An all-in-one version of a capacitively coupled contactless conductivity detector is introduced. The absence of moving parts (potentiometers and connectors) makes it compact (6.5 cm(3)) and robust. A local oscillator, working at 1.1 MHz, was optimized to use capillaries of id from 20 to 100 microm. Low noise circuitry and a high-resolution analog-to-digital converter (ADC) (21 bits effective) grant good sensitivities for capillaries and background electrolytes currently used in capillary electrophoresis. The fixed frequency and amplitude of the signal generator is a drawback that is compensated by the steady calibration curves for conductivity. Another advantage is the possibility of determining the inner diameter of a capillary by reading the ADC when air and subsequently water flow through the capillary. The difference of ADC reading may be converted into the inner diameter by a calibration curve. This feature is granted by the 21-bit ADC, which eliminates the necessity of baseline compensation by hardware. In a typical application, the limits of detection based on the 3sigma criterion (without baseline filtering) were 0.6, 0.4, 0.3, 0.5, 0.6, and 0.8 micromol/L for K(+), Ba(2+), Ca(2+), Na(+), Mg(2+), and Li(+), respectively, which is comparable to other high-quality implementations of a capacitively coupled contactless conductivity detector.

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A commercial system that is comprised of a CE coupled to an ESI triple quadrupole mass spectrometer was equipped with two capacitively coupled contactless conductivity detectors (C(4) Ds). The first C(4) D was positioned inside the original cartridge, and the second C(4) D was positioned as close as possible to the ESI probe entrance by using a 3D-printed support. The C(4) Ds electropherograms were matched to the ESI-MS electropherogram by correcting their timescales by the factor LT /LD , where LT and LD are the total capillary length and the length until the C(4) D, respectively. A general approach for method development supporting the simultaneous conductivity and MS detection is discussed, while application examples are introduced. These examples include the use of C(4) D as a simple device that dismiss the use of an EOF marker, a low-selectivity detector that continuously provide information about unexpected features of the sample, and even a detector that can be more sensitive than ESI-MS. The C(4) D used in this setup proved to have a smaller contribution to the peak broadening than ESI-MS, which allowed that a C(4) D, positioned at 12 cm from the inlet of an 80-cm-long capillary, could be used to foresee position and shape of the peaks being formed 6.8 times slower at the ESI-MS electropherogram.

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This paper describes the use of ionic solutions as sensing electrodes for capacitively coupled contactless conductivity detection on electrophoresis microchips. Initially, two channels were engraved in a PMMA holder by using a CO2 laser system and sealed with a thin adhesive membrane. PDMS electrophoresis chips were fabricated by soft lithography and reversibly sealed against the polymer membrane. Different ionic solutions were investigated as metalless electrodes. The electrode channels were filled with KCl solutions prepared in conductivity values from approximately 10 to 40 S/m. The best analytical response was achieved using the KCl solution with 21.9 S/m conductivity (2 mol/L). Besides KCl, we also tested NaCl and LiCl solutions for actuating as detection electrodes. Taking into account the same electrolyte concentration (2 mol/L), the best response was recorded with KCl solution due to its higher ionic conductivity. The optimum operating frequency (400 kHz) and the best sensing electrode (2 mol/L KCl) were used to monitor electrophoretic separations of a mixture containing K(+) , Na(+) , and Li(+) . The use of liquid solutions as sensing electrodes for capacitively coupled contactless conductivity detection measurements has revealed great performance to monitor separations on chip-based devices, avoiding complicated fabrication schemes to include metal deposition and encapsulation of electrodes. The LOD values were estimated to be 28, 40, and 58 μmol/L for K(+) , Na(+) , and Li(+) , respectively, what is comparable to that of conventional metal electrodes. When compared to the use metal electrodes, the proposed approach offers advantages regarding the easiness of fabrication, simplicity, and lower cost per device.

Controlled drug release holds promise to revolutionize medicine, particularly if short-term and long-term release can be combined in a single system. We present here a new pulsatile release system, in which the pulses were achieved using 3D scaffolds of poly(l-lactic acid), PLLA. From a morphological characterization of the scaffold’s surfaces, before and after releasing experiments at distinct pHs, we infer that release is governed by electrostatic interactions and the fractal geometry of the scaffolds. Furthermore, the scaffold can present short-term (within hours) or long-term (several days long) releasing profiles by varying the pH, which opens the way for unprecedented drug release control.

ESI sources continuously consume the liquid at the tip of the capillary, which causes the dragging of the BGE. The laminar nature of this flow causes the broadening of the peaks and loss of separation efficiency. The usual solution for this problem is to compensate this phenomenon by reducing the pressure at the inlet vial by either leveling of this vial or pumping off the air that is over it. However, one must know the pressure to be applied in order to prevent under- or over-compensation. The procedure herein introduced allows the easy calculation of this pressure by obtaining two electropherograms at two different values of separation voltage. The migration times of the peaks allow the calculation of the apparent mobilities even in the presence of the laminar flow. Therefore, one can calculate the contributions from both electrophoresis and hydrodynamic flow, and finally the pressure associated with the undesirable flow. This pressure is then applied as a negative pressure at the inlet vial in the following experiments. Increase of up to 192% in the number of plates was obtained in a simple experiment. In addition, the bubble forming caused by the ESI suction during injection was prevented by turning off the nebulizer gas during the changes of inlet vials.