Fabrication of monolithic frits and columns for chip-based multidimensional separation devices.

In this work, devices for two-dimensional separations are considered. The device contains a flow distributor, a first-dimension channel, and 17 second-dimension outlets. In the design, all connections between the first-dimension channel, the flow distributor, and the second-dimension outlets were tapered, with a minimal diameter of 20 µm. The use of photo-masking is explored for the fabrication of monolithic frits in all tapered connections. Monolithic frits with optimized permeability and length were successfully fabricated in all 33 tapered channels through light-induced polymerization, photo-masking, and selective exposure. The efficacy of the monolithic frits was demonstrated by creating a packed bed of 15-µm particles, confined within the first-dimension channel. The outlet of the first-dimension channel was successfully connected to a mass spectrometer. Effective flow confinement was demonstrated with a reversed-phase separation of a mixture of five standard peptides.

What's in this drink? Classification and adulterant detection in Irish Whiskey samples using near infrared spectroscopy combined with chemometrics.

BACKGROUND: Near-infrared (NIR) spectroscopy coupled with principal component analysis (PCA) and partial least squares (PLS) regression was used to analyse a series of different Irish Whiskey samples in order to define their spectral profile and to assess the capability of the NIR method to identify samples based on their origin and storage (e.g. distiller, method of maturation). The ability of NIR spectroscopy to quantify the level of potential chemical adulterants was also investigated. Samples were spiked with 0.1%, 0.5%, 1.0%, 1.5% and 2.0% v/v of each adulterant (e.g. methanol, ethyl acetate, etc.) prior to NIR analysis. RESULTS: The results of this study demonstrated the capability of NIR spectroscopy combined with PLS regression to classify the whiskey samples and to determine the level of adulteration. Moreover, the potential of NIR coupled with chemometric analysis as a rapid, portable, and non-destructive screening tool for quality control, traceability, and food/beverage adulteration for customs and other regulatory agencies, to mitigate beverage fraud was illustrated. CONCLUSION: Given the non-specificity of the NIR technique, these positive preliminary results indicated that this method of analysis has the potential to be applied to identify the level of adulteration in distilled spirits. The rapid nature of the technique and lack of consumables or sample preparation required allows for a far more time and cost-effective analysis per sample. © 2021 Society of Chemical Industry.

Fabrication of polymer monoliths within the confines of non-transparent 3D-printed polymer housings.

In the last decade, 3D-printing has emerged as a promising enabling technology in the field of analytical chemistry. Fused-deposition modelling (FDM) is a popular, low-cost and widely accessible technique. In this study, RPLC separations are achieved by in-situ fabrication of porous polymer monoliths, directly within the 3D-printed channels. Thermal polymerization was employed for the fabrication of monolithic columns in optically non-transparent column housings, 3D-printed using two different polypropylene materials. Both acrylate-based and polystyrene-based monoliths were created. Two approaches were used for monolith fabrication, viz. (i) in standard polypropylene (PP) a two-step process was developed, with a radical initiated wall-modification step 2,2'-azobis(2-methylpropionitrile) (AIBN) as the initiator, followed by a polymerization step to generate the monolith; (ii) for glass-reinforced PP (GPP) a silanization step or wall modification preceded the polymerization reaction. The success of wall attachment and the morphology of the monoliths were studied using scanning electron microscopy (SEM), and the permeability of the columns was studied in flow experiments. In both types of housings polystyrene-divinylbenzene (PS-DVB) monoliths were successfully fabricated with good wall attachment. Within the glass-reinforced polypropylene (GPP) printed housing, SEM pictures showed a radially homogenous monolithic structure. The feasibility of performing liquid-chromatographic separations in 3D-printed channels was demonstrated.

Confinement of Monolithic Stationary Phases in Targeted Regions of 3D-Printed Titanium Devices Using Thermal Polymerization.

In this study, we have prepared thermally initiated polymeric monolithic stationary phases within discrete regions of 3D-printed titanium devices. The devices were created with controllable hot and cold regions. The monolithic stationary phases were first locally created in capillaries inserted into the channels of the titanium devices. The homogeneity of the monolith structure and the interface length were studied by scanning a capacitively coupled conductivity contactless detector (C4D) along the length of the capillary. Homogeneous monolithic structures could be obtained within a titanium device equipped with a hot and cold jacket connected to two water baths. The confinement method was optimized in capillaries. The sharpest interfaces (between monolith and empty channel) were obtained with the hot region maintained at 70 °C and the cold region at 4 or 10 °C, with the latter temperature yielding better repeatability. The optimized conditions were used to create monoliths bound directly to the walls of the titanium channels. The fabricated monoliths were successfully used to separate a mixture of four intact proteins using reversed-phase liquid chromatography. Further chromatographic characterization showed a permeability (Kf) of ∼4 × 10-15 m2 and a total porosity of 60%.

Miniaturized capillary ion chromatograph with UV light-emitting diode based indirect absorbance detection for anion analysis in potable and environmental waters.

A miniaturized, flexible, and low-cost capillary ion chromatography system has been developed for anion analysis in water. The ion chromatography has an open platform, modular design, and allows for ease of modification. The assembled platform weighs ca. 0.6 kg and is 25 × 25 cm in size. Isocratic separation of common anions (F- , Cl- , NO2- , Br- , and NO3- ) could be achieved in under 15 min using sodium benzoate eluent at a flow rate of 3 µL/min, a packed capillary column (0.150 × 150 mm) containing Waters IC-Pak 10 µm anion exchange resin, and light-emitting diode based indirect UV detection. Several low UV light-emitting diodes were assessed in terms of sensitivity, including a new 235 nm light-emitting diode, however, the highest sensitivity was demonstrated using a 255 nm light-emitting diode. Linear calibration ranges applicable to typical natural water analysis were obtained. For retention time and peak area repeatability, relative standard deviation values ranged from 0.60-0.95 and 1.95-3.53%, respectively. Several water samples were analysed and accuracy (recovery) was demonstrated through analysis of a prepared mixed anion standard. Relative errors of -0.36, -1.25, -0.80, and -0.76% were obtained for fluoride, chloride, nitrite, and nitrate, respectively.

Direct Production of Microstructured Surfaces for Planar Chromatography Using 3D Printing.

Through optimization of the printing process and orientation, a suitably developed surface area has been realized upon a 3D printed polymer substrate to facilitate chromatographic separations in a planar configuration. Using an Objet Eden 260VS 3D printer, polymer thin layer chromatography platforms were directly fabricated without any additional surface functionalization and successfully applied to the separation of various dye and protein mixtures. The print material was characterized using gas chromatography coupled to mass spectrometry and spectroscopic techniques such as infrared and Raman. Preliminary studies included the separation of colored dyes, whereby the separation performance could be visualized optically. Subsequent separations were achieved using fluorescent dyes and fluorescently tagged proteins. The separation of proteins was affected by differences in the isoelectric point (pI) and the ion exchange properties of the printed substrate. The simple chromatographic separations are the first achieved using an unmodified 3D printed stationary phase.

Characterisation of graphene fibres and graphene coated fibres using capacitively coupled contactless conductivity detector.

The use of capacitively coupled contactless conductivity detection (C(4)D) for the characterisation of thin conductive graphene fibres, graphene composite fibres, and graphene coated fibrous materials is demonstrated for the first time. Within a few seconds, the non-destructive C(4)D detector provides a profile of the longetudinal physical homogeneity of the fibre, as well as extra information regarding fibre mophology and composition. In addition to the theoretical considerations related to the factors affect the output signal, this work evaluates the properties of graphene fibres using scanning C(4)D following the manufacturing process of wet-spinning. Furthermore, conductive graphene-coated fibrous materials and the effectiveness of the coating and reduction procedures applied could be investigated. Apart from the application of C(4)D in the monitoring of such processes, the feasibility of this small, highly sensitive and rapidly-responsive detector to monitor strain and elasticity responses of conductive and elastomeric composite fibres for applications in motion sensing, biomedical monitoring, and stretchable electronics was also demonstrated.

Stepped gradients on polymeric monolithic columns by photoinitiated grafting.

The surface of polymethacrylate monoliths was functionalized by a post-polymerization modification, by means of a novel photo-initiated graft procedure where the charged monomer, sulfopropyl methacrylate, was controllably grafted stepwise, i.e. with incremental graft energies. The grafting approach was optimized using scanning capacitively coupled contactless conductivity detection. The effect of the localized ion exchange capacity and resultant gradient stationary phase upon ion-exchange chromatographic retention, selectivity, and performance was investigated, and compared to a homogeneously grafted (isotropic) column. The gradient column provided reduced peak widths at half height for both cationic analytes, with a reduction of 34 and 33%, respectively, when compared to the isotropic column.

Polymethacrylate monolithic columns for hydrophilic interaction liquid chromatography prepared using a secondary surface polymerization.

Zwitterionic methacrylate based polymeric monolithic columns were prepared in two-step polymerizations, with reduced polymerization times. Characteristic properties such as hydrodynamic permeability, porosity, retention factors, and pore size distribution charts were used for column evaluation. A scaffold column was fabricated by polymerization of poly(lauryl methacrylate-co-tetraethyleneglycol dimethacrylate) and was used without further modification as a support for a poly(N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine-co-bisphenol A glycerolate dimethacrylate) second monolith layer with zwitterionic functionality, for HILIC separations. An additional internal structure was formed by the second monolithic layer. The fabrication procedure was reproducible with RSD<5%. Field emission scanning electron microscopy has also been used to investigate column pore morphology, using a novel technique where the polymeric material is imaged directly, without coverage with a conducting film or particles. The new polar monolithic columns were used for HILIC separations of phenolic acids, flavones, nucleosides, and bases of nucleic acids, with similar efficiencies but different selectivities for zwitterionic methacrylate monolithic columns recently prepared by single step polymerization.

Polymeric monolithic materials modified with nanoparticles for separation and detection of biomolecules: a review.

Polymer monolithic materials have found particularly utility in the field of bioanalysis, particularly in the area of separation science, for both enrichment and trapping of biomolecules and their analytical/preparative separations. Nanoparticle-modified monoliths have recently emerged as a new class of substrate, with unique characteristics and structure, and with selectively tailored surface chemistries for target molecules. Although several reviews exist on the applications of nanoparticles in analytical science, this review is the first to specifically summarise the applications in bioanalysis of nanoparticle-modified polymer monolithic materials. The review covers the range of nanoparticles being utilised in this way, their specific applications and future trends.

Production of novel polymer monolithic columns, with stationary phase gradients, using cyclic olefin co-polymer (COC) optical filters.

Polymer monolithic columns with controlled surface ligand density, providing stationary phase gradients within monolithic capillary columns, have been developed using photo-grafting through optical filters. Utilising commercially available cyclic olefin co-polymer (COC) films, the production of an optical filter capable of attenuating UV irradiation, in a tailored manner, was investigated. This novel optical filter was successfully applied to the surface modification of poly(BuMA-co-EDMA) monolithic columns in a multi-step grafting procedure. Fabricated columns were subjected to scanning capacitively coupled contactless conductivity (sC(4)D), to determine the distribution of the grafted functional groups, axially along the column. Further modification to produce a chelating stationary phase gradient of iminodiacetic acid (IDA) was demonstrated. To demonstrate the distribution of the IDA sites, a metal cation (Cu(2+)) was complexed to the IDA forming a chelate. Upon the formation of a complex of IDA with Cu(2+), an overall drop in conductive response was observed. The COC optical filter was also used in the fabrication of a grafted gradient of strong cation exchanger (SCX), sulphopropyl methacrylate (SPM) upon a polymer monolith, demonstrating the broader applicability of such a filter.

Fabrication and characterisation of capillary polymeric monoliths incorporating continuous stationary phase gradients.

Polymeric monoliths in capillary formats have been fabricated incorporating a gradient of charged functional groups along their length. Scanning capacitively coupled contactless conductivity detection (sC(4)D) was then used to measure the conductive response of the stationary phase and characterise the relative axial distribution of functional groups along the column length. Gradients of 2-acrylamido-2-methyl-1-propanesulphonic acid were prepared using either photografting methods or by filling a capillary column with segmented plugs of monomer mixtures each containing incrementally higher concentrations of the functional monomer. The utility of sC(4)D as a rapid and non-invasive tool for assessing the slope of a variety of gradient configurations is demonstrated. Repeatability of the sC(4)D measurements was <1.7% RSD. Columns with a gradient of covalently bonded iminodiacetic acid were also produced. Changes in the gradient slope were observed after chelation of copper on the stationary phase via a reduction of the conductive response. The effect upon the observed gradient profile of changing the co-monomer composition during column fabrication was studied.