An imaging spectrograph equipped with a CCD detector was employed to measure two-dimensional emission images from a glow discharge plasma in atomic emission spectrometry. The emission images at Zn I 334.50 nm for a zinc sample and at Cu I 324.75 nm for a copper sample could be obtained. Their emission intensities were not uniform in the radial direction of the plasma region but became weaker at larger distance from the central zone. The two-dimensional distribution would result from a spatial variation in the excitation efficiency of the plasma and thus provide useful information for understanding the excitation processes occurring in the plasma.
The direct molecular analysis of a live single cell viewed under a video-microscope has been developed. The cell contents are sucked into a nano-electrospray tip, and hundreds of peaks of ionic compounds of low molecular weight are detected by nano-ESI Q-TOF mass spectrometry (MS). Cell-specific MS peaks in a single mouse-embryonic fibroblasts cell are extracted by a t-test, and one of the peaks is proceeded to MS/MS analysis for molecular identification. This method is direct and quick to identify the molecules of a cell with simultaneous observation by a video-microscope.
The laser ablation (LA) method is an effective technique for quantitative analysis. In the present work, a new LA system was developed for the high-sensitivity analysis of metal materials using inductively coupled plasma mass spectrometry (ICP-MS). This system consists of a high-frequency Q-switched laser and 2 scanning mirrors for scanning the ablation spot in an adequately large area of the specimen without vacant spaces. The influence of elemental fractionation (non-stoichiometric generation of vapor species) can be eliminated by repetitive irradiation of this pattern on the same area. Particles generated with an average laser power of 0.6 W with the developed LA system gave intensity and stability substantially similar to that of a 500 µg/ml solution steel sample in solution ICP-MS. The analytical performance of the developed LA-ICP-MS was compared with that of a solution ICP-MS using NIST steel SRMs. The performance of the newly-developed system is comparable to that of conventional solution ICP-MS in both accuracy and precision. The correlation coefficients between the contents and the intensity ratios to Fe were over 0.99 for most elements. The relative standard deviation (RSD) obtained by LA-ICP-MS revealed that this system can analyze iron samples with good precision. The results of ultra trace level analysis of high-purity iron showed that developed LA-ICP-MS is capable of analyzing ppm concentration levels with a 20 - 30 ppb level standard deviation. The detection limit was on the order of 10 ppb for most elements.
This paper demonstrates a writing and reading methodology, which allows both to create and to detect sub-100-nm carboxyl-terminated patterns on light-transmissive quartz substrates by the same instrumental system. Such a technique, capable of creating carboxyl-terminated nanopatterns, offers several benefits for the miniaturization of biochips, since the carboxyl-terminated nanopatterns allow the easy immobilization of biomolecules by amide bond formation. As a consequence, increasingly miniaturized biochips require suitable analytical methods for the detection of nanopatterns. In our approach, carboxyl-terminated nanopatterns of down to 80 nm width were created using a photolabile silane coupling agent and a UV laser coupled to a near-field scanning optical microscope (NSOM). The same NSOM system was then used in a next step to detect the fabricated carboxyl-terminated nanopatterns after modification with a fluorescent label. Furthermore, as a first step towards biochip applications, the successful immobilization of several biomolecules, such as streptavidin, IgG and DNA on carboxyl-terminated nanopatterns was demonstrated. We have shown that our approach has the potential to lead to a new bioanalytical method, which enables one to write and to read biochips on a sub-100-nm scale by the same system.
Several redox enzymes were examined for enzymatic/electrochemical-recycling systems in order to measure p-aminophenol (PAP) with high sensitivity. Glucose oxidase (GOD) and diaphorase (DI) worked well as catalysts for recycling electrode systems: these enzymes effectively reduced p-iminoquinone (PIQ), the electrochemically-oxidized form of PAP, and caused an enhancement in the electrochemical signals (anodic currents in the voltammogram and amperogram) by ∼ 100 fold. The lower detection limits for PAP were estimated to be 50 nM with the GOD system and 2 nM with the DI system. We combined the enzymatic-recycling electrode using DI with an enzyme immunoassay system to measure atrial natriuretic peptide (ANP), an important marker peptide hormone involved in heart diseases. ANPs from serum samples at ppt-levels were determined appropriately using the present assay system.
The voltammetric behavior of wheat-germ agglutinin (WGA) on a chitin-modified carbon-paste electrode (CPE) was investigated using glucose labeled with an electroactive compound. WGA usually consists of two subunits, each with two binding sites for sugars. WGA was immobilized on the electrode surface by selective binding to a N-acetylglucosamine residue of chitin. Because glucose also combines with WGA, the glucose was coupled with electroactive daunomycin to evaluate the binding. When a WGA-labeled glucose complex was formed, the electroactive moiety became electroinactive. The binding caused a decrease in the peak current of the labeled glucose. In a measurement of only daunomycin used as a label, the peak current in a solution with WGA was similar to that in a solution without WGA. Therefore, it is clear that the labeled glucose was held in the remaining binding site of WGA on the electrode surface. Thus, a CPE modified with chitin would be powerful as a reaction field between sugar and lectin.
A sequential injection-square-wave anodic stripping voltammetry (SIA-SWASV) is proposed for the simultaneous determination of Pb(II), Cd(II) and Zn(II), employing an in situ plated bismuth film screen-printed carbon electrode (Bi-SPCE) as a working electrode and hydrochloric acid as a supporting electrolyte. Bi(III) and analyte metal ions were on-line deposited onto a SPCE at -1.4 V vs. Ag/AgCl for 180 s. At a stopped flow, a square-wave voltammogram was recorded from -1.3 to 0 V vs. Ag/AgCl. The experimental conditions were optimized. Under the optimum conditions, the linear ranges were 0 - 70 µg L-1 for Pb(II) and Cd(II), and 75 - 200 µg L-1 for Zn(II). The limits of detection (S/N = 3) were obtained at concentrations as low as 0.89 µg L-1 for Pb(II) and 0.69 µg L-1 for Cd(II) for a 180-s deposition time. The proposed method was applied to the determination of Pb(II), Cd(II) and Zn(II) in water samples with satisfactory results.
The analytical features of the reaction between N-phenylanthranilic acid (PAA) and potassium periodate in acidic medium are explored with the aim of improving the catalytic kinetic determination of iron in water samples. In the presence of Fe(II, III), PAA is oxidized by potassium periodate in a formic acid medium to form a violet-colored compound. The reaction is followed spectrophotometrically by measuring the increase in the absorbance of the oxidation product at 525 nm. The variables that affected the reaction rate were investigated and the reaction conditions were established. Calibration graphs are linear in the range of concentrations 2 - 500 ng mL-1. As low as 10-8 mol L-1 Fe(II, III) can be easily determined by the fixed time method. The established catalytic method was successfully applied to the determination of iron in tap water and in pharmaceutical samples.
The present work explores the slurry sampling approach for automatic, flow-based plant analysis. For this purpose, pinch valves were introduced into a multi-syringe flow injection analysis manifold to provide the repeatable aspiration of a few microliters of plant suspension before the material was further processed through the flow system. For validation of the proposed approach, the determination of potassium by flame emission spectrometry was implemented. Several parameters were studied: the concentration of plant particles in the sample suspension and the utilization of matrix modifiers. Microwave digestion was also implemented; no significant difference was found when certified reference material was analyzed with or without the in-line digestion step. The system was successfully applied to 13 samples within a concentration range of 2.5 to 100 mg g-1. A determination frequency of 28 h-1 was achieved and the precision was better than 4.0% (n = 12).
A method of high-performance size-exclusion chromatography (HPSEC) for a wide variety of soil humic acids (HAs) was developed. Two types of soil HAs (Cambisol and Andosol HAs), which have substantially different chemical properties, showed different effects of salt and organic solvent concentrations in the eluent on chromatograms. A Shodex OHpak SB-805 HQ column with 10 mM sodium phosphate buffer (pH 7.0) containing 25% of acetonitrile (v/v) was found to be applicable for different HAs, and showed high reproducibility and recovery (87.0 - 94.5%). The Cambisol HA was fractionated into five fractions using an ultrafiltration with different molecular-weight cut-offs. The order of the molecular weights of the five fractions calculated from the HPSEC analysis corresponded to that defined by ultrafiltration. This supported the reliability of the method.
Poly(4-vinylpyridine)-modified silica with high grafting density have been prepared by a grafting-from (g-from) approach through radical chain-transfer reactions. The widely used silane coupling agent 3-mercaptopropyltrimethoxysilane was used to prepare thiol-terminated silica. Chain-transfer reaction and polymerization of 4-vinylpyridine was carried out using α,α′-azobisisobutyronitrile as an initiator. Thiol-terminated silica and polymer-modified silica were both characterized qualitatively and quantitatively. The quantification of the organic phase has been done by thermogravimetric analysis and elemental analysis. Thus, the modified silica was used as a packing material and the retention behavior of polycyclic aromatic hydrocarbons (PAHs) was studied in normal-phase high-performance liquid chromatography. Results were compared with those of poly(4-vinylpyridine)-modified silica prepared by a grafting-to (g-to) approach. Commercially available aminopropyl-bonded silica and bare silica columns were also used as reference columns. The column of poly(4-vinylpyridine)-grafted silica prepared by the g-from method, having higher grafting density, provided the better retentivity and selectivity for PAHs compared to the other reference columns.
In this study, a gas chromatographic method is presented for the determination of calcium stearate after its conversion to stearic acid in a polymeric matrix. A solution of hydrochloric acid in 2-propanol is used as an extracting solvent of calcium stearate and its converter to stearic acid. For stearic acid preconcentration before its injection to a separation system, a recently presented extraction method, dispersive liquid-liquid microextraction, using carbon tetrachloride as an extracting solvent is used. Finally, 1 µL of the organic phase collected at the bottom of a conical test tube after centrifuging is injected into a gas chromatograph (GC) for quantification. This method has a relatively broad linear dynamic range (50 - 2000 mg/L) with a limit of detection (LOD) of 15 mg/L for stearic acid in solution. The LOD of the proposed method in a polymeric sample using 10 mg of polymer is 60 ppm as calcium stearate. Some effective parameters, such as the time and temperature of heating, the concentration of hydrochloric acid and the volume of distilled water, were studied.
In this study, a fast, simple and highly sensitive method that employs liquid phase microextraction (LPME)-GC/MS was developed to analyze trace benzophenones (BPs) in river-water samples. The tip of a 10-µl microsyringe filled with toluene (3 µl) was inserted into 2 ml of a river-water sample, and fixed at 5 mm below the water surface of the sample. A toluene droplet was made on the tip of the syringe, and extraction was conducted while agitating at 500 rpm for 15 min. After extraction, 2.0 µl of the extract was put into the syringe again, and directly introduced to GC/MS. The limits of detection (S/N = 3) and quantification (S/N >10) of BPs were 10 and 50 pg ml-1, respectively. The results of a recovery test ranged over 93.3 - 101.1% (RSD, less than 10%; n = 6). The results of BPs determinations in the river-water samples showed that BPs (ND - 68.9 pg ml-1) were detected.
The application of inductively coupled plasma mass spectrometry (ICP-MS) to forensic chemistry was studied. The developed method, air-segmented sample injection (ASSI) coupled with ICP-MS, allowed the determination of about 25 elements at the sub-ppb level with only 0.2 ml of a sample solution. The optimum sample flow rate was found to be 0.4 ml min-1, along with a sample suction time of 30 s. The proposed method was validated by determining trace elements in river-water certified reference material (SLRS-4) issued by National Research Council Canada. The analytical results of the proposed method were in good agreement with the certified values. This method was successfully applied to a human hair sample, the volume of which was 3 ml.
To determine the rate constants for the second order consecutive reactions of the form U + V —k1→ W —k2→ P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB® functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method.
An ensemble, a model-independent technique based on combining several models for classification/regression tasks, allows us to achieve a high accuracy that is often not achievable with single models. Such combinations have gained increasing attention in many fields. This paper proposes the use of random subspace (RS)-based regression ensemble as an alternative method for near-infrared (NIR) spectroscopic calibration of tobacco samples. Because of the considerable reduction of variables in a random subspace, multiple linear regression (MLR) is used as the base algorithm and the method is therefore also referred to as RS-MLR. The overall performance of the proposed RS-MLR method is compared to those of partial least square regression (PLSR), kernel principal component regression (KPCR) and kernel partial least square regression (KPLSR). The results reveal that the RS-MLR method not only has a simple concept but also can produce a more parsimonious and more accurate calibration model than PLSR, KPCR and KPLSR, at a lower computational cost. Besides, we also found that the RS-MLR method is very appropriate for the so-called small sample problems and that the calibration models built by RS-MLR are less sensitive to overfitting.
Sets of time domain reflectometry waveforms analyzed with appropriate chemometric methods, instead of typical single waveform analysis, enable one to detect and quantify differences between waveforms, even if they appear at the level of several orders of magnitude below the scale of the measurements. Typical applications of such an approach to samples of healthy and damaged grain showed that differences contributing five orders of magnitude below the scale are still detectable. Under more rigorous experimental conditions, the level of detectable differences can be expected to be even lower.
The reliability of neutron-induced prompt gamma-ray analysis (PGA) was examined for the determination of Na and Mg in geological and cosmochemical rock samples, because they tend to have been erroneously determined for such samples. JB-1 (basalt standard rock) and Allende (chondritic meteorite) powder samples were repeatedly analyzed by using thermal or cold neutron-guided beams of the JRR-3M research reactor at Japan Atomic Energy Agency. In critically evaluating calculated values for major prompt gamma-rays of Na and Mg, it was observed that a 472.2 keV peak for Na and a 2828.2 keV peak for Mg yielded reasonable consistency with corresponding recommended values. Sodium and Mg were determined for five lunar meteorites by PGA using these prompt gamma-rays, and were found to be consistent with their data obtained by instrumental neutron activation analysis.
Catechol-type chitosan resin and salicylic acid-type chitosan resin were easily synthesized for use in estimating the adsorption behavior of 34 elements at pH 1 - 7 in aquatic media. The catechol-type chitosan resin could adsorb Cu(II) at pH 3 - 7, In(III) at pH 4 - 6, Pb(II) and lanthanoids at pH 5 - 7, and U(VI) at pH 4 - 7 more effectively than the salicylic acid-type chitosan resin and the cross-linked chitosan resin (base material). Adsorption ability was in the order: catechol-type chitosan resin > salicylic acid-type chitosan resin > cross-linked chitosan resin.
In this study, a rapid flow injection-flame atomic absorption spectrometry for cyanide detection was developed. Different AgX (where X is Cl-, Br-, I- and N3-) solid-phase reagents (SPR) were tested for indirect determination of cyanide. In a single-line FIA system, the cyanide was allowed to react with AgX SPR, which in turn changed Ag ions in AgX to silver cyanide complexes in a sodium hydroxide carrier stream. The eluent containing the analyte as silver cyanide complexes was measured by FAAS. The calibration curve was linear up to 30 mg l-1 with a detection limit of 0.05 mg l-1 for cyanides. The sampling rate and the relative standard deviation were <1.09% and >200 h-1, respectively. The method was applied to the determination of cyanide in electroplating wastewater.
Using a spectrophotometric method after distillation separation is a standard test method widely employed for the determination of fluorine (F) in cement. Using a flow injection (FI) method after pyrolysis separation for quantification of fluorine in cement has recently been developed. Differences between the fluorine content values obtained by each method have been noted. This paper documents the differences between fluorine content (distillation F) measured spectrophotometrically after distillation and that (pyrolysis F) determined using the FI method after pyrolysis for fourteen commercial Portland cements and identifies a factor contributing to the differences between distillation F and pyrolysis F values. A highly significant relationship existed between distillation F and pyrolysis F values for fourteen cements (r2 = 0.998, p < 0.001).
The release process of phenol blue from a dibutyrylchitin microsphere, prepared with chitin from a silkworm, into an aqueous solution was kinetically analyzed by single microparticle injection/manipulation and absorption microspectroscopy. The distribution ratio and the release rate of phenol blue in the single microsphere/water system were significantly influenced by the pH of the solution. These results are discussed in terms of the protonation of phenol blue and dibutyrylchitin, and the pore and surface diffusion in the pores of the microsphere.
In the last decade, ionic liquids have shown great promise in a plethora of applications. Nevertheless, little attention has been paid to the characterization of the purity of these fluids, which ultimately lead to non-reproducible data in the literature. Derivatization with carbon disulfide is used to quantitatively determine primary and secondary non-aromatic amines (detection limit: 0.2 wt%), such as 1-butylamine, morpholine or pyrrolidine, in ionic liquids. The corresponding dithiocarbamates formed are analyzed by ultraviolet spectroscopy at wavelengths between 277 and 285 nm.