Low-cost electronic circuitry for photoacoustic gas sensing.

The circuitry comprises a sine wave generator based on direct digital synthesis, a laser diode driver module, a band-pass frequency filter, a synchronous detector with phase adjustment circuitry and a low pass filter to form an analog lock-in amplifier, and an analog-to-digital converter. A 32-bit ARM microcontroller programmed with the open source Mecrisp dialect of the Forth interpreter language is used to set the frequency, and read the data from the analog-to-digital converter. The circuitry is tethered via a serial interface to a personal computer. A graphical user interface written in Phython allows easy interaction with the microcontroller by sending the appropriate Forth commands. The data acquired is visualized and stored on the personal computer for further processing. The circuitry is easy to build as it is based on through-hole devices, except for two necessary surface mount items, which, however, still can be soldered with a fine tipped soldering iron. The performance of the circuitry was demonstrated by the photoacoustic detection of NO2 using a laser diode with a wavelength of 450 nm.

Ambient ionization source based on a dielectric barrier discharge for direct testing of pharmaceuticals using ion mobility spectrometry.

The instrument is based on a miniature plasma source mounted at an oblique angle close to the injection gate of the ion mobility spectrometer. The plasma torch consists of two 5 mm wide external cylindrical electrodes, 10 mm apart, which are placed coaxially around a fused silica tube (1.5 mm i.d. and 3.0 mm o.d.). A small helium plasma is created by applying a alternating voltage of 8 kV at 28 kHz and employed for the direct desorption and ionization of solid or liquid samples, which are placed on an electrically isolated support. The separation section of the ion mobility spectrometer has a drift tube of 10 cm length and an applied high voltage of 4 kV. The instrument was built in-house at low cost and can easily be duplicated. Its usefulness was demonstrated by the rapid identification of five different pharmaceutical drugs, namely acetaminophen, loratadine, norfloxacin, tadalafil, thiamine as well as caffeine in ground coffee beans.

Compact automated capillary electrophoresis instrument for coupling with mass spectrometry by using sheathless electrospray ionization.

The low-cost set-up is based on the flexible microfluidic breadboard approach. To avoid the use of electrically driven devices at the high voltage injection end of the capillary pneumatically actuated pumps and valves are employed. It is coupled to the mass spectrometer with a sheathless electrospray obtained in an electrodeless interface configuration. This simplification is achieved by carrying out the analysis in two distinct steps, firstly the separation without the formation of an electrospray, and secondly detection in which the electrospray is created while pumping out the content of the capillary. The performance of the instrument was tested by analysing three benzalkonium ions and the four pesticides pyrifenox, pirimicarb, cyprodinil and pyrimethanil. Detection limits between 0.36 and 0.76 µM and peak reproducibilities between 5.2% and 6.6% (50 µM standards) were obtained for the latter.

Modular instrumentation for capillary electrophoresis with laser induced fluorescence detection using plug-and-play microfluidic, electrophoretic and optic modules.

This study reports on the development of a novel instrument for capillary electrophoresis (CE) coupled with laser induced fluorescence (LIF) detection that is inspired by the Lego-toy concept. The Lego CE-LIF design is an evolution of purpose-made CE instrumentation, allowing the users to construct their own analytical device with a high degree of standardization (i.e. a "standard" setup) without requirement of mechanical and electronic workshop facilities. To allow instrument reproduction outside the original fabrication laboratory, which is not trivial for in-house-built CE systems, the new design is based on unprecedent 'plugging' hyphenation of various off-the-shelf parts available for microfluidics, optics and electrophoresis. To render the operation with Lego CE-LIF optimal, we developed a new background electrolyte (BGE), using for the first time extremely high concentrations of zwitterionic and large weakly charged species for much improvement of detection sensitivity. The Lego CE-LIF was demonstrated for separation and detection of oligosaccharides labelled with 8-aminopyrene-1,3,6-trisulfonic acid (APTS). The new gel-free BGE for oligosaccharide analysis also allowed simplification of the conventional CE-LIF protocol used with commercial instruments while keeping satisfactory separation performances. Furthermore, the new BGE is fully compatible with a non-thermostatted Lego CE instrument thanks to low current and therefore low heat generation under application of a high voltage.

Low-cost automated capillary electrophoresis instrument assembled from commercially available parts.

A CE instrument that can be assembled from commercially available components with minimal construction effort is described. Except for the electronic control circuitry no specially made parts are required. It is based on a flexible design of microfluidic, electropneumatic, and electronic sections and different configurations can easily be implemented. Automated injection into the capillary is performed hydrodynamically by the application of a pressure for a controlled length of time. The performance of the device was tested with a contactless conductivity detector by separating different metal ions. In addition, nine metal cations related to the quality of honey were separated in 2.3 min and four honey samples were analysed quantitatively to demonstrate the applicability of the method.

Interactive control of purpose built analytical instruments with Forth on microcontrollers - A tutorial.

The use of the computer language Forth for controlling experimental analytical instruments built in laboratories is described. Forth runs on a microcontroller and as it is an interpreted language the user can directly communicate with it by employing a terminal emulator program running on a personal computer. Thus the user can test attached hardware, such as pumps, valves, electronic pressure regulators, detectors and chemical sensors, directly from the keyboard. This overcomes the lack of interactivity, a significant shortcoming, of the computer languages C and C++, the default on such microcontroller platforms as the Arduinos, which have become very popular in recent years for laboratory applications. Common examples of purpose built experimental analytical laboratory instruments are sequential injection analysis systems, microfluidic devices, or automated sample extraction systems. Application examples from our laboratory are given, namely the regulation of mass-flow controllers for gases, the sequencing of an experimental capillary electrophoresis instrument and the acquisition of a signal from an alcohol sensor.

Injection system for fast capillary electrophoresis based on pressure regulation with flow restrictors.

A fast automated system for rapid electrophoretic separations in short conventional capillaries employing contactless conductivity detection is presented. The instrument is based on pneumatic pressurization and does not require a conventional pump. The required pressures and flow rates for the different steps of the injection and flushing processes are produced with the help of two flow restrictors. The device is implemented on a microfluidic breadboard with dimensions of ca. 13 × 20 cm and employs miniature valves. Nine inorganic cations, namely NH4+, K+ , Na+ , Ca2+ , Mg2+ , Mn2+ , Sr2+ , Li+ , and Ba2+ , could be separated in a capillary of 10 µm inner diameter and 6 cm effective length within 25 s. Following a reduction of the effective length to 4 cm, still five inorganic cations could be separated in a time span of 12 s. The repeatability of peak areas was better than 3.1 % and limits of detection between 3.5 and 5.5 µM were achieved.