Base line extrapolation

Measure the heights of each peak from the extrapolated base line, and the width of the peak at half peak height the approximate area is the product of these two values. 

All of the NTO samples examined so far contained protons in appreciable quantities. To prepare standards, therefore, known amounts of water are added over and above that which is already present and the calibration curve is extrapolated back to the base line. 

In an asymmetric spectrum, the center of the spectrum may not coincide with the "cross-over" point referred to as the base line. This uncertainty is removed when a hyperfine pattern is observed. In the absence of hyperfine structure, Blois et al. (15) have shown that it is necessary to run the sample in a series of tubes of different diameter, and the true g-value is then obtained by extrapolating to zero tube diameter. 

The upper critical field HdiT) was evaluated from the temperature dependence of the field-cooled magnetization. From the normal phase, the sample was cooled to the superconducting state in an external magnetic field (2 kOc < //ext < 50 kOe). We monitored the magnetization while heating the sample until the normal state is reached, with the applied field held constant. The intercept of a linear extrapolation of the magnetization in the superconducting state with the normal-state base line defines the transition temperature T, and the upper critical field Hci(,T) is equal to the applied field. 

The data passes the baseline with the required cumulative integral in the required time. If the time limit is exceeded, an extrapolated value from the peak difference on the curve is used to find a shorter base line crossing and cumulative integral. 

In the technique as generally applied, increasing amounts of an analyte standard are added to aliquots of the unknown sample solution then each aliquot is diluted to the same fixed volume. The response is extrapolated to a point on the base line concentration scale which corresponds to analyte concentration in the sample solution containing no added analyte. 

Figure 5. Diagram showing how Lloyd and Cunningham s controller equation was obtained (solid lines based on experimental data, dashed lines extrapolated, adapted from (39)...

Then, another 1 ml of 20 yM substrate solution was added to the remaining solution and beads, and 1 ml of the supernatant liquid was withdrawn after 2 min. The amount of AMC formed by thrombin in the remaining solution and adsorbed on the beads was estimated after 2 min by back-extrapolation on the recorder. (The 1 ml withdrawn solution was mixed with 1 ml of 10 yM substrate solution, which was used for the adjustment of the base line of fluorescence.) Finally, the activity of the thrombin adsorbed was deduced by subtracting the amount of AMC formed by thrombin in the first-withdrawn supernatant from the amount of AMC formed by thrombin in the remaining solution and on the beads. 

All the methods share a common problem - the need to identify the base line below the curve. One possibility is to run a curve on a blank solution containing none of the analyte, and use this as a baseline. However a real solution containing no analyte may not yield the same result as the theoretical result obtained by extrapolation of several curves to a theoretical zero analyte concentration. It is possible to extrapolate the flat plateau on either side of the peak to form a baseline. But, the true baseline might not be so flat Other methods contain assumptions. It is best to try several methods and use that which gives the most reproducible calibration with standards. This will all be dealt with later. 

In agreement with the ICTA definition the extrapolated onset is defined as the point of intersection of the tangent drawn at the point of greatest slope on the leading edge of the peak with the extrapolated base line. 

In Figure 4.2, the concentration-temperature diagram is shown for sodium dodecyl sulfate (SDS) in water. The solid line denotes the solnbility limit the dashed line is the solubility that is expected based on extrapolation of the behavior at low temperatures. The rate of solubility increases with temperatnre changes abruptly at about 10°C, which is known as the Krafft point. Below this temperatnre, no micelles are present and the solid surfactant, in which the hydrocarbon chains are rather rigid, is formed at the solubility limit. However, above the Krafft point, micelles whose hydrocarbon chains are much more fiexible form at con-centrahons above the dashed line, which represents the CMC. At much higher concentrahons (not shown), the solubility limit is ultimately reached and a liquid crystalline phase also having fiexible chains separates. Snch phases are discussed in Sechon 4. 

We have seen that Tafel line extrapolation conveniently yields lew nd by application of Faraday s law, the rate of corrosion at open circuit. Nevertheless, the method is based on certain assumptions that must be verified ... 

Fig. 7. Representative curve of heat flow versus temperature in the region of the Tg of a polymer To, temperature of departure from the base line To or Too, temperature of intercept of extrapolated base line and tangent to steepest slope Tq.s, temperature of 50% transition (A = B) Tp, temperature of maximum slope (peak of derivative plot) Tf, temperature at completion of the transition (24).

The microporous volume is obtained from a straight line extrapolated to a positive intercept on the ordinate. The estimation of t should be based on the reference isotherm, which yields the same BET constant (Cbet) as that of the material tested (40). The choice of the standard t function and the part of the V-t curve used for linear fitting drastically affect the values of the external surface and micropore volume. To avoid the foregoing complications. Sing (41) introduced and developed the method, in which the normalized adsorption, (= nlno.4), is derived from the isotherm of a reference material by using the amount adsorbed at a relative pressure of 0.4 (uo.a) as the normalization factor. Lecloux... 

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