Half-peak time

From the last result, the half-peak time 1 2 for t) is given by... 

Figure 12. Half-peak time ti,2 of coherent dynamic structure factor for atactic polystyrene plotted vs. Q. Left, CgD solution right, CS2 solution continuous lines, calculated results at T = 30 °C dashed line, at F = 70 °C. Experimental points from ref. 14. [Model assumptions and parameters same as in Figures 10 and 11, tB = 0.012.] (Reprinted with permission from ref. 14, Copyright 1984, American Chemical Society.)...

Q is the scattering vector and t 2 is the half-peak time of the dynamic structure factor, the larger is the chain stiffness, the smaller is the value of which may be as small as 2. 

The characteristic features of the tip current transients in Figure 6 are the peak current, peak time, and post-half-peak time. These features show interesting dependences on the tip/substrate separation and K (Fig. 7). The magnitude of the normalized peak current (Fig. 7a) increases as the values of both K and dla are decreased, whereas the time taken to reach the peak increases as the value of dJa is increased and K is decreased (Fig. 7b). This contrasting behavior allows both K and dla to be determined from a single transient measurement with good precision (6). In particular, kinetics are determinable from SG/TC measurements with no prior knowledge of the tip/ substrate separation (6). The post-half-peak time has a yet different dependence on dla and K. This increases as K decreases but shows only a minimal dependence on the normalized interelectrode separation (Fig. 7c). 

FIG. 7 Theoretical contour plots showing the variation of (a) peak current, (b) peak time, and (c) post-half-peak time with tip/substrate separation and normalized rate constant. The labels on the contours are values of the normalized current ratio 0 t,c/ t>) in (a) and normalized time (t) in (b) and (c). 

In establishing belt-conveyor tonnage requirements it is important to work with peak rather than average loads. Only occasionally, because of intentional or accidental variations in produ ion rates, are these two figures identical. The belt that runs empty half the time must cany t ce the average load when it is working. 

In this special case when the time between dosings is equal to the half-life time of the drug, we can deduce that the minimum (steady-state) plasma concentration with repeated dosing is equal to the peak concentration, obtained from a single dose. Under this condition, the corresponding maximum (steady-state) concentration is twice as much as the minimum one. 

The time of the peak can also be used to roughly estimate the absorption rate constant. If it is assumed that ka is at least 5 x kei, then it can be assumed that absorption is at least 95% complete at the peak time that is, the peak time represents approximately five absorption half-lives (see Table 1). The absorption half-life can then be calculated by dividing the time of the peak by 5, and the absorption rate constant can be calculated by dividing the absorption half-life into 0.693. 

Example. Inspection of Fig. 10 gives a peak time of about 2.5 hours. The absorption half-life can be estimated to be 0.5 h and the absorption rate constant, to be 1.4h-1. 

Bobrowski and Das33 studied the transient absorption phenomena observed in pulse radiolysis of several retinyl polyenes at submillimolar concentrations in acetone, n -hexane and 1,2-dichloroethane under conditions favourable for radical cation formation. The polyene radical cations are unreactive toward oxygen and are characterized by intense absorption with maxima at 575-635 nm. The peak of the absorption band was found to be almost independent of the functional group (aldehyde, alcohol, Schiff base ester, carboxylic acid). In acetone, the cations decay predominantly by first-order kinetics with half life times of 4-11 ps. The bimolecular rate constant for quenching of the radical cations by water, triethylamine and bromide ion in acetone are in the ranges (0.8-2) x 105, (0.3-2) x 108 and (3 — 5) x 1010 M 1 s 1, respectively. 

As each component exits the chromatographic column, it is channeled into an infrared (IR) gas cell and the component s IR spectrum obtained. A thermal conductivity detector (TCD) (see Chapter 13) can be used to determine when a component is emerging from the column. The TCD detector does not destroy the sample and none of the common gases used in GC have IR spectra, and thus do not interfere with the spectrum of eluting components. Half-peak height is a common time to obtain the spectrum of that component and the setup for detection and obtaining the spectrum can thus be automated [6,13],... 

The pulsed xenon lamp forms the basis for both fluorescence and phosphorescence measurement. The lamp has a pulse duration at half peak height of lOps. Fluorescence is measured at the instant of the flash. Phosphorescence is measured by delaying the time of measurement until the pulse has decayed to zero. 

Although it is difficult to generalize the dependence of the peak potential on e, in general, for an oxidative electrode mechanism, the position of the peak shifts to positive potentials by increasing the rate of the preceding chemical reaction. At the same time, the half-peak width is largely insensitive to the chemical reaction. If log( ) < -2, Ap vs. log(e) is a linear function with a slope of about 30 mV. 

Because of some peak tailing, the number of theoretical plates was based on peak width at one-half peak height Ns5.S4 he pooled standard deviation (all temperatures) of retention time measurements (dfs34) was t 0.007 minutes. 

Pharmacokinetic properties Butorphanol (Vachharajani et al., 1997) is rapidly inactivated by first pass metabolism in the gut. Intramuscular and nasal administration induces a peak effect between 0.5-1 hr and a duration of action of about 3 h, corresponding to the plasma half-life time of the compound. Butorphanol has a plasma protein binding of about 80%, metabolic inactivation includes hydroxylation,... 

Pharmacokinetic properties Due to intensive first-pass metabolism, nalbuphine has a low oral bioavailability of less than 10%. After intramuscular administration peak plasma concentrations are reached after 30 min, half-life time is about 5 h. The compound is metabolized by glucuronidation and to a minor extent by N-dealkylation, and less than 10% is excreted unmetabolized (Lo et al., 1987). 

The atmospheric concentration of natural and bomb-produced radionuclides has been measured at ground level for several years at three locations throughout the world. The manner in which the concentration decreased suggested a half-residence time for stratospheric aerosols of 11.8 months at 46°N latitude. The annual spring concentration maximum occurred one to four months earlier at 71°N than at 46°N. Cosmogenic 7Be attained a maximum concentration before the bomb-produced radionuclides at 71° N and later than the bomb-produced isotopes at 46°N. The rate of increase toward the annual peak concentration for most radionuclides could be approximated by an exponential in which the concentration doubled every 60 days likewise, the rate of decrease from the maximum concentration could be approximated by an exponential with a half-time of about 40 days for most radionuclides except 7Be at 46°N, which shows a half-time of about 60 days. 

This term denotes a potential whose nature depends on the technique used. Typical characteristic potentials are the half-wave potential in polarography, the quarter-transition-time potential in chronopotentiometry, and the peak or half-peak potential in stationary-electrode voltammetry. Regardless of its nature, the characteristic potential always depends on the identity of the electroactive substance, on the kinetics or thermodynamics of the electron-transfer process, and of course on the experimental conditions for any particular technique and under any completely defined set of experimental conditions the value of any characteristic potential is a reproducible property of the electroactive substance. 

Injection voltage is varied between +500 and + 2000 V and maintained for 5, 10, and 20 s. Separation is carried out by applying a voltage of +2000 V using a detection potential of +0.7 V and 50 mM Tris-based buffer pH 9.0. Choose optimal injection time/voltage taking into account of peak current (7P) and half-peak width (1U1/2). 

Optimal detection potential, separation voltage, and injection time/ voltage are used to determine parameters such as electroosmotic velocity (ueo = Leff/tm) and mobility (/[Pg.1282]

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