Current Analytical Chemistry - Volume 11, Issue 4, 2015

In this paper, platinum nanoclusters (PtNCs) were synthesized by less sophisticated equipments with low cost and tedious procedures, and then applied to construct a simple electrochemical hydrazine sensor rapidly within the applied potential. PtNCs were proved to have advantages over platinum nanoparticles (PtNPs) in modifying glassy carbon electrode (GCE) for electrochemical and sensing applications. The sensor’s electrochemical activities toward several compounds (ascorbic acid, glucose, sodium nitrite, L–cysteine, citric acid, potassium chloride, hydroquinone, and bismuth nitrate) were investigated. Furthermore, hydrazine was used as a typical analyte to exhibit the sensing performance of PtNCs. It was found that PtNCs modified GCE presented two linear detection ranges and low detection limit for hydrazine detection.

The rapid development of the analytical instrumentation, used in routine analysis tests in both laboratory and industrial scale, has been accompanied by the application of different smart software. Such combinations are recommended since they are inexpensive while at the same time they can readily ensure reliable results in short timeframe. The present work is an attempt to provide simple solutions in difficult analytical issues (e.g. the simultaneous determination of binary and/or more complex mixtures) through the development of three different methods. Therefore, metformin, phenformin, chlorpopamide, glipizide, tolbutamide and glibenclamide were employed to study techniques which differ in terms of experimental equipment, mathematical approach as well as data processing. The methods applied are: i) UV Spectrophotometry coupled with the chemometric technique derivative ratio or the multivariate method Partial Least Squares to Latent Structures (PLS), and ii) High Performance Liquid Chromatography (HPLC) in combination with experimental design methodology and crossed D-optimal process. Accuracy control includes preparation of a series of samples (solutions and compact formulations) with different drug concentration whose determination was tested. It was crucial to verify that the used techniques were versatile and handy as well as to evaluate them in terms of recovery and repeatability percentages and linearity.

A novel PVC-incorporated membrane electrode selective for iron(III) is described. The sensor is based on the use of novel tris(aminophenolate) sensing molecule Cis,cis-1,3,5-tris{(2- hydroxybenzyl)aminomethyl}cyclohexane (THAC, L). The optimized membrane containing THAC, PVC and o-nitrophenyloctyl ether in the ratio 4:33:63 exhibits the best performance by means of range of concentration (1.0x10-5 to 1.0x10-1M), slope (19.4 mV/decade) and detection limit (7.0x10-6 M). The sensor exhibited a firm response time (< 15 s), extensive working pH range (3.0-6.5), non-aqueous steadiness (up to 20%) and having sufficient long life time (120 days). The potentiometric selectivity coefficients obtained using match potential method (MPM) stipulates outstanding discrimination for Fe3+ ions among the various cations. Additionally, the sensor is found to be conveniently active like a potentiometric indicator electrode in the determination of Fe3+ ions against EDTA.

Screening bioactive constituents from herbal medicines or traditional Chinese medicines according to traditional phytochemical approach is time-consuming and laborious. The objective of the present study is to provide a strategy for rapid screening of active candidates from plant extract based on the Quantitative Patteren-Activity Relationship. The chromatographic fingerprint (Patteren) data sets were obtained by our previous proposed method and the antioxidant activity was measured by Ferric Reduction Ability Power assay. The correlation model was built by partial least squares and bioactive components were screened out by target projection. Variable selection and model evaluation were performed by 4-fold cross validation. The optimal model required 5 PLS components. The calibration and prediction multiple correlation coefficients were 0.990 and 0.975, respectively. And the calibration and prediction errors were 23.2 and 36.4, respectively. The projection result showed that the antioxidant activity was highly correlated to some variables/peaks, indicating that they are main antioxidants. 3'-Hydroxypuerarin, puerarin, 3'-methoxypuerarin and 6''-O-D-xylosylpuerarin were identified to be four main antioxidants by comparing their TOF MS patterns and retention times. Moreover, the model was found to predict accurately the antioxidant capacity of the Radix puerariae samples through their chromatographic fingerprint only. The results obtained in this work show clearly how simple and effective our proposed method is in bioactive constituent screening as well as drug lead compound discovery from herbal medicines.

A new HPLC method have been developed and validated for simultaneous determination of carprofen, vitamin B1, B6 and B12 in veterinary pharmaceutical preparations medicines. The method used a Hypersil GOLD aQ (250 x 4.6 mm, 5 μm) column, under the following chromatographic conditions: gradient elution, using a mobile phase composed by phosphate buffer (pH 2.65) and methanol as an organic modifier. The mobile phase was delivered at a flow rate of 1 mL/min and the detection was made by photodiode array (PDA) detector at 292 nm. This method was fully validated and applied on available pharmaceutical product. The limit of detection (LOD) and limit of quantitation (LOQ) for vitamin B1 were 0.5ng/mL and 1.5ng/mL respectively while for vitamin B12 were 1ng/mL and 5ng/mL respectively The main advantages of this HPLC method relies on the possibility to asses in a single run all the above mentioned drugs.

A multi-functional “turn-off” fluorescent probe, N-[[(6-Amino-1,2,3,4-tetrahydro-1,3- dimethyl-2,4-dioxo-5-pyrimidinyl)amino]thioxomethyl]- benzamide, was synthesized and characterized. The probe showed high sensitivity and selectivity towards copper(II), iron(III) and silver(I) ions via quenching of its fluorescence. The detection limits were found to be 4.0 – 16.0 ppb for the assayed cations. The thiourea linked uracil fluorescent probe is proved to be sensitive, selective, applicable in real samples and promise for practical applications.

New materials - silica-titania xerogels modified with polyphenols (caffeic acid, catechol, and quercetin) or hydrogen peroxide - have been used for solid phase spectrophotometric determination of fluoride ions. The fast and simple method is based on the xerogel incorporated titanium(IV) complexes discoloration in the presence of fluoride ions. Parameters, such as modifying reagent nature pH, and time of contact, affecting the interaction of fluoride with modified silica-titania xerogels have been investigated. A linear response for the fluoride determination has been observed in the concentration ranges: 50-200, 100-500 and 100-700 mg·L-1 for caffeic acid, catechol, and quercetin modified xerogels, accordingly. The developed method allows determining fluoride ions in ethanol-containing mouthwashes. The proposed method has been applied to the analysis of mouthwash solutions and toothpastes. Time of analysis is 5 min.

In this study, we demonstrated an oxidative method with free radical to generate 3,5,4´-trihydroxy-transstilbene (trans-resveratrol) metabolites and detect sequentially by an autosampler coupling with liquid chromatography electrospray ionization tandem mass spectrometer (LC-ESI–MS/MS). In this oxidative method, the free radical initiator, ammonium persulfate (APS), was placed in a sample bottle containing resveratrol to produce oxidative derivatives, and the reaction progress was tracked by autosampler sequencing. Resveratrol, a natural product with purported cancer preventative qualities, produces metabolites including dihydroresveratrol, 3,4´-dihydroxy-trans-stilbene, lunularin, resveratrol monosulfate, and dihydroresveratrol monosulfate by free radical oxidation. Using APS free radical, the concentrations of resveratrol derivatives differ as a function of time. Besides simple, convenient and time- and labor saving, the advantages of free radical oxidative method of its in situ generation of oxidative derivatives followed by LC-ESI–MS/MS can be utilized to evaluate different metabolites in various conditions.

Electrochemical sensors based on molecularly imprinted polymer (MIP) have attracted great attention over the past ten years. Among the strategies for the preparation of MIP modified electrode, electropolymerization is a potential technique, which can deposit a MIP film with special selectivity on the surface of the detector. In this work, the recent development of molecular imprinted electrochemical sensors based on electropolymerization technique was reviewed. The methods for the preparation of MIP film on electrode were introduced first. A section is dedicated to the choice of functional monomers, which is of paramount importance in electropolymerization. And the strategies for removal of the template are discussed. Different nanomaterials used in the sensors to achieve sensitive detection are also presented. In the end, several applications are mentioned, which highlight the potential of electrochemical sensors based on MIP technique in fields such as the analysis of proteins from biological fluids, pharmaceutical, agricultural and food analysis.