Yasutada Suzuki

Determination of very volatile organic compounds in water samples by purge and trap analysis with a needle-type extraction device.

Very volatile organic compounds (VVOCs), such as methanol, acetaldehyde, ethanol, acetone, acetonitrile, and dichloromethane, were extracted from water samples using a needle-type extraction device based on purge and trap analysis. The extracted analytes could then be determined by gas chromatography-mass spectrometry. By introducing carbon molecular sieves as the extraction medium, aqueous VVOCs could be successfully extracted using the extraction needle. The limit of quantification for methanol, acetaldehyde, ethanol, acetone, acetonitrile, and dichloromethane were 75, 75, 7.5, 0.5, 10 and 0.5 μg/L, respectively. This newly developed method was also successfully applied to the determination of VVOCs in commercial samples, such as fruit juice.

On-site Determination of Trace Arsenic by Reflection-Absorption Colorimetry of Molybdenum Blue Collected on a Membrane Filter

An on-site determination method for trace arsenic has been developed by collecting it as molybdenum blue (MB) in the presence of tetradecyldimethylbenzylammonium chloride on a mixed cellulose ester membrane filter and by measuring reflection absorbance (RA) of MB on the filter using a laboratory-made palm-top size reflection-absorbance colorimeter with a red light-emitting diode. The value of RA was proportional to the amount of arsenic up to 0.5 μg with a detection limit of 0.01 μg. The proposed method was successfully applied to soil extract and hot-spring water samples.

Kinetic Spectrophotometric Determination of Trace Cadmium in Environmental Fresh Water with 5,10,15,20-Tetraphenyl-21H,23H-porphinetetrasulfonic Acid

Cadmium-catalyzed complexation of zinc with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid (TPPS) was monitored spectrophotometrically. A kinetic parameter for the determination was obtained under kinetic consideration. Absorbance of zinc-TPPS at a fixed reaction time was proportional to the concentration of cadmium at pH 8 and 25°C. Tolerable concentration of interfering ions were 200, 200, 2000, 50, 500 and 1 μg L(-1) for Mg(II), Al(III), Ca(II), Fe(III), Zn(II) and Hg(II), respectively, in the determination of 20 μg L(-1) of cadmium, indicating Ca(II) and Mg(II) interferes with the analysis of natural fresh water. Such interference became tolerable at 5 mg L(-1) by the addition of an excess Ca(II) (50 mg L(-1)) in the reacting solution of sample and cadmium standards. A calibration curve of Cd(II) was linear up to 100 μg L(-1) with a detection limit of 2 μg L(-1). The reliability of the proposed method was confirmed by the recovery test of cadmium spiked into tap, river and reservoir water samples.

Ion-responsive Intramolecular Charge-transfer Absorption Using a Pyridinium Benzocrown Ether Conjugate.

A pyridinium benzocrown ether conjugated compound, 1, and its analogue with a non-crown ether unit, 2, have been prepared. Both compounds showed similar absorption spectra with two absorption bands at around 260 and 330 nm in acetonitrile. The bands at the longer wavelength side are associated with intramolecular charge transfer (ICT) absorption, in which the dialkoxyphenyl unit in benzocrown ether and the pyridinium unit act as the donor and acceptor, respectively. The addition of a guest, such as Li(+) or Mg(2+), caused a blue shift in the ICT absorption band for 1, but not for 2. This is explained by the formation of a 1:1 host-guest inclusion complex of 1 with the guest. The guest-induced absorption variation of 1 can be used for alkali and alkaline metal ion sensing. Compound 1 could detect divalent cations, especially for Mg(2+), rather than univalent ones (Li(+), Na(+), K(+), Rb(+), and Cs(+)), although Li(+) was detected with high sensitivity among the alkali metal ions. Compound 3, which has a pyridyl unit at the para position on the pyridinium of 1, showed a similar trend to that of 1 with lower sensitivity than that of 1. The fact that the Mg(2+)/Li(+) sensitivity ratio of 1 and 3 was estimated to be 8.63 and 5.08, respectively, suggests a higher Mg(2+)-preference of 1 rather than 3, while the Ca(2+)/Na(+) ones were 4.98 and 4.85, respectively, when compared ions with similar ionic radii. The sensitivity values of 1 were roughly proportional to their binding constants, as shown by the binding constants with Li(+), Na(+), Mg(2+), and Ca(2+) with values of 2100, 910, 11500, and 2000 M(-1) for 1, respectively. The binding constants of 3 were estimated to be 1710, 650, 3000, and 1400 M(-1) for Li(+), Na(+), Mg(2+), and Ca(2+), respectively, but could not be obtained for alkaline metal ions. The limit concentration for the detection of 1 for Mg(2+) was estimated to be 0.0156 mM, which was the smallest value in this system.

Droplet-counting Microtitration System for Precise On-site Analysis

A new microtitration system based on the counting of titrant droplets has been developed for precise on-site analysis. The dropping rate was controlled by inserting a capillary tube as a flow resistance in a laboratory-made micropipette. The error of titration was 3% in a simulated titration with 20 droplets. The pre-addition of a titrant was proposed for precise titration within an error of 0.5%. The analytical performances were evaluated for chelate titration, redox titration and acid-base titration.