U.S. patent number 3,882,011 [Application Number 05/427,471] was granted by the patent office on 1975-05-06 for electrode for electroanalytic studies.
This patent grant is currently assigned to Pine Instrument Company. Invention is credited to Theodore G. Hines, Dennis C. Johnson.
United States Patent |
3,882,011 |
Hines , et al. |
May 6, 1975 |
Electrode for electroanalytic studies
Abstract
An electrode construction for electroanalysis of fluids
comprises a first contact and a second contact closely spaced
therefrom, and conductive members electrically engaging the first
and second contacts respectively for establishing conductive paths
thereto. Arrangements are provided for electrically isolating the
first and second contacts from one another and the conductive
members from one another, and for sealing the contacts and the
conductive members against the entry of fluid so that fluid is
prevented from contacting the conductive members and any
non-contact surfaces of the first and second contacts. In a
modification of the invention the first contact is fabricated from
one of the group consisting of glassy carbon and the second contact
is made from platinum, gold silver, palladium, other noble metals
and glassy-carbon. In another modification of the invention,
particularly wherein the electrode is arranged for rotation during
the electroanalysis, desirably both of the contacts are made from
glassy-carbon. In another modification, the contacts are made from
glassy-carbon and platinum respectively.
Inventors: |
Hines; Theodore G. (Grove City,
PA), Johnson; Dennis C. (Ames, IA) |
Assignee: |
Pine Instrument Company (Grove
City, PA)
|
Family
ID: |
23695015 |
Appl.
No.: |
05/427,471 |
Filed: |
December 26, 1973 |
Current U.S.
Class: |
204/409; 204/434;
204/280 |
Current CPC
Class: |
G01N
27/30 (20130101) |
Current International
Class: |
G01N
27/30 (20060101); G01n 027/30 () |
Field of
Search: |
;204/280,195R,1T |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
F C. Cowlard et al., J. Materials Science, Vol. 2, pp. 507-512,
(1967). .
H. E. Zittel et al., Analytical Chem., Vol. 37, No. 2, pp. 200-203,
(1965)..
|
Primary Examiner: Kaplan; G. L.
Attorney, Agent or Firm: Smith; Donn J.
Claims
We claim:
1. A rotatable electrode construction for electroanalysis of a
fluid, said construction comprising a first contact and a second
contact spaced therefrom, conductive members electrically engaging
said first and said second contacts respectively for establishing
conductive paths thereto, means for electrically isolating said
first and said second contacts from one another and said conductive
members from one another, brush members mounted respectively on
said conductive members and spaced from said contacts, and means
for sealing said contacts and said conductive members against the
entry of said fluid so that said fluid is prevented from contacting
said conductive members and non-contact surfaces of said first and
said second contacts, at least one of said contacts being
fabricated from glassy-carbon.
2. The combination according to claim 1 wherein said first contact
is a disc-shaped member, and said second contact is a ring-shaped
member surrounding said disc member.
3. The combination according to claim 2 wherein both of said
contacts are fabricated from glassy-carbon.
4. The combination according to claim 2 wherein said disc-shaped
contact and said ring-shaped contact are mounted flushly in a face
surface of said electrode construction.
5. The combination according to claim 2 wherein the conductive
member of said first contact is an elongated rod extending along
the length of said electrode construction, said brush members are
mounted concentrically of said rod, and said rod protrudes
outwardly and coaxially of said brush members from a side thereof
remote from said contacts.
6. The combination according to claim 2 wherein said conductive
members are a rod and tube extending from said first and said
second contacts respectively, and non-conductive sheath members are
closely fitted between said rod and said tube and around said tube
respectively in sealing and electrically isolating
relationship.
7. The combination according to claim 1 wherein said first contact
is fabricated from glassy-carbon and said second contact is
fabricated from one of the group consisting of platinum, gold,
silver, palladium, other noble metals, and glassy-carbon.
8. The combination according to claim 1 wherein said first and said
second contacts are mounted flushly in a face surface of said
electrode construction.
9. The combination according to claim 1 wherein said brush members
are cylindrical and are spaced in tandem along the length of said
electrode construction.
10. The combination according to claim 1 including means for
rotating said electrode construction.
11. A rotatable electrode construction for electroanalysis of a
fluid, said construction comprising a first contact and a second
contact spaced therefrom, conductive members electrically engaging
said first and said second contacts respectively for establishing
conductive paths thereto, means for electrically isolating said
first and said second contacts from one another and said conductive
members from one another, and means for sealing said contacts and
said conductive members against the entry of said fluid so that
said fluid is prevented from contacting said conductive members and
non-contact surfaces of said first and said second contacts, at
least one of said contacts being fabricated from glassy-carbon,
said first contact being a disc-shaped member, said second contact
being a ring-shaped member surrounding said disc member, said disc
member being fabricated from glassy-carbon, and said ring member
being fabricated from platinum.
12. A rotatable electrode construction for electroanalysis of a
given fluid, said construction comprising a central conductive
support terminating in a first contact member, a conductive tube
spacedly surrounding at least a portion of the length of said
support and terminating in a second contact member disposed
adjacent said first contact member but spaced therefrom, a pair of
brush members spacedly mounted on said structure and electrically
engaging said support and said tube respectively, an electrically
isolating sheath member disposed between said tube and its brush
and contact members on the one hand and said support and its brush
and contact members on the other, said sheath member extending into
a gap between said brush members and into a gap between said
contact members, and means for electrically isolating the outer
surfaces of said tube and the adjacent outer surfaces of its
contact.
13. The combination according to claim 12 wherein said sheath
member has a flange at one end thereof for extension into the gap
between said brush members.
14. The combination according to claim 13 wherein said outer sheath
member is press-fitted about said conductive tube.
15. The combination according to claim 12 wherein at least said
first contact member is fabricated from glassy-carbon.
16. The combination according to claim 12 wherein said isolating
means includes an outer sheath member closely fitted about the
outer surfaces of said tube and the outer pheripheral surfaces of
said second contact member.
17. The combination according to claim 12 wherein said sheath
member is pressed-fitted between said support and said conductive
tube.
18. The combination according to claim 12 wherein said conductive
tube and its brush member are formed integrally.
Description
The present invention relates to electrodes for electroanalytic
measurements and designed for rotation more or less rapidly within
the medium being measured, and more particularly to an electrode of
the character described, which has at least one contact thereof
fabricated from glassy-carbon. The invention is particularly
directed to an electrode of this type which can be conveniently
assembled without the possibility of deterioration caused by
leakage corrosion or the like.
Various types of rotating electrodes have been employed in
chromatographic analyses for a number of years. Through voltametric
studies, various products of chemical reactions that are
electroactive, can be identified by their characteristic though
minute positive or negative responses.
A number of electrode contact materials have been utilized for
construction of rotatable electrodes in the past. These materials
have varying ranges of electrical response, which make them more or
less desirable in chromatographic applications. A platinum
electrode furnishes a fair range of electroresponse, but cannot be
used in negative solutions owing to oxide formation. Gold affords a
limited negative response but does not have the positive range of
platinum. Silver is not normally used in chromatographic studies as
its range of response is too narrow. Mercury has an adequate range
in negative solutions, but has the additional disadvantage that it
is not solid.
A glassy-carbon-mercury electrode has been proposed heretofore for
voltametry. This electrode was fabricated by molding glassy-carbon
into an epoxy rod with a central tube to permit a mercury contact.
Owing to the use of liquid mercury, however, the prior electrode is
difficult to handle, as noted above. Moreover, the
glassy-carbon-mercury electrode was not adapted for rotation in the
solution being monitored.
The present invention involves the use of a rotatable ring-disc
electrode in which at least the disc contact and desirably also the
ring contact are formed from glassy-carbon. The ring contact can,
however, be manufactured more easily from platinum or other
suitable material. Use of my novel electrode in voltammetric
stripping, for example, is characterized by a lower limit of
detection and a shorter period of deposition prior to stripping. In
certain applications, the disc electrode contact is constructed
from glassy-carbon and the ring electrode contact from platinum, or
vice versa, to advantage. The electrode contact or contacts which
are fabricated from glassy-carbon desirably are thicker than
contacts made from conventional materials owing to the fragility of
glassy-carbon. In other applications one of the contacts is
advantageously made from glassy-carbon and the other contact, from
one of the group consisting of platinum, gold, silver, palladium,
other noble metals, and glassy-carbon.
We have also found that our novel, rotatable electrode is capable
of detecting extremely minute traces of mercury and platinum for
example. The electrode of the invention provides a wider spectrum
of electrode response and is capable of detecting a broader
category of materials. For certain materials, the electrode of the
invention is unexpectedly of the order of one hundred times more
sensitive than comparable analytic procedures. This is especially
advantageous in the electroanalysis of sparingly soluble compounds
or elements.
The use of glassy-carbon in a rotating type electrode for
electroanalysis offers a number of unexpected advantages. When the
electrode is rotated more or less rapidly, the solution or medium
being analyzed is subject to a stirring action for more uniform
electroresponse. Initially, a plating voltage is briefly applied to
the central or disc contact so that a minute plating of one or more
solutes from the solution takes place on the central, or
glassy-carbon electrode. The use of glassy-carbon for one or both
contacts in this fashion facilitates the plating operation and at
the same time affords a wider electroresponse. For this application
the contacts also can be made from glassy-carbon and platinum,
respectively.
The voltage applied to the electrode contacts is then reversed
which deplates the plated materials from the glassy-carbon central
contact. This deplating operation is unexpectedly facilitated by
use of the glassy-carbon material for the central or disc contact.
As the deplated ions leave the disc contact the centrifugal action
at the face of the rotating electrode facilitates migration of
deplated ions from the central contact to the ring contact which
closely encircles the central contact. As the solution flows past
the ring contact by the centrifugal flows generated by rotation of
the electrode, the ions released from the central contact are
collected and a proportionate electroresponse is obtained by the
electrode and read on external metering circuitry. Use of
glassy-carbon material for the ring contact unexpectedly
facilitates gathering of the outwardly flowing ions, and further,
an extended range of electroresponse is obtained. Thus, the
electrode of the invention affords unexpected advantages when
glassy-carbon is employed for the central contact and additional,
unexpected advantages when glassy-carbon is employed for both the
disc and the ring contacts of the electrode.
Other unexpected advantages of the invention stem from the internal
structure of the electrode and are quite independent of the
particular contact materials. The electrode construction, as
elaborated upon hereinafter in detail, provides unexpectedly a
reliable electrical isolation and a virtual hermetic sealing of the
metallic components of the electrode against leakage from the
solution in which the electrode is rotated.
I overcome the disadvantages of the prior art and accomplish these
desirable results by providing an electrode construction for
electroananysis of fluids, said construction comprising a first
contact and a second contact closely spaced therefrom, conductive
members electrically engaging said first and said second contacts
respectively for establishing conductive paths thereto, means for
electrically isolating said first and said second contacts from one
another and said conductive members from one another, and means for
sealing said contacts and said conductive members against the entry
of said fluid so that said fluid is prevented from contacting said
conductive members and non-contact surfaces of said first and said
second contacts, at least one of said contacts being fabricated
from glassy-carbon.
I also desirably provide a similar electrode construction wherein
said first contact is a disc-shaped member, and said second contact
is a ring-shaped member rounding said disc member.
I also desirably provide a similar electrode construction wherein
said first contact is fabricated from glassy-carbon, and said
second contact is fabricated from one of the group consisting of
platinum, gold, silver, palladium, other noble metals, and
glassy-carbon.
I also desirably provide rotatable electrode construction for
electroanalyses of a given fluid, said construction comprising a
central conductive support terminating in a first contact member, a
conductive tube spacedly surrounding at least a portion of the
length of said support and terminating in a second contact member
disposed adjacent said first contact member but spaced therefrom, a
pair of brush members spacedly mounted on said structure and
electrically engaging said support and said tube respectively, an
electrically isolating sheath member disposed between said tube and
its brush and contact members on the one hand and said support and
its brush and contact members on the other, said sheath member
extending into a gap between said brush members and into a gap
between said contact members, and means for electrically isolating
the outer surfaces of said tube and the adjacent outer surfaces of
its contact.
I also desirably provide a similar electrode construction wherein
said sheath member has a flange at one end thereof for extension
into the gap between said brush members.
I am aware of a number of references disclosing various types of
electrodes for chromatography and related forms of electroanalysis.
Such references include 37- 2 Analytical Chemistry 200- 203 (A
Glassy Carbon Electrode for Voltammetry Zittel and Miller), U.S.
Pat. Nos. 2,758,079 and 2,621,671 and West German Offenlegungshrift
No. 2024008. None of these references, however, discloses the novel
features of the invention, as set forth above.
During the foregoing discussion, various objects, features and
advantages of the invention have been set forth. These and other
objects, features and advantages of the invention together with
structural details thereof will be elaborated upon during the
forthcoming description of certain presently preferred embodiments
of the invention and presently preferred methods of practicing the
same.
In the accompanying drawings we have shown certain presently
preferred embodiments of the invention and have illustrated certain
presently preferred methods of practicing the same wherein:
FIG. 1 is an isometric view of one form of rotatable electrode made
in accordance with the invention;
FIG. 2 is an enlarged isometric view of an end portion of the
electrode shown in the preceding figure, with portions cut away to
show the construction more clearly; and,
FIG. 3 is a longitudinally sectioned view of the electrode shown in
FIG. 1.
With reference now to the drawings in greater detail an exemplary
rotatable electrode 20 according to the invention includes a
conductive, axial support rod 22 to an end of which is secured an
electrode disc or contact 24 fabricated from a suitable contact
material, i.e. one of the group consisting of platinum, gold,
silver, palladium, other noble metals and glassy-carbon. A tubular
conductor 26, fabricated from brass or other suitable electrically
conductive material, is spacedly supported on the support rod 22
but is electrically isolated therefrom. A ring-shaped contact
member 28 is secured to the outward end of the conductive tube 26
and thus is juxtaposed to the central or disc contact 24, but is
electrically isolated therefrom, as described below. The ring
contact 28 also is fabricated from a suitable contact material,
such as one of those mentioned above. In the preferred form of the
invention, glassy-carbon is utilized although other materials can
be used while taking advantage of other features of the invention
described below. In certain applications, the central or disc
contact member 24 is fabricated from glassy-carbon and the ring
contact from platinum, or other noble metal to advantage. Excellent
results have been obtained in most applications, however, when both
the central or disc contact 24 and the ring contact 28 of the
electrode 20 are fabricated from glassy-carbon. Alternatively, the
disc contact 24 can be fabricated from platinum or other noble
metal, and the ring contact 28 from glassy-carbon to advantage and
in keeping with this feature of the inventive concept. As evident
from FIGS 1-3 the contacts 24, 28 are mounted flushly in the face
38 of the electrode 20 to avoid any obstruction to flow of fluid
across the electrode face.
In a specific embodiment of the invention the central support rod
22 is fabricated from stainless steel while the conductive tube 26
is formed from brass or copper. The disc and ring contacts 24, 28
are adhered to the support and conductive tube 22,26 respectively
by means of an electrically conductive epoxy resin. Other
electrically conductive cements or adhesives can be employed, or
alternatively, the adjacent surfaces of these components can be
nickel plated and soldered, although this last mode of connection
is less strong.
When the electrode 20 is rotated rapidly within a solution or the
like being measured, the minute currents generated by the electrode
20, upon plating and deplating of particular solutes at its
contacts 24, 28, are conducted to external meansuring circuitry
(not shown) through a pair of cylindrical brush members 30, 32, or
the like. One of the brush members, for example the brush member 30
is secured directly to the central conductive support 22 such that
an electrical path is established to the central or disc contact
member 24 through the conductive support 22, which projects
outwardly and preferably centrally of the brush members 30, 32 for
connection to suitable rotation means. The brush member 30 can be
shrunk-fitted on the central support 22 and/or an electrically
conductive epoxy resin can be interposed therebetween to ensure a
reliable, electrical engagement. The brush member 32 can be
similarly mounted on the conductive tube 26, or alternatively as
shown, the brush member 32 can be formed integrally with the
conductive tube 26. The brush member 30 likewise can be fabricated
integrally (not shown) with the central rod 22. In any event a
reliable conductive path is established between the brush member 32
and the ring contact 28.
As apparent from the foregoing, the brush member 32, the conductive
tube 26, and the ring contact 28 must be maintained reliably in
electrical isolation from the brush contact 30, the central
conductive support 22 and the disc contact 24. In addition to
thoroughly isolating the ring contact 28 and associated components
from the central or disc contact 24 and associated components, it
is vitally important that the overall electrode structure 20 be
leak-proof. That is to say, it is essential that a liquid or other
material being subjected to electroanalysis with the electrode 20
be excluded from electrical contact with any other conductive
component of the electrode 20, such as the conductive support rod
22 or the conductive tube 26, or the "non-contact" surfaces of the
contacts 24, 28, to avoid erroneous readings.
One arrangement for leak-proofing the electrode 20 and for
electrically isolating its disc and ring contacts 24, 28, includes
the use of non-conductive sheath or sleeve members 34, 36. The
inner diameter of the outer sheath member 34 desirably is slightly
smaller than the outer diameter of the conductive tube 26 such that
upon forcing the outer sheath 34 thereover a compression fit
results along the length of the conductive tube 26 and at the outer
periphery of the ring contact 28. Such compression fit forms an
impenetrable seal along the interface between the conductive tube
26 and the outer sheath 34, and particularly between the end
portion 38 of the outer sheath and the adjacent peripheral surfaces
of the ring contact 28. Accordingly no fluid, in which the
electrode 20 may be partially immersed, can penetrate into any
portion of the junction between the ring contact 28 and the outer
sheath member 34. Of course, the lengths of the conductive tube 26
and of juxtaposed components of the electrode 20 can be varied
depending upon the extent to which the disc and ring contacts 24,
28 will be inserted into a fluid monitored by the electrode 20.
Desirably the outer sheath 34 extends along the length of the
electrode 20 a greater portion of the overall electrode length than
that which is intended to be inserted into the aforementioned
fluid.
Desirably the sheath members 34, 36 are fabricated from Teflon (a
Trademark owned by Dupont for 2 bromo 1, 1, 1, 2 tetrafluoroethane)
or the like because of its toughness and imperviousness, but
sufficient plasticity to enable the sheath 34 to be forced over the
relatively oversized conductive tube 26. Another advantage in the
use of Teflon plastic for this purpose is its almost complete
inertness and concomitant negligible effect upon the readings or
measurements obtained from the electrode 20. Depending upon the
application of the invention, however, other materials such as the
epoxy resins can be employed although the latter are not as inert
as Teflon. The outer sheath 34 electrically isolates the conductive
tube 26 from the solution or other fluid in which the electrode 20
is partially immersed.
The inner sleeve or sheath 36 can be fabricated from Teflon plastic
as mentioned previously and thus provides a reliable, electrical
isolation between the ring and disc contacts 24, 28 between which
the end portion 40 of the inner sheath is inserted and also between
the conductive tube 26 and its cylindrical brush contact 32 on the
one hand and the conductive central electrode support 22 on the
other. Desirably, the inner diameter of the inner sheath 36 is
somewhat smaller than the outer diameter of the central support 22
such that when forced therein a compression seal is established
between the inner sheath 36 and the juxtaposed surfaces of the
central support 22 and the disc contact 24. This prevents any
possibility of liquid penetration between the inner sheath end
portion 40 and the contact disc 24.
On the other hand the outer diameter of the inner sheath 36 is
sized such that, when the sheath has been mounted on the central
support rod 22 as aforesaid, the outer diameter of the inner sheath
36 is somewhat larger than the inner diameter of the conductive
tube 26 and of its brush member 32. In consequence a similar
compression fit is established between the brush member 32 and the
conductive tube 26 and the ring contact 28 on the one hand and the
juxtaposed outer surfaces of the inner sheath member 36 on the
other, when the aforementioned components are forced over the
assembly comprising the inner sheath 36 and central support 22.
There is, in turn, no possibility of liquid penetration between the
outer surface of the inner sheath end portion 40 and the adjacent
inward surfaces of the ring contact 28. By employing the various
compression fits described previously, the contact or immersible
end portion 42 of the electrode 20 is virtually hermetically
sealed, and there is no liklihood of spurious readings from
unwanted fluid penetration along the non-contact or embedded
surfaces of the contacts 24, 28.
When the inner sheath member 36 has thus been installed on the
central conductive support 22, an end flange 44 of the inner sheath
36 desirably is seated flushly against the adjacent surfaces of the
brush member 30 for the conductive support 22, as evident from FIG.
3. Subsequently, when the assembly comprising the support 22, brush
member 30, and inner sheath 36 is forced into the conductive tube
26 and its brush member 32 and ring contact 28, a juxtaposed
surface of the brush member 32 is likewise seated against the
opposite side of the inner sheath flange 44. The flange 44, then,
not only ensures electrical isolation between the brush members 30,
32 but can also delimit the proper positioning of the conductive
tube 26 and associated components upon the electrode structure 20.
It will be apparent, of course, that the inner sheath flange 44 can
be omitted and the brush members 30, 32 assembled with an isolating
air gap therebetween, in place of the flange 44.
When the electrode 20 is thus assembled it can be rotated more or
less rapidly, while in contact with a fluid medium to be monitored,
by suitable rotation means such as an ASR rotator supplied by the
Pine Instrument Company, Grove City, Pennsylvania. Owing to the
compact construction of the electrode 20 and the provision of the
aforementioned compression fit, the electrode 20 can be rotated at
speeds in excess of 10,000 RPM.
From the foregoing it will be seen that a novel and efficient
Electrode for Electroanalytic Studies has been disclosed. The
descriptive and illustrative materials employed herein are utilized
for purposes of exemplifying the invention and not in limitation
thereof. Accordingly, numerous modifications of the invention will
occur to those skilled in the art without departing from the spirit
and scope of the invention. Moreover, it is to be understood that
certain features of the invention can be used to advantage without
a corresponding use of other features thereof.
* * * * *