Recent advances and applications of molecularly imprinted polymers in solid-phase extraction for real sample analysis.

Sample pretreatment is essential for the analysis of complicated real samples due to their complex matrices and low analyte concentrations. Among all sample pretreatment methods, solid-phase extraction is arguably the most frequently used one. However, the majority of available solid-phase extraction adsorbents suffer from limited selectivity. Molecularly imprinted polymers are a type of tailor-made artificial antibodies and receptors with specific recognition sites for target molecules. Using molecularly imprinted polymers instead of conventional adsorbents can greatly improve the selectivity of solid-phase extraction, and therefore molecularly imprinted polymer-based solid-phase extraction has been widely applied to separation, clean up and/or preconcentration of target analytes in various kinds of real samples. In this article, after a brief introduction, the recent developments and applications of molecularly imprinted polymer-based solid-phase extraction for determination of different analytes in complicated real samples during the 2015-2020 are reviewed systematically, including the solid-phase extraction modes, molecularly imprinted adsorbent types and their preparations, and the practical applications of solid-phase extraction to various real samples (environmental, food, biological, and pharmaceutical samples). Finally, the challenges and opportunities of using molecularly imprinted polymer-based solid-phase extraction for real sample analysis are discussed.

N-Doped graphene-supported PdCu nanoalloy as efficient catalyst for reducing Cr(vi) by formic acid.

Reducing Cr(vi) to Cr(iii) with formic acid is desirable for environmental protection, but the sluggish kinetics limits its practical application, which currently motivates the intensive study of efficient catalysts for this redox reaction. Here bimetallic PdCu nanoalloy (∼5 nm in size) supported by N-doped graphene was synthesized through a one-pot hydrothermal process. The catalytic activity of PdCu nanoalloy highly depends on the Pd/Cu atomic ratio and N-doped graphene support. The obtained Pd6Cu4/NG shows superior catalysis towards the Cr(vi) reduction by formic acid with a high kinetic constant (kn = 23.2 min-1 mg-1) and a low activation energy (Ea = 34.9 kJ mol-1). Active H atoms were found to be the exact reductant for the Cr(vi) reduction, quite different from the reported H2-reduction route. The enhanced catalysis originates from the electronic and geometric modification of active Pd after formation of PdCu alloy. Electron transfer from Cu to Pd enhances the electron density of Pd atoms, which favors the adsorption of the bridging formate intermediate and subsequent generation of active H atoms over PdCu/NG. The catalyst can be recycled five times without obvious loss of activity. Our work provides an example to explore the alloying effect on the catalytic behavior of PdCu alloy, which may shed light on developing other advanced nanoalloys for Cr(vi) reduction.

Advances in MXene-based luminescence sensing strategies.

MXenes have attracted the attention of many researchers as one of the latest two-dimensional (2D) materials over the last decade. Their great potential for biosensing has also been fully exploited after the discovery of their unique properties such as superior optical properties, excellent hydrophilicity, good thermal stability, excellent mechanical property, high electrical conductivity, biocompatibility, large surface area, and ease of surface functionalization. In the MXene-based luminescence sensing strategy, MXenes typically appear in the form of nanosheets, quantum dots and modified MXene nanocomposites, and they are utilized as different sensing platforms or as a luminescence source. In this review, we focused on the MXene-based luminescence sensing strategies, including fluorescence, electrochemiluminescence and chemiluminescence sensors and the comparison of their performance. Finally, the perspectives of the MXene-based luminescence sensors are discussed.

Size-controllable synthesis of large-size spherical 3D covalent organic frameworks as efficient on-line solid-phase extraction sorbents coupled to HPLC.

BACKGROUND: Covalent organic frameworks (COFs) have found promising applications in separation fields due to their large surface area and high adsorption capacity, but the exiting COFs can not be directly used as the packing materials of on-line solid-phase extraction (SPE) coupled to HPLC and HPLC because their nano/submicron size or irregular shapes might cause ultrahigh column back pressure and low column efficiency. To synthesize the large-size spherical COFs larger than 3 µm as sorbents might be able to address these problems, however it is still a great challenge till now. RESULTS: In this work, two large-size spherical 3D COFs (COF-320 and COF-300) were size-controllably synthesized within 10-90 µm via a two-step strategy. These two spherical COFs showed large surface area, fine crystallinity, good chemical/mechanical stability, and good reproducibility. As an application case, when used as the on-line SPE sorbents coupled to HPLC, the large-size spherical COF-320 displayed high binding capacity for bisphenol F (Qmax of 452.49 mg/g), low column back pressure (6-8 psi at flow rate of 1 mL/min), and good reusability (at least 30 cycles). The developed on-line-SPE-HPLC-UV method presented good analytical performance with enrichment factor of 667 folds, linear range of 1.0-400 ng/mL, limit of detection (LOD, S/N = 3) of 0.3 ng/mL, limit of quantification (LOQ, S/N = 10) of 1.0 ng/mL, and recoveries of 100.3-103.2 % (RSDs of 2.0-3.5 %) and 95.2-97.0 % (RSDs of 4.3-5.6 %) for tap water and lake water samples, respectively. SIGNIFICANCE: This is the first case to synthesize the large-size spherical COFs within 10-90 µm, and this work made it possible to directly use COFs as the filling materials of on-line SPE coupled to HPLC and HPLC. The developed analytical method can be potentially applied to the rapid and sensitive detection of trace bisphenol F in environmental water samples.

Large-size porous spherical 3D covalent organic framework for preconcentration of bisphenol F in water samples and orange juice.

Large-size spherical sorbents with particle size of 10-50 µm are widely applied in separation fields, however it is still a great challenge to synthesize such large-size spherical covalent organic framework (COF). In this work, a type of large-size porous 3D COF was size-controablly synthesized via a two-step strategy, in which a large-size porous 3D spherical polymer was prepared first through a Pickering emulsion polymerization using nano silica as the stabilizer, and subsequently it was converted into porous spherical 3D COF by a solvothermal method. The as-prepared porous spherical COF (COF-320 as a model) showed size-controllable uniform spherical morphology within 15-45 µm, large specific surface area, fine crystalline structure, and good chemical stability. When used as the sorbent for dispersive solid-phase extraction (d-SPE) of bisphenol F (BPF), the porous spherical COF-320 (15 µm) displayed high adsorption capacity (Qmax = 335.6 mg/g), high enrichment factor (80 folds), and good reusability (at least five cycles). By coupling the d-SPE method to HPLC, a new analytical approach was developed and successfully applied to the determination of trace BPF in two water samples, an orange juice and a standard sample with recoveries of 96.0-102.2 % (RSD = 1.1-1.5 %), 95.7-97.4 % (RSD = 1.4-4.4 %) and 98.7 % (RSD = 2.3 %), respectively. The limit of detection (S/N = 3) and limit of quantification (S/N = 10) were 0.1 and 0.3 ng/mL, respectively. The new synthesis strategy opens a viable way to prepare large-size porous spherical COFs, and the developed analytical method can be potentially applied to sensitively detect the trace BPF in water samples and beverages.

Sustainable triethylenetetramine modified sulfonated graphene oxide/chitosan composite for enhanced adsorption of Pb(II), Cd(II), and Ni(II) ions.

A novel sulfonated group and triethylenetetramine modified GO/chitosan (GO-CS) adsorbent (T-SGO-CS) was successfully prepared and utilized for the adsorption of heavy metal ions from single-metal, binary-metal, and ternary-metal solutions. In a single system, the adsorption capacity was 312.28 mg/g for Pb2+, 260.52 mg/g for Cd2+, and 84.61 mg/g for Ni2+, whereas, Adsorption of Pb(II), Cd(II), and Ni(II) in binary and ternary systems was systematically studied. In tertiary systems, the effect of competitive adsorption was more pronounced. In addition, T-SGO-CS exhibited a high adsorption capacity and was recyclable for Pb2+, Cd2+, and Ni2+. T-SGO-CS is a novel and highly efficient adsorbent for omnidirectionally enhancing the adsorption of Pb2+, Cd2+, and Ni2+, as demonstrated by these results. Therefore, T-SGO-CS could be investigated as a potential new material for future applications in heavy metal removal.

Miniaturized electroosmotic pump capable of generating pressures of more than 1200 bar.

The pressure output of a pump cannot be increased simply by connecting several of them in series. This barrier is eliminated with the micropump developed in this work. The pump is actually an assembly of a number of fundamental pump units connected in series. The maximum pressure output of this pump assembly is directly proportional to the number of serially connected pump units. Theoretically, one can always enhance the pressure output by adding more pump units in the assembly, but in reality the upper pressure is constrained by the microtees or microunions joining the pump components. With commercially available microtees and microunions, pressures of more than 1200 bar have been achieved. We have recently experimented using open capillaries to build this pump, but many capillaries have to be utilized in parallel to produce an adequate flow to drive HPLC separations. In this paper, we synthesize polymer monoliths inside 75 µm i.d. capillaries, use these monoliths to assemble miniaturized pumps, characterize the performance of these pumps, and employ these pumps for HPLC separations of intact proteins. By tuning the experimental parameters for monolith preparations, we obtain both negatively and positively charged submicrometer capillary channels conveniently. Each monolith in a 75 µm i.d. capillary is equivalent to several thousands of open capillaries.

Flow batteries for microfluidic networks: configuring an electroosmotic pump for nonterminal positions.

A micropump provides flow and pressure for a lab-on-chip device, just as a battery supplies current and voltage for an electronic system. Numerous micropumps have been developed, but none is as versatile as a battery. One cannot easily insert a micropump into a nonterminal position of a fluidic line without affecting the rest of the fluidic system, and one cannot simply connect several micropumps in series to enhance the pressure output, etc. In this work we develop a flow battery (or pressure power supply) to address this issue. A flow battery consists of a +EOP (in which the liquid flows in the same direction as the field gradient) and a -EOP (in which the liquid flows opposite to the electric field gradient), and the outlet of the +EOP is directly connected to the inlet of the -EOP. An external high voltage is applied to this outlet-inlet joint via a short gel-filled capillary that allows ions but not bulk liquid flow, while the +EOP's inlet and the -EOP's outlet (the flow battery's inlet and outlet) are grounded. This flow battery can be deployed anywhere in a fluidic network without electrically affecting the rest of the system. Several flow batteries can be connected in series to enhance the pressure output to drive HPLC separations. In a fluidic system powered by flow batteries, a hydraulic equivalent of Ohm's law can be applied to analyze system pressures and flow rates.

Application of nanomaterials decorated with cyclodextrins as sensing elements for environment analysis.

Environmental pollution has brought adverse socio-economic consequences. Organic pollutants and heavy metals are the main culprits of environmental pollution. It is of great importance to develop novel, simple, rapid, sensitive, and low-cost detection approaches for sensing trace pollutants in environmental samples. A lot of detection strategies which are based on varieties of nanomaterials have been developed for environmental analysis in past decades. In this review, we retrospect a variety of nanomaterials decorated with cyclodextrins (CDs), including carbon nanomaterials decorated with CDs, noble metal nanomaterials decorated with CDs and other nanomaterials decorated with CDs, and their application in environmental analysis. CDs is a type of ideal modifying molecules which could recognize targets, improve the solubility and dispersibility of corresponding functionalized materials, and enhance the detecting performance of designed sensors. CDs have been widely immobilized to carbon nanomaterials, noble metal nanomaterials, phosphorene (BP) nanocomposites, metal organic framework (MOF), and magnetic nanomaterials, and these nanocomposites have been utilized as the sensing elements for different target analytes. Immobilizing CDs on different nanomaterials could extremely expand the development of new sensing systems for environmental analysis based on these materials, greatly broaden the species of sensing targets, and apparently improve their sensing performance. Herein, the nanomaterials decorated with CDs, as sensing elements for environmental analysis, were reviewed including the types of nanomaterials decorated with CDs and their applications in various sensing strategies for environmental analysis. Finally, the perspectives of the nanomaterials decorated with CDs used as sensing elements were also discussed.

Thiol/methylthio-functionalized porous aromatic frameworks for simultaneous capture of aromatic pollutants and Hg(II) from water.

Simultaneously capturing organic pollutants and heavy metal can greatly reduce the water remediation time and cost, however it is still a great challenge presently. Herein, two novel thiol/methylthio-functionalized porous aromatic frameworks were synthesized as sorbents via the Sonogashira-Hagihara reaction of 1,3,5-triethynylbenzene and 1,3,5-tris(4-bromophenyl) benzene, the subsequent chloromethylation of the phenyl rings, and the final nucleophile substitution of -Cl groups by NaSH/NaSMe. These two sorbents were characterized by FT-IR spectra, energy dispersive X-ray spectra, scanning electron microscope, nitrogen adsorption analysis, thermo-gravimetric analysis, and elemental analyses. Adsorption experiments displayed that new sorbents had high uptake abilities and fast adsorption kinetics for aromatic pollutants and mercury (II) (Hg(II)). The maximum adsorption capacity (Qmax) of toluene and m-xylene on both new sorbents were 531.9-571.4 mg/g with the kinetic binding rate constants (kobs) of 0.00276-0.02422 g/mg/min, and the Qmax values of Hg(II) were 148.1-180.3 mg/g with kobs of 0.00592-0.01573 g/mg/min. Moreover, new sorbents indicated high simultaneous uptake abilities for these pollutants with good reusability, and finally they were successfully applied to the simultaneous remediation of these pollutants in two simulated sewages with high and low concentration, indicating their great practical application potential in wastewater remediation.

Monolithic silica capillary columns with immobilized cellulose tris(3,5-dimethylphenylcarbamate) for enantiomer separations in CEC.

Two types of monolithic silica capillary columns with an immobilized cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) selector were prepared for enantiomer separations in CEC. The monolithic columns were prepared by a sol-gel process in fused-silica capillaries. CDMPC was then either immobilized on a silica monolith through an intermolecular polycondensation of the cellulose derivative containing a triethoxysilyl group, or on a vinylized silica monolith through radical copolymerization of the cellulose derivative, which also contained a vinyl group. IR spectra confirmed the successful immobilization of CDMPC on both columns. Eleven chiral compounds were used to evaluate the enantioselectivity on both column types. Results indicated that the columns obtained via polycondensation had higher separation ability than those obtained via radical polymerization, and that they showed satisfactory run-to-run repeatability and stability. These new techniques thus provide strategies for preparing immobilized polysaccharide-based chiral silica monolithic capillary columns for chiral separations by means of CEC.

Removal of pharmaceuticals by novel magnetic genipin-crosslinked chitosan/graphene oxide-SO3H composite.

A novel magnetic adsorbent genipin-crosslinked chitosan/graphene oxide-SO3H (GC/MGO-SO3H) composite was prepared and used as adsorbents of environmental pollutant. The GC/MGO-SO3H exhibit typical superparamagnetic behavior. The adsorption characteristics of GC/MGO-SO3H composite to pharmaceuticals were investigated through batch experiments. The maximum adsorption capacity of ibuprofen and tetracycline increases from 113.27 to 138.16 mg/g and 473.25 to 556.28 mg/g with the increase in temperature from 298 to 313 K. The adsorption kinetics and isotherms were investigated in detail to reveal that the kinetics and equilibrium adsorptions are well described by pseudo-second-order kinetic and Freundlich isotherm model, respectively. This study has demonstrated that the GC/MGO-SO3H composite could be utilized as an efficient and with high speed.

Monolith columns for liquid chromatographic separations of intact proteins: A review of recent advances and applications.

In this article we survey 256 references (with an emphasis on the papers published in the past decade) on monolithic columns for intact protein separation. Protein enrichment and purification are included in the broadly defined separation. After a brief introduction, we describe the types of monolithic columns and modes of chromatographic separations employed for protein separations. While the majority of the work is still in the research and development phase, papers have been published toward utilizing monolithic columns for practical applications. We survey these papers as well in this review. Characteristics of selected methods along with their pros and cons will also be discussed.

Novel porous ß-cyclodextrin/pillar[5]arene copolymer for rapid removal of organic pollutants from water.

A novel porous ß-cyclodextrin/pillar[5]arene copolymer was prepared using tetrafluoroterephthalonitrile as cross-linker for rapid removal of variety of organic pollutants. The copolymer was characterized by water contact angle, scanning electron microscope, FT-IR spectrum, solid-state 13C NMR spectrum, thermo-gravimetric analysis, nitrogen adsorption-desorption isotherms, and elemental analysis. Results showed that the co-polymer had good water immersibility, co-existing micro-/meso-pores, and a large specific surface area (BET) of 479 m2/g. The copolymer presented high adsorption capacity with the maximum adsorption capacity of 258 mg/g for bisphenol A and good reusability and reproducibility. It also showed fast binding kinetics with the apparent second-order rate constants of 0.109-0.179 g/mg·min and simultaneously rapid removal ability with removal efficiencies of 74-90% within 30 s for variety of organic pollutants. The new copolymer can be potentially used as adsorbent for rapidly removing a wide range of organic pollutants in wastewater.

Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution.

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg(2+), Cu(2+), Co(2+), and Ni(2+), exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg(2+) and Cu(2+) ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag(+) ion ranging from 1.25 x 10(-7) to 5.0 x 10(-6)molL(-1) with a detection limit of 2.0 x 10(-8)molL(-1). The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern-Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 x 10(-8) to 7.50 x 10(-7)molL(-1) for Hg(2+) ion, 3.0 x 10(-7) to 1.0 x 10(-5)molL(-1) for Ni(2+) ion, 4.59 x 10(-8) to 2.295 x 10(-6)molL(-1) for Cu(2+) ion, and 1.20 x 10(-7) to 6.0 x 10(-6)molL(-1) Co(2+) ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.

Novel microporous ß-cyclodextrin polymer as sorbent for solid-phase extraction of bisphenols in water samples and orange juice.

A new microporous ß-cyclodextrin polymer (MP-CDP) was prepared for the simultaneous solid-phase extraction (SPE) of bisphenol F (BPF), bisphenol A (BPA) and bisphenol AF (BPAF). The MP-CDP was characterized by Fourier transform infrared spectroscopy, solid-phase 13C nuclear magnetic resonance, thermo-gravimetric analysis, scanning electron microscopy, and nitrogen adsorption and desorption analysis. Results indicated that the MP-CDP had micron-level particle size, microporous structure, a high BET surface area, and a high product yield. Adsorption tests showed that the MP-CDP sorbent had high adsorption ability and fast binding kinetics for bisphenols. Moreover, the MP-CDP presented high extraction efficiencies, high enrichment factor, good reusability and good batch-to-batch reproducibility for SPE of bisphenols. Based on the MP-CDP sorbent, a SPE-HPLC-UV method was developed and successfully applied to simultaneously detect three bisphenols in water samples and orange juice with the recoveries of 95.7-106.3% (RSD = 2.0-5.2%) for BPF, 92.9-107.0% (RSD = 1.5-5.1%) for BPA, and 96.0-103.5% (RSD = 1.7-5.0%) for BPAF, respectively. The limit of detection (S/N = 3) and the limit of quantification (S/N = 10) for all bisphenols in these samples were 0.15 ng/mL and 0.5 ng/mL, respectively. The new MP-CDP can be potentially utilized as a good sorbent for simultaneous SPE of trace bisphenols in environmental water samples and beverages.

Application of molecularly imprinted polymers to solid-phase extraction of analytes from real samples.

A review is presented of recent developments in the use of molecularly imprinted polymers (MIPs) as selective materials for solid-phase extraction. Compared with traditional sorbents, MIPs can not only concentrate but also selectively separate the target analytes from real samples, which is crucial for the quantitatively determination of analytes in complex samples. Consequently, as one of the most effective sorbents, MIPs have been successfully applied to the pretreatment of analytes in foods, drugs, and biological and environmental samples in the past five years.

Dummy molecularly imprinted magnetic nanoparticles for dispersive solid-phase extraction and determination of bisphenol A in water samples and orange juice.

A novel dummy molecularly imprinted magnetic nanoparticle (MI-MNP) was prepared by a hybrid imprinting technique for dispersive solid-phase extraction (d-SPE) and determination of bisphenol A (BPA). 2,2'-Bis(4-hydroxyphenyl)-hexafluoropropane was used as the template molecule and Fe3O4 nanoparticle as the magnetic core. The MI-MNPs were characterized by FT-IR spectroscopy, thermo- gravimetric analysis, X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer. The adsorption tests showed that the MI-MNPs had a high binding ability for BPA and presented a fast binding kinetics. When used as a d-SPE sorbent, the MI-MNP showed high extraction efficiency, high enrichment factor and good reusability for BPA, and it can be easily recycled by a magnet. Furthermore, the dummy imprinting strategy can completely avoid the interference of the residual template in sorbent to determination of BPA. Using the MI-MNPs as sorbent, a d-SPE-HPLC-UV method was developed and successfully applied to the analysis of BPA spiked in water samples and orange juice and that in a certified sample with recoveries of 95.0-106.2% (RSD=2.5-4.5%), 93.3-100.0% (RSD=1.2-5.0%) and 100.3% (RSD=3.5%), respectively. The limit of detection (S/N=3) for all samples was 0.3ngmL-1. The new MI-MNPs can be utilized as a good d-SPE sorbent for BPA in environmental water samples and beverages.

Novel surface dummy molecularly imprinted silica as sorbent for solid-phase extraction of bisphenol A from water samples.

A novel surface molecularly imprinted silica composite was prepared by a dummy-template imprinting strategy for the solid-phase extraction (SPE) of bisphenol A (BPA). 2,2-Bis(4-hydroxyphenyl) hexafluoropropane (BPAF) was chosen as the template molecule, and a hybrid technique was used for imprinting procedure. The imprinted silica was characterized by FT-IR spectroscopy, scanning electron microscope, thermo-gravimetric analysis, and nitrogen adsorption-desorption isotherms. The static binding test verified that the imprinted silica had much higher recognition ability for BPA than the non-imprinted silica, and the kinetic adsorption test presented the fast binding kinetics of the surface imprinted silica for BPA. When used as a SPE sorbent, the imprinted silica showed high extraction efficiencies and high enrichment factor for BPA. Based on the imprinted silica, a SPE-HPLC-UV method was developed and successfully applied to the detection of BPA in BPA-spiked lake water, tap water and drinking water samples with a high recovery of 97.3-106.0%, a RSD of 1.2-3.8% (n=3) and a limit of detection (S/N=3) of 0.3 ng/mL. The analysis results of a certified BPA sample also demonstrated the reliability of present method. The new surface dummy molecularly imprinted silica completely avoided the interference of the residual template molecules and greatly improved the binding kinetic of the target molecules. Therefore, it can be used as a good sorbent for SPE of BPA in environmental water samples.