Gas chromatographic-mass spectrometric method for trazodone and a deuterated analogue in plasma

A plasma assay method for trazodone and a 2H4 analogue is described which uses gas chromatography--electron-impact selected-ion monitoring mass spectrometry. Etoperidone is used as an internal standard. The analytes are extracted from basic medium into n-butyl chloride, then back extracted into aqueous 0.1 M hydrochloric acid. The aqueous layer is made basic and re-extracted with n-butyl chloride. The solvent is reduced under nitrogen at 35 degrees C and the residue is redissolved in toluene for gas chromatographic--mass spectrometric analysis. The ions monitored are m/z 231, 235, and 225 for trazodone, [2H4] trazodone and etoperidone, respectively. Quantitation is in the range 40-1000 ng/ml with acceptable precision and accuracy. The method is suitable for biopharmaceutical studies.     

Time-of-day corrections in measures of aircraft noise exposure

Results of a socio-acoustic study of human reaction to aircraft noise around Australian airports are described. The relative importance of night, evening, and daytime operations in determining overall reaction is assessed using a correlation analysis procedure. The results indicate that night-time weightings used in most existing noise exposure indices including NEF and DNL, are too large. However, other evidence suggests that both night and evening weightings should be greater than 0 dB. The optimal weightings found were about 3 dB for night-time operations and 9 dB for evening operations. However, other considerations indicate that in a practical noise index it may be more reasonable to apply a weighting of about 6 dB during both night and evening hours.     

Scale size of magnetic turbulence in tokamaks probed with 30-MeV electrons

Measurements of synchrotron radiation emitted by 30-MeV runaway electrons in the TEXTOR-94 tokamak show that the runaway population decays after switching on neutral beam injection (NBI). The decay starts only with a significant delay, which decreases with increasing NBI heating power. This delay provides direct evidence of the energy dependence of runaway confinement, which is expected if magnetic modes govern the loss of runaways. Application of the theory by Mynick and Strachan [Phys. Fluids 24, 695 (1981)] yields estimates for the "mode width" (delta) of magnetic perturbations: delta<0.5 cm in Ohmic discharges, increasing to delta = 4.4 cm for 0. 6 MW NBI.     

Development and validation of a high-performance liquid chromatography tandem mass spectrometry assay for atorvastatin, ortho-hydroxy atorvastatin, and para-hydroxy atorvastatin in human, dog, and rat plasma

A liquid chromatographic/mass spectrometric method to quantitate atorvastatin (AT) and its active metabolites ortho-hydroxy (o-AT) and para-hydroxy (p-AT) atorvastatin in human, dog, and rat plasma was validated. The method consisted of washing plasma samples at high pH with diethyl ether and subsequently extracting the analytes and two internal standards, [d ₅]-atorvastatin ([d ₅]-AT) and [d ₅]-ortho-hydroxy atorvastatin ([d ₅]-o-AT), from acidified plasma by using diethyl ether. The ether layer was evaporated to dryness and the residue reconstituted in ammonium acetate (20 mM, pH 4.0)-acetonitrile-isopropanol (60:40:1, v/v/v). Chromatographic separation of analytes was achieved by using a YMC J’Sphere H80 (C-18) 150 × 2 mm, 4 μm particle size, column with a mobile phase consisting of acetonitrile-0.1% acetic acid, (70:30, v/v). Analytes were detected by using MS/MS. Sample introduction and ionization was by electrospray ionization in the positive ion mode. The method proved suitable for routine quantitation of AT, o-AT, and p-AT over the concentration range of 0.250 to 25.0 ng/mL. Approximate retention time ranges of p-AT, o-AT, [d ₅]-o-AT, AT, and [d ₅]-AT were 2.27 ± 0.21, 3.36 ± 0.23, 3.54 ± 0.46, 4.12 ± 0.61, and 4.65 ± 0.65 min, respectively. No peaks interfering with quantitation were observed throughout the validation processes. Mean recoveries of AT, o-AT, and p-AT from plasma ranged 100%–107%, 70.6%–104%, and 47.6%–85.6%, respectively. Mean recoveries of the [d ₅]-AT and [d ₅]-o-AT internal standards ranged 98.0%–99.9% and 97.3%–97.9%, respectively. Interassay precision, based on the percent relative deviation for replicate quality controls for AT, o-AT, and p-AT, was ≤7.19%, 8.28%, and 12.7%, respectively. Interassay accuracy for AT, o-AT, and p-AT was ±10.6%, 5.86%, and 15.8%, respectively. AT, o-AT, and p-AT in human, dog, and rat plasma quality controls were stable to three freeze-thaw cycles. AT, o-AT, and p-AT were stable frozen for 127, 30 and 270 days in human, dog, and rat plasma quality control samples, respectively. Human plasma quality control samples containing AT, o-AT, and p-AT were stable for at least 4 days at ambient room temperature and 37 °C. The lower limit of quantitation for all analytes was 0.250 ng/mL for a 1.0-mL sample aliquot.     

Two-photon fluorescence scanning near-field microscopy based on a focused evanescent field under total internal reflection

We present two-photon fluorescence near-field microscopy based on an evanescent field focus produced by a ring beam under total internal reflection. The evanescent field produced by this method is focused by a high-numerical-aperture objective, producing a tightly confined volume that can effectively induce two-photon excitation. The imaging system is characterized by the two-photon-excited images of the nanocrystals, which show that the focused evanescent field is split into two lobes because of the enhancement of the longitudinal polarization component at the focus. This feature is confirmed by the theoretical prediction. Unlike other two-photon near-field probes, this method does not have the heating effect and requires no control mechanism of the distance between a sample and the probe.     

Sound propagation through vegetation

The propagation of sound through a large number of scatterers (i.e., trees) is treated in a similar way to a classical diffusion problem. A general differential equation governing the sound intensity is derived which is valid under certain conditions, notably that the depth of the belt of vegetation is large, and absorption small. The predictions of this theory are compared with results derived from a small scale model study, and with some field measurements. They are also compared with published field data. The implications of some of the conclusions reached for the practical achievement of effective sound attenuation are pointed out. In general, it would appear that significant noise reductions may be achieved for a predominantly high frequency source if the existing ground cover is acoustically hard, or if there is no “ground effect” attenuation between source and receiver for some other reason. In other cases, the noise reduction will be much lower and may be negative.