BUNSEKI KAGAKU Abstracts

Vol. 52 No. 7

July, 2003

Accounts

Ion sensors based on ion-selective adsorption and desorption processes at inorganic materials/solution interfaces

Yukinori Tani¹ and Yoshio Umezawa²

(Received 16 December 2002, Accepted 16 April 2003)

This account describes recent developments of ion sensors, mainly from the author's laboratory and their response mechanisms based on inorganic metal salt and oxide materials, which includes ion-selective electrodes (ISEs) and quartz crystal microbalance (QCM) sensors. The processes of the selective adsorption and desorption of insoluble inorganic salts at their solid/solution interfaces are fundamentally related to highly component-ion selective crystallization reactions at the solid/aqueous interfaces. This process is analytically relevant and still attractive as a nearly ideal ion/molecular recognition site, which is followed in situ by a membrane potential charge (ISE) and QCM. First, we relate the charge-separation process caused by primary ion adsorption with the potentiometric response of ion-selective electrodes based on insoluble inorganic salts, such as silver halides and metal sulfides. It is shown that QCM sensors modified with various insoluble inorganic salts can detect selective primary ion adsorption and/or multilayer salt deposition at solid/solution interfaces. This new approach allows most insoluble inorganic salts to be used to sense materials for this sensing system. Also discussed are the potentiometric response mechanisms of ion-selective electrodes based on inorganic materials having a three-dimensional network structure with interstitial ions.

Keywords : insoluble inorganic salt; ion-selective electrode; QCM sensor; charge separation; primary ion adsorption/desorption; multilayer salt deposition.

Research Papers

Study of thermal decomposition at a GC injector in an analysis of PBDDs/PBDFs by high-resolution GC/MS

Jun Onodera¹, Yoshihisa Ueda¹, Jae-Won Choi², Shunji Hashimoto², Noriyuki Suzuki², Masatoshi Morita² and Hisakuni Sato³

(Received 20 January 2003, Accepted 18 March 2003)

It is believed that PBDD/Fs will cause a big environmental problem, just as PCDD/Fs, in the near future. Therefore, the establishment of an analytical method for PBDD/Fs is very important and urgently necessary. However, information regarding this matter is insufficient. We examined the thermal-decomposition reaction of PBDD/Fs by a measurement using a high-resolution GC/MS method involving splitless injection. As a result, debrominated compounds of PBDD/Fs were detected in all temperature ranges for sufficient vaporization efficiency at the time of splittless injection. It is beleived that these debrominated compounds are the thermal-decomposition products produced by a momentary vaporization during injection, based on information from the mass spectra, the GC retention times and the peak shape of the chromatogram peaks. However, it was confirmed that the thermal decomposition was different between the different systems in the same setup, as well as on the same condition. It was thus found that thermal decomposition occurred remarkably when an element of the stainless-steel metal origin, such as nickel and cobalt, was made to exist together in the injector. We suppose that a difference in the delicate environment inside the injector greatly influences the thermal decomposition of PBDD/Fs. Therefore, it is necessary to confirm the thermal decomposition at first when a measurement of PBDD/Fs with high-resolution GC/MS is carried out.

Keywords : PBDD/Fs; HRGC/HRMS; splitless injection; thermal decomposition; debromination.

Determination of tellurium and arsenic in crude oils by oxyhydrogen-combustion/iron(III) coprecipitation/graphite furnace AAS

Yoshikazu Nakamoto¹, Naohiro Iwatani² and Koji Matusaki²

(Received 4 December 2002, Accepted 20 March 2003)

It is important to determine trace amounts of tellurium and arsenic in crude oils, since they are known to be catalyst poisons in refinery processes. The decomposition of crude oil by an oxyhydrogen-combustion method was used to determine tellurium and arsenic. By the decomposition procedure, organic tellurium and arsenic compounds were converted into corresponding inorganic species, which were absorbed by a 0.01 M hydrochloric acid solution. This solution was transferred to a beaker, and the pH of the solution was adjusted to 8 with sodium hydride after the addition of an iron(III) solution (containing 5.5 mg of iron). After filtering with a Millipore filter, the precipitate was dissolved in 2.0 ml of concentrated hydrochloric acid, and then diluted to 10 ml with deionized water. A 20 µl portion of this solution was injected into a graphite furnace attached to AAS, and the tellurium and arsenic were determined. The atomic absorption sensitivity of tellurium was enhanced by iron, which was dissolved in the test solution as a matrix modifier. This method was successfully applied to the determination of trace amounts tellurium and arsenic in crude oils. The detection limit of the proposed method was 1 ng g^-1 for both elements.

Keywords : tellurium; arsenic; oxyhydrogen-combustion; iron(III) hydroxide coprecipitation; matrix modifier; graphite furnace AAS; crude oil.

Simplified analytical method for organophosphorus pesticide in air using adsorbent filled tube and solvent extraction by ultrasonic wave

Junko Kawahara¹ and Yukio Yanagisawa¹

(Received 17 December 2002, Accepted 18 April 2003)

A simplified analytical method was developed for the determination of 11 organophosphorus pesticides in air. In this method, a sonicator was used for the extraction of the target pesticides from Chromosorb102^TM, the adsorbent for sampling. Also the volume of desorbing solvent was minimized in order to skip the process concentration. Desorption efficiency was about 90% with RSD below 5% when 100 µg target compounds were spiked to the adsorbents and sonicated in 2 ml acetone for 40 minutes. The detection limits were 5~10 ng/ml in a solvent and 0.5~1.0 ng/m³ in air by our standard air sampling method (20 m³, flow rate 2 l/min for 1 week, analytical instrument, GC-FPD). This detection limit is comparable to the existing methods which require concentration process. The detection limit is much lower than the guideline values in Japan. By this method we can make the analysis more efficient, and expect more data about airborne organophosphorus pesticides in the environment.

Keywords : organophosphorus pesticide; air; Chromosorb102^TM; solvent extraction; ultrasonic wave.

Technical Papers

Determination of minor constituents in silicates by an acid digestion/flow injection method

Hiroe Iida¹, Tetsuo Uchida¹, Akio Yuchi¹, Miwa Konishi¹, Satomi Ito¹ and Hirofumi Isoyama²

(Received 20 December 2002, Accepted 17 March 2003)

Minor constituents of TiO₂, MnO and P₂O₅ in standard silicates were determined sequentially using a single acid decomposed sample solution by FIA. The FIA system simply consisted of 2 streams without heating, common to all constituents. The residual F in the sample solution changed from 20 to 140 mM, proportional to the sum of the coexisting Al, Fe, Mg and Ca. The TiO₂-H₂O₂ complex was measured in 1 M HClO₄ and 0.2 M H₃BO₃, eliminating Fe and F interferences, respectively. Mn(II) was oxidized rapidly by NaIO₄ in the presence of MnO₄^- as an autocatalyzer in 0.2 M H₃PO₄. P₂O₅ was measured by the “Micell-molybdenum yellow method” using Triton X-100 to improve the sensitivity and to avoid F interference. The obtained analytical results were reproducible and agreed fairly well with those by batch and ICP-AES methods and with the certified values. The proposed sample decomposition was carried out for 10 samples/3 h in parallel.

Keywords : silicate; FIA; TiO₂; MnO; P₂O₅.

Determination of trace elements in high-purity aluminum by solid-phase extraction/ICP-MS

Shin-ichi Hasegawa¹, Hitoshi Yamaguchi¹, Shinji Itoh¹, Kunikazu Ide¹ and Takeshi Kobayashi¹

(Received 28 February 2003, Accepted 6 May 2003)

We attempted a simple pretreating method consisting of solid-phase extraction using bonded silica with benzenesulfonic acid (SCX) as the solid-phase sorbent to determine trace elements in pure aluminum samples by means of inductively coupled plasma mass spectrometry (ICP-MS). The acidic solutions were prepared by dissolving samples in sodium hydroxide, and subsequently adding nitric acid. The analytes could be separated as 1,10-phenanthroline chelate from the matrix by solid-phase extraction after adjusting the pH and adding 1,10-phenanthroline. The optimum condition for aluminum separation was pH 3 and 15 ml of 0.01 M 1,10-phenanthroline. As the eluant, 15 ml of 6 M nitric acid was used. In this method, some trace elements, such as Fe, Ni, Co, Cu, Zn, Ag, Cd, Ga and In, were determined by ICP-MS using the eluate. The limits of detection in ng/g were Fe, 0.69; Ni, 0.89; Co, 0.38; Cu, 3.66; Zn, 1.68; Ag, 0.62; Cd, 1.74; Ga, 1.13 and In, 0.08 ppb.

Keywords : inductively coupled plasma mass spectrometry; solid-phase extraction; bonded silica as a solid-phase sorbent; 1,10-phenanthroline as a chelating agent; iron; nickel; cobalt; copper; cadmium; zinc; gallium; indium; silver; trace analysis; pure aluminum.

Notes

Flow-injection analysis of iron in tap water using its catalytic effect on the oxidation of an azo compound

Kunihiro Watanabe¹, Takashi Watanabe¹ and Masayuki Itagaki¹

(Received 20 November 2002, Accepted 11 April 2003)

1-Amino-8-hydroxy-7-(o-hydroxy-p-methylphenylazo)-3,6-naphthalenedisulfonic acid (p-CH₃) reacts with KIO₄ in an acid solution to form a colorless azoxy compound. The reaction was enhanced with iron(III). Therefore, a flow-injection analysis (FIA) of iron was investigated by measuring the decrease in the absorbance of p-CH₃. The flow system used had three channels. Each carrier (distilled water), KIO₄ solution as a oxidizing agent and reagent(p-CH₃) solution was pumped at 1.0 cm³/min. A sample solution was injected manually into the carrier stream. Then, a p-CH₃ solution containing sample was mixed with a KIO₄ solution. Under the optimum conditions (temperature, 50°C; p-CH₃, 1.2×10^-4 M; KIO₄, 1.0×10^-5 M; HCl, 0.3 M; reaction coil length, 9 m, i.d. 1 mm; injection volume of sample, 1.0 cm³), Fe(III) could be determined in the concentration range of 1.4 to 16 ppb (ng cm^-3) by monitoring at 556 nm. The detection limit of Fe(III) was 0.48 ppb (S/N=5). Also, 15 samples could be analyzed per hour. Mn(II), Cr(VI) and V(V) at more than 0.8-fold, 5-fold and 50-fold concentrations of Fe(III)(8 ppb) showed positive interferences, respectively. However, these metal ions did not interfere with the determination of iron in tap water. As a result, the proposed method was applied to the determination of iron in tap water without any masking agents. The results of a trace iron determination in tap water showed a good agreement with the values obtained by ICP-AES.

Keywords : catalytic analysis; Fe(III); tap water; 1-amino-8-hydroxy-7-(o-hydroxy-p-methylphenylazo)-3,6-naphthalenedisulfonic acid.

Retention property of silica gel bonded with triacontyl groups as a packing material for GC

Tatsuro Nakagama¹, Ayumi Shibata¹, Katsumi Uchiyama¹, Toshiyuki Hobo¹ and Tsuneaki Maeda²

(Received 3 March 2003, Accepted 17 April 2003)

Recently, octadecyl (C₁₈), triacontyl (C₃₀) and other chemically-bonded silica gels have been developed for HPLC. In this study, a C₃₀ silica gel was selected and evaluated as a packing material for GC. Hexane, decane, tetradecane, ethyl acetate, 1-butanol, methyl isobutyl ketone and toluene were used as test samples. End-capped C₃₀ silica was packed into a stainless-steel column (1/8 i.d., 150 mm long). All samples were detected using a flame ionization detector (FID). A relatively good linear relationship (r=0.992, n=8) existed between the logarithm of the retention factor (log k) and the boiling point of test samples using the C₃₀ column at a column temperature of 150°C. Van't Hoff plots of test samples were also linear (r≥0.989) over the range of column temperatures from 50°C to 200°C. It was inferred that the chemically-bonded C₃₀ stationary phase behaved as a non-polar liquid phase and retained the sample by a gas-liquid partition chromatographic mode. The utility of a C₃₀ silica gel as a GC chemically-bonded packing was favorable.

Keywords : triacontyl-bonded silica; GC column packing; retention; Van't Hoff plot.

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