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This chapter focuses on the liquid chromatography (LC) techniques used in the petroleum industry. It provides a brief introduction into the basic principles of LC, LC hyphenated with mass spectrometry (LC‐MS), and two‐dimensional liquid chromatography (2D‐LC). The chapter provides an overview of contemporary LC techniques for samples related to oil, refining, and wastewater encountered in the oil and petrochemical industries. Group‐type separation is commonly used to analyze quantitatively or to preparatively obtain specific fractions of oil or refined products, such as fractions containing aromatics, resins, or saturates. Besides separating petroleum samples into different hydrocarbon groups, molecular‐weight distributions of petroleum samples or fractions can be determined. This can be achieved with size‐exclusion chromatography, which separates compounds based on the hydrodynamic volume. The chapter also describes how LC can be used as a pre‐separation technique for gas chromatography analysis.

This study discusses the design aspects for the construction of a microfluidic device for comprehensive spatial two-dimensional liquid chromatography. In spatial two-dimensional liquid chromatography each peak is characterized by its coordinates in the plane. After completing the first-dimension separation all fractions are analyzed in parallel second-dimension separations. Hence, spatial two-dimensional liquid chromatography potentially provides much higher peak-production rates than a coupled column multi-dimensional liquid chromatography approach in which the second-dimension analyses are performed sequentially. A chip for spatial two-dimensional liquid chromatography has been manufactured from cyclic olefin copolymer and features a first-dimension separation channel and 21 parallel second-dimension separation channels oriented perpendicularly to the former. Compartmentalization of first- and second-dimension developments by physical barriers allowed for a preferential flow path with a minimal dispersion into the second-dimension separation channels. To generate a homogenous flow across all the parallel second-dimension channels, a radially interconnected flow distributor containing two zones of diamond-shaped pillars was integrated on-chip. A methacrylate ester based monolithic stationary phase with optimized macroporous structure was created in situ in the confines of the microfluidic chip. In addition, the use of a photomask was explored to localize monolith formation in the parallel second-dimension channels. Finally, to connect the spatial chip to the liquid chromatography instrument, connector ports were integrated allowing the use of Viper fittings. As an alternative, a chip holder with adjustable clasp locks was designed that allows the clamping force to be adjusted.

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The need for miniaturized analytical systems arises from increasing demands to the separation performance and the need of small sample and eluent consumption. Nowadays, miniaturized systems, in the format of microfabricated chips, start to take an essential place in separation science. The most common type of separation domain in such chips is a flat rectangular channel. It is then essential to design a good way to transfer a fluid in and out of this channel. Therefore, a good flow distributor is needed to obtain a "radially" homogeneous velocity field and to improve the performance of the microfluidic device. Two main groups of flow distributors, viz. "bifurcating distributors" (BF) and "radially interconnected distributors" (RI), as well as some hybrid distributors were investigated. Computational fluid dynamics was used to evaluate the performance of the distributors and to establish the design yielding the most uniform velocity field and the smallest variance for the bands eluting from the distributor.Aminimum channel width of 100 µm was considered to allow the use of micro-milling techniques for chip fabrication. The main factors that influenced the values of peak variances were identified. A strong correlation was observed between the volume of the liquid contained in the flow distributor and its performance. The separation bed should be positioned immediately after, but not against the flow distributor. The bifurcating distributors outperformed the hexagon-shaped and diamond-shaped radially interconnected flow distributors and hybrid distributors. The values of peak variances for the BF distributor decreased with increasing angle between bifurcation branches (a) and the lowest value of 0.0096 mm2 was found for a = 175°. Both BF and RI flow distributors were found to perform reasonably well when imperfections were present in the structure. One possible reason for this apparent robustness was the presence of a separation bed with a high flow resistance. A smaller angle may increase the robustness of BF distributors. However, severe blockages (exceeding 75% of the cross-sectional area and length) of channels in, especially, BF flow distributors may jeopardize their performance. The qualitative conclusions of the present study are valid independent of the size of the flow-through channels, because the BF and RI distributors were compared in a generic way, i.e., for the same number and size of inlet and exit points.

As the population of the developed world is aging, medicine is transforming the nature of the healthcare from reactive to predictive, preventive and personalized healthcare. Direct access to point of care diagnostic (POCD) tests could lead to well-organized population screening, targeted prevention of the frequent diseases, minimally-invasive diagnostics, personalized patient treatment and substantial improvement of the quality of life. Our research aims at finding potential applications of innovative analytical technologies in the point-of-care diagnostic testing. A point of care diagnostic test should be able to handle very small volume of unprocessed sample such as one drop of blood, which is a sample volume that can be easily collected by the patient at home, where he is performing the POCD test. This test should have a short analysis time, a small size, and it should be safe, inexpensive and easy to use. The purpose of this study is to demonstrate the potential of a miniaturized simplified AF4 technique for a POCD device. The separation of macromolecules from a blood sample in our device is done by the asymmetrical flow field-flow fractionation (AF4), which is a versatile flow-assisted technique. Thanks to the fractionation channel design, a wide range of macromolecules of biological origin can be separated without a modification of their native structure. Analysis of a one drop of blood is quite challenging for analysis by AF4; however it can be done in a miniaturized AF4 channel. The miniaturization of the AF4 channel dimensions reduces the sample volume required for analysis, improves the detectability of the sample, and reduces the total analysis time and the carrier liquid consumption, which are necessary attributes for the future POCD device. Furthermore, in order to speed up the analysis in the AF4 channel and minimize the sample adhesion at the channel membrane, simplification of the separation process was done by incorporating a frit inlet into the fractionation channel. In this channel design, the sample injection, relaxation, and separation processes can be continuously performed without changing the direction of flow inside the channel or stopping the flow. A miniaturized simplified AF4 channel shows promising results for a future production of a POCD test for the analysis of macromolecules in body fluids. This study focuses on the analysis of marker

Liquid chromatography (LC) is a pervasive analytical technology that allows to separate mixtures that contain non-volatile analytes, also in combination with mass spectrometry (LC-MS). However, the demands on separation performance from, for example, the fields of medicine and (systems) biology cannot be met by state-of-the-art one-dimensional LC. To address such complex separations analytical chemists must use comprehensive two-dimensional LC (LC×LC). With LC×LC it is possible to achieve very high performance separations in terms of peak capacity (more than a 1000 in less than an hour) and unique selectivities, realizing applications that cannot be addressed in any other way. In order to achieve an efficient 2D separation typically a long first-dimension column with small internal diameter is combined with a short second-dimension column with a large internal diameter. This combination is advantageous since it minimizes injection band broadening in the second dimension column volume and allows fast and efficient second dimension runs. However, the inherent drawbacks of this configuration are dilution of the sample and the inevitable splitting of the high flow rates of the 2D LC to hyphenate the setup with mass spectrometry detection. In order to surpass the paradigm of this column combination we implemented an active modulator between the first dimension (strong cation-exchange) and the second dimension (reversed phase). Stationary-phase-assisted modulation allowed us to desalt the fractions from the first dimension and reduce the injection volumes in the second dimension. Narrow injection bands from the 1D (300-µm ID) were injected in a small second-dimension column (75-µm ID) operated at flow rates in the nanoliter/min range, allowing direct hyphenation with nanospray high-resolution mass spectrometry, making this approach very beneficial for proteomic analysis. The presentation focusses on the concept of stationary-phase-assisted modulation for comprehensive LC×LC in proteomic applications, investigating various modulators to identify the best configuration for the analyses of protein digests. The set-up will be demonstrated for the analysis of a complex yeast-proteome digest.

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A polymer-based microfluidic device has been designed and constructed for comprehensive spatial two-dimensional chromatography, with each peak being characterized by its coordinates in the plane. The device manufactured from cyclic olefin copolymer (COC) features a first-dimension (1D) separation channel and 21 parallel second-dimension (2D) separation channels orientated perpendicular to the 1D channel. Compartmentalization of 1D and 2D flow by a physical barrier allowed for a preferential mobile phase flow path mainly restricted to the 1D separation channel, with a minimal dispersion into the 2D separation channels. After a 1D separation was halted, a radially-interconnected flow distributor of diamond-shaped pillars with diverging side-walls introduced the mobile phase for the 2D separation, allowing eluent inside the 1D channel to be fractionated and simultaneously injected into the 2D channels. A hydrophobic methacrylate-based monolithic stationary phase was polymerized in-situ in desired locations via aUV-initiated polymerization reaction employing a photo mask.

On-line comprehensive two-dimensional liquid chromatography techniques promise to resolve samples that current one-dimensional liquid chromatography methods cannot adequately deal with. To make full use of the potential of two-dimensional liquid chromatography, optimization is required. Optimization of two-dimensional liquid chromatography is a relatively new yet important research topic the aim of which is to predict combinations of stationary and mobile phases, column formats, and chromatographic conditions that maximize resolving power and minimize analysis time. In on-line two-dimensional liquid chromatography, dilution-related issues play also an important role and these should be taken into account when developing optimization strategies. In this work, state-of-the-art strategies that support method development for on-line two-dimensional liquid chromatography through a rigorous choice of chromatographic parameters are critically reviewed. The final aim is to provide practitioners with a clear understanding of which aspects can be optimized using current on-line two-dimensional liquid chromatography strategies (and which ones cannot). In two-dimensional liquid chromatography, maximizing resolving power for a given analysis time and dilution requires optimizing efficiency, selectivity and retention. While great strides forward have been made in the optimization of efficiency-related issues, considerable effort needs still to be made in terms of (1) developing models that can predict the retention factors that given stationary/mobile phase systems can provide and (2) using this information for choosing the two ones that maximize two-dimensional liquid chromatography orthogonality. Because of this limitation, in two-dimensional liquid chromatography, this aspect is typically dealt with a posteriori through examining chromatograms. This review clearly shows that important progress in the optimization of on-line two-dimensional liquid chromatography has recently been made.

This article describes an optimization strategy to obtain the best possible performance in the shortest analysis time—called the peak production rate—for comprehensive off-line two-dimensional liquid chromatography. The demands on column technology (particle size and column length) and LC conditions (including sampling time, gradient time and slope, and column-equilibration time) are discussed. The potential of off-line 2D-LC coupled to tandem mass spectrometry detection is demonstrated with the analysis of proteomics samples of various complexities and a trade-off is made between the 1D-LC and off-line 2D-LC performance.

Contains fulltext : 112340.pdf (Publisher’s version ) (Open Access)

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