Separations, Volume 3, Issue 3 (September 2016) – 8 articles

The development of separation methods for the analysis and resolution of chiral drugs and solutes has been an area of ongoing interest in pharmaceutical research. The use of proteins as chiral binding agents in high-performance liquid chromatography (HPLC) has been an approach that has received particular attention in such work. This report provides an overview of proteins that have been used as binding agents to create chiral stationary phases (CSPs) and in the use of chromatographic methods to study these materials and protein-based chiral separations. The supports and methods that have been employed to prepare protein-based CSPs will also be discussed and compared. Specific types of CSPs that are considered include those that employ serum transport proteins (e.g., human serum albumin, bovine serum albumin, and alpha₁-acid glycoprotein), enzymes (e.g., penicillin G acylase, cellobiohydrolases, and α-chymotrypsin) or other types of proteins (e.g., ovomucoid, antibodies, and avidin or streptavidin). The properties and applications for each type of protein and CSP will also be discussed in terms of their use in chromatography and chiral separations. Full article

At present, gas chromatography–quadrupole mass spectrometry (GC-qMS) is considered the gold standard amongst analytical techniques for fire debris analysis in forensic laboratories worldwide, specifically for the detection and classification of ignitable liquids. Due to the highly complex and unpredictable nature of fire debris, traditional one-dimensional GC-qMS often produces chromatograms that display an unresolved complex mixture containing only trace levels of the ignitable liquid among numerous background pyrolysis products that interfere with pattern recognition necessary to verify the presence and identification of the ignitable liquid. To combat these challenges, this study presents a method optimized to achieve a near-theoretical maximum in peak capacity gain using comprehensive two-dimensional gas chromatography (GC×GC) coupled to time-of-flight mass spectrometry (TOFMS) for the forensic analysis of petroleum-based ignitable liquids. An overall peak capacity gain of ~9.3 was achieved, which is only ~17% below the system’s theoretical maximum of ~11.2. In addition, through the preservation of efficient separation in the first dimension and optimal stationary phase selection in the second dimension, the presented method demonstrated improved resolution, enhanced sensitivity, increased peak detectability and structured chromatograms well-suited for the rapid classification of ignitable liquids. As a result, the method generated extremely detailed fingerprints of petroleum-based ignitable liquids including gasoline, kerosene, mineral spirits and diesel fuel. The resultant data was also shown to be amenable to chromatographic alignment and multivariate statistical analysis for future evaluation of chemometric models for the rapid, objective and automated classification of ignitable liquids in fire debris extracts. Full article

This paper introduces organic phases with aligned carbonyl groups derived from l-aspartic acid, l-glutamic acid, and l-α-aminoadipic acid; their stationary phases are denoted as Sil-Asp-2C_n, Sil-Glu-2C_n, and Sil-Adi-2C_n, respectively. The stationary phases were used in high-performance liquid chromatography to investigate the alignment effect of carbonyl groups, which act as π-interaction sites, on molecular shape selectivity. The selectivities of the synthesized organic phases were evaluated using polyaromatic hydrocarbons (PAHs), including geometric isomers (e.g., cis- and trans-stilbenes). The PAH selectivities of the prepared stationary phases were higher than that of conventional octadecyl silica. Among the stationary phases prepared in this study, Sil-Glu-2C_n (n = 18) showed the highest selectivity toward terphenyl isomers with different twist configurations and the lowest selectivity toward planar PAHs with different aspect ratios. The results show that the molecular shape selectivity of the phases was affected by the alignment of interaction sites. As a practical application of the octadecylated amino acid derivative-bonded stationary phases, we evaluated their selectivity for tocopherol isomers and achieved good separation. Furthermore, Sil-Asp-2C_n (n = 1) showed hydrophilic interaction chromatography mode retention behavior for the separation of polar molecules like nucleosides. Full article

Forensic investigations often require postmortem examination of a body. However, the collection of evidence during autopsy is often destructive, meaning that the body can no longer be examined in its original state. In order to obtain an internal image of the body, whole body postmortem computed tomography (PMCT) has proven to be a valuable non-destructive tool and is currently used in medicolegal centers. PMCT can also be used to visually locate gas reservoirs inside a cadaver, which upon analysis can provide useful information regarding very volatile compounds that are produced after death. However, the non-targeted profiling of all potential volatile organic compounds (VOCs) present in these reservoirs has never been attempted. The aim of this study was to investigate the VOC profile of these reservoirs and to evaluate potential uses of such information to document circumstances surrounding death, cause of death and body taphonomy. Comprehensive two-dimensional gas chromatography coupled to time-of-flight high-resolution mass spectrometry (GC×GC-HRTOF-MS) was used for VOC measurements. This study demonstrated that the chemical composition of VOCs within the gas reservoirs differed between locations within a single body but also between individuals. In the future, this work could be expanded to investigate a novel, non-destructive cadaver screening approach prior to full autopsy procedures. Full article

Robinia pseudoacacia L. is a tree widely dispersed in France that is characterized by good growth rates and important biomass production, which produces wood with very high natural durability used for outdoor fence posts, timber, and barrels to age vinegars and wines. Its mature heartwood presents high resistance against wood fungi decay and contains two main flavonoid extractives, dihydrorobinetin—the most abundant—and robinetin that present interesting biological activities. The aim of the present study was to optimize a procedure allowing an important recovery of purified dihydrorobinetin from R. pseudoacacia wood, representing an interesting sustainable, local, highly available, and, consequently, economical source of bioactive components. The extraction of dihydrorobinetin was first optimized by evaluating the influence of various extraction parameters such as temperature, extraction time, solvent nature, and wood/solvent mass ratio to obtain an efficient, safe, and low cost extraction. Then, dihydrorobinetin was purified over 95% using centrifugal partition chromatography (CPC). CPC purification was first developed on a small volume column with low amounts of injected extract, then scaled-up on a 200 mL column with higher sample loading capacity in order to purify more than 1.3 g of dihydrorobinetin in one run. Full article

A simple and rapid capillary electrophoretic method was developed for the simultaneous determination of two sulfonylurea herbicides in water samples: metsulfuron-methyl (MSM) and nicosulfuron (NS). These herbicides are widely used in agricultural practices and their residues represent potential environment pollutants in waters and soils. The effect of the pH of the background electrolyte solution (BGE), the percentage of methanol in the BGE and the separation voltage were studied on the resolution of MSM and NS. A 2³ factorial design was used to identify the main factors which significantly influenced the separation of these compounds. Other parameters were evaluated by the univariate method. The experimental results show that using a BGE composed of 25 mmol·L⁻¹ sodium borate and 3% (v/v) of methanol at pH 8.5 and applying 15 kV, satisfactory analysis time and resolution between peaks can be obtained. The linear range for both analytes was 0.1–2.0 µg·mL⁻¹. The detection limits were 0.034 µg·mL⁻¹ for MSM and 0.044 µg·mL⁻¹ for NS. Surface water and groundwater samples were analyzed applying the new method, and the obtained results presented satisfactory recovery percentages (82%–102%). Full article

The majority of atmospheric measurements of volatile organic compounds (VOCs) are usually limited to a small range, either in volatility or time resolution. A combined heart-cut gas chromatography (GC) with comprehensive two-dimensional GC (GC×GC) instrument was developed, specifically to increase the number of VOCs analysed using a single instrument. The system uses valve based modulation and was fully automated, making it suitable for use in the field. A laboratory comparison to an existing dual-channel GC (DC-GC) instrument demonstrated that this new GC-GC×GC can accurately measure atmospheric mixing ratios of C ${}_5$ -C ${}_{13}$ VOC species with a wide range of functionalities. Approximately hourly field measurements were conducted at a remote marine atmospheric research station in Bachok, Malaysia. This region was shown to be influenced by clean marine air masses, local anthropogenic and biogenic emission sources and aged emissions transported from highly polluted South East Asian regions. A dramatic shift in air mass direction was observed each day associated with the development of a sea breeze, which influenced the diurnal profiles of species measured at the Bachok site. A proton-transfer-reaction mass spectrometer (PTR-MS) was also deployed at Bachok and compared to the new GC-GC×GC instrument. Overall, the GC-GC×GC instrument has been shown to perform well in lab comparisons and during field observations. This represents a good compromise between volatility and high complexity $online$ measurements of VOCs. Full article

Some commercial sweet sorghum syrups can be fraudulently or accidently adulterated with inexpensive sugar syrups, particularly high fructose corn syrup (HFCS) or corn syrup, and sold at a relatively low market price or even mis-branded. This undermines the economic stability of the current small-scale producers of food-grade sweet sorghum syrup as well as the developing large-scale bioproduct industry. An analytical method is urgently needed to evaluate adulterated commercial sweet sorghum syrups. Ion chromatography with integrated pulsed amperometric detection (IC-IPAD) has been previously used to differentiate white, refined sugars manufactured from sugarcane and sugar beet. By applying a strong IC-IPAD NaOH/NaOAc gradient method over 45 min, monosaccharides, oligosaccharides and oligosaccharide isomers of at least 2 to 12 dp, as well as sugar alcohols can be detected in multiple commercial sweet sorghum and other sugar syrups. Fingerprint IC oligosaccharide profiles are extremely selective, sensitive, and reliable. By using five characteristic marker chromatography peaks of high fructose corn syrup (HFCS), including isomaltose, maltose and maltotriose, in combination with a low sucrose peak, adulterated and mis-branded syrups were identified. The analysis of 7.0 Brix blind syrup samples, marker peaks allowed the detection of as low as 10% HFCS adulteration, which is within the lower limit of adulteration before action is taken. Full article