Bio‐Inspired Photonic‐Crystal Microchip for Fluorescent Ultratrace Detection

Ultratrace detection attracts great interest because it is still a challenge to the early diagnosis and drug testing. Enriching the targets from highly diluted solutions to the sensitive area is a promising method. Inspired by the fog‐collecting structure on Stenocara beetle’s back, a photonic‐crystal (PC) microchip with hydrophilic–hydrophobic micropattern was fabricated by inkjet printing. This device was used to realize high‐sensitive ultratrace detection of fluorescence analytes and fluorophore‐based assays. Coupled with the fluorescence enhancement effect of a PC, detection down to 10^?16 mol L^?1 was achieved. This design can be combined with biophotonic devices for the detection of drugs, diseases, and pollutions of the ecosystem.     

Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble’s surface temperature between 21–135 °C and its encapsulated water temperature between 21–74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12‐fold superior reaction rate constant for methylene blue degradation than at room temperature.     

Development of a microchip‐pulsed electrochemical method for rapid determination of L‐DOPA and tyrosine in Mucuna pruriens

L ‐3,4‐dihydroxyphenylalanine (L‐DOPA) is a well‐recognized therapeutic compound to Parkinson's disease. Tyrosine is a precursor for the biosynthesis of L‐DOPA, both of which are widely found in traditional medicinal material, Mucuna pruriens. In this paper, we described a validated novel analytical method based on microchip capillary electrophoresis with pulsed electrochemical detection for the simultaneous measurement of L‐DOPA and tyrosine in M. pruriens. This protocol adopted end‐channel amperometric detection using platinum disk electrode on a homemade glass/polydimethylsiloxane electrophoresis microchip. The background buffer consisted of 10 mM borate (pH 9.5) and 0.02 mM cetyltrimethylammonium bromide, which can produce an effective resolution for the two analytes. In the optimal condition, sufficient electrophoretic separation and sensitive detection for the target analytes can be realized within 60 s. Both tyrosine and L‐DOPA yielded linear response in the concentration range of 5.0–400 μM (R² > 0.99), and the LOD were 0.79 and 1.1 μM, respectively. The accuracy and precision of the established method were favorable. The present method shows several merits such as facile apparatus, high speed, low cost and minimal pollution, and provides a means for the pharmacologically active ingredients assay in M. pruriens.     

Simultaneous Determination of Ranitidine and Metronidazole at Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

Single‐walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs‐film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10^?8 mol L^?1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10^?8 mol L^?1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.     

Etching of gold nanorods: The effects of diameter on analytical performances

Gold nanorods (GNRs) have been well employed for sensing/bio-sensing based on analytes modulated morphology or self-assembly states. Herein, we employed H₂O₂ based etching system (H₂O₂ molecules themselves and H₂O₂-Fe²⁺ Fenton reagents) as an example to study the diameters of GNRs on the analytical performances, for the colorimetric platforms using GNRs as reporters. We have found that the thinner GNRs possess a higher sensitivity; while the thicker ones bring more abound color presentation during the etching processes, which is especially for naked eye detection. In addition, a red shift of the plasmonic bands is observed for three kinds of thinner GNRs at the initial stage of the etching reaction, and the mechanism is also discussed.     

Stability indicating liquid chromatographic method for simultaneous quantification of betamethasone valerate and tazarotene in in vitro and ex vivo studies of complex nanoformulation

Low‐potency corticosteroid betamethasone valerate and vitamin‐A tazarotene are used in combination for effective treatment of psoriasis. There is no robust high‐performance liquid chromatography analytical technique available for simultaneous estimation of betamethasone valerate and tazarotene in conventional and nanocarriers based formulations. A simple, accurate, robust isocratic high‐performance liquid chromatography method was developed for simultaneous estimation of betamethasone valerate and tazarotene in topical pharmaceutical formulations. The developed method was validated as per the regulatory guidelines. The validated method was linear over the concentration range of 150–6000 ng/mL (r² > 0.999) at 239 nm wavelength. Limits of detection and quantification of two analytes were 50 and 150 ng/mL, respectively. The %relative standard deviation for intraday and interday precision was less than 2%. The method was also evaluated in the presence of forced degradation conditions. The developed method was successfully applied for in vitro and ex vivo drug release studies of in‐house designed nanoformulations.     

Label‐Free Detection of Glycan–Protein Interactions for Array Development by Surface‐Enhanced Raman Spectroscopy (SERS)

A glyco‐array platform has been developed, in which glycans are attached to plasmonic nanoparticles through strain‐promoted azide‐alkyne cycloaddition. Glycan–protein binding events can then be detected in a label‐free manner employing surface‐enhanced Raman spectroscopy (SERS). As proof of concept, we have analyzed the binding of Gal1, Gal3, and influenza hemagglutinins (HAs) to various glycans and demonstrated that binding partners can be identified with high confidence. The attraction of SERS for optical sensing is that it can provide unique spectral signatures for glycan–protein complexes, confirm identity through statistical validation, and minimizes false positive results common to indirect methods. Furthermore, SERS is very sensitive and has multiplexing capabilities thereby allowing the simultaneous detection of multiple analytes.     

Nano‐structured gemini‐based supramolecular solvent for the microextraction of cyhalothrin and fenvalerate

A novel supramolecular solvent‐based microextraction followed by high‐performance liquid chromatography with ultraviolet detection method has been developed for the extraction and determination of two pyrethroid analytes, cyhalothrin and fenvalerate, in water and soil samples. The liquid–liquid‐phase separation of surfactants has been used in analytical extraction. The surfactant‐rich phase is a nano‐structured liquid, recently named as a supramolecular solvent, generated from the amphiphiles. The alkyl carboxylic acid based supramolecular solvents were introduced before. Coacervates made up of gemini surfactant, consisting of two amphiphilic moieties, were first used as solvent. The effective parameters on extraction (i.e., type of organic solvent, the amount of surfactant and volume of tetrahydrofuran, sample solution pH, salt addition, ultrasonic and centrifugation time) were investigated and optimized. Under the optimum conditions, preconcentration factors of 110 and 145 were obtained for the analytes. The linearity was 0.5–200.0 μg/L with the correlation of determination of (R²) ≥ 0.9984. The limit of detection of the method was (S/N = 3) 0.2 μg/L, and precisions in the range of 6.3–10.3% (RSDs, n = 5) were obtained. This method has been successfully applied to analyze real samples, and good recoveries in the range of 101.2–108.8% were obtained.     

Ultrasensitive high‐performance liquid chromatography determination of tetracycline antibiotics and their 4‐epimer derivatives based on dual effect of methanesulfonic acid

In reversed‐phase liquid chromatography, tetracycline antibiotics yield broad and asymmetrical peaks, as a result of their ionic interaction with the anionic free silanol groups and metal ion present in the silica‐based stationary phases (commonly derivatized with C18 groups). These frequently encountered difficulties were absolutely eliminated based on dual effect when methanesulfonic acid was employed as an eluent additive. The study revealed that the performance of methanesulfonic acid to minimize the “silanol effect” is mainly explained by both direct neutralization of the anionic silanol sites and electrostatic attraction with analytes. Based on these dual action mechanisms, an ultrasensitive method has been successfully developed for the simultaneous determination of tetracycline antibiotics and their derivatives (minocycline, oxytetracycline, tetracycline, chlortetracycline, metacycline, doxycycline, 4‐epitetracycline, and 4‐epichlortetracycline) in bovine milk with convenient ultraviolet detection within 15 min. Under the optimal conditions, the calibration curves showed good linearity (r² > 0.999) for all analytes in the range of 1～200 ng/mL with the instrument limits of detection as low as 0.3 ng/mL. The study sheds new light on suitable additives to analyze basic compounds with the advantage of good compatibility with MS detection.     

Comparative Study of the Determination of Parabens in Shampoos by Liquid Chromatography with Amperometric and Coulometric Detection

The simultaneous determination of four para‐hydroxybenzoic acid esters (parabens) in shampoos was studied by liquid chromatography (LC) with amperometric (LC‐AD) and coulometric (LC‐CD) detection. The parabens were separated on an ODS C18 reversed column by isocratic elution with a mobile phase based on methanol‐0.1 M acetic acid (60 : 40%, v/v) with 0.02 M NaClO₄ at a flow rate of 0.8 mL min^?1. The limit of detection (S/N>3) for the analytes was in the 15–25 pg (injected mass) range at an applied potential of 1.20 V vs. Ag/AgCl using the LC‐AD and in the 2–3 pg range at a potential of 0.790 V vs. Pd using the LC‐CD. The peak ratio of the internal standard peak (IS: 4‐hydroxybenzoic acid sec‐butyl ester) versus the analyte peak was found to be related to the amount injected from 0.1 ng to 100ng (r=0.996–0.999) with the LC‐AD and from 0.050 ng to 100 ng range (r=0.999–1.000) with the LC‐CD. The relative standard deviation (RSD, n=10) was comprised between 1.8 to 3.5% by LC‐AD ( 5 ng injected) and between 2.0 to 2.4% by LC‐CD (0.5 ng injected). The determination of four most used parabens in ten different shampoos was successfully realized.     

Combination of a sub‐3 μm superficially porous particle packed column with charged aerosol detection for the simple and sensitive measurement of nine macrolides in human urine

Due to the lack of chromophores in many macrolides, analytical methods based on mass spectrometry and electrochemical detection coupled to liquid chromatography have been suggested to be suitable for the quantification of macrolides in complex matrices. In this study, a simple and sensitive analytical method was established for the simultaneous measurement of nine macrolides in human urine by combining a sub‐3 μm superficially porous particle packed column with charged aerosol detection. After thorough investigation of various sample preparation methods, including two liquid–liquid extraction methods and four solid‐phase extraction methods, HLB solid‐phase extraction was selected and further optimized. Absolute recovery of the optimized sample preparation method ranged from 99.5–110.2%, indicating its very high extraction/clean‐up efficiency. For chromatography, parameters influencing macrolide separation were systematically optimized, and the resulting conditions allowed baseline separation of nine macrolides within 24 min using a very simple mobile phase. The established method was validated for linearity, limit of detection, limit of quantification, absolute recovery, and precision. Based on its limit of detection (0.025–0.100 μg/mL), the method had similar or greater sensitivity than most methods based on electrochemical detection. It was found that the current method was appropriate for application to real human urine samples after drug administration.     

Development of a sensitive LC‐MS/MS method for simultaneous quantification of eleven constituents in rat serum and its application to a pharmacokinetic study of a Chinese medicine Shengmai injection

A sensitive LC‐MS/MS method was developed and validated for simultaneous quantification of 11 constituents, ginsenoside Rg1, Re, Rf, Rg2, Rb1, Rd, Rc, ophiopogonin D, schisandrin, schisandrol B and schizandrin B, in rat serum using digoxin as the internal standard (IS). The serum samples were pretreated and extracted with a two‐step liquid–liquid extraction. Chromatographic separation was achieved on a C₁₈ analytical column with a proper gradient elution using 0.02% acetic acid aqueous solution and 0.02% acetic acid–acetonitrile as mobile phase at a flow rate of 0.5 mL/min. MS detection was performed using multiple reaction monitoring via an electrospray ionization source. Good linearity was observed in the validated concentration range for every analyte (r² ≥0.9929), and the lower limits of quantitation of the analytes were in the range of 0.044–1.190 ng/mL in rat serum. Intra‐ and inter‐day precisions were <14.2%. The accuracy expressed as recovery was within the range of 85.1–112.8%. The extraction recoveries were >75.8%.The validated method was successfully applied to a pharmacokinetic study of all analytes in rats after single intravenous administration of Shengmai injection. Copyright © 2014 John Wiley & Sons, Ltd.     

Residual detection of naproxen,methyltestosterone and 17α‐hydroxyprogesterone caproate in aquatic products by simple liquid–liquid extraction method coupled with liquid chromatography–tandem mass spectrometry

In the present study, we aimed to develop a reliable screening method based on liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) for the detection and quantification of naproxen, methyltestosterone and 17α‐hydroxyprogesterone caproate residues. The target analytes were extracted from samples of eel, flatfish and shrimp using acetonitrile with 1% acetic acid, followed by liquid–liquid purification with n‐hexane. Chromatographic separation was achieved on a reversed‐phase analytical column using 0.1% formic acid containing 10 mm ammonium formate in distilled water (A) and methanol (B) as mobile phases. All the matrix‐matched calibration curves were linear (R² ≥ 0.99) over the concentration range of the tested analytes. Recovery at three spiking levels (0.005, 0.01 and 0.02 mg/kg) ranged from 68 to 117% with intra‐ and inter‐day precisions <10%. Five market samples for each matrix (eel, flatfish and shrimp) were collected and tested for method application. In summary, the proposed method is feasible to screen and quantify the analytes with high selectivity in aquatic food products meant for human consumption.     

Cetyl‐alcohol‐reinforced hollow fiber solid/liquid‐phase microextraction and HPLC–DAD analysis of ezetimibe and simvastatin in human plasma and urine

A new cetyl‐alcohol‐reinforced hollow fiber solid/liquid‐phase microextraction (CA–HF–SLPME) followed by high‐performance liquid chromatography–diode array detection (HPLC–DAD) method was developed for simultaneous determination of ezetimibe and simvastatin in human plasma and urine samples. To prepare the CA–HF–SLPME device, the cetyl‐alcohol was immobilized into the pores of a 2.5 cm hollow fiber micro‐tube and the lumen of the micro‐tube was filled with 1‐octanol with the two ends sealed. Afterwards, the prepared device was introduced into 10 mL of the sample solution containing the analytes with agitation. Under optimized conditions, calibration curves plotted in spiked plasma and urine samples were linear in the ranges of 0.363–25/0.49–25 μg L^?1 for ezetimibe/simvastatin and 0.193–25/0.312–25 μg L^?1 for ezetimibe/simvastatin in plasma and urine samples, respectively. The limit of detection was 0.109/0.174 μg L^?1 for ezetimibe/simvastatin in plasma and 0.058/0.093 μg L^?1 for ezetimibe/simvastatin in urine. As a potential application, the proposed method was applied to determine the concentration of selected analytes in patient plasma and urine samples after medication and satisfactory results were achieved. In comparison with reference methods, the CA–HF–SLPME–HPLC–DAD method demonstrates considerable potential in the biopharmaceutical analysis of selected drugs.     

HPLC determination of γ‐aminobutyric acid and its analogs in human serum using precolumn fluorescence labeling with 4‐(carbazole‐9‐yl)‐benzyl chloroformate

In this study, a simple analytical method for the determination of γ‐aminobutyric acid, gabapentin, and baclofen by using high‐performance liquid chromatography with fluorescence detection was developed. An amidogen‐reactive fluorescence labeling reagent, 4‐(carbazole‐9‐yl)‐benzyl chloroformate was first used to sensitively label these analytes. The completed labeling of these analytes can be finished rapidly only within 5 min at the room temperature (25°C) to form 4‐(carbazole‐9‐yl)‐benzyl chloroformate labeled fluorescence derivatives. These labeled derivatives expressed strong fluorescence property with the maximum excitation and emission wavelengths of 280 and 380 nm, respectively. The labeled derivatives were analyzed using a reversed‐phase Eclipse SB‐C18 column within 10 min with satisfactory shapes. Excellent linearity (R² > 0.995) for all analytes was achieved with the limits of detection and the limits of quantitation in the range of 0.25?0.35 and 0.70?1.10 μg/L, respectively. The proposed method was used for the simultaneous determination of γ‐aminobutyric acid and its analogs in human serum with satisfactory recoveries in the range of 94.5–97.5%.     

Ultrafast capillary electrophoresis method for the simultaneous determination of ammonium and diphenhydramine in pharmaceutical samples

Ammonium and diphenhydramine are active ingredients commonly found in the same pharmaceutical preparations. We report, for the first time, a sub‐minute method for the simultaneous determination of ammonium and diphenhydramine. The method is based on capillary electrophoresis with capacitively coupled contactless conductivity detection. Both analytes can be quantified in a single run (∼80 injections/h) using 30 mmol/L 2‐(N‐morpholino)ethanesulfonic acid and 15 mmol/L lithium hydroxide (pH 6.0) as background electrolyte. The separation by capillary electrophoresis was achieved on a fused‐silica capillary (50 cm total length, 10 cm effective length, and 50 μm inside diameter). The limits of detection were 0.04 and 0.02 mmol/L for ammonium and diphenhydramine, respectively. The proposed method also provided adequate recovery values for spiked samples (100–106 and 97–104% for ammonium and diphenhydramine, respectively). The results obtained with the new capillary electrophoresis method were compared with those of the high‐performance liquid chromatography method for diphenhydramine and the Kjeldahl method for ammonium and no statistically significant differences were found (95% confidence level).     

Dispersive solid-phase extraction combined with dispersive liquid-liquid microextraction for the determination of polybrominated diphenyl ethers in plastic bottled beverage by GC-MS

A simple, inexpensive and reliable analytical method was developed for the determination of polybrominated diphenyl ethers (PBDEs) in polyethylene terephthalate (PET) bottled beverage using GC‐MS. The sample pretreatment using dispersive solid‐phase extraction (DSPE) for removing matrix and dispersive liquid–liquid microextraction (DLLME) for enriching analytes was performed. For the DSPE, different sorbents such as primary amine, secondary amine, C₁₈ and graphitized carbon black were tested for different sample matrices. By means of DSPE, 60–89% of the sample matrices could be removed. Acetonitrile solution obtained by DSPE cleanup was directly used as the dispersant for the subsequent DLLME, which made the combination of the DSPE with the DLLME much more straightforward. Under the optimal conditions, the enrichment factors (EFs) of PBDEs ranged from 199 to 292. Using matrix‐matched calibration, correlation coefficients above 0.994 were found and LODs ranged from 0.0023 to 0.15 μg/L. The recoveries were between 80 and 117% for beverages spiked at three different concentrations (1.0, 5.0 and 10 μg/L) with RSDs ranging from 3.7 to 14.7% (n=5). The results indicated that the combination of DSPE with DLLME was a powerful sample preparation tool for analysis of ultratrace analytes in complicated matrices.     

A paper‐based gas sensor for simultaneous noninstrumental colorimetric detection of nitrite and sulfide in waters

The use of paper‐based devices in combination with noninstrumental detection systems is becoming increasingly important in the analytical field due to its simplicity, rapidity, and low cost. However, their use for determination of volatile analyte derivatives is still relatively scarce. The present work reports on the assessment of a paper‐based gas‐sensing approach for the simultaneous noninstrumental colorimetric detection of nitrite and sulfide. Colorimetric systems based on the Griess and methylene blue assays, formation of colored metallic sulfides, and interaction/reaction with in situ generated metallic nanoparticles were preliminary evaluated. Then, the effect of experimental variables affecting the analytical performance of the paper‐based gas sensor was studied with two digitization systems, namely a scanner and a smartphone. Under optimal conditions, the developed system yielded limits of detection of 0.055 and 0.005 mg/L for nitrite and sulfide, respectively. The repeatability, expressed as relative standard deviation, was found to be 5.9 and 6.7% for nitrite and sulfide, respectively. The proposed method was finally applied to the analysis of water samples, showing recoveries in the range of 95–105%.     

Ultratrace Osmium,Ruthenium and Lead in Airborne Particulate Matter: Peak Area as Instrumental Datum to Improve Their Simultaneous Voltammetric Determination

Peak area as instrumental datum for determining the concentration of metals in solution instead of peak height is proposed for the simultaneous voltammetric determination in particulate matter of ultratrace Os(VIII), Ru(III) and Pb(II), species linked to vehicle emissions. In the case of species present at ultratrace concentration level or having low reversibility degree of the electrodic processes, the employment of peak area, instead of peak current, permits to achieve limits of detection lower even more of one order of magnitude. The method is based on the catalytic current of the Os(VIII)‐, Ru(III)‐ and Pb(II)‐bromate system by differential pulse voltammetry. 0.3 mol L^?1 acetate buffer pH 4.5+6.9×10^?2 mol L^?1 NaBrO₃+2.3×10^?4 mol L^?1 EDTA‐Na₂ was employed as the supporting electrolyte. For all the elements, the accuracy, expressed as relative error e%, and the precision, expressed as relative standard deviation s_r%, were satisfactory being lower than 6 %. To better validate the analytical procedure, a comparison with spectroscopic (electrothermal atomic absorption spectroscopy, ET‐AAS) is also reported.     

A sensitive and efficient method for trace analysis of some phenolic compounds using simultaneous derivatization and air‐assisted liquid–liquid microextraction from human urine and plasma samples followed by gas chromatography–nitrogen phosphorous detection

In present study, a simultaneous derivatization and air‐assisted liquid–liquid microextraction method combined with gas chromatography–nitrogen phosphorous detection has been developed for the determination of some phenolic compounds in biological samples. The analytes are derivatized and extracted simultaneously by a fast reaction with 1‐flouro‐2,4‐dinitrobenzene under mild conditions. Under optimal conditions low limits of detection in the range of 0.05–0.34 ng mL^?1 are achievable. The obtained extraction recoveries are between 84 and 97% and the relative standard deviations are less than 7.2% for intraday (n = 6) and interday (n = 4) precisions. The proposed method was demonstrated to be a simple and efficient method for the analysis of phenols in biological samples. Copyright © 2015 John Wiley & Sons, Ltd.