Peak area calculations

Gaussian curves are fitted to the data [28], and a peak area calculation program employed to integrate the area under each peak. This method is used to determine the evolution of peak area with time. The value of the extent of reaction, a, at a time t for any given Bragg reflection (hkl) is calculated using... 

The traceability of time measurement results can be established only if the pulser peak area can be compared with a stated uncertainty to die duration of a traceable time interval. Since the uncertainty of the pulser peak area calculated with general-purpose, peak analysing programs is inadequate, in principle, and does not account for the variability of the pulser peak area induced by the variability of its tails, the pulse peak area is calculated by a separate program. 

Both lead and mercury speciation has been performed by Shum and coworkers [43]. Direct injection nebulization and an ion-pair separation with a microbore LC column were used with ICP-MS detection. A mobile phase of 20 80% v/v ace-tonitrile/water with 5 mM ammonium pentanesulfonate ion pairing reagent at pH 3.4 was used to separate inorganic lead, inorganic mercury, and three organomer-cury species. Detection limits, based on peak area calculations, were 0.2 pg of Pb for all the lead compounds and 7-18 pg of Hg for the mercury compounds. Spiked urine samples were analyzed to evaluate the performance of the method. 

Peak measurement Peak area Calculation type Percent... 

Procedure Prepare a series of THI-DNPH Standard Solutions serially diluted from the Stock THI-DNPH Solution. Pipet 1, 2, and 5 mL, respectively, of the Stock THI-DNPH Solution, into separate 10-mL volumetric flasks, and dilute to volume with absolute, carbonyl-free methanol. Prepare a standard curve by injecting 5 p-L of the Stock THI-DNPH Solution, and the serially diluted THI-DNPH Standard Solutions into a 250-mm x 4-mm (id), 10-lm LiChrosorb RP-8 HPLC column (Alltech Associates, Inc., or equivalent) fitted with an ultraviolet detector set at 385 nm. The mobile phase is 50 50 (v/v) methanohO.l M phosphoric acid. Inject 5 pL of sample into the column. Adjustments in the mobile phase composition may be needed as column characteristics vary among manufacturers. At a mobile phase flow rate of 2 mL/ min and column dimensions of 250 x 4.6 mm, elute THI-DNPH at about 6.3 0.1 min. Measure the peak areas. Calculate the amount of THI in the sample from the standard curve. (For THI limits greater than 25 mg/kg, prepare a series of Standard THI-DNPH Solutions in a range encompassing the expected THI concentration in the sample.)... 

Calculate the response factors of the standards by dividing their concentrations by their peak areas. Calculate the concentration of each component in the sample by multiplying the individual peak areas corresponding to each component by the appropriate response factor calculated for its standard, giving the concentration in w/w percent. A comparison of sorbitol and dextrose peak areas shows that at least 95% of the sum of these peak areas is sorbitol. A similar comparison of maltitol and maltose peak areas shows that at least 95% is maltitol. Neither sorbitol nor maltitol fractions comprise more than 50% of the sample. 

As the integration algorithms were different between the two applications, an early decision in the migration was taken to avoid using the peak area calculations as a comparator between the... 

The detector response index has been featured as a means of defining linearity, but it can also be used to take into account any non-linearity that is present and appropriately modify the peak height or peak area calculations and thus improve quantitative accuracy. An example of two peaks constructed from Gaussian functions using response factors of 0.95 and 1.05 are shown in figure 5. Such values were considered to be outside those which would be acceptable for a detector to be defined as linear. 

When hysteresis produces a water vapor pressure (Pd) for desorption at a specific mass (A), which is greater than the observed Pc, the peak area calculated by the above equation represents an area difference proportional to (Pd-Pc)tc. The total mass entered into the column at tc is the product tcKt, which increases to the saturated state response at saturation or Aw l. The difference between this total mass and that related to the eluted peak area is given above as the mass of water sorbed at Pc. 

Since the peak width on the baseline may be affected by adsorption and tailing effects, the peak s half width is used in the area calculation. This procedure for peak area calculation should only be applied to symmetrical signals. The area thus calculated is proportional to the concentration but slightly smaller than the true value. For an accurate determination of the half widths, a high chart speed must be chosen. 

Table XI. An example of the effect of line peak width, i.e., the number of diodes summed for peak area calculation, on the measurement accuracy.

Fig. 65 Magnification of two regions in the DRIFT spectra of Kapton presented in Fig. 62. a Region of C-H stretching vibrations at 3080 cm-1 aromatic hydrocarbons at 2950 cm 1 aliphatic hydrocarbons. The baseline applied for the peak area calculation is shown as a dotted line in the spectrum for 31,500 pulses, b Region of conjugated double bonds and triple bonds at 2270 cm 1 the -N=C=0 stretching vibration at 2255 cm 1 the -C=C- stretching vibration and at 2230 cm-1 the -C=N stretching vibration. Around 2350 cm 1 the typical doublet of gas-phase C02 is present. REPRINTED WITH PERMISSION OF [Ref. 135], COPYRIGHT (2000) American Chemical Society...

The PEAK program permits the calculation of the parameters of any peak. Options include peak area calculations, peak maximum, minimum temperature or time, peak onset temperature or time, and the calculation of the peak height. 

Peak Measurement Peak Area Calculation Type Percent... 

Figure 4 Thermal curve of indium melting with a peak area calculation including the onset temperature and peak temperature. 

Figure 5 Thermal curve of polyethylene melting with the peak area calculation including the peak temperature.

The peak area calculation is used with the limits of the calculation on the flat portion of the baseline before and after the melting peak. Some thermal analysts use the horizontal flat portion of the first derivative curve as a guide to set the peak calculation limits (Figs. 4 and 5). 

As a rule of thumb, peak area calculations are sensitive to baseline variations, and therefore many trace analyses are quantified over the peak... 

These expressions are certainly correct for a single count plus background count, for example, from a simple beta counter. They are not valid for peak area calculations where Equation (5.40) must be used, resulting in the correct expression ... 

In both cases, the square root term is the standard deviation of the count, or of the estimated peak area, calculated in the normal manner, rather than of the background. You may notice that if N happens to be precisely zero, then Equations (5.58) and (5.59) reduce to the critical limit expressions (Equations (5.52) and (5.56)). Quite so. If the net count were zero, we would be 95 % certain that the true count were less than Lq - which is the definition of the critical limit. In spite of this, the upper and critical limits should not be used interchangeably. 

Efficiency calibration in a laboratory environment is straightforward take a reference source, or sources, containing known activities of nuclides for which well-defined nuclear data are available, measure a spectrum and, from the individual peak areas, calculate efficiencies over a range of gamma-ray energies. Such simplicity is not achievable when one needs a calibration relevant to measurement of a 220 L waste disposal drum, a transport... 

In principle, the net peak area should be assessed for significance using a critical limit, as discussed in Chapter 5, Section 5.6.1. If the peak area exceeds the critical limit, the peak area can be legitimately passed on to the activity calculation. If not, the peak should be declared NOT DETECTED and an upper limit to the peak area calculated (Chapter 5, Section 5.6.2). That upper limit should then be passed through the calculation as any other peak area and reported as an activity upper limit - that activity which we are 95 % certain exceeds the actual activity. 

Table 7.10 - Comparison of Normalized peak areas calculated from chromatograms of polystyrene solutions and polystyrene volatiles liberated by heating at 200 C...

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