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Application of Liquid Chromatography in Food Analysis
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Application of Liquid Chromatography in Food Analysis

A special issue of Foods (ISSN 2304-8158). This special issue belongs to the section "Food Analytical Methods".

Deadline for manuscript submissions: closed (31 December 2018) | Viewed by 60838

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Oscar Núñez

E-Mail Website
Guest Editor
1. Department of Chemical Engineering and Analytical Chemistry, Faculty of Chemistry, University of Barcelona, Martí i Franquès 1-11, E-08028 Barcelona, Spain
2. Research Institute in Food Nutrition and Food Safety, Universitat de Barcelona, Av. Prat de la Riba 171, Edifici Recerca (Gaudí), E-08921 Santa Coloma de Gramenet, Spain
Interests: food authentication; food characterization; food classification; food fraud identification; secondary metabolites; polyphenols; foodomics; bioactive compounds; liquid chromatography; mass spectrometry; high resolution mass spectrometry; ambient mass spectrometry; capillary electrophoresis; chemometrics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Paolo Lucci

E-Mail Website
Guest Editor
Department of Agri Food, Environmental and Animal Sciences, Universityof Udine, Via Sondrio 2A, I-33100 Udine, Italy
Interests: food authentication; food contaminants; edible oil characterization; food fraud identification; liquid chromatography; mass spectrometry; bioactive compounds
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Food products are very complex mixtures consisting of naturally-occurring compounds and other substances, generally originating from technological processes, agrochemical treatments, or packaging materials. Several of these compounds (e.g., veterinary drugs, pesticides, mycotoxins, etc.) are of particular concern because, although they are generally present in very small amounts, they are nonetheless often dangerous to human health. On the other hand, improved methods for the determination of authenticity, standardization, and efficacy of nutritional properties in natural food products are also required to guarantee their quality and for the growth and regulation of the market. Thus, food safety and food authentication are hot topics for both society and the food industry. Nowadays, liquid chromatography with ultraviolet (LC-UV) detection, or coupled to mass spectrometry (LC-MS) and high-resolution mass spectrometry (LC-HRMS), are among the most powerful techniques to address food safety issues and to guarantee food authenticity in order to prevent frauds. In this Special Issue, the role of liquid chromatography techniques in food analysis (including food safety issues, determination of nutritional properties, and authentication and prevention of frauds) will be addressed. Both, original research articles and reviews are welcome.

Dr. Oscar Núñez
Dr. Paolo Lucci
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Foods is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • liquid chromatography
  • food safety
  • food authentication
  • nutritional properties
  • UV-detection
  • mass spectrometry
  • high-resolution mass spectrometry

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Published Papers (7 papers)

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Editorial

Jump to: Research, Review

4 pages, 187 KiB  
Editorial
Application of Liquid Chromatography in Food Analysis
by Oscar Núñez and Paolo Lucci
Foods 2020, 9(9), 1277; https://doi.org/10.3390/foods9091277 - 11 Sep 2020
Cited by 17 | Viewed by 5760
Abstract
Food products are very complex mixtures consisting of naturally-occurring compounds and other substances, generally originating from technological processes, agrochemical treatments, or packaging materials [...] Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)

Research

Jump to: Editorial, Review

10 pages, 615 KiB  
Article
Native Colombian Fruits and Their by-Products: Phenolic Profile, Antioxidant Activity and Hypoglycaemic Potential
by Monica Rosa Loizzo, Paolo Lucci, Oscar Núñez, Rosa Tundis, Michele Balzano, Natale Giuseppe Frega, Lanfranco Conte, Sabrina Moret, Daria Filatova, Encarnación Moyano and Deborah Pacetti
Foods 2019, 8(3), 89; https://doi.org/10.3390/foods8030089 - 3 Mar 2019
Cited by 34 | Viewed by 6631
Abstract
The phenols and fatty acids profile and in vitro antioxidant and hypoglycaemic activity of seed, peel, pulp or pulp plus seeds of Colombian fruits from Solanaceae and Passifloraceae families were investigated. Ultra-High Performance Liquid Chromatography (UHPLC)-High Resolution Mass Spectrometry (HRMS) revealed the presence [...] Read more.
The phenols and fatty acids profile and in vitro antioxidant and hypoglycaemic activity of seed, peel, pulp or pulp plus seeds of Colombian fruits from Solanaceae and Passifloraceae families were investigated. Ultra-High Performance Liquid Chromatography (UHPLC)-High Resolution Mass Spectrometry (HRMS) revealed the presence of chlorogenic acid as dominant phenolic compound in Solanaceae samples. Based on the Relative Antioxidant Score (RACI) and Global Antioxidant Score (GAS) values, Solanum quitoense peel showed the highest antioxidant potential among Solanaceae samples while Passiflora tripartita fruits exhibited the highest antioxidant effects among Passifloraceae samples. P. ligularis seeds were the most active as hypoglycaemic agent with IC50 values of 22.6 and 24.8 μg/mL against α-amylase and α-glucosidase, respectively. Considering that some of the most promising results were obtained by the processing waste portion, its use as functional ingredients should be considered for the development of nutraceutical products intended for patients with disturbance of glucose metabolism. Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)
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Graphical abstract

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10 pages, 2141 KiB  
Article
Characterization of Sparkling Wines According to Polyphenolic Profiles Obtained by HPLC-UV/Vis and Principal Component Analysis
by Anaïs Izquierdo-Llopart and Javier Saurina
Foods 2019, 8(1), 22; https://doi.org/10.3390/foods8010022 - 10 Jan 2019
Cited by 19 | Viewed by 5798
Abstract
Cava is a sparkling wine obtained by a secondary fermentation in its own bottle. Grape skin contains several compounds, such as polyphenols, which act like natural protectors and provide flavor and color to the wines. In this paper, a previously optimized method based [...] Read more.
Cava is a sparkling wine obtained by a secondary fermentation in its own bottle. Grape skin contains several compounds, such as polyphenols, which act like natural protectors and provide flavor and color to the wines. In this paper, a previously optimized method based on reversed phase high performance liquid chromatography (HPLC) with ultraviolet/visible (UV/Vis) detection has been applied to determine polyphenols in cava wines. Compounds have been separated in a C18 core-shell column using 0.1% formic acid aqueous solution and methanol as the components of the mobile phase. Chromatograms have been recorded at 280, 310 and 370 nm to gain information on the composition of benzoic acids, hidroxycinnamic acids and flavonoids, respectively. HPLC-UV/vis data consisting of compositional profiles of relevant analytes has been exploited to characterize cava wines produced from different base wine blends using chemometrics. Other oenological variables, such as vintage, aging or malolatic fermentation, have been fixed over all the samples to avoid their influence on the description. Principal component analysis and other statistic methods have been used to extract of the underlying information, providing an excellent discrimination of samples according to grape varieties and coupages. Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Chromatograms recorded at 280 nm using the proposed HPLC-UV/vis method. (<b>A</b>) Standard solution at 5 mg L<sup>−1</sup>; (<b>B</b>) Rosé wine composed of Pinot Noir, Trepat and black Garnacha varieties (<b>C</b>) Classical grape varieties coupage composed of Macabeu, Xarel·lo and Parellada and (<b>D</b>) White cava composed of Chardonnay variety. Peaks assignment: (1) gallic acid, (2) homogentisic acid, (3) protocatechuic acid, (4) caftaric acid, (5) gentisic acid, (6) catechin, (7) vanillic acid, (8) caffeic acid, (9) syringic acid, (10) ethyl gallate, (11) epicatechin, (12) <span class="html-italic">p</span>-coumaric acid, (13) ferulic acid, (14) resveratrol, (15) rutin and (16) myricetin.</p> Full article ">Figure 2
<p>Boxplots with whiskers with the polyphenolic composition of the sets of (<b>A</b>) white and (<b>B</b>) rosé cava samples under study. Error bars indicated the variability in the concentration values.</p> Full article ">Figure 3
<p>Radial plots of polyphenolic concentrations in the different coupages. (<b>A</b>) Overall content of analytes; (<b>B</b>) gentisic acid; (<b>C</b>) syringic acid; (<b>D</b>) catechin; (<b>E</b>) vanillic acid. Solid line indicates the mean value; dotted lines indicated the ± standard deviation values. Variety assignation: Ma, Macabeu; Xa, Xarel·lo.</p> Full article ">Figure 4
<p>Principal component analysis of the dataset consisting of polyphenol concentrations of each cava sample. (<b>A</b>) Plot of scores of PC1 versus PC2; (<b>B</b>) plot of loadings of PC1 versus PC2. Acronyms: C Chardonnay; Ma Macabeu; Pa Parellada; Xa Xarel·lo; QC Quality control; R rosé. Symbols: Star = classical coupage (Ma + Xa + Pa); Triangle (vertex up) = rosé cava; Triangle (vertex down) = Chardonnay cava; circle = QC.</p> Full article ">
10 pages, 1005 KiB  
Article
Effect of Artificial LED Light and Far Infrared Irradiation on Phenolic Compound, Isoflavones and Antioxidant Capacity in Soybean (Glycine max L.) Sprout
by Md Obyedul Kalam Azad, Won Woo Kim, Cheol Ho Park and Dong Ha Cho
Foods 2018, 7(10), 174; https://doi.org/10.3390/foods7100174 - 22 Oct 2018
Cited by 40 | Viewed by 6159
Abstract
The effect of light emitting diode (LED) light and far infrared irradiation (FIR) on total phenol, isoflavones and antioxidant activity were investigated in soybean (Glycine max L.) sprout. Artificial blue (470 nm), green (530 nm) LED and florescent light (control) were applied [...] Read more.
The effect of light emitting diode (LED) light and far infrared irradiation (FIR) on total phenol, isoflavones and antioxidant activity were investigated in soybean (Glycine max L.) sprout. Artificial blue (470 nm), green (530 nm) LED and florescent light (control) were applied on soybean sprout, from three to seven days after sowing (DAS) in growth chamber. The photosynthetic photon flux density (PPFD) and photoperiod was 150 ± 5 μmol m−2s−1 and 16 h, respectively. The FIR was applied for 30, 60 and 120 min at 90, 110 and 130 °C on harvested sprout. Total phenolic content (TP) (59.81 mg/g), antioxidant capacity (AA: 75%, Ferric Reduction Antioxidant Power (FRAP): 1357 µM Fe2+) and total isoflavones content (TIC) (51.1 mg/g) were higher in blue LED compared to control (38.02 mg/g, 58%, 632 µM Fe2+ and 30.24 mg/g, respectively). On the other hand, TP (64.23 mg/g), AA (87%), FRAP (1568 µM Fe2+) and TIC (58.98 mg/g) were significantly increased by FIR at 110 °C for 120 min among the treatments. Result suggests that blue LED is the most suitable light to steady accumulation of secondary metabolites (SM) in growing soybean sprout. On the other hand, FIR at 110 °C for 120 min is the best ailment to induce SM in proceed soybean sprout. Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)
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Figure 1
<p>Chemical structures of isoflavones.</p> Full article ">Figure 2
<p>Total phenolic content in soybean sprouts grown under different light. Different lowercase letters within the row indicates significant differences (<span class="html-italic">p</span> &lt; 0.05) according to ANOVA. LED: light emitting diode.</p> Full article ">Figure 3
<p>Antioxidant capacity (DPPH and FRAP) of soybean sprout under different light treatment. The values are mean ± SE. (<span class="html-italic">n</span> = 3). DPPH, 2-diphenyl-1 picryl hydrazyl; FRAP, Ferric Reduction Antioxidant Power; SE, standard deviation. Different lowercase letters within the row indicates significant differences (<span class="html-italic">p</span> &lt; 0.05) according to ANOVA.</p> Full article ">Figure 4
<p>Antioxidant capacity (DPPH and FRAP) of soybean sprout under FIR treatment. The values are mean ± SE. (<span class="html-italic">n</span> = 3). FIR: far infrared irradiation.</p> Full article ">
15 pages, 1398 KiB  
Article
Authentication and Quantitation of Fraud in Extra Virgin Olive Oils Based on HPLC-UV Fingerprinting and Multivariate Calibration
by Núria Carranco, Mireia Farrés-Cebrián, Javier Saurina and Oscar Núñez
Foods 2018, 7(4), 44; https://doi.org/10.3390/foods7040044 - 21 Mar 2018
Cited by 61 | Viewed by 9016
Abstract
High performance liquid chromatography method with ultra-violet detection (HPLC-UV) fingerprinting was applied for the analysis and characterization of olive oils, and was performed using a Zorbax Eclipse XDB-C8 reversed-phase column under gradient elution, employing 0.1% formic acid aqueous solution and methanol as mobile [...] Read more.
High performance liquid chromatography method with ultra-violet detection (HPLC-UV) fingerprinting was applied for the analysis and characterization of olive oils, and was performed using a Zorbax Eclipse XDB-C8 reversed-phase column under gradient elution, employing 0.1% formic acid aqueous solution and methanol as mobile phase. More than 130 edible oils, including monovarietal extra-virgin olive oils (EVOOs) and other vegetable oils, were analyzed. Principal component analysis results showed a noticeable discrimination between olive oils and other vegetable oils using raw HPLC-UV chromatographic profiles as data descriptors. However, selected HPLC-UV chromatographic time-window segments were necessary to achieve discrimination among monovarietal EVOOs. Partial least square (PLS) regression was employed to tackle olive oil authentication of Arbequina EVOO adulterated with Picual EVOO, a refined olive oil, and sunflower oil. Highly satisfactory results were obtained after PLS analysis, with overall errors in the quantitation of adulteration in the Arbequina EVOO (minimum 2.5% adulterant) below 2.9%. Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)
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Figure 1

Figure 1
<p>Scatter score plots (PC1 vs. PC2) when processing raw HPLC-UV (High performance liquid chromatography method with ultra-violet detection) chromatographic fingerprints of 47 olive oils and 25 other fruit seed oils (sunflower, corn, soy, and some mixtures of them) registered at (<b>a</b>) 257 nm; (<b>b</b>) 280 nm; and (<b>c</b>) 316 nm. Ellipse is grouping the quality controls.</p> Full article ">Figure 2
<p>HPLC-UV chromatographic fingerprint registered at 257 nm for four extra-virgin olive oil (EVOOs) obtained from (<b>a</b>) Arbequina; (<b>b</b>) Picual; (<b>c</b>) Hojiblanca; and (<b>d</b>) Cornicabra monovarietal olive cultivars.</p> Full article ">Figure 3
<p>Principal component analysis (PCA) results (scatter score plot of PC1 vs. PC2) in the analysis of 66 EVOOs obtained from monovarietal olive cultivars by employing as data: (<b>a</b>) HPLC-UV chromatographic profile segments of 5–8 min, 13–21 min, and 23–26 min simultaneously (registered at 280 nm); and (<b>b</b>) a combination of the HPLC-UV chromatographic profile segments from 13 to 32 min obtained at 257, 280, and 316 nm, simultaneously.</p> Full article ">Figure 4
<p>Partial least square (PLS) regression results for the adulteration of an Arbequina monovarietal EVOO using a Picual monovarietal EVOO, a ROO, and a sunflower oil as adulterants. Data set: raw HPLC-UV chromatographic fingerprints registered at 257 nm. (<b>a</b>) Estimation of the optimum number of latent variables; (<b>b</b>) validation results in the calibration step; and (<b>c</b>) validation results in the prediction step. RMSECV: root-mean-square errors in cross validation.</p> Full article ">
10 pages, 648 KiB  
Article
Characterization and Determination of Interesterification Markers (Triacylglycerol Regioisomers) in Confectionery Oils by Liquid Chromatography-Mass Spectrometry
by Valentina Santoro, Federica Dal Bello, Riccardo Aigotti, Daniela Gastaldi, Francesco Romaniello, Emanuele Forte, Martina Magni, Claudio Baiocchi and Claudio Medana
Foods 2018, 7(2), 23; https://doi.org/10.3390/foods7020023 - 16 Feb 2018
Cited by 17 | Viewed by 5997
Abstract
Interesterification is an industrial transformation process aiming to change the physico-chemical properties of vegetable oils by redistributing fatty acid position within the original constituent of the triglycerides. In the confectionery industry, controlling formation degree of positional isomers is important in order to obtain [...] Read more.
Interesterification is an industrial transformation process aiming to change the physico-chemical properties of vegetable oils by redistributing fatty acid position within the original constituent of the triglycerides. In the confectionery industry, controlling formation degree of positional isomers is important in order to obtain fats with the desired properties. Silver ion HPLC (High Performance Liquid Chromatography) is the analytical technique usually adopted to separate triglycerides (TAGs) having different unsaturation degrees. However, separation of TAG positional isomers is a challenge when the number of double bonds is the same and the only difference is in their position within the triglyceride molecule. The TAG positional isomers involved in the present work have a structural specificity that require a separation method tailored to the needs of confectionery industry. The aim of this work was to obtain a chromatographic resolution that might allow reliable qualitative and quantitative evaluation of TAG positional isomers within reasonably rapid retention times and robust in respect of repeatability and reproducibility. The resulting analytical procedure was applied both to confectionery raw materials and final products. Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)
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Figure 1

Figure 1
<p>Chromatographic separation of standard TAG (triglyceride) regioisomers visualized at the extracted precursor ion m/z values.</p> Full article ">Figure 2
<p>Full mass spectra of isobaric positional isomers POP (palmitoyl-oleoyl-palmitoyl glycerol) (<b>a</b>) and PPO (palmitoyl-palmitoyl-oleoyl glycerol) (<b>b</b>) showing the specificity of thermal fragmentation mechanism.</p> Full article ">Figure 3
<p>Chromatographic separation of TAG regioisomers typical of interesterified Shea oil (<b>a</b>) and Palm oil (<b>b</b>) visualized at the extracted precursor ion m/z values.</p> Full article ">Figure 4
<p>LC-MS (Liquid chromatography-mass spectrometry) chromatograms of cocoa butter samples pre deodorization (<b>a</b>) and deodorized at two different temperatures 220 °C (<b>b</b>) and 260 °C (<b>c</b>), corresponding to the absence and to the presence of thermally formed positional isomers, respectively.</p> Full article ">

Review

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63 pages, 3522 KiB  
Review
Liquid Chromatography Analysis of Common Nutritional Components, in Feed and Food
by Carolina Cortés-Herrera, Graciela Artavia, Astrid Leiva and Fabio Granados-Chinchilla
Foods 2019, 8(1), 1; https://doi.org/10.3390/foods8010001 - 20 Dec 2018
Cited by 44 | Viewed by 19155
Abstract
Food and feed laboratories share several similarities when facing the implementation of liquid-chromatographic analysis. Using the experience acquired over the years, through application chemistry in food and feed research, selected analytes of relevance for both areas were discussed. This review focused on the [...] Read more.
Food and feed laboratories share several similarities when facing the implementation of liquid-chromatographic analysis. Using the experience acquired over the years, through application chemistry in food and feed research, selected analytes of relevance for both areas were discussed. This review focused on the common obstacles and peculiarities that each analyte offers (during the sample treatment or the chromatographic separation) throughout the implementation of said methods. A brief description of the techniques which we considered to be more pertinent, commonly used to assay such analytes is provided, including approaches using commonly available detectors (especially in starter labs) as well as mass detection. This manuscript consists of three sections: feed analysis (as the start of the food chain); food destined for human consumption determinations (the end of the food chain); and finally, assays shared by either matrices or laboratories. Analytes discussed consist of both those considered undesirable substances, contaminants, additives, and those related to nutritional quality. Our review is comprised of the examination of polyphenols, capsaicinoids, theobromine and caffeine, cholesterol, mycotoxins, antibiotics, amino acids, triphenylmethane dyes, nitrates/nitrites, ethanol soluble carbohydrates/sugars, organic acids, carotenoids, hydro and liposoluble vitamins. All analytes are currently assayed in our laboratories. Full article
(This article belongs to the Special Issue Application of Liquid Chromatography in Food Analysis)
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Figure 1

Figure 1
<p>Polyphenols structure and classification [<a href="#B97-foods-08-00001" class="html-bibr">97</a>]. Highly functionalized structures account for the molecules radical scavenging, metal ion chelating, and enzyme inhibition. Hydrogen bonding can stabilize phenoxyl radicals.</p> Full article ">Figure 2
<p>Chemical structures for (<b>A</b>) capsaicin (8-methyl-<span class="html-italic">N</span>-vanillylamide) and (<b>B</b>) dihydrocapsaicin (8-methyl-<span class="html-italic">N</span>-vanillylnonamide), the aromatic vanillyl radical is shown in red.</p> Full article ">Figure 3
<p>Chemical structures for (<b>A</b>) caffeine (1,3,7-trimethylxanthine), (<b>B</b>) theobromine (3,7-dimethylxanthine), (<b>C</b>) theophylline (1,3-dimethylxanthine), (<b>D</b>) paraxanthine (1,7-dimethylxanthine), and (<b>E</b>) antipyrine (2,3-Dimethyl-1-phenyl-3-pyrazoline-5-one or phenazone). (<b>F</b>) Caffeine biotransformation pathway is dependent on the CYP1A2 and CYP2A6 enzyme system. <b>1</b>. 1,3,7-trimethylxanthine <b>2</b>. 1,7-dimethylxanthine <b>3</b>. 7-methylxanthine <b>4</b>. 7-methyluric acid <b>5</b>. 1-mthyluric acid <b>6</b>. 5-acetylamino-6-formylamino-3-methyluracil <b>7</b>. 1,7-dimethyluric acid <b>8</b>. 5-acetylamino-6-amino-3-methyluracil [<a href="#B145-foods-08-00001" class="html-bibr">145</a>].</p> Full article ">Figure 4
<p>Chemical structures for (<b>A</b>) ochratoxin A, (<b>B</b>) ochratoxin B, (<b>C</b>) ochratoxin C, blue colored circles represent changes in the structure between ochratoxins, loss of Cl and OH in ochratoxin B and C respectively render a more lipophilic molecule. Et = C<sub>2</sub>H<sub>5</sub>, and (<b>D</b>) are the general backbone of Fumonisins. FB<sub>1</sub> = 721.83 g mol<sup>−1</sup> R<sub>1</sub>: H R<sub>2</sub>: OH R<sub>3</sub>: OH; FB<sub>2</sub> = 705.84 g mol<sup>−1</sup> R<sub>1</sub>: OH R<sub>2</sub>: H R<sub>3</sub>: OH; FB<sub>3</sub> = 705.84 g mol<sup>−1</sup> R<sub>1</sub>: H R<sub>2</sub>: H R<sub>3</sub>: OH; FB<sub>4</sub> = 689.84 g mol<sup>−1</sup> R<sub>1</sub>: H R<sub>2</sub>: H R<sub>3</sub>: H. Functional groups colored in green and red represent a positively and negatively ionizable moiety, respectively.</p> Full article ">Figure 5
<p>Chemical structures for three triphenylmethane dyes which are sharing a common phenyl backbone sharing a methylidyne. Each molecule has extended π-delocalized electrons justifying their crystal coloration and visible light absorption (ca. 621 nm for malachite green).</p> Full article ">Figure 6
<p>Schematic representation for the interaction of nitrite ion with (<b>A</b>) a cation exchange stationary phase or (<b>B</b>) interaction with TBAHS present in the mobile phase and stationary phase C<sub>18</sub>.</p> Full article ">Figure 7
<p>Chromatograph of (<b>A</b>) an aqueous 10 mg L<sup>−1</sup> nitrite (4.95 min) and nitrate (6.26 min) standard (<b>B</b>) hay sample after extraction with hot water, SPE cleanup, and micropore filtration presence of nitrite (4.91 min) and nitrate (6.23 min) is evident.</p> Full article ">Figure 8
<p>Chromatographs of (<b>A</b>) 2 g/100 mL standard mixture of four sugars including fructose (5.24 min), glucose (6.26 min), sucrose (9.12 min), and lactose (13.09 min) separated using amino column (Zorbax Carbohydrate, 0.7 mL min<sup>−1</sup>, 80 ACN: 20 H<sub>2</sub>O). (<b>B</b>) Sugar content of a molasses sample after hot water extraction, fructose (5.18 min) and glucose (6.31 min) signals are evident. (<b>C</b>) 1 g/100 mL standard solution for arabinose (3.89 min) (<b>D</b>) 1 g/100 mL standard solution for xylose (4.30 min) (<b>E</b>) 1 g/100 mL standard solution for ribose (4.76 min), and (<b>F</b>) 1 g/100 mL standard solution for mannose (5.42 min). Signal at ca. 1.80 min corresponds to the solvent front; constant in all injections.</p> Full article ">Figure 9
<p>Schematic representation of sugar interaction mechanism using (<b>A</b>) amine based (<b>B</b>) calcium ion-based ligand exchange column.</p> Full article ">Figure 10
<p>Chromatographs of (<b>A</b>) Mix of organic acid standards malic acid (9.24 min) methanoic acid (formic acid, 10.92 min), ethanoic acid (acetic acid, 11.65 min), propanoic acid (propionic acid, 12.62 min), lactic acid (14.92 min), 2-methylpropanoic acid (isobutyric acid, 17.22 min), butanoic acid (butyric acid, 18.52 min). (<b>B</b>) A silage sample after extraction with acid 0.01 mol L<sup>−1</sup> H<sub>2</sub>SO<sub>4</sub>. Fermentation products identified at 18.499 min, 14.903 min, 12.606 min. The signal at ca. 5.70 min corresponds to the solvent front.</p> Full article ">Figure 11
<p>Single quadrupole LC/MS ESI<sup>+</sup> chromatographs of (<b>A</b>) Total ion chromatogram α-tocopherol (a 1 mg L<sup>−1</sup> solution in butanol) signal positively identified at 11.75 min (<b>B</b>) Mass spectra for α-tocopherol (a 1 mg L<sup>−1</sup> solution in butanol) using a cone energy of 120 V extracted from a signal with a retention time of 11.71 min (<b>C</b>) α-tocopherol (retention time 11.77 min) identified in a chicken plasma sample after extraction with chloroform and butanol (<b>D</b>) α-tocopherol in selected ion monitoring (SIM) mode using a cone energy of 120 V extracted from signal with a retention time of 11.82 min (<b>E</b>). α-tocopherol acetate in an injectable vitamin E solution for veterinary use using a “dilute and shoot” approach (16.32 min), and (<b>F</b>) α-tocopherol acetate in SIM mode using a cone energy of 60 V extracted from signal with a retention time of 16.34 min.</p> Full article ">Figure 12
<p>Hydrosoluble vitamin analysis based on ion pairing [<a href="#B383-foods-08-00001" class="html-bibr">383</a>]. (<b>A</b>) Successful separation of 7 complex B vitamins including niacin (nicotinic acid, B<sub>3</sub>, 6.67 min), FMN (B<sub>2</sub>, 14.12 min), pyridoxal (B<sub>6</sub>, 17.007 min), pyridoxamine (B<sub>6</sub>, 18.607 min), pyridoxine (B6, 19.963 min), folic acid (B9, 20.630 min), and thiamine (B<sub>1</sub>, 25.074 min). (<b>B</b>) Analysis of a vitamin premix destined for feed formulation. Another advantage presented is that the separation can be performed using a reverse phase C<sub>18</sub> column.</p> Full article ">Figure 13
<p>Chromatographs for vitamin A standards mixtures separated with C<sub>8</sub> column at 325 nm and 50 °C, of (<b>A</b>) retinyl acetate (3.11 min) and retinyl palmitate (17.63 min) using MeOH/H<sub>2</sub>O (90:10) and (<b>B</b>) retinyl acetate (2.89 min) and retinyl palmitate (13.30 min) using MeOH/2-propanol/acetonitrile (95:1.5:3.5).</p> Full article ">Figure 14
<p>Separation for vitamin D<sub>2</sub>+D<sub>3</sub> standards at 264 nm using (<b>A</b>) a C<sub>8</sub> column and (<b>B</b>) a C<sub>18</sub> column D<sub>2</sub> (16.47 min) y D<sub>3</sub> (17.24 min). Analysis performed at 30 °C using MeOH/2-propanol/ACN (90:3:7) (<b>C</b>) Superposed chromatograms for vitamin D<sub>2</sub> + D<sub>3</sub> (blue line) and δ/γ/α-tocopherol standards using a C<sub>18</sub> column and MeOH/H<sub>2</sub>O (90:10), 30 °C.</p> Full article ">
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