Spectrometer sweep time

In general, the longer the sweep time the better the sensitivity since the filter time constant parameter can be set longer with consequent improvement in signal-to-noise ratio. In practice, however, sweep times are usually set in accordance with the expected lifetime of the radical species, the stability of the instrument, and the patience of the operator. Decay of the radical or drift of the spectrometer during a scan is clearly undesirable. The sweep time is most commonly set in the range 4-10 min. 

The 1H NMR spectra of parbendazole was recorded with a JEOL-PS 100 NMR spectrometer operating at a frequency of 100 MHz and a magnetic field strength of 2.349 T. Spectra were determined over the region 10.8-0.0 parts per million (ppm), with a sweep time of 250 s. Chemical shifts were recorded as S (delta) ppm downfield from tetra-methylsilane (TMS). Proton noise and off-resonance decoupled 13C NMR spectra were measured on a JEOL FX 90Q Fourier Transform NMR spectrometer operating at 90 MHR and spectral width of 5000 Hz (220 ppm). All measurements were obtained with the compound being dissolved in deuterated dimethyl sulfoxide (DMSO-d6) for dT NMR and in deuterated trifluoroacetic acid (TFA-dx) for 13C NMR. 

Detection of hydroxyl radical. For detection of hydroxyl radicals, a spin trapping agent, DMPO was obtained from Sigma-Aldrich.4 The water containing 500 pM DMPO was circulated for 30 min in exPCAW-l,and the water was sampled at 0, 1, 5, 10, 15, 20, 30 min of circulation and exposure to UV, USW and elevated 02. The samples in a flat-shaped quartz ESR cell were analyzed with an electron spin resonance spectrometer (JEOL-TE200, X-band). DMPO-OH signal were collected with a sweep width of 5 mM, a 100 kHz modulation frequency, 60 s sweep time, a time constant of 0.1 s and microwave power of 10 mW, at room temperature of 20-25°C. 

Before the advent of Fourier transform spectrometers, wide-line NMR was done by sweeping the magnetic field and observing the dispersion signal, or by pulsing the radiofrequency and observing the free Induction decay without transformation. The very broad spectral widths have caused problems with baselines and faithful representations of the entire llneshapes. Various techniques, such as the quadrupole echo (lA), progressive phase alternation of the excitation pulse and detector, short spectrometer dead times, and post-acquisition spectral correction (15) have circumvented most of these. 

EPR signals were recorded with a JES-RE2X EPR spectrometer at room temperature using a flat cell. The instrument conditions were as follows, for tyrosine radical micropower, 5 mW sweep time, 4 min modulation amplitude, 0.32 mT time constant, 0.03 s receiver gain, 1 X 1000. The conditions for Mn were same as for tyrosine radical except modulation amplitude was 1.0 mT. 

EPR experiments were carried out using an X-band spectrometer employing an E102-E bridge, field modulation 100 kHz and 16G, lock-in sensitivity 100 mV, sweep time 10 min, time constant 1 s, microwave frequency 9 055 GHz and microwave power 50 mW. The temperature was maintained between 7-lOK using a He-flow cryostat. 

Many of the analytical signals that must be analyzed can be viewed as time series data, since the data are gathered over time as some instrumental parameter or experimental condition is varied, e.g., m/z sweep in a mass spectrometer or time in a chromatographic experiment. Filtering or smoothing can be done to these time domain signals direaly. 

Figure 6 Scheme of a typical spin trapping experiment in an isolated heart. Coronary effluents are collected and immediately frozen in liquid N2 to prevent spin adduct decay. Frozen samples are thawed just before EPR measurement and EPR spectra are recorded using 160 or 250 pL flat cells. Typical spectrometer conditions are as follows magnetic field 3350 G, power 8 mW, response 0.3 s, modulation amplitude 1.0-1.25 G, receiver gain 6.5 X 10 sweep time 2 min, modulation frequency 100 kHz and temperature 23-28°C. 

EPR measurements were made with a Bruker EMX X-band continuous wave spectrometer equipped with a Bruker ER 4116 DM rectangular cavity operating at 9.658 GHz. Experiments were performed at room temperature (300K) with a hyper frequency power of 1 mW and a modulation amplitude of 0.5 G. The amplitude of the magnetic field modulation and microwave power were adjusted so that no line-shape distortion was observable. The received gain was 63,200 and the sweep time was 42 s. Absolute quantification was obtained by comparison with a TEMPO sample of known concentration after double integration of EPR spectra. 

The Imass Dynastat (283) is a mechanical spectrometer noted for its rapid response, stable electronics, and exact control over long periods of time. It is capable of making both transient experiments (creep and stress relaxation) and dynamic frequency sweeps with specimen geometries that include tension-compression, three-point flexure, and sandwich shear. The frequency range is 0.01—100 H2 (0.1—200 H2 optional), the temperature range is —150 to 250°C (extendable to 380°C), and the modulus range is 10" —10 Pa. 

NMR Spectroscopy. All proton-decoupled carbon-13 spectra were obtained on a General Electric GN-500 spectrometer. The vinylldene chloride isobutylene sample was run at 24 degrees centigrade. A 45 degree (3.4us) pulse was used with a Inter-pulse delay of 1.5s (prepulse delay + acquisition time). Over 2400 scans were acquired with 16k complex data points and a sweep width of +/- 5000Hz. Measured spin-lattice relaxation times (Tl) were approximately 4s for the non-protonated carbons, 3s for the methyl groups, and 0.3s for the methylene carbons. 

With this spectrometer, a difference mid-IR spectrum at a selected time after sample excitation is recorded by sweeping from 1640 to 940 cm in steps that may be as short as approximately equal to the spectral resolution of the spectrometer—in this case, 8 cm. The sample solution is pumped through a flow cell that has IR-transmitting Cap2 windows set with a 0.1-mm optical pathlength. The Bap2 windows have also been used for the sample cell. ... 

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