Ion‐pair cloud‐point extraction: A new method for the determination of water‐soluble vitamins in plasma and urine

A novel, simple, and effective ion‐pair cloud‐point extraction coupled with a gradient high‐performance liquid chromatography method was developed for determination of thiamine (vitamin B₁), niacinamide (vitamin B₃), pyridoxine (vitamin B₆), and riboflavin (vitamin B₂) in plasma and urine samples. The extraction and separation of vitamins were achieved based on an ion‐pair formation approach between these ionizable analytes and 1‐heptanesulfonic acid sodium salt as an ion‐pairing agent. Influential variables on the ion‐pair cloud‐point extraction efficiency, such as the ion‐pairing agent concentration, ionic strength, pH, volume of Triton X‐100, extraction temperature, and incubation time have been fully evaluated and optimized. Water‐soluble vitamins were successfully extracted by 1‐heptanesulfonic acid sodium salt (0.2% w/v) as ion‐pairing agent with Triton X‐100 (4% w/v) as surfactant phase at 50°C for 10 min. The calibration curves showed good linearity (r² > 0.9916) and precision in the concentration ranges of 1‐50 μg/mL for thiamine and niacinamide, 5–100 μg/mL for pyridoxine, and 0.5–20 μg/mL for riboflavin. The recoveries were in the range of 78.0–88.0% with relative standard deviations ranging from 6.2 to 8.2%.     

Residue determination of glyphosate in environmental water samples with high-performance liquid chromatography and UV detection after derivatization with 4-chloro-3,5-dinitrobenzotrifluoride

A pre-column derivatization high-performance liquid chromatographic method for glyphosate analysis has been developed. Derivatization of glyphosate was performed with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF). In pH 9.5 H₃BO₃-Na₂B₄O₇ media, the reaction of glyphosate with CNBF completed at 60 °C for 30 min. The labeled glyphosate was separated on a Kromasil C18 column (250 mm × 4.6 mm, 5 μm) at room temperature and UV detection was applied at 360 nm. The separation of labeled glyphosate was achieved within 15 min by gradient elution mode. Compared to other pre-column derivatization, this derivatization was performed more mildly, the derivative was more stable, and the detection limits of a few reagents were higher than CNBF, except 9-fluorenylmethyl chloroformate (FMOC-Cl) using fluorescence and mass spectrometry, however, this reagent avoid to be removed after derivatization like FMOC-Cl. The detection limit of glyphosate was 0.009 mg L⁻¹ (S/N = 3) without preconcentration and reach MRL, which is set at the level of 0.1 mg L⁻¹ in China. The method linearity correlation coefficient was 0.9999, in concentrations ranging from 0.3 to 48.5 mg L⁻¹. The proposed method has been applied to the quantitative determination of glyphosate in environmental water with recoveries of 91.80-100.20% and R.S.D. of 2.27-6.80, depending on the sample investigated.     

Fe3O4 nanoparticles coated with polyhedral oligomeric silsesquioxanes and β‐cyclodextrin for magnetic solid‐phase extraction of carbaryl and carbofuran

In this study, porous sandwich structure Fe₃O₄ nanoparticles coated by polyhedral oligomeric silsesquioxanes and β‐cyclodextrin were prepared by surface polymerization and were used as the magnetic solid phase extraction adsorbent for the extraction and determination of carbaryl and carbofuran. The Fe₃O₄ nanoparticles coated with polyhedral oligomeric silsesquioxanes and β‐cyclodextrin were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, vibrating sample magnetometry, and scanning electron microscopy. After optimizing the extraction conditions, a method that combined magnetic solid phase extraction with high‐performance liquid chromatography was developed for the determination of carbaryl and carbofuran in apple. The method exhibited a good linearity in the range of 2–400 μg/kg for carbaryl and carbofuran (R² = 0.9995), respectively. The limits of detection were 0.5 μg/kg of carbaryl and 0.7 μg/kg for carbofuran in apple, respectively. Extraction recoveries ranged from 94.2 to 103.1% with the preconcentration factor of 300 and the relative standard deviations were less than 5.9%. These results indicated that the method combined magnetic solid phase extraction with high‐performance liquid chromatography and was promising for the determination of carbaryl and carbofuran at trace amounts.     

Sulfonated poly(styrene‐divinylbenzene) modified with amines and the application for pipette‐tip solid‐phase extraction of carbendazim in apples

Sulfonated poly(styrene‐divinylbenzene) modified with five kinds of amine functional groups was applied to the determination of carbendazim in apple samples with a pipette‐tip solid‐phase extraction method. The structures of the polymers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Five different modifications of the solid‐phase extraction sorbent based on sulfonated poly(styrene‐divinylbenzene) were tested under static and pipette‐tip solid‐phase extraction conditions. The polymer modified with p‐methoxyaniline showed the best recognition capacity and adsorption amount for carbendazim. Under the optimum conditions, 3.00 mg of the adsorbent, 1.00 mL of ethyl acetate as washing solvent, and 1.00 mL of ammonia/acetonitrile (5:95, v/v) as elution solvent were used in the pretreatment procedure of apple samples. The calibration graphs of carbendazim in methanol were linear over 5.00–200.00 μg/mL, and the limits of detection and quantification were 0.01 and 0.03 μg/mL, respectively. The method recoveries of carbendazim were in the range of 91.31–98.13% with associated intraday relative standard deviations of 0.76–2.13% and interday relative standard deviations of 1.10–1.85%. Sulfonated poly(styrene‐divinylbenzene) modified with p‐methoxyaniline showed satisfactory results (recovery: 97.96%) and potential for the rapid purification of carbendazim in apple samples combined with the pipette‐tip solid‐phase extraction.     

Determination of Fluorescent Whitening Agents in Infant Clothes and Paper Materials by Ion‐Pair Chromatography and Fluorescence Detection

A simple and rapid method was developed to simultaneously determine four stilbene‐type disulfonate and one distyrylbiphenyl‐type fluorescent whitening agents (FWAs) in infant clothes and paper materials by ion‐pair chromatography. FWAs were extracted from cloth and papers samples using a hot‐water extraction. The aqueous extract was then mixed with ion‐pair reagent, extracted with C₁₈‐SPE cartridges and eluted with methanol. The contents of FWAs were determined by an isocratic ion‐pair chromatography with RP‐C₁₈ column and equipped with fluorescence detection. Limits of quantitation were 0.04 to 0.45 ng/g in 10 g of samples. Recovery of FWAs in spiked infant cloth and paper samples was between 76 to 92% and precision (RSD) ranging from 2.0 to 4.0%. Analysis of three infant clothes and six paper materials found concentrations of selected FWAs ranging between n.d. to 24 μg/g and n.d. to 3.8 μg/g, respectively.     

Immunosensors Based on Layer‐by‐Layer Self‐Assembled Au Colloidal Electrode for the Electrochemical Detection of Antigen

Colloidal Au particles have been deposited on the gold electrode through layer‐by‐layer self‐assembly using cysteamine as cross‐linkers. Self‐assembly of colloidal Au on the gold electrode resulted in an easier attachment of antibody, larger electrode surface and ideal electrode behavior. The redox reactions of [Fe(CN)₆]^4?/[Fe(CN)₆]^3? on the gold surface were blocked due to antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.0 with various concentrations of antigen at 37 °C for 30 min. Further, an amplification strategy to use biotin conjugated antibody was introduced for improving the sensitivity of impedance measurements. Thus, the sensor based on this immobilization method exhibits a large linear dynamic range, from 5–400 μg/L for detection of Human IgG. The detection limit is about 0.5 μg/L.     

Determination of Cyanuric Acid in Milk Powder and Swimming Pool Water by Ion‐pair Reversed‐phase Liquid Chromatography

An ion‐pair reversed‐phase high‐performance liquid chromatographic method, using tetrabutylammonium bromide (TBAB) as ion‐pair reagent, has been developed for the analysis of cyanuric acid (CA) in milk powder and swimming pool water. It was found that the effect of the concentrations of ion‐pair reagent on the retention of cyanuric acid was different for standard solution and different real samples. The separation was carried out on a reversed‐phase C₁₈ column with 85:15 (V/V) water‐acetonitrile (ACN) containing different concentration of TBAB as mobile phase for different samples. The linear range of the calibration curve for CA was 0.1–100 mg·L^?1. The detection limits calculated at S/N=3 was 0.11 mg·L^?1 for the analysis of milk powder and 0.31 mg·L^?1 for the analysis of swimming pool water, respectively. The method was successfully applied to the analysis of CA in milk powder and swimming pool water.     

A new solid-phase extraction and HPLC method for determination of patulin in apple products and hawthorn juice in China

A new solid‐phase extraction (SPE) pretreatment method using a home‐made polyvinylpolypyrrolidone‐florisil (PVPP‐F) column was developed for the analysis of patulin in apple and hawthorn products in China. Fifty samples (25 apple juices, 12 apple jams, and 13 hawthorn juices) were prepared using the new method and then analyzed by high performance liquid chromatography with diode array detection (HPLC‐DAD) on an Agela Venusil MP C₁₈ reversed‐phase column (4.6 mm × 250 mm, 5 μm). The cleanup results for all samples using home‐made PVPP‐F column were compared with those obtained using a MycoSep®228 AflaPat column. The correlation coefficient R (0.9998) fulfilled the requirement of linearity for patulin in the concentration range of 2.5–250 μg/kg. The limits of detection (LODs) and quantification (LOQs) of patulin were 3.99 and 9.64 μg/kg for PVPP‐F column, and 3.56 and 8.07 μg/kg for MycoSep®228 AflaPat column, respectively. Samples were spiked with patulin at levels ranging from 25 to 250 μg/kg, and recoveries using PVPP‐F and MycoSep®228 AflaPat columns were in the range of 81.9–100.9% and 86.4–103.9%, respectively. Naturally occurring patulin was found in 2 of 25 apple juice samples (8.0%) and 1 of 13 hawthorn juice samples (7.7%) at concentrations ranging from 12.26 to 36.81 μg/kg. The positive results were further confirmed by liquid chromatography electrospray ionization mass spectrometry (LC‐ESI‐MS).     

Temperature‐controlled ionic liquid dispersive liquid‐phase microextraction combined with HPLC with ultraviolet detector for the determination of fungicides

Present study described a simple, environmental benign, easy to operate, and determination method for fungicides including thiram, metalaxyl, diethofencarb, myclobutanil, and tebuconazole. The method is based on temperature‐controlled ionic liquid dispersive liquid phase microextraction coupled to HPLC with ultraviolet detector. In the enrichment procedure, ionic liquid 1‐octyl‐3‐methylimidazolium hexafluorophosphate [C₈MIM][PF₆] was used as the extraction solvent. Variable affecting parameters such as the volume of [C₈MIM][PF₆], temperature, extraction time, centrifuging time, and salting‐out effect have been optimized in detail. Under the optimal conditions, this method has been found to have good linear relationship in the concentration range of 1.0–100 μg/L and excellent detection sensitivity with LODs (S/N = 3) in the range of 0.32–0.79 μg/L. Precisions of proposed method were in the range of 3.7–5.9% for intraday and 7.8–11.0% for interday (RSDs, n = 6). The proposed method was used for the analysis of real water samples and good spiked recoveries at two different spiked levels were achieved in the range of 84.6–102%.     

Monodisperse silica nanoparticles coated with gold nanoparticles as a sorbent for the extraction of phenol and dihydroxybenzenes from water samples based on dispersive micro‐solid‐phase extraction: Response surface methodology

A selective and sensitive method was developed based on dispersive micro‐solid‐phase extraction for the extraction of hydroquinone, resorcinol, pyrocatechol and phenol from water samples prior to high‐performance liquid chromatography with UV detection. SiO₂, SiO₂@MPTES, and SiO₂@MPTES@Au nanoparticles (MPTES = 3‐mercaptopropyltriethoxysilane) were synthesized and characterized by scanning electronic microscopy, thermogravimetric analysis, differential thermogravimetric analysis, and infrared spectroscopy. Variables such as the amount of sorbent (mg), pH and ionic strength of sample the solution, the volume of eluent solvent (μL), vortex and ultrasonic times (min) were investigated by Plackett–Burman design. The significant variables optimized by a Box–Behnken design were combined by a desirability function. Under optimized conditions, the calibration graphs of phenol and dihydroxybenzenes were linear in a concentration range of 1–500 μg/L, and with correlation coefficients more than 0.995. The limits of detection for hydroquinone, resorcinol, pyrocatechol, and phenol were 0.54, 0.58, 0.46, and 1.24 μg/L, and the limits of quantification were 1.81, 1.93, 1.54, and 4.23 μg/L, respectively. This procedure was successfully employed to determine target analytes in spiked water samples; the relative mean recoveries ranged from 93.5 to 98.9%.     

Vortex‐ and CO2‐gas‐assisted liquid–liquid microextraction with salt addition for the high‐performance liquid chromatographic determination of furanic compounds in concentrated juices and dried fruits

A novel microextraction method based on vortex‐ and CO₂‐assisted liquid–liquid microextraction with salt addition for the isolation of furanic compounds (5‐hydroxymethyl‐2‐furaldehyde, 5‐methyl‐2‐furaldehyde, 2‐furaldehyde, 3‐furaldehyde, 2‐furoic and 3‐furoic acids) was developed. Purging the sample with CO₂ was applied after vortexing to enhance the phase separation and mass transfer of the analytes. The optimum extraction conditions were: extraction solvent (volume), propyl acetate (125 μL); sample pH, 2.4; vortexing time, 45 s; salt concentration, 25% w/v and purging time, 5 min. The analytes were separated using an ODS Hypersil C₁₈ column (250×4.6 mm i.d, 5 μm) under gradient flow. The proposed method showed good linearities (r² >0.999), low detection limits (0.08–1.9 μg/L) and good recoveries (80.7–122%). The validated method was successfully applied for the determination of the furanic compounds in concentrated juice (mango, date, orange, pomegranate, roselle, mangosteen and soursop) and dried fruit (prune, date and apricot paste) samples.     

The determination of capreomycin in human plasma by LC–MS/MS using ion‐pairing chromatography and solid‐phase extraction

A bioanalytical method was developed and validated for the quantification of capreomycin (Cm) analogs, Cm IA and Cm IB, in human plasma. This implemented ion‐pairing solid phase extraction, followed by ion‐pairing high‐performance liquid chromatography, with tandem mass spectrometry detection. Chromatographic separation was achieved using a Discovery C₁₈, 5 μm, 4.6 × 50 mm analytical column. An isocratic mobile phase consisting of water and acetonitrile with 0.1% formic acid and 4mm heptafluorobutyric acid (80:20; v/v) was used at a flow‐rate of 500 μL/min. An AB Sciex API 3000 mass spectrometer at unit resolution, in multiple reaction monitoring mode, was used for detection. Electrospray ionization was used for ion production. The method was successfully validated for the range 469–30,000 ng/mL for Cm IA and for Cm IB, with cefotaxime as the internal standard. The within‐ and between‐day precision determinations for Cm IA and IB, expressed as the percentage coefficient of variation, were < 20.0% at the lower limit of quantification (LLOQ) and < 8.2% at all other test concentrations. Recovery of both analogs was > 72.3% and reproducible at the low, medium and high end of the calibration range. No significant matrix effects were observed for the analyte. The assay performed well when applied to clinical samples generated from children in a clinical multidrug resistant tuberculosis research study in South Africa.     

Capillary electrophoresis‐laser‐induced fluorescence detection of rat brain catecholamines with microwave‐assisted derivatization

In this study, a rapid and sensitive method is described for the catecholamines detection in rat brain. CE with LIF detection for the determination of FITC derivatized catecholamines (dopamine, epinephrine, and norepinephrine) was demonstrated. Conventional water bath and microwave‐assisted derivatization methods were employed and a significant reduction in the derivatization time from 2 h for the conventional water bath at room temperature (ca. 25°C) to 2 min for the microwave‐assisted derivatization was achieved. Online sample concentration of field‐amplified sample stacking (FASS) method was employed to achieve higher sensitivities (the detection limits obtained in the normal injection mode ranged from 2.6 to 4.5 ng L^?1 and in the FASS mode ranged from 22 to 34 pg L^?1). Furthermore, this microwave‐assisted derivatization CE–LIF method successfully determined catecholamines in rat brain with as low as 100 ng L^?1 (FASS mode) to 10 μg L^?1 (normal injection mode). This CE–LIF method provided better detection ability when compared to the best reports on catecholamines analyses.     

A fast and accurate isotope dilution GC‐IT‐MS/MS method for determination of eugenol in different tissues of fish: Application to a depletion study in mandarin fish

An accurate, rapid and effective method was established for determination of eugenol in plasma, muscle, skin, liver, kidney and gill of fish using gas chromatography–ion trap tandem mass spectrometry. Samples of muscle, skin, liver, kidney and gill were prepared using the modified QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure, and a plasma sample was prepared by a liquid–liquid extraction procedure. Eugenol was monitored in <7 min using an electron‐ionization source in MS/MS mode and quantified by an internal standard of eugenol‐d₃. The limit of detection was 5.0 μg/kg, and the limit of quantification was 10.0 μg/kg. The calibration curve was linear in the range of 5–1000 μg/L (R² = 0.9996). Intra‐ and inter‐day precisions of eugenol expressed as relative standard deviation were within 9.74%, and the accuracy exhibited a relative error ranging from −2.20 to 8.89%. The developed method was successfully used to study the elimination regularity of eugenol in mandarin fish.     

Quantitation and pharmacokinetics of 1,4‐diamino‐2,3‐dicyano‐1,4‐bis (2‐aminophenylthio) butadiene (U0126) in rat plasma by liquid chromatography‐tandem mass spectrometry

A simple, robust, and rapid LC‐MS/MS method was developed for the quantitation of U0126 and validated in rat plasma. Plasma samples (20 μL) were deproteinized using 200 μL ACN containing 30 ng/mL of chlorpropamide, internal standard. Chromatographic separation performed on an Agilent Poroshell 120 EC‐C₁₈ column (4.6 × 50 mm, 2.7 μm particle size) with an isocratic mobile phase consisting of a 70:30 v/v mixture of ACN and 0.1% aqueous formic acid. Each sample was run at 0.6 mL/min for a total run time of 2 min per sample. Detection and quantification were performed using a mass spectrometer in selected reaction‐monitoring mode with positive ESI at m/z 381 → 123.9 for U0126 and m/z 277 → 175 for the internal standard. The standard curve was linear over a concentration range of 20–5000 ng/mL with correlation coefficients greater than 0.9965. Precision, both intra‐ and interday, was less than 10.1% with an accuracy of 90.7–99.4%. No matrix effects were observed. U0126 in rat plasma degraded approximately 41.3% after 3‐h storage at room temperature. To prevent degradation, sample handling should be on an ice bath and all solutions kept at 4°C. This method was successfully applied to a pharmacokinetic study of U0126 at various doses in rats.     

Determination of neonicotinoid insecticides in environmental samples by micellar electrokinetic chromatography using solid‐phase treatments

A sensitive and reliable method based on MEKC has been developed and validated for trace determination of neonicotinoid insecticides (thiamethoxam, acetamiprid, and imidacloprid) and the metabolite 6‐chloronicotinic acid in water and soil matrices. Optimum separation of the neonicotinoid insecticides was obtained on a 58 cm long capillary (75 μm id) using as the running electrolyte 40 mM SDS, 5 mM borate (pH 10.4), and 5% (v/v) methanol at a temperature of 25°C, a voltage of 25 kV and with hydrodynamic injection (10 s). The analysis time was less than 7 min. Prior to MEKC determination, the samples were purified and enriched by carrying out extraction‐preconcentration steps. For aqueous samples, off‐line SPE with a sorptive material such as Strata‐X (polymeric hydrophobic sorbent) and octadecylsilane (C₁₈) was carried out to clean up and preconcentrate the insecticides. However, for soil samples, matrix solid‐phase dispersion (MSPD) was applied with C₁₈ used as the dispersant. Good linearity, accuracy, and precision were obtained and the detection limits were in the range between 0.01 and 0.07 μg mL^?1 for river water and 0.17 and 0.37 μg g^?1 for soil samples. Recovery levels reached greater than 92% for all of the assayed neonicotinoids in river water samples with Strata‐X. In soil matrices, the best recoveries (63–99%) were obtained with MSPD.     

A rapid and sensitive LC–MS/MS method for quantification of quercetin‐3‐O‐β‐d‐glucopyranosyl‐7‐O‐β‐d‐gentiobioside in plasma and its application to a pharmacokinetic study

A rapid and sensitive LC–MS/MS method with good accuracy and precision was developed and validated for the pharmacokinetic study of quercetin‐3‐O‐β‐d ‐glucopyranosyl‐7‐O‐β‐d ‐gentiobioside (QGG) in Sprague–Dawley rats. Plasma samples were simply precipitated by methanol and then analyzed by LC–MS/MS. A Venusil® ASB C₁₈ column (2.1 × 50 mm, i.d. 5 μm) was used for separation, with methanol–water (50:50, v/v) as the mobile phase at a flow rate of 300 μL/min. The optimized mass transition ion‐pairs (m/z) for quantitation were 787.3/301.3 for QGG, and 725.3/293.3 for internal standard. The linear range was 7.32–1830 ng/mL with an average correlation coefficient of 0.9992, and the limit of quantification was 7.32 ng/mL. The intra‐ and inter‐day precision and accuracy were less than ±15%. At low, medium and high quality control concentrations, the recovery and matrix effect of the analyte and IS were in the range of 89.06–92.43 and 88.58–97.62%, respectively. The method was applied for the pharmacokinetic study of QGG in Sprague–Dawley rats. Copyright © 2016 John Wiley & Sons, Ltd.     

An HPLC‐UV method for determining plasma dimethylacetamide concentrations in patients receiving intravenous busulfan

Dimethylacetamide (DMA) is a solvent used in the preparation of intravenous busulfan, an alkylating agent used in blood or marrow transplantation. DMA may contribute to hepatic toxicity, so it is important to monitor its clearance. The aim of this study was to develop an HPLC‐UV assay for measurement of DMA in human plasma. After precipitation of plasma proteins with acetonitrile followed by dilution (1:4) with water, the extract was injected onto the HPLC and detected at 195 nm. Separation was performed using a Cogent‐HPS 5 μm C₁₈ column (250 × 4.6 mm) preceded by a Brownlee 7 μm RP₁₈, pre‐column (1.5 cm × 3.2 mm). The mobile phase was 25 mm sodium phosphate buffer (pH 3), containing 2.5% (v /v) acetonitrile and 0.0005% (v /v) sodium‐octyl‐sulfonate. Using a flow rate of 1 mL/min, the retention times of DMA and the internal standard (IS), 2‐chloroacetamide, were 9.5 and 3.5 min, respectively. Peak area ratio (DMA:IS) was a linear function of concentration from 1 to 1000 μg/mL. There was excellent intraday precision (<5% for 5–700 μg/mL DMA), accuracy (<3% deviation from the true concentration) and recovery (74–98%). The limits of detection and quantification were 1 and 5 μg/mL, respectively. In eight children who received intravenous busulfan, DMA concentrations ranged from 110 to 438 μg/mL.     

Study of immobilized metal affinity chromatography sorbents for the analysis of peptides by on‐line solid‐phase extraction capillary electrophoresis‐mass spectrometry

Several commercial immobilized metal affinity chromatography sorbents were evaluated in this study for the analysis of two small peptide fragments of the amyloid β‐protein (Aβ) (Aβ(1–15) and Aβ(10–20) peptides) by on‐line immobilized metal affinity SPE‐CE (IMA‐SPE‐CE). The performance of a nickel metal ion (Ni(II)) sorbent based on nitrilotriacetic acid as a chelating agent was significantly better than two copper metal ion (Cu(II)) sorbents based on iminodiacetic acid. A BGE of 25 mM phosphate (pH 7.4) and an eluent of 50 mM imidazole (in BGE) yielded a 25‐fold and 5‐fold decrease in the LODs by IMA‐SPE‐CE‐UV for Aβ(1–15) and Aβ(10–20) peptides (0.1 and 0.5 μg/mL, respectively) with regard to CE‐UV (2.5 μg/mL for both peptides). The phosphate BGE was also used in IMA‐SPE‐CE‐MS, but the eluent needed to be substituted by a 0.5% HAc v/v solution. Under optimum preconcentration and detection conditions, reproducibility of peak areas and migration times was acceptable (23.2 and 12.0%RSD, respectively). The method was more sensitive for Aβ(10–20) peptide, which could be detected until 0.25 μg/mL. Linearity for Aβ(10–20) peptide was good in a narrow concentration range (0.25–2.5 μg/mL, R² = 0.93). Lastly, the potential of the optimized Ni(II)‐IMA‐SPE‐CE‐MS method for the analysis of amyloid peptides in biological fluids was evaluated by analyzing spiked plasma and serum samples.     

Chaotropic‐Anion‐Induced Supramolecular Self‐Assembly of Ionic Polymeric Micelles

Traditional micelle self‐assembly is driven by the association of hydrophobic segments of amphiphilic molecules forming distinctive core–shell nanostructures in water. Here we report a surprising chaotropic‐anion‐induced micellization of cationic ammonium‐containing block copolymers. The resulting micelle nanoparticle consists of a large number of ion pairs (≈60 000) in each hydrophobic core. Unlike chaotropic anions (e.g. ClO₄^?), kosmotropic anions (e.g. SO₄^2?) were not able to induce micelle formation. A positive cooperativity was observed during micellization, for which only a three‐fold increase in ClO₄^? concentration was necessary for micelle formation, similar to our previously reported ultra‐pH‐responsive behavior. This unique ion‐pair‐containing micelle provides a useful model system to study the complex interplay of noncovalent interactions (e.g. electrostatic, van der Waals, and hydrophobic forces) during micelle self‐assembly.