Abstract: In this report we demonstrate a practical multivariate design of experiment (DoE) approach for asymmetric flow field-flow fractionation (AF4) method optimization using separation of lipoprotein subclasses as an example. First, with the aid of commercially available software, we built a full factorial screening design where the theoretical outcomes were calculated by applying established formulas that govern AF4 channel performance for a 5–35 nm particle size range of interest for lipid particles. Second, using the desirable ranges of instrumental parameters established from theoretical optimization, we performed fractional factorial DoE for AF4 separation of pure albumin and ferritin with UV detection to narrow the range of instrumental parameters and allow optimum size resolution while minimizing losses from membrane immobilization. Third, the optimal range of conditions were tested using response surface DoE for sub-fractionation of high and low density lipoproteins (HDL and LDL) in human serum, where the recovery of the analytes were monitored by fraction collection and isotope-dilution LC-MS/MS analysis of each individual fraction for cholesterol and apolipoproteins (ApoA-1 and ApoB-100). Our results show that DoE is an effective tool in combining AF4 theoretical knowledge and experimental data in finding the most optimal set of AF4 instrumental parameters for quantitative coupling with LC-MS/MS measurements.
Abstract: Monolithic columns are gaining interest as excellent substitutes to conventional particle-packed columns. These columns show higher permeability and lower flow resistance than conventional liquid chromatography columns, providing high-throughput performance, resolution and separation in short run times. Monoliths possess also great potential for the clean-up and preparation of complex mixtures. In situ polymerization inside appropriate supports allows the development of several microextraction formats, such as in-tube solid-phase and pipette tip-based extractions. These techniques using porous monoliths offer several advantages, including miniaturization and on-line coupling with analytical instruments. Additionally, monoliths are ideal support media for imprinting template-specific sites, resulting in the so-called molecularly-imprinted monoliths, with ultra-high selectivity. In this review, time-saving LC columns and preparative applications applied to the analysis of residues and contaminants in food in 2010–2014 are described, focusing on recent improvements in design and with emphasis in automated on-line systems and innovative materials and formats.
Abstract: A method for the determination of trichloroethylene (TCE) in water using portable gas chromatography/mass spectrometry (GC/MS) was developed. A novel sample preparation method, liquid–liquid microextraction assisted solid phase microextraction (LLME–SPME), is introduced. In this method, 20 µL of hexane was added to 10 mL of TCE contaminated aqueous samples to assist headspace SPME. The extraction efficiency of SPME was significantly improved with the addition of minute amounts of organic solvents (i.e., 20 µL hexane). The absolute recoveries of TCE at different concentrations were increased from 11%–17% for the samples extracted by SPME to 29%–41% for the samples extracted by LLME–SPME. The method was demonstrated to be linear from 10 to 1000 ng mL−1 for TCE in water. The improvements on extraction efficiencies were also observed for toluene and 1, 2, 4-trichlorobenzene in water by using LLME–SPME method. The LLME–SPME method was optimized by using response surface modeling (RSM).
Abstract: Monolithic column materials offer great advantages as chromatographic media in bioseparations and as solid-supports in biocatalysis. These single-piece porous materials have an interconnected ligament structure that limits the void volume inside the column, thus increasing the efficiency without sacrificing the permeability. The preparation of monolithic materials is easy, reproducible and has available a wide range of chemistries to utilize. Complex, heterogeneous and isobaric glycan structures require preparation methods that may include glycan release, separation and enrichment prior to a comprehensive and site-specific glycosylation analysis. Monolithic column materials aid that demand, as shown by the results reported by the research works presented in this review. These works include selective capture of glycans and glycoproteins via their interactions with lectins, boronic acids, hydrophobic, and hydrophilic/polar functional groups on monolith surfaces. It also includes immobilization of enzymes trypsin and PNGase F on monoliths to digest and deglycosylate glycoproteins and glycopeptides, respectively. The use of monolithic capillary columns for glycan separations through nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) and coupling these columns to MS instruments to create multidimensional systems show the potential in the development of miniaturized, high-throughput and automated systems of glycan separation and analysis.
Abstract: Fruit leathers (FLs) production produces some not-to-specification material, which contains valuable ingredients like fruit pulp, sugars and acidulates. Recovery of FL for product recycling requires decolorization. In earlier research, we proved the efficiency of an ozone-based decolorization process; however, it produces carbonyls as major byproducts, which could be of concern. A headspace solid-phase microextraction with on-fiber derivatization followed by gas chromatography-mass spectrometry was developed for 10 carbonyls analysis in ozonated FL solution/suspension. Effects of dopant concentration, derivatization temperature and time were studied. The adapted method was used to analyze ozonated FL solution/suspension samples. Dopant concentration and derivatization temperature were optimized to 17 mg/mL and 60 °C, respectively. Competitive extraction was studied, and 5 s extraction time was used to avoid non-linear derivatization of 2-furfural. The detection limits (LODs) for target carbonyls ranged from 0.016 and 0.030 µg/L. A much lower LOD (0.016 ppb) for 2-furfural was achieved compared with 6 and 35 ppb in previous studies. Analysis results confirmed the robustness of the adapted method for quantification of carbonyls in recycled process water treated with ozone-based decolorization. Ethanal, hexanal, 2-furfural, and benzaldehyde were identified as byproducts of known toxicity but all found below levels for concern.