Ferrite nanospheres-based magnetic solid-phase extraction for determination of domoic acid in seawater samples using high-performance liquid chromatography with tandem mass spectrometry

Mechanochemical synthesis ionic covalent organic frameworks/cotton composites for pipette tip solid-phase extraction of domoic acid in seafood

Pipette tip solid-phase extraction (PT-SPE) as a miniaturized solid-phase extraction technique have a wide range of applications in the field of sample pretreatment. In this study, ionic covalent organic frameworks@cotton (iCOF@cotton) were facilely synthesized by mechanochemical grinding method only in half an hour, and used as the adsorbents of PT-SPE. The synthesized iCOF@cotton not only had high specific surface area, suitable pore structure and cationic charge groups of iCOF that can extract polar targets quickly, but also reduced the problem of high back pressure of PT-SPE by the addition of cotton, thus accelerating extraction time. Combined with high performance liquid chromatographic tandem mass spectrometry (HPLC-MS/MS), an efficient and sensitive method was established for detection of domoic acid (DA, a toxin produced by algae). Under the optimal conditions, the proposed analysis method displayed excellent analytical performance, including broad range of linearity (10-1000 pg mL-1), low limit of detection (LOD, 5 pg mL-1), high correlation coefficient (0.9993), satisfactory precision (RSDs ≤6.4 %). In addition, the developed method was applied to the detection of DA in marine samples, and detected trace DA (18.6 pg mL-1) with satisfactory recovery (85.7%-107.2 %). The above results indicated that the prepared iCOF@cotton have great potential as the adsorbents for PT-SPE.

Measuring Marine Biotoxins in a Hypersaline Coastal Lagoon

Marine biotoxins have posed a persistent problem along various coasts for many years. Coastal lagoons are ecosystems prone to phytoplankton blooms when altered by eutrophication. The Mar Menor is the largest hypersaline coastal lagoon in Europe. Sixteen marine toxins, including lipophilic toxins, yessotoxins, and domoic acid (DA), in seawater samples from the Mar Menor coastal lagoon were measured in one year. Only DA was detected in the range of 44.9-173.8 ng L-1. Environmental stressors and mechanisms controlling the presence of DA in the lagoon are discussed. As an enrichment and clean-up method, we employed solid phase extraction to filter and acidify 75 mL of the sample, followed by pre-concentration through a C18 SPE cartridge. The analytes were recovered in aqueous solutions and directly injected into the liquid chromatography system (LC-MS), which was equipped with a C18 column. The system operated in gradient mode, and we used tandem mass spectrometry (MS/MS) with a triple quadrupole (QqQ) in the multiple reaction monitoring mode (MRM) for analysis. The absence of matrix effects was checked and the limits of detection for most toxins were low, ranging from 0.05 to 91.2 ng L-1, depending on the compound. To validate the measurements, we performed recovery studies, falling in the range of 74-122%, with an intraday precision below 14.9% RSD.

Effective extraction of the metabolites of toluene and xylene based on a postsynthetic-modified magnetic covalent organic polymer

Toluene and xylene are volatile organic compounds, and long-term exposure to toluene and xylene may cause brain structure and nervous system damage. To evaluate exposure to toluene and xylene in the environment, it is usually possible to monitor their metabolites in organisms, hippuric acid (HA) and methylhippuric acid (MHA). In this work, we designed a new magnetic solid phase extraction (MSPE) sorbent, zirconium postsynthetic-modified magnetic covalent organic polymer (Fe₃O₄@COP-COOZr), for purifying and enriching HA and 4-MHA. Zirconium ions were immobilized on the magnetic COP surface by postsynthetic modification without the use of additional coating layers or chelating ligands. The developed Fe₃O₄@COP-COOZr interacted with HA and 4-MHA through the π-π stacking effect and electrostatic interactions, as well as strong chelation with coordinatively unsaturated zirconium sites. The promising affinity material of Fe₃O₄@COP-COOZr in MSPE had high stability and recyclability. The established MSPE-HPLC-UV method showed low sorbent consumption (10 mg) and high sensitivity (LODs less than 0.1 μg L^-1), and can be used for the analysis of HA and 4-MHA in real samples. The recoveries of the proposed method in real urine samples for the simultaneous determination of HA and 4-MHA were in the range of 83.5-103.2 %, and the RSDs were 0.9-7.1 %.

Highly sensitive detection of okadaic acid in seawater by magnetic solid-phase extraction based on low-cost metal/nitrogen-doped carbon nanotubes

Algae toxins pose a severe threat to human health all over the world. In this study, magnetic metal/nitrogen-doped carbon nanotubes (M-NCNTs) were facilely synthesized based on one-step carbonization and applied for magnetic solid-phase extraction of okadaic acid (OA) from seawater followed by high performance liquid chromatographic tandem mass spectrometry (HPLC-MS/MS) analyses. Differences in the physicochemical properties of the three prepared materials (Fe/Co/Ni-NCNTs) were investigated to confirm the best extraction material. Among them, Ni-NCNTs demonstrated a faster extraction rate (10 min) and higher adsorption capacity (223.5 mg g^-1), mainly due to the higher specific surface area, suitable pore structure and more abundant pyridine nitrogen ring. Under the optimal conditions, the calibration curve was linear over the range (1.0-800.0 pg mL^-1) with good determination coefficients (R) of 0.9992. The limit of detection (LOD) obtained in multiple replicates was 0.4 pg mL^-1. Three seawater samples were measured by the developed method, 12.3 pg mL^-1 of OA was detected with a satisfying recovery (88.6%-106.7%) and acceptable repeatability (RSD ≤ 4.8%, n = 6). The results demonstrate that M-NCNTs materials are a promising candidate for magnetic solid-phase extraction. Benefiting from its high extraction and interference resistance, the established analytical method is expected to be extended to detect other marine environmental pollutions.

Preparation of chitosan-modified magnetic Schiff base network composite nanospheres for effective enrichment and detection of hippuric acid and 4-methyl hippuric acid

Chitosan-modified magnetic Schiff base network composite nanospheres (Fe₃O₄@SNW@Chitosan) were prepared for the enrichment and detection of hippuric acid (HA) and 4-methyl hippuric acid (4-MHA) via magnetic solid phase extraction (MSPE) connected with HPLC. The SNW was one of the covalent organic framework, which constructed through covalent bonds, shown comprising solvent stability, low density and accessible pores. The obtained Fe₃O₄@SNW@Chitosan has many merits as a magnetic sorbent, including a hydrophilic surface, uniform pore size, unique ordered channel structure, and superparamagnetism. The favourable linearity of this MSPE-HPLC method was in the range of 1-1000 μg L^-1, and LODs of HA and 4-MHA were 0.3 μg L^-1 and 0.2 μg L^-1, respectively. The recoveries in urine samples were range from 95.3 to 109.0 % with the RSD less than 9.6 %. When employed for the enrichment of HA and 4-MHA, Fe₃O₄@SNW@Chitosan exhibited great potential as a candidate for preconcentration.

Rapid extraction of domoic acid by a magnetic molecularly imprinted silica before HPLC measurement

A magnetic molecularly imprinted silica solid was obtained by sol-gel polymerization for the separation of domoic acid. The solid showed rapid adsorption kinetics with an adsorption equilibrium time of 5 min. The solid showed affinity to domoic acid under the interference of tryptophan and could be repeatedly used for 5 times at least. The solid was used as a solid-phase-extraction sorbent for the extraction of domoic acid from clam samples before measurement with liquid chromatography. The detection limit of 0.20 mg kg-1 was lower than the allowable limits in several countries or areas. The recoveries in the spiked samples were 88% approximately.

A fish scale-like magnetic nanomaterial as a highly efficient sorbent for monitoring the changes in auxin levels under cadmium stress

Sorbents with high surface utilization and good dispersibility are of great importance for the extraction performance of magnetic solid-phase extraction (MSPE). In this study, a fish scale-like magnetic nanomaterial (Co@Co3O4/OCN) was synthesized, which can be used as a highly efficient MSPE sorbent due to its strong magnetism, special morphology, doping of N element, numerous micro-mesopore cavities and organic functional groups (hydroxyl and carboxyl). Furthermore, a Co@Co3O4/OCN-based MSPE method for monitoring the changes in the levels of three auxins (indole-3-acetic acid, indole-3-propionic acid and 3-indole butyric acid) was successfully established. Wide linear ranges (1.0-1000.0 pg mL-1) with good correlation coefficients (R > 0.9992), low limits of detection (LODs, 0.2-4.0 pg mL-1) and satisfactory repeatability (RSD ≤5.9%, n = 3) were obtained. Using the developed method, various growth parts and different growth periods of plants under Cd stress were monitored. The results showed that auxins in various parts of plants showed differential response under Cd stress, and there was a threshold for the changes in auxin levels against Cd stress. This indicates that the developed fish scale-like Co@Co3O4/OCN nanomaterial has a good application prospect for enriching small molecular targets containing hydroxyl and carboxyl groups.

Simultaneous Pre-Concentration and HPLC-MS/MS Quantification of Phycotoxins and Cyanotoxins in Inland and Coastal Waters

The purpose of this study was to set up a sensitive method for the simultaneous determination of phycotoxins and cyanotoxins-Emerging pollutants with different structures and harmful properties (hepatotoxicity, neurotoxicity and cytotoxicity)-In environmental waters. Due to the low concentrations detected in these samples, a pre-concentration step is required and here it was performed in a single step with a commercial cartridge (Strata™-X), achieving enrichment factors up to 200 and satisfactory recovery (R = 70-118%) in different aqueous matrices. After solid-phase extraction (SPE), toxins were separated and quantified by High Performance Liquid Chromatography- Heated ElectroSpray Ionisation Tandem Mass Spectrometry (HPLC-HESI-MS/MS) in Multiple Reaction Monitoring (MRM) mode. An analytical evaluation of the proposed method was done based on the analytical figures of merit, such as precision and trueness, linearity, selectivity, and sensitivity, and it turned out to be a robust tool for the quantification of ng L^-1 levels, phycotoxins and cyanotoxins in both freshwater and saltwater samples.

Production of domoic acid from large-scale cultures of Pseudo-nitzschia multiseries: A feasibility study

The commercial demand for domoic acid (DA), the phycotoxin responsible for Amnesic Shellfish Poisoning, is currently met by extraction from a diminishing supply of stockpiled contaminated mussels (Mytilus edulis). As this supply becomes scarce, a more reliable source is needed. Purification of the toxin from an algal source would be easier and more economical than from shellfish tissue if algal growth and yield of toxin were maximized. This project was initiated to determine if DA could be produced using large-scale semi-continuous algal cultures, which should reduce labour and shorten the time required for biomass production. Pseudo-nitzschia multiseries was grown in 300-L fibreglass photobioreactors called a Brite-Box™. The effect of temperature and nutrient depletion on the yield of DA by P. multiseries was examined. A decline in maximum cell number without a substantial increase in cellular DA was associated with increased temperature. Maximum total cellular DA (8.8 pg cell^-1) was achieved at 20 °C. Semi-continuous culture of P. multiseries is accompanied by increasing amounts of DA lost to the medium. The process was deemed to be feasible for growing P. multiseries but methods to recover this extracellular DA are necessary for this process to be economical.

Validated HPLC-MS/MS Method To Quantify Low Levels of Domoic Acid in Plasma and Urine after Subacute Exposure

Domoic acid (DA) is a marine neurotoxin produced by several species of Pseudo-nitzschia. DA causes severe neurological toxicity in humans and animals. To address the current analytical need to quantify low levels of DA in human and animal body fluids, a sensitive and selective high performance liquid chromatography-tandem mass spectrometry method was developed to measure DA in plasma and urine. This method was fully validated to accurately and precisely quantify DA between 0.31 and 16 ng/mL in plasma and between 7.8 and 1000 ng/mL in urine. Our group introduced the use of a novel internal standard, tetrahydrodomoic acid to control for matrix effects and other sources of variability. This validated method will be useful to assess DA concentrations in biological samples of human or animal origin after suspected DA exposure from contaminated food. It will also be applicable to sentinel programs and research studies to analyze body fluids with low levels of DA.

Selective extraction of theophylline from plasma by copper-doped magnetic microspheres prior to its quantification by HPLC

The authors describe the preparation of copper-doped magnetic microspheres (Cu-Fe₃O₄) by a solvothermal method. Due to their good magnetic property and high affinity for compounds containing an imidazole moiety (containing N-H), they are excellent adsorbents for such compounds as tested by eighteen compounds. Specifically, a method has been developed for magnetic solid-phase extraction (MSPE) of theophylline (TP) from plasma. The method enables selective enrichment of TP over many potential interferents that can occur in plasma. Following elution with alkaline methanol, TP was quantified by HPLC-UV at a detection wavelength of 272 nm. Under the optimized conditions, a linear response is found for the 0.02 to 20 μg·mL^-1 concentration range, and the limit of detection is as low as 3 ng·mL^-1. Recoveries from spiked samples range from 91.2 to 100.4%, and the repeatabilities are between 2.9 and 12% (for n = 6). The method was successfully applied to the determination of TP in rabbit and rat plasma. Graphical abstract Copper-doped magnetic microspheres are described that show good magnetic property and high affinity for compounds containing an imidazole moiety (containing an N-H group). They were successfully applied to the selective extraction of theophylline in plasma.

Sensitive profiling of trace neurotoxin domoic acid by pressurized capillary electrochromatography with laser-induced fluorescence detection

A stable, sensitive and low-reagent consumption method for the quantification of trace neurotoxin domoic acid (DA) was presented by pressurized capillary electrochromatography (pCEC) with laser-induced fluorescence (LIF) detection.