Stereoselective separation and detection of phenoxy acid herbicide enantiomers by cyclodextrin-modified capillary zone electrophoresis–electrospray ionization mass spectrometry

Machine learning-based models for the qualitative classification of potassium ferrocyanide using electrochemical methods

Iron is one of the trace elements that plays a vital role in the human immune system, especially against variants of SARS-CoV-2 virus. Electrochemical methods are convenient for the detection due to the simplicity of instrumentation available for different analyses. The square wave voltammetry (SQWV) and differential pulse voltammetry (DPV) are useful electrochemical voltammetric techniques for diverse types of compounds such as heavy metals. The basic reason is the increased sensitivity by lowering the capacitive current. In this study, machine learning models were improved to classify concentrations of an analyte depending on the voltammograms obtained alone. SQWV and DPV were used to quantify the concentrations of ferrous ions (Fe+ 2 ) in potassium ferrocyanide (K4 Fe(CN)6 ), validated by machine learning models for the data classifications. The greatest classifier algorithms models Backpropagation Neural Networks, Gaussian Naive Bayes, Logistic Regression, K-Nearest Neighbors Algorithm, K-Means clustering, and Random Forest were used as data classifiers, based on the data sets obtained from the measured chemical. Once competed to other algorithms models used previously for the data classification, ours get greater accuracy, maximum accuracy of 100% was obtained for each analyte in 25 s for the datasets.

Nanomaterial-based immunosensors for ultrasensitive detection of pesticides/herbicides: Current status and perspectives

The increasing level of pesticides and herbicides in food and water sources is a growing threat to human health and the environment. The development of portable, sensitive, specific, simple, and cost-effective sensors is hence in high demand to avoid exposure or consumption of these chemicals through efficient monitoring of their levels in food as well as water samples. The use of nanomaterials (NMs) for the construction of an immunosensing system was demonstrated to be an efficient and effective option to realize selective sensing against pesticides/herbicides. The potential of such applications has hence been demonstrated for a variety of NMs including graphene, carbon nanotubes (CNTs), metal nanoparticles, and nano-polymers either in pristine or composite forms based on diverse sensing principles (e.g., electrochemical, optical, and quartz crystal microbalance (QCM)). This article evaluates the development, applicability, and performances of NM-based immunosensors for the measurement of pesticides and herbicides in water, food, and soil samples. The performance of all the surveyed sensors has been evaluated on the basis of key parameters, e.g., detection limit (DL), sensing range, and response time.

Chiral capillary electrophoresis-mass spectrometry

Capillary electrophoresis-mass spectrometry (CE-MS) is a powerful analytical tool, especially in the case of chiral separations, due to the fact that it combines the high efficiency, short analysis time, and versatility of the CE with the sensitivity, selectivity, and the capacity for the identification of unknown chiral compounds offered by MS detection. This chapter describes three methodologies enabling the chiral separation of cationic and anionic compounds using different strategies, illustrating the most employed approaches used in chiral CE-MS. The first methodology uses the partial filling technique for the enantioseparation of a cationic compound using a neutral cyclodextrin. Secondly, the enantioseparation of a cationic compound using low concentrations of a neutral cyclodextrin under acidic conditions is described. Finally, a methodology for the chiral separation of an anionic compound employing low concentrations of a native cyclodextrin under basic conditions is illustrated.

Chiral CE-MS

This review article addresses the developments and applications of capillary electromigration methods coupled on-line with MS for chiral analysis. The multiple enantiomeric applications of this hyphenated technology are covered including chiral analysis of drugs, food compounds, pesticides, natural metabolites, etc. in different matrices such as plasma, urine, medicines, foods, etc. This work intends to provide an updated overview (including works published till September 2009) on the principal chiral applications carried out by CZE-MS, CEC-MS and MEKC-MS, discussing their main advantages and drawbacks in all their different areas of application as well as their foreseeable development in the not too distant future.

The role of cyclodextrins in chiral capillary electrophoresis

The members of the enantiomeric pairs frequently show rather different biological effects, so their chiral selective synthesis, pharmacological studies and analysis are necessary. CE has unique advantages in chiral analysis. The most frequently used chiral selectors are CDs in this field. This paper gives a short view on the advantages on CE in direct chiral separations, emphasizing the role of CDs. The reason for the broad selectivity spectra of CDs is discussed in detail. The physical background of chiral selective separations is briefly shown in CE. Their interaction mechanisms are shortly defined. The general trend of their use is statistically evaluated. Most frequently used CDs and CD derivatives are characterized. Advantages of ionizable CDs and single-isomer derivatives are shown. The general trend of their use is established.

Nonaqueous electrokinetic chromatography–electrospray ionization mass spectrometry using anionic cyclodextrins

The set-up of an on-line method for coupling nonaqueous electrokinetic chromatography (NAEKC) and electrospray ionization mass spectrometry (ESI-MS) is presented. It allows the use of the single-isomer derivative anionic cyclodextrins heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) and heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin (HDAS-beta-CD) for chiral and achiral separations of positively charged analytes. The effect of the cyclodextrins (CDs) on the MS signal intensities of model compounds was studied. When a voltage is applied over the CE capillary, the overall mobility of the CDs is towards the inlet vial preventing CDs from entering the ion source. However, the sodium counter ions of the CDs still enter the ion source and appeared to cause ionization suppression. Nevertheless, significant analyte signals could still be detected with detection limits in the sub-microg/ml. System parameters such as sheath liquid composition and flow rate, nebulizing gas pressure, capillary position in the sprayer and the drying gas flow and temperature were studied and optimized. The selection of a relatively low nebulizing gas pressure appeared to be important to achieve optimum sensitivity. The chiral selectivity of the NAEKC-ESI-MS system could be improved by addition of camphorsulfonate to the background electrolyte. Using mixtures of drugs and drug-related compounds, the NAEKC-ESI-MS system is shown to offer potential for (chiral) drug profiling.

Chiral separation of three agrochemical toxins enantiomers by high-performance liquid chromatography on a vancomycin crystalline degradation products-chiral stationary phase

This work aims to evaluate for the enantiomeric separations of three agrochemical toxins: haloxyfop-methyl, fenoxaprop-p-ethyl and indoxacarb on crystalline degradation products-chiral stationary phase (CDP-CSP) of high-performance liquid chromatography (HPLC) under normal and polar organic phases. In the normal phase, the mobile phase was n-hexane with alcohols including methanol and isopropanol as polar modifiers. In the polar organic phase mode, the mobile phase was methanol with different percentages of triethylammunium acetate. The influence of flow rate (0.3-0.9 mL/min), analyte concentration and silica gel particle sizes (10, 15 and 30 microm) was investigated. This new chiral stationary phase showed excellent stereoselectivity for the two enantiomers of haloxyfop-methyl and fenoxaprop-p-ethyl and chiral recognition for indoxacarb under normal-phase mode. However, under polar organic phase, only indoxacarb was separated (alpha < 1.5). The chromatographic results were compared with commercial chiral columns.

Sample treatments prior to capillary electrophoresis-mass spectrometry

Sample preparation is a crucial part of chemical analysis and in most cases can become the bottleneck of the whole analytical process. Its adequacy is a key factor in determining the success of the analysis and, therefore, careful selection and optimization of the parameters controlling sample treatment should be carried out. This work revises the different strategies that have been developed for sample preparation prior to capillary electrophoresis-mass spectrometry (CE-MS). Namely the present work presents an exhaustive and critical revision of the different samples treatments used together with on-line CE-MS including works published from January 2000 to July 2006.

Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry

The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host-guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid-liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.

Environmental fate processes and biochemical transformations of chiral emerging organic pollutants

This review highlights the analytical chemistry, environmental occurrence, and environmental fate of individual stereoisomers of chiral emerging pollutants, which are modern current-use chemicals of growing environmental concern due to their presence in the environment and potential for deleterious effects. Comparatively little is known about individual stereoisomers of pollutants, which can have differential toxicological effects and can be tracers of biochemical weathering in the environment. Stereoisomers are resolved by gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis (CE). Separation techniques in environmental analysis are typically coupled to mass spectrometry (MS) and tandem mass spectrometry (MS/MS), as these provide the sensitivity and selectivity needed. The enantiomer composition of phenoxyalkanoic and acetamide herbicides, organophosphorus and pyrethroid pesticides, chiral polychlorinated biphenyl metabolites, synthetic musks, hexabromocyclododecane, and pharmaceuticals in the environment show species-dependent enantioselectivity from biotransformation and other biologically mediated processes affecting enantiomers differentially. These enantiomer compositions are useful in detecting biologically mediated environmental reactions, apportioning sources of pollutants, and gaining insight into the biochemical fate of chiral pollutants in the environment, which are needed for accurate risk assessment of such chemicals.

Chiral analysis of pollutants and their metabolites by capillary electromigration methods

Chiral separation of enantiomers is one of the most challenging tasks for any analytical technique including CE. Since the first report in 1985 showing the great possibilities of CE for the separation of chiral compounds, the amount of publications concerning this topic has quickly increased. Although chiral electromigration methods have mainly been used for enantioseparation of drugs and pharmaceuticals, they have also been applied to analyze chiral pollutants. This article intends to provide an updated overview, including works published till January 2005, on the principal applications of CE to the chiral analysis of pollutants and their metabolites, with special emphasis on articles published in the last 10 years. The main advantages and drawbacks regarding the use of CE for chiral separation of pollutants are addressed including some discussion on the foreseen trends of electromigration procedures applied to chiral analysis of contaminants.

Capillary electrophoresis-mass spectrometry in food analysis

This work provides an updated overview (including works published till June 2004) on the principal applications of capillary electrophoresis-mass spectrometry (CE-MS) together with their main advantages and drawbacks in food science. Thus, analysis of amino acids, peptides, proteins, carbohydrates, or polyphenols by CE-MS in different foods is reviewed. Also, other natural compounds (e.g., alkaloids) and toxins analyzed by CE-MS in foods are revised. Moreover, exogenous substances with a potential risk for human health (e.g., pesticides, drugs) detected in foods by CE-MS are included in this work. The usefulness of CE-MS for food analysis and the information that this coupling can provide in terms of processing, composition, authenticity, quality, or safety of foods is also discussed.

Analytical approaches to expanding the use of capillary electrophoresis in routine food analysis

Capillary Electrophoresis (CE) is becoming an ever more powerful analytical technique for the separation, identification, and quantification of a wide variety of compounds of interest in many application fields. Particularly in food analysis this technique can offer interesting advantages over chromatographic techniques because of its greater simplicity and efficiency. Nevertheless, CE needs to advance with regard to compatibility with sample matrices, sensitivity, and robustness of the methodologies in order to gain even wider acceptance in food analysis laboratories, specially for routine work. This article presents various approaches to expanding the analytical usefulness of CE in food analysis, discussing their advantages over conventional CE. These approaches focus on sample screening, automated sample preparation with on-line CE arrangements, and the automatic integration of calibration in routine analytical work with CE.

Analysis of pesticides in soy milk combining solid-phase extraction and capillary electrophoresis-mass spectrometry

In this work, the determination of a group of triazolopyrimidine sulfoanilide herbicides (cloransulam-methyl, metosulam, flumetsulam, florasulam, and diclosulam) in soy milk by capillary electrophoresis-mass spectrometry (CE-MS) is presented. The main electrospray interface (ESI) parameters (nebulizer pressure, dry gas flow rate, dry gas temperature, and composition of the sheath liquid) are optimized using a central composite design. To increase the sensitivity of the CE-MS method, an off-line sample preconcentration procedure based on solid-phase extraction (SPE) is combined with an on-line stacking procedure (i.e. normal stacking mode, NSM). Samples could be injected for up to 100 s, providing limits of detection (LODs) down to 74 microg/L, i.e., at the low ppb level, with relative standard deviation values (RSD,%) between 3.8% and 6.4% for peak areas on the same day, and between 6.5% and 8.1% on three different days. The usefulness of the optimized SPE-NSM-CE-MS procedure is demonstrated through the sensitive quantification of the selected pesticides in soy milk samples.

Analysis of drugs, natural and bioactive compounds containing phenolic groups by capillary electrophoresis coupled to mass spectrometry

This review summarizes the use of capillary electrophoresis (CE) coupled to mass spectrometry (MS) for the analysis of phenolic compounds and its latest developments. Special attention is paid to the different interfaces. The instrumental setups are discussed and demonstrated in a high number of real applications.

Pesticide analysis by capillary electrophoresis

In this work, a critical and updated revision of the current situation of the analysis of pesticides by Capillary Electrophoresis (CE) is presented. The review has been written in two main sections. The first one presents a thorough revision of the various offline and on-line sample preconcentration procedures that have been used in conjunction with CE to analyze these compounds. The second part reviews the various detection strategies (i.e., UV, LIF, MS, and electrochemical) and CE modes that have been applied to the analysis of pesticides. Future trends that can be expected from this hot research area are also discussed.

Highly sensitive analysis of multiple pesticides in foods combining solid-phase microextraction, capillary electrophoresis-mass spectrometry, and chemometrics

A highly sensitive procedure to detect multiple pesticides at trace levels in foods is presented. Initially a comparative study between capillary electrophoresis (CE)-UV and CE-mass spectrometry (MS) is carried out analyzing five pesticides not studied up to now (pyrimethanil, pyrifenox, cyprodinil, cyromazine, and pirimicarb). The comparison between CE-UV and CE-MS is established in terms of separation efficiency, speed of analysis, reproducibility, and sensitivity. A good separation of these compounds is achieved by both techniques using a volatile aqueous buffer containing 0.3 M ammonium acetate/acetic acid at pH 4. Time analysis reproducibility is studied for the same day (n = 5) and three different days (n = 15), showing no significant differences between CE-UV and CE-MS. The study on peak areas reproducibility shows a slightly worse reproducibility for CE-MS compared with CE-UV. The best limit of detection (LOD) that can be achieved for these pesticides using CE-UV was 0.6 microg/mL. CE-MS provides LODs one order of magnitude better than CE-UV. Chemometrics are used to optimize the multiple parameters that play a role in solid-phase microextraction (SPME) and CE-MS analysis (e.g., extraction and desorption times, nebulizer pressure, dry gas flow, dry gas temperature, percentage of organic solvent and acid in the sheath liquid, etc.). The combined use of chemometrics and SPME-CE-MS clearly improves the LODs that can be achieved allowing the detection of pesticides at concentrations down to 15 ng/mL. The usefulness of this approach is demonstrated detecting multiple pesticides in different food samples as grapes and orange juice in a single run. The concentrations detected are below the maximum residue limits (MRLs) permitted for these pesticides in foods corroborating the value of our approach. This work demonstrates, to our knowledge for the first time, the good possibilities of the combined use of SPME-CE-MS and chemometrics.

Quantitative analysis of imazamox herbicide in environmental water samples by capillary electrophoresis electrospray ionization mass spectrometry

Capillary electrophoresis-mass spectrometry (CE-MS) with an electrospray ionization interface was applied for the quantitative analysis of imazamox pesticide in well water, potable water, and pond water. The detector response for imazamox was determined to be linear over the concentration range of 50-1 ng/ml. The limits of quantitation and detection of the method were determined to be 200 and 20 ng/l for imazamox compound in each type of water sample, respectively. The total sample preparation and CE-MS analysis time was under 2 h.

Off-line solid-phase microextraction and capillary electrophoresis mass spectrometry to determine acidic pesticides in fruits

A method based on solid-phase microextraction (SPME) and capillary electrophoresis/mass spectrometry (CE/ MS) is described for determining simultaneously five acidic pesticides (o-phenylphenol, ioxynil, haloxyfop, acifluorfen, picloram) in fruits. The CE device is coupled to an electrospray interface by a commercial sheath-flow adapter. Emphasis is placed on fulfillment of the speed and sensitivity requirements. The best separation is achieved using 32 mM ammonium formate/acid formic buffer at pH 3.1, with a working voltage of 25 kV. The MS detection of the five pesticides was performed in negative ionization mode. Full-scan spectra with base peaks corresponding to [M-H]- were obtained except for acifluorfen, which gives [M-H-CO2]- as most abundant ion. Compared with the conventional EC-UV, the limits of detection were lower for acifluorfen, haloxyfop, ioxynil, and picloram, by a factor of 20, 20, 50, and 2, respectively. Extraction involved fruit sample homogenization with an acetone-water solution (5:1), filtration, and acetone evaporation prior to fiber extraction. SPME conditions such as time, pH, ion strength, stationary phase of the fiber, sample matrix, and desorption solvents were examined. The recovery of the analytes ranged from 7 to 94%, and the relative standard deviation was between 3 and, 13%. The method was found to be linear between 0.02 and 500 mg kg(-1) with correlation coefficients ranging from 0.992 to 0.997. The limits of quantification were from 0.02 to 5 mg kg(-1). The optimized method was successfully applied to the analysis of acid pesticides in fruit samples.

On-line coupling of packed capillary electrochromatography with coordination ion spray-mass spectrometry for the separation of enantiomers

Pressure-supported packed capillary electrochromatography (CEC) and packed capillary high-performance liquid chromatography (pHPLC) have been coupled on-line to electrospray ionization-mass spectrometry (ESI-MS) and coordination ion spray-mass spectrometry (CIS-MS). Separation of enantiomers of barbiturates and chlorinated alkyl phenoxypropanoates were performed on a permethylated beta-cyclodextrin stationary phase by pressure-supported CEC. For on-line detection with ESI- and CIS-MS, a modified sheath-liquid interface was used. CIS-MS is a universal, novel ionization technique which improves the selectivity as well as the sensitivity. Charged complexes were formed through the addition of central complexing ions such as silver(I), cobalt(II), copper(II), and lithium(I) to the sheath flow. Advantages of CIS-MS detection compared to the ESI-MS mode are discussed. In the CIS-MS mode, increased sensitivity and high selectivity was attained through different possibilities of complexation. The superiority of pressure-supported CEC compared to pHPLC in the hyphenation with CIS-MS is demonstrated.

Mechanism of chiral recognition in the enantioseparation of 2-aryloxypropionic acids on new brush-type chiral stationary phases

New brush-type chiral stationary phases (CSP I-IV) comprising N-3,5,6-trichloro-2,4-dicyanophenyl-L-alpha-amino acids (1-4) were prepared by binding of chiral selectors 1-4 to gamma-aminopropyl silica gel. To check the role of excess free aminopropyl groups, CSP V was prepared by binding N-3,5,6-trichloro-2,4-dicyanophenyl-L-alanyl-(3-triethoxysilyl)propylamide to unmodified silica gel. The best separation of racemic 2-aryloxypropionic acids (TR-1-13) was obtained with CSP I; the -(-)-S enantiomer were regularly eluted first, as determined by a CD detector. The mechanism of chiral recognition implies a synergistic interaction of carboxylic acid analyte with the chiral selector and achiral free gamma-aminopropyl units on silica. In fact, CSP V, which is lacking an achiral aminopropyl spacer, shows a lower separation ability for 2-aryloxypropionic acids, but a similar enantioselective discrimination of esters TR-19-20, in comparison with CSP I. CSP I-IV retain unaltered separation ability after a few months of continuous work using a large number of various mobile phases.

Enantiomeric separation of drugs and herbicides on a beta-cyclodextrin-bonded stationary phase

A chemically bonded beta-cyclodextrin chiral stationary phase for HPLC was prepared in a "one pot" process by the reaction of a phenylated beta-cyclodextrin with silica gel. Various racemic analytes such as drugs (aminoalcohol adrenergic beta-blockers, benzodiazepine anxiolytics, arylpropionic acid antiinflammatory agents) and herbicides (aryloxypropionic acids and esters) were separated on the prepared material. The column showed good chiral recognition ability for most of the solutes tested when using heptane and either 2-propanol or chloroform as organic mobile phase modifiers.

On-line capillary electrophoresis-electrospray mass spectrometry for the stereoselective analysis of drugs and metabolites

The on-line combination of partial-filling capillary electrophoresis and electrospray ionization mass spectrometry was demonstrated for the enantioseparation of pharmaceutical drugs and metabolites, namely amphetamines, methadone, venlafaxine and selected tropane alkaloids. The partial-filling technique proved to be a suitable and efficient approach to avoid mass spectrometry (MS) source contamination, as well as signal suppression due to nonvolatile additives. To achieve chiral separation, various chiral selectors were applied, including neutral and particularly negatively charged cyclodextrins. Because of the countercurrent contribution, charged cyclodextrins were found more suitable for the on-line MS detection of separated enantiomers. Hyphenation of capillary electrophoresis (CE) with mass spectrometry was found appropriate for the stereoselective analysis of methadone in real serum samples. Moreover, the use of MS in the selected ion monitoring mode resulted in a very high selectivity, as well as improved sensitivity compared to UV detection. Finally, with atropine as a model compound, the quantitative performances of the method were evaluated and showed high sensitivity, as well as good repeatability in terms of migration time and peak area ratio.

Enantiomeric separation of chiral phenoxy acid herbicides by electrokinetic chromatography. Application to the determination of analyte-selector apparent binding constants for enantiomers

The enantiomeric resolution of chiral phenoxy acid herbicides was performed by electrokinetic chromatography using a cyclodextrin as chiral pseudophase (CD-EKC). A systematic evaluation of several neutral and charged cyclodextrins was made. Among the cyclodextrins tested, (2-hydroxy)propyl beta-cyclodextrin (HP-beta-CD) was found to be the most appropriate for the enantioseparation of phenoxy acids. The influence of some experimental conditions, such as nature and pH of the background electrolyte, chiral selector concentration, and temperature, on the enantiomeric separation of phenoxy acids was also studied. The use of a 50 mM electrolyte solution in ammonium formate at pH 5 and a temperature of 40 degrees C enabled the enantiomeric resolution of four of the six phenoxy acids investigated (2-phenoxypropionic acid, 2(3-chlorophenoxy)propionic acid, 2-(4-chlorophenoxy)propionic acid, and 2-(2,4-dichlorophenoxy)propionic acid) obtaining migration times ranging from 9 to 15 min. Mixtures of the two phenoxy acids not enantiomerically resolved (2-(4-chlorophenoxy)-2-methylpropionic acid and 2-(2,4,5-trichlorophenoxy)propionic acid) and up to three of the phenoxy acids enantiomerically resolved were separated in about 15 min. Finally, the apparent binding constants for each enantiomer-HP-beta-CD pair were calculated at two temperature values (20 and 40 degrees C).

Efficient applications of capillary electrophoresis-tandem mass spectrometry to the analysis of adrenoreceptor antagonist enantiomers using a partial filling technique

Throughout the separation of chiral basic drugs by capillary electrophoresis (CE) with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as chiral selector, the sensitivity of detection can be improved by using tandem mass spectrometric (MS-MS) detection with a partial filling technique rather than with UV spectrometric detection. Prior to sample injection. the capillary was partly filled with HP-beta-CD dissolved in volatile ammonium formate buffer (pH 4, ionic strength 50 mM). The effects of modifying the HP-beta-CD concentration in the selector zone and the length of the separation zone on the enantioresolution and the signal-to-noise ratio of the pseudo-molecular MH+ ion were investigated. For a given selector zone length, as the concentration of the neutral cyclodextrin increases, the resolution between enantiomers becomes higher (the opposite of the behavior of the signal-to-noise ratio) and then reaches an optimum value. The decrease of the selector zone length lowered the resolution between the enantiomers but increased peak efficiencies and signal-to-noise ratio values. Accordingly, partial capillary filling at 80% (v/v) and 10 mM concentration of HP-beta-CD was selected as a suitable compromise between resolution and sensitivity of MS detection. Limits of detection for each adrenoreceptor antagonist enantiomer were 5 ng/ml (0.02 microM) in CE-MS-MS instead of 150 ng/ml (0.60 microM) in CE-UV, which enhances sensitivity by a factor of 30.

Ionization of dichlorophenols for their analysis by capillary electrophoresis-mass spectrometry

In order to develop an advanced analytical method using capillary electrophoresis (CE) for non-volatile environmental pollutants such as endocrine disruptors, combination with mass spectrometry (MS) is necessary for their identification. We chose dichlorophenols (DCPs) as test samples because one of their isomers, 2,4-DCP, is suspected to have endocrine disrupting effects. A preliminary study on their separation by CE-MS was performed using a laboratory-made electrospray ionization (ESI) interface. For the effective ionization of 2,4-DCP at the

Recent advances in capillary electrophoresis/electrospray-mass spectrometry

In this review, the progress in hyphenation of capillary electrophoresis (CE) with electrospray ionization-mass spectrometry (ESI-MS) since the article of Banks (Banks, J. F., Electrophoresis 1997, 18, 2255-2266) is reported. In all capillary-based electromigration techniques, such as capillary gel electrophoresis (CGE), capillary isotachophoresis (CITP), capillary isoelectric focussing (CIEF), micellar electrokinetic chromatography (MEKC), affinity capillary electrophoresis (ACE), as well as in the hybrid techniques capillary electrochromatography (CEC), and pressurized capillary electrochromatography (pCEC) progress has been made in experimental setups, and for many groups of analytes, such as peptides, proteins, nucleotides, saccharides, drugs and their metabolites, CE/ESI-MS has been successfully applied. Electromigration is further miniaturized. New preconcentration methods allow the investigation of compounds, which are not sensitively detected with ESI-MS. Coordination ion spray (CIS) MS is another method for sensitivity enhancement by on-line formation of charged coordination compounds.

On-line coupling of partial filling-capillary zone electrophoresis with mass spectrometry for the separation of clenbuterol enantiomers

The on-line coupling of capillary zone electrophoresis with mass spectrometry (CZE-MS) for the separation of enantiomers is hampered by the presence of nonvolatile chiral selectors such as cyclodextrins in the separation buffer. This problem can be overcome by use of the partial filling technique where only a part of the capillary is filled with the separation buffer containing chiral selectors. Since the electroosmotic flow is almost completely suppressed at acidic pH, that dimethyl-beta-cyclodextrin is neutral, no free cyclodextrin would reach the MS detector when using a partially filled capillary. By this method, clenbuterol enantiomers were successfully resolved and separated from salbutamol (internal standard) in aqueous solution and in plasma samples. A solid-phase extraction (SPE) was used for the preparation of plasma samples before analysis.

Analysis of agrochemicals by capillary electrophoresis

An increasing amount of articles using capillary electrophoresis as an investigation tool for pesticides and environmental pollutants were found over the last few years in analytical chemistry oriented journals. This review covers a wide literature range of the 1990s and concentrates on the analysis of organic agrochemicals (herbicides, fungicides, insecticides, acaricides, etc.) with capillary electrophoresis (capillary zone electrophoresis, micellar electrokinetic chromatography with CE-UV-visible or laser-induced fluorescence detection) as well as with the on-coming hyphenated techniques like capillary electrophoresis-electrospray ionization mass spectrometry. The principal preconcentration methods that allowed real sample analysis with CE are also briefly discussed. The pesticides, the separation methods, the used electrolytes, the detection types, the detection limits and the preconcentration methods were classified and presented in tabulated form as a rapid information tool.

The high performance liquid chromatography electrospray ionization mass spectrometry analysis of diverse basic pharmaceuticals on cyanopropyl and pentafluorophenylpropyl stationary phases

Cyanopropyl (CN) and pentafluorophenylpropyl (PFPP) modified silica columns give good retention and good peak shape for the high performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI/MS) analysis of several classes of basic drugs. These phases enhance the ESI-MS signal by providing good retention of basic drugs with a mobile phase containing 90% acetonitrile. With C18 columns, in order to achieve good retention of basic drugs, only a mobile phase containing less than 40% acetonitrile can be used. Higher concentrations of acetonitrile produce a larger MS signal in the ESI process; the MS signal was a factor of 9 and 12 times greater on the CN and PFPP phases when compared with the C18 phase for the analysis of codeine. The C18 phase required only 4.0-6.0% acetonitrile to obtain the same retention time for codeine. The CN and PFPP stationary phases can be used for the analysis of a range of basic drugs, including many compounds which are poorly retained on the popular C18 and C8 stationary phases. Applications of CN and PFPP columns in the HPLC/ESI/MS of basic drugs include the analysis of antimalarials, such as quinine, bronchodilators, such as salbutamol and tulobuterol, cardioactive drugs, such as procainamide and beta-blockers, tricyclic antidepressants (TCAs), such as protriptyline and trimipramine and alkaloids, such as morphine and codeine. The CN and PFPP phases are also useful for the analysis of bufuralol and its metabolite, hydroxy-bufuralol. All the above analyses were performed using the same mobile phase, 90% acetonitrile; thus the HPLC method development process was expedited. The CN and PFPP phases also gave reproducible retention times and peak shape after more than 8 h of analyses.

Determination of rice herbicides, their transformation products and clofibric acid using on-line solid-phase extraction followed by liquid chromatography with diode array and atmospheric pressure chemical ionization mass spectrometric detection

A simultaneous method for the trace determination of acidic, neutral herbicides and their transformation products in estuarine waters has been developed through an on-line solid-phase extraction method followed by liquid chromatography with diode array and mass spectrometric detection. An atmospheric pressure chemical ionization (APCI) interface was used in the negative ionization mode after optimization of the main APCI parameters. Limits of detection ranged from 0.1 to 0.02 ng/ml for 50 ml of acidified estuarine waters preconcentrated into polymeric precolumns and using time-scheduled selected ion monitoring mode. Two degradation products of the acidic herbicides (4-chloro-2-methylphenol and 2,4-dichlorophenol) did not show good signal response using APCI-MS at the concentration studied due to the higher fragmentor voltage needed for their determination. For molinate and the major degradation product of propanil, 3,4-dichloroaniline, positive ion mode was needed for APCI-MS detection. The proposed method was applied to the determination of herbicides in drainage waters from rice fields of the Delta del Ebro (Spain). During the 3-month monitoring of the herbicides, 8-hydroxybentazone and 4-chloro-2-methylphenoxyacetic acid were successively found in those samples.

Enantioselective determination by capillary electrophoresis with cyclodextrins as chiral selectors

This review surveys the separation of enantiomers by capillary electrophoresis using cyclodextrins as chiral selector. Cyclodextrins or their derivatives have been widely employed for the direct chiral resolution of a wide number of enantiomers, mainly of pharmaceutical interest, selected examples are reported in the tables. For method optimisation, several parameters influencing the enantioresolution, e.g., cyclodextrin type and concentration, buffer pH and composition, presence of organic solvents or complexing additives in the buffer were considered and discussed. Finally, selected applications to real samples such as pharmaceutical formulations, biological and medical samples are also discussed.

Enantiomer separation of drugs by capillary electromigration techniques

The review summarizes the most recent developments in the field of enantioseparation of chiral drugs using capillary electromigration techniques. The basic principles of enantioseparations in CE are discussed. Recent developments in sample introduction, separation and detection in capillary electrophoresis and capillary electrochromatography are summarized. The applications are arbitrarily divided into the following three groups: (a) racemates and artificial mixtures of enantiomers, (b) drug forms and (c) chiral drugs and their metabolites in biological fluids. Among the various techniques involved the relatively new developments such as CEC in aqueous and nonaqueous buffers, on-line CE-MS coupling, etc. are emphasized.

Separation of enantiomers by capillary electrophoresis-mass spectrometry employing a partial filling technique with a chiral crown ether

Enantiomer separations were performed by capillary electrophoresis-mass spectrometry (CE-MS) with (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H4) as a chiral selector. In order to prevent the introduction of the nonvolatile chiral, selector, 18C6H4, into the nozzle of the CE-MS interface and/or the orifice plate, a partial filling technique was employed in this study. By the partial filling technique, the contamination caused by the nonvolatile chiral selector was avoided not only during the analysis but also during the washing of capillary with the separation solution prior to the run. Several racemic compounds having a primary amino group were successfully separated. Racemic 3-aminopyrrolidine and racemic alpha-amino-epsilon-caprolactam have no strong UV absorption, but such compounds were detected with a high sensitivity by MS detection. In this paper, the effects of the length of separation zone and those of the 18C6H4 concentration were described. As the length of the separation zone was longer or as the concentration of 18C6H4 was higher, the enantiomer resolution was enhanced more and more. However, the optimization of 18C6H4 concentration was practically enough to obtain the baseline separation.

Enantiomeric separation of an aryloxyphenoxypropanoic acid by CE and LC

A capillary electrophoresis (CE) and an high performance liquid chromatography (HPLC) chiral separation have been developed for an aryloxyphenoxypropanoic acid, 2-[4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid, a new antitumor agent. The racemic mixture is analyzed, without derivatization, as the free acids. The CE assay is based on inclusion complexation with hydroxypropyl-beta-cyclodextrin. HPLC separation is achieved with a CSP column with the glycopeptide, teicoplanin, as the chiral selector. Both methods give baseline resolution to the R-and S-isomers. The methods were validated for assay and for optical purity assessment of the R-isomer. For assay, the HPLC method is precise (RSD < 0.6%), accurate (error, 0.5%) and linear (r2 = 0.9998). It is able to precisely (RSD = 0.5%) and accurately (error, 0.9%) detect 0.3-6.0% of one isomer (S) in the other (R). The CE assay is much less precise and accurate than HPLC. It is a good alternative to separate and detect the enantiomers, however.

Multi-residue analysis of N-methylcarbamate pesticides and their hydrolytic metabolites in environmental waters by use of solid-phase extraction and micellar electrokinetic chromatography

A method for the simultaneous separation and determination of N-methylcarbamate pesticides and their hydrolytic metabolites by micellar electrokinetic chromatography (MEKC) was developed. A mixture of five pesticides (carbaryl, propuxur, carbofuran, aminocarb, and methiocarb) and their corresponding phenols was studied to optimize the separation of its components in terms of various electrophoretic parameters such as buffer type, pH and concentration, sodium dodecyl sulfate concentration, injection conditions, and applied voltage. Excellent separation of all ten analytes was achieved within about 20 min. The optimized method was used for determinations in environmental water samples. Sample volumes of 250 mL were first preconcentrated in the pesticides and metabolites by passage through a LiChrolut EN sorbent column and then further enriched by on-column stacking. Dynamic ranges of 40 ng/L - 6 microg/L, limits of detection at the nanogram-per-liter level, and relative standard deviations from 2.6 to 7.4% were obtained. The proposed method surpasses high-performance liquid chromatography (HPLC) in separation efficiency. In fact, it provides more expeditious separations and allows more flexible adjustment of the selectivity. Also, it enables the quantification for the analytes studied in this work with decreased limits of detection.

Capillary electrophoresis and electrochromatography of pesticides and metabolites

Synthetic pesticides are important chemicals since they are widely used to control many types of weeds, insects and other pests in a wide variety of agricultural and nonagricultural settings. This review article is aimed at describing the recent progress made in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of pesticides and their metabolites. The various electrophoretic systems and detection schemes that have been introduced so far for the CE and CEC of pesticides are discussed. Also included in this review article are the various approaches for trace enrichment that are involved in the analysis of dilute pesticide samples.

Identification, quantitation, and characterization of biomolecules by capillary electrophoretic analysis of binding interactions

The high resolving power of capillary electrophoresis combined with the specificity of binding interactions may be used with advantage to characterize the structure-function relationship of biomolecules, to quantitate specific analytes in complex sample matrices, and to determine the purity of pharmaceutical and other molecules. We here review recent and innovative methodologies and applications of high resolution affinity electrophoresis within the fields of binding constant determination, structure-activity studies, quantitative microassays, analysis of drug purity and protein conformation, and immobilized affinity ligands. Despite the virtues of these approaches with respect to applicability, resolving power, speed, and low sample consumption, problems remain with respect to analyte identification and low concentration limits of detection. The ongoing development of new detector technologies for capillary electrophoresis such as mass spectrometry, and possibly nuclear magnetic resonance and other spectroscopic methods, is therefore very promising for the continued increased use of affinity capillary electrophoresis.