Thermodynamic properties of citric acid and the system citric acid-water

The binary system citric acid-water has been investigated with static vapour pressure measurements, adiabatic calorimetry, solution calorimetry, solubility measurements and powder X-ray measurements. The data are correlated by thermodynamics and a large part of the phase diagram is given. Molar heat capacities of citric acid are given from 90 to 330 K and for citric acid monohydrate from 120 to 300 K. The enthalpy of compound formation Δ_comH (298.15 K)=(?11.8±1) kJ mole^?1.     

A low-cost 2D fluorescence detection system for μm sized beads on-chip

In this paper we describe a compact fluorescence detection system for on-chip analysis of beads, comprising a low-cost optical HD-DVD pickup. The complete system consists of a fluorescence detection unit, a control unit and a microfluidic chip containing microchannels and optical markers. With these markers the laser beam of the optical pickup can be automatically focused at the centre of the microchannel. With the complete system a two-dimensional fluorescent profile across the channel width can be obtained such that there is no need for hydrodynamic or electrokinetic focusing of the particles in a specific part of the channel. Fluorescent μm sized beads suspended in medium have been detected with the system. Since on both sides of the main beam two additional laser beams at a known distance are generated, also the velocity of individual beads has been determined.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

A new floating electrode structure for generating homogeneous electrical fields in microfluidic channels

In this article a new parallel electrode structure in a microfluidic channel is described that makes use of a floating electrode to get a homogeneous electrical field. Compared to existing parallel electrode structures, the new structure has an easier production process and there is no need for an electrical connection to both sides of the microfluidic chip. With the new chip design, polystyrene beads suspended in background electrolyte have been detected using electrical impedance measurements. The results of electrical impedance changes caused by beads passing the electrodes are compared with results in a similar planar electrode configuration. It is shown that in the new configuration the coefficient of variation of the impedance changes is lower compared to the planar configuration (0.39 versus 0.56) and less dependent on the position of the beads passage in the channel as a result of the homogeneous electrical field. To our knowledge this is the first time that a floating electrode is used for the realization of a parallel electrode structure. The proposed production method for parallel electrodes in microfluidic channels can easily be applied to other applications.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.