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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
This book focuses on the chemistry of additives for high performance applications and a large number of chemical formulas are displayed in the text. The additives applications include: * Analysis and separation techniques, such as high performance liquid chromatography, for example ionic liquids. * Additives for electrical applications, such as capacitors, electrokinetic micropumps, lithium-ion batteries, and other battery types. * Additives for solar cells for control of the active layer nanomorphology are documented as are additives for electrolyte membranes, fuel cells, such as membrane exchange humidifiers and coolant additives. * Medical applications include high performance additives for the manufacture of scaffolds, controlled drug release, and nanofibers. * Additives for lubricants including the deposit control, anti-wear additives, fluid loss control additives in drilling applications. * Additives for concrete uses such as set retarders, curing accelerators, defoamers, permeability control additives, and corrosion protection additives.
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Veröffentlichungsjahr: 2016
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Contents
Cover
Title page
Copyright page
Preface
Chapter 1: Analysis and Separation Techniques
1.1 High Performance Liquid Chromatography
1.2 Chelation Ion Chromatography
1.3 Membranes
References
Chapter 2: Electrical Applications
2.1 Capacitors
2.2 Electrokinetic Micropumps
2.3 Lead-Acid Batteries
2.4 Lithium-Ion Batteries
2.5 Nickel Batteries
2.6 Sodium-Ion Batteries
2.7 Solar Cells
2.8 Fuel Cells
References
Chapter 3: Medical Uses
3.1 High Performance Additive Manufactured Scaffolds
References
Chapter 4: Lubricants
4.1 Fuels
4.2 Lubricant Additives
4.3 Anti-Wear Additives
4.4 Fluid Loss Control Additives
4.5 Warm Mix Asphalt Additives
References
Chapter 5: Concrete Additives
5.1 Properties of Concrete
5.2 Set Retarders
5.3 Accelerators
5.4 Dispersants and Thinners
5.5 Defoamers
5.6 Shrinkage Compensation
5.7 Permeability
5.8 Air Entraining Agents
5.9 Corrosion Protection
5.10 Superabsorbent Polymers
5.11 Fibers
5.12 Additives from Wastes
References
Chapter 6: Other Uses
6.1 High Performance Additive for Powder Coatings
6.2 Radiation Shielding
6.3 Superabsorbent Polymers
6.4 Laser Additive Manufacturing of High Performance Materials
6.5 High Temperature Cooling Application
References
Index
Tradenames
Acronyms
Chemicals
General Index
End User License Agreement
Guide
Cover
Copyright
Contents
Begin Reading
List of Illustrations
Chapter 1
Figure 1.1
Ionic liquids.
Figure 1.2
Acetonitrile.
Figure 1.3
1-Butyl-3-methylimidazolium chloride.
Figure 1.4
Sudans and Para Red.
Figure 1.5
1-Butyl-3-methylimidazolium hexafluorophosphate.
Figure 1.6
Nucleotides.
Figure 1.7
Ionic liquids.
Figure 1.8
Catecholamines.
Figure 1.9
Fluoroquinolone antibiotics.
Figure 1.10
4,4′-Diaminostilbene-2,2′-disulfonic acid.
Figure 1.11
Propyl propane thiosulfonate.
Figure 1.12
Phenothiazine.
Figure 1.13
Imidazole compounds.
Figure 1.14
Inhibitors and passivators (33).
Figure 1.15
Atrolactic acid.
Figure 1.16
Mandelic acid derivatives.
Figure 1.17
Vancomycin.
Figure 1.18
Actaplanin.
Figure 1.19
Dansyl amino acids.
Figure 1.20
5-(Dimethylamino)naphthalene-1-sulfonyl chloride.
Figure 1.21
Flavonoid racemates.
Figure 1.22
Hydroxypropyl-
β
-cydodextrin.
Figure 1.23
Oxybutynin.
Figure 1.24
Amino alcohols.
Figure 1.25
Morpholine and trifluoroacetic acid.
Figure 1.26
1,4-Dihydroxy-2-naphthoic acid and Dithiothreitol.
Figure 1.27
Acidic drugs.
Figure 1.28
Iminodiacetic acid.
Figure 1.29
Complexing agents.
Chapter 2
Figure 2.1
3,4-Ethylene-dioxythiophene.
Figure 2.2
Trimethylammoniopropane sulfonate.
Figure 2.3
N,N
′-
o
-Phenylenedimaleimide.
Figure 2.4
Functional electrolytes (33).
Figure 2.5
In-situ
coating additives.
Figure 2.6
Charging curve of a device without lithium polysulfide (37).
Figure 2.7
Charging and discharging curves of a device containing lithium polysulfide (37).
Figure 2.8
N
-Methyl-2-pyrrolidone.
Figure 2.9
Functional electrolyte additives (42).
Figure 2.10
Synthesis of methylene ethylene carbonate (53).
Figure 2.11
Cyclic carbonates.
Figure 2.12
Borate-based anion receptors (58).
Figure 2.13
Borate compounds.
Figure 2.14
Synthesis of a salicyclic organoborate (63).
Figure 2.15
Trimethylboroxine.
Figure 2.16
1-Propylphosphonic acid cyclic anhydride.
Figure 2.17
2-(Triphenylphosphoranylidene) succinic anhydride.
Figure 2.18
Methylene methanedisulfonate.
Figure 2.19
Synthesis of 3,3′-sulfonyldipropionitrile (75).
Figure 2.20
Additives for performance improvement.
Figure 2.21
Electrolyte solvents.
Figure 2.22
1,3-Propane sultone.
Figure 2.23
Preparation of disultones (90).
Figure 2.24
Di(methylsulfonyl) methane.
Figure 2.25
Isothiocyanates.
Figure 2.26
Polymerization of an isothiocyanate.
Figure 2.27
N,N
′-4,4′-diphenylmethane-bismaleimide.
Figure 2.28
Allyloxytrimethylsilane.
Figure 2.29
1,2-Bis(difluoromethylsilyl)ethane.
Figure 2.30
Additive used for testing (103).
Figure 2.31
Aromatic hydrocarbon-based nonaqueous organic solvents.
Figure 2.32
Nitrile-based compounds.
Figure 2.33
Polyalkyleneglycol diglycidylether.
Figure 2.36
Synthesis of star molecules (121).
Figure 2.35
Organo-sulfur compounds.
Figure 2.36
Synthesis of star molecules (121).
Figure 2.37
Synthesis of star molecules (127).
Figure 2.38
N
-Butyl-
N′
-(4-pyridylheptyl)imidazolium bromide.
Figure 2.39
1-Methyl-3-propyl-imidazolinium iodide.
Figure 2.40
Diethyl oxalate and 4-
tert
-Butyl pyridine.
Figure 2.41
Co-additives for nanomorphology control.
Figure 2.42
Polymer from thieno[3,2-b][1]benzothiophene isoindigo, R=2-decyltetradecyl.
Figure 2.43
Indenothiophene and benzothiadiazole.
Figure 2.44
Hemin.
Chapter 3
Figure 3.1
γ
-Glycidoxypropyltrimethoxysilane.
Figure 3.2
Chitosan.
Figure 3.3
Clorhexidine.
Chapter 4
Figure 4.1
Amine type antioxidants.
Figure 4.2
Phenol type antioxidants.
Figure 4.3
Anti-rust additives.
Figure 4.4
Additives for greases.
Figure 4.5
Zinc di
-n
-butyldithiocarbamate.
Figure 4.6
Surfactants for ionic liquids.
Figure 4.7
Thiophosphite derivative.
Chapter 5
Figure 5.1
Effects of commonly used pozzolanic materials on the amount of calcium hydroxide (5).
Figure 5.2
2-Hydroxyethyl methacrylate.
Figure 5.3
Xylonic acid.
Figure 5.4
Synthesis of an ethoxylated fatty alcohol acrylate.
Figure 5.5
Melanin and tyrosine.
Figure 5.6
Melt spinning apparatus (53).
Chapter 6
Figure 6.1
Aniline and anhydride monomers.
Figure 6.2
Silane compounds.
Figure 6.3
Compatibility increasers.
List of Tables
Chapter 1
Table 1.1
Chemical names of the dyes.
Table 1.2
Detection limits and recoveries for Sudan dyes and Para Red (7).
Table 1.3
Properties of certain ionic liquids (8, 12, 13).
Table 1.4
Ionic liquids and antibiotics (15).
Table 1.5
Solvents tested for extraction of stabilizers (40).
Table 1.6
Dansyl amino acids (46).
Table 1.7
Zinc dithiophosphates (68).
Table 1.8
Acidic drugs (69).
Chapter 2
Table 2.1
Supercapacitor electrode composition (7).
Table 2.2
Electrolyte for bipolar architectures (37).
Table 2.3
Highest occupied molecular orbitals (HOMO), lowest unoccupied molecular orbitals (LUMO), oxidation potentials (OP), reduction potentials (RP), and BE F
–
binding affinity values in
e
V
.
Table 2.4
Charge and discharge capacities and initial coulombic efficiencies (65).
Table 2.5
Isothiocyanates (93).
Table 2.6
Additive used for testing (103).
Table 2.7
Carbonate-based solvents (104).
Table 2.8
Aromatic nonaqueous organic solvents (104).
Table 2.9
Nitrile-based compounds (104).
Table 2.10
Nonaqueous electrolytes and aprotic organic solvents (105).
Table 2.11
Organo-sulfur compounds (106).
Table 2.12
Fluorinated cycloaliphatic additives (151).
Table 2.13
Inhibitor additives for fuel cells (154, 155).
Table 2.14
Tradenames in References.
Chapter 4
Table 4.1
Types of additives (10).
Table 4.2
Amine type antioxidants (10).
Table 4.3
Phenol type antioxidants (10).
Table 4.4
Anti-rust additives (10).
Table 4.5
Antioxidants (14).
Table 4.6
Extreme pressure and anti-wear additives (14).
Table 4.7
Friction modifiers (14).
Table 4.8
Rust and corrosion inhibitors (14).
Table 4.9
Structure modifiers (14).
Table 4.10
Standards used for the evaluation (14).
Table 4.11
Surfactants for ionic liquids (21).
Table 4.12
Tradenames in References.
Chapter 5
Table 5.1
Components in calcium aluminate cement (8).
Table 5.2
Air entraining agents (40).
Table 5.3
Superabsorbent polymers (43).
Table 5.4
Formulations with a superabsorbent polymer (43).
Table 5.5
Tradenames in References.
Chapter 6
Table 6.1
Materials for superabsorbent polymers (8).
Table 6.2
Additives for superabsorbent polymers (8).
Table 6.3
Organic additives for cold storage (32).
Table 6.4
Tradenames in References.
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Scrivener Publishing 100 Cummings Center, Suite 541J Beverly, MA 01915-6106
Publishers at Scrivener Martin Scrivener([email protected]) Phillip Carmical ([email protected])
Additives for High Performance Applications
Chemistry and Applications
Johannes Karl Fink
Copyright © 2017 by Scrivener Publishing LLC. All rights reserved.
Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Beverly, Massachusetts. Published simultaneously in Canada.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
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Library of Congress Cataloging-in-Publication Data:
ISBN 978-1-119-36361-3
Preface
This book focuses on the chemistry of additives for high performance uses in analytical applications, electrical applications, medical applications, and others, as well as special exemplified uses of these additives.
The text focuses on the literature of the past decade. Beyond education, this book may serve the needs of engineers and specialists who have only a passing knowledge of these issues, but need to know more.
How to Use This Book
Utmost care has been taken to present reliable data. Because of the vast variety of material presented here, however, the text cannot be complete in all aspects, and it is recommended that the reader study the original literature for more complete information.
The reader should be aware that mostly US patents have been cited where available, but not the corresponding equivalent patents of other countries.
For this reason, the author cannot assume responsibility for the completeness, validity or consequences of the use of the material presented here. Every attempt has been made to identify trademarks; however, there were some that the author was unable to locate.
Index
There are four indices: an index of tradenames, an index of acronyms, an index of chemicals, and a general index. In the index of chemicals, compounds that occur extensively, e.g., acetone, are not included at every occurrence, but rather when they appear in an important context. When a compound is found in a figure, the entry is marked in boldface letters in the chemical index.
Acknowledgements
I am indebted to our university librarians, Dr. Christian Hasenhüttl, Dr. Johann Delanoy, Franz Jurek, Margit Keshmiri, Dolores Knabl, Friedrich Scheer, Christian Slamenik, Renate Tschabuschnig, and Elisabeth Groß for their support in literature acquisition. In addition, many thanks to the head of my department, Professor Wolfgang Kern, for his interest and permission to prepare this text.
I also want to express my gratitude to all the scientists who have carefully published their results concerning the topics dealt with herein. This book could not have been otherwise compiled.
Last, but not least, I want to thank the publisher, Martin Scrivener, for his abiding interest and help in the preparation of the text. In addition, my thanks go to Jean Markovic, who made the final copyedit with utmost care.
Johannes Fink Leoben, 6th September 2016
Chapter 1Analysis and Separation Techniques
1.1 High Performance Liquid Chromatography
1.1.1 Ionic Liquids as Mobile Phase Additives
The popularity of ionic liquids has grown in several analytical separation techniques. Thus, the reports concerning the applications of ionic liquids are still increasing. The use of ionic liquids, mainly imidazolium-based, associated with chloride and tetrafluoroborate as mobile phase additives in high performance liquid chromatography (HPLC) has been reviewed (1).
Mostly, ionic liquids just function as salts, but keep several kinds of intermolecular interactions, which are useful for chromatographic separations. Both cation and anion can be adsorbed on the stationary phase, creating a bilayer. This gives rise to hydrophobic, electrostatic and other specific interactions with the stationary phase and solutes, which modify the retention behavior and peak shape (1).
1.1.1.1 Imidazolium Compounds
The beneficial effects of several ionic liquids as mobile phase additives in HPLC using an electrochemical detection for the determination of heterocyclic aromatic amines have been evaluated (2). The tested ionic liquids were 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, and 1-methyl-3-octylimidazolium tetrafluoroborate. These compounds are shown in Figure 1.1.
Figure 1.1 Ionic liquids.
Several chromatographic parameters have been evaluated in the presence or absence of ionic liquids, or using ammonium acetate as the most common mobile phase additive, with three different C18 stationary phases. The effect of the acetonitrile content was also studied. Acetonitrile is shown in Figure 1.2.
Figure 1.2 Acetonitrile.
Best resolution, lower peak-widths, and lower retention factors were obtained when using ionic liquids rather than ammonium acetate as mobile phase additives. The best chromatographic conditions were found when using 1-butyl-3-methylimidazolium tetrafluoroborate as the mobile phase additive (2).
1-Butyl-3-methylimidazolium chloride, cf. Figure 1.3, 1-octyl-3-methylimidazolium chloride, and 1-decyl-3-methylimidazolium chloride were used as mobile phase additives in the HPLC to simultaneously separate phenoxy acid herbicides and phenols at neutral pH (3). It was found that when using 1-butyl-3-methylimidazolium chloride, a good baseline separation and good chromatograms for all the acid compounds were obtained on a normal reversed phase C18 column.
Figure 1.3 1-Butyl-3-methylimidazolium chloride.
The retention time of the target acid compounds was shortened with the increase of the alkyl chain length and the concentrations of ionic liquids, probably due to the delocalization of the positive charge on the imidazolium cation, the repulsion between chlorine ions of ionic liquids and the acid compounds, as well as the stereohindrance effect (3).
Extraction of Sudan Dyes. Sudan dyes are typically used as coloring additives in the manufacturing of wax, textile, and floor and shoe polishes (4, 5). Sudan I has been classified as a category 3 carcinogen by the International Agency for Research on Cancer (IARC). Also, Para Red could be a genotoxic carcinogen (6). The structures of the coloring additives are shown in Figure 1.4. The chemical names of the dyes are summarized in Table 1.1.
Figure 1.4 Sudans and Para Red.
Table 1.1 Chemical names of the dyes.
Short name
Chemical name
Sudan I
1-[(2,4-Dimethylphenyl)azo]-2-naphthalenol
Sudan II
1-(Phenylazo)-2-naphthol
Sudan III
1-(4-Phenylazophenylazo)-2-naphthol
Sudan IV
o
-Tolyazo-
o
-tolylazo-
β
-naphthol
Para Red
1-p-Nitrobenzeneazo-2-naphthol
A method for the analysis of such dyes has been developed. The method is based on coupling of ionic liquid-based extraction with HPLC. In this way, Sudan dyes and Para Red in chili powder, chili oil, and food additive samples can be found.
Two ionic liquids, i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, cf. Figure 1.5, and 1-octyl-3-methylimidazolium hexafluorophosphate have been compared as extraction solvents. It was found that 1-octyl-3-methylimidazolium hexafluorophosphate showed higher recoveries for each analyte.
Figure 1.5 1-Butyl-3-methylimidazolium hexafluorophosphate.
Also, the conditions for the extraction of Sudan dyes and Para Red were optimized. Under optimal conditions, a good reproducibility of extraction performance was obtained, with relative standard deviation values of 2.0–3.5% (7).
The ionic liquids were prepared according to a previously reported method (8, 9). The Sudan dyes and Para Red standard solutions were obtained from Zhejiang Entry-Exit Inspection and Quarantine Bureau (Hangzhou, China).
The detection limits and the recoveries are summarized in Table 1.2.
Table 1.2 Detection limits and recoveries for Sudan dyes and Para Red (7).
Material
Chili powder
Chili oil
Food additives
Nucleotides Separation. A method for the separation of nucleotides has been developed (10). These nucleotides include 5′-monophosphate adenosine, 5′-monophosphate cytidine, 5′-monophosphate uridine, 5′-monophosphate guanosine, and 5′-monophosphate inosine. Some of these compounds are shown in Figure 1.6.
Figure 1.6 Nucleotides.
The essential feature of the method is that 1-alkyl-3-methylimidazolium salts are used as mobile phase additives, resulting in a baseline separation of nucleotides without the need for gradient elution and organic solvent addition, as usually used in reversed phase HPLC (10).
Amine Separation. By varying the lengths and branching of alkyl chains of the anionic core and the cationic precursor, it is possible to design solvents for specific applications. Because of these characteristic properties, ionic liquids are widely used as new solvent media in heterogeneous catalysis, synthesis, electrochemistry, sensors, battery applications, analysis and separation techniques (11).
Some amines, including benzidine, benzylamine, N-ethylaniline and N,N′-dimethylaniline could be separated using ionic liquids as additives for the mobile phase in HPLC (12).
The compounds 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIm][BF4]) and 1-butyl-3-methylimidazolium bromide ([BMIm]-[Br]) were used as ionic liquids. Some of these compounds are shown in Figure 1.7. Some properties are summarized in Table 1.3.
Figure 1.7 Ionic liquids.
Table 1.3 Properties of certain ionic liquids (8, 12, 13).
1-Ethyl-3-methylimidazolium tetrafluoroborate
1-Butyl-3-methylimidazolium tetrafluoroborate
1-Hexyl-3-methylimidazolium tetrafluoroborate
1-Butyl-3-methylimidazolium bromide
The effects of the length of alkyl chain or counterions on different ionic liquids and their concentrations on the separation of these analytes have been assessed (12).
The differences between the ionic liquids and tetrabutyl ammonium bromide on the separation of o-phthalic acid, m-phthalic acid, and p-phthalic acid have been compared. The results indicated that ionic liquids act as ion-pair reagents, although their hydrophobicity and hydrogen bonding also play important roles (12).
Catecholamines. The use of 1-alkyl-3-methylimidazolium salts and N-butyl-pyridinium salts as mobile phase additives for the separation of catecholamines in reversed phase HPLC has been reported (14). As catecholamines, norepinephrine, epinephrine and dopamine were investigated. These compounds are shown in Figure 1.8.
Figure 1.8 Catecholamines.
A good separation could be achieved with these additives. The effects of pH of the mobile phase, the concentration of ionic liquids, and different alkyl substituents on the cations, and different counterions of the ionic liquids were investigated. The separation occurs by molecular interactions between the ionic liquids and the catecholamines (14).
Fluoroquinolone Antibiotics. Ionic liquids differing in the length of the alkyl chain were tested as mobile phase additives for the separation using HPLC of fluoroquinolone antibiotics (15). The materials are listed in Table 1.4. Fluoroquinolone antibiotics are shown in Figure 1.9
Figure 1.9 Fluoroquinolone antibiotics.
Table 1.4 Ionic liquids and antibiotics (15).
1-Ethyl-3-methylimidazolium tetrafluoroborate
1-Butyl-3-methylimidazolium tetrafluoroborate
1-Hexyl-3-methylimidazolium tetrafluoroborate
1-Methyl-3-octylimidazolium tetrafluoroborate
Tetraethylammonium tetrafluroborate
Fleroxacin
Ciprofloxacin
Lomefloxacin
Danofloxacin
Enrofloxacin
Sarafloxacin
Difloxacin
A conventional reversed phase Nova-Pak C18 column and fluorescence detection were used. 1-Butyl-3-methylimidazolium tetrafluoroborate enabled an effective separation of the antibiotics with a relatively low analysis time of 14 min. The best separation was achieved by isocratic elution at 1 mlmin–1 with 5 mmol l–1 1-butyl-3-methylimidazolium tetrafluoroborate and 10 mmol l–1 ammonium acetate at a pH of 3.0 with 13% by volume acetonitrile (15).
The use of 1-ethyl-3-methylimidazolium tetrafluoroborate as mobile phase additive has been evaluated for the analysis by HPLC with fluorescence detection for seven basic fluoroquinolone antibiotics, i.e., fleroxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, sarafloxacin and difloxacin, in different milk samples (16).
1-Ethyl-3-methylimidazolium tetrafluoroborate was found to be superior in comparison to 1-butyl-3-methylimidazolium tetrafluoroborate for the separation of the analytes from chromatographic interferences of the sample matrix.
The optimized method was used for the analysis of ovine, caprine and bovine milk, in the last case in either skimmed, semi-skimmed and full-cream milk, after suitable acidic deproteination followed by a solid phase extraction procedure.
Recovery values between 73% and 113% were obtained for the three types of bovine milk samples, as well as for ovine and caprine milk. The limits of detection were in the range of 0.5–8.1 μgl–1 (16).
Nucleic Compounds. The chromatographic behavior of nucleic compounds, i.e., nucleobases, nucleosides, and nucleotides was investigated using reversed phase HPLC on a C18 column (17). Several different mobile phase additives were used, including 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium methylsulfate ionic liquids, ammonium formate, and potassium phosphate.
The effect of the alkyl group length, the imidazolium ring, and the counterions of the ionic liquid on the retention and the resolution of the samples were tested. The nature of the modifiers can affect the separation of ionic analytes. The two ionic liquids tested have an improved effect on the retention and resolution of nucleic compounds.
The length of the alkyl on the imidazolium ring and its counterion can also affect the resolution, because part of the ionic liquids coated on the surface of the stationary phase could suppress the free silanols of the surface. The comparison of the ionic liquids with standard mobile phase additives, such as ammonium formate, showed that the ionic liquids have advantages as silanol suppressors in HPLC (17).
1.1.1.2 Fluorescent Whitening Agents
Fluorescent whitening agents based on 4,4′-diaminostilbene-2,2′-disulfonic acid, cf. Figure 1.10, with different numbers of sulfonic acid groups were separated by using an ionic liquid as a mobile phase additive in high performance liquid chromatography using a fluorescence detection method (18).
Figure 1.10 4,4′-Diaminostilbene-2,2′-disulfonic acid.
The effects of ionic liquid concentration, the pH of the mobile phase B, and the composition of mobile phase A on the separation of fluorescent whitening agents have been systematically investigated.
It was found that the ionic liquid tetrabutyl ammonium tetrafluoroborate is superior to tetrabutyl ammonium bromide for the separation of the fluorescent whitening agents. The optimal separation conditions were an ionic liquid concentration at 8 mM and the pH of mobile phase B at 8.5 with methanol as mobile phase A.
The established method exhibited only low limits of detection (0.04–0.07 ng ml–1) and wide linearity ranges (0.30–20 ng ml–1) with high linear correlation coefficients from 0.9994 to 0.9998. The optimized procedure was applied to analyze target analytes in paper samples with satisfactory results.
Eleven target analytes were quantified, and the recoveries of spiked paper samples were in the range of 85–105% with the relative standard deviations from 2.1 to 5.1%. The obtained results indicated that the method is efficient for the analysis of a series of fluorescent whitening agents (18).
1.1.2 Food Additives
1.1.2.1 Analysis of Natural Food Additives
Propyl propane thiosulfonate, cf. Figure 1.11, is an active ingredient from Allium spp., like onion and shallot (19). This compound has been proposed as a natural additive for feed as an efficient alternative to antibiotics and use as growth promoter due to its efficiency of improving animal health.
Figure 1.11 Propyl propane thiosulfonate.
A new simple analytical method for monitoring propyl propane thiosulfonate in animal feed has been developed. Reversed phase liquid chromatography with UV detection has been used and a previous sample treatment based on solid-liquid extraction has been optimized in order to extract propyl propane thiosulfonate from a feed for laying hens using acetone as extraction solvent.
The method has been characterized and limits of detection and quantification of 11.2 and 37.3 mg kg–1 respectively, were obtained, which are lower than the concentrations expected in samples containing this additive (19).
1.1.2.2 Analysis of Synthetic Food Additives
An efficient and accurate analytical method was developed for the simultaneous determination of 20 synthetic food additives using HPLC with a photodiode array detector (20). These additives include sweeteners, food colorants, synthetic preservatives and caffeine.
The method allows the detection of food additives at very low concentrations of 5–150 ng ml–1. The applicability was verified by the determination of food additives present in various foodstuffs (20).
1.1.2.3 Analysis of Carbohydrates
A method has been developed for the determination of large amounts of carbohydrates (glucose, lactose, maltose, mannose, sucrose, and fructose) and sweeteners (xylitol and sorbitol) by reversed phase liquid chromatography with refractive index detection without any need of derivatization (21).
The limits of determination for glucose, fructose, and sucrose in liquid samples were 0.1 g l–1, and for xylite, lactose, maltose, mannose, and sorbite, 1 g l–1. In solid samples the limits of determination for glucose, fructose, and sucrose were 0.1%, and for xylite, lactose, maltose, mannose, and sorbite, 0.6%.
The method is applicable to the analysis of samples of wine, juice, honey, cookies, dairy products, and biologically active additives (21).
Boric acid. HPLC was used for the analysis of ribose, arabinose and ribulose mixtures obtained from chemical and biochemical isomerization processes (22). These processes have gained importance since the molecules can be used for the synthesis of antiviral therapeutics.
The HPLC method uses boric acid as a mobile phase additive to enhance the separation on an Aminex HPX-87K column.
By complexing with boric acid, the carbohydrates become negatively charged, thus elute faster from the column by means of ion exclusion and are separated because the complexation capacity with boric acid differs from one carbohydrate to another. An excellent separation between ribose, ribulose and arabinose was achieved with concentrations between 0.1 and 10 g l–1 of discrete sugar (22).
1.1.3 Chaotropicity
1.1.3.1 Imidazolium Salts
The use of 1-butyl-3-methylimidazolium of varying anion chaotropicity as a mobile phase additive for separation and chromatographic behavior studies of acidic, basic, and amphoteric compounds in reversed phase liquid chromatography has been reported (23). Two hydrophobic columns were used: Zorbax XDB-C18 and Zorbax SB-Phenyl. Satisfactory separations could be achieved by the use of carefully optimized chromatographic systems modified with the additive.
Biogenic amines are derived from neutral or basic amino acids via decarboxylation (24). Some prominent examples of biogenic amines include: serotonin, catecholamine neurotransmitters: epinephrine, norepinephrine and dopamine.
Highly hydrophilic compounds belonging to biogenic amines were analyzed in a reversed phase system, modified with the addition of ionic liquids: 1-Ethyl-3-methylimidazolium hexafluorophosphate and the chaotropic salt NaPF6 on a Discovery HS C18 column under acidic conditions. The effect of the additives concentration and the presence of organic solvent on the analytes’ chromatographic parameters, such as retention factor, tailing factor and theoretical plate numbers, were determined (24).
The effect of chaotropic salt additives to the mobile phase on the chromatographic parameters was investigated (25). A buffered acetonitrile-water mobile phase was chosen because of the significant retention of added liophilic ions due to strong dispersive π-π interactions. The addition of a salt, such as hexafluorophosphate, perchlorate or trifluoroacetate, leads to an increase in retention, efficiency and separation selectivity. The influence of added salts on increase in retention parameters increases as follows: H2PO4–, CF3COO–, ClO4–, PF6–. This order is in agreement with ability of salts to the salting-in effect according to the Hofmeister series (25). The Hofmeister series is a classification of ions in order of their ability to salt out or salt in proteins (26, 27).
It was established that the presence of an organic solvent with a low dielectric constant and ionic liquid with both chaotropic ions allows achieving a typical Langmuir shape. The investigated mobile phase additives are comparable according to their efficiency and selectivity towards the analysis of biogenic amines. However, the sensitivity was found to be better for the eluent system that was modified with the chaotropic salt (24).
1.1.3.2 Phenothiazine Derivatives
Ionogenic basic compounds belonging to phenothiazine derivatives, cf. Figure 1.12, were analyzed in a reversed phase HPLC system and were modified by the addition of three ionic liquids: 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-butyl-3-methylimidazolium chloride.
Figure 1.12 Phenothiazine.
Phenothiazines contain positively charged amine groups in a mobile phase at low pH. Therefore, they are retained in the presence of ionic liquids through the combination of electrostatic interactions and hydrophobic effects. The effects of the concentration and the type of ionic liquid on the retention of the analytes, peak symmetry, and efficiency were examined. The following trends increase the retention factor of the analytes and improve system efficiency: 1-butyl-3-methylimidazolium hexafluorophosphate > 1-ethyl-3-methylimidazolium hexafluorophosphate > 1-butyl-3-methylimidazolium chloride.
With its asymmetric cation enlarged with hydrophobic substituents and a chaotropic anion, 1-butyl-3-methylimidazolium hexafluorophosphate appeared to be the most advantageous one. The isotherm of adsorption of this reagent presents a typical Langmuir adsorption behavior.
By the application of high performance liquid chromatography, lipophilicity parameters were established for the investigated compounds. Chromatographic systems modified with these ionic liquids have been compared to buffered organic-aqueous mobile phase and eluent containing a chaotropic salt additive (28).
It could be demonstrated that the ionic liquids are useful as mobile phase additives in reversed phase chromatography of phenothiazine derivatives. A very important feature of these additives is their ability to decrease the peak width. In the absence of such strong ion-ion interaction reagents, wide peaks for cationic analytes are usually observed (28).
1.1.4 Cigarette Additives
Ultrahigh performance liquid chromatography was used for the determination of imidazole, 4-methylimidazole, and 2-methylimidazole in cigarette additives (29). These compounds are shown in Figure 1.13. After a solid phase extraction and filtration, the analytes were separated using isocratic elution with 5 mmol l–1 acetonitrile-ammonium formate at a volume ratio of 80:20 0.5 ml min–1. The quantification of these analytes was achieved with an external standard method on a diode-array detector at 215 nm.
Figure 1.13 Imidazole compounds.
The linear dynamic ranges for imidazole, 4-methylimidazole, and 2-methylimidazole were between 0.0375 and 18.0300 mg kg–1. The limits of detection for the analytes were 0.0094 mg kg–1. The recoveries and the relative standard deviations at fortification levels of 0.1322–1.6220 mg kg–1 were 95.20–101.93% and 0.55–2.54%, respectively.
In summary, the method offers an easy operation, rapid analysis, and accurate results, and is suitable for the determination of imidazole, 4-methylimidazole, and 2-methylimidazole in cigarette additives (29).
1.1.4.1 Additives in Insulating Mineral Oils
Often, insulating mineral oils contain additives that improve their inherent characteristics, such as oxidation stability, electrostatic charging tendency, and compatibility with other materials.
Standard test methods are available for the detection of these individual additives (30–32), but none of these test methods are suitable for the simultaneous detection of additives for different purposes (33). The simultaneous determination of antioxidants and passivators that are most frequently added to mineral insulating oils has been reported (33).
The tested compounds included three inhibitors (N-phenyl-1-naphthylamine, 2,6-di-tert-butylphenol, and 2,6-di-tert-butyl-p-cresol) and two passivators (benzotriazole and another tolutriazole derivative, Irgamet 39). The chemical structure of these additives is shown in Figure 1.14.
Figure 1.14 Inhibitors and passivators (33).
A solid phase extraction step for the reduction of the matrix oil components was optimized. Because of the hydrophobic characteristics of the additives, a reversed phase chromatographic separation method was used and optimized. The so developed method was used for the analysis of inhibited and passivated transformer oils (33).
1.1.4.2 Microwave-Assisted Extraction of Additives
Traditionally, the extraction of additives in polyolefins is performed as (34):
Three 6
h
refluxing of chlorinated solvents under magnetic stirring.
Twelve 16
h
boiling with chlorinated solvents in a Soxhlet apparatus (35).
Dissolution of polymer with either substituted aromatic or hydrogenated naphthalene solvents followed by coagulation with alcohol (36).
Extraction in aliphatic solvents using an ultrasonic technique (37).
Supercritical fluid extraction (38).
Pressurized liquid extraction (39).
It has been shown that microwave-assisted extraction for the systematic analysis of organic additives in polyolefins can be done by two processes (34):
The one-step microwave-assisted extraction is useful for additives with low-medium dipolarity, like stabilizers, flame retardant, antistatics, slip and processing agents. The two-step microwave-assisted extraction is useful for additives with either high dipolarity, like organic salts, antigasfading, antiacid, nucleating agent, or high molecular mass, such as polymeric hindered amine light stabilizers.
A method for the determination and quantification of frequently used stabilizers in polyolefins has been reported (40).
The extraction of the stabilizers from the polymeric matrix was investigated for several different solvents and solvent mixtures in a monomode microwave reaction system. The solvents tested are summarized in Table 1.5.
Table 1.5 Solvents tested for extraction of stabilizers (40).
Solvent
Grade
Acetonitrile
HPLC gradient grade
Ethyl acetate
Pesticide residue analysis
Toluene
Analytical reagent grade
Methanol
HPLC gradient grade
Cyclohexane
i
-Propanol
Among the solvents listed in Table 1.5, ethyl acetate showed the best extraction performance with respect to easy and rapid sample preparation. For this solvent, a systematic and comprehensive survey of time- and temperature-dependence of extraction efficiency was carried out.
Extractions utilizing ethyl acetate for 30 min at 130°C showed the best overall performance for all investigated analytes. In addition, the influence of the physical form of the polyolefin sample was investigated. The extraction of pellets and powder was compared and, regardless of the physical form, the reproducibility for the whole method developed for all chosen analytes was below 2% (40).
1.1.5 Chiral Separation
1.1.5.1 Atrolactic Acids
A method for the enantioseparation of atrolactic acids has been presented. HPLC is used with sulfobutyl ether-β-cyclodextrin as a chiral mobile phase additive and a C18 reversed phase column (41).
Atrolactic acid is also addressed as 2-hydroxy-2-phenylpropionic acid or α-methylmandelic acid and shown in Figure 1.15. The configuration of atrolactic acid and methods of synthesis and reactions have been described (42).
Figure 1.15 Atrolactic acid.
The influences of the different types of cyclodextrin derivatives, the concentration of chiral mobile phase additive, pH value of the mobile phase, the flow rate and column temperature on the peak resolution were investigated.
The retention times of atrolactic acids were 26.65 min and 28.28 min and a peak resolution of 1.68 could be achieved (41).
1.1.5.2 Mandelic Acid
The enantioseparation of ten mandelic acid derivatives was done using reverse phase HPLC with hydroxypropyl-β-cyclodextrin or sulfobutyl ether-β-cyclodextrin as chiral mobile phase additives (43). The mandelic acid derivatives are shown in Figure 1.16.
Figure 1.16 Mandelic acid derivatives.
Cyclodextrins, also called cycloamyloses, are a family of compounds made up of sugar molecules bound together in a ring. So they are cyclic oligosaccharides (44). β-Cyclodextrin is a ring from seven members of amylose and also called cyclohepta amylose.
The inclusion complex formations between the cyclodextrins and the mandelic acid enantiomers were evaluated. The effects of various factors such as the composition of the mobile phase, concentration of cyclodextrins and the column temperature on the retention and the enantioselectivity were studied.
It was found that the peak resolutions and retention time of the enantiomers were strongly affected by pH, the organic modifier and the type of the β-cyclodextrin in the mobile phase. On the other hand, the concentration of the buffer solution and the temperature had a comparatively low effect on the resolution.
The enantioseparations could be successfully achieved on a Shimpack CLC-ODS column. The mobile phase was a mixture of acetonitrile and 0.10 moll–1 of phosphate buffer at pH 2.68 containing 20 mmoll–1 of hydroxypropyl-β-cyclodextrin or sulfobutyl ether-β-cyclodextrin (43).
