Programmed scanning rate

In practice, the true heating rates (dT/dt)ca and (dT/dt)cb are assumed to be equal to the programmed scan rate j3, and the true heat flow rate difference (heat flow rate difference, Ao, which reflects the intrinsic thermal asymmetry of the differential measuring system ... 

Figure 6,16 Cyclic voltammograms as a function of scan rate. This figure comprises traces simulated by the DigiSim program for a reversible one-electron couple, with the fastest scan rate being shown outermost. Reprinted with permission from Current Separations, Vol. 15, pp. 25-30, copyright Bioanalytical Systems, Inc., 1996.

The term voltammetry refers to measurements of the current as a function of the potential. In linear sweep and cyclic voltammetry, the potential steps used in CA and DPSCA are replaced by linear potential sweeps between the potential values. A triangular potentialtime waveform with equal positive and negative slopes is most often used (Fig. 6.8). If only the first half-cycle of the potential-time program is used, the method is referred to as linear sweep voltammetry (LSV) when both half-cycles are used, it is cyclic voltammetry (CV). The rate by which the potential varies with time is called the voltage sweep (or scan) rate, v, and the potential at which the direction of the voltage sweep is reversed is usually referred to... 

Temporal Devices. A temporal dispersive device uses a single channel which is scanned as a function or time to yield information on the intensities present in various resolution elements. Two basic approaches are possible (1) the detector may be scanned across a fixed spectrum or (2) the spectrum may be scanned across a fixed detector. In addition, these systems may be further differentiated on the basis of the manner in which the spectrum is scanned. Thus, linear-scan systems scan the spectrum at a constant, fixed rate. In contrast, programmed-scan systems have the capability of momentarily stopping at wavelengths of analytical interest, while spectral regions of little interest are rapidly scanned. For a complete review of the area of rapid-scanning spectrometry up to 1968, the interested reader should consult Volume T of Applied Optics which was entirely devoted to this subject. 

Polarogram — Figure. Potential program and the respective (a) direct current (DC) (staircase ramp), (b) normal pulse (NP) and (c), differential pulse (DP) polarograms of 0.1 mM Cd(NC>3)2. All measurements were in water with 0.1 M KC1, E is versus a SCE, scan rate = 2 mVs-1 and drop time = 2 s. Differential pulse height = 10 mV... 

Exchanged zeolites were characterized by N2 adsorption at 77K, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), immersion calorimetry and NHs-temperature programmed desorption (NH3-TPD). X-ray diffraction patterns (XRD) were obtained with a JSO Debye-Flex 2002 system, from Seifert, fitted with a Cu cathode and a Ni filter, using CuXa radiation (A,=1.5419) and 2°min of scanning rate. X-ray photoelectron spectroscopy (XPS) spectra were acquired with a VG-Microtech Multilab 3000 spectrometer equipped with a hemispherical electron analyzer and Mg Ka (1253.6 eV) 300W X-ray source. 

Instruments IR-85 Fourier Transform infrared spectrometer, through an IBM GC-IR interface. The interface consisted of a gold-coated Pyrex light-pipe with potassium bromide windows. A scan rate of 6 scans/sec and a spectral resolution of 8 cm- - were used for data acquisition. Samples were introduced into the system via splitless injections. A fused silica capillary column, 30 m x 0.32 mm i d DB-WAX (dj 1.0 pm), was employed with the outlet end connected directly to the GC-IR light-pipe entrance. Helium was used as the carrier gas at an average linear velocity of 41.4 cm/sec (35°C). No make-up gas was employed in the system. The column temperature was programmed from 35°C to 180°C at 2°C/min. The GC-IR light-pipe assembly was maintained at 170°C. 

The temperature programmed reduction (TPR) experiments were performed in a SETARAM TGDTA 92 microbalance. After evacuation of the sample to 10 mbar, the sample was equilibrated at room temperature with a 65 ml/min pure argon flow. The temperature was then raised with rate of 10 K/min up to 823 K and kept at this temperature for 1 h. Then the sample was cooled down to 360 K and 50 ral/min of the argon flow was replaced by the equal amount of hydrogen (80 kPa Hz in the total flow). Finally the sample was purged in hydrogen at 360 K for 15 min and TPR was performed at a scan rate 10 K/min up to 1073 K. 

Co., Palo Alto, CA.) One rL of each extract was injected (splitless mode 30 s valve delay 200 0 injector temperature) into a capillary column (DB-wax or DB-Sms. 60 m length x 0.25 mm i.d. x 0.25 pm film thickness (d,) J W Scientific, Poison, CA). Helium was u.scd as carrier gas at a constant How rate of 0.96 mI7min. Oven temperature was programmed from 40 C to 200 0 at a rate of 3 Omin with initial and final hold times of 5 and 60 min, re.speclively. MSD conditions were as follows capillary direct interface temperature, 280 C ionization energy, 70 eV mass range, 33-350 a.in.u. BM voltage, 1956 (Atune + 200V) scan rate, 2.2 scans/s. Bach SDB or DE extract was analyzed in duplicate. 

Powder diffraction patterns were obtained with a Philips-Norelco diffractometer using monochromatic high-intensity CuKoi radiation CX 1.5405A). For qualitative identification of the phases present, the patterns were taken from 12 < 29 < 72 with a scan rate of 1 26/min and a chart speed of 30 in/hr. The scan rate used to obtain x-ray patterns for precision cell constant determination was 0.25° 20/min with a chart speed of 30 in/hr. Cell parameters were determined by a least-squares refinement of the reflections using a computer program which corrects for the systematic errors of the measurement. 

To sweep a frequency band the synthesiser generates a series of incremental frequency steps at programmed intervals, say 1000 steps of 50 Hz to the -th harmonic of which the Gunn source will follow, as explained earlier. As important as frequency stability and resolution is the settling time between steps of the frequency synthesiser and indeed the other parts of the control circuits, which dictates the scan rate and the ability to step between spectral lines quickly. In the example above, a settling time of 1 ms would dictate a sweep time not less than... 

Data were acquired under the following GC conditions inlet temperature 150 C, carrier gas helium at 1.1 mL/min, split ratio 1 2, detector temperature 280 C, temperature program initial temperature 2 C, initial time 4 min, rate 20 C/min to 50 C then 5°C/min, final temperature 250 C, final time 2 min. The MS was held at 190 C in the ion source using ionization energy of 70 eV and a scan rate of 0.9 scans/s. Tentative identities were assigned to peaks with respect to the Wiley mass spectral library. 

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