Chemometric processing of second-order liquid chromatographic data with UV–vis and fluorescence detection. A comparison of multivariate curve resolution and parallel factor analysis 2

Second-order liquid chromatographic data with multivariate spectral (UV–vis or fluorescence) detection usually show changes in elution time profiles from sample to sample, causing a loss of trilinearity in the data. In order to analyze them with an appropriate model, the latter should permit a given component to have different time profiles in different samples. Two popular models in this regard are multivariate curve resolution-alternating least-squares (MCR-ALS) and parallel factor analysis 2 (PARAFAC2). The conditions to be fulfilled for successful application of the latter model are discussed on the basis of simple chromatographic concepts. An exhaustive analysis of the multivariate calibration models is carried out, employing both simulated and experimental chromatographic data sets. The latter involve the quantitation of benzimidazolic and carbamate pesticides in fruit and juice samples using liquid chromatography with diode array detection, and of polycyclic aromatic hydrocarbons in water samples, in both cases in the presence of potential interferents using liquid chromatography with fluorescence spectral detection, thereby achieving the second-order advantage. The overall results seem to favor MCR-ALS over PARAFAC2, especially in the presence of potential interferents.     

Sensitive electrochemical sensor using a graphene–polyaniline nanocomposite for simultaneous detection of Zn(II), Cd(II), and Pb(II)

This work describes the development of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene–polyaniline (G/PANI) nanocomposite electrode prepared by reverse-phase polymerization in the presence of polyvinylpyrrolidone (PVP). Two substrate materials (plastic film and filter paper) and two nanocomposite deposition methods (drop-casting and electrospraying) were investigated. Square-wave anodic stripping voltammetry currents were higher for plastic vs. paper substrates. Performance of the G/PANI nanocomposites was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. The G/PANI-modified electrode exhibited high electrochemical conductivity, producing a three-fold increase in anodic peak current (vs. the unmodified electrode). The G/PANI-modified electrode also showed evidence of increased surface area under SEM. Square-wave anodic stripping voltammetry was used to measure Zn(II), Cd(II), and Pb(II) in the presence of Bi(III). A linear working range of 1–300 μg L⁻¹ was established between anodic current and metal ion concentration with detection limits (S/N = 3) of 1.0 μg L⁻¹ for Zn(II), and 0.1 μg L⁻¹ for both Cd(II) and Pb(II). The G/PANI-modified electrode allowed selective determination of the target metals in the presence of common metal interferences including Mn(II), Cu(II), Fe(III), Fe(II), Co(III), and Ni(II). Repeat assays on the same device demonstrated good reproducibility (%RSD < 11) over 10 serial runs. Finally, this system was utilized for determining Zn(II), Cd(II), and Pb(II) in human serum using the standard addition method.     

UV–vis and fluorescence detection by receptors based on an isophthalamide bearing a phenylethynyl group

We have successfully prepared 5-(2-phenylethynyl)isophathalilc acid as a signaling unit and the corresponding derivatives for an anion receptor 2 and a barbiturate receptor 4. Receptor 2 showed characteristic UV–vis changes and dramatic fluorescence quenching upon the addition of anions and receptor 4 showed UV–vis and an OFF-ON fluorescence changes upon the addition of dibutylbarbituric acid based on the diphenylethyne moiety.     

The role of the βAsp residue in copper(II) binding by modified peptides

The synthesis and binding abilities of peptides containing β-amino acids towards Cu(II) ions are presented. The peptides studied were: Ala-βAsp-Ser-Gly and Arg-Lys-βAsp-Val-Tyr. Potentiometric titrations were carried out to establish the stoichiometry of the resulting metal-ligand complexes. The copper(II) coordination mode of the complexes was investigated by performing detailed spectroscopic analyses (UV–Vis, CD) in strict correlation with potentiometric measurements. The results obtained on the β-peptides studied allowed the characterization of the influence of this structural modification on the coordination abilities of the peptides. Moreover, the role of the α-Asp position in the peptide chain was also described.     

An optical and electrochemical anion sensor of F− investigated by UV–vis, 1H NMR and cyclic voltammetry

A new anion receptor: 1,1′-di-(2″,4″-di-nitrophenylhydrazino-β-carbonyl)-ferrocene (1) based on ferrocene has been designed and synthesized as a highly colorimetric and electrochemical sensitive sensor for F^?. The binding mode with F^? was further investigated by UV–vis titration and ¹H NMR titration experiments. In addition, the cyclic voltammetry (CV) was performed to discuss the electrochemical sensing for F^?.     

Carrier‐Mediated Transport of Hg(II) through Bulk and Supported Liquid Membranes

The transport of Hg (II) ions from an aqueous solution into an aqueous receiving solution through bulk and supported liquid membranes containing a calix[4]arene derivative 1 as a carrier was examined. The kinetic parameters of bulk liquid membrane studies were analyzed assuming two consecutive, irreversible first‐order reactions. The influence of temperature, stirring rate, carrier concentration and solvent on the kinetic parameters (k₁, k₂, R_m ^max, t_max, J_d ^max, J_a ^max) has also been investigated. The membrane entrance rate, k₁, and the membrane exit rate, k₂, increased with increasing temperature and stirring rate. The activation energy values are calculated as 4.87 and 48.63 kj mol^?1 for extraction and reextraction, respectively. The values of calculated activation energy indicate that the process is diffusionally controlled by species. Also, the transport behavior of Hg²⁺ from aqueous solution through a flat‐sheet supported liquid membrane has been investigated by the use of calix[4]arene derivative 1 as carrier and Celgard 2500 as the solid support. A Danesi mass transfer model was used to calculate the permeability coefficients for each parameter studied. The highest values of permeability were obtained with 2‐nitrophenyloctyl‐ether (NPOE) solvent and the influence was found to be in the order of NPOE>chloroform>xylene.     

A ratiometric electrochemical biosensor for sensitive detection of Hg based on thymine–Hg–thymine structure

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg²⁺) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg²⁺, the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg²⁺-mediated coordination of T–Hg²⁺–T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB (I_MB), accompanied with the increase of that of Fc (I_Fc). The logarithmic value of I_Fc/I_MB is linear with the logarithm of Hg²⁺ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg²⁺. This strategy provides a simple and rapid approach for the detection of Hg²⁺, and has promising application in the detection of Hg²⁺ in real environmental samples.     

Determination of Mercury(II) in Drinking Water by Total Reflection X-ray Fluorescence Spectrometry and Liquid–Liquid Microextraction

The total reflection X-ray fluorescence determination of mercury(II) in drinking water at concentrations of 7?×?10^?2 to 3.0?µg/L is reported. The mercury(II) preconcentration protocol includes directly suspended droplet microextraction with benzene as a molecular iodine complex. The proposed approach is highly selective. The elements Cr, Mn, Fe, Co, Ni, Zn, and Pb at concentrations up to 0.1?g/L did not interfere with the extraction of trace mercury(II). The method is characterized by high sensitivity (limit of detection of 21?ng/L) and suitable reproducibility (relative standard deviation of 0.12 for 100?ng/L). The accuracy of the results was confirmed by recovery and the method of standard addition.     

LC–UV Methodology for Simultaneous Determination of Lamivudine and Zidovudine in Plasma by Liquid–Liquid Extraction

This study describes an accurate, sensitive, and specific chromatographic method for the simultaneous quantitative determination of lamivudine and zidovudine in human blood plasma, using stavudine as an internal standard. The chromatographic separation was performed using a C8 column (150 × 4.6 mm, 5 μm), and ultraviolet absorbency detection at 270 nm with gradient elution. Two mobile phases were used. Phase A contained 10 mM potassium phosphate and 3% acetonitrile, whereas Phase B contained methanol. A linear gradient was used with a variability of A-B phase proportion from 98–2% to 72–28%, respectively. The drug extraction was performed with two 4 mL aliquots of ethyl acetate.     

Raman and UV–vis spectroscopy studies on luteolin–Al(III) complexes

Luteolin is one of the most common flavonoids, but its ability to complex metal ions (e.g. aluminum) is still being discussed. This work presents the results of structural investigation of the luteolin–Al(III) complexes in methanol:water solutions and in the solid state. The analysis was carried out using UV–vis and FT-Raman spectroscopy accompanied by Factor Analysis, deconvolution and quantum-chemical calculations. It was found that in acidic solutions two complexes of luteolin–Al(III) of 1:1 and 1:2 ligand:metal ratio are formed, where luteolin is one- and twofold deprotonated, respectively. Additionally, a third complex precipitated from a basic solution of 1:2 stoichiometry with a threefold deprotonated ligand was obtained.     

Liquid–Liquid Microextraction of Nitrophenols Using Supramolecular Solvent and Their Determination by HPLC with UV Detection

A novel, efficient, and environmentally friendly method—supramolecular solvent liquid–liquid microextraction (SMS-LLME) combined with high-performance liquid chromatography (HPLC)—was first established for the determination of p-nitrophenol and o-nitrophenol in water samples. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, temperature, salt effect, extraction time, and stirring rate, were optimized in detail. Under the optimal conditions, the enrichment factor was 166 for p-nitrophenol and 160 for o-nitrophenol, and the limits of detection by HPLC were 0.26 and 0.58 μg L^?1, respectively. Excellent linearity with coefficients of correlation from 0.9996 to 0.9997 was observed in the concentration range of 2–1,000 μg L^?1. The ranges of intra- and interday precision (n = 5) at 100 μg L^?1 of nitrophenols were 5.85–7.76 and 10.2–11.9 %, respectively. The SMS-LLME method was successfully applied for preconcentration of nitrophenols in environmental water samples.     

Liquid–Liquid Microextraction of Nitrophenols Using Supramolecular Solvent and Their Determination by HPLC with UV Detection

A novel, efficient, and environmentally friendly method—supramolecular solvent liquid–liquid microextraction (SMS-LLME) combined with high-performance liquid chromatography (HPLC)—was first established for the determination of p-nitrophenol and o-nitrophenol in water samples. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, temperature, salt effect, extraction time, and stirring rate, were optimized in detail. Under the optimal conditions, the enrichment factor was 166 for p-nitrophenol and 160 for o-nitrophenol, and the limits of detection by HPLC were 0.26 and 0.58 μg L⁻¹, respectively. Excellent linearity with coefficients of correlation from 0.9996 to 0.9997 was observed in the concentration range of 2–1,000 μg L⁻¹. The ranges of intra- and interday precision (n = 5) at 100 μg L⁻¹ of nitrophenols were 5.85–7.76 and 10.2–11.9 %, respectively. The SMS-LLME method was successfully applied for preconcentration of nitrophenols in environmental water samples.

     

Sensitive detection of biothiols and histidine based on the recovered fluorescence of the carbon quantum dots–Hg(II) system

In this paper, we presented a novel, rapid and highly sensitive sensor for glutathione (GSH), cysteine (Cys) and histidine (His) based on the recovered fluorescence of the carbon quantum dots (CQDs)–Hg(II) system. The CQDs were synthesized by microwave-assisted approach in one pot according to our previous report. The fluorescence of CQDs could be quenched in the presence of Hg(II) due to the coordination occurring between Hg(II) and functional groups on the surface of CQDs. Subsequently, the fluorescence of the CQDs–Hg(II) system was recovered gradually with the addition of GSH, Cys or His due to their stronger affinity with Hg(II). A good linear relationship was obtained from 0.10 to 20 μmol L⁻¹ for GSH, from 0.20 to 45 μmol L⁻¹ for Cys and from 0.50 to 60 μmol L⁻¹ for His, respectively. This method has been successfully applied to the trace detection of GSH, Cys or His in human serum samples with satisfactory results. The proposed method was simple in design and fast in operation, which demonstrated great potential in bio-sensing fields.     

Compatibility of sildenafil citrate and pharmaceutical excipients by thermal analysis and LC–UV

The evaluation of sildenafil citrate (SC), the best-selling drug for treatment of impotence, for compatibility with various excipients was investigated using thermal and isothermal stress testing. Differential scanning calorimetry (DSC), hot-stage microscopy (HSM) and liquid chromatography (LC) with ultraviolet detection were successfully employed to investigate the compatibility between SC and various excipients commonly used in solid form in the pharmaceutical industry. The studies were performed using 1:1 (m/m) drug/excipient physical mixtures and samples were stored under accelerated stability conditions (40 °C at 75% relative humidity). All excipients tested (such as colloidal silicon dioxide, croscarmellose sodium, lactose, mannitol and sucrose) showed potential incompatibilities by DSC and LC analysis after accelerated stability testing. However, some incompatibilities were not detected by the DSC method and were observed only when LC analysis was performed. HSM was able to differentiate active pharmaceutical ingredient degradation from solubilisation, supporting the interpretation of DSC in excipients where thermal events either overlapped or disappeared. The combination of both the analytical techniques (DSC and LC) and use of a stability chamber is extremely helpful in detecting incompatibilities and providing more robust and accurate approaches for pre-formulation studies.     

Two types of rhodamine–naphthalimide-based fluorescence sensors for different ratiometric detection of Hg(II) or Fe(III)

Two types of rhodamine–naphthalimide sensors 1a–1c and RND with different polyamine linkers and terminal chains were designed and synthesized for different ratiometric detection of Fe(III) or Hg(II). The fluorescent properties including response time, pH effect, selectivity, anti-interference, fluorescence titration and reproducibility were investigated and compared in details. Sensor RND possessing two recognition groups of rhodamine and 1-(pyridin-2-ylmethyl)piperazine displayed good response and selectivity to Hg(II) with a detection limit of 1.72 μmol/L, whereas 1a–1c with piperidine instead of 1-(pyridin-2-ylmethyl)piperazine showed quite different recognition to Fe(III) and the detection limit of 1b was the lowest (1.92 μmol/L). The Hg(II)/Fe(III) chelation-induced dual/single recognition mechanisms as well as the structure–fluorescence properties relationships (SFPRs) were discussed in detail with the aid of quantum chemical density functional theory (DFT) calculations. Through adjusting the linker and introducing other recognition groups to rhodamine- naphthalimide system, novel sensors with selective recognition of different metal ions should be achieved.

     

Stoichiometry of Zn(II)–heparin–glycine complex,determined using data from elemental and thermal analysis

Russian Journal of Physical Chemistry A - Ternary polymer Zn(II)–heparin–glycine complex with the composition {Na3[ZnHepGly]·H2O} n , where Hep4− is the monomer chain of a...     

Synthesis of Co–Pd alloys by co-electroreduction of aquachloro-cobalt(II) and palladium(II) complexes

The work presents results of the studies on the synthesis of Co–Pd alloys from acid electrolytes containing chloride ions. The main aim of the tests was to identify reactions responsible for alloy formation and to determine an influence of the electrolysis parameters, i.e. working electrode potential, electrolyte composition and temperature on the composition of the resulted alloy coatings. Electrochemical investigations were performed by applying cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM). The electrolyte composition was selected based on a thermodynamic analysis and spectrophotometric tests which were described in our previous papers [1, 2]. They allowed determination of equilibrium distribution of the metals complex forms and a stability analysis of the electrolyte. The alloys were synthesized within the potential range from ?0.7 to ?1.1 V. The tests indicate a possibility of alloys synthesis already at the potential range 相似文献   

Analysis of phenanthrene biodegradation by using FTIR,UV and GC–MS

The aim of this paper is to assess the biodegradation of phenanthrene by Flavobacteria FCN2 which was isolated from coke plant sludge via a classical shaken liquid medium enrichment method. The strain FCN2 can decompose phenanthrene (50 mg l^?1) completely within 5 days. The values of pH decrease to 6.7 from 7.2 during degradation periods. And a detailed phenanthrene metabolism was assayed by using FTIR, UV and GC–MS. For FTIR, appearance of new broad absorption bands at 2858 cm^?1, 2927 cm^?1, 2955 cm^?1 and another new strong absorption band at 1734 cm^?1 in metabolites demonstrates that carboxyl group produced during phenanthrene degradation. Besides this, a very strong absorption band appears at 1260 cm^?1. It is ascribed to C–C stretching vibration band in carbonyl group of arone. Two weak adsorption at 334 nm and 349 nm in UV spectra were assigned to the n-π* transition of CO of aldehyde. Two metabolites, phenanthrene-dihydrodiol and naphthalene-1-diol were identified in neutral fraction of phenanthrene degradation by using GC–MS. As a result carboxylic acids and arone were generated during biodegradation of phenanthrene by Flavobacteria FCN2.     

Organotin analysis by gas chromatography–pulsed flame-photometric detection (GC–PFPD)

Monobutyltin (MBuT), dibutyltin (DBuT), and tributyltin (TBuT) mixtures have been separated and quantified by gas chromatography with pulsed flame-photometric detection (GC–PFPD). The compounds were first derivatized with NaBEt₄, then extracted with hexane and injected into the GC in splitless mode. Optimum GC and detector conditions were established. For GC, various injector temperatures and oven temperature programs were tested. For the PFPD detector, gate settings (gate delay and gate width) and detector temperature were optimized. A very good linearity was obtained up to 100–150 ppb for all organotin compounds. The detection limits obtained were: MBuT (0.7 ppb), DBuT (0.8 ppb), and TBuT (0.6 ppb). RSD for repeatability and reproducibility were well below 20% when the instrument was in routine operation. A biological sample (CRM 477) was also analyzed for organotins. Extraction from the biological matrix was performed with TMAH. Besides the increased risk of contamination, the derivatization step seemed to be critical. pH and amount of derivatizing agent were tested. When using an internal standard (TPrT) between 90% and 110% of the certified amounts of organotin were recovered.