Effect of Citric Acid on Prolonging the Half-life of Dissolved Ozone in Water.

To elucidate the effect of citric acid on the stability of dissolved ozone, half-lives of ozone in a citric acid solution was investigated. Prolongation of the half-life of ozone was clearly shown in the presence of citric acid in ozonized water. In the presence of ethylenediaminetetraacetic acid (EDTA), the half-life of ozone was decreased. The addition of various concentrations of citric acid to the EDTA solution, however, reversed the half-life in a concentration-dependent manner. These indicate that citric acid suppresses ozone self-decomposition in water. A citric acid-mediated suppression mechanism of ozone self-decomposition involving hydroxy radical (HO•) was proposed as follows: HO• formed by the radical chain reaction process of ozone is scavenged by a way of abstracting the hydrogen atom bound to a carbon atom located α-position of a carbonyl group. The radical chain reaction of ozone is, thus, suppressed. These findings demonstrate that the addition of citric acid to ozonized water is useful for the stabilization of ozone. This ability may contribute to the application of ozone sterilization in food production processes.

The identification of vitamin E homologues in medicinal plant samples using ESI(+)-LC-MS3.

The aim of this study was to elucidate the presence of vitamin E homologues in medicinal plants. To identify various homologues in the matrix of medicinal plant samples, a method for simultaneous determination was developed using ESI(+)-LC-MS3. A complete separation of each homologue was achieved within 20 min using a PFP column and an isocratic elution system of water/methanol (10:90, v/v) at a flow rate of 0.5 mL/min. The ESI-MS condition for each homologue was optimized, and the m/z value and the fragmentation pathway of each homologue were summarized. This LC-MS3 method made it possible to detect the homologues without the effect of matrix; therefore, high sensitive analysis was established, and then, the MS3 makes it possible to extract from plants with methanol only. The LC-MS3 method was applied to identify the eight vitamin E homologues in 11 medicinal plants.

[Test method of methanol content in detergent].

A test method of methanol content in detergent using a headspace-GC method was established. A 1 g aliquot of test sample was mixed with 0.4 mg of 2-propanol and made up to 20 mL with water. Then, 5 mL of test solution was placed in a headspace vial. The vial was sealed and incubated for 30 min at 60°C, then the headspace gas was analyzed by GC-FID. The recovery from spiked 1 mg/g of methanol was 95.6-100.6%. The determination limit was 0.1 mg/g. Using this method, the methanol content in 14 kinds of detergents was quantified. Methanol was detected from two detergents at the levels of 0.13 and 0.27 mg/g.

[Survey of plasticizers in polyvinyl chloride toys].

Plasticizers in 101 samples of polyvinyl chloride (PVC) toys on the Japanese market were surveyed. No phthalates were detected in designated toys, though bis(2-ethylhexyl)phthalate, diisononyl phthalate, diisobutyl phthalate, dibutyl phthalate, diisodecyl phthalate and benzyl butyl phthalate were detected in more than half of other toys. 2,2,4-Tributyl-1,3-pentanediol diisobutylate, o-acetyl tributyl citrate, adipates and diacetyl lauroyl glycerol, which are alternative plasticizers to phthalates, were detected. The results of structural analysis confirmed the presence of di(2-ethylhexyl)terephthalate, tributyl citrate, diisononyl 1,2-cyclohexanedicarboxylate and neopentyl glycol esters; these have not previonsly been reported in Japan. There appears to be a shift in plasticizers used for designated toys from phthalates to new plasticizers, and the number of different plasticizers is increasing.

[Test method for 6 phthalates in polyvinyl chloride].

A test method for 6 phthalates, bis(2-ethylhexyl)phthalate, dibutyl phthalate, benzyl butyl phthalate, diisononyl phthalate, diisodecyl phthalate and di-n-octyl phthalate, in polyvinyl chloride (PVC) was developed. GC/MS was used in the SIM mode for the separation and detection of phthalates. For preparation of the test solution, the extraction method with acetone-hexane mixture (3 : 7) and the dissolution method with tetrahydrofuran and ethanol were compared and it was confirmed that each method gave good recoveries. Dilution of the test solution was effective to reduce the influence of PVC. In a collaborative study with nine laboratories, the intra-laboratory variations showed good repeatability, but the measurements at some laboratories deviated widely. It appears that this method is unsuitable for the judgment of acceptability, but it may be suitable for the determination of phthalate content in PVC products.

Analytical methods for SiO2 and other inorganic oxides in titanium dioxide or certain silicates for food additive specifications.

An analytical method has been developed for the detection of SiO(2) and other oxides in titanium dioxide and certain silicates used in food additives using inductively coupled plasma (ICP) atomic emission spectrometry without hydrofluoric acid. SiO(2) and other oxides in titanium dioxide or certain silicates were resolved by alkali fusion with KOH and boric acid and then dissolved in dilute hydrochloric acid as a test solution for ICP. The recovery of SiO(2) and Al(2)O(3) added at 0.1 and 1.0%, respectively, in TiO(2) was 88-104%; coefficient of variation was <4%. The limit of determination of SiO(2) and Al(2)O(3) was about 0.08%, and the accuracy of the ICP method was better than that of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) test method. The recovery of SiO(2) and other oxides in silicates was 95-107% with a coefficient of variation of <4%. Using energy dispersive X-ray fluorescence spectrometry (EDX) with fundamental parameter determination, the content of SiO(2) and other oxide in titanium dioxide and silicate showed good agreement with the ICP results. ICP with alkali fusion proved suitable as a test method for SiO(2), Al(2)O(3) and other oxides in titanium dioxide and certain silicates, and EDX proves useful for screening such impurities in titanium dioxide and componential analysis of certain silicates.

[Discrimination of plasticizers and screening of phthalates in polyvinyl chloride using DART-TOF/MS].

A technique using a direct analysis in real time (DART) ion source coupled with time of flight/mass spectrometry (TOF/MS) was developed to discriminate plasticizers and to screen phthalates in polyvinyl chloride (PVC). In DART-TOF/MS analysis of 40 plasticizers, the protonated molecular ion, [M+H](+), was detected for most plasticizers, and the molecular weight could be easily predicted. In the analysis of PVC sheets and toys, mass spectra of plasticizers were successfully detected, and accordingly, plasticizers in PVC were easily discriminated. PVC with a phthalates content in excess of 0.1% could be screened accurately according to the DART-TOF/MS ion intensity of phthalates corresponding to the limit of detection or a suitable criterion value. DART-TOF/MS analysis is a simple and rapid technique that is suitable for the discrimination of plasticizers and for screening of phthalates in PVC.

[Screening method for the determination of 199 pesticides in agricultural products by gas chromatography/ion trap mass spectrometry (GC/MS/MS)].

A screening method is described for determining 200 pesticides, except dimethipin, divided into four groups by means of gas chromatography/tandem mass spectrometry (GC/MS/MS) using an ion trap mass spectrometer equipped with automated gain control (AGC). The quantitation limit for 194 pesticides was 0.01 mg/kg on a crop basis, except for allidochlor, dimethoate, hexythiazox, methamidophos and triadimenol. The calibration curve of each pesticide was linear in the range of 0.04-5.0 microg/mL. One hundred and ninety-nine pesticides were added to matrix of potato, spinach, cabbage, apple, orange, soybean and unpolished rice at twice the limits of quantitation. The recoveries of 194 pesticides from all crops were satisfactory (50-150%) for screening purposes. Although some pesticides in apple and orange were not determined by selected ion monitoring (SIM) analysis at the limits of quantitation, all of them were identified by ion-trap GC/MS/MS at the same concentration. Thus, the ion trap GC/MS/MS technique is useful for the screening of residual pesticides present at low levels in agricultural products.

[Applicability of GC, GC/MS and liquid chromatography with tandem mass spectrometry to screening for 140 pesticides in agricultural products].

The applicability of GC, GC/MS and liquid chromatography with tandem mass spectrometry (LC/MS/MS) to screening for 140 pesticides in agricultural products was examined. Validation of multi-residue screening methods for the determination of 88 pesticides in 12 crops (asparagus, cauliflower, burdock, carrot, broccoli, spinach, matsutake mushroom, orange, soybean, sesame, millet and tea) was done by GC and GC/MS. Of the 88 pesticides, 63 were obtained with recoveries in the range from 50 to 150% at the 0.1 microg/g level in the 12 crops. Applicability of the official methods in Japan to 74 pesticides, including 22 pesticides with low recovery (< 50%) by GC or GC/MS analysis, was also examined by LC/MS/MS. LC/MS/MS acquisition parameters were established for 67 pesticides in positive and negative electrospray ionization (ESI) modes. Of 67 pesticides validated in 7 crops using LC/MS/MS at the 0.1 microg/g level, 44 showed recoveries in the range from 50 to 150%. The occurrence of matrix interference in LC/MS/MS can lead to false-positive detection of MCPA in spinach, cabbage and orange and false-negative detection of four pesticides in orange, spinach, apple and unpolished rice. Good linearity was observed in the studied ranges by GC, GC/MS (r > 0.990) and LC/MS/MS (r > 0.995). Of the total of 140 pesticides validated by GC, GC/MS and LC/MS/MS, 107 were newly recognized as suitable subjects for screening.

Aqueous photodegradation of fenthion by ultraviolet B irradiation: contribution of singlet oxygen in photodegradation and photochemical hydrolysis.

The objective of this study was to evaluate the photodegradation of the organophosphorus pesticide fenthion in the environment from a human health effect viewpoint. The major photodegradation products of fenthion in an aqueous solution under UVB irradiation (280-320nm radiation) were identified as fenthion sulfoxide, 3-methyl-4-methylthiophenol (MMTP), dimethyl phosphorothioate and 3-methyl-4-methylsulfinylphenol (MMSP). MMTP, dimethyl phosphorothioate and MMSP were discovered as novel photodegradation products of fenthion. Kinetic analysis of these products showed the formation of MMTP and dimethyl phosphorothioate by the photochemical hydrolysis of fenthion, which was accelerated under alkaline conditions. The former was further oxidized to MMSP. Fenthion sulfoxide was directly produced by the oxidative reaction of fenthion. Contribution of dissolved oxygen in this photooxidation was observed by replacing the air with nitrogen gas in the reaction system, which prevented oxidative formation of fenthion sulfoxide from fenthion and MMSP from MMTP. These oxidative compounds were also formed from fenthion in the presence of singlet oxygen (1O2) generated by the visible light irradiation of rose bengal solution, while 1O2 scavengers, L-histidine and sodium azide (NaN3) inhibited this reaction. The aqueous photolysis mechanisms of fenthion were proposed from a kinetic photolysis experiment study as follows: there were two kinds of UVB photodegradation pathways of fenthion, one being photochemical hydrolysis of the phosphorus-O-phenyl ester to form MMTP and dimethyl phosphorothioate, and the other oxygenation triggered by 1O2 and producing fenthion sulfoxide and MMSP. Therefore, the steady photodegradation products of fenthion in the water environment may be fenthion sulfoxide and MMSP.

[Determination of low-level pesticide residues in agricultural products by ion-trap GC/MS/MS].

The objective of this study was to elucidate the utility of ion-trap GC/MS/MS for the analysis of pesticides in extracted matrices from various agricultural products. Identification and quantitative analysis of pesticides in matrices were performed by quadrupole GC/MS and ion-trap GC/MS/MS. Chlorpyrifos was added to the matrix of spinach, soybean in the pod or corn, and aldrin, dieldrin, endrin, alpha-BHC, beta-BHC, gamma-BHC, delta-BHC, p,p'-DDD, p,p'-DDE, o,p'-DDT and p,p'-DDT were added to each matrix of green tea, black tea or oolong tea. Although most of the pesticides in the matrix could not be determined by quadrupole GC/MS-Scan analysis at 0.1 microgram/mL, every pesticide was identified from the mass spectrum using ion-trap GC/MS/MS at the same concentration. The quantitation limit of every pesticide in each matrix by ion-trap GC/MS/MS analysis was higher than that by GC/MS-SIM analysis. The calibration curves obtained by GC/MS/MS were linear in the range of 0.01-0.25 microgram/mL of each pesticide. The recoveries of each pesticide from four kinds of samples spiked at the levels of 0.01 ppm to 0.02 ppm in extracts were 61.2-138.3% with SD values in the range from 1.2 to 15.4%. This study revealed that ion-trap GC/MS/MS was useful for the identification and quantitative analysis of low-level pesticides residues in matrices of agricultural products.

Analysis of Phenothrin and Its Metabolite 3-Phenoxybenzoic Acid (PBA) in Agricultural Products by GC and Ion-Trap GC/MS.

A sensitive method for analysis of phenothrin and its metabolite 3-phenoxybenzoic acid (PBA) in agricultural products by gas chromatography with electron capture detection (ECD-GC) and ion-trap gas chromatography/mass spectrometry (GC/MS) with chemical ionization (Cl) was investigated. After phenothrin in vegetables, fruits, potatoes, starches, and tea had been extracted with acetone, or in cereals and beans had been extracted with acetonitrile followed by Florisi! column chromatography, it was reextracted into n-hexane. PBA was determined by ECD-GC after esterification with hexafluoroisopropyl alcohol (HFIP) and diisopropylcarbodiimide (DIC). Phenothrin was determined by monitoring its molecular ion peak using ion-trap GC/MS and was confirmed by observing its spectral pattern. The detection limit for phenothrin by ECD-GC and ion-trap GC/MS by this method was 0.01 ppm. The detection limit for PBA by ECD-GC was 0.001 ppm. When phenothrin and PBA were added to samples at 0.2 and 1.0 ppm, the recoveries of phenothrin in each agricultural product ranged between 60.2 and 88.5% and those of PBA ranged between 37.8 and 89.5%. An actual-conditions surveillance analysis of six agricultural products imported from October to December 1994 indicated no phenothrin, but PBA was detected in all products.