Effective Extraction of Domoic Acid from Seafood Based on

Subscriber access provided by UNIV OF BARCELONA

Article

Effective extraction of domoic acid from seafood based on postsynthetic modified magnetic zeolite imidazolate framework-8 particles Chuanhui Huang, Xuezhi Qiao, Wei-Ming Sun, Hui Chen, Xiang-Yu Chen, Lan Zhang, and Tie Wang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b05202 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 5, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Effective extraction of domoic acid from seafood based on postsynthetic modified magnetic zeolite imidazolate framework-8 particles Chuanhui Huang,1 Xuezhi Qiao,2 Weiming Sun,3 Hui Chen,1 Xiangyu Chen,2 Lan Zhang,1* and Tie Wang2* 1Key

laboratory for analytical science of food safety and biology, MOE, College of Chemistry, Fuzhou University, Fuzhou, Fujian, 350116, China 2Beijing

National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China 3The

Department of Basic Chemistry, The School of Pharmacy, Fujian Medical University, Fuzhou, Fujian, 350108, China. ABSTRACT: Domoic acid (DA) is a naturally occurring neurotoxin known to bioaccumulate in marine products. Despite its hypertoxicity, the enrichment and analysis of trace DA in complex marine organisms remains a challenge. We describe herein the fabrication of a postsynthetic-modified magnetic zeolite imidazolate framework-8 (Fe3O4 SPs@ZIF-8/Zn2+), based on Fe3O4 superparticles, for the adsorption of DA from complex biological matrices. The adsorption of DA is rapid (~5 min) and occurs through strong electrostatic interactions and chelation with coordinatively unsaturated zinc sites on the surface of Fe3O4 SPs@ZIF8/Zn2+. Employing our Fe3O4 SPs@ZIF-8/Zn2+ sorbent in a magnetic solid-phase extraction, followed by liquid chromatographic separation and tandem mass spectrometric detection, resulted in a facile, rapid, efficient, and sensitive method for the enrichment and detection of trace DA in marine products. After optimization, this method yielded satisfactory precision (relative standard deviation ≤ 3.4%; n = 5) with a high degree of linearity from 1.0 to 1000.0 pg mL-1 (r2 = 0.9997) and a detection limit of 0.2 pg mL1 (S/N = 3). Recoveries of 93.1 to 102.3% were obtained in spiked aquatic products. In addition, trace levels of DA (49.2 pg mL-1) were found in shellfish samples, confirming the applicability of our Fe3O4 SPs@ZIF-8/Zn2+ adsorbent for the detection of DA in seafood.

Domoic acid (DA) is a naturally occurring neurotoxic amino acid produced by diatoms of the genus Pseudo-nitzschia1 and is a leading cause of amnesic shellfish poisoning. During algal blooms it can bioaccumulate in marine organisms such as fish, shrimp, crab, and shellfish.2 Consuming DA-contaminated seafood can cause gastrointestinal and neurological disorders and in severe cases, death.3,4 To protect public health, most countries or regions have set a regulatory limit of no more than 20 μg DA per gram of wet tissue.5 Several analytical methods have been developed for the quantitative determination of DA levels in tissue.6-8 Among them, highperformance liquid chromatography coupled with tandem mass spectrometry (HPLC–MS/MS) is regarded as one of the most powerful techniques for both quantifying and monitoring the DA content of marine organisms due to its high sensitivity and selectivity. * Address correspondence to [email protected] [email protected]

The concentration of DA in marine organisms is usually extremely low. The analytical matrix, which consists of animal tissues, contains an abundance of potential interferents,9,10 including proteins, vitamins, unsaturated fatty acids, and ionic species, including K+, Na+, Ca2+, Fe3+, Mn2+, Zn2+, Cu2+, and Cl−. Therefore, samples for DA analysis require some level of pretreatment to purify and enrich the DA as much as possible prior to instrumental analysis. Magnetic solid-phase extraction (MSPE) is the most common sample pretreatment technique used with marine organism samples.11,12 MSPE sorbents are typically dispersed throughout a sample solution or suspension, allowing a greater degree of interaction between the sorbent and target analytes. Phase separation, and removal of the sorbent material, is easily induced by introducing an external magnetic field. It is this separation step that overcomes the shortcomings of traditional SPE when dealing with complex matrices. Metal-organic frameworks (MOFs) are a class of porous crystalline materials composed of metal centers that are linked with various organic moieties. MOFs boast tunable pore sizes

ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

and high surface areas and have been used extensively in the fields of chemistry and materials science.13 Due to their high stability, favorable dispersibility, and adsorption capacity for various analytes, MOFs have been employed to great success as sorbent materials in MSPE applications.14-16 As a typical MOF, ZIF-8 (Zn(HMeIM)2, HMeIM = 2-methylimidazole, Figure S1),17,18 has been applied successfully to the extraction and separation of histidine-rich proteins,19 linear alkanes,20 and tetracyclines.21 Compared to other MOFs, the magnetization of ZIF-8 is simple,22 resulting in good batch-to-batch reproducibility of magnetized products. ZIF-8 also contains abundant Zn2+ sites that can chelate the O and N atoms of DA (Figure S2). However, immediately after synthesis, the zinc sites in ZIF-8 are fully coordinated with organic ligands,23,24 resulting in steric hindrance and a low adsorbate capacity. Therefore, newly synthesized; i.e., pristine, ZIF-8 must be modified to effectively chelate DA. Postsynthetic modification, a powerful synthetic approach, has grown in popularity and resulted in a number of advances in the functionalization and application of MOFs.25 Herein, we describe a facile and effective postsynthetic modified strategy for preparing Fe3O4 SPs@ZIF-8/Zn2+ microspheres with numerous, surface-localized, under-coordinated zinc sites. These magnetic microspheres were used as the sorbent material in an MSPE-based sample preparation for DA analyses in marine products. Our Fe3O4 SPs@ZIF-8/Zn2+ particles exhibited several advantages over unmodified Fe3O4 SPs@ZIF-8 particles, including high chemical and hydrothermal stability, and stronger electrostatic interactions with DA, resulting in excellent sensitivity. Finally, MSPEbased sample preparation with Fe3O4 SPs@ZIF-8/Zn2+ was combined with HPLC-MS/MS for the detection of DA in marine products. The resulting method was rapid, efficient, and sensitive to DA concentration with a limit of detection (LOD) of 0.2 pg mL-1. Pretreatment time was short (5 min) and analyses were free of interference from common ions and matrix components that are typically present in real seafood samples.

Page 2 of 8

structures with a D8 Advance diffractometer (Bruker, Germany). Nitrogen adsorption and desorption isotherms were measured with an ASAP 2020 (Micromeritics, USA). The Brunauer–Emmett–Teller (BET) equation and the non-local density functional theory model were adopted for calculations of surface area and pore size distribution, respectively. Fourier-transform infrared (FTIR) spectra were acquired on a Nicolet 6700 spectrometer (Thermo Fisher, USA) in a KBr pellet. Magnetization curves were acquired on an MPMS-XL7 (Quantum Design, USA) vibrating sample magnetometer (VSM) at room temperature. HPLC-MS/MS analyses were performed using an HPLC system coupled to a TSQ Quantum Access MaxTM triple quadrupole mass spectrometer (Thermo Fisher) with a Hypersil GOLD aQ column (5 µm particle size, 150 × 2.1 mm) at room temperature. Elution was isocratic with a mobile phase of 80% water and 20% acetonitrile, both containing 0.1% formic acid, at a flow rate of 200 µL min-1 for 5 min. The sample injection volume was 10 µL. MS/MS analyses were performed in selected reaction monitoring mode (SRM) with the ion source in positive mode. System parameters were obtained by autotuning: analyte ion transition (DA, m/z 312 → 266), collision energy (16 eV), and tube lens (96). Other parameters of the MS/MS system were optimized to ensure the highest possible sensitivity. The ion spray voltage for electrospray ionization was +3000 V. The vaporizer and capillary were held at 300°C and 350°C, respectively. The sheath gas and auxiliary gas (both nitrogen) settings were 35 and 10 arbitrary units, respectively. High-purity argon (≥ 99.999%) was employed as the collision gas. Data acquisition and processing were performed with onboard software (LC quan 2.7, Thermo Fisher).

EXPERIMENTAL METHODS Materials and general procedures. All reagents were of analytical grade or better. Ferric chloride hexahydrate (FeCl3·6H2O), oleic acid (OLA, 90%), 1-octadecene (ODE, 90%), 1-tetradecene (TDE, 92%), and sodium oleate (97%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole (HMeIM), used in the formation of the ZIF-8 shell, were obtained from Sinopharm Chemical Reagent Co., Ltd. and Aladdin Chemistry Co., Ltd. (Shanghai, China), respectively. DA (≥ 90%) was purchased from Sigma-Aldrich Co., Ltd. (Shanghai, China). Deionized water (18.2 M.cm) was prepared with a Milli-Q ultrapure water system (Millipore, USA). Marine organism samples were purchased from a local market. To ascertain the morphology and structural features of the magnetic particles, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images were acquired on an F250/F430 SEM instrument (FEI, USA) and a Tecnai G2 F20 (FEI, USA) at 200 kV, respectively. X-ray powder diffraction (XRD) was used to determine crystal

Scheme 1. Scheme of the preparation of Fe3O4 SPs@ZIF8/Zn2+ particles and the MSPE process for DA. Preparation of Fe3O4 superparticles (SPs) and Fe3O4 SPs@ZIF-8/Zn2+ particles. Iron-oxide nanocrystals were synthesized in boiling solvents as reported previously.26 Then, 1 mL of a chloroform solution containing 5 mg of Fe3O4 nanocrystals and 1 mL of aqueous DTAB (20 mg·mL-1) were thoroughly mixed by vortexing for 1 min. After mixing, the chloroform was removed from the mixture by bubbling with Ar at 60°C to obtain a clear, purple, aqueous solution of Fe3O4 SPs. One milliliter of aqueous polyvinyl pyrrolidone (PVP; MW = 55,000, 50 mg·mL-1) was added and the solution was stirred magnetically for 6 h at room temperature. The resulting Fe3O4 SPs were collected by centrifugation (3000 r·min-1, 2 min) and redispersed in water.

2 ACS Paragon Plus Environment

Page 3 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry Twenty microliters of aqueous DTAB (20 mg·mL-1) were added to an aqueous solution of 2-MeIm (1.5 M) and the mixture was vortexed for 1 min. One milliliter of aqueous Zn(NO3)2·6H2O (25 mM) was injected into the mixture followed by the addition of 1 mL of aqueous Fe3O4 SPs (containing 2.5 mg Fe3O4 SP) 10 s after. The mixture was then vortexed for 1 min. After mixing, the reaction mixture was left undisturbed at room temperature for 3 h. The products were collected by centrifugation (8000 r·min-1, 8 min), washed three times each with water and ethanol, and vacuum dried at 100°C for 12 h. To obtain Fe3O4 SPs@ZIF-8/Zn2+ particles, assynthesized Fe3O4 SPs@ZIF-8 particles were immersed in a methanolic solution of 1.0 mol L-1 Zn2+ for 15 min. The product was dried as described above. Preparation of real sample. Real samples were prepared according to a previously published method with slight modifications.6 Briefly, soft tissues were removed from the organism and drained for approximately 5 min. Fifty grams of tissue was homogenized in a blender and 5 g of the homogenate was accurately weighed into a 50 mL centrifuge tube. An extraction solution of 10 mL of methanol/water (1:1, v/v) was added to the tube and the sample was sonicated for 15 min. The resulting slurry was centrifuged at 4000 rpm for 20 min at room temperature. The supernatant was collected and the precipitate was extracted twice more with 5 mL of methanol/water (1:1, v/v). The supernatants from each extraction step were combined in a 250-mL volumetric flask. After diluting to the mark with water, the resulting crude extract was passed through a 0.22 μm filter and stored at 4 °C until analysis. Operation procedure of MSPE. MSPE was performed with Fe3O4 SPs@ZIF-8/Zn2+ particles as a magnetic sorbent. Typically, 1.0 mg of Fe3O4 SPs@ZIF-8/Zn2+ particles was added to a 50 mL centrifuge tube containing 20 mL of DA standard solution (250 pg mL-1) or a sample crude extract. The mixture was then eddied for 7 min to facilitate the adsorption of DA onto the sorbent material. After adsorption, a strong magnet was placed beside the tube to isolate the magnetic sorbent particles from the sample solution. The supernatant was discarded. Next, 0.4 mL of an aqueous histidine solution (3 mmol L-1) was added to facilitate DA desorption under vortex for 2 min. The sorbent particles were then magnetically separated from the desorption solution, and the supernatant was pipetted into an autosampler vial for HPLC–MS/MS analyses. Theoretical models and computational details. All of the geometric parameters of the studied compounds have been fully optimized without any constraints using the global hybrid generalized gradient approximation M06-2X functional,27 which is suitable for weak- and medium-strength interaction systems. The Los Alamos double-zeta-type LANL2DZ and effective core potential basis sets were used for Zn, while the 6-311+G(d) split valence basis set was used for the other atoms during geometric optimization. All isomers were characterized as local minima by harmonic vibrational frequency analysis at the same theoretical level after optimization. The polarizable continuum model28 was employed to take the effect of solvent (water) into account. Binding energies were calculated to evaluate the binding strength between a ZiF-8 unit (a HMeIM coordinated with a

zinc atom) and various molecules and ions. Here, binding strength is defined as the difference between the zero-pointcorrected energies of a complex and separate ZiF-8 and molecule/ion entities. The counterpoise procedure,29 where the whole basis set was used for the subunit energy calculations to eliminate the basis set superposition error (BSSE) effect.30 All calculations were carried out using the GAUSSIAN 09 software package.31 Dimensional plots of molecular structures were generated with GaussView.32

RESULTS AND DISCUSSION Synthesis and characterization of Fe3O4 SPs@ZIF-8/Zn2+. A general scheme for the preparation of Fe3O4 SPs@ZIF8/Zn2+ and the MSPE process is illustrated in Scheme 1. Fe3O4 nanoparticles were highly monodispersed with a mean diameter of 6.2 ± 0.3 nm (Figure 1a; Figure S3). The Fe3O4 SPs were synthesized using a modified oil-in-water microemulsion assembly method to obtain a superparticle average diameter of 140 ± 30 nm (Figure 1b). Subsequently, PVP was introduced to maintain the stability of Fe3O4 SPs and to facilitate the growth of MOF shells33. Each Fe3O4 nanoparticle within a Fe3O4 SP was precisely arranged in close proximity to neighboring nanoparticles, resulting in a perfect superlattice with a face-centered cubic structure. Cross fringes in the [011] projection gave an angle of 70.5° (Figure 1c). Finally, the Fe3O4 SPs were embedded as the cores in coreshell composite structures. A ~170 nm thick ZIF-8 crystal served as the shell (Figure 1d; Figure S4). The as-synthesized Fe3O4 SPs@ZIF-8 particles were then exposed to a high concentration of zinc ion, which served to expose numerous under-coordinated zinc sites for the chelation of DA. The crystalline structure of our Fe3O4 SPs@ZIF-8/Zn2+ particles was determined by the XRD diffractogram shown in Figure 1e. Peaks corresponding to Fe3O4 SPs@ZIF-8/Zn2+ and their relative intensities are in good accordance with those observed with Fe3O4 (JCPDS card 19-0629) and the overall pattern is characteristic of ZIF-8, which indicates the successful fabrication of as-prepared product. The FTIR spectra of Fe3O4 SPs@ZIF-8/Zn2+ particles (Figure S5) contained several peaks consistent with ZIF-8. Peaks at 2923 and 3134 cm-1 correspond to aromatic and methyl C-H stretching vibrations, respectively. Other characteristic peaks between 995 and 1307 cm-1 and at 1417 cm-1 are related to plane bending and stretching of the imidazole ring, respectively. A peak corresponding to the Zn-N stretching vibration can be observed at 416 cm-1. The magnetic hysteresis loops in Figure S6 show that both Fe3O4 SPs@ZIF-8/Zn2+ and Fe3O4 were superparamagnetic materials. At room temperature, the saturation magnetization of Fe3O4 SPs@ZIF-8/Zn2+ particles was as high as 45.7 emu g1. These particles could be collected within 30 s by an external magnetic field and quickly redispersed by slightly shaking (Figure S6, inset). The good dispersibility and magnetic response of Fe3O4 SPs@ZIF-8/Zn2+ particles make them suitable for use as an MSPE sorbent. The elemental composition and valence states of asprepared Fe3O4 SPs@ZIF-8 were measured by X-ray photoelectron spectroscopy (XPS). XPS spectra of two kinds of magnetic particles (Figure 1f) indicated the presence of carbon, nitrogen, oxygen, iron, and zinc species. An increase



in zinc content, from 6.92% in Fe3O4 SPs@ZIF-8 to 11.74% in Fe3O4 SPs@ZIF-8/Zn2+, indicates the adsorption and immobilization of zinc on the surface of ZIF-8 crystals. Zinc ion on the surface of Fe3O4 SPs@ZIF-8/Zn2+ should interact strongly with the carboxyl group in DA. Nitrogen adsorption-desorption isotherms (Figure 1g) were obtained at 77K. Isotherms of Fe3O4 SPs@ZIF-8/Zn2+ indicated Type-I behavior. The BET surface area of Fe3O4 SPs@ZIF-8/Zn2+ was large (459.6 m2 g-1) with a mean pore volume of 0.499 m3 g-1. The pore diameter was between 1.00 and 1.23 nm (Figure 1g, inset), which approximates the cage size (1.16 nm) of a ZIF-8 crystal.34

Figure 1. (a) TEM micrographs show the monodispersity of synthesized Fe3O4 nanoparticles. Scale bar: 100 nm. (b) TEM micrograph of Fe3O4 SPs made from monodispersed gold nanoparticles with an average diameter of ≈6.2 nm. Scale bar: 100 nm. (c) TEM micrograph of a Fe3O4 SPs viewed along the [011] zone axis. Scale bar: 100 nm. (d) TEM images of Fe3O4 SPs@ZIF-8/Zn2+, scale bars: 500 nm. (e) XRD patterns of Fe3O4 SPs@ZIF-8 and Fe3O4 SPs@ZIF-8/Zn2+, the standard diffraction lines of Fe3O4 (JCPDS card 19-629) and simulated pattern of the published ZIF-8 structure data; (f) XPS profiles of Fe3O4 SPs@ZIF-8, Fe3O4 SPs@ZIF-8/Zn2+ particles. (g) N2 adsorption-desorption isotherms of Fe3O4 SPs@ZIF-8 and Fe3O4 SPs@ZIF-8/Zn2+ particles and the pore size distribution (inset image). Effect of solution pH. The pH of the sample solution can affect the electrostatic interaction and chelation between an adsorbent and a target. Electrostatic interactions between DA and Fe3O4 SPs@ZIF-8/Zn2+ particles, and coordination reactions between Zn2+ on the particle surface and carboxylic acid groups on DA, can strongly influence the efficiency of DA adsorption. As shown in Figure S2, the structure of DA contains three carboxylic acid moieties (pKa 1.85, 4.47, and 4.75) and a secondary amine moiety (pKa 10.60).35 Thus, the

Page 4 of 8

charge state of DA is undoubtedly affected by the pH of the surrounding solution. Sample pH was adjusted between pH 4.0 and 10.0 and optimized for maximum DA adsorption. The data in Figure S7a show that the recovery of DA increased significantly with increasing pH from 4.0 to 6.0 and then decreased sharply from pH 6.0 to 10.0. Thus, maximum recovery was observed at a sample pH of 6.0. Generally, a pHsensitive molecule will be mostly deprotonated when the solution pH is higher than its pKa. Therefore, in an acidic solution, DA likely exists in its protonated and neutral form. In such a state, there would be little to no electrostatic attraction between DA and Zn2+ cations on the sorbent surface, resulting in very little adsorption and a low extraction efficiency. With increasing pH, deprotonated sites on DA are able to chelate Zn2+ cations on the surface of Fe3O4 SPs@ZIF-8/Zn2+, resulting in a greater degree of adsorption and higher extraction efficiency. The gradual decline in recovery at pH > 6.0 may be the result of decreasing positive charge on the sorbent surface. Given these data, a sample pH of 6.0 was used in all further experiments. Other potential factors, including the amount of sorbent material, the time allowed for adsorption and desorption, and the composition and volume of the eluent were also optimized for DA detection and recovery (Figure S7). The MSPE conditions were as follows: amount of sorbent, 1.0 mg; extraction time, 4.0 min; desorption time, 1 min; and desorption solvent, 0.4 mL of aqueous histidine (3 mmol L-1). Reproducibility of Fe3O4 SPs@ZIF-8/Zn2+ particles. To estimate the reproducibility of Fe3O4 SPs@ZIF-8/Zn2+ synthesis and performance, five batches of particles were made using the method described above. For each batch, 1.0 mg of Fe3O4 SPs@ZIF-8/Zn2+ particles was added to 20 mL of shellfish sample that had been spiked with DA (250 pg mL-1). MSPE was then performed using the optimal conditions described above. The results are presented in Figure S8. The Fe3O4 SPs@ZIF-8/Zn2+ particles exhibited excellent reproducibility and a batch-to-batch relative standard deviation (RSD) of 3.6% (n = 5). Furthermore, the data in Figure S9 show that the recovery of DA remained nearly unchanged after four cycles of reuse, indicating high degrees of stability and recyclability. Development of quantitative method. The standard curve generated with DA standard solutions between 1.0 and 1000.0 pg mL-1 was linear (line equation, y = 114.79x + 376.42) with a correlation coefficient approaching unity (r2 = 0.9997). The LOD (S/N = 3) and limit of quantification (S/N = 10) of the method were 0.2 and 0.67 pg mL-1, respectively. Inter- and intra-day precision metrics were determined as the RSD of multiple measurements performed on the same day or over several days, respectively, calculated with DA spiked to a concentration of 50 pg mL-1. The inter-day precision was 3.4% (n = 5) while the intra-day precision was 2.4% (n = 3). These data indicate that the reproducibility of the developed method is satisfactory. Comparison of developed method with previously reported results. To evaluate the analytical performance of the developed method for the quantitation of DA in marine organisms, a comprehensive comparison was performed with other reported methods. The data in Table S1 show that the developed method required a relatively small amount of


Page 5 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry sorbent material (1.0 mg) and a short pretreatment time (5 min) to obtain satisfactory recoveries. The pretreatment time of the method described herein was much shorter than those of previous studies and yielded significantly lower LODs (0.2 pg mL-1). In addition, the batch-to-batch reproducibility of Fe3O4 SPs@ZIF-8/Zn2+ is conducive to most practical applications. Overall, the developed method was shown to be simple, rapid, and highly sensitive to DA, even in complex matrices such as seafood samples.

Figure 2. (a) Schematic of the interaction between Fe3O4 SPs@ZIF-8/Zn2+ and DA molecule; (b) The performance of three magnetic particles for MSPE of DA (25 ng mL-1); (c)The ζ potential of the magnetic particles at pH=6; (d) XPS profiles of Zn2p of Fe3O4 SPs@ZIF-8, Fe3O4 SPs@ZIF-8/Zn2+ before and after Fe3O4 SPs@ZIF-8/Zn2+ adsorption of DA. Mechanism analysis. We hypothesize that positively charged zinc sites on the surface of Fe3O4 SPs@ZIF-8/Zn2+ particles interact strongly, via electrostatics and/or chelation reactions, with the nitrogen atoms and negatively charged oxygen atoms of DA (Figure 2a). This hypothesis is supported by three empirical observations. First, the recovery of DA was significantly higher when using the Fe3O4 SPs@ZIF-8/Zn2+ particles, which contained a greater concentration of surfacelocalized zinc than the Fe3O4 or Fe3O4 SPs SPs@ZIF-8 particles (Figure 2b). Second, the role of under-coordinated zinc sites in the adsorption of DA can be estimated by examining the ζ potentials of the different particles used in this study (Figure 2c). The ζ potential of a particle is a measure of its charge distribution in solution. After being dipped in a solution containing zinc ion, the resulting Fe3O4 SPs@ZIF8/Zn2+ particles were approximately ten times more electropositive than Fe3O4 SPs@ZIF-8 particles. This change was attributed to the binding of Zn2+ ions on the surface of Fe3O4 SPs@ZIF-8. The ζ potential of Fe3O4 SPs@ZIF-8/Zn2+ dropped significantly after the introduction of DA, indicating the adsorption of numerous electronegative DA molecules onto Fe3O4 SPs@ZIF-8/Zn2+ particles. Third, shifts in the binding energy of Zn (2p) photoelectrons, shown in Figure 2d, were consistent with interactions between DA molecules and Zn2+ species. Prior to the introduction of DA, the Zn (2p) binding energies of Fe3O4 SPs@ZIF-8 and Fe3O4 SPs@ZIF8/Zn2+ were similar. However, DA adsorption shifted these

peaks from 1021.20 and 1044.20 eV to 1022.10 and 1045.00 eV, respectively. These shifts indicate a change in the local chemical environment of Zn2+ as one would expect with coordination reactions between Zn2+ and DA. Interference of matrix and ionic species. Seafood matrices are complex and contain high levels of protein, vitamins, unsaturated fatty acids, cholesterol, amino acids, and several ionic species including anions (Cl−) and cations (Na+, Ca2+, and Fe3+) that can negatively affect the extraction of DA. To estimate the effects of potentially interfering matrix components on DA analyses, the binding energies between the zinc ion and various ligands were obtained via DFT calculations. For simplicity, the matrix was divided into two parts: a carbon chain and functional groups as shown in Figure 3a (for optimized geometries see Figure S10). For potential ionic interferents, one anion (Cl−) and three cations (K+, Ca2+, and Fe3+) were taken into consideration. Carboxylate ion exhibited much higher binding energies (38.14 Kcal mol-1) with zinc than did ester groups (3.93 Kcal mol-1) or sulfhydryl groups (11.37 Kcal mol-1). Note, however, that other functional groups, such as hydroxyl groups (15.54 Kcal mol-1), peptide bonds (17.54 Kcal mol-1), and amino groups (37.15 Kcal mol-1), also exhibited relatively high binding energies. Therefore, it is reasonable to propose that DA, a small molecule with three carboxylic acid groups and one pyrrolidine group, binds strongly to the zinc ion with competitive adsorption of matrix components. Furthermore, under-coordinated zinc sites on the surface of Fe3O4 SPs@ZIF-8/Zn2+ particles may act as electropositive “shields” that help eliminate interference from cationic species via electrostatic repulsion. Chlorine is the most abundant anion in seawater. Our simulations showed that a zinc-carboxyl bond is much more stable than a zinc-chloride bond, suggesting that interference from anions is negligible.

Figure 3. (a) The DFT calculation of the binding energy between the Zn2+ ion and various molecules. (b) The interference of matrix and ionic species on the recovery. (c) HPLC chromatograms of the shellfish sample, the shellfish



sample spiked at 10.0 pg mL-1, 100.0-pg mL-1 and 500.0 pg mL-1, respectively. To empirically assess the effects of potential interferents on the extraction of DA (250 pg mL−1), the proposed method was carried out in the presence of various organic compounds, anions, and cations (Figure 3b). The data in Table S2 show that the recovery of DA was acceptable in all cases (relative error less than 10%), suggesting that DA interacts more strongly with Fe3O4 SPs@ZIF-8/Zn2+ than with any other matrix components. The proposed method was demonstrably reliable and free from the interference of common matrix and ionic species in marine organisms (Table S2). Method applications in the real sample. The pretreatment method described herein was applied to quantitative HPLCMS/MS measurements of DA levels in seafood (shellfish, sea cucumber, crayfish, and crab). The data in Table 1 show that trace levels of DA (49.2 pg mL-1) were identified in shellfish samples after undergoing the developed pretreatment. By contrast, no obvious DA was detected in crude extract that had not undergone our pretreatment process. Furthermore, four additional samples were spiked with DA at three levels: 10.0, 100.0, and 500.0 pg mL-1, respectively. The obtained recoveries ranged from 93.1 to 102.3%, indicating that the developed method is suitable for determining DA levels in seafood. The chromatograms in Figure 3c show that the analyses were not influenced by matrix interference. Table 1. Analytical results of real samples (mean ± SDa, n = 3). Sample

Shellfis h

Cucum ber fish

Crayfis h

Crab

a

DA (pg mL-1)

49.2±5. 9

N.D.b

N.D.b

N.D.b

Spikes level (pg mL-1)

Found (pg mL-1)

Recovery (%)

10.0

58.6 ± 0.5

94.5 ± 5.9

100.0

150.5 ±1.1

500.0

558.4 ± 3.8

10.0 100.0

9.6 ± 0.8 99.3 ± 1.7

500.0

509 ± 2.4

10.0 100.0

9.5 ± 0.6 98.7 ± 1.1

500.0

501 ± 2.8

10.0

9.3 ± 0.9

100.0

102.3 ± 1.5

500.0

507.1 ± 3.4

Standard deviation. b Not detected.

CONCLUSIONS

101.3± 1.2 101.8± 0.8 96.4 ± 5.7 99.3 ± 0.9 101.8± 1.8 95.1 ± 3.5 98.7 ± 0.6 100.2± 1.2 93.1 ± 5.9 102.3± 1.2 101.4± 0.8

Page 6 of 8

Postsynthetic-modified Fe3O4 SPs@ZIF-8 particles were employed as a sorbent material for MSPE. The presence of under-coordinated Zn2+ on the ZIF-8 surface resulted in a high binding capacity for DA. Fe3O4 SPs@ZIF-8/Zn2+ particles were easily dispersed in aqueous solutions and could be quickly separated by magnetic extraction. The entire pretreatment process required only 5 min. MSPE incorporating Fe3O4 SPs@ZIF-8/Zn2+ particles was demonstrably free of matrix interference from organic compounds, anions, and cations at concentrations typical of real samples. When combined with HPLC-MS/MS analysis, the developed pretreatment method was highly efficient, and exhibited high sensitivity and satisfactory recoveries. Thus, the developed method is potentially applicable to DA analyses in real seafood samples.

ASSOCIATED CONTENT Supporting Information The structure of ZIF-8 and domoic acid, the particle size distribution of Fe3O4, SEM image, FTIR spectra and Hysteresis loops, Factors affecting the extraction efficiency, Reproducibility and Recyclability of the adsorbent, Optimized geometries for DFT, Comparison of different methods and the interference of potential matrix and ions are shown in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected]. Phone: +86-591-22866135. Email: [email protected]. Phone: +86-10-82362042 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by the 1,000 Young Talents Program, the National Science Foundation of China Grant Nos. 21827807, 21621062, 21635002, 21575028, 21605022 and the Chinese Academy of Sciences. The Program for Changjiang Scholar and Innovative Research Team in University (No. IRT15R11), China.

REFERENCES (1) Buck, K.; Uttalcooke, L.; Pilskaln, C.; Roelke, D.; Villac, M.; Fryxell, G.; Cifuentes, L.; Chavez, F. Autecology of the diatom Pseudonitzschia australis, a domoic acid producer, from Monterey Bay, California. Mar. Ecol. Prog. 1992, 84, 293-302. (2) He, Y.; Fekete, A.; Chen, G.; Harir, M.; Zhang, L.; Tong, P.; Schmittkopplin, P. Analytical approaches for an important shellfish poisoning agent: domoic Acid. J. Agric. Food Chem. 2010, 58, 11525-11533. (3) Debonnel, G.; Beauchesne, L.; De, M. C. Domoic acid, the alleged "mussel toxin," might produce its neurotoxic effect through kainate receptor activation: an electrophysiological study in the dorsal hippocampus. Can. J. Physiol. Pharmacol. 1989, 67, 29-33. (4) Jeffery, B.; Barlow, T.; Moizer, K.; Paul, S.; Boyle, C.


Page 7 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry Amnesic shellfish poison. Food Chem. Toxicol. 2004, 42, 545557. (5) Egmond, H. V.; Apeldoorn, M. V.; Speijers, G. Amnesic shellfish poisoning (ASP). Food and Agriculture Organization of the United Nations: Rome, 2004. (6) Regueiro, J.; Álvarez, G.; Mauriz, A.; Blanco, J. High throughput analysis of amnesic shellfish poisoning toxins in bivalve molluscs by dispersive solid-phase extraction and high-performance liquid chromatography using a monolithic column. Food Chem. 2011, 127, 1884-1891. (7) Yu, F. Y.; Liu, B. H.; Wu, T. S.; Chi, T. F.; Su, M. C. Development of a sensitive enzyme-linked immunosorbent assay for the determination of domoic Acid in shellfish. J Agric. Food Chem. 2004, 52, 5334-5339. (8) Top, H. J. V. D.; Elliott, C. T.; Haughey, S. A.; Vilariño, N.; Egmond, H. P. V.; Botana, L. M.; Campbell, K.; Chem, A. Surface plasmon resonance biosensor screening method for paralytic shellfish poisoning toxins: a pilot interlaboratory study. Anal. Chem. 2011, 83, 4206-4213. (9) Nettleton, J. A.; Exler, J. Nutrients in Wild and Farmed Fish and Shellfish. J. Food Sci. 1992, 57, 257–260. (10) Mahaffey, K. R. Fish and shellfish as dietary sources of methylmercury and the ω-3 fatty acids, eicosahexaenoic acid and docosahexaenoic acid: risks and benefits. Environ. Res. 2004, 95, 414-428. (11) Zhang, Q.; Li, G.; Xiao, X.; Zhan, S.; Cao, Y. Efficient and Selective Enrichment of Ultratrace Cytokinins in Plant Samples by Magnetic Perhydroxy-Cucurbit[8]uril Microspheres. Anal. Chem. 2016, 88, 4055-4062. (12) Zhou, L.; Hu, Y.; Li, G. Conjugated Microporous Polymers with Built-in Magnetic Nanoparticles for Excellent Enrichment of Trace Hydroxylated Polycyclic Aromatic Hydrocarbons in Human Urine. Anal. Chem. 2016, 88, 69306938. (13) Gu, Z. Y.; Yang, C. X.; Chang, N.; Yan, X. P. Metalorganic frameworks for analytical chemistry: from sample collection to chromatographic separation. Acc. Chem. Res. 2012, 45, 734-745. (14) Liu, Y.; Gao, Z.; Wu, R.; Wang, Z.; Chen, X.; Chan, T. D. Magnetic porous carbon derived from a bimetallic metalorganic framework for magnetic solid-phase extraction of organochlorine pesticides from drinking and environmental water samples. J. Chromatogr. A 2017, 1479, 55-61. (15) Ma, J.; Wu, G.; Li, S.; Tan, W.; Wang, X.; Li, J.; Chen, L. Magnetic solid-phase extraction of heterocyclic pesticides in environmental water samples using metal-organic frameworks coupled to high performance liquid chromatography determination. J. Chromatogr. A 2018, 1553, 57-66. (16) Chen, X.; Ding, N.; Zang, H.; Yeung, H.; Zhao, R. S.; Cheng, C.; Liu, J.; Chan, T. W. Fe3O4@MOF core-shell magnetic microspheres for magnetic solid-phase extraction of polychlorinated biphenyls from environmental water samples. J. Chromatogr. A 2013, 1304, 241-245. (17) Wang, B.; Côté, A. P.; Furukawa, H.; O'Keeffe, M.; Yaghi, O. M. Colossal cages in zeolitic imidazolate frameworks as selective carbon dioxide reservoirs. Nature 2008, 453, 207.

(18) Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O'Keeffe, M.; Yaghi, O. M. High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture. Science 2008, 319, 939-943. (19) Zheng, J.; Lin, Z.; Lin, G.; Yang, H.; Zhang, L. Preparation of magnetic metal-organic framework nanocomposites for highly specific separation of histidine-rich proteins. J. Mater. Chem. B 2015, 3, 2185-2191. (20) Chang, N.; Gu, Z. Y.; Yan, X. P. Zeolitic imidazolate framework-8 nanocrystal coated capillary for molecular sieving of branched alkanes from linear alkanes along with high-resolution chromatographic separation of linear alkanes. J. Am. Chem. Soc. 2010, 132, 13645-13647. (21) Yang, X. Q.; Yang, C. X.; Yan, X. P. Zeolite imidazolate framework-8 as sorbent for on-line solid-phase extraction coupled with high-performance liquid chromatography for the determination of tetracyclines in water and milk samples. J. Chromatogr. A 2013, 1304, 28-33. (22) Zhao, M.; Deng, C.; Zhang, X. The design and synthesis of a hydrophilic core-shell-shell structured magnetic metalorganic framework as a novel immobilized metal ion affinity platform for phosphoproteome research. Chem. Commun. 2014, 50, 6228-6231. (23) Kida, K.; Okita, M.; Fujita, K.; Tanaka, S.; Miyake, Y. Formation of high crystalline ZIF-8 in an aqueous solution. CrystEngComm 2013, 15, 1794-1801. (24) Pan, Y.; Liu, Y.; Zeng, G.; Zhao, L.; Lai, Z. Rapid synthesis of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals in an aqueous system. Chem. Commun. 2011, 47, 2071-2073. (25) Tanabe, K. K.; Cohen, S. M. Postsynthetic modification of metal–organic frameworks—a progress report. Chem. Soc. Rev. 2011, 40, 498-519. (26) Lynch, J.; Zhuang, J.; Wang, T.; LaMontagne, D.; Wu, H.; Cao, Y. C. Gas-Bubble Effects on the Formation of Colloidal Iron Oxide Nanocrystals. J. Am. Chem. Soc. 2011, 133, 1266412674. (27) Zhao, Y.; Truhlar, D. G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215-241. (28) Tomasi, J.; Mennucci, B.; Cammi, R. Quantum Mechanical Continuum Solvation Models. Chem. Rev. 2005, 105, 2999-3094. (29) Boys, S. F.; Bernardi, F. The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol. Phys. 1970, 19, 553-566. (30) Alkorta, I.; Elguero, J. Theoretical Study of Strong Hydrogen Bonds between Neutral Molecules: The Case of Amine Oxides and Phosphine Oxides as Hydrogen Bond Acceptors. J. Phys. Chem. A 1999, 103, 272-279. (31) Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.; Cheeseman, J.; Scalmani, G.; Barone, V.; Mennucci, B.;



Petersson, G. Gaussian 09, Revision B. 01, Gaussian. Inc., Wallingford, CT 2010. (32) Dennington, R.; Keith, T.; Millam, J. GaussView, version 5. Semichem Inc., Shawnee Mission, KS 2009. (33) Qiao, X.; Su, B.; Liu, C.; Song, Q.; Luo, D.; Mo, G.; Wang, T. Selective Surface Enhanced Raman Scattering for Quantitative Detection of Lung Cancer Biomarkers in Superparticle@MOF Structure. Adv. Mater. 2018, 30, 1702275.

Page 8 of 8

(34) Schejn, A.; Balan, L.; Falk, V.; Aranda, L.; Medjahdi, G.; Schneider, R. Controlling ZIF-8 nano- and microcrystal formation and reactivity through zinc salt variations. CrystEngComm 2014, 16, 4493-4500. (35) Janos, W. A. NMR study of the protonation of domoic acid. Can. J. Chem. 1992, 70, 1156-1161.

Table of contents


Effective Extraction of Domoic Acid from Seafood Based on

Recommend Documents