BUNSEKI KAGAKU Abstracts

The determination of the ratio of Cr(III)/Cr(VI) in soil samples was investigated by X-ray absorption fine structure (XAFS), which is one of the useful means for nondestructive analysis. In previous methods, the normalization energy of the Cr K-edge in X-ray absorption near-edge structure (XANES) spectra was not clearly defined. Therefore, we investigated to find the best normalization energy in the XANES spectra for improvements in the determination of Cr(VI) in soil. It was considered that the peak in the spectrum of the standard reference was due to the transition of Cr(III). The peak observed near 6010 eV in the K-edge is peculiar to Cr(III), ascribed to the transition of 1s (a_1g)→3d (t_2g²e_g). By normalization at this position, we were able to obtain a better calibration curve (R² = 0.9880). In order to estimate the behavior of Cr(VI) in soil, we observed the valence of Cr in soil after spiking a Cr(VI) solution by XAFS. Andosol (0-25 cm) and Brown forest soil (0-20 cm) were spiked with a Cr(VI) 1000 μg mL⁻¹ solution. After spiking, soil samples were pressed out of a column and separated into each 1 cm. All layers were measured by XANES just after spiking and after 24 hours. The ratios of Cr(III)/Cr(VI) in soil samples were calculated based on the area of the pre-edge peak in the Cr K-edge XANES spectra of standard reference samples. After 24 hours, the reduction of Cr(VI) was observed in all samples of the two different types of soil. The reduction to Cr(III) started just after Cr(VI) adsorbed to soil; 20% of the total Cr(VI) was reduced to Cr(III) in 24 hours.

To analyze low-molecular compounds, such as pesticides and mycotoxin in food samples, an improved method of antibody preparation and determination methods using antibodies were examined. These methods were evaluated by applying them to real samples and by marketing them as commercially available products. Monoclonal antibodies (MoAbs) corresponding to required specifications in the field were necessary to develop determination methods with high reliability. We have designed the optimally modified constitution of low molecular compounds that successfully give immunogenicity to compounds, and prepared targeted MoAbs among many candidates by a unique screening method. Using the specified MoAbs, direct competitive ELISA (enzyme-linked immunosorbent assay) was developed for pesticide analysis, and an immuno-affinity column was developed for mycotoxin analysis. ELISA and the column have been commercialized as test kits and pre-packed columns, respectively, and are being actively used for food analysis.

In order to characterize metal species in natural water, the coupling of capillary electrophoresis (CE) and ESI-MS (CE-MS) has been developed. In many cases, natural water contains a lot of metals, such as sodium, potassium, magnesium, calcium and so on. These metals disturb the measurement of the minor metal species. To measure metal species, ESI interface was required with the facility. ESI voltage is simultaneously applied with nebulizing at the tip. Therefore, an ESI interface was modified to connect CE and ESI-MS. In this study, strontium was used as a metal speciation target. 1) A solution containing strontium was measured by ESI-MS and CE-MS, respectively. Although some of hydrated strontium species by CE-MS agreed with those observed by ESI-MS, some complexes derived from CE electrolyte, which is acetic acid, were also observed by CE-MS. It was confirmed that the composition and condition of the CE electrolyte gave highly effective influences in metal species by CE-MS analysis, and should be improved to detect metal species while keeping their original chemical forms in the solution. 2) NaCl or KCl was added to a strontium solution, and these matrix solutions were measured by ESI-MS and CE-MS. In analysis by ESI-MS, the ionization of strontium species was prevented by the coexisting matrix, such as KCl, in solution. However, the strontium species could be detected by CE-MS without suppression caused by the component of the matrix. Therefore, It should be expected that the CE-MS will become a useful technique to examine the hydrated metal species by removing matrix (e.g. NaCl, KCl and other salts), and will have a potential to obtain information of metal species in natural water.

In this study, a data-analysis technique for vegetable oil discrimination was discussed and offered using Ion Attachment Ionization (IA) Mass Spectrometry, which has a completely soft ionization technique with no fragmentation during ionization. In IA ionization mass spectra, only quasi-molecular ion peaks are obtained, so that the mass spectra showed the characteristic pattern, which reflected the states in the sample, even if there was no pre-separation technique, such as gas-chromatography. Referring to the database of soft-ionization mass spectra for nine kinds of vegetable oils, which was processed beforehand, oil discrimination and estimated values of mixed ratio were possible to be carried out with principal-component and cluster analyses, and a different calculation method of regression analysis, respectively. These methods should be useful for selective marking to the trace impurity in oils, e.g., 0.4 wt% signal of coconut oil in olive oil was detected.

Metachromagy of Toluidine Blue (TB) with poly(4-styrenesulfonate) (PSS) and poly(vinyl sulfate) (PVS) were studied by visible observation using a micro-plate, visible spectra, and ¹H-NMR spectra in light water. It was found that the negative metachromagy of poly(styrene sulfonate) was due to the π-stacking of TB onto poly(4-styenesulfonate). The π-stacking interaction brings about the random ion-association of TB onto PSS and causes a dim color change of TB at the end-point on the visible colloidal titration with PSS. Tetradecyltrimethylbenzyl ammonium (Zeph) and poly(diaryldimethyl ammonium) (PDADMAC) were titrated by potentiometric colloidal titration with PSS using an ion surfactant electrode. The potentiometric titration curve of Zeph indicated a typical sigmoid curve without TB. The potentiometric titration curve of PDADMAC indicated a clear decrease in potential change to TB at the end-point. Both potentiometric colloidal titrations were quantitative. Thus, PSS is able to become a standard polyanion titrant as well as PVS. When Zeph was used as a standard cation on colloidal titration, the determination result of PDADMAC with PSS agreed with the result of colloidal titration with PVS within 2% of the relative difference.

This paper describes a simple analytical method for the simultaneous determination of 3 kinds of pesticides for golf courses by high-performance liquid chromatography (UV) with ultraviolet detection (UV) after solid-phase extraction (SPE). This method provides high linearity of the working curve for calibration as well as repeatability and reproducibility. The correlation coefficient of the working curve for calibration were estimated to be from 0.9991 to 0.9998 for the 3 kinds of pesticides for golf courses in the concentration range from 0.5 mg L⁻¹ to 5.0 mg L⁻¹. The limits of detection (LOD) calculated on 3 σ at 0.5 mg L⁻¹ were 0.10 mg L⁻¹ for oxine copper, 0.14 mg L⁻¹ for thiamethoxam, and 0.11 mg L⁻¹ for clothianidin. The limits of quantification (LOQ) calculated on 10 σ at 0.5 mg L⁻¹ were 0.34 mg L⁻¹ for oxine copper, 0.48 mg L⁻¹ for thiamethoxam, and 0.36 mg L⁻¹ for clothianidin. Solid-phase extraction using the stylene-methacrylate copolymer (MA-SDVB) and elution with acetonitrile was recommended for enriching the 3 kind of pesticides. The recoveries from 500 mL of spiked river-water samples at a concentration level of 0.005 mg L⁻¹, concentrated 500 times, were 91.2 ∼ 95.6%, and the relative standard deviations were 3.8 ∼ 5.6%. This method could be successfully applied to the determination of 3 kinds of pesticides for golf courses in river-water samples.

A simultaneous multi-component analytical method for 20 types of elements in raw and tap-water samples (Cd, Se, Pb, As, Cr, B, Zn, Al, Fe, Cu, Mn, Sb, U, Ni, Ba, Bi, Ag and Mo, as listed in the “Water Works Law”, and Li and Sr, which are not-listed but are frequently detected) was studied using DRC-ICP/MS. The investigation revealed 1) that the optimum cell-gas flow rates to control plasma-based interferences was 0.3 mL min⁻¹ for As and 0.6 mL min⁻¹ for the other elements (Cr, Mn, Fe, Ni, Cu, Zn and Se), and 2) that Be, Ga, In and Tl are the most appropriate elements for the internal standards, except in the cases of Co and Y, which are influenced by their concentration level in raw water. Under these analytical conditions, verification by spiked recovery tests exhibited that the recovery rate is 90 – 110%, and that the variation coefficient is below 10%. The levels of the determination limits for each element were ng L⁻¹ – μg L⁻¹, which demonstrates the possibility of measurements for low-concentration samples. From all of these results, this analytical method has been confirmed to be both highly sensitive and accurate. Furthermore, studies of the removal performance for 20 different elements from raw to tap water in an advanced water-purification facility showed that Mn, U, Fe, Bi, Ag and Al can be easily removed (removal ratio of over 80%). On the other hand, Se, Li, Sb, Ba, B, Mo and Sr can hardly be removed (removal ratio of below 20%).

We studied using an ammonium peroxodisulfate as the oxidizing reagent instead of potassium hexacyanoferrate(III) on the 4-aminoantipyrine spectrometry for the determination of phenol. Suitable color development was obtained by the addition of 1 - 5 mL of ammonium peroxodisulfate solution (pH 10, 220 mmol/L) and 2 mL of 4-aminoantipyrine solution (98 mmol/L) to a 100 mL sample solution at pH 10 buffered with an ammonium chloride - ammonia solution (9.8 mol/L). The proposed procedure was applied to methyl benzoate extraction for determining small amounts of phenol in water. Results obtained by the proposed method were in agreement with that by the JIS method.

Determination of cyanide, fluoride, and phenol in industrial wastewater by continuous flow analysis (CFA) after continuous flow sample distillation has been studied. This analytical method provides high linearity of the calibration curve as well as both repeatability and reproducibility. The correlation coefficients of the calibration curve were estimated to be from 0.9950 to 0.9989 for cyanide, fluoride, and phenol in the concentration range from 0.1 mg L⁻¹ to 1.0 mg L⁻¹. The detection limits calculated on 3 σ at 0.5 mg L⁻¹ were 0.012 mg L⁻¹ for cyanide, 0.014 mg L⁻¹ for fluoride, and 0.008 mg L⁻¹ for phenol. The determination limits calculated on 10 σ at 0.5 mg L⁻¹ were 0.041 mg L⁻¹ for cyanide, 0.045 mg L⁻¹ for fluoride, and 0.028 mg L⁻¹ for phenol. The good results were obtained in recovery tests by using industrial wastewater. This analytical method could be successfully applied to the determination of cyanide, fluoride, and phenol in industrial wastewater.