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How Reversed-Phase Liquid Chromatography WorksThis tutorial on reversed-phase LC explains the role of solvent, chain conformation, solute position, and retention dynamics.
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Separation of Lactulose and EpilactoseLactulose, a semi-synthetic disaccharide, is a useful indicator for heat induced modifications in milk. Lactulose can be derived from lactose by alkaline isomerization or enzymatic transgalactosylation of fructose.
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A Day at the RacesThe Column spoke to Steve Maynard, Lab Director at LGC's HFL Sport Science, about his work in the world of horse doping and his laboratory's involvement in this years Olympic and Paralympic Games.
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Analyzing Synthetic Cathinones Using Direct Sample Analysis Time-of-Flight Mass SpectrometryDirect sample analysis coupled to high-resolution time-of-flight mass spectrometry (TOF-MS) may be effective at analyzing synthetic cathinones, especially for qualitative analysis, because it does not require potentially tedious sample preparation.
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Current Practices and Considerations for a Stability-Indicating Method in Pharmaceutical AnalysisWhat are the characteristics and relevant considerations for the development and validation of a stability-indicating method?
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The Use of Light-Scattering Detection with SEC and HPLC for Protein and Antibody Studies, Part II: Examples and Comparison to Mass SpectrometryDetailed examples of light-scattering techniques are presented as well as how their performance compares to MS and other methods.
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The Modulator in Comprehensive Two-Dimensional Liquid ChromatographyThe interface between the two separation dimensions is a key element of any comprehensive two‑dimensional liquid chromatography (LC×LC) system. LC×LC has typically been implemented by using one or more switching valves, equipped with either sampling loops or trap column(s). Temperature manipulation is a relatively unexplored yet promising route towards non-valve-based LC×LC. The fairly recent emergence of thermal modulation has provided a less conventional method for performing LC×LC separations. This article illustrates the variety of commonly used modulators, paying specific attention to focusing modulators.
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Modern Trends and Best Practices in Mobile-Phase Selection in Reversed-Phase ChromatographyThis instalment provides an overview of the modern trends and best practices in mobile-phase selection for reversed-phase liquid chromatography (LC). In particular, we focus on selection criteria and rationales for enhancing analytical performance and ease of preparation.
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A New Method for Quality by Design Robust Optimization in Liquid ChromatographyA new method to optimize liquid chromatography (LC) methods using a Quality by Design (QbD) approach is presented. This method is based on the use of design of experiments (DOE) and independent component analysis (ICA) to accurately estimate the modeled responses (that is, the retention times at the beginning, the apex, and the end) of each peak, even for coeluted peaks. This method was applied to the optimization of the separation of nine compounds in a mixture, yielding the design space and the demonstration of robustness of the method.
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Development of an Ultrasensitive LC–MS-MS Method for Determination of 5-Fluorouracil in Mouse Plasma5-Fluorouracil (5-FU) is a low-molecular-weight anticancer drug in clinical use for several solid tumors in humans. Currently, the most widely used methodology for 5-FU quantitation is liquid chromatography–tandem mass spectrometry (LC–MS-MS) with either liquid–liquid extraction (LLE), protein precipitation, or a combination of both as sample cleanup procedures.
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Advantages of HILIC Mobile Phases for LC–ESI–MS–MS Analysis of NeurotransmittersThe aim of this work was to find the optimal conditions to achieve sufficient limits of detection (LOD) that would permit the detection of neurotransmitters by LC–MS–MS in biological samples. An optimized HILIC–ESI–MS–MS system for the analysis of the 12 selected compounds was proposed.
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Maximizing Robustness and Throughput in Liquid Chromatography by Using Pressure-Controlled OperationAnalysis time can be reduced 10–30% by switching from constant-flow-rate mode to a constant-pressure gradient-elution mode.
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Variable Retention Times — A Case StudyThis troubleshooting study of a problem of retention time variation provides a good example of how to track down the source of a problem and how to speculate on probable cause.
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Analysis of Low Level Pyrethroid Pesticides in WaterA method for the determination of pyrethroids in water at ultra-low-level concentrations of 0.02 and 0.10 ng/mL was developed using solid-phase extraction (SPE) for pre-concentration and subsequent analysis by GC with PTV injection.
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Determination of Contaminants in Beer Using LC–MS/MS and ICP-MSThe German Beer Purity Law of 1516 makes beer one of the best analyzed food products with the highest standards regarding quality, freshness, appearance, and flavor. According to this law, beer is allowed to contain hops, malt, yeast, and water as ingredients. Of course, beer also contains major B vitamins, bitter substances, and minerals and trace elements (such as Ca, Na, Mg, and Zn) that are important for human nutrition. However, undesirable substances such as pesticides and heavy metals (for instance Cd, Pb, Hg, Sb, and As) can be found as well, mostly as contaminants in brewing water and grains. In particular, the herbicide glyphosate has to be monitored carefully since it is discussed as a possible carcinogenic. The chromatography of glyphosate is challenging because of its high polarity. A well-established method including a derivatization step with 9-fluorenylmethyl chloroformate (FMOC) followed by LC–MS analysis is time-consuming and also susceptible to errors. A sample pretreatment without derivatization is desirable because it is faster and cheaper. A triple quadrupole mass spectrometer optimizes the analytical procedure and establishes a routine method for the analysis of glyphosate in beer. For the determination of low element concentrations, such as As, Se, Pb, Cd, and Zn, inductively coupled plasma-mass spectrometry (ICP-MS) is applied.
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Applying LC with Low-Resolution MS/ MS and Subsequent Library Search for Reliable Compound Identification in Systematic Toxicological AnalysisSystematic toxicological analysis is an important step in medicolegal investigations of death, poisoning, and drug use. The primary goal is the detection and confirmation of potentially toxic compounds in evidence. This article describes a workflow using nontargeted liquid chromatography–tandem mass spectrometry (LC–MS/MS) for reliable compound identification.
Latest:
A New Method for Quality by Design Robust Optimization in Liquid ChromatographyA new method to optimize liquid chromatography (LC) methods using a Quality by Design (QbD) approach is presented. This method is based on the use of design of experiments (DOE) and independent component analysis (ICA) to accurately estimate the modeled responses (that is, the retention times at the beginning, the apex, and the end) of each peak, even for coeluted peaks. This method was applied to the optimization of the separation of nine compounds in a mixture, yielding the design space and the demonstration of robustness of the method.
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Application of Pyrolysis–Gas Chromatography–Mass Spectrometry for the Identification of Polymeric MaterialsThe pyrolysis–GC–MS method enables direct analysis of solid or liquid polymers without sample pretreatment, as illustrated here for various materials, including a dental filling material and a car wrapping foil.
