Baseline Assessment for the Consistency of Raman Shifts Acquired with 26 Different Raman Systems and Necessity of a Standardized Calibration Protocol.

Although Raman shifts originate from molecular vibrations and in theory must be independent of analytical systems, acquired Raman shifts, in practice, are not so. Since the consistency of Raman shifts acquired with different systems has not been investigated previously, we have compared the Raman spectra of polystyrene, benzonitrile, and cyclohexane obtained with 26 different systems. The medians of 26 measurements for the characteristic peaks were found to be 1001.3, 1001.1, and 802.0 cm-1 for polystyrene, benzonitrile, and cyclohexane, respectively, and were consistent with their corresponding ASTM E1840 values, which have been widely used for the calibration of Raman systems. However, only 16 measurements of the Raman shift of the polystyrene peak (1001.4 cm-1) met the tolerance standard of the European Pharmacopoeia (±1.5 cm-1). Thus, consistency of Raman shifts obtained using different systems is low, and this mainly originates from differences in the Raman systems rather than materials. Although correction of the offset using the Raman shift of the peaks of cyclohexane (802.0 or 2852.4 cm-1) could improve the consistency of the Raman shifts acquired with different systems, the magnitude of improvement was not uniform over the range of shift values. Thus, there is a need for a standardized calibration protocol that can be used for multiple Raman shifts of common materials to improve the consistency of Raman shifts for different systems.

[Interlaboratory Study on Evaporation Residue Test for Food Contact Products (Report 1)].

An interlaboratory study was performed to evaluate the equivalence between an official method and a modified method of evaporation residue test using three food-simulating solvents (water, 4% acetic acid and 20% ethanol), based on the Japanese Food Sanitation Law for food contact products. Twenty-three laboratories participated, and tested the evaporation residues of nine test solutions as blind duplicates. For evaporation, a water bath was used in the official method, and a hot plate in the modified method. In most laboratories, the test solutions were heated until just prior to evaporation to dryness, and then allowed to dry under residual heat. Statistical analysis revealed that there was no significant difference between the two methods, regardless of the heating equipment used. Accordingly, the modified method provides performance equal to the official method, and is available as an alternative method.

[Interlaboratory Study on Evaporation Residue Test for Food Contact Products (Report 2)].

An interlaboratory study was performed to evaluate the equivalence between an official method and a modified method of evaporation residue test using heptane as a food-simulating solvent for oily or fatty foods, based on the Japanese Food Sanitation Law for food contact products. Twenty-three laboratories participated, and tested the evaporation residues of nine test solutions as blind duplicates. In the official method, heating for evaporation was done with a water bath. In the modified method, a hot plate was used for evaporation, and/or a vacuum concentration procedure was skipped. In most laboratories, the test solutions were heated until just prior to dryness, and then allowed to dry under residual heat. Statistical analysis revealed that there was no significant difference between the two methods. Accordingly, the modified method provides performance equal to the official method, and is available as an alternative method. Furthermore, an interlaboratory study was performed to evaluate and compare two leaching solutions (95% ethanol and isooctane) used as food-simulating solvents for oily or fatty foods in the EU. The results demonstrated that there was no significant difference between heptane and these two leaching solutions.

A practical evaluation of measurement uncertainty in gamma-ray efficiency curve determination through an analytical approach.

An example of uncertainty evaluation of an efficiency curve is reported. In the applied method, the efficiency curve is determined through the weighted least square method based on measured efficiencies employing a mixed-radionuclide standard source. The variance-covariance matrix of the efficiencies is determined by evaluating the uncertainties of the counting, the calibrated radioactivities, the correction factors for true coincidence summing, and the inadequacy of the fitting function. The proposed method can be a basis to develop a more general procedure.

Interlaboratory Study on Caprolactam Test for Food-Contact Nylon Products.

The Japanese Food Sanitation Law sets a limit on the migration level of caprolactam for food-contacting nylon products. Here, we carried out an interlaboratory study in twenty laboratories to evaluate the performance of the official GC-FID test method and a GC-MS method as an alternative test method to the official method. Each laboratory quantified caprolactam in three test solutions in 20% ethanol as blind duplicates using GC-FID or GC-MS. The official method (GC-FID with absolute calibration) gave trueness, repeatability (RSDr) and reproducibility (RSDr) values of 96-97%, 3.3-5.4% and 4.0-6.7%, respectively. These values met the target criteria (trueness: 80-110%, RSDr: 10%, RSDr: 25%). The performance of the method was further improved by the introduction of heptalactam as an internal standard. As for GC-MS method, some values of the RSDr exceeded 10% when absolute calibration was used. However, when an internal standard was introduced, the trueness, RSDr and RSDr of GC-MS method were all acceptable at 94-96%, 2.0-4.4% and 7.0-9.4%, respectively. Therefore, GC-MS with an internal standard is available as an alternative test method to the official method.

[Interlaboratory Study on Zinc Test for Food-Contact Rubber Products].

Using six kinds of zinc solution in water and 4% acetic acid as samples, an interlaboratory study was performed to evaluate a zinc (Zn) test method for food-contact rubber products, based on the Japanese Food Sanitation Law. Eighteen laboratories participated, and quantified Zn in six test solutions as blind duplicates using flame atomic absorption spectrometry, induced coupled plasma-optical emission spectrometry or induced coupled plasma-mass spectrometry. Statistical analysis revealed that the trueness, repeatability (RSDr) and reproducibility (RSDr) were 97-103%, 0.7-4.9% and 1.7-8.9% by all measuring methods. The values of the performance parameter fulfilled the target value (trueness: 80-110%, RSDr: 10%, RSDr: 25%). The performance of these methods is sufficient for testing the adherence of samples to the specifications.

[Interlaboratory study on migration test of antimony and germanium for food-contact polyethylene terephthalate].

An interlaboratory study was performed to evaluate a migration test method of antimony (Sb) and germanium (Ge), based on the Japanese Food Sanitation Law for food- contact polyethylene terephthalate. Eighteen laboratories participated, and quantified Sb and Ge in three test solutions as blind duplicates using graphite furnace atomic absorption spectrometry (GF-AAS), inductively coupled plasma-optical emission spectrometry (ICP-OES) or induced coupled plasma-mass spectrometry (ICP-MS). Statistical analysis revealed that the trueness, repeatability and reproducibility were 98-107%, 1.7-7.5% and 2.0-18.8% by using GF-AAS and ICP-OES. The performance of these methods is sufficient for testing the specifications. The performance parameters of ICP-MS were 99-106%, 0.7-2.2% and 2.2-10.5%, respectively. ICP-MS is available as an alternative measuring method. However, in some laboratories, the quantitative values of Sb were higher than the addition levels. We found that Sb in working solutions is absorbed on glass vessels. Careful control of concentration in working solutions is required for Sb analysis.

Molecular simulation of ion transport in silica nanopores.

Ion distribution and transport of KCl aqueous solutions at the junction of hydrophobic and hydrophilic regions inside silica nanopores were studied by using two kinds of molecular simulation: grand canonical Monte Carlo (GCMC) simulations and nonequilibrium molecular dynamics (NEMD) simulations. The nanopores were 2 nm diameter silica pores in which surface functional groups, -SiOH, had been modified by hydrophobic surface functional groups, -SiCH(3), within three different lengths along the pore direction (z-direction), L(z0) = 0, 2, and 4 nm. If L(z0) is long enough, water could not enter the hydrophobic region, but for all L(z0) studied here, water entered the hydrophobic region. When an external electric field was applied along the z-direction, ions could not pass through the hydrophobic region when the external electric field was less than a threshold level, E(0), whereas the ionic current increased relatively linearly with increasing electric field strength above E(0). In 2 nm diameter fluidic pores, the electrical potential barrier appeared at the junction between the hydrophilic and hydrophobic regions due to the difference in dipole moment of the surface functional groups, although the overall surface charge of the pore was neutral. This junction formed an electrical potential threshold, and the ionic current could be modulated by adjusting the external electric field.

Nanofluidic diode and bipolar transistor.

Theoretical modeling of ionic distribution and transport in a nanochannel containing a surface charge on its wall, 30 nm high and 5 microm long, suggests that ionic current can be controlled by locally modifying the surface charge density through a gate electrode, even if the electrical double layers are not overlapped. When the surface charge densities at the right and left halves of a channel are the same absolute value but of different signs, this could form the basis of a nanofluidic diode. When the surface charge density at the middle part of a channel is modified, this could form the basis of a nanofluidic bipolar transistor.

Molecular dynamics study of hydrated faujasite-type zeolites.

Molecular dynamics (MD) simulations of hydrated zeolite NaX (Si/Al = 1.0) and NaY (Si/Al = 2.0) were done at a temperature of 300 K. The calculation results show that the adsorption of water occurs via a three-step mechanism in zeolite NaX: (1) adsorption around Na, (2) formation of a monolayer on the walls, and (3) pore filling in the supercage during which adsorbed water molecules are localized around the 12-membered rings. Zeolite NaY adsorbs in a similar manner. However, at intermediate hydration states, cluster formation occurs around Na instead of monolayer formation. The calculated energy distribution functions suggest that in zeolite NaX, the water vapor adsorption can be expressed by using the Langmuir model with two adsorption sites, but in zeolite NaY, it is not Langmuir-type adsorption.