The nature of “hot spots” in surface-enhanced Raman scattering (SERS) and the novel fabrication of Ag thin films for efficient SERS measurements are the main focus of this review. By using 4-aminobenzenthiol or 1,4-phenylenediisocyanide molecules we can characterize the nanogap formed by a metal nanoparticle and a flat metal substrate, or the gap between two spherical metal nanoparticles. These nanogaps are indeed SERS-active sites and the apparent size of “hot spots” is found to be very limited. To use SERS for routine chemical identifications, the substrates should be stable, reproducibly prepared, inexpensive, and easy to make. We introduce a method for the facile fabrication of Ag thin films, simply by soaking glass substrates in ethanolic solutions of AgNO3 and butylamine, and their application as efficient SERS substrates. Ag-coated glass capillary and Ag deposited magnetic nanoparticles can be used for the microanalysis of bio- and hazardous chemicals.
Conservation methods applied to historical shipwrecks increasingly rely on combining modern analytical techniques to obtain new insights for specially adapted conservation treatments. Crystalline salts formed on waterlogged wood are identified by powder X-ray diffraction while X-ray fluorescence measurements along wood cores show penetration profiles of contaminating elements. Dedicated synchrotron-based X-ray absorption spectroscopy, especially sulfur and iron K-edge XANES, allows speciation of the large amounts of detrimental sulfur and iron compounds that often are found accumulated within the hull timbers, while high resolution X-ray imaging shows the distribution within the wood microstructure. By fitting spectra of model compounds to high quality sulfur K-edge XANES spectra one can obtain the relative amounts of different types of functional sulfur groups. FT-IR, NMR, ESCA, MALDI-TOF mass spectrometry and size exclusion chromatography are other useful techniques to analyze the status of the wood and of the consolidation agent polyethylene glycol. Examples are given from analyses of famous artifacts.
When ternary mixed solutions of water–hydrophilic/hydrophobic organic solvents are fed into a microspace under laminar flow conditions, the solvent molecules are radially distributed in the microspace. The specific fluidic behavior of the solvents is termed “tube radial distribution phenomenon” (TRDP). In this study, water–acetonitrile–ethyl acetate mixed solutions (3:8:4 volume ratio) containing fluorescent dyes, perylene (0.1 mM) and Eosin Y (1 mM), were fed into fused-silica capillary tubes (75 μm i.d.) for investigating the TRDP with a fluorescence microscope-CCD camera under various analytical conditions. The pressure at the observation point for the fluorescence on the tube was changed by altering the flow rates, capillary total lengths, and capillary effective lengths. The obtained fluorescence images showed that the TRDP in the capillary tube created the inner and outer phases, i.e., the organic solvent-rich major inner and the water-rich minor outer phases in this case, providing the kinetic liquid–liquid interface. The formation of the inner and outer phases in the capillary tube was observed at flow rates of 0.5 – 2.0 μL min−1 under the present analytical conditions. We also discuss the specific formation locations of the major and minor solvents.
A new type of optical rotation (OR) detector based on the phase retardation of the first-order diffraction beam has been constructed. The proposed detector responded to only OR properties by eliminating the circular dichroism (CD) effect. Thus, it could measure the optical rotatory dispersion curves in the Cotton band. Although the optical system requires the incident beam in which the phase retardation is 0.5π, the actual retardation was estimated to be around 0.3π. It means that the OR signal intensity can be doubled. Since the proposed detector works over a range of UV wavelengths, there was a compound whose OR signal intensity was higher than the CD signal intensity. The OR detection was superior to CD in stability and in defining the baseline.
This paper describes the performance of our automated acidic (CH3COOH, HCOOH, HCl, HNO2, SO2, and HNO3) gases monitor utilizing a parallel-plate wet denuder (PPWD). The PPWD quantitatively collects gaseous contaminants at a high sample flow rate (∼8 dm3 min−1) compared to the conventional methods used in a clean room. Rapid response to any variability in the sample concentration enables near-real-time monitoring. In the developed monitor, the analyte collected with the PPWD is pumped into one of two preconcentration columns for 15 min, and determined by means of ion chromatography. While one preconcentration column is used for chromatographic separation, the other is used for loading the sample solution. The system allows continuous monitoring of the common acidic gases in an advanced semiconductor manufacturing clean room.
Novel polymer-coated fiber-packed microcolumns in liquid chromatography (LC) have been developed. Typical polymeric materials, such as polydimethylsiloxane and polyethyleneglycol, which are conventional stationary phases of capillary columns in gas chromatography (GC), have been employed as coating materials onto the surface of fine filaments. Packed longitudinally with a bundle of polymer-coated filaments into a stainless-steel capillary of 0.8 mm i.d., 150 mm length, several types of polymer-coated fiber-packed columns were prepared, and the retention behavior of aromatic compounds on these columns has been studied. A good linear relationship was obtained for van’t Hoff plots over the temperature range between 0 and 200°C, clearly indicating an excellent heat-resistant property of these polymer-coated fibrous stationary phases. Taking advantage of the heat-resistant feature of the fibrous stationary phases, the separation of several test mixtures with temperature-programmed elution was studied, where a solvent gradient program was additionally introduced if needed. Separation was also carried out with pure water as the mobile phase using an appropriate temperature program.
A solution of polyhexamethylene biguanide hydrochloride (PHMB-HCl) was titrated with a standard solution of potassium poly(vinyl sulfate) (PVSK) using crystal violet (CV) as an photometric indicator cation. The end point was detected by a sharp absorbance change due to an abrupt decrease in the concentration of CV. A linear relationship between the concentration of PHMB-HCl and the end-point volume of the titrant existed in the concentration range from 2 to 10 × 10−6 eq mol L−1. Back-titration was based on adding an excess amount of PVSK to a sample solution containing CV, which was titrated with a standard solution of poly(diallyldimethylammonium chloride) (PDADMAC). The calibration curve of the PHMB-HCl concentration to the end point volume of the titrant was also linear in the concentration range from 2 to 8 × 10−6 eq mol L−1. Both photometric titrations were applied to the determination of PHMB-HCl in a few contact-lens detergents. Back-titration showed a clear end point, but direct titration showed an unclear end point. The results of the back-titration of PHMB-HCl were compared with the content registered in its labels.
Yeast cells displaying organophosphorus hydrolase (OPH), which was anchored using a lectin-like cell-wall protein (Flo1p), were used as a biocatalyst for the detection of organophosphorus compounds (OPs). The concentration of p-nitrophenol produced by the hydrolysis of the OPs paraoxon was calculated from the absorbance change at 415 nm during a 30-min reaction. The apparent Michaelis–Menten constant (K′m) for surface-displayed OPH was estimated to be approximately 50 μM, which is consistent with the value of purified OPH, and shows that cell-surface expression is a useful strategy to overcome the mass-transport resistance of substrates across the cell membrane. Notably, the long-term storage stability of the enzyme activity exceeded 40 days when cells displaying OPH were preserved at temperatures below –4°C. A fiber-optic biosensing system was also constructed using a commercial optical-fiber detection device and yeast cells with surface-displayed OPH. A linear relationship was obtained for paraoxon concentrations of up to 50 ppm (182 μM), with a detection sensitivity of 0.0043 A.U. per ppm (R2 = 0.9574) and a detection limit of 5 ppm (18 μM).
An automated multi-pumping flow system was developed for the in-line generation of singlet oxygen (1O2) and subsequent assessment of the scavenging capacity against this reactive species. 1O2 was generated by dismutation of hydrogen peroxide catalyzed by molybdate ions. The evaluation of the scavenging capacity was based on the inhibition of the chemiluminescence reaction of luminol with 1O2. The proposed system used solenoid micro-pumps as the only active components of the flow manifold, enabling the reproducible insertion and efficient mixing of sample and reagents as well as the transportation of the sample zone towards detection for chemiluminescence measurement, assuring a strictly reproducible timing of all analytical tasks. Several compounds were evaluated as possible 1O2 scavengers. The obtained results showed that only ascorbic acid, dipyrone and tryptophan exhibited scavenging capacity, with IC50 values of 3.36 × 10−5, 7.84 × 10−5 and 1.28 × 10−2 mol L−1, respectively.
The applicability of poly(acrylamide) grafted onto cross-linked poly(4-vinyl pyridine) (P4-VP-g-PAm) has been investigated for the separation, preconcentration and speciation of Hg(II) and MeHg(I). In batch experiments, Hg(II) was quantitatively retained (≥95%) in the pH range of 1.0 – 8.0, whereas the sorption of MeHg(I) was insignificant in the pH range of 1.0 – 2.0. Freundlich and Langmuir isotherm models were investigated in order to characterize the sorption, and the capacity of the sorbent was found to be 817 mg Hg(II) g−1. The limit of detection (3δ above blank) was 2 ng L−1. The sorbent has excellent selectivity for Hg(II) in the presence of Pb(II), Zn(II), Cu(II), Cd(II) and Fe(III) ions. The method was successfully applied to the determination of Hg(II) and MeHg(I) in seawater and estuarine water. The sorbent can remove Hg(II) at pH 2.0, and therefore makes the determination of MeHg(I) possible, even if the sample contains a high amount of Hg(II).
No exact and digital diagnostic methods for depression have been found. In this study, we prepared a 5-HT biosensor based on screen-printed electrode and applied it to a rat depression model caused by chronic unpredictable mild stress (CUMS). During CUMS, the blood 5-HT and the depression behavior of the depressed rats and the rats treated by antidepressants were recorded. The correlation coefficient of 5-HT was 0.9966 (0 – 4 × 10−6 M) on the sensor. Results demonstrated that 5-HT level of the depressed rats declined while the depression behavior was aggravated. Fluoxetine (20 mg/kg) and lentinan (10, 20 mg/kg) mildly elevated 5-HT level and slowly regulated the behavior. Mifepristone (20 mg/kg) and Rhizoma Coptidis water extract (10, 20, 100 mg/kg) quickly reversed 5-HT level and the depression behavior. This sensor can accurately test blood 5-HT and might be applied to rapid diagnosis for depression and evaluation of antidepressants effect.
A spectrometric method for the determination of anionic surfactants in environmental water samples using the [Co(III)-(5-Cl-PADAP)2]+ chromophore was technically improved for practical use. An anisole-extraction procedure was alternatively introduced and optimized in place of the earlier benzene-extraction procedure. The molar absorptivity for SDS found by the Co(III)-5-Cl-PADAP/anisole method was 72000 L mol−1 cm−1 at 560 nm, which was ca. 1.3-times higher than those by the Co(III)-5-Cl-PADAP/benzene method. The analytical sensitivity was almost independent of the kind of anionic surfactants. The calibration lines for SDS, LAS, and SSS were all linear between 1.0 × 10−7 and 1.0 × 10−5 mol L−1 with acceptable r2 values of 0.9998, 0.9995, and 0.9999, respectively. The method was applied to the analyses of river, well, and seawater samples, providing the compatible results by means of the standard-addition method. In the case of seawater, a phase-washing treatment of the extracted species using dilute HCl was effective to decrease the high blank absorbance. The Co(III)-5-Cl-PADAP/anisole method, showing no glass-adsorption problem, is more advantageous than the methylene-blue and ethyl-violet methods.
Carboxymethyl-β-cyclodextrin (CMCD)-capped ZnO/ZnS/MgO nanocomposites, which combined water-soluble host molecules with multi-shelled nanocrystals, have been prepared. The nanocomposites have good fluorescence performance and host-guest complexation. Thus, a novel fluorescent sensor for the determination of p-nitroaniline based on the molecular recognition of water-soluble CMCD-capped ZnO/ZnS/MgO nanocomposites has been proposed. Factors affecting the p-nitroaniline detection were investigated, and the optimum conditions were determined. Under the optimum conditions, the relative fluorescence intensity of CMCD-capped ZnO/ZnS/MgO nanocomposites was linearly proportional to the concentration of p-nitroaniline over the range from 8.33 × 10−7 to 5.83 × 10−5 mol L−1 with a correlation coefficient of 0.9967 and a detection limit of 6.38 × 10−7 mol L−1. The proposed method was successfully applied to the determination of p-nitroaniline in water samples. The related mechanisms were also discussed.
We describe a new practical capillary electrophoresis/electrospray ionization–mass spectrometry (CE/ESI-MS) method for the forensic analysis of phosphorus-containing amino acid-type herbicides, glyphosate (GLYP), glufosinate (GLUF) and bialaphos (BIAL). A new sheathless interface, a high sensitivity porous sprayer (HSPS), was used in this study. The limits of detections of GLYP, GLUF and BIAL were 7.6, 0.61 and 0.57 pg, respectively. These values were 4 – 36 times lower than these obtained by conventional CE/ESI-MS using a sheath liquid. The developed method was successfully applied to the analysis of beverages spiked with the herbicides.
NH4+ concentration in an individual droplet was determined by forming a Liesegang ring on a gelatin film containing NaB(C6H5)4. The NH4+ concentration (mol L−1 abbreviated to M) was calculated from the NH4+ amount (mol) ascertained in a droplet using pixel count measurements. The droplet volume (L) was calculated by measurement of the diameter of a droplet print on the gelatin film. For rainwater, the NH4+ concentration estimated using this method corresponded with results obtained using ion chromatography.
A rapid and sensitive method has been developed for the determination of benzaldehyde, a toxic oxidation product of the widely used preservative and co-solvent benzyl alcohol in injectable formulations of non-steroidal anti-inflammatory drugs, diclofenac, vitamin B-complex and Voltaren injection solutions by using dispersive liquid–liquid microextraction followed by gas chromatography. This method involves the use of an appropriate mixture of extraction solvent (43.0 μL 1,2-dichloroethane) and disperser solvent (1.0 mL acetonitrile) for the formation of a cloudy solution in a 5.0-mL aqueous sample containing benzaldehyde. The linear range was 1.0 – 1000 μg L−1, and the limit of detection was 0.2 μg L−1 for benzaldehyde.
On page 544, Table 4 should be replaced as follows. In the new table, the values in the Slope and Intercept columns have been changed. Accordingly, the values of Flack of fit have been newly calculated.