Standard Liquid Research Articles

Voltammetric determination of taurine in energy drinks after o-phthalaldehyde-ethanethiol derivatization

A completely new voltammetric method has been developed for quantitative determination of food additive Taurine (Tau) in energy drinks. This electroanalytical method is based on voltammetric oxidation of o-phthalaldehyde-ethanthiol derivative of Tau at glassy carbon electrode in 95% methanol containing 0.1 mol L−1 lithium perchlorate. Working conditions necessary for quantitative Tau derivatization reaction and electrochemical detection using square wave voltammetry were optimized. Linear range from 1.0 × 10−5 to 1.0 × 10−4 mol L−1 characterized by coefficient of determination 0.9998, limits of quantification 6.8 × 10−6 mol L−1 and detection 2.1 × 10−6 mol L−1 were obtained at pulse amplitude 50 mV and frequency 80 Hz. Analytical method of calibration curve was used for evaluation of Tau content in several commercially available energy drinks. The procedure was validated using standard reference high performance liquid chromatography (HPLC) method. Both methods showed nearly identical Tau content, around 0.35% (w/w). Besides its reliability to the Tau determination, that is totally comparable to reference method used, present voltammetric approach is more advantageous on the economic and simplicity basis. Finally, developed voltammetric method could find employment in food quality control.

Identification of autoinducing thiodepsipeptides from staphylococci enabled by native chemical ligation.

Staphylococci secrete autoinducing peptides (AIPs) as signalling molecules to regulate population-wide behaviour. AIPs from non-Staphylococcus aureus staphylococci have received attention as potential antivirulence agents to inhibit quorum sensing and virulence gene expression in the human pathogen Staphylococcus aureus. However, only a limited number of AIP structures from non-S. aureus staphylococci have been identified to date, as the minute amounts secreted in complex media render it difficult. Here, we report a method for the identification of AIPs by exploiting their thiolactone functionality for chemoselective trapping and enrichment of the compounds from the bacterial supernatant. Standard liquid chromatography mass spectrometry analysis, guided by genome sequencing data, then readily provides the AIP identities. Using this approach, we confirm the identity of five known AIPs and identify the AIPs of eleven non-S. aureus species, and we expect that the method should be extendable to AIP-expressing Gram-positive bacteria beyond the Staphylococcus genus.

Simulation of magnetohydrodynamics and radiative heat transport in convectively heated stratified flow of Jeffrey nanofluid

The rising requirement regarding energy worldwide necessitates that consideration be devoted to formulating and functioning thermal mechanisms and heat exchangers to utilize and resuscitate thermal energy. Hence new heat transportation liquids subjected to improved heat transport characteristics are required to rise convection heat transportation, and nanoliquids have been proved effective substitutes to standard heat transportation liquids. With such intention, here we formulated mixed convective Jeffrey nanoliquid stratified flow considering magnetohydrodynamics. Heat absorption and heat generation aspects in addition to convective conditions and thermal radiation are considered for formulation. Mathematical modeling is based on theory of boundary-layer. Ordinary systems are acquired from partial ones via implementation of apposite variables. Effectiveness of significant variables is reported through graphical outcomes. It is visualized that thermal radiation consideration corresponds to higher temperature in comparison to stratification phenomenon.

Poly(ionic-liquid) from imidazoline-functionalized siloxane prepared by simple sol-gel route for efficient quasi-solid-state DSSC

Poly(ionic-liquids) (PILs) are promising electrolyte compounds for improving the stability and durability of electrochemical devices, such as quasi-solid-state dye-sensitized solar cells (QSS-DSSCs). The present study described the preparation and characterizations of a PIL from a modified siloxane-bearing imidazoline by a simple sol-gel route. The infrared and nuclear magnetic resonance spectroscopies confirmed the formation of polymer cross-linking network and the protonation of the imidazoline ring. Therefore, in this PIL, the ionic liquid cations are attached to the main polymer network by covalent bonds, which make it so different from common composite polymer electrolytes. Such cations immobilization makes this PIL becomes more chemically stable and reduced phase separation. The fabricated DSSCs using this PIL exhibited a photovoltaic performance similar to that of the reference cells in this work, which used a standard ionic liquid electrolyte. The present study results then show the potential applications of this kind of PIL as the electrolyte materials in DSSC.

Interactive antimicrobial and toxicity profiles of Pittosporum angustifolium Lodd. extracts with conventional antimicrobials

ObjectivePittosporum angustifolium Lodd. is used to treat a variety of pathogenic diseases and inflammation by Australian aborigines. Practitioners of complementary medicine frequently use herbal medicines concurrently with conventional antibiotics. There is a need to evaluate their effects in combination. MethodsThe bacterial growth inhibitory activity of P. angustifolium leaf extracts was assessed against a panel of pathogenic triggers of some autoimmune diseases by standard disc diffusion and liquid dilution minimum inhibitory concentration (MIC) methods. Combinational effects between the extracts and conventional antimicrobials were classified using the sum of the fractional inhibitory concentration. Synergistic interactions were further assessed across a range of ratios by isobologram analysis. The toxicity of the individual samples and combinations was evaluated by Artemia lethality and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) human dermal fibroblast cell viability assays. ResultsP. angustifolium leaf extracts strongly inhibited the growth of several bacterial triggers of autoimmune diseases. The methanolic, aqueous and ethyl acetate extracts were particularly good inhibitors of Proteus mirabilis and Klebsiella pneumonia growth (MIC = 26 and 57 µg/mL respectively). Some combinations of the extracts and conventional antibiotics significantly potentiated the combined inhibitory activity compared to the individual components. Of the 250 combinations studied, approximately 0.02% showed synergistic interactions, 49.6% were additive, 46.8% showed indifferent interactions and antagonism occurred in only 0.02% of the combinations. Interestingly, all of the synergistic and antagonistic combinations contained tetracycline as their antibiotic component. ConclusionP. angustifolium leaf extracts inhibit the growth of pathogenic triggers of some autoimmune diseases. Some extracts also potentiated the activity of conventional antibiotics, without significantly affecting the toxicity of the combination.

A novel sensitive and selective electrochemical sensor based on integration of molecularly imprinted with hollow silver nanospheres for determination of carbamazepine

An electrochemical sensor based on hollow silver nanospheres (hAgNS) and molecularly imprinted polymer (MIP) was developed for drug analysis by using carbamazepine (CBZ) as a model analyte. hAgNS, serving as a support material for MIP immobilization, possesses large accessible surface area with superb electric conductivity, while electrochemically synthesized MIP film warrants improved selectivity for CBZ. Quantification based on the “MIP/gate effect” was performed by employing Fe(CN)63−/4− as the probe to indicate the current intensity. The sensor materials were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimal conditions, a linear relationship of the electrical signal versus the concentration of CBZ was obtained in the range from 8.0 × 10−11 to 6.0 × 10−8 M with a detection limit of 3.2 × 10−11 M (S/N = 3). Moreover, the prepared sensor exhibited specific detection of CBZ over its structural analogues and interferents, and the established electrochemical method was validated using the standard method-high performance liquid chromatography (HPLC). Eventually, rapid and accurate determination of CBZ in rat serum and cell samples was carried out after easy sample pretreatment.

A novel structure design and fabrication method for low liquid consumption and high precision device of colorimeter in water quality detection

Colorimeters based on the Lambert Beer law is now being widely used in water quality detection system. In this paper, we reported a novel colorimeter with low liquid consumption and high precision by optimizing the design of its transition zone and detection area, which would improve the absorbance for specific elements. Combined with stereoscopic fabrication method, six parts including the entrance and exit parts of liquid, the fluid transition path, the detection area, the light intensity enhanced board and the accessories can be assembled on a miniaturized chip. Experimental results show that when the width of the main fluid path for the as-made system is 600 μm, the liquid consumption for every determination is 0.001 mg reducing agent, 0.003 mg chromogenic agent and 0.007 mL standard testing liquid, which was four times lower than traditional structures. The high precision and low liquid consumption have shown our colorimeter possessing the potential of improved absorbance and portable integrated structure for in situ water detection system.

Capillary gap flow cell as capillary-end electrochemical detector in flow-based analysis

A gap flow cell (gap-FC) as a capillary-end electrochemical (EC) detector, incorporating exchangeable screen-printed electrodes, that facilitates adjustment of the gap distance between the capillary outlet and working electrode down to 30 μm was investigated. The analytical performance of the gap-FC was assessed in terms of detector response (current), the efficiency of EC conversion of ferrocyanide, and effective cell volume, as a function of flow rate and gap distance, within a range of 0.1–200 μL min−1 and 30–100 μm, respectively. As a result, an efficiency of EC conversion within the range of ∼1.5–11% (∼3–16 times higher than wall-jet FC), at an effective cell volume of ∼30–75 nL, was achieved. The gap-FC was applied as a liquid chromatography EC detector, coupled with standard and capillary format liquid chromatographs, where the analytical performance of gap-FC was compared with that of a UV detector. With the standard LC, the sensitivity for ascorbic acid, 2,3-dihydroxybenzoic acid and pyrocatechol, was greater than with the UV detector, with limits of detection (LODs) one order of magnitude lower for the gap-FC (0.10 μM, 0.09 μM, 0.19 μM, respectively, RSD 1.35–3.8%, n = 9, linearity r2 ∼0.99 for concentration range 1–100 μM). LODs of test electroactive solutes using the gap-FC were ∼2 times lower than LODs reported in existing literature using standard EC detectors, including wall-jet and thin-layer FCs.

Self-induced liquid crystal q-plate by photoelectric interface activation

Here, we report on the experimental demonstration that highly efficient self-induced spin-orbit optical vortex generation can be achieved by using standard liquid crystal materials and surface treatment agents. This is done by revisiting the recent attempt by Zolot'ko and coworkers to produce self-induced liquid crystal vortex plates using the dc electric field [I. A. Budagovsky, S. A. Shvetsov, and A. S. Zolot'ko, Mol. Cryst. Liq. Cryst. 637, 47 (2016)] that remains, so far, limited to moderate efficiencies. The phenomenon is the result of the self-back-action of light arising from the spontaneous creation of a liquid crystal topological defect. These results demonstrate photo-electric interface activation as a candidate towards the development of a self-adapted spin-orbit photonic toolbox, thus enabling agile management of the orbital angular momentum of light.

A Torque-Sensorless Viscometer for Food Processing Applications

Our study aims to develop a small handy low-cost viscometer for nursing care food management. There are many methods to measure the viscosity of a fluid. In this research, the rotational viscometer employing the observer-based method instead of the actual torque transducer has been developed. The digitally controlled motor has been used to estimate the viscosity in real time with high accuracy. In order to verify the effectiveness of the developed viscosity estimation method, a prototype viscometer has been constructed and tested the viscosity estimation accuracy with standard liquids. As a result, the viscosity accuracy is equivalent to that of the conventional torque transducer-equipped viscometer.

Interfacing a Personal Glucose Meter with Cell-Free Protein Synthesis for Rapid Analysis of Amino Acids.

We developed a method to analyze amino acids using a personal glucose meter (PGM). In this method, the principles of protein biosynthesis were interfaced with the sensing mechanism of a PGM to enable simple and ubiquitous measurement of amino acids. A reaction mixture for cell-free protein synthesis was designed to synthesize a bacterial invertase in response to exogenous addition of a specific amino acid. The invertase synthesized upon addition of an assay sample containing the amino acid of interest was used to convert sucrose into glucose, which was detected using a PGM. The titers of the amino acid in assay samples were precisely represented by the readouts of a PGM. In addition to the convenience provided by use of a PGM, the accuracy and reproducibility of this method were comparable to those of standard high-performance liquid chromatography based methods.

The use ofSaccharomyces cerevisiaeimmobilized on activated alumina, and alumina silicate beads for the reduction of Aflatoxin M1in vitro

This study was aimed to investigate the immobilization of Saccharomyces cerevisiae on two different types of ceramic beads (activated alumina and alumina silicate) and comparing the supports for reduction aflatoxin M1 (AFM1) in vitro. The immobilization of S. cerevisiae was done on ceramic beads for 24 and 48 hr. The best immobilization was achieved at 48 hr. The images of scanning electron microscope confirmed that the immobilization of yeast cells on the activated alumina was better than the alumina silicate (P < 0.05). The ceramic beads with immobilized yeasts were applied to remove the AFM1 from contaminated standard liquid (0.2 µg/L) by 5, 10, and 20 min circulation time. Results showed that the AFM1 concentration in the solution after 20 min circulation was minimal and the highest AFM1 reduction was 75%, when the contaminated solution passed through the activated alumina beads. There was no Si or Al residue in standard liquid. Practical applications This study indicated that the activated alumina and alumina silicate can provide a perfect support for immobilization and the immobilization of Saccharomyces cerevisiae cells on ceramic beads can be used practically to detoxify AFM1-contaminated liquid food.

Optical second harmonic generation in a ferromagnetic liquid crystal.

A comparative experimental investigation of the dependence of second harmonic generation (SHG) on an applied external voltage between a standard nematic liquid crystalline material and an analogue ferromagnetic nematic liquid crystalline material was performed by using a fundamental optical beam at an 800 nm wavelength. For the ferromagnetic material, the dependence of SHG on an applied magnetic field was also examined. Three different polarization combinations of the fundamental and the second harmonic radiation were analysed. The SHG signal observed in the former material is attributed to a combination of electric field-induced SHG (EFISHG) and flexoelectric deformation-induced SHG, while the SHG signal observed in the latter material is attributed solely to flexoelectric deformation-induced SHG. The obtained dependences of the SHG signal on the associated optical retardation show that, in the most favourable polarization combination, the two contributions generate about the same effective nonlinear optical susceptibility.

Quality consistency evaluation of Fufanggancao tablets based on the control mode of standard preparation and quantitative fingerprint

The control mode of standard preparation (SP) and quantitative high performance liquid chromatography (HPLC) fingerprint of Fufanggancao tablets (FFGCTs) combined with the quantification of five markers were successfully developed and applied to the precise and accurate assessment of the quality consistency of 145 FFGCTs from nine manufacturers. The profiling was determined by reversed-phase HPLC at 220 nm wavelength, where the reference fingerprint (RFP) of the FFGCTs reserved as standard preparation was established. Subsequently, the SP-RFP was considered as the evaluation standard, and a systematic quantitative fingerprint method was applied to the integrative quality discrimination of 145 batches of FFGCTs, from both qualitative and quantitative perspectives. Besides, the chromatographic systematic error of quantitative fingerprints was corrected by the double marker calibration method. The results showed that the qualities of the FFGCTs from the nine manufacturers were completely qualified. Moreover, all raw herb fingerprints and the simulated sample were determined by using the combined chromatographic conditions applied to the FFGCTs, which helped identify the source of the profiling peaks in the preparation and establish the correlation between the raw herb fingerprints and the preparation fingerprints. This eventually aided the intelligent prediction of the quality of the preparation or raw herbs and effective prevention of the inputs of inferior raw materials. In addition, we employed the ultraviolet full fingerprint dissolution method to differentiate the FFGCTs from five manufacturer dissolution, in which the rationality of the preparation process was evaluated. The method is feasible and accurate, and it can be applied to evaluate the quality and process technology consistency of FFGCTs. This paper provides a fundamental standard preparation evaluation mode and the basic operation procedure for the quality consistency assessment of traditional Chinese medicine.

A method for the quantitative determination of glycerophospholipid regioisomers by UPLC-ESI-MS/MS

Diacyl glycerophospholipids (GPs) belong to the most abundant lipid species in living organisms and consist of a glycerol backbone with fatty acyl groups in sn-1 and sn-2 and a polar head group in the sn-3 position. Regioisomeric mixed diacyl GPs have the same fatty acyl composition but differ in their allocation to sn-1 or sn-2 of the glycerol unit. In-depth analysis of regioisomeric mixed diacyl GP species composed of fatty acyl moieties that are similar in length and degree of saturation typically requires either chemical derivatization or sophisticated analytical instrumentation, since these types of regioisomers are not well resolved under standard ultra-performance liquid chromatography (UPLC) conditions. Here, we introduce a simple and fast method for diacyl GP regioisomer analysis employing UPLC tandem mass spectrometry (MS/MS). This GP regioisomer analysis is based both on minor chromatographic retention time shifts and on major differences in relative abundances of the two fatty acyl anion fragments observed in MS/MS. To monitor these differences with optimal precision, MS/MS spectra are recorded continuously over the UPLC elution profile of the lipid species of interest. Quantification of relative abundances of the regioisomers was performed by algorithms that we have developed for this purpose. The method was applied to commercially available mixed diacyl GP standards and to total lipid extracts of Escherichia coli (E. coli) and bovine liver. To validate our results, we determined regioisomeric ratios of phosphatidylcholine (PC) standards using phospholipase A2-specific release of fatty acids from the sn-2 position of the glycerol backbone. Our results show that most analyzed mixed diacyl GPs of biological origin exhibit significantly higher regioisomeric purity than synthetic lipid standards. In summary, this method can be implemented in routine LC-MS/MS-based lipidomics workflows without the necessity for additional chemical additives, derivatizations, or instrumentation.

Effect of aqueous hydrochloric acid and zwitterionic betaine on the mutual solubility between a protic betainium-based ionic liquid and water

The solubility of hydrophobic betainium bis(trifluoromethylsulfonyl)imide ionic liquid in an aqueous phase with controlled acidity has been investigated by a standard liquid–liquid extraction technique. The effect of zwitterionic betaine added into the aqueous phase has also been studied. Quantitative NMR was employed to characterize the distribution behavior of the ionic liquid constituents between the two phases. A mathematical model to describe the ionic liquid solubility in the aqueous phase was developed. This approach was utilized to estimate the conditional solubility product constant of the ionic liquid. The possibility of the transfer of some dissociation products back into the organic phase was investigated.

Nucleotide Spin Labeling for ESR Spectroscopy of ATP-Binding Proteins.

Site-directed spin labeling of proteins by chemical modification of engineered cysteine residues with the molecule MTSSL (1-Oxyl-2,2,5,5-tetramethylpyrroline-3-methyl methanethiosulfonate) has been an invaluable tool for conducting double electron electron resonance (DEER) spectroscopy experiments. However, this method is generally limited to recombinant proteins with a limited number of reactive Cys residues that when modified will not impair protein function. Here we present a method that allows for spin-labeling of protein nucleotide binding sites by adenosine diphosphate (ADP) modified with a nitroxide moiety on the β-phosphate (ADP-β-S-SL). The synthesis of this ADP analog is straightforward and isolation of pure product is readily achieved on a standard reverse-phase high-performance liquid chromatography (HPLC) system. Furthermore, analyses of isolated ADP-β-S-SL by LC-mass spectrometry confirm that the molecule is extremely stable under ambient conditions. The crystal structure of ADP-β-S-SL bound to the ATP pocket of the histidine kinase CheA reveals specific targeting of the probe, whose nitroxide moiety is mobile on the protein surface. Continuous wave and pulsed ESR measurements demonstrate the capability of ADP-β-S-SL to report on active site environment and provide reliable DEER distance constraints.

Determination of fats, oils and greases in food service establishment wastewater using a modification of the Gerber method

AbstractDischarges from food service establishments (FSEs) are a major source of fat, oil and grease (FOG) which cause blockages in sewer networks. Previous research has identified that current methods are unsuitable for quantifying FOG in FSE wastewater owing to interference from surfactants in detergents, and protein from food residuals which emulsify FOG. A novel quantification method, based on the dairy industry Gerber method, has been developed which negates the impact of surfactants. Moreover, the method allows free and emulsified oil to be quantified separately providing greater insight into FOG management strategies. Trials in synthetic and real FSE wastewaters indicate the novel method is more reliable than standard liquid–liquid and solid phase extraction in FOG‐rich systems.

Advantage of liquid chromatography with high-resolution mass spectrometry for the detection of the small and polar molecules trifluoroacetic acid and sulfamic acid.

This study addresses the selectivity of liquid chromatography with tandem mass spectrometry for the analysis of the polar analytes trifluoroacetic acid and sulfamic acid in water samples. Such analytes often lack sufficient retention in standard reversed-phase liquid chromatography and rarely produce mass spectrometry transition products of high diagnostic evidence by collision-induced dissociation. The chromatography based on an extra-dense bonding liquid chromatography column for trifluoroacetic acid and on hydrophilic interaction chromatography for sulfamic acid. This enabled sufficient retention of more than twice the void volume for both analytes. Liquid chromatography coupled to low-resolution mass spectrometry was compared with high-resolution mass spectrometry. The limits of quantification for direct injection analysis were determined to<0.05μg/L for trifluoroacetic acid and<0.5μg/L for sulfamic acid. Correction of matrix effects either by internal standards or the standard addition is strongly recommended as matrix effects may vary strongly. The concentrations determined for trifluoroacetic acid and sulfamic acid for real samples were comparable between low and high-resolution mass spectrometry. However, low-resolution mass spectrometry does not fulfill the identification criteria of the analytes following the European Commission council directive 96/23/EC or the SANTE/11945/2015. Since low-resolution mass spectrometry for these analytes may result in false-positive findings, such findings may be controlled by high-resolution mass spectrometry.

Fabricating a high performance composite separator with a small thickness for lithium ion batteries

Separator is a porous membrane that physically separates the cathode and anode, yet ensures the lithium ion transport between these two electrodes. This work attempts to develop a high performance composite separator that can also provide a low cost potential when produced at a large scale. For this purpose, a non-woven reinforced macroporous polyaramid separator with a thickness comparable to mainstream commercial products was developed to achieve improved separator mechanical performance and uniformity. The separator consists of a polymer phase with a uniform porous structure and a non-woven reinforcement. The non-woven structure made using a wet-laid process provides the increased separator mechanical strength, while the macroporous polyaramid phase modified with nano and submicron ceramic particles optimizes the pore structure for improved battery electrochemical performance. Compared with the commercial polyolefin separator, this developed separator showed superior mechanical and physical robustness at elevated temperatures. The separator wettability by the standard liquid electrolyte was also much improved. A stable cycle performance and an improved rate capability have been observed when the separator was evaluated in full coin cells.