Deposition of In2O3 nanofibers on polyimide substrates to construct high-performance and flexible trimethylamine sensor

Flexible trimethylamine sensor has been realized based on In₂O₃ nanofibers via electrospinning and a deposition technique. The web-like In₂O₃ nanofibers with high length-to-diameter ratios are benefit for gas adsorption and desorption. High trimethylamine sensing properties are observed. The sensors can detect trimethylamine gas down to 1 ppm at 80 °C with the response up to 3.8. Additionally, rapid response (6 s) and recovery (10 s) behavior can also be obtained. Good reliability and flexibility are observed in 100 bending/extending cycles. Our results open a new route to construct flexible gas sensors in practice.     

Preparation and application of trimethylamine amination polychloromethyl styrene nanolatex coated capillary column for the determination of bromate by field‐amplified sample stacking open‐tubular capillary electrochromatography

A new trimethylamine amination polychloromethyl styrene nanolatex (TMAPL) and TMAPL coated capillary column (ccc‐TMAPL) were successfully prepared. The TMAPL coating was characterized with reversed steady EOF values of ca. ?16.8 × 10^?5 cm² V^?1 s^?1. It was applied to establish open‐tubular (OT) CEC and field‐amplified sample stacking (FASS) OT‐CEC methods for the determination of bromate in tap water. Compared to OT‐CEC, the LOD with FASS‐OT‐CEC was improved from 80 to 8 ng/mL. The developed FASS‐OT‐CEC method was practically used for the analysis of bromate in tap water samples with recoveries ranging from 93.6 to 103.5%.     

Convergence of the density functional one-centre expansion for the molecular continuum: N2 and (CH3)3N

A large-scale one-centre expansion with a radial B-spline basis set is implemented for bound and continuum states. A Kohn-Sham hamiltonian is employed with Hartree and exchange-correlation potentials calculated from the SCF electron density taken from a previous LCAO calculation. An inverse iteration method is used to obtain the continuum wavefunction, from which the cross section and asymmetry parameter are calculated. The convergence with respect to angular momentum and cut-off radius is analysed for N₂. The relevance of multipolar contributions even at large distances is shown and suggestions for further improvements are given. In order to show that the present method is suitable to treat systems of moderate size, the (CH₃)₃N molecule has also been calculated and the results are compared with experiment. Received: 19 May 1998 / Accepted: 20 August 1998 / Published online: 7 December 1998     

A combination of Tedlar bag sampling and solid-phase microextraction for the analysis of trimethylamine in air: Relationship between concentration level and sample size

To extend the experimental applicability of the solid-phase microextraction (SPME) method to the analysis of trimethylamine (TMA) by the grab sampling method (i.e., Tedlar bag sampler), we investigated how experimental results are affected by the interaction between the concentration level of TMA standard and the volume size of its sample that is exposed to SPME fiber. To obtain comparative data sets for TMA analysis, all standards were analyzed as triplicate at five different concentrations (10, 20, 50, 100, and 200 ppb) each of which was prepared in four different bag sizes (1, 3, 5, and 10 L capacity). The sorptive characteristics of TMA were then evaluated in terms of recovery rate (RR) values derived by relationship between added and found quantities of TMA standard. The results of randomized block design showed that the determination of TMA is affected by the two major variables (i.e., TMA concentration level and sample size) at 95% confidence interval.     

Intact chemoreceptor biosensors based on Hawaiian aquatic species

Two species of Hawaiian crustaceans, Portunis sanguinolentus and Podophthalmis vigil, are shown to be effective for the construction of antennular receptrodes. The resulting chemoreceptor-based biosensors respond to stimulant compounds at levels below 10^?15 M with very short response times. Experimental studies focused on trimethylamine oxide as a novel test compound, combined with chemometric techniques for data analysis, yield quantitative dose-response data over a wide concentration range.     

Seafood freshness determination through vapour phase Fourier transform infrared spectroscopy

A new vapour-phase manifold has been developed to determine trimethylamine (TMA) in fish and cephalopod samples by Fourier transform infrared (FT-IR) spectroscopy. Samples were treated off-line for 1 h with trichloroacetic acid (TCA), filtered and washed. The obtained extracts were aspirated and alkalinized with NaOH 2.0 M, in an on-line system. TMA was separated from the solution in a gas phase separator and then transported by means of a nitrogen carrier into a home made 10 cm pathlength IR gas cell, where the corresponding FT-IR spectra were acquired by accumulating 30 scans per spectrum with 2 cm⁻¹ nominal resolution. The method was applied to the determination of TMA in natural samples providing concentration values statistically comparables with those obtained by a head space gas chromatography (HS-GC) reference procedure. The sample throughput by FT-IR is increased by a factor of 6 as compared with HS-GC.     

Flow injection potentiometric detection of trimethylamine in seafood using tungsten oxide electrode

A simple flow injection gas/diffusion method for the determination of trimethylamine (TMA) in seafood with potentiometric detection using tungsten oxide electrode has been developed. The method is based on the diffusion of TMA through a PTFE membrane from a sodium hydroxide donor stream to a phosphate buffer acceptor stream. The TMA in the acceptor stream passes through an electrochemical flow cell containing a tungsten oxide wire and a silver/silver chloride electrode, where TMA was sensitively detected. The parameters affecting the sensitivity of the electrode such as sodium hydroxide concentration, buffer concentration, pH, flow rate and injected volume were studied in details. The electrode response was linear in the concentration range from 1 to 10 μg ml⁻¹ TMA with a correlation coefficient (R²) of 0.991 and a detection limit of 0.05 μg ml⁻¹ TMA. The intra- and inter-days precision (R.S.D.) was found to be, respectively, 1.20 and 1.6% (n=6). The method was applied to the determination of TMA in fish tissue and recoveries of 99-100% were obtained for fish extracts. Results were in close agreement with those obtained by the existing classical official method. Common interference from those species that can diffuse through the membrane were removed by the addition of formaldehyde to the seafood extract. The method is simple, feasible with satisfactory accuracy and precision and thus, could be used for monitoring seafood quality with a sampling rate of 20±2 sample h⁻¹.     

Preparation of TMS protected trifluoromethylated alcohols using trimethylamine N-oxide and trifluoromethyltrimethylsilane (TMSCF3)

A catalytic trifluoromethylation of aldehydes using trimethylamine N-oxide and trifluoromethyltrimethylsilane (TMSCF₃) is described. Aromatic, aliphatic and α,β-unsaturated aldehydes provided good to excellent yields of the corresponding trifluoromethylated products.     

Determination of volatile biogenic amines in muscle food products by ion mobility spectrometry

The extent of spoilage of muscle food products was determined through measurement of volatile biogenic amines that emanated from food samples. The release of the amines was enhanced by addition of a few drops of an alkaline solution and the amines were monitored by ion mobility spectrometry (IMS). The limit of detection of the method for trimethylamine (TMA) was 2 ng and the measurement was completed within <2 min with short and long term reproducibility of 15 and 25%, respectively, for replicate samples. The method provides qualitative information as it distinguishes between different amines, as well as quantitative data for the key compounds. A good correlation was found between the IMS results and the microorganism populations in microbiological cultures. The effects of storage time and temperature and of the type of meat on the formation of biogenic amines were examined, and as expected, the higher the storage temperature the faster the spoilage. Thus, this pilot study shows that the measurement of biogenic amines can serve as an indicator for food spoilage or freshness.     

中性三甲胺双聚体的红外-真空紫外光谱研究

Infrared-vacuum ultraviolet (IR-VUV) spectra of neutral trimethylamine dimer were measured in the 2500-3800 cm^-1 region. Quantum chemical calculations were performed to identify the structure of the low-lying isomers and to assign the observed spectral features. The bands at 2975 and 2949 cm^-1 were assigned to the antisymmetric C-H stretching and the band at 2823 cm^-1 to the symmetric C-H stretching, respectively. The 2739 cm^-1 band was due to the CH₃ bending overtone, which disappeared at low IR laser power of 1 mJ/mm². The extra band at 2773 cm^-1 could be due to Fermi resonance behavior of the light isotopologue, these are often close in energy and can strongly mix through cubic terms in the potential function. Experimental and theoretical results indicate the likely coexistence of multiple structures. The peak widths of IR spectra of neutral trimethylamine dimer are not significantly affected by the structural transformation, allowing the stretching modes to be well resolved.