Sample pre-fractionation of environmental and food samples using LC-GC multidimensional techniques

A novel olfactory biosensor based on ZIF-8@SWCNT integrated with nanosome-AuNPs/Prussian blue for sensitive detection of hexanal

Hexanal is considered as an important volatile compound indicator for the assessment of freshness and maturity of foods. Therefore, sensitive and stable monitoring of hexanal is highly desired. Herein, an efficient receptor immobilization strategy based on ZIF-8@ Single-walled carbon nanotube (SWCNT) and nanosomes-AuNPs/Prussian blue (PB) was proposed for the development of olfactory biosensors. ZIF-8@SWCNT as dual support materials provided a high density of active sites for nanosomes loading. Moreover, the co-electrodeposition of nanosomes-AuNPs and PB on the sensor interface effectively amplified the electrochemical signal and maintained the activity of the receptor. The combination of ZIF-8@SWCNT with AuNPs/PB imparts excellent sensing performance of the biosensor with a wide detection range of 10-16-10-9 M, a low detection limit of 10-16 M for hexanal, and a long storage stability of 15 days. These results indicate that our biosensor can be a powerful tool for versatile applications in food and other related industries.

Determination of mineral oil hydrocarbon contamination in Citrus essential oils by using on-line liquid-gas chromatography: critical aspects

The present manuscript reports and discusses critical issues related to the determination of mineral oil hydrocarbon contamination in Citrus essential oils (EOs); an on-line liquid-gas chromatography system equipped with a Y-interface was used (with no additional off-line step for pre-concentration). In total, eighteen samples were analyzed, specifically eleven cold-pressed (CP) and seven distilled EOs. With regard to the CP EOs, various degrees of mineral oil saturated hydrocarbon (MOSH) contamination were detected, ranging between 10.7 and 338.4 mg kg-1 (only one sample was MOSH-free); different MOSH sub-fractions were determined, with the  > C25- ≤ C35 sub-fraction always present, with an average concentration of 74.5 mg kg-1. Based on the EO composition, different sample amounts were injected to avoid the overloading of the LC column and consequently the GC one, thus leading to different limits of quantification (LoQ), which were either 2 mg kg-1 (for bergamot EO) or 5 mg kg-1 (for all the other investigated samples). For all samples, the mineral oil aromatic hydrocarbon level was always lower than the LoQ.

The role of comprehensive two-dimensional gas chromatography in mineral oil determination

Mineral oil hydrocarbons (MOH) contain a wide structural diversity of molecules, for which the reference method of analysis is the online coupled liquid chromatography-gas chromatography with flame ionization detection (LC-GC-FID). These compounds are very heterogeneous from a toxicological viewpoint, and an accurate risk assessment when dealing with a MOH contamination can only be performed if sufficient information is available on the types of structures present (i.e., number of carbons, degree of alkylation, number of aromatic rings). Unfortunately, the separation performances of the current LC-GC-FID method are insufficient for such characterization, not even mentioning the possible coelution of interfering compounds which additionally hinder MOH determination. Comprehensive two-dimensional gas chromatography (GC × GC), while mostly used for confirmation purposes in the past, starts to prove its relevance for overcoming the weaknesses of the LC-GC method and reaching even better the analytical requirements defined in the latest EFSA opinion. The present paper therefore aims at highlighting how GC × GC has contributed to the understanding of the MOH topic, how it has developed to meet the requirements of MOH determination, and how it could play a role in the field for overcoming many of the current analytical and toxicological challenges related to the topic.

Multidimensional Chromatography and Its Applications in Food Products, Biological Samples and Toxin Products: A Comprehensive Review

Food, drugs, dyes, extracts, and minerals are all made up of complex elements, and utilizing unidimensional chromatography to separate them is inefficient and insensitive. This has sparked the invention of several linked chromatography methods, each of them with distinct separation principles and affinity for the analyte of interest. Multidimensional chromatography consists of the combination of multiple chromatography techniques, with great benefits at the level of efficiency, peak capacity, precision, and accuracy of the analysis, while reducing the time required for the analysis. Various coupled chromatography techniques have recently emerged, including liquid chromatography–gas chromatography (LC–GC), gas chromatography–gas chromatography (GC–GC), liquid chromatography–liquid chromatography (LC–LC), GCMS–MS, LCMS–MS, supercritical fluid techniques with chromatography techniques, and electro-driven multidimensional separation techniques. In this paper, the different coupled chromatography techniques will be discussed, along with their wide spectrum of applications for food, flavor, and environmental analysis, as well as their usefulness for the pharmaceutical, color, and dyes industries.

Occurrence of n-Alkanes in Vegetable Oils and Their Analytical Determination

Vegetable oils contain endogenous linear hydrocarbons, namely n-alkanes, ranging from n-C21 to n-C35, with odd chain lengths prevalent. Different vegetable oils, as well as oils of the same type, but of different variety and provenience, show typical n-alkane patterns, which could be used as a fingerprint to characterize them. In the first part of this review, data on the occurrence of n-alkanes in different vegetable oils (total and predominant n-alkanes) are given, with a focus on obtaining information regarding variety and geographical origin. The second part aims to provide the state of the art on available analytical methods for their determination. In particular, a detailed description of the sample preparation protocols and analytical determination is reported, pointing out the main drawbacks of traditional sample preparation and possible solutions to implement the analysis with the aim to shift toward rapid and solvent-sparing methods.

Improving enantiomeric resolutions by avoiding peak distortion effects in on-line coupled liquid chromatography to gas chromatography

In this work, we study the effect of different variables affecting elution profile distortion on the enantiomeric resolution eventually achievable when working with on-line coupled liquid chromatography to gas chromatography (LC-GC). Specifically, the proposed configuration combines achiral reversed-phase liquid chromatography (RPLC) and chiral gas chromatography (enantio-GC), with heptakis-(2,3,6-tri-O-methyl)-β-cyclodextrin as enantioselective stationary phase to analyse target fractions transferred (from LC to GC) via the through oven transfer adsorption desorption (TOTAD) interface. The high degree of orthogonality resulting from the combination of two chromatographic columns having very different separation mechanisms (and also requiring mobile phases in distinct physical states), as well as integration of the sample preparation step in the first dimension of the system, significantly contributed to exploit the performance of the proposed two-dimensional approach. Occasional adverse effects, which may result in severe peak distortions during LC-GC analysis and could be explained by flow instabilities due to viscous fingering, are circumvented by using the outstanding capacity of the TOTAD interface for achieving effective elimination of the eluent arriving from the LC preseparation.

Separation and Analysis of Sucrose Esters in Tobacco by Online Liquid Chromatography-Gas Chromatography/Mass Spectrometry

In this work, a strategy of in-series combination of ultrasound-assisted extraction and online LC-GC/MS was constructed for effective separation and analysis of sucrose esters in tobacco. Sucrose esters were first extracted by ultrasound-assisted extraction with high efficiency and easyhandling. Online LC-GC/MS was then applied for sucrose ester clean-up and analysis. To better evaluate the effectiveness of this strategy, we limited our focus to five groups of sucrose ester isomers. Each group differed in mass from the next by 14 Da. The obtained coefficient of the calibration curve was 0.9986. Limit of detection (LOD) and limit of quantitation (LOQ) were 0.05 and 0.16 μg/ mL, respectively. The recovery was above 90% and the reproducibility was below 4%. This strategy was subsequently applied to the comparison of relative amounts of five groups of sucrose esters extracted from three different parts of aromatic tobacco. The satisfactory performance indicated that this strategy has great prospect for the rapid and high-throughput analysis of sucrose esters in tobacco.

Exploration of scalp surface lipids reveals squalene peroxide as a potential actor in dandruff condition

Dandruff is a common but complex disorder with three major contributing factors: (1) individual predisposition, (2) scalp sebum and (3) Malassezia yeast colonization. To obtain further insights into the role of sebum in dandruff biogenesis, we analyzed scalp lipid species in a cohort of ten dandruff-free (control) and ten dandruff-afflicted volunteers by gas chromatography coupled to mass spectrometry. Lipid peroxidation levels and biochemical markers of oxidative stress were also assessed. Squalene, a major sebum component, was significantly more peroxidized in dandruff-affected scalps, resulting in significantly higher ratios of squalene monohydroperoxide (SQOOH)/squalene. This was observed when comparing dandruff-affected zones of dandruff subjects to both their non-affected zones and control subjects. In addition, other biomarkers such as malondialdehyde indicated that oxidative stress levels were raised on dandruff scalps. Surprisingly, differences regarding either free or bound fatty acids were fairly rare and minor. Certain novel findings, especially squalene peroxidation levels, were then confirmed in a validation cohort of 24 dandruff-affected subjects, by comparing dandruff-affected and non-dandruff zones from the same individuals. As SQOOH can induce both keratinocyte inflammatory responses and hyperproliferation in vitro, we hypothesized that increased SQOOH could be considered as a new etiological dandruff factor via its ability to impair scalp barrier function. Our results also indicated that Malassezia could be a major source of squalene peroxidation on the scalp.

On-line coupled reversed phase liquid chromatography and gas chromatography: a new sealing design for the TOTAD interface

Total elimination of the eluent resulting from the pre-separation step is the critical point when coupling LC to GC. As a helium flow is applied during transfer to eliminate the solvent, the interface used for linking the two chromatographic systems must be properly sealed to prevent gas leaks and to achieve an effective evaporation of the eluent. The aim of this work was to improve the performance of the Through Oven Transfer Adsorption Desorption (TOTAD) interface to remove the eluent coming from LC by modifying the way in which the injector sealing system is held in place. As with the original design, the new approach makes it possible to transfer high volumes at a high rate, but the proposed modification also simplifies the experimental work because the displacement risk of the sealing system is reduced. Analyses of an ester mixture by RPLC-GC were performed to confirm the applicability of the system modification. In this work, volumes of up to 5 ml, at flow rates as high as 2 ml/min, were transferred from LC to GC with almost complete solvent removal even when working in reversed phase mode in the LC step.