Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.
Potential-modulation spectroelectrochemical methods at solid/liquid and liquid/liquid interfaces are reviewed. After a brief summary of the basic features and advantages of the methods, practical applications of potential-modulation spectroscopy are demonstrated using our recent studies of solid/liquid and liquid/liquid interfaces, including reflection measurements for a redox protein on a modified gold electrode and fluorescence measurements for various dyes at a polarized water/1,2-dichloroethane interface. For both interfaces, the use of linearly polarized incident light enabled an estimation of the molecular orientation. The use of a potential-modulated transmission-absorption measurement for an optically transparent electrode with immobilized metal nanoparticles is also described. The ability of potential-modulated fluorescence spectroscopy to clearly elucidate the charge transfer and adsorption mechanisms at liquid/liquid interfaces is highlighted.
A new type of salt bridge composed of a hydrophobic room-temperature ionic liquid, recently proposed (T. Kakiuchi and T. Yoshimatsu, Bull. Chem. Soc. Jpn., 2006, 79, 1017), has been shown to be satisfactorily usable in dilute aqueous solutions of submillimolar range. A stable phase-boundary potential has been demonstrated between an ionic liquid, 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C8mim+][C1C1N-), and an aqueous KCl solution of submillimolar level, which is lower than the solubility of [C8mim+][C1C1N-] in water, 1.6 mmol dm-3 at 25°C. The phase-boundary potential between [C8mim+][C1C1N-] and water is maintained constant over more than four orders of magnitude change in the concentration of an aqueous electrolyte solution. The ionic-liquid salt bridge is a superior alternative to salt bridges based on equitransferent electrolytes in practical applications, particularly, the potentiometry of samples of low ionic strengths, such as potentiometric pH measurements of rainwater.
Two simple, precise, inexpensive and sensitive voltammetric methods for the determination of lomefloxacin (LFX), sparfloxacin hydrochloride (SFX), gatifloxacin (GFX), and moxifloxacin (MFX) were developed. The present methods were first used to explore the adsorption behavior of the four investigated antibacterial agents at a hanging mercury dropping electrode (HMDE), by a direct method and secondly by a modification via their complexation with PdCl2. For the direct method, drugs were accumulated on HMDE, and a well-defined reduction peak was obtained in Britton-Robinson buffer of pH 7 for LFX and SFX, and pH 6 for GFX and MFX. The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH, accumulation time and potential. For the modified method, the adsorptive behavior of Pd(II)-4-quinolone complexes at the HMDE developed a strippining voltammetry peak at a more negative potential than that of the free Pd(II) ions (-1.05 V). The limits of detection (LOD) were 2 × 10-8 M, while the limits of quantification (LOQ) were 6 × 10-8 M for the investigated drugs. The methods were applied to the determination of LFX, SFX, GFX, and MFX in biological samples and pharmaceutical preparations, and also compared with the official reference methods. Complete validation of the proposed methods was also done.
A disposable electrochemical immunosensor for carcinoembryonic antigen (CEA) was proposed based on the antigen immobilized in a colloidal gold nanoparticles modified chitosan membrane on the surface of an indium-tin oxide (ITO) electrode. The different membranes were characterized by scanning electron microscope and electrochemical methods. Based on a competitive immunoassay format, the immobilized antigen of the immunosensor was incubated with a horseradish peroxidase (HRP) labeled antibody and sample CEA antigen, and the formed immunoconjugate in the immunosensor was detected by an o-phenylenediamine-H2O2-HRP electrochemical system. Under the optimal experimental conditions, the electrocatalytic current decreased linearly with the competitive mechanism. CEA could be determined in the linear range from 2.0 to 20 ng/ml with a detection limit of 1.0 ng/ml. The prepared CEA immunosensor is not only economic due to the low-cost ITO electrode obtained from industrial mass production, but is also capable with good stability and reproducibility for batch fabrication.
A voltammetric method for the determination of Cu(II) and Pb(II) in gasoline using sample preparation as three-component solutions (gasoline:propan-1-ol:water, 25:60:15 v/v/v) is proposed. HNO3 was employed as a supporting electrolyte and to allow the use of aqueous inorganic standards for calibration, even if the analyte species originally in gasoline is present as a metallo-organic form. A square-wave anodic sequential determination was used by measuring the stripping current of Cu(II) (at +104 mV) using a glassy carbon electrode (GCE) and, in a second run, measuring the Pb(II) stripping current (at -470 mV) using a bismuth-film deposited on the surface of the GCE. The method allowed the quantification of 1.7 × 10-9 mol L-1 of Cu and 1.4 × 10-10 mol L-1 of Pb employing a 1500-s accumulation time. Recovery tests using analyte spiked three-component solutions prepared with commercial gasoline samples enabled recoveries of Cu and Pb from 97 ± 8 to 102 ± 5%.
The stochastic properties of baseline noise in HPLC systems with a UV photo-diode array, photo-multiplier and γ-ray detector were examined by dividing the noise into auto-correlated random process (Markov process) and an independent process (white noise). The present work focused on the effect of the stochastic noise properties on a theoretical estimation of the standard deviation (SD) of area measurements in instrumental analyses. An estimation theory, called FUMI theory (Function of Mutual Information), was taken as an example. A computer simulation of noise was also used. It was shown that the reliability (confidence intervals) of theoretical SD estimates mainly depends on the following factors: the ratio of the white noise and Markov process occurring in the baselines; the number of data points used for the estimation; the width of a target peak for which the SD is estimated.
The rapid separation of inorganic anions was determined by capillary ion chromatography using monolithic silica capillary columns modified with dilauryldimethylammonium bromide. The stability of the modified stationary phase was satisfactory owing to a strong hydrophobic interaction between the lauryl groups of the reagent, even if the eluent did not contain dilauryldimethylammonium ion. Bromide in seawater samples could be determined by the present system. The repeatability of a retention time of bromide for six successive measurements was around 1.8% when a 500 mM sodium chloride aqueous solution was used as the eluent. Seawater samples were directly injected onto the prepared column without any interference of matrix ions, because an aqueous solution of high-concentration sodium chloride could be used as the eluent. Bromide in seawater samples could be determined within 2 min.
CdSe/CdS nanocrystals (NCs) have been synthesized in aqueous solution by using mercaptoethylamine as a stabilizer. The results of TEM, UV-Vis and FL spectra show that the product is of excellent crystal structure, uniform in radius, with extraordinary fluorescence characters. These CdSe/CdS NCs allow the ultrasensitive quantitative detection of DNA. Under the optimum conditions, linear relationships have been found between the relative fluorescence intensity and the DNA concentration in the ranges 0 - 10 and 10 - 100 µg mL-1; the linear equations are ΔF = 210 + 80.91C and ΔF = 946 + 10.57C (C, µg mL-1), respectively. The detection limits are 0.251 and 1.920 µg mL-1, correspondingly. The proposed method has been applied to the determination of DNA in pig liver. It is indicated that these NCs could become a newly kind of DNA probe. In addition, the mechanism of the binding reaction has also been explored. It is considered that the binding reaction is mainly due to static electricity forces.
The oral acute in vivo toxicity of 32 amine and amide drugs was related to their structural-dependent properties. Genetic algorithm-partial least-squares and stepwise variable selection was applied to select of meaningful descriptors. Multiple linear regression (MLR), artificial neural network (ANN) and partial least square (PLS) models were created with selected descriptors. The predictive ability of all three models was evaluated and compared on a set of five drugs, which were not used in modeling steps. Average errors of 0.168, 0.169 and 0.259 were obtained for MLR, ANN and PLS, respectively.
This work deals with As determination in marine sediment using ultrasound for sample preparation. It is shown that As can be quantitatively extracted from marine sediment using 20% (v/v) HCl and sonication. The slurry is centrifuged and the analyte is determined in the supernatant by hydride generation atomic absorption spectrometry (HG AAS). A flow injection (FI) system is employed for hydride generation, with 0.5% (m/v) NaBH4 used as reducdant and a 20% (v/v) HCl used as sample carrier. The limit of quantification is 1.6 µg g-1 of As, which is based on 800 µl of sample solution and 0.200 g of sample mass in a volume of 50 mL. Certified and non certified marine sediment samples were analyzed; the results were in accordance with the certified or reference values. Speciation analysis by HPLC-ICP-MS showed that As(V) is the only detectable As species present in the supernatant of the centrifuged sample.
A simple and highly sensitive spectrophotometric method for the determination of spermine (Spm) was established based on the ternary complex formation reaction of Spm with o-hydroxyhydroquinonephthalein (QP) as a xanthene dye and manganese(II) as a metal ion in the presence of a dispersion agent. The apparent molar absorptivity at 555 nm and the relative standard deviation of the proposed method were 1.4 × 105 dm3 mol-1 cm-1 and 0.50% (n = 10), respectively. In the method for flow-injection analysis (FIA), which employs a single-channel flow manifold system, a good linear relationship was observed over the 2 - 20 pg µl-1 range of Spm by direct injection.
A simple and sensitive flow-injection on-line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for ultra-trace lead determination in water, wine, and rice samples, with the salient advantages of its minimization of transition-metal interferences and tolerance to an ethanol matrix. A lead hydroxide precipitate was achieved by the on-line merging of a sample and an ammonium buffer solution and collected onto the inner walls of a knotted reactor (KR). Removal of the residual solution from KR was achieved by air flow, and dissolution of the precipitate was carried out by using 0.2 mol l-1 HCl. With a sample consumption of 11.7 ml, an enhancement factor of 16 was obtained at a sample throughput of 30 h-1. The limit of detection (3s) was 16 ng l-1 and the precision (RSD) for 1.0 µg l-1 Pb was 3.4%.
Halogens (fluorine, chlorine, bromine and iodine) were determined by activation analyses (neutron activation analysis (NAA), photon activation analysis (PAA) and prompt gamma-ray analysis (PGA)) for geological and cosmochemical solid samples. We studied how each analytical method was for the determination of trace amounts of halogens in rock samples. Radiochemical NAA (RNAA) showed the highest analytical reliability for three halogens (chlorine, bromine and iodine), whereas a set of four halogens (fluorine, chlorine, bromine and iodine) could be determined in principle by radiochemical PAA (RPAA) from a single specimen. Although it is a non-destructive method, PGA showed an analytical sensitivity for chlorine comparable to those of RNAA and RPAA.
A sensitive method was proposed and optimized for the determination of total mercury in fish tissue by using wet digestion, followed by cold vapor atomic absorption spectrometry (CVAAS) at the main resonance line of mercury (184.9 nm). The measurements were made using a new type of a non-dispersive mercury minianalyzer. This instrument was initially designed and built for atmospheric mercury-vapor detection. For determining mercury in aqueous samples, the minianalyzer was linked with a mercury/hydride system, Perkin Elmer Model MHS-10. To check the method, the analyzed samples were spiked with a standard solution of mercury. The recoveries of mercury spiked to wet fish tissue were >90% for 0.5 - 0.8 g samples. The results showed a better sensitivity (about 2.5 times higher) when using the mercury absorption line at 184.9 nm compared with the sensitivity obtained by conventional CVAAS at 253.7 nm.
Emisson spectra and time-resolved two-dimensional (2D) emission images of the electron-ion dielectronic recombination (i.e. a reversal process of auto-ionization) line of neutral Cu atoms, the selectively excited Cu ionic line, and normal Cu atomic line were observed for understanding the excitation mechanisms of Cu neutral and ionic lines in a low-pressure laser-induced plasma (LP-LIP) of Ar. From the observations, the number of charged particles around the emitting species seems to increase with increasing Ar pressure. Different time-resolved 2D emission images were observed among the selectively excited Cu ionic line and other Cu emission lines resulting from the different excitation mechanisms of the respective emission lines. Collisions of the second kind and electron-ion recombinations were found to be one of the major excitation mechanisms of Cu in Ar LP-LIP.
The emission characteristics of several Cu lines emitted from a Ne-Ar mixed gas glow discharge plasma were investigated. The addition of small amounts of Ar to a Ne plasma increases the sputtering rate of a Cu sample because Ar ions, which work as the impinging ions for cathode sputtering, are predominantly produced through Penning ionization collisions between Ne metastables and Ar atoms. Ar addition also elevates the number density of electrons in the plasma. These changes occurring in the Ne-Ar mixed gas plasma result in enhanced emission intensities of the Cu lines. The Cu II 270.10-nm and the Cu II 224.70-nm lines yield different intensity dependence on the Ar partial pressure added. This phenomenon is because these Cu II lines are excited principally through different charge transfer processes: collisions with Ne ions for the Cu II 270.10-nm line and collisions with Ar ions for the Cu II 224.70-nm line. The shape of sputtered craters in the Ne-Ar glow discharge plasma was measured. The depth resolution was improved when Ar was added to a Ne plasma because the crater bottoms were flatter with larger Ar partial pressures.
The hydroxyl radical (OH radical) formation rates from the photo-Fenton reaction in river and rain water samples were determined by using deferoxamine mesylate (DFOM), which makes a stable and strong complex with Fe(III), resulting in a suppression of the photo-Fenton reaction. The difference between the OH radical formation rates with and without added DFOM denotes the rate from the photo-Fenton reaction. The photoformation rates from the photo-Fenton reaction were in the range of 0.7 - 45.8 × 10-12 and 2.7 - 32.3 × 10-12 M s-1 in river and rain water samples, respectively. A strong positive correlation between the OH radical formation rate from the photo-Fenton reaction and the amount of fluorescent matter in river water suggests that fluorescent matter, such as humic substances, plays an important role in the photo-Fenton reaction. In rain water, direct photolysis of hydrogen peroxide was an important source of OH radicals as well as the photo-Fenton reaction. The contributions of the photo-Fenton reaction to the OH radical photoformation rates in river and rain water samples were in the ranges of 2 - 29 and 5 - 38%, respectively. Taking into account the photo-Fenton reaction, 33 - 110 (mean: 80) and 42 - 110 (mean: 84)% of OH radical sources in river and rain water samples, respectively, collected in Hiroshima prefecture were elucidated.
Photo-modulation voltammetry with a 325-nm beam from a He-Cd laser was applied to an examination of a photochemical reaction of p-aminodiphenylamine. The photo-modulation voltammogram exhibited a peaked wave proportional to the concentration of p-aminodiphenylamine, and essentially agreed with a difference between linear scan voltammograms under irradiation and non-irradiation. From the absorption spectra of p-aminodiphenylamine and a pH dependence of the voltammograms, it was inferred that a dimer dication of p-aminodiphenylamine was photochemically formed and transferred from the aqueous solution to the 1,2-dichloroethane solution.
A micellar solution of cetylpyridinium chloride (CPC) can separate into two phases due to a temperature change or to the addition of salts. Platinum(II), (IV) and palladium(II) reacted with chloride ions to form stable anionic complexes of PtCl42-, PtCl62- and PdCl42-, respectively, and were adsorbed onto the CPC gel phase. The CPC phase plays the role of an ion-exchange adsorbent for the anionic complexes. By such a procedure, the precious metals of platinum and palladium could be separated from base metals such as copper, zinc and iron. The kinetic separation was performed by a ligand exchange reaction of the palladium(II) chloro-complex with EDTA at 60°C. The anionic palladium(II)-EDTA complex could not bind the opposite charged CP+ and was desorbed from the CPC phase. In the aqueous phase, the recovery of palladium(II) by the double-desorption was 101.1 ± 1.2%. The platinum(II) and (IV) chloro-complexes were stable for at least 30 min and remained in the CPC phase.
An intercomparison exercise was conducted using the recently developed Reference Material for Nutrients in Seawater (RMNS). Discrepancies of reported values among laboratories were greater than the homogeneity of RMNS samples and the reported analytical precision of nutrients. The variability of in-house standards of the participating laboratories might be the most likely source of interlaboratory discrepancies. Therefore, the use of common reference materials, i.e. certified RM, is essential to establish and improve the comparability of nutrient data of the world's oceans.