Linearity and dynamic response range

From the lower detection limit near lOnM to approximately 200 o,M H2S, the PHSS signal is best lit by a linear regression (see Fig. 8.7), with coefficient of regression typically 0.98. However, the amperometric signal loses linearity at higher H2S concentrations. This behavior has also been observed in other micro polarographic sulfide sensors [42]. It is likely that the small electrolyte volume at the sensor tip becomes saturated at higher H2S concentrations as the rate of H2S diffusion becomes more rapid than the rate at which ferrocyanide is reoxidized at the platinum anode. 

In response to step H2S changes by addition or removal, the PHSS typically takes less than 10 s to reach 90% of the new signal (see Fig. 8.5), in agreement with previous experiments performed with the macro PHSS at 20°C [36]. With a freshly prepared PHSS, we often observe that the first H2S injection to the chamber results in a somewhat slower response time, approximately 30 s, to reach 90% of the new signal. This slower response is not observed with subsequent injections, suggesting that for a newly prepared PHSS, initial electrolyte conditioning occurs upon first exposure to H2S. 

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The dynamic response range of an IMS-based detector is less than two to three orders of magnitude, compared to five or six of other detection technologies. The concentration versus response relationship is exponential rather than linear. As dis-cnssed earlier, due to the limitation of total available ions in the ionization region, the response may reach its saturation level rather quickly such that a furtho- increase in concentration will not lead to a much stronger signal (Figure 6.3), and thus the relationship is not hnear. 

The non linear viscoelasticity of various particles filled rubber is addressed in range of studies. It is found that the carbon black filled-elastomer exhibit quasi-static and dynamic response of nonlinearity. Hartmann reported a state of stress which is the superposition of a time independent, long-term, response (hyperelastic) and a time dependent, short-term, response in carbon black filled-rubber when loaded with time-dependent external forces. The short term stresses were larger than the long term hyperelastic ones. The authors had done a comparative study for the non linear viscoelastic models undergoing relaxation, creep and hysteresis tests [20-22]. For reproducible and accurate viscoelastic parameters an experimental procedure is developed using an ad hoc nonlinear optimization algorithm. 

Linear dynamic response ranges for capillary (IC-AED extend from the upper linear analyte-carr3ring column capacity, at ca.l00 ng, down to the detection limit for the element (1-100 pg). Chemical, dopant gas and plasma-wall interaction effects modify the limits. 

Figure 1.19 Methods for Calculating the dynamic and linear response ranges for chroMtographic detectors.

The mechanical response of polypropylene foam was studied over a wide range of strain rates and the linear and non-linear viscoelastic behaviour was analysed. The material was tested in creep and dynamic mechanical experiments and a correlation between strain rate effects and viscoelastic properties of the foam was obtained using viscoelasticity theory and separating strain and time effects. A scheme for the prediction of the stress-strain curve at any strain rate was developed in which a strain rate-dependent scaling factor was introduced. An energy absorption diagram was constructed. 14 refs. 

One major aspect of quantitative analysis is sensitivity and dynamic range of linearity. Such data have been reviewed (2) for the gas density, thermal conductivity, and flame ionization detectors. Since response is a function of molecular weight in the gas density detector, it is difficult to make comparisons in a simple manner. In general, however, the sensitivity of the gas density cell is about twice that of comparable thermal conductivity cells and about one-tenth that of flame ionization detectors (when bleed of the column is limiting). 

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