Peak area sample mass effects

Figure 3. Laser-desorption time-of-flight mass spectra of molecular carbon samples, (a, left) Pure Cm and Cw samples. The ions are produced by SO mJ pulses (over a I-mm area) of 266 nm radiation. Small peaks at lower masses are due to fragmentation occurring during desorption, (b, center) Enriched samples of the larger fullerenes. (c, right) Effect of desorbing laser pulse fluence on the mass spectrum of pure samples (pulse energies indicated in pJ per pulse).

System peaks are always obseiwed with indirect detection and need attention (see Section 19.9). In quantitative analysis it is important to note that peak areas are not only a function of sample mass but also of k values (in relation to the k value of the system peak) and of the concentration of the detectable component in the mobile phase. The effects were explained by Sehili and Crommen. 

The effect of sample mass on the peak area will be discussed in greater detail in the sections on quantitative DTA and DSC. 

In another very early investigation, Wittels (101) found that the area enclosed by the curve peak was proportional to the heat absorbed in the decomposition of calcite, CaC03. A linear relationship was found, using sample weights from 0.30 to 3.00 mg. In another study, Wittels (102) elucidated the effect of heating rate and sample mass on the peak areas obtained by the thermal decomposition of tremolite, Ca2MgsSi8022(OH)2. The relationship... 

Emmerich and Bayreuther (75) found that in their simultaneous TG-EGD apparatus, the EGD peak area was proportional to the sample mass for the evolution of EUO.CO. and COz from the thermal decomposition of CaC204-UNO. This proportionality is shown by the curves in Figure 8.24, which have a linearity of wiihin — 2%. They also studied the effect of gas flow quantity and peak height, half-width, and peak area using calibrated amounts of air injected into the carrier gas stream. The peak area and half-width decreased, whereas the peak height increased with an increase in gas flow. Thus, better... 

Errors in sample application are among the most significant sources of inaccuracy. The technique of spotting can have a marked effect on delivery volumes between I and 5 pL. A constant slat ting zone size should be maintained so that a given amount of substance applied in the form of different volumes will yield spots with identical areas, whereas different amounts spotted at constant volume will exhibit a linear relationship in a plot of peak area (from recordings of densitometer scans) versus mass. 

Finally, the apparatus function (see Section 6.3) should be known because it yields the apparatus-caused smearing of the thermal effect and the time constant. The apparatus function is obtained by generating a heat pulse in the sample and dividing the obtained heat flow rate function by the peak area (normalization) (see Section 6.3.4 and Figure 9.4). Such parameters as the sample mass, the magnitude of the heat pulse, and occasionally the heating rate are to be varied. If all the normalized curves obtained in this manner are identical, there is one single apparatus function, and the measured heat flow rate function of the calorimeter can be desmeared (see Section 6.3). The halfwidth of the apparatus function yields approximately the time constant of the calorimeter. 

Matrix Effects The matrix effects in the mass spectrometer (that is, signal suppression or enhancement) were assessed using a method described by Matuszewski et al. (2003). To that end, the peak area of the analyte in the sample extract spiked after extraction (B) was compared with the peak area of the corresponding analyte in the standard solution (A). The matrix effects (ME) were calculated as follows ... 

IR spectra did not show differences between the intermediate phase and the disordered cancrinite. Therefore, IR techniques fail when were used to identify these phases. One more effective way to identify disordered cancrinite and the intermediate phase is by using X-ray diffraction (XRD). Fig 1 shows the diffractogram of both tectosilicates. In the intermediate phase, the observed peaks correspond with those reported in the literature[4]. The main differences between both spectra correspond to those peaks placed between 25°<20<35°, which are more intense for the disordered cancrinite [9]. Likewise, the results of specific surface area for the intermediate phase (sample 5) and the disordered cancrinite (sample 6) were 35 and 41 m2/g respectively. The antacid capacity test was carried out with the samples 5 and 6. Fig. 2 shows the relationship between experimental pH versus the mass content of the tectosilicates. The neutralization capacity of these solids is related with its carbonate content which reacts with the synthetic gastric juice to neutralize it. In general, the behaviour of solids is similar the pH increases as the weight of the studied solid is increased. However, a less disordered cancrinite mass amount must be employed to reach a pH= 4 in comparison... 

Normalization is performed in order to remove. systematic variation. iisuaHy a.ssociatcd with the total amount of sample. common example of this is normalizing to the largest nt/e peak in mass spectrometry (Howe ct at., 19S1, p. 19). In chromatography, normalization of the entire chromatogram to unit area is used to remove the effect of variable injection volume. Normalizing to... 

Experiments run in the air. Data in parentheses give area in mm2 under peak recalculated on 100.00-mg samples. Shoulders are denoted by "s". En and Ex denote endothermic and exothermic effects, respectively. The range of temperature in which mass indicated is lost is given in parentheses. The height of peak (X 10"2 mg) is given in parentheses. Shoulders are denoted by s. ... 

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