Masahiko Numata

Comparison of low-level polycyclic aromatic hydrocarbons in sediment revealed by Soxhlet extraction, microwave-assisted extraction, and pressurized liquid extraction.

We analyzed polycyclic aromatic hydrocarbons (PAHs) present in lake sediment at low levels (<1 microg g(-1)) by using Soxhlet extraction (Soxhlet), microwave-assisted extraction (MAE), and pressurized liquid extraction (PLE) in combination with gas chromatography and isotope-dilution mass spectrometry. Although all extraction techniques showed good repeatability for five target PAHs (relative standard deviation <5.2%, n=3), the results decreased in the order PLE>MAE>Soxhlet. Differences in the results originated mainly from differences in the extraction efficiencies of the techniques for native PAHs, because all techniques gave comparable recovery yields of corresponding 13C-labeled PAHs (13C-PAHs) (51-84%). Since non-negligible amounts of both native PAHs and 13C-PAHs were re-adsorbed on matrix in MAE, not only recovery yields of 13C-PAHs but also efficiencies of extraction of native PAHs should be examined to evaluate the appropriateness of any analytical procedures.

Alkaline extraction in combination with microwave-assisted extraction followed by solid-phase extraction treatment for polycyclic aromatic hydrocarbons in a sediment sample

Microwave-assisted extraction using 1M KOH/methanol (alkaline-MAE) in combination with solid-phase extraction treatment was developed and applied to polycyclic aromatic hydrocarbons (PAHs) in a sediment sample. Although various conditions were examined (100 or 150 degrees C for 10 or 30 min), comparable concentrations of PAHs to those obtained by conventional extraction with 1M KOH/methanol at 70 degrees C for 4h were obtained, even at 100 degrees C for 10 min. The concentrations obtained by using MeOH at 150 degrees C for 30 min without KOH were lower (by 1.3-37%) than those obtained by alkaline-MAE at 150 degrees C for 30 min. Since the developed technique can introduce higher concentration of benzo[ghi]perylene relative to those using pressurized liquid extraction (toluene, 150 degrees C, 15 MPa, 10 min, two cycles), the developed alkaline-MAE is a effective technique.

Development of apple certified reference material for quantification of organophosphorus and pyrethroid pesticides

An apple certified reference material for the analysis of pesticide residues was issued by the National Metrology Institute of Japan. Organophosphorus and pyrethroid pesticides were sprayed on apples, and these were used as raw materials of certified reference material. The harvested apples were cut into small pieces, freeze-dried, pulverized, sieved, placed into 200 brown glass bottles (3g each), and sterilized by γ-irradiation. Stability and homogeneity assessment was performed, and the relative uncertainties due to instability (for an expiry date of 32 months) and inhomogeneity were 10.3-25.0% and 4.0-6.8%, respectively. The characterization was carried out using multiple analytical methods to ensure the reliability of analytical results; the values of target pesticides were obtained by isotope dilution mass spectrometry. Certified values were 2.28 ± 0.82 mg/kg for diazinon, 3.14 ± 0.79 mg/kg for fenitrothion, 1.55 ± 0.81 mg/kg for cypermethrin, and 2.81 ± 0.70 mg/kg for permethrin.

Accurate quantification of polycyclic aromatic hydrocarbons in dust samples using microwave-assisted solvent extraction combined with isotope-dilution mass spectrometry.

For accurate quantification of polycyclic aromatic hydrocarbons (PAHs) in dust samples, we investigated the use of microwave-assisted solvent extraction (MAE) combined with isotope-dilution mass spectrometry (IDMS) using deuterium-labelled PAHs (D-PAHs). Although MAE with a methanol/toluene mixture (1:3 by volume) at 160°C for 40 min was best for extracting PAHs from tunnel dust among examined, the recovery yields of D-PAHs decreased with increasing molecular weight (<40% for MW≥264; that of deuterium-labelled indeno[123-cd]pyrene (D-IcdP) was only 7.1%). Although the residues were extracted a second time, the observed concentrations did not change dramatically (<5%), and the recovery yields of heavier D-PAHs (i.e., MW≥264) were approximately half of those of the first extract, including D-IcdP (3.4%). These results suggest that both partitioning and isotopic equilibria of PAHs and D-PAHs between sample and solvent were achieved for extractable heavier PAHs under the condition. Thus, the observed concentrations of PAHs obtained by MAE-IDMS were reasonable, even though recovery yields of D-PAHs were <50%. From the results of carbon analyses and extractable contents, lower recovery yields of D-PAHs from the tunnel dust were due to a large content of char with low extractable contents.

Preparation of a sulfoxide group and ammonium-salt bonded silica stationary phase for separation of polychlorinated biphenyls from mineral oils

In this study, a silica stationary phase modified with sulfoxide group and ammonium-salt was prepared for the separation of polychlorinated biphenyls (PCBs) from mineral oils, and its properties were investigated. Organic sulfide was attached to a diamino (primary and secondary amino) bonded silica surface by an amide bond, and the bonded sulfide groups were oxidized with periodate to afford sulfoxide groups bonded to the stationary phase. The secondary amino groups in the spacer chain were converted to ammonium-salt by the addition of hydrochloric acid. The sulfoxide group and ammonium-salt bonded stationary phase was tested for their suitability as adsorbent for SPE-type preparative short columns and for an analytical HPLC-type separation. The new stationary phase (1.2 mmol of sulfur bonded per gram) separated PCBs from mineral oils (paraffin-based transformer oils) more efficiently than previously reported stationary phases including sulfoxide group or ammonium-salt bonded ones. The quantitative chromatographic parameters for an aliphatic hydrocarbon (eicosane) and some PCB congeners also indicated strong retention of highly chlorinated biphenyls by the sulfoxide and ammonium-salt bonded silica compared with simple aminopropyl, sulfoxide group or ammonium-salt bonded ones. A cleanup procedure was established for simple determination of PCBs in mineral oil samples using sulfoxide group and ammonium-salt bonded silica packed column fractionation. The analytical method, combination of the cleanup procedure, and measurement with a GC-high resolution (magnetic sector) MS or a GC-quadrupole MS were validated using mineral oil certified reference materials.

Development of soybean certified reference material for pesticide residue analysis

A soybean certified reference material for pesticide residue analysis was developed by the National Metrology Institute of Japan. Three organophosphorus (diazinon, fenitrothion, chlorphyrifos) and one pyrethroid (permethrin) pesticides were sprayed on soybeans three times before harvest. These soybeans were freeze pulverized, homogenized, bottled, and sterilized by γ-irradiation to prepare the candidate material. Three isotope-dilution mass spectrometric methods that varied in terms of the solvents used for extraction of the target pesticides, the clean-up procedure, and the injection techniques and columns used for quantification via gas chromatography/mass spectrometry were applied to the characterization. Each target pesticide was quantified by two of these analytical methods, and the results were in good agreement. Homogeneity and stability assessment of the material demonstrated that the relative standard uncertainties due to the inhomogeneity and the instability for an expiry date of 55 months were 1.89-4.00% and 6.65-11.5%, respectively. The certified pesticide concentrations with expanded uncertainties (coverage factor k=2, approximate 95% confidence interval) calculated using the results of the characterization and the homogeneity and stability assessment were 21.7 ± 3.2 μg/kg for diazinon, 88 ± 21 μg/kg for fenitrothion, 11.1 ± 3.2 μg/kg for chlorpyrifos, and 20.1 ± 4.3 μg/kg for permethrin (as the sum of the constituent isomers).

Development of green onion and cabbage certified reference materials for quantification of organophosphorus and pyrethroid pesticides.

Green onion and cabbage certified reference materials for the analysis of pesticide residues were issued by the National Metrology Institute of Japan, part of the National Institute of Advanced Industrial Science and Technology. Green onion and cabbage samples were grown so as to contain several kinds of organophosphorus and pyrethroid pesticides, and those were collected from a field in the Kochi Prefecture in Japan. The certification was carried out by using multiple analytical methods to ensure the reliability of analytical results; the values of target pesticides (diazinon, fenitrothion, cypermethrin, etofenprox, and permethrin for green onion and chlorpyrifos, fenitrothion, and permethrin for cabbage) were obtained by isotope dilution mass spectrometry. Certified values of target pesticides were 0.96-13.9 and 2.41-6.9 mg/kg for green onion and cabbage, respectively. These are the first green onion and cabbage powder certified reference materials in which organophosphorus and pyrethroid pesticides are determined.

MECHANISM OF IONIZATION OF POLYCYCLIC AROMATIC HYDROCARBONS BY A TOLUENE/ANISOLE MIXTURE AS A DOPANT IN LIQUID CHROMATOGRAPHY/DOPANT-ASSISTED ATMOSPHERIC-PRESSURE PHOTOIONIZATION/MASS SPECTROMETRY

Ionization mechanisms of 16 polycyclic aromatic hydrocarbons (PAHs) by dopant-assisted atmospheric-pressure photoionization (DA-APPI) with a toluene/anisole mixture as a dopant were examined in the reversed-phase liquid chromatography mode with a methanol/water to acetonitrile linear gradient mobile phase. When toluene/anisole mixtures were used as dopants, their characteristics were governed by anisole. Since the IE of anisole (8.20 eV) is below that of toluene (8.83 eV), anisole is ionized not only by photons from the krypton lamp but also by charge transfer from toluene radical cations. In the latter half of chromatogram, when acetonitrile was dominant in the eluent, ions originating from both toluene and anisole decreased while acetonitrile-cluster ions began to increase. Because acetonitrile-cluster ions are not formed with anisole alone, but are formed with toluene alone, toluene radical cations would be consumed to form acetonitrile-cluster ions.

Proficiency testing for determination of pesticide residues in soybean: comparison of assigned values from participants' results and isotope-dilution mass spectrometric determination.

Proficiency testing (PT) for the determination of pesticide residues in soybean samples was organized by the National Metrology Institute of Japan (NMIJ). The candidate certified reference material, NMIJ CRM 7509-a, that was prepared from the raw soybeans containing target pesticides (diazinon, fenitrothion, chlorpyrifos, and permethrin) was used as the test sample. Forty participants submitted two sets of analytical results along with the details of the analytical method and conditions they applied. Two types of assigned values were established for each target pesticide: one was derived from the analytical results of the participants, and the other was provided from the analytical results by isotope-dilution mass spectrometry (IDMS). The latter values were 7.4-16% higher than the former values, plausibly because the analytical values from the IDMS measurements were not affected by the recovery ratio of the target pesticides during the analytical process. Thus, two kinds of z-scores were calculated for individual participants using the corresponding assigned values: one (z1-score) showed the relative performance score for the present PT and the other (z2-score) could be used for evaluation of the trueness of their analytical methods.

Certification of water content in NMIJ CRM 4222-a, water standard solution 0.1 mg g−1, by coulometric and volumetric Karl Fischer titration

The precise determination of water content is a very important issue and in high demand in many fields. To ensure precise and reliable measurements, certified reference materials (CRM) of water standards, whose concentrations are traceable to the International System of Units (SI), are required. The National Metrology Institute of Japan (NMIJ) has issued a CRM of water in mesitylene (0.1 mg g−1) (NMIJ CRM 4222-a), with a very small uncertainty, for use in controlling the quality of analyses of trace water contents and confirming the validity of Karl Fischer (KF) titrators. This CRM is homogeneous, stable and low-hygroscopic under normal laboratory conditions; therefore, complex sample handling is not required. Characterization of the CRM was performed by coulometric and volumetric KF titrations. The certified value of the CRM (mass fraction of water) is 0.134 mg g−1, and its expanded uncertainty is 0.004 mg g−1 with a coverage factor of 2, and is metrologically traceable to SI. We describe the measurement procedures and assays of trace water contents with linkage to SI and the technical details of the characterization of water in NMIJ CRM 4222-a. The developed CRM is particularly suitable for the quality control and validation of coulometric KF instruments and will be valuable in analyzing trace water contents.