Integrated 3D printed heaters for microfluidic applications: Ammonium analysis within environmental water.

A multi-material 3D printed microfluidic reactor with integrated heating is presented, which was applied within a manifold for the colorimetric determination of ammonium in natural waters. Graphene doped polymer was used to provide localised heating when connected to a power source, achieving temperatures of up to 120 °C at 12 V, 0.7 A. An electrically insulating layer of acrylonitrile butadiene styrene (ABS) polymer or a new microdiamond-ABS polymer composite was used as a heater coating. The microdiamond polymer composite provided higher thermal conductivity and uniform heating of the serpentine microreactor which resulted in greater temperature control and accuracy in comparison to pure ABS polymer. The developed heater was then applied and demonstrated using a modified Berthelot reaction for ammonium analysis, in which the microreactor was configured at a predetermined optimised temperature. A 5-fold increase in reaction speed was observed compared to previously reported reaction rates. A simple flow injection analysis set up, comprising the microfluidic heater along with an LED-photodiode based optical detector, was assembled for ammonium analysis. Two river water samples and two blind ammonium standards were analysed and estimated concentrations were compared to concentrations determined using benchtop IC. The highest relative error observed following the analysis of the environmental samples was 11% and for the blind standards was 5%.

Preconcentration by solvent removal: techniques and applications.

Preconcentration is the aspect of analytical method development covering the need to improve detection sensitivity. This review collects the advances in a diversity of approaches to achieve preconcentration by solvent removal. Evaporation in microfluidic and paper-based devices is reported in a variety of forms and later compared to membrane-assisted evaporation. Sample partitioning in an immiscible fluid is also described. The reported methodologies highlight the need to achieve good control of the gas-liquid interface to obtain accurate results. A comprehensive comparison of different strategies is presented here discussing their benefits and drawbacks as well as the research needs in this area. Graphical abstract ᅟ.

On-line solvent exchange system: Automation from extraction to analysis.

Removal of organic solvent from sample extracts is required before analysis by reversed phase HPLC to preserve chromatographic performance and allow for bigger injection volumes, boosting sensitivity. Herein, an automated on-line extraction evaporation procedure is integrated with HPLC analysis. The evaporation occurs inside a 200 µm microfluidic channel confined by a vapor permeable membrane. A feedback control algorithm regulates evaporation rate keeping the output flow rate constant. The evaporation process across this membrane was firstly characterized with water/solvent mixtures showing organic solvent removal capabilities. This system allowed continuous methanol, ethanol and acetonitrile removal from samples containing up to 80% organic solvent. An evaporative injection procedure was developed demonstrating the use of the device for fully integrated extract reconstitution coupled to HPLC analysis, applied to analysis of the antibiotic chloramphenicol in milk samples. Sample reconstitution and collection was performed in less than 10 min and can be executed simultaneously to HPLC analysis of the previous sample in a routine workflow, thus having minimal impact on the total sample analysis time when run in a sequence.

Effect of vinylpyrrolidone polymers on the solubility and supersaturation of drugs; a study using the Cheqsol method.

The development of methods to increase the bioavailability of drugs is of great interest, especially for those which are poorly soluble or permeable. One of the strategies to enhance the solubility (which in turn has the potential of increase bioavailability) of drugs is the use of additives in the formulation process, so that the drug can stay supersaturated in biological fluids for a period of time long enough to allow absorption. The use of polymers as pharmaceutical excipients in order to stabilize the supersaturation of drugs is common practice. In this work, the ability of different polymers of vinylpyrrolidone (K-12, K-17, K-25, K-29/32, K-90) and a copolymer of vinylpyrrolidone and vinylacetate (S-630) have been tested for their impact on the supersaturation of drugs. Sixteen drugs of different chemical nature have been selected, and analyzed using the Cheqsol method. The results of the drug alone, and of physical mixtures with the different polymers at several polymer:drug ratios have been compared in terms of supersaturation extent and duration. It has been observed that acidic compounds displayed enhanced solubility in different ways: sometimes the supersaturated state of the drug is maintained for a long time, due to the precipitation of an amorphous solid, as determined by X-ray diffraction studies; on other occasions supersaturation increases but only for a short time, compared to the drug alone, and then the drug precipitates to a crystalline form. Only a few basic drugs displayed enhanced solubility in the presence of PVP polymers, in contrast to acidic compounds.

Evaporative membrane modulation for comprehensive two-dimensional liquid chromatography.

An evaporative membrane modulator was developed, built and evaluated to avoid loss of performance in the second dimension when coupling two-dimensional liquid chromatography systems. The automated interface reduces the volume after 1D elution on-line by a pre-determined factor, regardless of the separation gradient. This volume reduction ensures that the injection volume in the 2D is appropriate for the second column, avoiding the detrimental effects of overloading. In addition, the fraction solvent composition is constant over the length of the separation increasing reproducibility of 2D separations. The evaporative membrane modulator was demonstrated with a 10-fold reduction, reducing the injection volume from 50 to 5 µL. A consequence of the EMM device is a reduction in the capacity of the first dimension, which is decreased by a factor of 2.4, but the peak width at half maximum was reduced by up to 22% in the second dimension. When band broadening is considered, the corrected peak capacity with the modulator was only 10% lower than that without the modulator, but with a gain in peak height of 2-3, and a decrease in retention time between subsequent peak-slices reduced from 4s to be negligible. This improves peak shape and shows potential to facilitate peak identification and quantification in more complex applications.