Curve stripping method

This can well be seen from Fig. 24 showing three measured PDC-elution curves of the same standard anionic polystyrene PCC K-l 10000 (Pw = 1080) at 23 °C (very narrow), 17 °C (medium broad) and 15 °C (very broad). Only the very broad elution curve at 15 °C allows a simple caclulation of the MWD by means of the strip method S , because only 8% of the curve-width is caused by spreading and 92% by resolution (crD/cr = 0.08), whereas the inversion method G or K described above must be applied when the MWD is calculated from the elution curve 17 °C or even 23 °C, where 73 % of the curve-width is caused by spreading and only 27 %... 

Fig. 25. Distribution of the degree of polymerization of polystyrene sample PCC K-l 10,000 calculated from the elution curves Fig. 24 at 15 °C (O), at 23 °C ( ), and at 25 °C ( ) (not shown in Fig. 24, cf. text). For comparison incorrect distribution of the degree of polymerization of the same sample calculated from GPC without correction for spreading (strip method, A)...

Other approaches have been used for more complex models. These include curve stripping or the method of residuals,either manually or using a computer program such as CSTRIP and ESTRIF. These techniques can separate a multiexponential curve into its component parts for initial estimates. Other techniques include deconvolution methods specific to the one and two compartment pharmacokinetic models. The objective of the deconvolution method is to mathematically subtract the results obtained after IV administration from the oral or extravascular data. This results in information about the input or absorption process alone. More general methods have been presented by various researchers that do not rely on a particular compartmental model. ... 

Peeling, curve stripping, or the method of residuals is an old technique advocated in some of the classic textbooks on pharmacokinetics (Gibaldi and Perrier, 1982) as a method to obtain initial estimates. The method will not be described in detail the reader is referred to the references for details. Its use will be briefly illustrated. Consider the biexponential model... 

From Equation 12.8 a plot of Qater - C vs. time on semilog graph paper provides an estimate of k, the absorption rate constant. The technique of curve stripping or method of residuals can be applied to equations involving multiple exponential terms when they differ by at least fivefold. 

The absorption rate constant is determined by a method known as "feathering," "method of residuals" or "curve stripping." The method allows the separation of the monoexponential constituents of a biexponential plot of plasma concentration against time. From the plasma concentration... 

The method of residuals is a commonly employed technique for resolving a curve into various exponential terms. This method is also known as feathering or curve stripping (see p.l02). The curve from the observed data and that for the extrapolated line are depicted in Fig. 13.11. Table 13.2 gives the headings for the data that can be extracted from the figure. 

In the conductivity, potentiometric, and voltam-metric measurements the response is correlated to concentration or activity of the analyte usually by using calibration curves. In coulometry, however, the charge measured gives directly the amount of substance and therefore no calibration is needed. However, in coulometry the sample is consumed in the measurements and the problem is that the method requires 100% current efficiency to be reliable. Conductimetry and potentiometry are sample nonconsuming methods. In voltammetry, only an insignificant amount of the sample is consumed and therefore the measurement can be repeated. Only in voltammetric stripping methods of very low concentrations of the analyte the amount consumed at the electrode reaction has to be considered if repeated measurements are to be done. 

Regardless of the procedure used, certain initial steps must be taken for the determination or specification of certain product properties and yields based on the TBP distillation curve of the column feed, method of providing column reflux, column-operating pressure, type of condenser, and type of side-cut strippers ana stripping requirements. These steps are developed and ilhistrated with several detailed examples by Watkins (op. cit.). Only one example, modified from one given by Watkins, is considered briefly here to indicate the approach taken during the initial steps. 

Figure 14-6 illustrates the graphical method for a three-theoretical-plate system. Note that in gas absorption the operating line is above the equihbrium curve, whereas in distillation this does not happen. In gas stripping, the operating line will be below the equihbrium curve. 

The Metrohm 646 VA processor and 647 VA stand is based on a polaro-graphic/voltammetric analyser with method memory and automatic curve evaluation, combined with a multi-mode stand (see Fig. 5.9). The following four determination techniques for polarography, voltammetry and stripping... 

Astheimer and Schwochau have applied the voltametry method to the determination of low technetium concentrations in the presence of molybdate and perrhenate ions. Using a Kemula electrode technetium is concentrated on a mercury drop from alkaline solution of 6.0 x 10 M KTcO by electrolysis at a potential of — 1.0 V vs. SCE. Anodic stripping in 1 M NaOH yields a characteristic stripping curve (Fig. 14). The height of the peak at —0.33 V is proportional to the concentration of technetium in the range of 10 to 3 x 10 M. Technetium can be detected with an accuracy of +4%. The determination of 0.5 ng of technetium in a 10 fold molar excess of ReO or MoO is possible. 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

Fig. 7.3. PSA curves and the calibration plot (inset) using non-modified GECE. Constant-current method for different lead concentrations The composition of the cell was 25 mL of 0.1 M acetate buffer pH = 3.76 with 0.5 ppm of Pb. The other electrodes were Auxiliary platinum electrode reference electrode Ag/ AgCl Deposition potential —0.9 V Accumulation time 60 s stripping current 1 pA potential limit —0.2 V Max. time of measurement 300 s. Adapted from Ref. [33].

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