Separation of toxic peptides (microcystins) in capillary electrophoresis, with the aid of organic mobile phase modifiers

A Mini-Review on Detection Methods of Microcystins

Cyanobacterial harmful algal blooms (CyanoHABs) produce microcystins (MCs) which are associated with animal and human hepatotoxicity. Over 270 variants of MC exist. MCs have been continually studied due of their toxic consequences. Monitoring water quality to assess the presence of MCs is of utmost importance although it is often difficult because CyanoHABs may generate multiple MC variants, and their low concentration in water. To effectively manage and control these toxins and prevent their health risks, sensitive, fast, and reliable methods capable of detecting MCs are required. This paper aims to review the three main analytical methods used to detect MCs ranging from biological (mouse bioassay), biochemical (protein phosphatase inhibition assay and enzyme linked immunosorbent assay), and chemical (high performance liquid chromatography, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, and gas chromatography), as well as the newly emerging biosensor methods. In addition, the current state of these methods regarding their novel development and usage, as well as merits and limitations are presented. Finally, this paper also provides recommendations and future research directions towards method application and improvement.

Determination of sulfa antibiotic residues in river and particulate matter by field-amplified sample injection-capillary zone electrophoresis

In the present research, field-amplified sample injection-CZE (FASI-CZE) coupled with a diode array detector was established to determine trace level sulfa antibiotic. Sulfathiazole, sulfadiazine, sulfamethazine, sulfadimethoxine, sulfamethoxazole, and sulfisoxazole were selected as analytes for the experiments. The background electrolyte solution consisted of 70.0 mmol/L borax and 60.0 mmol/L boric acid (including 10% methanol, pH 9.1). The plug was 2.5 mmol/L borax, which was injected into the capillary at a pressure of 0.5 psi for 5 s. Then the sample was injected into the capillary at an injection voltage of -10 kV for 20 s. The electrophoretic separation was carried out under a voltage of +19 kV. The capillary temperature was maintained at 20˚C throughout the analysis, and six sulfonamides were completely separated within 35 min. Compared with pressure injection-CZE, the sensitivity of FASI-CZE was increased by 6.25-10.0 times, and the LODs were reduced from 0.2-0.5 to 0.02-0.05 μg/mL. The method was applied to the determination of sulfonamides in river water and particulate matter samples. The recoveries were 78.59-106.59%. The intraday and interday precisions were 2.89-7.35% and 2.77-7.09%, respectively. This provides a simpler and faster method for the analysis of sulfa antibiotic residues in environmental samples.

Determination of microcystins in environmental samples using capillary electrophoresis

The applicability of capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) methods for the simultaneous determination of two frequently occurring microcystins (MCs-LR and -YR) and a new variant (MC-YA) in crude extracts of Hungarian bloom samples and cyanobacterial cultures was studied. It was found that the comparison of the results obtained by both CZE and MEKC measurements (due to the differences in their separation mechanisms) for the same sample can guarantee the reliability of the quantitative results. In our work environmental samples like lake waters, water bloom samples, cyanobacterial isolates were analysed. The three microcystins could be directly determined in water bloom samples collected from Hungarian lakes and laboratory culture samples of cyanobacteria.

Reversed-phase liquid chromatographic–mass spectrometric determination of microcystin-LR in cyanobacteria blooms under alkaline conditions

Reversed-phase HPLC coupled to the atmospheric pressure ionization-electrospray ionization (API-ESI) MS was used for microcystin-LR detection and quantitation in samples of dried Microcystis aeruginosa cells. An alkaline linear gradient (20 mmol/l ammonium hydroxide-acetonitrile, pH 9.7) was used for elution of the toxic peptides. Limit of detection was 1 microg/ml (20 ng per injection) in the scan mode of MS and 0.1 microg/ml (2 ng per injection) in the case of selective ion monitoring.

Cloud-point extraction and preconcentration of cyanobacterial toxins (microcystins) from natural waters using a cationic surfactant

A new cloud-point extraction and preconcentration method using a cationic surfactant, Aliquat-336 (tricaprylylmethylammonium chloride), has been developed for the determination of cyanobacterial toxins, microcystins, in natural waters. Sodium sulfate was used to induce phase separation at 25 degrees C. The phase behavior of Aliquat-336 with respect to concentration of Na2SO4 was studied. The cloud-point system revealed a very high phase volume ratio compared to other established systems of nonionic, anionic, and cationic surfactants. At pH 6-7, it showed an outstanding selectivity in analyte extraction for anionic species. Only MC-LR and MC-YR, which are known to be predominantly anionic, were extracted (with averaged recoveries of 113.9 +/- 9% and 87.1 +/- 7%, respectively). MC-RR, which is likely to be amphoteric at the above pH range, was not detectable in the extract. Coupled to HPLC/UV separation and detection, the cloud-point extraction method (with 2.5 mM Aliquat-336 and 75 mM Na2SO4 at 25 degrees C) offered detection limits of 150 +/- 7 and 470 +/- 72 pg/mL for MC-LR and MC-YR, respectively, in 25 mL of deionized water. Repeatability of the method was 7.6% for MC-LR and 7.3% for MC-YR. The cloud-point extraction process can be completed within 10-15 min with no cleanup steps required. Applicability of the new method to the determination of microcystins in real samples was demonstrated using natural surface waters collected from a local river and a local duck pond spiked with realistic concentrations of microcystins. Effects of salinity and organic matter (TOC) content in the water sample on the extraction efficiency were also studied.

Capillary electrophoretic assay and purification of cylindrospermopsin, a cyanobacterial toxin from Aphanizomenon ovalisporum, by plant test (blue-green Sinapis test)

Toxic cyanobacteria are known to produce cyanotoxins, toxic secondary metabolites. In recent years the cylindrospermopsin (tricyclic guanidinyl hydroxymethyluracil)-producing organisms Aphanizomenon ovalisporum, Cylindrospermopsis raciborskii, and Umezakia natans have been inhabiting polluted fresh waters. Cylindrospermopsin, a potent hepatotoxic cyanotoxin, has been implicated in cases of human poisoning as well. This study describes the isolation and purification of cylindrospermopsin from A. ovalisporum with the help of a slightly modified Blue-Green Sinapis Test, a plant test suitable for determining the cyanotoxin content of chromatographic fractions besides plankton samples. The recent modification, using microtiter plates for the assay, improves the method and reduces the amount of sample needed for the assay. This approach proved that plant growth and metabolism, at least in the case of etiolated Sinapis alba seedlings, are inhibited by cylindrospermopsin. The establishment of capillary electrophoresis of cylindrospermopsin and consideration of the results reported here lead us to the expectation that capillary electrophoresis of cylindrospermopsin may be a powerful and useful analytical method for investigating cyanobacterial blooms for potential cylindrospermopsin content and toxicity. Confirmation of chemical identity of the purified compound is performed by UV spectrophotometry, NMR, and MALDI-TOF.

Analysis of lipophilic peptides and therapeutic drugs: on-line-nonaqueous capillary electrophoresis-mass spectrometry

This minireview addresses the usefulness of nonaqueous capillary electrophoresis-mass spectrometry (NACE-MS), mainly in the analysis of lipophilic peptides such as gramicidin S and bacitracin, and therapeutic drugs such as pyrazoloacridine, the H2-antagonist mifentidine, tamoxifen, and their metabolites. The beneficial effects of NACE-MS in typical bioanalytical applications are analyzed case by case. A suitable and widely applicable NACE-MS analysis is identified, which is an electrolyte buffer containing ammonium acetate (5-50 mM) and/or acetic acid (up to 100 mM) with varying composition of organic solvents. Either acetonitrile or methanol or a mixture of the two are mostly utilized in the nonaqueous media. Primary considerations in developing NACE-MS are also discussed.

Selectivity in capillary electrophoresis in the presence of micelles, chiral selectors and non-aqueous media

In addition to high efficiency, short analysis times and small sample volumes, a further attractive feature of capillary electrophoretic techniques is the possibility to achieve, high selectivities. Usually, selectivity control also allows improvement in the resolution. A simple way to enhance the selectivity of capillary electrophoretic separations is to add one or more surfactants above their critical micelle concentration, or in the case of chiral separations to add a chiral selector to the background electrolyte. Because of the dynamic structure of micelles, the aggregation of monomers and size of the micelles can be easily adjusted. This review describes the various type of surfactants used in micellar electrokinetic capillary chromatography, and the chiral selectors employed in enantiomeric separations by capillary electrophoresis. Factors affecting the selectivity are noted. A brief discussion is included of the selectivity enhancement obtainable in non-aqueous media.

Capillary zone electrophoresis of proteins

This review article with 237 references is focused on capillary zone electrophoresis (CZE) of proteins. It includes discussion of modeling electrophoretic migration of proteins, sample pretreatment before the analysis, methods reducing the sorptions of proteins on the capillary wall, and techniques for increasing selectivity by using electrolyte additives including the sieving matrices. Significant progress in detection techniques, namely in laser-induced fluorescence and mass spectrometry, is emphasized. Modifications of CZE using specific interactions, such as affinity capillary electrophoresis or capillary immunoelectrophoresis, are debated as well as combination of CZE with other separation methods such as high performance liquid chromatography (HPLC). A number of practical applications of CZE of proteins are described.

Capillary electrophoresis of natural products

Capillary electrophoresis (CE) and micellar electrokinetic chromatography were used for the separation of widely different compounds from natural materials including antibiotics, humic substances, flavonoids, isoflavonoids, illicit drugs, coumarins, alkaloids, steroids, Chinese herbal preparations, nicotine, caffeine, amphetamines, toxins such as aflatoxins B1, B2, G1, G2, mycotoxins, heptapeptide toxins and others, ephedrine compounds, mineral elements, and natural compounds in biological samples. A discussion of sample extraction and clean-up and the advantages of using CE is also presented.