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The Theory of HPLC

Introduction to Ion Chromatography

Aims and Objectives

Aims and Objectives

Aims

To introduce some of the working principles of ion chromatography and related techniques

To highlight the various approaches to analyzing ions in solution

To explain the equipment / eluent modifiers necessary for ion chromatography Objectives At the end of this Section you should be able to:

Recognise ion chromatography as a set of chromatographic techniques, suitable for analyzing ionic species

Describe the correct approach for analysing ions in solution using a variety of eluent additives and instrumentation

Recognise application types where ion chromatography approaches may be required

© Crawford Scientific www.chromacademy.com

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Content Introduction 3 The HPLC Process 4 Types of Ion Chromatography 5 Acid-Base Chemistry 6 Ion Exchange Chromatography – Overview 7 General Ion Exchange Considerations 8 Ion Exchange – Mechanisms 12 Ion Exchange Elution Considerations 13 Ion Exclusion Chromatography – Overview 15 Ion Exclusion Chromatography – Process 16 Ion Pair Chromatography 17 Ion Suppression 18 The Ion Chromatographic System 19 Ion Chromatography Columns 21 Detection 24 Hyphenated Ion Chromatography 26 Applications 27 References 34


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Introduction The Russian botanist Mikhail Tswett first used the term ‘chromatography’ (Greek for ‘coloured writing’) in 1906. He used the term to describe the separation that occurred when solutions of plant pigments were passed through columns of calcium carbonate or alumina using petroleum ether.[1] Ion chromatography, a form of liquid chromatography, describes the efficient chromatographic separation of ionic species using any number of automatic detection techniques.[2,3,4] Ion chromatography is the technology of choice for the analysis of ionic (or ionisable) species in solution from a variety of different application types including food analysis, pharmaceutical development, corrosion studies, oil exploration, nuclear power plant water quality control and many more. The primary objective of this module is to describe in a clear and concise manner the principles, methods and different chemical and instrument based approaches to ion chromatography currently used in the modern analytical lab.

A typical Liquid Chromatograph

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Where: 1: The mobile phase composition (usually water and an organic solvent plus other additives) needs to be optimised in order to gain good separation. 2: Degassers are often used to remove air from the mobile phase –leading to better chromatographic baselines. 3: The detector conditions are chosen to give the best response to the analytes of interest and achieving good sensitivity. 4: The column dimensions and stationary phase chemistry are chosen and optimised to give separations of the quality required. 5: The autosampler introduces a plug of sample into the mobile phase flow which is then swept onto the column. 6: Dual reciprocating pumps are used to deliver the mobile phase at back pressures of up to 400Bar. As steady stream of liquid delivered at constant flow rate is important. The HPLC Process The HPLC process requires a continuous flow of mobile phase, a column that shows affinity for the sample and a detection system capable of detecting the separated sample components. The HPLC pumping system must provide a constant flow of mobile phase and should be capable of dynamic mixing of the eluent system components where required. Because the mobile phase flow should not be interrupted during analysis or air introduced, especially designed HPLC injectors are commonly used to introduce a plug of sample into the HPLC system.

Liquid chromatographic process

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Once the sample is introduced, the mixture of components is carried in a narrow band to the top of the column (where the chromatographic separation will begin). Some compounds in the sample mixture will have a greater preference for the stationary phase than for the mobile phase and will be retained in the column longer. The longer the selected column, the more opportunities for interaction with the stationary phase and the greater the separation within certain limiting factors. Once the separation is performed, a detection system is then used to respond to a physico-chemical property of the analyte. This response is digitally amplified and sent to a data system where it is recorded as the ‘chromatogram’.[1] Types of Ion Chromatography Ion chromatography is a generic term that applies to any method for chromatographic separation of ionic or ionisable species in solution. The term ion chromatography (IC) encompasses a range of different techniques; however, the most important forms of IC are based on each of the following four separation mechanisms:[5]

Ion-exchange chromatography

Ion-exclusion chromatography

Ion-pair chromatography

Ion-suppression chromatography

Although some of the above mechanisms (like ion-suppression) do not involve traditional ‘ion exchange’ separation mechanisms, they are still considered forms of ion chromatography and are critical concepts within many ion chromatographic separations.

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Acid-Base Chemistry The Brönsted-Lowry theory states that acids are substances that donate protons; in a similar way bases are substances that accept protons.[26] Polyprotic acids can lose more than one proton (acquiring more than one negative charge); similarly polyprotic bases can gain more than one proton (acquiring more than one positive charge). Strong acids are substances that ionise completely in an aqueous solution (by losing one proton), therefore they will always be ionised, at least in some part, over the entire pH range. Ion exchange functional groups based on strong acidic functional groups (like sulfonic functional groups) are known as strong cation exchangers and are denoted by SCX. In a similar way, Ion exchange functional groups based on weak acidic (like carboxylic acids), acidic compounds that do not fully ionise in an aqueous solutions and as such can be fully ion suppressed below certain pH values are known as weak cation exchangers and are denoted by WCX. Strong bases are chemical compounds able to deprotonate very weak acids and will remain ionised, to some extent, over the entire pH range. Ion exchange functional groups based on quaternary amines are known as strong anion exchangers and are denoted by SAX. Weak anion exchangers and are denoted by WAX and usually present primary, secondary or tertiary amino functional groups and are capable of being fully ion-suppressed at a sufficiently high pH.

A Brönsted-Lowry acid DONATES A PROTON

A Brönsted-Lowry base ACCEPTS A PROTON


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Ion Exchange Chromatography – Overview Nowadays the vast majority of ion chromatographic separations are dominated by ion exchange mechanisms using stationary phases with charged functional groups.[6] These types of mechanisms dominate the separation of analytes that permanently hold electrostatic charges (i.e. strongly acidic/basic species or inorganic ions). Ion-exchange chromatography (IEC) is based on the different affinities of the analyte ions for the oppositely charged ionic functional groups in the stationary phase or adsorbed counterions.[7,8] Depending on the charge of the exchange centres on the surface, the resin could be either an anion-exchanger (positive ionic functional groups on the surface) or cation-exchanger (negative functional groups on the surface). In ion-exchange chromatography, retention is based on the affinity of different analyte and counter ions for the charged site on the stationary phase surface and on a number of other solution parameters like pH, ionic strength, counterion type, etc. Ion-exchange chromatography is used for the separation of both organic and inorganic ions.

Anion exchange

Cation exchange

Because the hydrophobic moiety of the charged species don’t strongly contribute to analyte retention, selectivity in ion-exchange chromatography is limited.

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General Ion Exchange Considerations In ion exchange chromatography, separation is mainly dependent upon the different degrees of interaction with the exchanger. As expected, these interactions can be controlled by altering the charge state of either analytes or ionic functional groups from the stationary phase.[27,28] The pKa of any ionic functional group determine the conditions of pH at which it will hold charge:

For a cation to be charged, the pH must be kept around two units above its pKa

For an anion to be charged, the pH must be kept around two units below its pKa

The above considerations for ionic functional groups are valid not only in the case of the analytes but in the case of stationary phases. As expected, the charge state of functional groups within a molecule will determine the correct chromatographic conditions for its separation to take place. As a consequence, analyte retention in ion chromatography can be controlled through correct modification of pH.

Degree of dissociation of an acidic compound as a function of pH

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Degree of dissociation of a basic compound as a function of pH

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Effect of pH in analyte retention

Effect of pH in analyte retention


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Ion Exchange – Mechanisms

Consider the exchange of two ions A and

B between the solution and exchange resin R :

ARBBRA

The equilibrium constant for this process is:

]][[

]][[

RAB

RBAK

K essentially determines the relative affinity of both cations to the exchange centres on the surface. If the constant is equal to one, then no discriminating ability is expected for

the system. Similarly, the exchange of two ions C and

D between the solution and

exchange resin E :

CEDDEC

Depending on the charge of the exchange centres on the surface, the resin could be either an anion-exchanger (positive ionic functional groups on the surface) or cation-exchanger (negative functional groups on the surface).

Oversimplified separation mechanism of cationic analytes (K+ in this example) on a cation-

exchange resin column

HKSOKHSO 33 sinResinRe

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Ion Exchange Elution Considerations The ionic strength of the mobile phase plays a major role in the retentive conditions of any ion exchange separation. Eluent systems presenting high ionic strength facilitate analyte desorption and are used to elute species from the column.

Low ionic strength buffer – no analyte elution

Analyte elution facilitated by high ionic strength buffer

As previously explained, analyte retention in ion chromatography can be controlled through correct pH modification. This is a common practice in ion exchange chromatography where the charge state of both analyte molecules and stationary phase dominate the chromatographic process.

a b i

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Analyte elution through analyte neutralisation

Analyte elution through surface neutralisation

In ion exchange chromatography, analyte retention can also be controlled by altering the concentration of counterions present in the eluting system. As expected, the nature (strength) of the counterion will also affect analyte retention.

Analyte elution using strong counter ion

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Ion Exclusion Chromatography – Overview Ion-exclusion chromatography (IEC), a very useful chromatographic technique, has been used for the separation of relatively small weak acids (like carbonic and carboxylic acids), weak bases (like ammonia) and hydrophilic molecular species (such as carbohydrates). This technique uses strong anion or cation exchange resins for the separation of ionic solutes.

Ion exclusion chromatography is based mainly on exclusion effects such as differences in molecular size, shape and charge. The term size-exclusion chromatography may be used when separation is based solely on molecular size. The term ion-exclusion chromatography is specifically used for the separation of ions in an aqueous phase.[9,10] Ion exclusion chromatography is an analytical technique that actually involves the separation of molecular species rather than ions.[10] In the representation opposite, only molecules of certain size can actually interact with the resin to be absorbed. The resin, as is going to be explained on the next page, contains an occluded liquid which acts as the medium in which molecules absorb.

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Ion Exclusion Chromatography – Process In the ion exclusion process shown opposite, a mixture consisting of CH3COOH (weak acid) and HCl (strong acid) is subjected to exchange process on a cation exchange resin using water as an eluent system.

COOCHCOOHCH 33

Fully dissociated species are excluded from the stationary phase, anions are repelled from the negatively charged surface (chlorine and acetate anions cannot approach the surface of the resin) and they do not undergo any chromatographic separation. The retention volume for these species is the so-called exclusion volume Ve. By using a dilute solution of a strong acid as the mobile phase, a perimeter of water molecules (occluded liquid phase) will be established a short distance from the surface of the stationary phase. This perimeter is known as the Donnan membrane.

Molecules in their neutral state can approach and pass through the Donnan membrane to finally move into the occluded liquid phase. The size of each molecule will determine whether or not it absorbs into the occluded liquid phase.[11] Bear in mind that the ion exclusion process on an anion exchange resin would be similar to the one already presented.

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Ion Pair Chromatography The use of salt modifiers and ionic liquids to enhance strongly acidic or basic analyte retention has been firmly established for many years in reversed phase HPLC. This approach has fallen out of favour in recent years due to the limiting factorings of running gradients, suppressing MS signals and irreversibly modifying and reducing column lifetimes and has been superseded by reversed phases capable of retaining ionisable analytes. Because ion-pairing reagents can be used to suppress charge, the ionic equilibrium of certain analytes can be altered to increase analyte retention under reversed phase conditions:

BABA

Where A is the cationic analyte of interest B is the anionic ion pairing reagent

BA is the neutral ion pair formed If the analyte ion of interest is anionic, then a similar analysis can be performed (note how the required ion paring reagent would be of cationic nature). Ion pair chromatography is performed on standard reversed phase columns. The mobile phase consists of modifier(s) and a buffer solution, to which an ion pair reagent is added at low concentration.[12]

Ion pairs are neutral species formed by electrostatic attraction between oppositely charged ions in solution. The ion pair formation is dependent on the ions size, solvent, and temperature. Ion Pair Chromatography (IPC) is used for ionic compounds which are difficult to separate on a covalently bonded ion-exchange resins and for samples with widely different components, e.g mixtures of acidic and basic analytes or zwitterions.


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Ion Suppression The technique of using pH to suppress ionisation and therefore gaining retention for ionisable analytes in reverse phase HPLC is termed “Ion suppression” and is applicable to weakly acidic or basic compounds only. The pH of a solution will influence the charge state of an acidic or basic analyte. For example, addition of an acid to an aqueous solution of a basic analyte will increase the concentration of charged analyte in solution. Conversely, raising the pH by addition of a base will increase the concentration of the neutral form of the basic analyte. This principle was first described by Le Chatelier and the converse applies to acidic analyte species. It is important to realise that the two forms of ionisable analyte molecules give different retention characteristics. The ionised form is much more polar, and its retention in reverse phase HPLC is much lower (shorter retention time (tR), smaller retention factor (k’)). This behaviour is expected, as the more polar (charged) analyte form has a higher affinity for the more polar mobile phase and moves more quickly through the column. The converse is true of the non-ionised form as it is much more hydrophobic, relative to the ionised form.[13]

If a separation of mixtures of weak acids and bases (or amphoteric analytes) is required, then ion suppression by pH control is of limited use. The ionisation of acidic functional groups can be suppressed at the same conditions of pH at which basic functional groups are ionised. This situation will result in a non-robust methodology. In practice, a combination of ion-suppression and ion-pair chromatography is used. In the case of strong acids and bases, where effective ion suppression is achieved at extreme conditions of pH, ion suppression is not recommended as the optimum pH may lie outside the working range of traditional HPLC columns.

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The Ion Chromatographic System In general terms there are only a few additions to a traditional HPLC system in order to achieve ion chromatographic separations; primarily because the critical elements required for a good chromatographic separation remain the same (good mass transfer, low dead volume, suitable mobile and stationary phases).[14] As in traditional HPLC, ion chromatography pumping systems use reciprocating pumps which cope with the pressure and volumetric needs of most ion chromatography applications. Columns packed with suitable materials have been developed to provide good separation performance in minimum time. The working life of the column can be increased by using a filtering system (guard column and/or in-line filter) between the autosampler and the column. In terms of detection, ion chromatography implements similar types of detectors traditionally used in HPLC separations. The electrical conductivity detector is one of the most important detection types for ion chromatography. It actually measures the conductivity of the mobile phase and therefore it is not a solute property detector but a bulk property detector. The principles and working principles of detectors for ion chromatography will be given in another chapter.

The IC system.

Pre column

Heat exchanger

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Where: Solvent: Choose a mobile phase composition and gradient ramp rate that elutes the analyte with the narrowest peak possible. Solvent Degasser: Removing dissolved air and other gases from incoming solvent streams is critical to insure proper functioning of the pump check valves and to avoid outgassing of dissolved gases in detector flow cells. Pump: Pump performance is critical to ensuring good chromatography and a poorly performing pump will cause baseline disturbance, retention time drift and poor reproducibility (both qualitative and quantitative). Select Binary pumps when rapid and accurate gradients are required and quaternary pumps where more than two mobile phase components need to be mixed simultaneously. HPLC pumps are designed to eliminate pulsation (multiple action pumps, in-damper built, etc) providing uniform flow over a wide range of pressures. Injector: The function of the injector is to place the sample into the high-pressure flow in as narrow a band as possible (to maintain high efficiency) so that the sample enters the column as a homogeneus, low-volume plug. To minimize spreading of the injected volume during transport to the column, the shortest possible length of tubing should be used from the injector to the column, with the minimum number of zero dead volume connections. Filter: A major cause of column deterioration and damage is the build up of particulate and chemical contamination at the head of the column. This can lead to increased back pressure and anomalous chromatographic results. HPLC Columns normally contain stainless steel inlet and outlet frits (acting as filters) and retain the column packing. The pore size of the frit must be smaller than the particle diameter of the packing, e.g., a 0.5 μm frit for 1.8 μm packing. HPLC filters are designed for maximum filtration of particulate matter with minimal dead volume or back pressure. Pre-Column Heat Exchanger: Temperature impacts on peak efficiency, if the temperature difference between the column and the incoming mobile phase is too large, band broadening results. For the best column temperature control and most uniform results, it is often necessary to pre-heat or pre-cool the mobile phase before it enters the chromatographic column Guard Column: A guard column is inserted between the injector and analytical column to protect the latter from damage or loss of efficiency due to the presence of particulate matter or strongly adsorbed impurities from analytical samples. For maximum protection against contaminants and particulate matter, the guard column can be placed between a set of frits (that act as filters). Colum: HPLC columns are designed considering a variety of factors such as separation performance, durability and column pressure. These columns achieve good balance between separation efficiency and pressure. Thermostatted Compartment: The ability to accurately and reproducibly control the column temperature is critical to promoting the sample diffusion rates required to achieve ionic separations. This device eliminates thermal gradients across the column, resulting in better column performance and precise retention times.


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Post-Column Heat Exchanger: The column’s effluent is delivered at high temperatures. When the detection system is affected by the column’s effluent temperature (for example when measuring the refractive index) then a post-column heat exchanger is required to cool down the eluent. Electrolytic Suppressor: The coupling of IC to certain detection types (like MS) can be done by implementing post-column ion suppressors; they act to selectively reduce the ionic strength of the column’s effluent. Detector: As with any chromatographic technique, the detector measures some physico-chemical property of the mobile phase/analyte as it elutes from the column. The response of the detector will change due to changes in the column’s effluent. Ion Chromatography Columns The column is the only device in ion chromatography which actually separates an injected mixture. The stationary phase is responsible for the separation and its properties are of primary importance for successful separations. The lifetime of the ion chromatography column is maximized through the use of stable bonding chemistry, high purity silica and optimal proprietary packing procedures. When selecting a column for a particular separation, the chromatographer should be able to decide whether a packed, capillary, or monolithic column is needed and what the desired characteristics of the packing material should be. As expected, different packing materials have been developed to speed up the ion chromatography separation process.[7, 10, 11]

Mobile phase versus stationary phase polarity for selected types of chromatography.

Where: IC: Ion Chromatography IPC: Ion Pair Chromatography NPC: Normal Phase Chromatography RPC: Reversed Phase Chromatography


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Anion Exchangers:

Diethylaminoethyl (weak anion exchanger)

Quaternary aminoethyl (strong anion exchanger)

Quaternary ammonium (strong anion exchanger)

Cation Exchangers:

Carboxymethyl (weak cation exchanger)

Methyl sulphonate (strong cation exchanger)


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Detection The ion chromatography detection system is used to monitor the passage of the components as they emerge from the column.[5] As with any chromatographic technique, the detector measures some physico-chemical property of the mobile phase/analyte as it elutes from the column. The response of the detector will change due to changes in the column’s effluent. The most common detection types currently used for IC separations are as follows (click to get more information):

Electrochemical Detection

Conductivity

Amperometry

Coulometry

Voltammetry

Optical Detection

UV-Vis

Fluorescence

Refractive Index

Others

Mass Spectroscopy


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Because electrolytic suppressors are designed to reduce ionic strength, the column’s effluent can be detected by any traditional HPLC detection system.

The conductivity detector.

In the upper part of the diagram, no ions are passing through the detector and despite the applied voltage, no current is measured. Ions in solution help to transport current (bottom) Conductivity is measured by a detection system consisting of two electrodes to which an alternating potential is applied. The corresponding current is proportional to the conductivity of the ionic solution in which the cell is dipped. Selected detection types in ion chromatography

Detector Selectivity Sensitivity

Refractive Index Low 1 – 5 μg

Conductivity Low 10 – 50 ng

UV/Visible Medium 0.5 – 1.0 ng

Electrochemical High 50 – 500 pg

Fluorescence High 10 – 100 pg

Mass Spectrometer High 10 – 100 pg

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Hyphenated Ion Chromatography Ion chromatography has been hyphenated to a range of techniques including mass spectrometry and atomic absorption. The coupling of IC to these techniques can be accomplished with the implementation of post-column ion suppressors. Ion suppressors are designed to lower the ionic strength of the column’s effluent, allowing the use of the full range of traditional HPLC detectors. The ion suppressor device shown below,[14] uses platinum electrodes for the hydrolysis of water to produce H+/OH- ions and semi-permeable ion exchange membranes to selectively reduce the ionic strength of the eluent system. Organic solvent may be added as a makeup flow to aid the desolvation process in the electrospray interface but this is often not required.

Post-column anion suppressors work in a similar manner to cation suppressors but with opposite charges.

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Applications The determination of ionic species is a classical analytical problem that can be found in many different application areas. Aqueous or water-miscible samples can be directly analyzed by IC. Water-immiscible liquids, solids and gases must be extracted into or dissolved in aqueous solution before analysis. To list the full range of IC application areas is prohibitive since its flexibility makes it suitable to a multitude of application types. Examples of some interesting applications are shown below: Agrochemistry Mono-chlorophenols (MCPs) and di-chlorophenols (DCPs) are used as disinfectant agents and as the base for different pesticides; however, due to new environmental regulations their use has been restricted.

IC-MS trace of a river water sample preconcentrated by SPE for gradient elution.

Sample: 1= 2-CP; 2= 4-CP; 3= 3-CP; 4= 2,6-DCP; 5= 2,3-DCP; 6= 2,5-DCP; 7= 2,4-DCP; 8= 3,4-DCP; 9= 3,5-DCP Column: anion exchange column 250mm×4.0mm. Eluent system: 0–4.5 min, 20 mM KOH; 4.5–10.0 min, 20–40 mM KOH (linear gradient); 10.0–12.0 min, 40 mM KOH. Eluent flow rate: 1.0 mL/min


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Biotechnology An enormous effort in providing new methods of detection and analysis of gene sequences has been made and Ion Chromatography has played a central role.

High-performance ion-exchange chromatographic analysis of a mixture of peptide nucleic

acids (UV detection at 260nm) Sample: PNA1= H-AGAGTCAGCTT-NH2; DNA3= 5’-AAGCTGACTCT-3’; DNA5= 5’-AGAGTCAGCTT-3’. Column: polystyrene–divinylbenzene column 50mm×7.5mm. Eluent system: linear gradient from 100% A (0.05 M tris–HCl in water, pH 8) to 100% B (0.05 M tris–HCl, 0.5 M NaCl in water, pH 8) in 60 min. Where tris = tris(hydroxymethyl) aminomethane Eluent flow rate: 1.0 mL/min Cements In the production of cements, the levels of chlorides and sulphates determine the quality of the final product.

IC determination of chlorine and sulphur species in a commercial Portland cement sample

Column: anion exchange column 250mm×4.0mm. Eluent system: deionised water

Eluent flow rate: 1.0 mL/min


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Clinical Chemistry The determination of metal ions in physiological fluids is of considerable diagnostic interest in clinical chemistry.

Separation of heavy metal ions with spectrophotometric detection (530nm) after post

column derivatization. (1) standard solution, (2) serum sample. Column: ethylvinylbenzene functionalized with ammonium and sulfonate functional groups 250mm×4.6mm, 9μm. Eluent system: 1.4 mM pyridine-2,6-dicarboxylicacid + 13.2 mM potassium hydroxide + 1.1 mM potassium hydroxide + 14.8 mM formic acid (pH = 4.2 ± 0.1) Detection: postcolumn reagent 0.5mM (4-(2-pyridylazo) resorcinol) + 1.0 M 2-dimethylaminoethanol + 0.5 M ammonium hydroxide + 0.3 M sodium bicarbonate (pH = 10.4 ± 0.2) Eluent flow rate: 0.3mL/min Environmental Chemistry Fresh water shortages and new findings on multiple toxicity of several arsenic species have intensified the As remediation problem in recent years.

IC-MS separation of As-species at pH = 8.2.


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Analytes: monomethylarsonate (MMA), dimethylarsonate (DM), arsenobetaine (AsB). Column: low hydrophobic anion exchange column 250mm×2.0mm, 13μm. Eluent system: solution a (0.5 mM ammonia/HNO3 pH = 8.2) and solution b (100 ammonia/HNO3 pH = 8.2). Gradient: 100% A for 2.0 mins, gradient step to 30% A in 5.0 min abd then 2.0 mins at this concentration. Eluent flow rate: 0.44 mL/min Food Analysis Sulfites have been widely used as preservatives and blanching agents for many years in a large variety of foodstuffs and beverages. Before 1986 sulfites were incorrectly considered harmless but asthmatic reactions and food intolerance symptoms are related with high consumtion of these species.

IC analysis of not-compliant cow fresh meat sample, with an observed SO2 content of

121.7mg/kg. Column: high-capacity carbonate eluent anion-exchange column 250mm×4.0mm, 9μm. Eluent system: solution a (8.0 mM Na2CO3 + 2.3 mM NaOH) and solution b (24 mM NaOH). Gradient: 100% A for 15 mins, gradient step to 50% A in 1.0 min abd then 4.0 mins at this concentration. Eluent flow rate: 1.0 mL/min


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Industrial Waste Analysis Antimony has been extensively used in various industrial applications ,however, it is a toxic cumulative element with similar chemical and toxicological properties to arsenic.

Isocratic IC separation of Sb-species present in waste water

Column: polystyrene–divinylbenzene-based anion-exchange column 250mm×4.1mm, 10μm. Eluent system: 12mM tetramethylammonium hydroxide (TMAOH) at pH = 12. Petroleum Exploration The chemical analysis of oilfield waters has an important role in the exploration and production of oil.

Isocratic IC analysis of oilfield water

Column: anion exchange column 250mm×4.0mm. Eluent system: 20.0 mM methane sulfonic acid solution Eluent flow rate: 1.0 mL/min


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Pharmaceuticals Alkylsulfonic acids are typically used as catalysts, solvents and blocking agents in the synthesis of many organic compounds and pharmaceutical drugs.

IC separation of alkylsulfonic acids

Sample: 1= methanesulfonic acid; 2= ethanesulfonic acid; 3= propanesulfonic acid; 4= butanesulfonic acid; 5= pentanesulfonic acid; 6= hexanesulfonic acid; 7= heptanesulfonic acid. Column: mixed anion-exchange and polymeric reversed-phase retention column 250mm×4.0mm. Eluent system: A (0.5 mM sodium carbonate + 1.0% acetonitrile), B (10 mM sodium carbonate + 40.0% acetonitrile) linear gradient from 100% A for 15 mins, then increase B to 100% in 20 mins. Eluent flow rate: 1.0 mL/min Polymers Epichlorohydrin is an organic liquid with a garlic-like odour. It is mainly used in the production of glycerine, certain plastics and polymers. Exposure to epichlorohydrin for relatively short periods of time can damage skin, liver, kidneys and the central nervous system.

Reaction between sulfur(IV) and epichlorohydrin.


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IC analysis of derivatized epichlorohydrin with sulphur (IV)

Power Generation Power plants use different additives to decrease the corrosive effects of water.

IC separation of some inorganic cations and commonly used corrosion inhibitor additives

to power industry waters. Sample: 1= Lithium; 2= sodium; 3= 2-diethylaminoethanol; 4= morpholine; 5= ethanolamine; 6= ammonium; 7= 5-amino-1-pentanol; 8= magnesium; 9= calcium; 10= 3-dimethylaminopropylamine; 11= potassium; 12= cyclohexylamine. Column: anion exchange column 250mm×4.0mm. Eluent system: 9 mM methanesulfonic acid + 10.7% MEK, gradient from 6 to 9 min to 27 mM methanesulfonic acid + 10% MEK Eluent flow rate: 1.0 mL/min

Column: anion exchange column 250mm×4.0mm. Eluent system: 5 mM NaOH Eluent flow rate: 1.0 mL/min


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21. R. Miravet, J.F. López-Sánchez, R. Rubio. “New considerations about the separation and quantification of antimony species by ion chromatography–hydride generation atomic fluorescence spectrometry” Journal of Chromatography A, 1052 (2004) 121–129 22. Mona El-Said, Mahmoud Ramzi, Thanaa Abdel-Moghny. “Analysis of oilfield waters by ion chromatography to determine the composition of scale deposition” Desalination 249 (2009) 748–756 23. P.L. Annable. “Determination of alkyl sulfonic acids in pharmaceuticals by ion chromatography” Journal of Chromatography A, 724 (1996) 199-206 24. Corrado Sarzanini, Maria Concetta Bruzzoniti, Edoardo Mentasti. “Determination of epichlorohydrin by ion chromatography” Journal of Chromatography A, 884 (2000) 251–259 25. Christopher Pohl, Maria Rey, Detlef Jensen, Jutta Kerth. “Determination of sodium and ammonium ions in disproportionate concentration ratios by ion chromatography” Journal of Chromatography A, 850 (1999) 239–245 26. G.H. Jeffery, J. Bassett, J. Mendham and R.C. Denney. “Vogel's Textbook of Quantitative Chemical Analysis” Fifth edition Longman Group UK Limited 1989. Pp 19-23, 31-34 27. Ion-Pair Chromatography Module from “The theory of HPLC”. 28. Controlling the Extent of Ionisation. Reverse Phase (partition) Chromatography from “The theory of HPLC”.

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