Analysis of Pesticide Degradation Products by Tandem High-Performance Immunoaffinity Chromatography and Reversed-Phase Liquid Chromatography

Applications of chromatographic methods in metabolomics: A review

Chromatography is a robust and reliable separation method that can use various stationary phases to separate complex mixtures commonly seen in metabolomics. This review examines the types of chromatography and stationary phases that have been used in targeted or untargeted metabolomics with methods such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. General considerations for sample pretreatment and separations in metabolomics are considered, along with the various supports and separation formats for chromatography that have been used in such work. The types of liquid chromatography (LC) that have been most extensively used in metabolomics will be examined, such as reversed-phase liquid chromatography and hydrophilic liquid interaction chromatography. In addition, other forms of LC that have been used in more limited applications for metabolomics (e.g., ion-exchange, size-exclusion, and affinity methods) will be discussed to illustrate how these techniques may be utilized for new and future research in this field. Multidimensional LC methods are also discussed, as well as the use of gas chromatography and supercritical fluid chromatography in metabolomics. In addition, the roles of chromatography in NMR- vs. MS-based metabolomics are considered. Applications are given within the field of metabolomics for each type of chromatography, along with potential advantages or limitations of these separation methods.

Affinity extraction of emerging contaminants from water based on bovine serum albumin as a binding agent

Affinity sorbents using bovine serum albumin as a binding agent were developed and tested for the extraction of environmental contaminants from water. Computer simulations based on a countercurrent distribution model were also used to study the behavior of these sorbents. Several model drugs, pesticides, and hormones of interest as emerging contaminants were considered in this work, with carbamazepine being used as a representative analyte when coupling the albumin column on-line with liquid chromatography and tandem mass spectrometry. The albumin column was found to be capable of extracting carbamazepine from aqueous solutions that contained trace levels of this analyte. Further studies of the bovine serum albumin sorbent indicated that it had higher retention under aqueous conditions than a traditional C₁₈ support for most of the tested emerging contaminants. Potential advantages of using these protein-based sorbents included the low cost of bovine serum albumin and its ability to bind to a relatively wide range of drugs and related compounds. It was also shown how simulations could be used to describe the elution behavior of the model compounds on the bovine serum albumin sorbents as an aid in optimizing the retention and selectivity of these supports for use with liquid chromatography or methods such as liquid chromatography with tandem mass spectrometry.

Chromatographic immunoassays: strategies and recent developments in the analysis of drugs and biological agents

A chromatographic immunoassay is a technique in which an antibody or antibody-related agent is used as part of a chromatographic system for the isolation or measurement of a specific target. Various binding agents, detection methods, supports and assay formats have been developed for this group of methods, and applications have been reported that range from drugs, hormones and herbicides to peptides, proteins and bacteria. This review discusses the general principles and applications of chromatographic immunoassays, with an emphasis being given to methods and formats that have been developed for the analysis of drugs and biological agents. The relative advantages or limitations of each format are discussed. Recent developments and research in this field, as well as possible future directions, are also considered.

Clinical applications of capillary electrophoresis based immunoassays

Immunoassays have long been an important set of tools in clinical laboratories for the detection, diagnosis, and treatment of disease. Over the last two decades, there has been growing interest in utilizing CE as a means for conducting immunoassays with clinical samples. The resulting method is known as a CE immunoassay. This approach makes use of the selective and strong binding of antibodies for their targets, as is employed in a traditional immunoassay, and combines this with the speed, efficiency, and small sample requirements of CE. This review discusses the variety of ways in which CE immunoassays have been employed with clinical samples. An overview of the formats and detection modes that have been employed in these applications is first presented. A more detailed discussion is then given on the type of clinical targets and samples that have been measured or studied by using CE immunoassays. Particular attention is given to the use of this method in the fields of endocrinology, pharmaceutical measurements, protein and peptide analysis, immunology, infectious disease detection, and oncology. Representative applications in each of these areas are described, with these examples involving work with both traditional and microanalytical CE systems.

Immunoaffinity chromatography: an introduction to applications and recent developments

Immunoaffinity chromatography (IAC) combines the use of LC with the specific binding of antibodies or related agents. The resulting method can be used in assays for a particular target or for purification and concentration of analytes prior to further examination by another technique. This review discusses the history and principles of IAC and the various formats that can be used with this method. An overview is given of the general properties of antibodies and of antibody-production methods. The supports and immobilization methods used with antibodies in IAC and the selection of application and elution conditions for IAC are also discussed. Several applications of IAC are considered, including its use in purification, immunodepletion, direct sample analysis, chromatographic immunoassays and combined analysis methods. Recent developments include the use of IAC with CE or MS, ultrafast immunoextraction methods and the use of immunoaffinity columns in microanalytical systems.

Biointeraction analysis by high-performance affinity chromatography: Kinetic studies of immobilized antibodies

A system based on high-performance affinity chromatography was developed for characterizing the binding, elution and regeneration kinetics of immobilized antibodies and immunoaffinity supports. This information was provided by using a combination of frontal analysis, split-peak analysis and peak decay analysis to determine the rate constants for antibody-antigen interactions under typical sample application and elution conditions. This technique was tested using immunoaffinity supports that contained monoclonal antibodies for 2,4-dichlorophenoxyacetic acid (2,4-D). Association equilibrium constants measured by frontal analysis for 2,4-D and related compounds with the immobilized antibodies were 1.7-12x10(6)M(-1) at pH 7.0 and 25 degrees C. Split-peak analysis gave association rate constants of 1.4-12x10(5)M(-1)s(-1) and calculated dissociation rate constants of 0.01-0.4s(-1) under the application conditions. Elution at pH 2.5 for the analytes from the antibodies was examined by peak decay analysis and gave dissociation rate constants of 0.056-0.17s(-1). A comparison of frontal analysis results after various periods of column regeneration allowed the rate of antibody regeneration to be examined, with the results giving a first-order regeneration rate constant of 2.4x10(-4)s(-1). This combined approach and the information it provides should be useful in the design and optimization of immunoaffinity chromatography and other analytical methods that employ immobilized antibodies. The methods described are not limited to the particular analytes and antibodies employed in this study but should be useful in characterizing other targets, ligands and supports.

Quantitative determination of fenoterol and fenoterol derivatives in rat plasma using on-line immunoextraction and liquid chromatography/mass spectrometry

An on-line immunoextraction and liquid chromatography/mass spectrometry (LC/MS) method was developed and validated for the determination of R,R'-fenoterol, R,R'-methoxyfenoterol and R,S'-naphthylfenoterol in rat plasma. Sample preparation involved immunoextraction of analytes using an antibody raised against R,R'- and R,S'-aminofenoterol that was immobilized onto chromatographic support. LC was performed on a Waters hydrophilic interaction chromatography (HILIC) column (150 mm x 2.1mm), using an isocratic mobile phase of methanol:ammonium acetate (10mM, pH 6.8) (90:10, v/v) at a flow rate of 0.2 ml/min. The MS was operated in the single ion monitoring mode (m/z 304.2 for R,R'-fenoterol, m/z 318.1 for R,R'-methoxyfenoterol, and m/z 339.2 for R,S'-naphthylfenoterol). Optimization of analytes desorption process from the immunoextraction column was performed by factorial analysis and the sample calibration curves were made with spiked rat plasma samples containing 0.5-100 ng/ml of drugs. The cross-selectivity studies of the antibody were determined and the results suggested high selectivities toward R,R'-fenoterol, R,R'-methoxyfenoterol and R,S'-naphthylfenoterol. The accuracy of assay was more than 96% while intra- and inter-day precision of assay were less than 12.4%. Stability studies (2h benchtop, freeze/thaw, and autosampler stability) were conducted and the analytes were stable through out studies. The validated method was used to determine the plasma concentration-time profiles of drugs after oral administration to rats of R,R'-fenoterol, R,R'-methoxyfenoterol and R,S'-naphthylfenoterol.

Capillary electrophoresis-based immunoassays: principles and quantitative applications

The use of CE as a tool to conduct immunoassays has been an area of increasing interest over the last decade. This approach combines the efficiency, small sample requirements, and relatively high speed of CE with the selectivity of antibodies as binding agents. This review examines the various assay formats and detection modes that have been reported for these assays, along with some representative applications. Most CE immunoassays in the past have employed homogeneous methods in which the sample and reagents are allowed to react in solution. These homogeneous methods have been conducted as both competitive binding immunoassays and as noncompetitive binding immunoassays. Fluorescent labels are most commonly used for detection in these assays, but enzyme labels have also been utilized for such work. Some additional work has been performed in CE immunoassays with heterogeneous methods in which either antibodies or an analog of the analyte is immobilized to a solid support. These heterogeneous methods can be used for the selective isolation of analytes prior to their separation by CE or to remove a given species from a sample/reagent mixture prior to analysis by CE. These CE immunoassays can be used with a variety of detection modes, such as fluorescence, UV/Vis absorbance, chemiluminescence, electrochemical measurements, MS, and surface plasmon resonance.

A comparative evaluation of random and site-specific immobilization techniques for the preparation of antibody-based chiral stationary phases

In this study, one random and four site-directed conjugation strategies were applied to immobilize an mAb, which stereoselectively binds to L-amino acids, onto silica particles. The resulting chiral stationary phases (CSPs) were used for enantiomer separation of the model-analyte D,L-phenylalanine and further examined in frontal affinity chromatography. Although random immobilization of the antibody onto discuccinimidyl carbonate-activated silica resulted in a CSP that enabled baseline separation of the enantiomers of D,L-phenylalanine, the amount of available binding sites was considerably lower compared to the CSPs prepared by site-directed strategies. Immobilization of antibody via its carbohydrate chains, either directly via hydrazone bonds between the support and the protein or indirectly via binding carbohydrate-biotinylated antibody to streptavidin-derivatized silica, resulted in medium column efficiencies. Higher amounts of available active sites were obtained by immobilizing the antibody indirectly through the "crystallizable fragment (Fc)" receptor protein A/G. The best results with regard to amount of available binding sites and column efficiency were obtained by first biotinylating the antibody specifically at its C-termini using carboxypeptidase Y and immobilizing the biotinylated antibody on streptavidin-derivatized silica.

Applications of silica supports in affinity chromatography

The combined use of silica-based chromatographic supports with immobilized affinity ligands can be used in many preparative and analytical applications. One example is the use of silica-based affinity columns in HPLC, giving rise to a method known as high-performance affinity chromatography (HPAC). This review discusses the role that silica has played in the development of affinity chromatography and HPAC and the applications of silica in these methods. This includes a discussion of the types of ligands that have been employed with silica and the methods by which these ligands have been immobilized. Various formats have also been presented for the use of silica in affinity chromatographic methods, including assays involving direct or indirect analyte detection, on-line or off-line affinity extraction, and chiral separations. The use of silica-based affinity columns in studies of biological systems based on zonal elution and frontal analysis methods will also be considered.

Development and integration of an immunoaffinity monolithic disk for the on-line solid-phase extraction and HPLC determination with fluorescence detection of aflatoxin B1 in aqueous solutions

The development and characterization of an anti-aflatoxin B1 (anti-AFB1) immunoaffinity monolithic disk is reported. Polyclonal anti-AFB1 was covalently immobilized in batch on an epoxy-activated monolithic Convective Interaction Media (CIM) disk (12 mm x 3 mm i.d.) by a one-step reaction via epoxy groups of the polymer surface. 0.96 mg of antibody were immobilized and the binding capacity of the CIM disk was determined by frontal analysis. The CIM disk was coupled through a switching valve to a reversed-phase column, namely Chromolith Performance RP-18e. A fully automated HPLC method with fluorescence detection for the determination of aflatoxin B1 in aqueous solution was developed. The total analysis time with the integrated system is 46 min and the retention time of AFB1 is approximately 29 min. The binding capacity of the immunoaffinity disk was evaluated in terms of linearity, precision and accuracy of the extraction procedure. The immunoaffinity support was stable after repeated runs.

Development of sulfhydryl-reactive silica for protein immobilization in high-performance affinity chromatography

Two techniques were developed for the immobilization of proteins and other ligands to silica through sulfhydryl groups. These methods made use of maleimide-activated silica (the SMCC method) or iodoacetyl-activated silica (the SIA method). The resulting supports were tested for use in high-performance affinity chromatography by employing human serum albumin (HSA) as a model protein. Studies with normal and iodoacetamide-modified HSA indicated that these methods had a high selectivity for sulfhydryl groups on this protein, which accounted for the coupling of 77-81% of this protein to maleimide- or iodoacetyl-activated silica. These supports were also evaluated in terms of their total protein content, binding capacity, specific activity, nonspecific binding, stability, and chiral selectivity for several test solutes. HSA columns prepared using maleimide-activated silica gave the best overall results for these properties when compared to HSA that had been immobilized to silica through the Schiff base method (i.e., an amine-based coupling technique). A key advantage of the supports developed in this work is that they offer the potential of giving greater site-selective immobilization and ligand activity than amine-based coupling methods. These features make these supports attractive in the development of protein columns for such applications as the study of biological interactions and chiral separations.

Affinity monoliths for ultrafast immunoextraction

Affinity monoliths based on a copolymer of glycidyl methacrylate and ethylene dimethacrylate were developed for ultrafast immunoextractions. Rabbit immunoglobulin G (IgG) and anti-FITC antibodies were used as model ligands for this work. The antibody content of the monoliths was optimized by varying both the polymerization and immobilization conditions for preparing such supports. The temperature and porogen composition used during polymerization showed significant effects on monolith morphology and on the amount of antibodies that could be coupled to these materials. The effects of various immobilization procedures and coupling conditions were also evaluated, including the coupling temperature, pH, protein concentration, and use of high buffer concentrations. The maximum ligand density obtained for rabbit IgG was approximately 60 mg/g. When a 4.5 mm i.d. x 0.95 mm monolith disk containing anti-FITC antibodies was used, 95% extraction of fluorescein was achieved in 100 ms. These properties make such monoliths attractive for work in the rapid isolation of analytes from biological samples. Similar columns can be developed for other targets by varying the types of antibodies or binding agents placed within the monoliths.

Retention mechanism of analytes in the solid-phase extraction process using molecularly imprinted polymers

Two molecularly imprinted polymers (MIPs), prepared in dichloromethane with terbutylazine and ametryn as template molecules, were evaluated for the selective extraction of triazines from complex matrices. Various parameters affecting extraction recoveries on MIPs were studied in order to obtain an optimized extraction procedure allowing to reduce non-specific interactions. In order to test the selectivity of the MIPs, the same procedure was applied to the extraction of compounds possessing the same polarity and size as the triazines. By means of molecular modeling, the effects of the electric charge distribution and of the size of the molecules on the retention mechanism were studied. The value of capacity for terbutylazine MIP was also measured. At last, the high selectivity resulting from the use of MIPs was clearly demonstrated by their applications to the clean-up of grape juice and soil extracts spiked with triazines. In addition, the soil extract was cleaned-up by immunoextraction allowing the comparison of both approaches in terms of selectivity.

Development of a Portable Immunoextraction-Reversed-Phase Liquid Chromatography System for Field Studies of Herbicide Residues

A portable system based on immunoextraction and reversed-phase HPLC was developed for the field analysis of herbicides in groundwater and surface water. Atrazine, simazine, and cyanazine were used as model analytes for this work. These were measured in water by using three coupled columns: an anti-atrazine antibody column for the selective extraction of these analytes, a reversed-phase precolumn for their reconcentration, and a reversed-phase analytical column for their separation. Various factors were considered in the optimization of this system, including the binding properties of the immunoextraction column, the effect of flow rate on the performance of each column, the selection of sample volume, and the choice of mobile phases for the RPLC columns. A typical analysis with this system allowed the injection of one sample every 7.5 min and provided results for all three of the tested herbicides in less than 10 min. In the analysis of atrazine alone, samples could be injected every 4 min and results were obtained within 8 min. There was good correlation between this technique and a comparable benchtop system. The lower limits of detection for the given analytes were approximately 0.2-0.25 microg/L, with a linear range that extended to 20 microg/L and a dynamic range that went up to at least 100 microg/L. The use of this technique in the field was demonstrated through applications that involved the development of time and location profiles for triazine herbicides in environmental samples.

Optimization of the class-selective extraction of triazines from aqueous samples using a molecularly imprinted polymer by a comprehensive approach of the retention mechanism

Direct, selective solid-phase extraction of triazines from aqueous samples is presented using a molecularly imprinted polymer (MIP) made with terbutylazine as template molecule. After optimization of the steps of the procedure, 14 triazines including degradation products were studied and satisfactory extraction recoveries were obtained except for thiotriazines. By comparing results obtained with the terbutylazine MIP and a similar non-imprinted polymer, it was determined that retention was achieved via specific interactions except for hydroxyterbutylazine. Selectivity of the extraction procedure was also verified by applying the MIP for the extraction of phenylureas that were not retained on it. The effects of the charge distribution and of molecular volume of the triazines (obtained by molecular modeling) on the selectivity of interactions between the analytes and the MIP were studied. However, when the optimized procedure was applied to real samples, low extraction recoveries were obtained due to strong matrix effects: ion-exchange occurs between the carboxylate groups of the MIP and the ionic species of the sample, that prevents subsequent specific interactions. By introducing an acid wash step, the procedure was successfully applied for the class-selective extraction of triazines from industrial effluent and surface water samples. Finally, increased extraction recoveries were achieved for the polar degradation products of triazines by using a mixed-phase composed of a polymeric sorbent and the MIP.

On-line coupling of sol-gel-generated immunoaffinity columns with high-performance liquid chromatography

The paper demonstrates the possibility to use sol-gel-generated immunoaffinity columns as selective sample preparation step in on-line combination with HPLC. In the past sol-gel-generated immunoaffinity columns have only been included in off-line sample preparation schemes. Compared with conventional RP-materials on-line coupling of sol-gel-generated silica matrices with a pore structure designed to retain antibodies poses additional problems caused by their lower pressure tolerance and by the necessity to match the mobile phases not only to take into account the chromatographic properties but also the conformational stability of the antibodies. These problems have been overcome by an on-line system which can be regarded as a prototype for similar systems which exploit the selectivity of sol-gel immunoaffinity columns. The system consists of a sol-gel-generated immunoaffinity column coupled to an RP enrichment column and an analytical column. The practicality of such systems is demonstrated using the example of anti-pyrene immunoaffinity columns applied for the determination of pyrene in aqueous solutions.

Development of sandwich HPLC microcolumns for analyte adsorption on the millisecond time scale

A new class of columns is reported that uses only microgram quantities of active support and that provides for the retention of biological compounds and other analytes on the millisecond time scale. This was accomplished by packing standard HPLC supports into layers as small as 60 microm in length and using only 90 microg of support material. This provided columns with effective residence times in the millisecond time range when routine HPLC flow rates and pressures were used. The retention of analytes by such columns was examined under both adsorption- and diffusion-limited conditions. The RPLC adsorption of hemoglobin (a system with diffusion-limited retention) was found to give 95% binding in as little as 4 ms. The adsorption of fluorescein by an anti-fluorescein antibody column (an adsorption-limited system) gave 95% retention in 100-120 ms. One application examined for these columns was their use in a chromatographic-based competitive binding immunoassay. This used bovine serum albumin (BSA) as the model analyte, and fluorescein-labeled BSA was used for detection. The resulting approach had a contact time of 180 ms between the sample and an anti-BSA immunoaffinity microcolumn and provided a signal within 5-25 s after sample injection. The columns developed in this work should also be useful in other situations that involve a small amount of a stationary phase or that require short column residence times.

Analytical method for the determination of atrazine and its dealkylated chlorotriazine metabolites in water using gas chromatography/mass selective detection

A multiresidue method is reported for the determination of atrazine and its dealkylated chlorotriazine metabolites in water. Water samples are buffered to pH 10 and partitioned in ethyl acetate. Final analysis is accomplished using gas chromatography/mass selective detection (GC/MSD) in the selected ion monitoring (SIM) mode. The limit of detection (LOD) is 0.050 ng and the limit of quantification (LOQ) is 0.10 ppb for 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-amino-4-chloro-6-(isopropylamino)-s-triazine (G-30033), 2-amino-4-chloro-6-(ethylamino)-s-triazine (G-28279), and 2, 4-diamino-6-chloro-s-triazine (G-28273). The mean procedural recoveries were 90, 92, 98, and 85% and the standard deviations were 12, 13, 16, and 20% for atrazine, G-30033, G-28279, and G-28273, respectively (n = 30). The study was conducted under U.S. EPA FIFRA Good Laboratory Practice Guidelines 40 CFR 160 for method validation. The reported procedure accounts for residues of G-28273 in water that are not included in EPA Method 507.

Coupling immunoassays with chromatographic separation techniques

Coupling immunoassays with HPLC separation techniques is becoming increasingly useful in the analysis of biological and nonbiological samples of both large and small molecules. This is because it provides both sensitivity and selectivity for molecular analysis at relatively low cost, low maintenance and with excellent potential for automation. This paper reviews application of this hyphenated approach both in the pre-column immunoextraction and post-column immunodetection modes. Systems in which immunoassays are interfaced to chromatographic separations in order to separate bound and free fractions of the immunoassay will not be included since these systems do not provide the enhanced selectivity common to hyphenated systems. Post-column immunodetection is based on various immunoassay formats such as direct detection, one-site, competitive and sandwich immunoassays. Homogeneous immunodetectors are more convenient than heterogeneous immunodectors since there are no separation and column regeneration steps involved in homogeneous immunoassays. On the other hand, heterogeneous immunoassays are generally more sensitive than homogeneous immunoassays since interfering substances are removed prior to immunodetection. Advantages and limitations for the various approaches will be discussed.

Antibody immobilization to high-performance liquid chromatography supports. Characterization of maximum loading capacity for intact immunoglobulin G and Fab fragments

This study examined various factors that affect the maximum amount of intact immunoglobulin G (IgG) or Fab fragments that can be covalently immobilized to silica and other HPLC-grade supports for use in immunoaffinity chromatography or immunoextractions. Factors that were considered included the amount of surface area available for immobilization, the pore size of the support, the type of immobilization method and the nature of the support matrix. The main factor in determining the extent of immobilization was found to be the relationship between the support's surface area and the ability of the IgG or Fab fragments to reach this surface. Access to the support surface was a function of the size of the protein being immobilized and the support porosity, with maximum immobilization being obtained with supports having pore sizes of approximately 300 A for intact IgG and 100 A for Fab fragments. Some differences in the maximum level of immobilization were noted between different coupling methods. Supports like Poros and Emphaze gave similar results to those seen with HPLC-grade silica when a comparison was made between materials with comparable pore sizes. Many of the trends observed in this work for IgG and Fab fragments should apply to other proteins that are to be immobilized to HPLC supports.

Immuno-affinity solid-phase extraction

The measurement of trace organics such as drugs and pesticides at low concentration in biological and environmental samples is a challenging analytical task. Despite recent advances in instrumentation most analysts regard sample preparation as the rate-limiting step in the overall analytical method. In recent years there has been a lot of interest in immobilising antibodies onto solid supports such as silica to provide highly selective solid-phase extraction. This paper reviews the use of immuno-affinity for solid-phase extraction. It uses as examples extraction of chlortoluron and isoproturon from water and morphine and clenbuterol in urine and plasma respectively. An extensive list of other examples is given. Optimisation procedures are discussed in detail.

Immunoaffinity solid-phase extraction for the trace-analysis of low-molecular-mass analytes in complex sample matrices

Immunoaffinity solid-phase extraction (SPE) sorbents, so-called immunosorbents (ISs), are based upon molecular recognition using antibodies. Thanks to the high affinity and high selectivity of the antigen-antibody interaction, they allow a high degree of molecular selectivity and have shown to be a unique tool in the sample preparation area these last few years. Extraction and clean-up of complex biological and environmental aqueous samples are achieved in the same step and from large volumes when required. Their application to extracts from solid matrixes is solvent-free and more simple than any other clean-up procedure. Single analytes can be targeted, but since an antibody can also bind one or more analytes having structure similar to the one used for its preparation, ISs have been developed for targeting a single analyte and its metabolites. The cross-reactivity was also exploited for developing ISs that could selectively extract a whole class of structurally related compounds. This review describes the current technology used for the synthesis of the ISs, their properties and their field of application. The different parameters governing the antigen-antibody interactions and the solid-phase extraction process are discussed. Emphasis is given to the optimisation of the SPE sequence, especially to the desorption and regeneration steps. The importance of the capacity and its relationship with the analytes recovery and breakthrough volumes is highlighted for class-specific ISs. Multi-class-selective ISs are also presented. Validation studies are reviewed using various certified reference materials. Relevant examples, involving combination with chromatography in both off-line and on-line mode, illustrate the high selectivity provided in various complex matrixes. Miniaturisation is also described, since it allows high throughput of samples.

Tandem solid-phase extraction of atrazine ozonation products in water

The preconcentration of aqueous solutions containing atrazine degradation products was investigated using solid-phase extraction on octadecyl and cation-exchanger silica phases. The retention and elution steps were studied and evaluated separately in order to define and optimize the critical experimental parameters involved. A strategy which combines sequentially both phases is proposed to fractionate compounds into two groups of increasing polarities: firstly, the native pesticide, hydroxyatrazine and most chlorotriazines on octadecyl support, and secondly monodealkylated hydroxytriazines, ammeline and ammelide on cation-exchanger. This tandem procedure was successfully applied for analysing and quantifying atrazine ozonation products and its efficiency demonstrated using [U-ring 14C]-labelled atrazine experiments.

Development of a theoretical model for chromatographic-based competitive binding immunoassays with simultaneous injection of sample and label

This study examined the theory and behavior of an HPLC-based chromatographic competitive binding immunoassay with the simultaneous injection of sample and a labeled analyte analogue. Equations based on nonlinear chromatographic theory were derived to describe the calibration curve for this assay in a system with adsorption-limited kinetics and homogeneous binding sites. These equations related the assay response (B/Bo) to the column's binding capacity, the moles of injected analyte or labeled analogue, and the flow rate/adsorption kinetics of the system. There was good agreement between the predicted theoretical response and experimental data obtained for the binding of human serum albumin (HSA) to an immobilized anti-HSA antibody column. This theory was also successful in describing the changes that occurred in the calibration curve when the flow rate or amount of labeled analogue applied to the column was varied. A comparison was made between the results of this study and previous theoretical work that examined the behavior of a related, sequential injection competitive binding method. On the basis of the results reported in this work, several general guidelines were developed for the design and optimization of simultaneous injection methods for use in such areas as clinical testing, pharmaceutical analysis, and environmental monitoring.

Survey of recent advances in analytical applications of immunoaffinity chromatography

Methods that use immunoaffinity chromatography (IAC) for sample preparation or detection are becoming increasingly popular as tools in the analysis of biological and nonbiological compounds. This paper presents an overview of immunoaffinity chromatography and examines some recent developments of this technique in analytical applications. The emphasis is placed on HPLC-based IAC methods or those that combine IAC with other instrumental techniques; however, novel approaches that employ low-performance IAC columns for chemical quantitation are also considered. Particular applications that are examined include (1) the use of IAC in the direct detection of analytes, (2) the extraction of samples by IAC prior to on- or off-line detection by other methods, (3) the use of IAC in chromatographic-based immunoassays, and (4) the development of postcolumn reactors based on IAC for the detection of analytes as they elute from other types of chromatographic columns. The advantages and limitations for each approach are considered. In addition, a summary is provided of reports in the literature that have used IAC for these various formats.

Non-linear elution effects in split-peak chromatography. II. Role of ligand heterogeneity in solute binding to columns with adsorption-limited kinetics

The split-peak effect is a useful phenomenon in studying the kinetic behavior of chromatographic supports. This work examined the combined role of ligand heterogeneity and non-linear elution conditions (i.e., sample load dependence) on the solute free fractions that are measured during split-peak studies. Exact expressions were derived to describe the effects of ligand heterogeneity under linear elution conditions, and simulation models were developed to specifically examine the combined effects of ligand heterogeneity and non-linear elution in systems with adsorption-limited rates for solute binding. The simulations showed that ligand heterogeneity increased the amount of free solute seen at any flow-rate or sample size, with this being most noticeable when using low flow-rates or large samples. One application in which these increases were examined in detail concerned the use of the split-peak effect for association rate constant measurements. It was found that linear extrapolation methods developed for homogeneous systems (as a correction for non-linear elution conditions) could successfully be applied to columns containing heterogeneous ligands. Columns containing immobilized protein A and/or protein G were used as experimental models to test the validity of the simulations; the behavior of these columns showed good quantitative and qualitative agreement with the predicted theoretical results.