Chromatography-immunology coupling, a powerful tool for environmental analysis

Development of a microcolumn one-site immunometric assay for a protein biomarker: Analysis of alpha1-acid glycoprotein

A one-site immunometric assay based on affinity microcolumns was developed for the analysis of alpha₁-acid glycoprotein (AGP) as a model protein biomarker. In this assay, a sample containing AGP was incubated with an excess amount of a labeled binding agent, such as fluorescein-labeled anti-AGP antibodies or F_ab fragments. The excess binding agent was removed by passing this mixture through a microcolumn that contained an immobilized form of AGP, while the signal was measured for the binding agent-AGP complex in the non-retained fraction. Theoretical and practical factors were both considered in selecting the concentration of labeled binding agent, the incubation time of this agent with the sample, and the application conditions for this mixture onto the microcolumn. The effects of using various labeling methods and intact antibodies vs F_ab fragments were also considered. The final assay was performed with fluorescein-labeled anti-AGP antibodies and a 2.1 mm i.d. × 1.0 cm AGP microcolumn operated at 0.30 mL min^-1. This method required only 1 µL of serum or plasma, had a detection limit of 0.63 nM AGP, and gave a potential throughput of 2 min per sample. This assay was used to measure AGP in normal serum and plasma from patients with systemic lupus erythematosus, giving good agreement with the literature and a reference method. The same approach and guidelines can be used to create assays for other protein biomarkers by changing the labeled binding agent and immobilized protein within the microcolumn.

Phenolics: occurrence and immunochemical detection in environment and food

Phenolic compounds may be of natural or anthropogenic origin and be present in the environment as well as in food. They comprise a large and diverse group of compounds that may be either beneficial or harmful for consumers. In this review first a non-exhausting overview of interesting phenolics is given, in particular with regards to their presence in environment and food. For some of these compounds, beneficial, toxicological and/or optionally endocrine disrupting activities will be presented. Further, immunochemical detection and/or isolation methods developed will be discussed, including advantages and disadvantages thereof in comparison with conventional analytical methods such as HPLC, GC, MS. A short overview of new sensor-like methods will also be included for present and future application.

Optimisation of a heterogeneous non-competitive flow immunoassay comparing fluorescein, peroxidase and alkaline phosphatase as labels

Off- and on-line strategies for a non-competitive heterogeneous flow immunoassay were developed comparing three different labels. The samples, containing the model compounds digoxin or digoxigenin, were either pre-incubated off-line or on-line in a mixing coil with excess of labelled anti-digoxigenin Fab-fragments. The excess of Fab-fragments was then separated from the digoxin bound Fab-fragments by passing the sample through a column with immobilised digoxin. The off-line immunochemical detection system is suitable for sensitive high through-put screening of the analytes, whereas the on-line system is more suitable for coupling as a post-column detection unit to liquid chromatography. The digoxin and digoxigenin content in the sample were quantified using fluorescein (F) and enzyme (peroxidase (POD), alkaline phosphatase (AP)) labelled Fab-fragments. The fluorescein label was directly measured with the fluorescence detector, whereas a fluorescent enzyme product was measured in the two enzyme based systems, using 3-(p-hydroxyphenyl)-propionic acid (HPPA) and hydrogen peroxide for POD and, and 4-methylumbelliferyl phosphate (4-MUP) for AP. The highest sensitivity and lowest limit of detection (LOD) was obtained with the Fab-POD system with LODs for digoxin and digoxigenin in the off- and on-line configurations of 0.025 and 0.01 nM, respectively. The sample through-put for the off- and on-line systems were 43 and 32 samples per hour, respectively.

Immunochromatographic analysis of bovine growth hormone releasing factor involving reversed-phase high-performance liquid chromatography-immunodetection

We have developed high-performance immunoaffinity chromatography (HPIAC) methods for the detection and quantitation of bovine growth hormone releasing factor (GHRF), which could also be applicable to its metabolites in biofluids. These approaches have involved a combination of IAC using immobilized antibody (Ab) to GHRF, together with reversed-phase high-performance liquid chromatography (RP-HPLC) separations of initially isolated and concentrated protein, followed by selective detection, involving on-line immunodetection (ID) schemes. ID methods involved HPIAC supports of the Ab, together with synthesized Ab-fluorescein isothiocyanate conjugates. We have demonstrated optimization methods for each step of the entire hyphenated technique (IAC-HPLC-ID), and then actually quantitated GHRF using this overall system. The minimum detectable concentration was about 1 ng/5 ml (200 ppt) with fluorescence detection (excitation wavelength, 490 nm; emission wavelength, 510-650 nm). We have also tested a single blind, spiked biological sample (bovine plasma), spiked with a known level of GHRF. Accuracy (7.4%) and precision (S.D. = +/- 22%) were quite acceptable for a double immunoassay method.