Analytica Chimica Acta (v.855, #C)

Thin-film voltammetry and its analytical applications: A review by Huihui Tian; Yunchao Li; Huibo Shao; Hua-Zhong Yu (1-12).
Display OmittedElectrochemical reactions at the interfaces of immiscible electrolyte solutions (ITIES) are of fundamental importance in the fields of chemical, biological and pharmaceutical sciences. Four-electrode cell setup, scanning electrochemical microscopy (SECM) and thin-film voltammetry are the three most frequently used methods for studying the electrochemical processes at these interfaces. The principle, experimental design, advantages and challenges of the three methods are described and compared. The thin-film voltammetry is highlighted for its simplicity in experimental operation and kinetic data analysis. Its versatile analytical applications are discussed in detail, including the study of redox properties of hydrophobic compounds, evaluation of interfacial electron transfer kinetics, synthesis of nanoparticles/nanostructures, and illustration of cross-membrane ion transport phenomena.
Keywords: Thin-film voltammetry; Liquid–liquid interface; Electron transfer; Ion transport; Biomembranes;

Display OmittedThis text presents a novel method for the separation and detection of phosphorothioate oligonucleotides with the use of ion pair ultra high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry The research showed that hexafluoroisopropanol/triethylamine based mobile phases may be successfully used when liquid chromatography is coupled with such elemental detection. However, the concentration of both HFIP and TEA influences the final result. The lower concentration of HFIP, the lower the background in ICP-MS and the greater the sensitivity. The method applied for the analysis of serum samples was based on high resolution inductively coupled plasma mass spectrometry. Utilization of this method allows determination of fifty times lower quantity of phosphorothioate oligonucleotides than in the case of quadrupole mass analyzer. Monitoring of 31P may be used to quantify these compounds at the level of 80 μg L−1, while simultaneous determination of sulfur is very useful for qualitative analysis. Moreover, the results presented in this paper demonstrate the practical applicability of coupling LC with ICP-MS in determining phosphorothioate oligonucleotides and their metabolites in serum within 7 min with a very good sensitivity. The method was linear in the concentration range between 0.2 and 3 mg L−1. The limit of detection was in the range of 0.07 and 0.13 mg L−1. Accuracy varied with concentration, but was in the range of 3%.
Keywords: Phosphorothioate oligonucleotides; Inductively coupled plasma mass spectrometry; Ion pair chromatography; Hexafluoroisopropanol/triethylamine; Serum;

Definition and detection of data-based uniqueness in evaluating bilinear (two-way) chemical measurements by Róbert Rajkó; Hamid Abdollahi; Samira Beyramysoltan; Nematollah Omidikia (21-33).
Display OmittedMultivariate curve resolution methods, frequently used in analyzing bilinear data sets, result in ambiguous decomposition in general. Implementing the adequate constraints may lead to reduce the so-called rotational ambiguity drastically, and in the most favorable cases to the unique solution. However, in some special cases, non-negativity constraint as minimal information of the system is a sufficient condition to resolve profiles uniquely. Although, several studies on exploring the uniqueness of the bilinear non-negatively constrained multivariate curve resolution methods have been made in the literature, it has still remained a mysterious question. In 1995, Manne published his profile-based theorems giving the necessary and sufficient conditions of the unique resolution. In this study, a new term, i.e., data-based uniqueness is defined and investigated in details, and a general procedure is suggested for detection of uniquely recovered profile(s) on the basis of data set structure in the abstract space. Close inspection of Borgen plots of these data sets leads to realize the comprehensive information of local rank, and these argumentations furnish a basis for data-based uniqueness theorem. The reported phenomenon and its exploration is a new stage (it can be said fundament) in understanding and describing the bilinear (matrix-type) chemical data in general.Our proposed detection tool is restricted to three-component systems because of the visual limitations of the Borgen plot, but the theorem is universal for systems with more than three components. A recently published experimental four-component system is used for illustrating this theorem in the case of systems with more than three components.
Keywords: Bilinear data set; Uniqueness; Rotational ambiguity; Borgen plot; Self-modeling/multivariate curve resolution;

Antimony film screen-printed carbon electrode for stripping analysis of Cd(II), Pb(II), and Cu(II) in natural samples by Velia Sosa; Cristian Barceló; Núria Serrano; Cristina Ariño; José Manuel Díaz-Cruz; Miquel Esteban (34-40).
Display OmittedAn in-situ antimony film screen-printed carbon electrode (in-situ SbSPCE) was successfully used for the determination of Cu(II) simultaneously with Cd(II) and Pb(II) ions, by means of differential pulse anodic stripping voltammetry (DPASV), in a certified reference groundwater sample with a very high reproducibility and good trueness. This electrode is proposed as a valuable alternative to in-situ bismuth film electrodes, since no competition between the electrodeposited copper and antimony for surface sites was noticed. In-situ SbSPCE was microscopically characterized and experimental parameters such as deposition potential, accumulation time and pH were optimized. The best voltammetric response for the simultaneous determination of Cd(II), Pb(II) and Cu(II) ions was achieved when deposition potential was −1.2 V, accumulation time 120 s and pH 4.5. The detection and quantification limits at levels of μg L−1 suggest that the in-situ SbSPCE could be fully suitable for the determination of Cd(II), Pb(II) and Cu(II) ions in natural samples.
Keywords: Antimony film electrodes; Screen-printed electrodes; Stripping voltammetry; Metal ions;

Display OmittedA simple, sensitive, reliable, and fast analytical method was developed for the simultaneous determination of amphenicols residues in raw milk by combining fabric phase sorptive extraction (FPSE) and high-performance liquid chromatography-diode array detection. FPSE, a new generation green sample preparation technique, efficiently incorporates the advanced and tunable material properties of sol–gel derived microextraction sorbents with the rich surface chemistry of a cellulose fabric substrate, resulting in a flexible, highly sensitive, and fast microextraction device capable of extracting target analytes directly from complicated sample matrices. Due to the strong chemical bonding between the sol–gel sorbent and substrate, the microextraction device demonstrates a very high chemical and solvent stability. Therefore, any organic solvent/solvent mixture can be used as the eluent/back-extraction solvent.Herein, a highly polar polymer coated FPSE media was created using short-chain poly(ethylene glycol) (PEG) and the applicability of this novel microextraction device to extract highly polar amphenicol antibiotics from raw milk was investigated. Due to the intense affinity of amphenicols towards the strongly polar sol–gel PEG-coated FPSE device, absolute recovery of the selected antibiotics residues were found to be 44% for thiamphenicol, 66.4% for florfenicol, and 81.4% for chloramphenicol. The developed method was validated in terms of sensitivity, linearity, accuracy, precision, and selectivity according to European Decision 657/2002/EC. Decision limit (CCα) values were 52.49 μg kg−1 for thiamphenicol, 55.23 μg kg−1 for florfenicol, and 53.8 μg kg−1 for chloramphenicol, while the corresponding results for detection capability (CCβ) were 56.8 μg kg−1, 58.99 μg kg−1, and 55.9 μg kg−1, respectively.
Keywords: Amphenicols; Milk; Sample preparation; Sorptive extraction; Fabric phase sorptive extraction (FPSE);

A method for rapid screening of interactions of pharmacologically active compounds with albumin by Aldona Majcher; Anna Lewandrowska; Franciszek Herold; Jacek Stefanowicz; Tomasz Słowiński; Aleksander P. Mazurek; Stefan A. Wieczorek; Robert Hołyst (51-59).
Display OmittedWe determine the association constants for ligand–protein complex formation using the flow injection method. We carry out the measurements at high flow rates (F  = 1 mL min−1) of a carrier phase. Therefore, determination of the association constant takes only a few minutes. Injection of 1 nM of the ligand (10 μL of 1 μM concentration of the ligand solution) is sufficient for a single measurement. This method is tested and verified for a number of complexes of selected drugs (cefaclor, etodolac, sulindac) with albumin (BSA). We obtain K  = 4.45 × 103  M−1 for cefaclor, K  = 1.00 × 105  M−1 for etodolac and K  = 1.03 × 105  M−1 for sulindac in agreement with the literature data. We also determine the association constants of 20 newly synthesized 3β- and 3α-aminotropane derivatives with potential antipsychotic activity – ligands of 5-HT1A, 5-HT2A and D 2 receptors with the albumin. Results of the studies reported here indicate that potential antipsychotic drugs bind weakly to the transporter protein (BSA) with K  ≈ 102–103  M−1. Our method allows measuring K in a wide range of values (102–109  M−1). This range depends only on the solubility of the ligand and sensitivity of the detector.
Keywords: Association constant; Drug–protein interactions; Potential drugs; Taylor dispersion analysis;

Display OmittedA novel analytical system for gas-chromatographic investigation of complex samples has been developed, that combines the advantages of several analytical principles to enhance the analytical information. Decomposition of high molecular weight structures is achieved by pyrolysis and a high separation capacity due to the chromatographic step provides both an universal as well as a selective and sensitive substance detection. The latter is achieved by simultaneously applying electron ionization quadrupole mass spectrometry (EI-QMS) for structural elucidation and [1 + 1]-resonance-enhanced-multi-photon ionization (REMPI) combined with time-of-flight mass spectrometry (ToFMS). The system has been evaluated and tested with polycyclic aromatic hydrocarbon (PAH) standards. It was applied to crude oil samples for the first time. In such highly complex samples several thousands of compounds are present and the identification especially of low concentrated chemical species such as PAH or their polycyclic aromatic sulfur containing heterocyclic (PASH) derivatives is often difficult. Detection of unalkylated and alkylated PAH together with PASH is considerably enhanced by REMPI–ToFMS, at times revealing aromatic structures which are not observable by EI-QMS due to their low abundance. On the other hand, the databased structure proposals of the EI-QMS analysis are needed to confirm structural information and isomers distinction. The technique allows a complex structure analysis as well as selective assessment of aromatic substances in one measurement. Information about the content of sulfur containing compounds plays a significant role for the increase of efficiency in the processing of petroleum.
Keywords: Pyrolysis–GC/MS; Resonance enhanced multi-photon ionization; Electron ionization; Crude oil; Polycyclic aromatic hydrocarbons;

Display OmittedA simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core–shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5 × 10−11  M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material.
Keywords: Surface-enhanced Raman scattering; Magnetic concentration; Iron oxide nanoparticles; Gold nanoparticles;