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In high-pressure die casting, attention has been paid to the J factor, which is defined by the speed of the metal injected at the gate and the shape of the gate. In casting experiments using a piston die, the porosity of the product can be reduced by increasing the J factor such that the metal flow passing through the gate forms an atomized flow. To clarify the underlying mechanisms, we developed a system for simulating a two-phase flow of air and aluminum by large-scale calculations of turbulent flow. During the development of the system, we injected metal into an open space and performed imaging to confirm the state of the atomized flow. The system was then verified by reproducing the atomized flow. The analysis results visualized the many small turbulent vortices generated in the thick part far from the gate. We demonstrated that the change from small to longitudinal vortices promoted entrainment of air into the aluminum and increased the efficiency of air expulsion outside the die through an increase in the J factor.

Rationale: Synthesis of copolymer is one of the major approaches to establish sophisticated polymers. In copolymer analysis in mass spectrometry (MS), an increase in the number of monomer unit species and/or the polymer molecular weight results in complex mass spectra, and a method is required to solve this problem. Methods: In this study, electrospray ionization‐ion mobility spectrometry‐mass spectrometry was employed to analyze styrene/methyl methacrylate/n‐butyl acrylate (St/MMA/nBA) terpolymers via Kendrick mass defect (KMD) analysis. An expanded Fourier transform‐based noise reduction method for the copolymer was developed to improve the decrease in the signal/noise ratio observed in the higher m/z region. Results: Low‐mass terpolymers (0.7 kDa) were identified by comparing the observed and theoretical results using a two‐dimensional KMD plot. For the 1.5 kDa terpolymer, the signal overlap, of which KMD value was not matched with the theoretical one, was interpreted by the shift from the theoretical value in the KMD plot. For the 3.0 kDa terpolymers, the compositional candidates were determined by the prediction based on the compositional information of low‐mass terpolymers previously analyzed. The 4.5 kDa terpolymer was interpreted after the expanded noise filtering. Conclusions: The terpolymers, whose molecular weight was up to 4.5 kDa, were successfully characterized at a molecular level. The dependency of the St/MMA/nBA composition on molecular weight was observed; that is, the nBA content decreased with an increase in the molecular weight. [ABSTRACT FROM AUTHOR]

A phenomenon was found whereby the application of an alternating voltage to a capillary column can vary the capacity factor of a sample solute. The alternating voltage-induced variation in the capacity factor was studied using an anion exchange mini-bed (a short capillary column 12 mm long). The capacity factor varied according to both the amplitude and frequency of an applied alternating voltage. The variation greatly depended on the kinds of sample solutes and packing materials. A new separation mode for capillary electrochromatography using an alternating voltage, that is, alternating voltage capillary electrochromatography (AV-CEC), was proposed as an application of this phenomenon to control the retention of a sample solute. The chromatographic behavior of three organic acids (benzoic acid, phthalic acid, and salicylic acid) was studied in AV-CEC using an anion exchange column.

Rationale: We recently developed the characterization method for synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization‐ion mobility spectrometry‐tandem mass spectrometry, in which the m/z value of the most abundant peak was used for characterization. However, the identification of the most abundant peak from the isotopic peaks was often difficult due to the background noise. Methods: Here, we employed a noise reduction method using Fourier transform (FT) filtering. In the power spectrum obtained using FT of the mass spectrum of the multiple charged analytes, the significant signals in the low‐frequency region and at frequency z are observed for the analytes of z charges. When the signals in both regions were used for inversed FT (i.e., the signals in other regions were zero padded), a noise‐filtered mass spectrum was obtained. Results: In the analysis of poly(methylmethacrylate)s weighing 13–17 kDa, mass spectra without noise filtering with relatively high‐intensity noise (than signal) were complicated to identify the most abundant peak. On the contrary, the most abundant peak was clearly identified from the mass spectra after FT‐based noise filtering, and end group composition was estimated successfully. Conclusions: The proposed FT‐based noise filtering for the mass spectrum is effective to characterize multiply charged synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization‐ion mobility spectrometry‐tandem mass spectrometry. [ABSTRACT FROM AUTHOR]

The separation of the structural isomers of OLED materials was carried out by using high performance liquid chromatography‐mass spectrometry (HPLC‐MS) and ion mobility‐mass spectrometry (IM‐MS). Almost all isomeric OLED materials were separated by using HPLC, however, some isomers were not distinguished with each other. On the other hand, by using IM, inseparable isomers by HPLC were separated and the structural information was obtained by MS/MS technique. [ABSTRACT FROM AUTHOR]

Rationale: Analyzing polymer end groups using pyrolysis (Py) gas chromatography/mass spectrometry (GC/MS) in multi‐component polymer samples is not an easy task because of the insufficient sensitivity, selectivity, and mass resolution of conventional Py‐GC/MS systems. Methods: A new Py‐GC/MS system using an atmospheric pressure chemical ionization (APCI) source combined with high‐resolution time‐of‐flight mass spectrometry (TOFMS) was used for end‐group analysis of a methyl methacrylate (MMA)‐styrene (St)‐butyl acrylate (BA) terpolymer (P (MMA‐St‐BA)), which was radically polymerized using 2,2′‐azobis(2‐methylbutyronitrile) (AMBN) as an initiator. Results: Five possible pyrolyzates, comprising an AMBN fragment and a monomer unit, formed during the initiation reactions from one of the three types of end groups, were selectively detected and exclusively identified in their respective extracted ion chromatograms for molecule‐related ions, such as M+ and [M + H]+, with a narrow mass window of ±2 milli m/z units. Conclusions: It was demonstrated that Py‐APCI‐TOFMS is a powerful technique to characterize in detail the complex end groups in multi‐component polymer samples, because of the soft ionization nature of APCI and the high mass resolution of TOFMS. [ABSTRACT FROM AUTHOR]

Polymers with large molecular weight are difficult to interpret using electrospray ionization-mass spectrometry (ESI-MS) due to the generation of various highly multiply charged analytes. Although ESI-ion mobility spectrometry (IMS)-MS is effective in reducing the complexity of the mass spectrum, this approach is insufficient for analyzing highly multiply charged polymers. In this study, we propose a method combining tandem mass spectrometry (quadrupole and high-resolution time-of-flight MS, QMS/TOFMS), IMS, and collision-induced charge stripping (CICS) for analyzing large intact polymers (∼40 kDa), which are highly multiply charged. The number of charges can be estimated from a Fourier transform power spectrum of a mass spectrum when the charge number is less than approximately 20. Interpretations of the spectra of poly(ethylene oxide)s (PEOs) weighing 20 kDa, poly(methyl methacrylate)s weighing 22 kDa, and methoxy-PEO-maleimide weighing 40 kDa were successfully demonstrated with isotope level and polymerization degree level separations, respectively. In the proposed method, a mixture can be analyzed for relatively small (a few kDa) and large (a few tens of kDa) polymers simultaneously without any sample pretreatment. [ABSTRACT FROM AUTHOR]

Multiplex high-performance liquid chromatograph-mass spectrometry (HPLC-MS), in which multiple HPLCs and one MS are hyphenated, is an approach for high throughput analysis in HPLC-MS. A general multiplex HPLC-MS method employs a column-switching technology, and only one HPLC is connected to one MS at a time. In the present study, we propose a novel multiplex HPLC-MS system for simultaneous HPLC-MS analyses. In this study, multiple HPLCs are hyphenated with one MS without a column-switching mechanism, and a mixed-chromatogram is observed by the MS. Here, we employ a frequency division multiplexing (FDM) technique used in communication engineering to extract any chromatogram from the mixed-chromatogram. When a modulator (chopper or ion-gate type) is set between each ion source and the MS, each modulator blocks each sample stream with an individual frequency. In theory, each chromatogram can be extracted from the mixed-chromatogram via a signal processing based on a Fourier transform (FT), frequency-based signal extraction, and reversed FT. In the actual experiment, two HPLCs are hyphenated with one MS (2HPLC-1MS). The use of chopper type modulators leads to the extraction and restoration of each chromatogram from the mixed-chromatogram. However, each restored-chromatogram involves signal interference. On the other hand, the ion-gate modulation system successfully resulted in restored-chromatograms without interference. The potential of the novel multiplex HPLC-MS system based on FDM is confirmed with respect to the simultaneous and continuous analyses of plural samples. [ABSTRACT FROM AUTHOR]