Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-08-31
2003-04-08
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S416000, C204S403010, C204S403140, C422S082010
Reexamination Certificate
active
06544393
ABSTRACT:
The invention concerns an analytical flow cell with a planar film sensor comprising a cell volume in contact with the film sensor, an input line to this cell volume and the sensor, and an output line for through-flow of a fluid medium to be analyzed. The invention further concerns a film sensor for such an analytical flow cell.
Analytical flow cells with film sensors, especially with thin-film electrodes, are known, and are commonly used now in, for example, gas chromatography or HPLC detectors. Film sensors are also often particularly suitable for miniaturization, and so are suitable for use in miniaturized analytical systems (e. g., “lab-on-a-chip” systems). Here, a detector is considered to be a unit of the actual analytical cell with the sensor and an electronic measuring unit, such as a potentiostat and a signal amplifier. Use of thin film sensors or thin film electrodes in the analytical cell has provided significant advantages for analytical technology. It makes further miniaturization possible, and can make a substantial saving in sensor material. That has led to decidedly more economical measurement cells when the electrode materials are expensive, such as platinum or gold. Thin-film sensors have film thicknesses in the range of nanometers to micrometers. Thick-film sensors with film thicknesses in the micrometer range are being used for certain purposes.
The printed 3-electrode pattern is currently the standard for electrochemical thin-film cells. In such cells the working electrode, reference electrode and auxiliary electrode are printed, with quite varied patterns, and contacts are applied to a carrier. The thin-film or thick-film electrode pattern can also be produced in other manners. Various processes are available for that.
The analytical, or measurement cell, also called a thin-film cell, comprises a cell volume on the electrode side of the carrier, past the electrode, to hold the fluid medium to be analyzed, such as a liquid in HPLC or gas in GC, as well as an inlet and an outlet allowing the medium to flow through, so that the cell is made as a flow cell. Cell volumes are currently generally from one to a few microliters. Cell volumes in the nanoliter region are possible today.
Aside from various electrode geometries, quite varied cell patterns have already been tested and used to attain the best possible flow properties and high sensitivity with the best possible resolution. Dead volumes should be avoided. In one of the cell patterns now in use, the medium being analyzed, i. e., the mobile phase, the mobile phase is directed obliquely in a jet onto the thin film, and removed obliquely again on the opposite side. Another possibility is that of directing the medium being investigated perpendicularly onto the electrode, as much as possible at a point, and removing it at the sides.
In examination of liquids, another problem arises because gases dissolved in the liquid can separate easily at solid surfaces, forming small gas bubbles on the electrode or electrodes during operation. That causes signal distortion and impairs the measurement.
The objective of the invention is to design an analytical flow cell of the type stated initially, and a corresponding film sensor, so as to attain high sensitivity with good resolution even at small cell volumes and, in particular, to avoid formation of bubbles by separation of gases from the liquid being examined at the electrodes or, generally, at the sensor.
To reach this objective, the invention provides for an analytical flow cell with a planar sensor in contact with the cell volume, and an inlet to this cell volume and to the sensor, and an outlet to allow fluid flow, that the sensor has at least one defined passage transverse to the sensor film for fluid medium being analyzed so that the input and outlet are on opposite sides of the film.
The accompanying film sensor for the analysis flow cell according to the invention is correspondingly characterized by the fact that the sensor has at least one defined passage transverse to the sensor film for the passage of a fluid medium to be analyzed.
A “defined passage” in the terminology used in this application, is an opening adapted to the cell geometry, which forms a short channel through the sensor film, transverse to the film, and, optionally, through an underlying carrier.
It was found, surprisingly, that substantial advantages for measurement technology appear if the fluid medium being analyzed is conducted “through the electrode toward the back”. Because of the thinness of a film sensor, contact times are short, so that resolution is good. The fluid medium can be moved through the cell by pressure or suction. That also allows potential technological variations not possible with other cell geometries. The amount of gas bubbles forming on the film sensor is distinctly reduced. The new geometry also makes it possible to keep the active cell volume of the flow cell considerably smaller and to avoid dead volumes for the most part.
The cell volume can be adapted to the type of measurement to be done. For instance, the cell volume on the sensor, which makes contact possible between the fluid medium and the sensor, can be designed approximately cylindrical with the axis of the cylinder perpendicular to the sensor film; or it can have approximately conical geometry, with the base of the cone adjacent to the sensitive surface of the film sensor and the tip of the one opening into the inlet. Various cell volumes, larger or smaller in the general range of a few nanoliters up to about 50 microliters, can be produced. There can also be a collecting volume acting as a buffer volume for the fluid medium directly behind the sensor.
The measurement can optionally be multiplied in the form of several parallel or series measurements by use of multiple inputs and outlets and several electrodes.
The analytical flow cell can also advantageously be integrated into a holder which combines all the components of the cell. The holder comprises connections for input and output of the medium being analyzed, and for conducting the signals obtained with the sensor to a detector unit. The holder also comprises means to pick off signals from the sensor which are preferably conducted to a plug as a connector, from which they can be taken off with the usual connecting means, as well as means for separably mounting the sensor in a position in contact with the cell volume.
For the latter, the holder can comprise at least parts separably connected, between which the sensor is placed or mounted in a combination held together by its shape, or clamped. The two separably connected parts can advantageously be connected with a joint or a clamp so that the holder with at least 2 parts can be unfolded. That makes it possible to change the film sensor, which is printed on a carrier with the contacts, in a particularly simple manner. Alternatively, the sensor can be solidly integrated in a unit so that it is not replaceable but is instead firmly combined with the analysis unit, i.e., the microsystem. For instance, it can be completely welded all around, between films, for instance.
The holder can be made of metal or plastic or other suitable material such as ceramic. In one preferred embodiment, the entire cell geometry with the cell volume, collecting volume optionally placed behind the sensor, inputs, outlets, feed and return connections, is integrally formed in this holder. That is, for instance, it is milled from the holder material, or combined into a fluidic part placed in the holder.
Other preferred embodiments are those in which the film sensor is not replaceable, but instead is integrated into a miniaturized analytical system (“microsystem”) such as a “lab-on-a-chip” system. Then, for example, the sensor can be heat-sealed inside a microsystem, as stated above. “Lab-on-a-chip” is the term for miniaturized analytical systems. They are also called &mgr;TAS, “micro total analysis systems”. Advances in microtechnology and progress in integration of microelectronic circuits will in the near future provide complete
Noguerola Alex
Trace Biotech AG
Tung T.
Whitham Curtis & Christofferson, PC
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