Discrimination of plastic waste pyrolysis oil feedstocks using supercritical fluid chromatography.

Advanced chemical recycling techniques provide new avenues for handling and recycling mixed plastic waste; pyrolysis is a prominent approach involving heating plastic waste in an oxygen-free environment to create pyrolysis oils. Pyrolysis oils must be thoroughly characterized before being refined into fuels and chemical feedstocks. Here, a method based on supercritical fluid chromatography with ultraviolet detection was developed to analyze plastic waste pyrolysis oils. Multiple stationary phases were examined, and 2-ethyl pyridine was chosen as the best stationary phase for resolving pyrolysis oil components. Different standards and different plastic waste pyrolysis oils were compared across the different stationary phases. Up to three columns were serially coupled to increase efficiency and column capacity. It was found that a general method using ethanol as a modifier and two 2-ethyl pyridine columns could effectively resolve plastic waste pyrolysis oils. The potential for differentiating polyethylene and polypropylene feedstocks was demonstrated using principal component analysis.

Use of N-(4-aminophenyl)piperidine derivatization to improve organic acid detection with supercritical fluid chromatography-mass spectrometry.

The analysis of organic acids in complex mixtures by LC-MS can often prove challenging, especially due to the poor sensitivity of negative ionization mode required for detection of these compounds in their native (i.e., underivatized or untagged) form. These compounds have also been difficult to measure using supercritical fluid chromatography (SFC)-MS, a technique of growing importance for metabolomic analysis, with similar limitations based on negative ionization. In this report, the use of a high proton affinity N-(4-aminophenyl)piperidine derivatization tag is explored for the improvement of organic acid detection by SFC-MS. Four organic acids (lactic, succinic, malic, and citric acids) with varying numbers of carboxylate groups were derivatized with N-(4-aminophenyl)piperidine to achieve detection limits down to 0.5 ppb, with overall improvements in detection limit ranging from 25-to-2100-fold. The effect of the derivatization group on sensitivity, which increased by at least 200-fold for compounds that were detectable in their native form, and mass spectrometric detection are also described. Preliminary investigations into the separation of these derivatized compounds identified multiple stationary phases that could be used for complete separation of all four compounds by SFC. This derivatization technique provides an improved approach for the analysis of organic acids by SFC-MS, especially for those that are undetectable in their native form.

Utility of low-cost, miniaturized peristaltic and Venturi pumps in droplet microfluidics.

Many laboratory applications utilizing droplet microfluidics rely on precision syringe pumps for flow generation. In this study, the use of an open-source peristaltic pump primarily composed of 3D printed parts and a low-cost commercial Venturi pump are explored for their use as an alternative to syringe pumps for droplet microfluidics. Both devices provided stable flow (<2% RSD) over a range of 1-7 µL/min and high reproducibility in signal intensity at a droplet generation rate around 0.25 Hz (<3% RSD), which are comparable in performance to similar measurements on standard syringe pumps. As a novel flow generation source for microfluidic applications, the use of the miniaturized Venturi pump was also applied to droplet signal monitoring studies used to measure changes in concentration over time, with average signal reproducibility <4% RSD for both single-stream fluorometric and reagent addition colorimetric applications. These low-cost flow methods provide stable flow sufficient for common droplet microfluidic approaches and can be implemented in a wide variety of simple, and potentially portable, analytical measurement devices.

Two-dimensional separation techniques using supercritical fluid chromatography.

High-resolution separation systems are essential for the analysis of complex mixtures in a wide variety of application areas. To increase resolution, multidimensional chromatographic techniques have been one key solution. Supercritical fluid chromatography provides a unique opportunity in these multidimensional separations based on its potential for high solvent compatibility, rapid duty cycles, and orthogonality to other separation modes. This review focuses on two-dimensional chromatography methods from the past decade that use supercritical fluid chromatography because of these advantages. Valving schemes and modulation strategies used to interface supercritical fluid chromatography with other liquid chromatography and gas chromatography techniques are described. Particular applications of multidimensional separations using supercritical fluid chromatography for the analysis of oils and chiral separations of pharmaceutical compounds are highlighted. Limitations of and a potential trajectory for supercritical fluid chromatography in this field are also discussed.