Next Issue
Previous Issue

Table of Contents

Chromatography, Volume 2, Issue 3 (September 2015), Pages 293-593

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-15
Export citation of selected articles as:

Research

Jump to: Review

Open AccessArticle Automated Analysis of Oxytocin by On-Line in-Tube Solid-Phase Microextraction Coupled with Liquid Chromatography-Tandem Mass Spectrometry
Chromatography 2015, 2(3), 382-391; doi:10.3390/chromatography2030382
Received: 12 May 2015 / Revised: 21 June 2015 / Accepted: 26 June 2015 / Published: 30 June 2015
Cited by 2 | PDF Full-text (1727 KB) | HTML Full-text | XML Full-text
Abstract
A simple and sensitive method for the analysis of oxytocin was developed using automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC–MS/MS). Oxytocin was separated within 3 min on a Zorbax Eclipse XDB-C8 column, with water/methanol (10/90, v/v) as
[...] Read more.
A simple and sensitive method for the analysis of oxytocin was developed using automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC–MS/MS). Oxytocin was separated within 3 min on a Zorbax Eclipse XDB-C8 column, with water/methanol (10/90, v/v) as the mobile phase at a flow rate of 0.2 mL min−1. Electrospray ionization conditions in the positive ion mode were optimized for MS/MS detection by multiple reaction monitoring. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 µL sample at a flow rate of 250 µL min−1 using a Supel-Q PLOT capillary column as an extraction device. The extracted oxytocin was easily desorbed from the capillary by passage of the mobile phase, and no carryover was observed. The calibration curves for oxytocin were linear (r = 0.9981) in the range of 0−5.0 ng mL−1, and the relative standard deviations at each point were below 14.7% (n = 3). The limit of detection of this method was 4.0 pg mL−1, and its sensitivity was 58-fold higher than that of the direct injection method. This method was applied successfully to the analysis of oxytocin in saliva samples without any other interference peaks. Full article
(This article belongs to the Special Issue Solid Phase Micro-Extraction)
Figures

Open AccessArticle Adverse-Mode FFF: Multi-Force Ideal Retention Theory
Chromatography 2015, 2(3), 392-409; doi:10.3390/chromatography2030392
Received: 31 May 2015 / Revised: 25 June 2015 / Accepted: 29 June 2015 / Published: 7 July 2015
PDF Full-text (446 KB) | HTML Full-text | XML Full-text
Abstract
A novel field-flow fractionation (FFF) technique, in which two opposing external forces act on the solute particles, is proposed. When the two external forces are sufficiently strong and scale differently as a function of the solutes’ property of interest (such as the solute
[...] Read more.
A novel field-flow fractionation (FFF) technique, in which two opposing external forces act on the solute particles, is proposed. When the two external forces are sufficiently strong and scale differently as a function of the solutes’ property of interest (such as the solute particle size), a sharp peak in the retention ratio (dramatic drop in elution time) is predicted to exist. Because the external forces oppose one another, we refer to this novel technique as adverse-mode FFF. The location of this peak is theoretically predicted and its ideal width estimated. The peak can become quite sharp by simultaneously increasing the strength of both fields, suggesting that adverse-mode FFF could be a useful technique for accurately measuring single species solute size. Full article
(This article belongs to the Special Issue Field-Flow Fractionation)
Open AccessArticle Determination of Sesquiterpenes in Wines by HS-SPME Coupled with GC-MS
Chromatography 2015, 2(3), 410-421; doi:10.3390/chromatography2030410
Received: 26 March 2015 / Revised: 24 June 2015 / Accepted: 3 July 2015 / Published: 9 July 2015
Cited by 5 | PDF Full-text (1011 KB) | HTML Full-text | XML Full-text
Abstract
The sesquiterpene compounds present in red wines were characterized and quantified by Headspace Solid-Phase Microextraction in combination with Gas Chromatography–Mass Spectrometry (HS-SPME-GC-MS). Sixteen sesquiterpenes were identified, mainly hydrocarbons but also derived oxygenated compounds. Sesquiterpenes were acyclic, monocyclic, byciclic and tryciclic. Sesquiterpenes were detected
[...] Read more.
The sesquiterpene compounds present in red wines were characterized and quantified by Headspace Solid-Phase Microextraction in combination with Gas Chromatography–Mass Spectrometry (HS-SPME-GC-MS). Sixteen sesquiterpenes were identified, mainly hydrocarbons but also derived oxygenated compounds. Sesquiterpenes were acyclic, monocyclic, byciclic and tryciclic. Sesquiterpenes were detected in SIM (selected ion monitoring) mode using their characteristics ions. All the sesquiterpenes were identified by mass spectral data, linear retention indices (LRI), literature data and injection of standards where available. Quantitative results were obtained using the method of standard additions. The method showed an average LOD = 0.05 µg L−1 and LOQ = 0.15 µg L−1. The monocyclic sesquiterpene with the germacrene skeleton, Germacrene D and the bicyclic sesquiterpene with the muurolane skeleton, α-muurolene were present in all the wine samples analysed. Syrah wines were the samples richest in sesquiterpenes in agreement with their typical spicy and woody notes. The results evidenced the possibility to use sesquiterpenes for wine authenticity and traceability. Full article
(This article belongs to the Special Issue Solid Phase Micro-Extraction)
Figures

Open AccessCommunication Fractionation and Characterization of High Aspect Ratio Gold Nanorods Using Asymmetric-Flow Field Flow Fractionation and Single Particle Inductively Coupled Plasma Mass Spectrometry
Chromatography 2015, 2(3), 422-435; doi:10.3390/chromatography2030422
Received: 4 June 2015 / Revised: 6 July 2015 / Accepted: 7 July 2015 / Published: 14 July 2015
Cited by 1 | PDF Full-text (2342 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Gold nanorods (GNRs) are of particular interest for biomedical applications due to their unique size-dependent longitudinal surface plasmon resonance band in the visible to near-infrared. Purified GNRs are essential for the advancement of technologies based on these materials. Used in concert, asymmetric-flow field
[...] Read more.
Gold nanorods (GNRs) are of particular interest for biomedical applications due to their unique size-dependent longitudinal surface plasmon resonance band in the visible to near-infrared. Purified GNRs are essential for the advancement of technologies based on these materials. Used in concert, asymmetric-flow field flow fractionation (A4F) and single particle inductively coupled mass spectrometry (spICP-MS) provide unique advantages for fractionating and analyzing the typically complex mixtures produced by common synthetic procedures. A4F fractions collected at specific elution times were analyzed off-line by spICP-MS. The individual particle masses were obtained by conversion of the ICP-MS pulse intensity for each detected particle event, using a defined calibration procedure. Size distributions were then derived by transforming particle mass to length assuming a fixed diameter. The resulting particle lengths correlated closely with ex situ transmission electron microscopy. In contrast to our previously reported observations on the fractionation of low-aspect ratio (AR) GNRs (AR < 4), under optimal A4F separation conditions the results for high-AR GNRs of fixed diameter (≈20 nm) suggest normal, rather than steric, mode elution (i.e., shorter rods with lower AR generally elute first). The relatively narrow populations in late eluting fractions suggest the method can be used to collect and analyze specific length fractions; it is feasible that A4F could be appropriately modified for industrial scale purification of GNRs. Full article
(This article belongs to the Special Issue Field-Flow Fractionation)
Figures

Open AccessArticle Poly(N-isopropylacrylamide) Hydrogels for Storage and Delivery of Reagents to Paper-Based Analytical Devices
Chromatography 2015, 2(3), 436-451; doi:10.3390/chromatography2030436
Received: 4 May 2015 / Revised: 29 June 2015 / Accepted: 10 July 2015 / Published: 17 July 2015
Cited by 3 | PDF Full-text (2519 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The thermally responsive hydrogel N,N'-methylenebisacrylamide-cross-linked poly(N-isopropylacrylamide) (PNIPAM) was developed and evaluated as a reagent storage and delivery system for microfluidic paper-based analytical devices (microPADs). PNIPAM was shown to successfully deliver multiple solutions to microPADs in specific sequences or simultaneously in
[...] Read more.
The thermally responsive hydrogel N,N'-methylenebisacrylamide-cross-linked poly(N-isopropylacrylamide) (PNIPAM) was developed and evaluated as a reagent storage and delivery system for microfluidic paper-based analytical devices (microPADs). PNIPAM was shown to successfully deliver multiple solutions to microPADs in specific sequences or simultaneously in laminar-flow configuration and was found to be suitable for delivering four classes of reagents to the devices: Small molecules, enzymes, antibodies and DNA. PNIPAM was also able to successfully deliver a series of standard glucose solutions to microPADs equipped to perform a colorimetric glucose assay. The results of these tests were used to produce an external calibration curve, which in turn was used to determine the concentration of glucose in sample solutions. Finally, PNIPAM was used to store the enzyme horseradish peroxidase for 35 days under ambient conditions with no significant loss of activity. The combination of PNIPAM and microPADs may allow for more complex assays to be performed on paper-based devices, facilitate the preparation of external calibration curves in the field, and extend the shelf life of microPADs by stabilizing reagents in an easy-to-use format. Full article
(This article belongs to the Special Issue Microfluidic Paper-Based Analytical Devices)
Figures

Open AccessArticle Field-Amplified Sample Injection-Micellar Electrokinetic Chromatography for the Determination of Benzophenones in Food Simulants
Chromatography 2015, 2(3), 452-471; doi:10.3390/chromatography2030452
Received: 15 June 2015 / Revised: 13 July 2015 / Accepted: 14 July 2015 / Published: 20 July 2015
PDF Full-text (1811 KB) | HTML Full-text | XML Full-text
Abstract
A field-amplified sample injection-micellar electrokinetic chromatography (FASI-MEKC) method for the determination of 14 benzophenones (BPs) in a food simulant used in migration studies of food packaging materials was developed, allowing almost baseline separation in less than 21 min. The use of a 10
[...] Read more.
A field-amplified sample injection-micellar electrokinetic chromatography (FASI-MEKC) method for the determination of 14 benzophenones (BPs) in a food simulant used in migration studies of food packaging materials was developed, allowing almost baseline separation in less than 21 min. The use of a 10 mM sodium dodecyl sulfate (SDS) solution as sample matrix was mandatory to achieve FASI enhancement of the analyzed BPs. A 21- to 784-fold sensitivity enhancement was achieved with FASI-MEKC, obtaining limits of detection down to 5.1–68.4 µg/L, with acceptable run-to-run precisions (RSD values lower than 22.3%) and accuracy (relative errors lower than 21.0%). Method performance was evaluated by quantifying BPs in the food simulant spiked at 500 µg/L (bellow the established specific migration limit for BP (600 µg/L) by EU legislation). For a 95% confidence level, no statistical differences were observed between found and spiked concentrations (probability at the confidence level, p value, of 0.55), showing that the proposed FASI-MEKC method is suitable for the analysis of BPs in food packaging migration studies at the levels established by EU legislation. Full article
(This article belongs to the Special Issue Electrophoretic Analyses in Capillaries and Microfluidic Devices)
Open AccessArticle An Improved Model for the Steric-Entropic Effect on the Retention of Rod-like Particles in Field-Flow Fractionation: Discussion of Aspect Ratio-Based Separation
Chromatography 2015, 2(3), 472-487; doi:10.3390/chromatography2030472
Received: 29 April 2015 / Revised: 21 July 2015 / Accepted: 22 July 2015 / Published: 28 July 2015
Cited by 1 | PDF Full-text (2131 KB) | HTML Full-text | XML Full-text
Abstract
We developed an improved model for predicting the steric-entropic effect on the separation behaviors of rod-like particles in flow field-flow fractionation. Our new model incorporates the “pole-vault” rotation of a rod-like particle near a wall under shear flow into the original model developed
[...] Read more.
We developed an improved model for predicting the steric-entropic effect on the separation behaviors of rod-like particles in flow field-flow fractionation. Our new model incorporates the “pole-vault” rotation of a rod-like particle near a wall under shear flow into the original model developed by Beckett and Giddings which considered only Brownian rotation. We investigated the effect of the aspect ratio on the retention ratios and the cross-sectional concentration distribution in the separation of rods in field-flow fractionation (FFF). Our analyses involved comparing the results predicted using the original model and those from the new model under various rod geometries and flow conditions. We found that the new model can show the aspect ratio-enhanced elution trend in certain flow conditions for the assumption of non-constant cloud thickness (ratio between the cross flow rate and the rod diffusivity). We also deducted that the flow conditions allowing for the aspect ratio-enhanced elution are related to the interplay among the axial flow rate, cloud thickness, and rod geometry. The new model can be viewed as a prototype to qualitatively show the aspect ratio-enhanced trend since its quantitative agreement with the experimental data must be improved for our future work. Full article
(This article belongs to the Special Issue Field-Flow Fractionation)
Open AccessArticle A Novel Micro Pressurized Liquid Extraction Method for Rapid Sample Preparation of Polycyclic Aromatic Hydrocarbons in Various Solids
Chromatography 2015, 2(3), 488-501; doi:10.3390/chromatography2030488
Received: 8 May 2015 / Revised: 2 July 2015 / Accepted: 24 July 2015 / Published: 3 August 2015
Cited by 1 | PDF Full-text (797 KB) | HTML Full-text | XML Full-text
Abstract
The use of a novel micro pressurized liquid extraction (µPLE) method for the isolation of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) from various solid samples is explored. The technique employs rapid heating in a single static extraction mode to remove analytes in
[...] Read more.
The use of a novel micro pressurized liquid extraction (µPLE) method for the isolation of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) from various solid samples is explored. The technique employs rapid heating in a single static extraction mode to remove analytes in a matter of seconds from 5–10 mg samples using only 125 µL of solvent. For example, results show that 30 s extractions with toluene at 200 °C produce respective PAH recovery ranges of 90%–130% and 88%–114% from samples of soil and smoked chicken. Comparatively, solids containing significant amounts of biochar were more challenging to extract from. For instance, when using a pure biochar sample matrix, recoveries for the 16 PAHs range from only 33%–66% after 60 s of extraction with toluene at 200 °C. Overall, these extraction results agree very well with those reported when using conventional methods on similar samples. Therefore, the findings indicate that µPLE can potentially provide an alternative sample preparation method for PAHs that is both very rapid and requires little solvent. Full article
(This article belongs to the Special Issue Microscale Separation and Analysis)
Figures

Open AccessArticle Evaluation of 5 μm Superficially Porous Particles for Capillary and Microfluidic LC Columns
Chromatography 2015, 2(3), 502-514; doi:10.3390/chromatography2030502
Received: 26 May 2015 / Revised: 10 July 2015 / Accepted: 24 July 2015 / Published: 4 August 2015
Cited by 3 | PDF Full-text (1286 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Large-size (4–5 µm) superficially porous particles yield lower plate heights (e.g., the minimal reduced plate height or hmin ≈ 1.5) than fully porous particles of a similar size when packed into large-bore columns. This property allows for better chromatographic performance without the
[...] Read more.
Large-size (4–5 µm) superficially porous particles yield lower plate heights (e.g., the minimal reduced plate height or hmin ≈ 1.5) than fully porous particles of a similar size when packed into large-bore columns. This property allows for better chromatographic performance without the higher pressures required for smaller particles. This study explores the use of such particles in microfluidic LC columns where materials and fitting pressure limits can constrain the size of particle used. The theoretically predicted performance improvements compared to fully porous particles were not demonstrated in capillary columns (with hmin ≈ 2 for both particle types), in agreement with previous studies that examined smaller superficially porous particles. Microfluidic columns were then compared to capillary columns. Capillary columns significantly outperformed microfluidic columns due to imperfections imposed by microfluidic channel asymmetry and world-to-chip connection at the optimal flow rate; however, superficially porous particles packed in microfluidic LC columns had flatter plate height versus flow rate curves indicating potential for better performance at high reduced velocities. Full article
(This article belongs to the Special Issue Microscale Separation and Analysis)
Open AccessArticle Evaluation of Carbon Nanotubes Functionalized Polydimethylsiloxane Based Coatings for In-Tube Solid Phase Microextraction Coupled to Capillary Liquid Chromatography
Chromatography 2015, 2(3), 515-528; doi:10.3390/chromatography2030515
Received: 30 March 2015 / Revised: 17 July 2015 / Accepted: 31 July 2015 / Published: 10 August 2015
Cited by 3 | PDF Full-text (1820 KB) | HTML Full-text | XML Full-text
Abstract
In the present work, the performance of carbon nanotubes (c-CNTs) functionalized polydimethylsiloxane (PDMS) based coatings as extractive phases for in-tube solid phase microextraction (IT-SPME) coupled to Capillary LC (CapLC) has been evaluated. Carboxylic-single walled carbon nanotubes (c-SWNTs) and carboxylic-multi walled carbon nanotubes (c-MWNTs)
[...] Read more.
In the present work, the performance of carbon nanotubes (c-CNTs) functionalized polydimethylsiloxane (PDMS) based coatings as extractive phases for in-tube solid phase microextraction (IT-SPME) coupled to Capillary LC (CapLC) has been evaluated. Carboxylic-single walled carbon nanotubes (c-SWNTs) and carboxylic-multi walled carbon nanotubes (c-MWNTs) have been immobilized on the activated surface of PDMS capillary columns. The effect of different percentages of diphenyl groups in the PDMS extractive phase has also been evaluated. The extraction capability of the capillary columns has been tested for different organic pollutants, nitrogen heterocyclic compounds and polycyclic aromatic compounds (PAHs). The results indicated that the use of the c-CNTs-PDMS capillary columns improve pyriproxyfen and mainly PAH extraction. Triazines were better extracted by unmodified TRB-35 and modified c-CNTs-PDMSTRB-5. The results showed that the extraction capability of the c-CNT capillary columns depends not only on the polarity of the analytes (as it occurs with PDMS columns) but also on the interactions that the analytes can establish with the immobilized c-CNTs on the PDMS columns. The extraction efficiency has been evaluated on the basis of the preconcentration rate that can be achieved, and, in this sense, the best c-CNTs-PDMS capillary column for each group of compounds can be proposed. Full article
(This article belongs to the Special Issue Solid Phase Micro-Extraction)
Open AccessArticle The Dramatic Modulatory Role of the 2'N Substitution of the Terminal Amino Hexose of Globotetraosylceramide in Determining Binding by Members of the Verotoxin Family
Chromatography 2015, 2(3), 529-544; doi:10.3390/chromatography2030529
Received: 27 April 2015 / Revised: 8 July 2015 / Accepted: 5 August 2015 / Published: 14 August 2015
PDF Full-text (3747 KB) | HTML Full-text | XML Full-text
Abstract
Although globotetraosylceramide (Gb4) is only recognized by a single member of the verotoxin family namely, the pig edema disease toxin (VT2e), removal of the acetyl group from the terminal N-acetyl hexosamine of Gb4 to generate the free amino sugar containing
[...] Read more.
Although globotetraosylceramide (Gb4) is only recognized by a single member of the verotoxin family namely, the pig edema disease toxin (VT2e), removal of the acetyl group from the terminal N-acetyl hexosamine of Gb4 to generate the free amino sugar containing species (aminoGb4) results in the generation of a glycolipid preferentially recognized by all members of the verotoxin family (i.e., VT1, VT2, VT2c, and VT2e). GT3, a site-specific mutant of VT2e, in which Gb4 recognition is lost but Gb3 binding is retained, also binds aminoGb4. We have now compared the binding of VT1, VT2, VT2e, and GT3 to a series of aminoGb4 derivatives using a TLC overlay technique. DimethylaminoGb4 is bound by VT1 and VT2 but not VT2e or GT3; formylaminoGb4 binds all toxins but poorly to VT2 and preferentially VT2e; trifluoroacetylaminoGb4 binds only VT2e and GT3; isopropylaminoGb4 binds VT1 and poorly to VT2; benzylaminoGb4 binds all four toxins. Thus, there is a marked distinction between the permissible amino substitutions for VT1 and VT2e binding. GT3 is a hybrid between these in that, according to the substitution, it behaves similarly either to VT1 or to VT2e. For each species, GT3 does not however, show a hybrid binding between that of VT1 and VT2e. Analysis of the binding as a function of pH shows opposite effects for VT1 and VT2e: decreased pH increases VT1, but decreases VT2e receptor glycolipid binding. Full article
(This article belongs to the Special Issue New Trends in Thin-Layer Chromatography)
Open AccessArticle Synthetic Smectite Colloids: Characterization of Nanoparticles after Co-Precipitation in the Presence of Lanthanides and Tetravalent Elements (Zr, Th)
Chromatography 2015, 2(3), 545-566; doi:10.3390/chromatography2030545
Received: 28 May 2015 / Revised: 21 July 2015 / Accepted: 31 July 2015 / Published: 1 September 2015
Cited by 1 | PDF Full-text (1853 KB) | HTML Full-text | XML Full-text
Abstract
The magnesian smectite hectorite is a corrosion product frequently detected in nuclear waste glass alteration experiments. The structural incorporation of a single trivalent lanthanide was previously demonstrated. Hectorite was presently synthesized, for the first time, in the presence of several lanthanides (La, Eu,
[...] Read more.
The magnesian smectite hectorite is a corrosion product frequently detected in nuclear waste glass alteration experiments. The structural incorporation of a single trivalent lanthanide was previously demonstrated. Hectorite was presently synthesized, for the first time, in the presence of several lanthanides (La, Eu, Yb) following a multi-step synthesis protocol. The smallest-sized particles (nanoparticles, NPs) were isolated by centrifugation and analyzed by asymmetrical flow field-flow fractionation (AsFlFFF) coupled to ICP-MS, in order to obtain information on the elemental composition and distribution as a function of the size. Nanoparticles can be separated from the bulk smectite phase. The particles are able to accommodate even the larger-sized lanthanides such as La, however, with lower efficiency. We, therefore, assume that the incorporation proceeds by substitution for octahedral Mg accompanied by a concomitant lattice strain that increases with the size of the lanthanides. The presence of a mixture does not seem to affect the incorporation extent of any specific element. Furthermore, syntheses were performed where in addition the tetravalent zirconium or thorium elements were admixed, as this oxidation state may prevail for many actinide ions in a nuclear waste repository. The results show that they can be incorporated as well. Full article
(This article belongs to the Special Issue Field-Flow Fractionation)
Figures

Open AccessArticle Nanoparticle-Surface Interactions in Geometrical Separation Devices
Chromatography 2015, 2(3), 567-579; doi:10.3390/chromatography2030567
Received: 24 June 2015 / Revised: 31 July 2015 / Accepted: 3 September 2015 / Published: 11 September 2015
PDF Full-text (5615 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study sought to demonstrate the impact of surface-target interactions in a device bearing geometrical features through evaluations of chemical modification to the surface and alteration of the charge state of both surface and targets. The movement of commercial fluorescent nanoparticles through a
[...] Read more.
This study sought to demonstrate the impact of surface-target interactions in a device bearing geometrical features through evaluations of chemical modification to the surface and alteration of the charge state of both surface and targets. The movement of commercial fluorescent nanoparticles through a field of geometric features was monitored based on the output of the field measured at different points transverse to the direction of flow. Modification of the device surfaces using carboxylate, amine, phenyl, and fluorinated groups was considered. The functional group on the surface was found to significantly impact biased particle movement in the device with amine groups leading to the greatest differences. Other factors, such as flow rate, pH, and initial particle concentration, were also found to have a significant impact on particle concentrations across the feature field. Full article
Figures

Open AccessArticle Conductivity-Dependent Flow Field-Flow Fractionation of Fulvic and Humic Acid Aggregates
Chromatography 2015, 2(3), 580-593; doi:10.3390/chromatography2030580
Received: 22 July 2015 / Revised: 15 September 2015 / Accepted: 15 September 2015 / Published: 22 September 2015
Cited by 1 | PDF Full-text (1393 KB) | HTML Full-text | XML Full-text
Abstract
Fulvic (FAs) and humic acids (HAs) are chemically fascinating. In water, they have a strong propensity to aggregate, but this research reveals that tendency is regulated by ionic strength. In the environment, conductivity extremes occur naturally—freshwater to seawater—warranting consideration at low and high
[...] Read more.
Fulvic (FAs) and humic acids (HAs) are chemically fascinating. In water, they have a strong propensity to aggregate, but this research reveals that tendency is regulated by ionic strength. In the environment, conductivity extremes occur naturally—freshwater to seawater—warranting consideration at low and high values. The flow field flow fractionation (flow FFF) of FAs and HAs is observed to be concentration dependent in low ionic strength solutions whereas the corresponding flow FFF fractograms in high ionic strength solutions are concentration independent. Dynamic light scattering (DLS) also reveals insight into the conductivity-dependent behavior of humic substances (HSs). Four particle size ranges for FAs and humic acid aggregates are examined: (1) <10 nm; (2) 10 nm–6 µm; (3) 6–100 µm; and (4) >100 µm. Representative components of the different size ranges are observed to dynamically coexist in solution. The character of the various aggregates observed—such as random-extended-coiled macromolecules, hydrogels, supramolecular, and micellar—as influenced by electrolytic conductivity, is discussed. The disaggregation/aggregation of HSs is proposed to be a dynamic equilibrium process for which the rate of aggregate formation is controlled by the electrolytic conductivity of the solution. Full article
(This article belongs to the Special Issue Field-Flow Fractionation)
Figures

Review

Jump to: Research

Open AccessReview Recent Developments and Applications of Solid Phase Microextraction (SPME) in Food and Environmental Analysis—A Review
Chromatography 2015, 2(3), 293-381; doi:10.3390/chromatography2030293
Received: 1 April 2015 / Revised: 10 June 2015 / Accepted: 11 June 2015 / Published: 30 June 2015
Cited by 15 | PDF Full-text (1618 KB) | HTML Full-text | XML Full-text
Abstract
Solid-phase microextraction (SPME) is a simple, sensitive, rapid and solvent-free technique for the extraction of analytes from gaseous, liquid and solid samples and takes a leading position among microextraction methods. Application of SPME in sample preparation has been increasing continuously over the last
[...] Read more.
Solid-phase microextraction (SPME) is a simple, sensitive, rapid and solvent-free technique for the extraction of analytes from gaseous, liquid and solid samples and takes a leading position among microextraction methods. Application of SPME in sample preparation has been increasing continuously over the last decade. It is most often used as an automatized fiber injection system coupled to chromatographic separation modules for the extraction of volatile and semivolatile organic compounds and also allows for the trace analysis of compounds in complex matrices. Since SPME was first introduced in the early 1990s, several modifications have been made to adapt the procedure to specific application requirements. More robust fiber assemblies and coatings with higher extraction efficiencies, selectivity and stability have been commercialized. Automation and on-line coupling to analytical instruments have been achieved in many applications and new derivatization strategies as well as improved calibration procedures have been developed to overcome existing limitations regarding quantitation. Furthermore, devices using tubes, needles or tips for extraction instead of a fiber have been designed. In the field of food analysis, SPME has been most often applied to fruit/vegetables, fats/oils, wine, meat products, dairy and beverages whereas environmental applications focus on the analysis of air, water, soil and sediment samples. Full article
(This article belongs to the Special Issue Solid Phase Micro-Extraction)
Figures

Journal Contact

MDPI AG
Chromatography Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
E-Mail: 
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Chromatography Edit a special issue Review for Chromatography
logo
loading...
Back to Top