invention, and the dimensions for the outer diameter of the
needle tip and the inner diameter of the sealing member's insertion
hole are not necessarily limited to those disclosed. The outer
diameter of the needle tip is, however, 0.6 mm at most. From the
perspective of reducing contact area, it is desirable to reduce the
outer diameter of the needle to the extent possible, but mechanical
strength is reduced in proportion to the reduction in the outer
diameter. Moreover, since a channel is formed inside the needle,
reducing the channel's inner diameter too much would make it
difficult to secure the necessary flow rate. Judging generally from
these factors, the outer diameter of the needle tip needs to be at
least 0.1 mm.
[0041] In addition, if the inner diameter of the sealing member's
insertion hole is too small, the insertion of the tip of the needle
10 would be too shallow to ensure a sufficient level of
fluid-tightness. If the inner diameter is too large, on the other
hand, the insertion length of the tip of the needle 10 would be
deep, and increase the contact area. Thus, the inner diameter must
be set appropriately in correspondence with the outer diameter of
the tip of the needle used.
[0042] The disclosure of Japanese Patent Application No.
2004-223321 is incorporated herein.
[0043] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
* * * * *