A fluorescent pyrazine derivative, 3,5-diamino-6-chloro-2-pyrazine carbonitrile (DCPC), is presented as a promising light-up ligand for single-nucleotide polymorphisms (SNPs) typing. In solutions buffered to pH 7.0 (I = 0.11 M, at 5°C), DCPC can bind to thymine selectively over other nucleobases opposite an abasic site in DNA duplexes (5′-GTGTG CGTTG ANA TGGAC GCAGA-3′/3′-CACAC GCAAC TXT ACCTG CGTCT-5′, X = abasic site, N = target nucleotide) with a dissociation constant of 2.6 µM. The binding of DCPC is accompanied by a significant enhancement of its fluorescence (λmax, 412 nm), and the response is highly selective to thymine base. These binding and sensing properties allow a clear detection of thymine-related mutations present in polymerase chain reaction (PCR) amplification products.
A novel synergistic extraction system was investigated for the possible selective separation of light lanthanoids using an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, as an extraction solvent and 2-thenoyltrifluoroacetone and 18-crown-6 as extractants. Trivalent lanthanum was efficiently extracted as a cationic ternary complex by the cation-exchange process, whereas europium and lutetium showed relatively low extractability without forming respective ternary complexes. This result is thought to originate in a size-fitting effect of 18-crown-6 to lanthanum and the unique nature of the ionic liquid as a chelate extraction solvent.
The paper describes the fabrication and chemical applications of polymer microchannel chips, with special reference to in situ observations of the chemical/physical processes occurring in polystyrene microchannel chips, including those in microchannel-microelectrode/microheater chips. On the basis of absorption/fluorescence microspectroscopy and microelectrochemistry techniques, we show some characteristic features of liquid/liquid extraction, electrochemical responses, and photochemical/electrochemical/thermal synthetic reactions in microchannel chips.
A novel electrochemical DNA-based biosensor for the detection of deep DNA damage was designed employing the bionanocomposite layer of multiwalled carbon nanotubes (MWNT) in chitosan (CHIT) deposited on a screen printed carbon electrode (SPCE). The biocomponent represented by double-stranded (ds) herring sperm DNA was immobilized on this composite using layer-by-layer coverage to form a robust film. Individual and complex electrode modifiers are characterized by a differential pulse voltammetry (DPV) with the DNA redox marker [Co(phen)3]3+, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)6]3- as a redox probe in a phosphate buffer solution (PBS). A good correlation between the CV and EIS parameters has been found, thus confirming a strong effect of MWNT on the enhancement of the electroconductivity of the electrode surface and that of CHIT on the MWNT distribution at the electrode surface. Differences between the CV and EIS signals of the electrodes without and with DNA are used to detect deep damage to DNA, advantageously using simple working procedures in the same experiment.
The binding between glucose residues and wheat germ agglutinin (WGA) on thionine/glucose-modified magnetic microbeads was evaluated using voltammetry. Thionine is an electroactive compound and has two amino groups. Thionine was immobilized to magnetic beads via cross-linking of the amino groups on the beads with an amino group on thionine. Glucose was bound to the other amino group of thionine via the formation of a Schiff base. The beads were only several micrometers in size the same size, as cells. WGA-binding to glucose on the bead surface blankets the thionine moiety. Thus, WGA-binding could be detected as a decrease in peak current of the thionine moiety.
A method for the determination of ascorbic acid in vitamin C tablets based on a very simple paptode design on TLC strips is described. This procedure is based on the reduction of iron(III) with ascorbic acid and the formation of a colorful red complex with immobilized 2,2′-dipyridyl (dipy) on TLC strips. The linear range of the system was 20 - 200 ppm with a detection limit of 1 ppm and a relative standard deviation of 1.5% (n = 28). The parameters, such as pH, concentration of iron(III), concentration of dipy and the volume of dipy per 1 cm2 of TLC strips, were optimized. The proposed sensor was successfully applied for the determination of ascorbic acid in vitamin C tablets.
Fluorescent sensor molecules were synthesized by conjugation of iminodiacetamide derivatives with fluorescent moieties of different structures and their UV-visible and fluorescent properties were characterized in acetonitrile solvent. The fluorescent measurements revealed that the N-(2-naphthyl) and N-phenyl derivatives exhibit a distinct zinc ion-selectivity over alkali and alkaline earth metal ions, while N-(anthrylmethyl) and N-(3-methoxyphenyl) derivatives do not possess any ion-selectivities. In contrast to the fluorescent measurements, all ligands show Zn2+ selectivity over Ca2+ and Mg2+ ions in plasticized PVC membranes using potentiometric signal transduction. This observation found for N-(anthrylmethyl) and N-(3-methoxyphenyl) derivatives can be ascribed to the more hindered interaction between the signalling group of the ionophore and the central metal ion in PVC membranes than in acetonitrile solution upon complexation. From the fluorescent measurements it can also be concluded that the ligands with metal ions form complexes mainly with 2:1 stoichiometry (L2M). On complex formation a considerable decrease in the fluorescent intensity was observed for all ligands except the N-(anthrylmethyl) derivative, where a 25 - 30 fold fluorescence enhancement was found, which is explained by the photoinduced electron transfer (PET) mechanism. All ionophores exhibited serious hydrogen ion interference, therefore complexation-induced spectral changes were measured in aprotic acetonitrile solution.
Dual-gradient capillary electrochromatography (DG-CEC) was developed to provide superior performance with regard to the separation of ionized analytes; in this method, both the eluent composition and the applied voltage are varied during the separation procedure. As for the gradient in the eluent composition, a shift in the pH is employed to control not only the electrophoretic mobility, but also the retention factor of the analytes. The dual-gradient method was shown to be effective in increasing the resolution and reducing the chromatographic period of ionized analytes. Fourteen kinds of o-phthalaldehyde labeled amino acids were separated within 8 min using DG-CEC with multistage enlargement in the applied voltage. The separation efficiency increased particularly for highly retained amino acids in the dual-gradient, as compared to those in the ordinary single-gradient for the eluent.
A robotized sample-preparation method for the determination of Pu, which is recovered by extraction reprocessing of spent nuclear fuel, by isotope dilution mass spectrometry (IDMS) is described. The automated system uses a six-axis industrial robot, whose motility is very fast, accurate, and flexible, installed in a glove box. The automation of the weighing and dilution steps enables operator-unattended sample pretreatment for the high-precision analysis of Pu in aqueous solutions. Using the developed system, the Pu concentration in a HNO3 medium was successfully determined using a set of subsequent mass spectrometric measurements. The relative uncertainty in determining the Pu concentration by IDMS using this system was estimated to be less than 0.1% (k = 2), which is equal to that expected of a talented analyst. The operation time required was the same as that for a skilled operator.
The effect of heating on the refractive index (RI) and trace elemental compositions of glass was investigated in order to develop an accurate discrimination method of glass fragments exposed to the high temperature of fire on illegal entrance into a crime scene for robbery. Fragments taken from 5 different sheet glasses were subjected to RI measurement and analysis of trace elements using ICP-MS before and after heating at 764°C for 2 min. The difference in the RI between the heated and non-heated fragments ranged from 0.0012 to 0.0015, which corresponds to 6 times more than the variation of the RI within a pane of glass. In contrast, profiles of 10 elements (Co, Rb, Sr, Zr, Mo, Ba, La, Ce, Nd and Pb) in glass exhibited no significant difference between the heated and non-heated ones. In conclusion, the forensic discrimination of glass fragments must be performed not by RI measurement, but by analysis of the elemental compositions when glass evidence could be exposed to the high temperature of fire.
A coprecipitation method has been developed for the determination of Cr(III), Mn(II), Fe(III), Co(II), Cu(II), Cd(II) and Pb(II) ions in aqueous samples by flame atomic absorption spectrometry (FAAS) with the combination of pyridine, nickel(II) as a carrier element and potassium thiocyanate as an auxiliary complexing agent. The obtained coprecipitates were dissolved with nitric acid and measured by FAAS. The coprecipitation conditions, such as the effect of the pH, amounts of nickel, pyridine and potassium thiocyanate, sample volume, and the standing time of the precipitate formation were examined in detail. It was found that the metal ions studied were quantitatively coprecipitated with tetrakis(pyridine)-nickel(II)bis(thiocyanate) precipitate (TP-Ni-BT) in the pH range of 9.0 - 10.5. The reliability of the results was evaluated by recovery tests, using synthetic seawater solutions spiked with the analyte metal ions. The obtained recoveries ranged from 96 to 101% for all of the metal ions investigated. The proposed method was validated by analyses of two certified reference materials (NIST SRM 2711 Montana soil and HPS Certified Waste Water Trace Metals Lot #D532205). It was also successfully applied to seawater and dialysis solution samples. The detection limits (n = 25, 3s) were in the range of 0.01 - 2.44 µg l-1 for the studied elements and the relative standard deviations were ≤6%, which indicated that this method could fully satisfy the requiremets for analysis of such samples as seawater and dialysis solution having high salt contents.
A new method for the determination of linoleic acid (LA) in toothpaste by a routine analysis has been proposed. Studies were based on the ISO 5509 procedure, which was modified for the purpose of LA determination in the toothpaste. Gas chromatography (GC) was employed for the qualitative and quantitative determination of linoleic acid methyl ester. The content of LA (5.31%) in sunflower oil added to the toothpaste composition (0.5%) was determined, and then the optimization studies for the determination of LA in the toothpaste samples were carried out. The relative standard deviation (RSD) of the procedure developed was 9.96% (n = 9). The quantitative analysis showed that the content of LA in the toothpaste samples studied was 0.0258 ± 0.0011%. The detection limit of LA in toothpaste was approximately 0.001%.
C2-Symmetric two bis(amino alcohol)oxalamides (diamidediols) were synthesized and fully characterized. A new method was developed and successfully applied for the simultaneous preconcentration of both trace and toxic metals in water, by using C2-symmetric compounds. Under the optimum experimental conditions (i.e. pH = 10.0 ± 0.2, 2.75 × 10-3 mol L-1N,N′-bis[(1R)-1-ethyl-2-hydroxyethyl]ethanediamide (DAD1), 1.75 × 10-3 mol L-1N,N′-bis[(1S)-1-benzyl-2-hydroxyethyl]-ethanediamide (DAD2), 0.10% w/v octylphenoxy-polyethoxyethanol (Triton X-114)), calibration graphs were linear in the range of 2.5 - 25.0 ng mL-1 for Cu and Cd, 5.0 - 25.0 ng mL-1 for Co and Ni. The enrichment factors were 18, 23, 18 and 20 for Cd, Cu, Co and Ni in the case of DAD1, respectively; 20, 22, 17 and 20 for Cd, Cu, Co and Ni in the case of DAD2. The limits of detection for DAD1 were found to be 0.45, 0.50, 1.25 and 0.60 ng mL-1 for Cd, Cu, Co and Ni, respectively, and for DAD2 were found to be 0.44, 0.25, 0.60 and 1.55 ng mL-1 for Cd, Cu, Co and Ni, respectively. The developed method was applied to the determination of Cu, Cd, Co and Ni in water samples and certified reference materials with satisfactory results.
A rapid, relatively sensitive, and low-cost method for the determination of water-soluble urea content in dermatological therapy products and cosmetics is proposed using a new spectrophotometric assay with water as the only extraction solvent. Spectrophotometric methods involve addition of a known excess of bromate to urea in an acid medium, followed by the determination of residual bromine and chlorine reacting with methyl orange and measurement of absorbance at 505 nm. The absorbance increases linearly with urea concentration (r = 0.9998). The systems obey Beer's law for 6 - 90 µg ml-1. The calculated apparent molar absorbance values are found to be 4.537 × 103 dm3 mol-1 cm-1 and the Sandell's sensitivity is 0.013 µg cm-2. The variables affecting the rate of the reaction were investigated. The relative standard deviation for five-replication determination of 60 µg ml-1 urea was 2.1% and the detection limit of the method is 0.34 ng ml-1.
In the present study, chemometric analysis of visible spectral data of phospho-and silico-molybdenum blue complexes was used to develop artificial neural networks (ANNs) for the simultaneous determination of the phosphate and silicate. Combinations of principal component analysis (PCA) with feed-forward neural networks (FFNNs) and radial basis function networks (RBFNs) were built and investigated. The structures of the models were simplified by using the corresponding important principal components as input instead of the original spectra. Number of inputs and hidden nodes, learning rate, transfer functions and number of epochs and SPREAD values were optimized. Performances of methods were tested with root mean square errors prediction (RMSEP, %), using synthetic solutions. The obtained satisfactory results indicate the applicability of this ANN approach based on PCA input selection for determination in highly spectral overlapping. The results obtained by FFNNs and by RBF networks were compared. The applicability of methods was investigated for synthetic samples, for detergent formulations, and for a river water sample.
A two-dimensionally imaging spectrometer system was employed to measure spatial variations in the intensities of emission lines in a Cu-Mn-Ni alloy sample when they were excited from a laser-induced plasma with krypton gas. The emission zone of these lines shrank and had greater emission intensities with increasing gas pressure, and the intensities of their background also became more intense. It was thus found that the optimum observation zone for the analytical application varied with the pressure of the plasma gas. The two-dimensional distribution of the signal-to-background ratio for each analytical line was investigated to determine the measuring conditions for the emission analysis, indicating that the spatially-resolved measurement was generally superior to the conventional spatially-integrated measurement over the plasma region.
Both 206Pb-labeled trimethyllead (TML) and triethyllead (TEL) were synthesized from 206Pb-enriched metallic Pb certified reference material (NIST SRM 983) and iodomethane or iodoethane through a one-process reaction in a closed system using centrifuge tubes, respectively. Organolead compounds in an urban dust reference material (BCR CRM 605) were extracted with an acetic acid/methanol (1:1) solution, which was mechanically shaken for 24 h. After adjusting the pH of the extracted solution to pH 5, the extracted organolead compounds were derivatized by tetrabutylammonium tetrabutylborate (TATB) and measured with GC-ICPMS. The analytical results of TML and TEL for BCR CRM 605 were 8.22 ± 0.04 µg kg-1 (mean ± standard deviation, n = 3) and 1.12 ± 0.06 µg kg-1, respectively. The analytical results of TML agreed well with the certified value (7.9 ± 1.2 µg kg-1).
The use of electrospray ionization mass spectrometry (ESI-MS) in negative ion mode was investigated as a direct probe for identifying Al species in Al-accumulating hydrangea (Hydrangea macrophylla) samples. Cell sap solutions of hydrangea leaves were purified using Sephadex G-10 liquid chromatography and each fraction was analyzed using ESI-MS and ESI-MS/MS to identify Al species. In hydrangea leaves, a 1:1 Al-citrate complex was found as [AlH-1cit]- (m/z 215), where H3cit denotes citric acid. This result is consistent with that of Ma et al. who used 27Al-NMR.
A new method is described for the determination of silver based on triple-phase microextraction using diethyldithio-carbamate (DDTC) and thioaminophenol. Ag is separated and preconcentrated from the matrix of the sample solution, and finally determined by electrothermal atomic-absorption spectroscopy. The parameters that affect the efficiency were investigated. Under the optimized conditions, a 30-fold preconcentration factor with a detection limit of 0.05 µg L-1 was achieved. The relative standard deviation was 10% (5 determinations). The developed method was applied to the determination of trace Ag in water samples.
Two methods for the determination of potassium nitrate in mouthwashes, used against dentin hypersensitivity, have been simultaneously implemented in an sequence injection analysis (SIA) system. In addition to in-line dilution of the samples, the equipment simultaneously detected potassium and nitrate using two tubular potentiometric detectors, selective to each ion, providing a real-time assessment of the quality of the results. Both determinations were shown to be precise and accurate and the obtained results do not statistically differ from those furnished by applying the AES and HPLC reference methods.
An optical sensor for the detection of anionic surfactants was developed. The optical sensing membrane is a 2-nitrophenyloctyl ether-plasticized poly(vinyl chloride) membrane incorporating a lactone-form Rhodamine B (L-RB). The response of the optical membrane to anionic surfactants was a result of the ion-pair coextraction of an anionic surfactant and a proton into the PVC membrane. The L-RB forms an ion associate with the extracted anionic surfactant; simultaneously, the formed L-RB ion associate is accompanied by a spectral change. Namely, the extracted anionic surfactant changes the color of the membrane from light pink to dark pink (absorption maximum; 558 nm). The optical membrane responds to anionic surfactants, such as dodecylbenzenesulfonate, dodecylsulfate and di-2-ethylhexyl sulfosuccinate in the concentration range from 1 to 50 µM.
A new apparatus has been built that annexes a normal electrocardiograph, ECG, with the aim to enhance its capacity. It adds the normal ECG power to superpose multiple records of ECG altogether and averages out them and, further, makes sophisticated analysis, such as normalizing the peak heights, evaluating the half-line widths of the peaks, or that of the standard deviations of measurements like the inter peak distances. The results of the said calculations have not been obtainable using the former instruments, and are expected to be useful for clinicians.
We have developed an 8-ch capillary-based dispensing workstation with a variable capillary pitch mechanism. The capillary intervals can be varied from 1 to 9 mm to dispense different solutions simultaneously at an arbitrary dispensing pitch, allowing direct dispensing from microplates to integrated analytical systems. To evaluate the precision of its dispensing performance, droplets of Rhodamine G dye were dispensed onto glass slides and the values of the optical volume were analyzed. The error in the dispensed volume proved to be 0.54 nL when dispensing 20 nL. In dispensing small volumes, the volume error for this workstation was found to be about 100-fold less than that seen in conventional dispensers. Even highly viscous solutions containing 50% glycerol could be dispensed with precision. Rapid dispensing was also achieved. Moreover, the application of the workstation to preparing addressable 8 × 12 microsensor array chips was demonstrated, providing an independent and reproducible spot array.