In this contribution, a novel measurement approach for miniaturized capillary electrophoresis (CE) devices is presented: End-to-end differential capacitively coupled contactless conductivity measurement. This measurement technique is applied to a miniaturized CE device fabricated in low-temperature cofired ceramics (LTCC) multilayer technology. The working principle is based on the placement of two distinct detector areas near both ends of the fluid inlet and outlet of the separation channel. Both output signals are subtracted from each other, and the resulting differential signal is amplified and measured. This measurement approach has several advantages over established, single-end detectors: The high baseline level resulting from parasitic stray capacitance and buffer conductivity is reduced, leading to better signal-to-noise ratio and hence higher measurement sensitivity. Furthermore, temperature and, thus, baseline drift effects are diminished owing to the differentiating nature of the system. By comparing the peak widths measured with both detectors, valuable information about zone dispersion effects arising during the separation is obtained. Additionally, the novel measurement scheme allows the determination of dispersion effects that occur at the time of sample injection. Optical means of dispersion evaluation are ineffective because of the opaque LTCC substrate. Electrophoretic separation experiments of inorganic ions show sensitivity enhancements by about a factor of 30-60 compared to the single-end measurement scheme.

In this paper a novel micromachined contactless conductivity CE device produced in low temperature co-fired ceramics (LTCC) is introduced. The application of LTCC multilayer technology provides a promising method for the contactless detection of conductive compounds because of its increased dielectric constant compared with glass or plastics. The capacitive coupling of the excitation signal into the microchannel across the LTCC substrate is improved, resulting in better detection sensitivity. Two silver electrodes located externally at opposite sides at the end of the separation channel act as detector. Impedance variations in the channel are measured without galvanic contact between electrodes and fluid. Inorganic ions are separated in less than 1 min with this novel ceramic device. The limit of detection is 10 microM for potassium.

We present a microchip capillary electrophoresis (CE) device build-up in low temperature co-fired ceramics (LTCC) multilayer technology for the analysis of major inorganic ions in water samples in less than 80 s. Contactless conductivity measurement is employed as a robust alternative to direct-contact conductivity detection schemes. The measurement electrodes are placed in a planar way at the top side of the CE chip and are realized by screen printing. Laser-cutting of channel and double-T injector structures is used to minimize irregularities and wall defects, elevating plate numbers per meter up to values of 110,000. Lowest limit of detection is 6 microM. The cost efficient LTCC module is attractive particularly for portable instruments in environmental applications because of its chemical inertness, hermeticity and easy three-dimensional integration capabilities of fluidic, electrical and mechanical components.

In diesem Beitrag wird ein miniaturisierter Sensor zur Bestimmung von Ionenkonzentrationen in Flü ssigkeiten vorgestellt, der gä nzlich in Keramikfolientechnologie, der so genannten Low Temperature Co-fired Ceramic(LTCC)-Technologie, aufgebaut ist. Die Ionen werden zunä chst mit Hilfe des Prinzips der Kapillarelektrophorese (CE) separiert und anschließend mit einer kontaktlosen Leitfä higkeitsmessung detektiert. Die Vorteile von LTCC liegen in einer einfachen Verarbeitung und einer besseren Einkopplung des Messsignals in den Mikrokanal, da LTCC hohe relative Permittivitä tszahlen aufweist. Dies fü hrt in der Folge zu hö heren Detektionssensitivitä ten. Mit dem Sensorprototyp in Keramiktechnologie wurden erste erfolgreiche CE-Separationen von anorganischen Ionen durchgefü hrt.Schlü sselwö rter: kontaktlose Leitfä higkeitsmessung; Kapillarelektrophorese; LTCC On-chip capillary electrophoresis in ceramics technology for the measurement of ion concentrations.In this work we present a miniaturized sensor build up entirely in Low Temperature Co-fired Ceramic (LTCC) technology for the determination of ion concentrations in fluids. Ions are first separated using a principle called capillary electrophoresis (CE) and are then sensed using contactless conductivity measurement. The device presented has the advantage of simple fabrication and good capacitive coupling to the measurement channel due to the high dielectric constants of the LTCC material.We show the first successful measurements with this setup confirming the feasibility of contactless conductivity detection of inorganic ions after CE separation in a LTCC-fabricated microchannel.

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