Capillary device

A cross or T-shaped device is disclosed for use in capillary electrophoresis or capillary chromatography. The device includes a first capillary tube and a second capillary tube connected to the first tube at a point between the two ends of the first tube so that the contents flowing in the second tube will mix with a fluid flowing in the first tube. The two tubes enclose spaces with cross-sectional dimensions less than about 200 microns. The two tubes are connected so that there is substantially no dead space at the connection. The device is made by boring a hole at a selected location in the first tube, introducing an elongated guide member into the hole, threading the member into the second tube until the second tube contacts the first tube. The second tube is then permanently connected to the first tube and the guide member is then removed to form a T-shaped device. To form the cross-shaped device, a second hole is drilled at a location opposite to the first hole and a guide member is introduced into the second hole as well. A third tube is threaded onto the guide member on the opposite side of the second tube until it contacts the first tube. The third tube is also permanently connected to the first tube and the guide member is removed to yield a device with a cross-shaped configuration.

BACKGROUND OF THE INVENTION 
This invention relates in general to capillary devices and in particular to 
a capillary device useful in capillary electrophoresis and capillary 
chromatography. 
Capillary zone electrophoresis (CZE) in small capillaries has proven useful 
as an efficient method for the separation of solutes. An electric field is 
applied between the two ends of a capillary tube into which an electrolyte 
containing the solutes is introduced. The electric field causes the 
electrolyte to flow through the tube. Some solutes will have higher 
electrokinetic mobilities than other solutes so that the solutes form 
zones in the capillary tube during the flow of the electrolytes through 
the capillary. To aid the analysis of the contents of the electrolyte or 
to aid the detection of such contents, fluids have been introduced in a 
second capillary connected to the main capillary through which the 
electrolyte flows. This causes the fluid introduced in the second 
capillary to mix with portions of the electrolyte in the main capillary to 
aid the analysis, detection or separation in the CZE process. 
In order to introduce another fluid into the electrolyte in the main 
capillary, the main capillary has to be connected at a location between 
its two ends to a second capillary tube. One type of connection is formed 
by breaking the main capillary into two parts and connecting the two parts 
to a third tube through a T-shaped connector. This and other types of 
connectors for introducing another fluid to mix with the electrolyte are 
disadvantageous because they contain too much dead space at the connection 
between the two capillaries. 
It is frequently desirable to detect compounds in the electrolyte occurring 
in very small quantities. For this reason, the CZE process is performed 
with very small capillaries to enhance the separation of such trace 
compounds from other constituents of the electrolyte. Such traces will be 
detected when certain peaks occur in electropherograms. When such trace 
compounds pass through the connection, the dead space at such connection 
will cause the trace compounds to be mixed with other constituents in the 
electrolyte; this has the effect of broadening the peaks in the 
electropherograms. This reduces the sensitivity of detection and 
resolution of traces of compounds and is therefore undesirable. It is 
therefore desirable to provide devices which permit a fluid to be 
introduced into the electrolyte during its flow in a CZE process in which 
the peak broadening effects are reduced. 
In capillary chromatography, analysis and separation are achieved in a 
manner similar to the CZE process except that the fluid in the capillary 
is moved by pressure instead of by an electric field. For considerations 
similar to those described above, it is desirable to provide a capillary 
device which permits a second fluid to be introduced at any point in the 
flow of a first fluid through a main capillary in capillary chromatography 
where peak broadening effects are reduced. 
SUMMARY OF THE INVENTION 
The device of this invention is for use in capillary electrophoresis or 
capillary chromatography. The device comprises a first capillary tube 
enclosing a first space with cross-sectional dimensions less than about 
200 microns and a second capillary tube enclosing a second space with 
cross-sectional dimensions less than about 200 microns. The second tube is 
connected to the first tube at a point between the two ends of the first 
tube so that when a first fluid is flowing in the first tube, a second 
fluid flowing in the second tube will mix with the fluid in the first 
tube, wherein the two tubes are connected so that there is substantially 
no dead space at the connection. 
The device is made by boring a hole at a selected location into the first 
tube, where the location is between the two ends of the first tube, 
introducing an elongated guide member into the hole, threading the member 
into the second tube until the second tube is in contact with the first 
tube. The second tube is then permanently connected to the first tube and 
the guide member is then removed. A T-shaped device is the result. In the 
preferred embodiment, a second hole is drilled into the first tube at a 
location substantially opposite to the first hole and the guide member is 
introduced through the second hole as well. A third tube is moved relative 
to the member and the first tube so that the member is threaded into the 
third tube and the third tube contacts the first tube and forms a 
cross-shape configuration with the first and second tubes. The third tube 
is also permanently connected to the first tube and the guide member is 
removed from the third tube as well so that a cross-shaped configuration 
formed by the first, second and third tubes result.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a schematic view of an electrophoretic system for performing CZE 
processes employing device 10 to illustrate the preferred embodiment of 
the invention. As shown in FIG. 1; device 10 comprises a main capillary 
tube which includes two portions 12, 14, and a second capillary tube 
comprising two portions 16, 18 where the two tubes are connected at 
connection 20 in a manner so that a second fluid flowing in the second 
tube will mix with a first fluid flowing in the main capillary tube. The 
two ends 12', 14' of the main capillary tube are in containers 22, 24 
which may be beakers. Containers 22, 24 contain electrolytes 26, 28 
respectively. An electrical potential is applied between the two 
electrolytes as shown in FIG. 1, causing the electrolyte 26 to flow 
through portion 12 and then portion 14 of the main capillary to container 
24. During its flow, the constituents of the electrolyte 26 are detected 
by detector 34. 
To aid the separation and analysis in the CZE process, a second fluid is 
introduced and mixed with the electrolyte 26 during its flow through 
portion 14 by means of the second capillary tube. The ends 16', 18' of the 
second capillary are placed in containers 36, 38 respectively. A liquid 42 
is placed in container 36 and container 36 is placed at a higher elevation 
than container 38. After liquid 42 is introduced in the portion 16, it 
will flow towards connection 20 to portion 18 and is subsequently 
discharged into container 38. Since the space enclosed by the second 
capillary are connected to the space enclosed by the main capillary at 
connection 20, a small portion of the liquid 42 will become mixed with the 
portion of the electrolyte in the main capillary and the mixture will flow 
through portion 14. Thus separation can be enhanced and such separation 
can be detected by detector 34. 
Device 10 differs from existing devices in that both the first and second 
capillary tubes enclose spaces whose cross-sectional dimensions are less 
than 200 microns, and in that the two capillaries are connected so that 
the spaces enclosed therein are also connected with substantially no dead 
space at the connection. This reduces or eliminates the peak broadening 
effect of existing capillary devices. Preferably both the main and 
secondary capillary tubes enclose spaces whose cross-sectional dimensions 
are substantially between 5 and 200 microns. 
The above described device is useful in capillary chromatography (GC or LC) 
or in CZE processes. Thus, device 10 is useful: 
1. To provide on-column derivatization of the contents of the main 
capillary to aid analysis/separation; 
2. To introduce a change in the contents of the main capillary, such as a 
pH change, or a salt ion concentration change, to aid separation/analysis; 
3. To place a reference electrode in intimate contact with the contents of 
the main capillary for electrochemical detection purposes; 
4. To introduce scintillation fluid into the main capillary by means of the 
second capillary to aid radioactive decay detection; and 
5. To permit selective removal of the contents of the first capillary in 
the vicinity of the connection 20. 
While in the preferred embodiment, device 10 is cross-shaped, device 10 can 
also be a T-shaped device instead. In such configuration, device 10 will 
simply comprise the main capillary having portions 12, 14 and the 
secondary capillary having only portion 16. When such a device is used in 
CZE processes, as described above in reference to FIG. 1, liquid 42 
introduced into the second capillary 16 will flow entirely into portion 14 
of the main capillary. For some applications, the cross-shaped 
configuration of device 10 is advantageous over the T-shaped configuration 
since only a small portion of the liquid 42 introduced into the second 
capillary will be introduced into portion 14 of the main capillary. In 
either the cross-shaped or the T-shaped configurations, there is 
substantially no dead volume at connection 20 so that peak broadening is 
reduced. 
FIG. 2 is a schematic view of a capillary chromatographic system to 
illustrate the invention. As shown in FIG. 2, the device 10' is of the 
type described above having a T-shaped configuration. Identical parts in 
FIGS. 1, 2 are labeled by the same numerals. As shown in FIG. 2, instead 
of using an electrical means, the fluid in portions 12, 14 of the main 
capillary as well as liquid 42 in the second capillary 16 are moved by 
pressure generating devices such as pumps P1, P2 instead of electrical 
means as in FIG. 1. Since device 10' is such that there is substantially 
no dead space or volume at connection 20, band broadening is reduced. 
Another aspect of the invention is directed towards a method for making 
devices 10, 10' of FIGS. 1 and 2. FIGS. 3A-3F are partial cross-sectional 
views of portions 12, 14, 16, 18 of FIG. 1 as well as other elements used 
for connecting the two capillary tubes to illustrate a preferred method 
for making device 10 of FIG. 1. First a hole is drilled in opposing walls 
of the main capillary as shown in FIG. 3A; the holes in the opposing walls 
are located so that they are substantially opposite to each other. The two 
capillaries are preferably composed of an insulating material such as 
fused quartz although other insulating materials such as Teflon, glass or 
ceramic may also be used. The holes may be drilled by means of a carbon 
dioxide laser using an X-Y translation stage and a microscope, although 
other lasers and instruments may also be used instead. The main capillary 
is preferably 5-200 microns in inside diameter. The holes drilled are 
preferably 5-50 microns in diameter. A guide member 50 which is of a 
dimension which fits snuggly inside the holes serves to guide the 
connection of the second capillary to the main capillary as described 
below. A metal wire which is of sufficient stiffness may be used as the 
guide member. 
FIG. 3B shows the configuration after the guide member has been inserted 
into the holes. Portions 16, 18 of a second capillary tube are then moved 
relative to the guide member and portions 12, 14 until the two portions 
are threaded onto the guide wire and until they contact portions 12, 14 as 
shown in FIG. 3C. A masking agent is then introduced to mask the member; 
such masking agent may be wax or liquified polyethylene glycol. The 
masking agent can be introduced simply by depositing a small quantity of 
the agent at connection 20 and slightly warming the agent to melt it so 
that the agent defuses into the space between the wire and the inner 
surfaces of the two capillary tubes as shown in FIG. 3D. Excess masking 
agent remaining on the outside surfaces of portions 12-18 may be removed. 
The result is shown in FIG. 3D. Portions 12, 14, 16, 18 are then 
permanently connected or attached. This can be accomplished with epoxy 
resin or other chemically inert adhesives. This is shown in FIG. 3E. After 
curing, wire 50 is removed by heating slightly the connection 20. Since 
the guide member is prevented from being permanently attached to the two 
capillary tubes by the masking agent, a slight heating of connection 20 
will melt the agent to facilitate the withdrawal of the guide member. 
From the above-description, it will be evident that there is substantially 
no dead space or volume at connection 20. 
If a T-shaped device such as device 10' of FIG. 2 is desired, the above 
described procedure needs to be modified only as follows. A hole is 
drilled in only one side wall of the main capillary and the guide wire is 
introduced into such single hole. Only one tube such as tube 16 is 
threaded onto the wire. The masking agent is introduced in the same manner 
as described above and the three tubes are glued together by epoxy and the 
guide member withdrawn in the same manner described above. 
While the above-described method has been found to be satisfactory, a 
device with better qualities is formed by connecting the two capillary 
tubes not by adhesives such as an epoxy resin but by heating connection 20 
until the material of the two capillaries such as quartz or glass melts at 
the connection so that the portions 12, 14, 16, 18 are permanently 
connected when the melted quartz or glass is cooled. Thus in the preferred 
embodiment, the two capillary tubes are connected without any adhesives. 
Since no adhesives are used in the preferred embodiment, the guiding 
member will not become attached to the tubes so that no masking agent will 
be required. This has the advantage of simplifying the process for making 
the device. Thus in the preferred method, the steps of applying a masking 
agent and applying adhesives and of warming the connection in order to 
remove the guide member are omitted. 
The above description of the details of implementation, method and 
composition are merely illustrative of the invention. Different variations 
may be within the scope of the invention which is to be limited only by 
the appended claims.