Base line method

Procedure Dissolve accurately 22.5 mg of /ram-clomiphene citrate and 52.5 mg of cis-clomiphene citrate (approx. 1 2.3) into 10 ml of DW in a clean 50 ml separating funnel. Add to it 1 ml solution of sodium hydroxide (5% w/v in DW). In the alkaline medium the base is liberated which is extracted successively with 3 portions of solvent ether (10 ml each). The combined ethereal layer is washed with two portions of DW (10 ml each). The resulting ethereal fraction is dried over anhydrous sodium sulphate, filter, evaporate to diyness carefully over an electric water-bath and dissolve the residue in 1 ml of CS2. Now, record the absorption curve in a 0.2 mm cell over the range 12.50 to 14.00 pm. Calculate the absorbance for the peaks at 13.16 and 13.51 pm respectively by employing the base-line method (see section 3. l. B in this chapter) between the minima at 12.66 and 13.89 pm. 

The intensity of the incident radiation (/q) and the intensity of the transmitted radiation (/) can be measured by the base-line method illustrated in Fig. 10. In the FTIR spectrometer, the computer is capable of converting the transmittance into absorbance, subtracting the background or the solvent interference from the sample spectrum, generating a calibration curve, and calculating the unknown concentration. 

The suspension was divided over a number of ampoules which were sealed under air or nitrogen. The ampoules were heated at 116 °C, removed at various time intervals and assayed spectrophotometrically by the base-line method (principle see Figure 4-A). From the obtained data, shown in Table 2, it was concluded that during a sterilization period of 30 minutes at 116 °C only a slight, acceptable degradation occurs. 

A base-line method was used by three authors [22,23,24]. In all cases a correlation between the ultraviolet method and HPLC was observed, in those cases where the concentration was considerably higher than the detection limit. The detection limit was 0.27 mg per kg [22,23] or 0.3 to 1.7 mg per kg [24]. The latter range was found in an interlaboratory study (see also Section 7.5.3). The base-line method used differed from the original method for determination of natamycin in pharmaceuticals [1, page 547]. In the latter the base-line absorbance was calculated from the absorbances at the minima at 295 and 311 nm and the maximum at 303 nm (Figure 4-A). 

For cheese extracts this method is not suitable due to the interference of the matrix. However, it works well if a part of the spectrum at higher wavelengths is used for the calculation. This alternative base-line method uses the straight line between the absorbance at 311 and 329 nm as die base line. The net absorbance may be taken from the UV spectrum as the difference between the absorbance at the maximum at 317 nm and the base-line (Figure 4-B). It may also be calculated from ... 

A popular method for measuring Zq is the base line method. This is illustrated in Fig. 2.10, which shows part of a recorded spectrum of the sample in the solvent. It is the method for getting a background Iq that gives the method its name. In the figure a base line is drawn tangent to the spectrum at the wings of the analytical band, and its intersection with a vertical line at the analytical wavenumber is used for Zq. Alternately the base line may... 

Fig. 2,10. Base line method for determining absorbance or transmittance.

Under the conditions of identical ATj and ATf, one can make use of the base-line method for the heat of fusion determination A//f is simply all the area above the base line, multiplied by K, the calibration constant. The cross-hatched area accounts for the sum of the vertically shaded area and the correction term. Even if ATj is not exactly equal to ATf, this method may still be useful as a first approximation. For more accurate determinations, however, Eq. (20) has to be evaluated fully. 

FIGURE 15 Part of an infrared spectrum showing the base line construction for the base line method used in quantitative analysis. 

A more sophisticated and increasingly popular method of on-condItion maintenance is to monitor the performance of equipment on-line. For example, a piece of rotating equipment such as a turbine may be monitored for vibration and mechanical performance (speed, inlet and outlet pressure, throughput). If a base-line performance is established, then deviations from this may indicate that the turbine has a mechanical problem which will reduce its performance or lead to failure. This would be used to alert the operators that some form of repair is required. 

Tangents Method. The tangents on either side of the peak are drawn through the inflection points until the baseline. For an ideal Gaussian peak the resulting base line interval Wi, is equal to 4or. Equation (1) becomes with the width (Wb) ... 

Post-exposure techniques are well documented for a variety of metals (ASTM and NACE). A disadvantage of coupon techniques is that the response to severe corrosion that may occur for short periods of time is not detected because the response measured is only an average for the period of exposure, although coupons can be withdrawn at intervals of time provided a sufficient number are placed at the start of exposure. The important aspect of coupons is that data obtained from their use can be used as base-line and therefore can be used to correlate corrosion data from other methods. 

Ballew, R. M. and Demas, J. N. (1991). Error analysis of the rapid lifetime determination method for single exponential decays with a nonzero base-line. Anal. Chim. Acta 245, 121-7. 

Pulse methods In these techniques, the surface is prepared in a steady-state form with a stationary coverage of the intermediate. The current or potential is then rapidly altered, and the resultant potential or current changes monitored. From these measurements, following correction for base-line effects, the charge associated with the change in coverage of the intermediate can be obtained. 

Geiser et al. [50,51] illustrated the screening of different chiral stationary phases and the separation of highly polar amine hydrochlorides using EEL methanol/C02 mixtures and the columns, Chiralpak-AD-H, Chiralpak-AS. This method is advantageous because no acid or base additive was required to achieve base line separation of the racemates and conversion to free base form for enantiomer separation was not required. Preparative-scale separations of the amine-hydrochloride were accomplished using similar mobile phase conditions [51], Furthermore, this is believed to be the first chiral separation of highly polar solutes without the addition of acid or base additive to effect the separation. 

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