The Application Notebook July 2017

July 2017 | Volume 30, Issue 2
Environmental
Polycyclic aromatic hydrocarbons (PAHs) are found worldwide and are emitted from a number of sources including fossil fuel, coal and shale oil derivatives, coke production, and burning wood for home heating, and generally arise from incomplete combustion. Surface water supplies, such as water in ponds, may be used for recreational purposes or become a drinking water source. Characterization of PAHs and their concentration is of interest in maintaining public health.
By LCGC Editors
Perfluorinated alkyl acids are man-made fluorochemicals used as surface-active agents in the manufacture of a variety of products, such as firefighting foams, coating additives, textiles, and cleaning products. They have been detected in the environment globally and are used in very large quantities around the world. These fluorochemicals are extremely persistent and resistant to typical environmental degradation processes. As a result, they are widely distributed across the higher trophic levels and are found in soil, air, groundwater, municipal refuse, and landfill leachates. The toxicity, mobility, and bioaccumulation potential of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), in particular, pose potential adverse effects for the environment and human health.
Food and Beverage
Honey is a high-value commodity, whose quality is defined both by its botanical and geographical origin. This generates a strong consumer demand for certain, premium-priced products, which have become the target for adulterations. A useful tool to detect the addition of sugar to honey products is based on the well-documented difference in δ13C values between C3 (natural honey) and C4 (added sugar) plants. Coupling high performance liquid chromatography (HPLC) with isotope ratio mass spectrometry (LC–IRMS) has the unrivaled advantage of the simultaneous determination of δ13C values from glucose, fructose, di-, tri-, and oligo-saccharides, allowing the detection of more sophisticated honey adulteration with a simple user-friendly analytical system.
By LCGC Editors
Mycotoxins are secondary metabolites produced by several species of fungi and are considered one of the most significant contaminants of agricultural commodities, both in the field and in storage. Agricultural products that may be affected include cereals, spices, dried fruits, and various nuts. Although hundreds of mycotoxins are known, relatively few are considered to pose a significant health risk. Aflatoxins, in particular aflatoxin B1, are genotoxic and carcinogenic and may cause liver cancer in humans, whilst ochratoxin A and the trichothecenes HT-2 and T-2 can cause various toxic effects. Monitoring and control of certain mycotoxins is important within the food industry because of their potential toxicity at low levels to both humans and animals.
Hydrophilic interaction liquid chromatography coupled to electrospray ionization mass spectrometry (HILIC–ESI-MS) has been established as a method to separate and quantify polar and ionic analytes in a direct way for two decades. HILIC separation is based on the polarity of analytes, so the more polar analytes have stronger retention on a HILIC column.
This study shows that the organic compounds giving rise to the flavour of a variety of beverages can be identified by high-capacity sorptive extraction using PDMS probes, with analysis by thermal desorption–GC–MS.
Gas chromatography–mass spectrometry (GC–MS) allows isolation and identification of individual analytes within a complex mixture. Helium has traditionally been the first-choice carrier gas, owing to its inertness, performance, and relatively cheap price. Since 2001, however, helium has become increasingly expensive with a reported global increase in price of 500% between 2001 and 2016 (1). In 2012–2013, the global helium shortage increased the number of GC users switching to alternative carrier gases and improved the availability of information on their use.
Coffee is one of the most widely consumed beverages in the world, partly because of the stimulating effect of its caffeine content. Like most crops, the application of pesticides in coffee cultivation is a common practice to increase production yields. This application note details an optimized method for the extraction and cleanup of pesticide residues from coffee using a QuEChERS extraction procedure followed by a silica gel solid-phase extraction (SPE) cleanup.
Medical/Biological
By LCGC Editors
While on-line multi-angle light scattering (MALS) is one of the most important techniques for macromolecular characterization, it can be made even more versatile with the addition of a quasielastic light scattering (QELS, a.k.a. dynamic light scattering) module for determination of hydrodynamic radius. QELS can be added to a Wyatt MALS system as a WyattQELS™ module embedded in the MALS instrument, or by connecting the MALS flow cell to a batch DLS instrument such as a DynaPro® NanoStar® or Mobius® via optical fibre. The QELS instruments can be used to determine the hydrodynamic radius, rh , for a variety of samples in a continuous‑flow mode. The combined MALS-QELS system will measure simultaneously rg, rh, and the absolute molar mass.
By LCGC Editors
Quality and consistency in reagents is critical to successful drug discovery and development. When targeting a particular protein of interest, in vitro experiments should be performed with proteins of biological properties similar to those for in vivo tests. It is important that molecularity, purity, shape, and degree of heterogeneity remain the same when any alterations are made to the model protein or the formulation buffer. Multi-angle light scattering (MALS) combined with size-exclusion chromatography (SEC-MALS) is a very useful technique to monitor the solution properties of the protein as changes to reagents are made.
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