Retention Index System Research Articles

Quality Control of Coumarins, Furocoumarins and Polymethoxyflavones in Citrus Essential Oils: In Silico Analysis

AbstractCitrus essential oils (EOs) contain a variety of secondary metabolites, including coumarins (Cs), furocoumarins (FCs) and polymethoxyflavones (PMFs), all with different biological activities. While Regulation (EC) No 1334/2008 strictly regulates the use of coumarins, undesirable side effects of consuming furocoumarins remain without established maximum toxicity limits for human dietary intake. This study is based on an in‐silico approach aimed at determining these toxicity limits for the oxygenated heterocyclic compounds of citrus EOs approved for use in food. In addition, an innovative quantitative structure‐property relationship (QSPR) using the linear retention index system was explored to characterize the oxygenated heterocyclic compounds (COHs) present in these essential oils. Molecular docking of the studied compounds provided crucial insights into the structure‐odor relationships, offering insights into their mechanisms of action. In addition, an analysis of the pharmacokinetic and pharmacodynamic properties through ADME‐Tox deconstruction provides insight into the potential side effects of their consumption. The results are consolidated by dynamic simulations, providing crucial data for the development of regulations on the maximum toxicity limits of citrus EOs, given the health implications of the various compounds such as coumarins, furocoumarins and polymethoxyflavones present in these essential oils.

Alignment method for metabolite chromatographic peaks using an N-acyl glycine retention index system

Peak alignment is a crucial data-processing step in untargeted metabolomics analysis that aims to integrate metabolite data from multiple liquid chromatography-mass spectrometry (LC-MS) batches for enhanced comparability and reliability. However, slight variations in the chromatographic separation conditions can result in retention time (RT) shifts between consecutive analyses, adversely affecting peak alignment accuracy. In this study, we present a retention index (RI)-based chromatographic peak-shift correction (CPSC) strategy to address RT shifts and align chromatographic peaks for metabolomics studies. A series of N-acyl glycine homologues (C2-C23) was synthesized as calibrants, and an LC RI system was established. This system effectively corrected RT shifts arising from variations in flow rate, gradient elution, instrument systems, and chromatographic columns. Leveraging the RI system, we successfully adjusted the RT of raw data to mitigate RT shifts and then implemented the Joint Aligner algorithm for peak alignment. We assessed the accuracy of the RI-based CPSC strategy using pooled human fecal samples as a test model. Notably, the application of the RI-based CPSC strategy to a long-term dataset spanning 157 d as an illustration revealed a significant enhancement in peak alignment accuracy from 15.5% to 80.9%, indicating its ability to substantially improve peak-alignment precision in multibatch LC-MS analyses.

Novel Peak Shift Correction Method Based on the Retention Index for Peak Alignment in Untargeted Metabolomics.

Peak alignment is a crucial step in liquid chromatography-mass spectrometry (LC-MS)-based large-scale untargeted metabolomics workflows, as it enables the integration of metabolite peaks across multiple samples, which is essential for accurate data interpretation. Slight differences or fluctuations in chromatographic separation conditions, however, can cause the chromatographic retention time (RT) shift between consecutive analyses, ultimately affecting the accuracy of peak alignment between samples. Here, we introduce a novel RT shift correction method based on the retention index (RI) and apply it to peak alignment. We synthesized a series of N-acyl glycine (C2-C23) homologues via the amidation reaction between glycine with normal saturated fatty acids (C2-C23) as calibrants able to respond proficiently in both mass spectrometric positive- and negative-ion modes. Using these calibrants, we established an N-acyl glycine RI system. This RI system is capable of covering a broad chromatographic space and addressing chromatographic RT shift caused by variations in flow rate, gradient elution, instrument systems, and LC separation columns. Moreover, based on the RI system, we developed a peak shift correction model to enhance peak alignment accuracy. Applying the model resulted in a significant improvement in the accuracy of peak alignment from 15.5 to 80.9% across long-term data spanning a period of 157 days. To facilitate practical application, we developed a Python-based program, which is freely available at https://github.com/WHU-Fenglab/RI-based-CPSC.

Development of Liquid Chromatographic Retention Index Based on Cocamide Diethanolamine Homologous Series (C(n)-DEA).

There is a growing need for indexing and harmonizing retention time (tR) data in liquid chromatography derived under different conditions to aid in the identification of compounds in high resolution mass spectrometry (HRMS) based suspect and nontarget screening of environmental samples. In this study, a rigorously tested, inexpensive, and simple system-independent retention index (RI) approach is presented for liquid chromatography (LC), based on the cocamide diethanolamine homologous series (C(n = 0-23)-DEA). The validation of the CDEA based RI system was checked rigorously on eight different instrumentation and LC conditions. The RI values were modeled using molecular descriptor free technique based on structural barcoding and convolutional neural network deep learning. The effect of pH on the elution pattern of more than 402 emerging contaminants were studied under diverse LC settings. The uncertainty associated with the CDEA RI model and the pH effect were addressed and the first RI bank based on CDEA calibrants was developed. The proposed RI system was used to enhance identification confidence in suspect and nontarget screening while facilitating successful comparability of retention index data between various LC settings. The CDEA RI app can be accessed at https://github.com/raalizadeh/RIdea.

Non-psychoactive cannabinoids identification by linear retention index approach applied to a hand-portable capillary liquid chromatography platform.

The aim of the present research was the application of the linear retention index (LRI) system for the identification of non-psychoactive cannabinoids using a portable LC instrument. The miniaturization, viz. the use of very low quantities of mobile phase, enabled the development of a compact mobile system to be used for in situ analysis, also according to a green and cost-saving approach. In particular, new capillary LC (cap-LC) methods coupled with UV detection were developed for the analysis of extracts of Cannabis sativa L. Two setups were explored to achieve the efficient separation of twenty-four cannabinoids: a single column setup which exploited a sub-2µm packing to increase the chromatographic resolution, and a dual-column setup based on the serial connection of two different stationary phases, each coupled to an UV detector. The latter allowed the determination of two LRI values for each analyte, thus increasing the identification power. Moreover, since two different wavelengths were used on the LED-based UV detectors, the ratio of the absorbances measured on each chromatographic trace represented a third identification criterion, thus fulfilling the recommendations of the Scientific Working Group for The Analysis of Seized Drugs (SWDRUG) about the categories of analytical techniques to be used and the minimum number of parameters required for the unambiguous identification of drugs. The obtained results could be used for the development of a novel analytical method for fast and automatic in situ forensic investigations and hemp breeding programs, also minimizing the consumption of both sample and solvent.

Dietary Intake of Coumarins and Furocoumarins through Citrus Beverages: A Detailed Estimation by a HPLC-MS/MS Method Combined with the Linear Retention Index System.

Official regulations concerning the maximum number of substances in food are introduced as a consequence of possible adverse effects, after oral administration. In this regard, analytical methods are necessary in order to determine specific targets. Among oxygen heterocyclic compounds (OHCs, that are furocoumarins, coumarins and polymethoxyflavones), only coumarin is subject to restriction by the Regulation (EC) No 1334/2008 of the European Parliament. Furocoumarins are known for their phototoxicity and other side effects due to their dietary intake; however, an official limit about the maximum content of these compounds in food is still missing. The lack of information about the real amount of these compounds in food is responsible for the conflicting opinions about the introduction of an official limit. The HPLC-MS/MS method here proposed, in combination with the linear retention index system, represents an innovative analytical strategy for the characterization of OHCs in citrus beverages. Several types of drinks were analysed in order to quantify 35 OHCs in total. This method is suitable for the quality control of OHCs in food and the obtained results may be considered as informative data useful for the regulatory authorities in the emission of new opinions and for a potential new regulation in this field.

Linear retention index approach applied to liquid chromatography coupled to triple quadrupole mass spectrometry to determine oxygen heterocyclic compounds at trace level in finished cosmetics

In the European Union, cosmetic products are regulated by the Cosmetics Regulation (EC) No. 1223/2009. The Analytical Working Group of the International Fragrance Association (IFRA) suggested that a new sensitive analytical method is needed to determine psoralens in finished cosmetic products. This research provides an HPLC-MS/MS method for the quality control of 20 furocoumarins, 8 coumarins and 7 polymethoxyflavones in cosmetics. Thanks to the high sensitivity of the tandem mass spectrometry detection in Multiple Reaction Monitoring mode, psoralens contained in trace have been quantified in different products. The Limits of Quantifications were in the range 0.3-74 μg L−1. A reliable identification was achieved combining the Linear Retention Index (LRI) system with the MS and MS/MS libraries. In particular, the attribution was based on the spectra similarity filtered by the LRI parameter. The robustness and reproducibility of the LRI approach was demonstrated by the comparison of the HPLC-MS/MS results here reported with those obtained in our previous study, by using an HPLC-PDA system.This method could be taken into account for quality control of furocoumarins in cosmetics, and by the main associations, such as IFRA, for the purpose of issuing new opinions.

Influence of Citrus Flavor Addition in Brewing Process: Characterization of the Volatile and Non-Volatile Profile to Prevent Frauds and Adulterations

In the last few years, the flavored beer market has increased significantly. In particular, consumers showed a growing interest in citrus-flavored beers. Citrus fruits contain, among other class of compounds, terpenes and terpenoids and oxygenated heterocyclic compounds. The absence of a specific legislation concerning beer flavored production and ingredients reported on the labels makes these beers subject to possible adulterations. Solid phase micro extraction (SPME) followed by gas chromatographic–mass spectrometry (GC-MS) and gas chromatographic-flame ionization detector (GC-FID) analysis of the volatile profile together with the characterization of the oxygen heterocyclic compounds through high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) demonstrated to be a powerful analytical strategy for quality control. In this study, we combined the volatile and non-volatile profiles of “citrus flavored mainstream beers”, in order to evaluate the authenticity and determine markers to prevent food frauds. The changes in the aroma composition of the unflavored types after the addition of peel, or citrus essential oil were also evaluated. The linear retention index (LRI) system was used for both techniques; in particular, its application in liquid chromatography is still limited and represents a novelty. The coupling of the high sensitivity of the HPLC MS/MS method with the LRI system, it has made possible for the first time a reliable identification and an accurate quantification of furocoumarins in citrus-flavored beers.

Normalization of LC-MS mycotoxin determination using the N-alkylpyridinium-3-sulfonates (NAPS) retention index system

A major challenge for LC-MS analysis is the ability to compare data between laboratories and across instrument platforms. Currently, mycotoxin determination relies on dereplication strategies based on physicochemical properties such as the m/z of the precursor and product ions. Unlike these intrinsic properties, retention time (tR) is an extrinsic property impacted by LC conditions, including mobile phases and column chemistry, making exchange of data between groups difficult. To address this, we are introducing the concept of incorporating an electrospray compatible, retention index (RI) system based on a series of N-alkylpyridinium-3-sulfonates (NAPS) into routine mycotoxin determination. These standards of differing alkyl chain length span RI units from 100 to 2000, are UV active and have fixed positive and negative charges for electrospray ionization in either mode. Using high resolution LC-MS/MS, the RIs of 96 mycotoxins and fungal secondary metabolites were normalized as a proof of concept with the NAPS RI system under multiple pH, column and gradient chromatographic conditions. This method was then applied to the analysis of a crude extract of Penicillium roqueforti, where we were able to decrease the number of false positives by implementing an RI filter as well as a secondary correction factor. Additionally, we developed software that allows users to convert published RIs to a predicted tR values. Integration of the NAPS RI system into routine LC-MS analysis will improve compound identifications and help facilitate ease of data sharing.

Evaluation of antioxidant active ingredients of spikenard essential oil by ultra-fast gas chromatography electronic nose and radical scavenging mechanism

As a new rapid detection technology, ultra-fast gas chromatography electronic nose (E-nose) can accurately distinguish and identify different odor ingredients based on the retention index and data processing system in a short time. The chemical components of spikenard (Nardostachys chinensis) essential oil (SEO) were detected by E-nose and verified by GC–MS with 94 % accuracy. Combining E-nose with traditional chemical methodology including E-nose-DPPH, E-nose-ABTS and E-nose−OH were used to quickly evaluate the antioxidant activity of each component of SEO. The results showed that the main components of SEO were calarene, β-maaliene, valerena-4,7(11)-diene, aristolene, γ-terpinene, and seychellene. Furthermore, SEO showed the best scavenging ability in ABTS than DPPH or OH radicals, and the highest scavenging rates are 95.0 % for ABTS, 72.4 % for DPPH and 73.0 % for OH radical, respectively. Among all ingredients of SEO, β-maaliene (70.6 %, 52.3 %, 26.4 %), calarene (69.5 %, 41.6 %, 22.5 %), valerena-4,7(11)-diene (78.1 %, 46.2 %, 6.4 %) and β-cadinene (78.8 %, 51.4 %, 7.1 %) have scavenging effects for ABTS, DPPH and OH radicals.

Lipid profile of fish species by liquid chromatography coupled to mass spectrometry and a novel linear retention index database.

In a previous article, Rigano etal. established a new linear retention index system for the identification of triacylglycerols by liquid chromatography methods only on the basis of the retention behavior and independently from many experimental parameters. In that work, a database of 209 compounds was built, but only 54 of them, typical of vegetable oils, were confirmed by mass spectrometry. The aim of the present research is to extend the applicability of the novel approach to more complex samples, such as fish lipid extracts, and assess the complementarity between mass spectromtery and retention information to achieve univocal identification. With this purpose, a new software was implemented to make the identification process easy and automatic as in gas chromatography-mass spectrometry where the retention index filter is added in the spectral search to discriminate between compounds with similar mass spectrometry spectra. A total of 69 species were identified and, thanks to their baseline separation obtained by an ultra high performance liquid chromatography method, a semiquantification was also performed. The species under investigation were Dicentrarchus labrax, coming from aquaculture and the wild. Some differences in their native lipid composition were observed, probably related to a different diet. A major number of samples would be necessary to confirm such a preliminary finding.

Proposal of a Linear Retention Index System for Improving Identification Reliability of Triacylglycerol Profiles in Lipid Samples by Liquid Chromatography Methods.

The retention index system was proposed in 1958 by Kováts. It is based on the correlation between the retention time of the analytes and the ones of a series of reference standards, making retention data dependent on the chromatographic phenomenon only, viz., on the three-term interaction analyte-stationary phase-mobile phase. Particularly in GC, because the mobile phase has a negligible influence, the retention of the analytes depends almost entirely on the stationary phase and it is as independent as possible from operating conditions. This makes retention index databases usable in samples identification at both the intra- and interlaboratory levels. The scope of this research was to create a similar identification system in LC, where the identification of unknowns is still a challenge because of the unavailability of spectral databases related to the low reproducibility of mass spectra generated by means of the atmospheric pressure ionization technique normally interfaced to LC. Lipid compounds, specifically triacylglycerols, were selected as target analytes mainly due to their regular chromatographic LC profile under reversed phase conditions. The odd carbon chain number triacylglycerol series from trinonain to trinonadecanoin was chosen as the basis of the retention index scale and a database of 209 triacylglycerols was built. For this purpose an ultra high-performance LC method, able to maximize the baseline separation of triacylglycerols in different real-world samples (vegetable oils, fish, and milk samples) was developed.

SPME-GC/MS combined with AMDIS analysis of the volatile compounds in fish sauce from different origins

Objective:Identifing the volatile compounds of fish sauce from different origins. Methods:Gas chromatography-mass spectrometry and headspace solid phase microextraction were applied to the examination of the volatile compounds of fish sauce from different origins. Retention index and automatic mass spectral deconvolution system were used to determine the nature of the volatile compound as well. Results:93 kinds of volatile compounds were detected, and the content of esters and aromatic compounds were higher in Guangdong fish sauces than others, and the content of ketones compounds were higher in Thailand fish sauce, and the content of acids and heterocyclic compounds were higher in Vietnamese fish sauce, and the content of aldehydes and alcohols compounds in fish sauce made in laboratory were higher than others. Assignment Validator and Integrator was used for automatic peak alignment of different samples, and satisfactory results were received. 35 kinds of unique volatile compounds and 11 kinds of common volatile compounds were detected in five fish sauce samples. The common volatile compounds were used in principal component analysis, and fish sauces from different origins can be easily separated in the principal component graph. Conclusion:This study identified the characteristics of volatile compounds of fish sauces from different regions, and provided a traceabale method and work flow of using GC-MS to analysis volatile compounds.

A retention index system for comprehensive two-dimensional gas chromatography using polyethylene glycols

The characterization and identification of compounds in complex real-world samples is quite difficult and new concepts and workflows are highly desirable. Retention indices (RIs) are widely used in gas chromatography (GC) to support the identification of unknown compounds. Several attempts have been made to introduce a similar concept for the second dimension in comprehensive two-dimensional (2D) GC (GC × GC) but, an easily applicable and robust system remains elusive.In the present study, a new RI system for GC × GC was developed. Polyethylene glycols (PEGs) were used in combination with a simple linear regression, with n-alkanes as reference points for virtually unretained compounds and PEG homologs as reference compounds for second-dimension RIs (PEG-2I). The n-alkanes were assigned a PEG-2I of zero and the distance between consecutive PEG homologs from PEG-2 (diethylene glycol) and higher were assigned a PEG-2I value of 10. We used ethylene glycol and PEG-2 through PEG-10 as reference compounds, thereby covering a PEG-2I range from 20.0 for ethylene glycol, over 50.0 for diethylene glycol (PEG-2) to 130.0 for decaethylene glycol (PEG-10); additional PEGs can be added to cover a wider polarity range. The PEG-2I system was initially evaluated using a 30 m × 0.25 mm non-polar (5% phenyl, 0.25 μm film thickness) first-dimension column and a 1.6 m × 0.18 mm polar (50% phenyl, 0.18 μm film thickness) second-dimension column. This system was validated for use with non-polar first-dimension columns and a semi-polar (50% phenyl) second-dimension column, and exhibited robustness to changes in the carrier gas flow velocity, oven temperature ramping rate, and secondary oven temperature offset. An average relative standard deviation of 2.7%, equal to a 95% confidence interval of 1.27 PEG-2I units, was obtained for the PEG-2I values of 72 environmental pollutants. Additionally, the system was found to be applicable over a wide range of boiling points (in the current case, from n-heptane to n-dotriacontane (C7–C32)) and can be used with various column dimensions. Changing the second-dimension column to either a narrower 0.1 mm column or a wider 0.25 mm column, yielded similar 95%-percentiles to that of the 0.18 mm column, differing by only 3.20 and 2.80 PEG-2I units, respectively. Moreover, methods for improving the system were suggested.

Transfer of retention patterns in gas chromatography by means of response surface methodology

Accurate transfer of retention patterns in temperature-programmed gas chromatography is challenging because minor variations in column properties and experimental conditions may have significant impact on the elution patterns. An experimental method for accurate transfer of retention indices is proposed and validated. The methodology is based on response surface methodology and experimental design. The temperature rate and the start temperature of the rate are varied systematically in the region where the optimal conditions are expected to be found. Response surfaces that explain the absolute deviation to the target retention indices are calculated for each compound. These response surfaces are thereafter averaged and the minimum in the average surface is regarded as optimal conditions for reproduction of the retention pattern. The methodology was applied on fatty acid methyl esters using equivalent chain lengths as the retention index system. Two different target patterns were tested on two BPX-70 columns with different dimensions. Validation of the proposed conditions showed that the retention patterns could be reproduced with an error that was only fractions of a peak width.

A New Miniaturized Planar Chromatography

Planar chromatography or thin-layer chromatography (TLC) is one of the oldest and most versatile techniques within the huge family of modern separation science methods. Without doubt, the main advantage of TLC is its simplicity. Fast and efficient fractionation and/or separation of multicomponent mixtures can be performed using just small strip of filter paper (working as the stationary phase) and few milliliters of water or water-organic solvent (acting as the mobile phase) poured into a glass jar operating as the chromatographic chamber. But even this equipment may be reduced if we replace the container with mobile phase by a small glass capillary or syringe tip filled with the liquid phase (Fig. 1). Under such conditions the movement of a given eluent through the paper is entirely driven by capillary forces. Therefore, no pump or any different pressure gradient device is required for the chromatographic run, which may be also performed in two dimensions. It should be noted that contrary to its column counterpart, a number of individual samples may be analyzed simultaneously. TLC allows parallel separations limited only by the plate width along the start line direction. If the components of interest are colored the eye can act as surprisingly sensitive detector. Colorless substances can be simply detected via a number of selective (like ninhydrin) or non-selective (e.g. iodine vapor) visualization reagents. Planar chromatography based on common filter paper provides probably the simplest and cheapest experimental setup for an effective separation of selected optical isomers, e.g., amino acids, considering the fact that native cellulose (operating as the chromatographic stationary phase) has chiral properties. Interestingly, in its simplest form, circular micro-planar chromatography has been reported as a fast optimization and mobile phase selection tool for complex sample separation [1]. In general, planar chromatography has enormous educational potential for demonstration and teaching of separation science principles, including all aspects of qualitative and quantitative analysis [2]. During my postgraduate education I was really lucky to start my experience with chromatography working under supervision of Professor Henryk Lamparczyk, who prematurely passed away at the end of 2012. He was an enthusiast for solving any complex research problems via the simplest possible, methodological approach. Therefore, in his laboratory, despite GC and HPLC machines, he applied planar chromatography extensively as a fast experimental data acquisition tool. Such TLC-generated retention data sets were often used for further chemometric calculations and physicochemical investigations. He successfully supervised and mentored a number of important research projects concerning temperature effects in planar chromatography, focusing on the thermodynamic study of macrocycles and their interaction with n-alcohols and the separation of bile acids using temperature-controlled TLC. Based on planar chromatographic data, he clearly demonstrated, that the general behavior of the solute molecules in chromatographic systems can be explained on the basis of solutephase reversible interactions like electrostatic (van der Waals) forces and stereoselective molecular fitting to stationary and mobile phases. Lamparczyk successfully proposed an electrostatic retention index system common to GC, HPLC and TLC based on the experimental data Published in the topical collection Miniaturized and New Featured Planar Chromatography and Related Techniques with guest editor Pawel K. Zarzycki.

미더덕의 향기 성분

미더덕 육과 체액을 이용한 천연 조미료의 제조를 위하여 본래의 향과 가열에 따른 변화를 비교해보기 위하여 SDE법과 SPME법으로 미더덕 향기성분을 분석하였다. SDE 추출법으로 얻어진 미더덕 육에 함유된 주요 성분으로서는 hexanal <TEX>$371.3\;{\mu}g/g$</TEX>, 1-tridecanol <TEX>$80.1\;{\mu}g/g$</TEX>, (Z)-4,5-dimethyhex02-en-4-ol <TEX>$72.1\;{\mu}g/g$</TEX> 등이 있었고, 그 외 다량의 alcohol, aldehydes 및 acids가 얻어졌다. SDE 추출법으로 얻어진 alcohol은 농도도 높았지만 미더덕 육향기성분의 주체가 되는 것으로 나타났다. SPME 추출법으로 얻어진 미더덕 육에는 9종의 alcohols, 1종의 acid, 1종의 aldehyde, 1종의 hydrocarbon, 1종의 ester, 1종의 amine 및 2종의 ketones이 포함되어 있었다. 이들 중 함량이 가장 높았으며 그 중 1-nonanol, 1-decanol 및 1-tridecanol이 주성분이었다. SPME법으로 얻어진 향기성분 중 1-nonanol <TEX>$31.6\;{\mu}g/g$</TEX>, (E)-2-butanoic acid dibutylester <TEX>$20.3\;{\mu}g/g$</TEX> 및 heptadecanoic acid <TEX>$26.7\;{\mu}g/g$</TEX>으로 전체 향기성분 추출물의 62.1%를 차지하였다. 따라서 SPME법으로 얻어진 향기성분이 SDE법보다 추출효율은 낮았지만 원래 향에 가까운 것으로 나타났다. The flavor extracts of Mideoduck muscle and its juices were concentrated by simultaneous distillation and extraction (SDE) and solid-phase microextraction (SPME) methods. Each component present in the extracts was identified with GC and GC-MS by the n-paraffin hydrocarbon retention index and standard MS library data system. By SDE, <TEX>$371.3\;{\mu}g/g$</TEX> of hexanal, <TEX>$80.1\;{\mu}g/g$</TEX> of 1-tridecanol, <TEX>$72.1\;{\mu}g/g$</TEX> of (Z)-4,5-dimethylhex-2-en-4-ol with other alcohols, aldehydes and acids were present in the flavor extracts, with the alcohols having the highest composition and being the most important factor in Mideoduck muscle flavor. By SPME, 9 alcohols, 1 acid, 1 aldehyde, 1 hydrocarbon, 1 ester, 1 amine and 2 ketones were detected in the extracts, with alcohol such as 1-nonanol, 1-decanol and 1-tridecanol as the major components. In SPME, the muscle sample, consisting of <TEX>$31.6\;{\mu}g/g$</TEX> of 1-nonanol, <TEX>$20.3\;{\mu}g/g$</TEX> of (E)-2-butenedioic acid dibutylester, and <TEX>$26.7\;{\mu}g/g$</TEX> of heptadecanoic acid made up the 62.1% of total flavor extracts of Mideoduck muscle. The results of the SPME methods were similar to the composition of the raw material flavor of the sample even at a low concentration.

ALKYLARYLKETONE HOMOLOGOUS SERIES FOR DETERMINATION OF KOVATS RETENTION INDICES WITH RP-HPLC USING ACETONITRILE/WATER SYSTEM

Some factors such as the changes of the stationary phase, temperature, pH-value, mobile-phase composition and flow rate play a crucial role in effecting the sensitivity of retention times in high performance liquid chromatography (HPLC) system. Utilizing a retention index system is one of the methods to minimize those effects. Besides the mentioned factors, dead-time influences on determining the retention index as well. In comparison with Gas Chromatography (GC), the retention Index determination method in HPLC is still widely discussed, due to the difficulty of utilizing n-alkane as standard. In addition, the solutes in HPLC interact with the mobile-phase, thus the retention behavior also depend on the mobile-phase. Actually, It is difficult to use n-alkanes in HPLC as standards in case of some considerable problems, due to they are very non polar but also large retention times which lack of chromophores. Therefore, using n-alkane in routine analysis could be inconvenient. In comparison with n-alkanes, the alkylarylketones homologous series are stable compounds, commercially available and easily detected by a UV detector. This paper introduces Determination of Kovats Retention Index in the HPLC using Alkylarylketone homologous series and then is connected with n-alkane as a frame of reference. Steroids were used as test substance for calculating Kovats retention index values in acetonitrile/water system. Keywords: Kovats Retention Index, RP- HPLC, n-alkane, alkylarylketone

Prediction of retention indices. VI: Isothermal and temperature-programmed retention indices, methylene value, functionality constant, electronic and steric effects

The Kováts retention index system with n-alkanes as reference standards has properties not fully explored when single, isolated or stand-alone analytes are analyzed by isothermal gas chromatography. When a homologous series of analytes are analyzed by either linear or non-linear temperature-programmed gas chromatography, the retention data of the entire series can be treated systematically to produce an I vs. Z plot that is linear, thereby giving insight into the relationship between chemical structure and retention index. Dead time t M is both instrument and temperature dependent. With no dead time t M adjustment, the retention indices of analytes calculated from experimental retention times by the method of either linear or logarithmic interpolation give statistically identical values. Linear regression analysis of the data shows the slope as methylene value ( A) and intercept as functionality constant or group retention factor ( GRF) of the homologous series. The A and ( GRF) values vary with chemical structures, intermolecular electronic and steric interactions, and polarity of column liquid phases, and can link gas chromatographic retention index to chemical structure. Examples of the influence of molecular electronic effects and steric effects on retention index are given and discussed.

Nontargeted Multicomponent Analytical Screening of Plastic Food Contact Materials Using Fast Interpretation of Deliverables via Expert Structure-Activity Relationship Software

Plastic packaging materials may release compounds into packed foodstuffs. To identify potential migrants of toxicological concern, resins, and multilayer foils (mainly polyethylene) intended for the production of food contact materials were extracted and analyzed by GC/mass spectrometry. To identify even compounds of low concentrations, AMDIS software was used and data evaluation was safeguarded by the Kovats retention index (RI) system. In this way, 46 compounds were identified as possible migrants. The expert structure-activity relationship software DEREK for Windows was utilized to evaluate all identified substances in terms of carcinogenicity, genotoxicity, thyroid toxicity, and miscellaneous endpoints for humans. Additionally, a literature search for these compounds was performed with Sci-Finder, but relevant data were missing for 28 substances. Seven compounds with adverse toxicological effects were identified. In addition, the RIs of 24 commercial additive standards, measured with a GC capillary column of intermediate polarity, are given.