Reproducibility peak intensity

In order to avoid experiments which are very long, the sampling time was fixed at 60 min. In these conditions, the partition equilibrium for diterpenes extraction is not achieved and SPME does not have maximum sensitivity. However, peak intensities are sufficiently high to detect the presence of diterpenes in a sample. Moreover, a proportional relationship exists between the amount of analyte adsorbed by the SPME fibre and its initial concentration in the sample matrix before reaching partition equilibrium [5, 59]. SPME quantifications are then feasible if necessary, by rigorously reproducing the experimental conditions. 

Fig. 2.13.5. Absolute peak intensities of [M — H] and [2M — H], and the two fragments (C12-CAPB concentration lmgLF1) (from [1], 2001. John Wiley Sons Limited. Reproduced with permission).

B) X-Ray intensities (or peak intensities) depend on sample moisture content. Therefore, to obtain reproducible data, the moisture contents of all the samples analyzed in the experiment should be constant (usually between 10-18% w/w) depending on the analytical requirements. 

Figure 20. Structural parameters as a function of time extracted by fitting the data shown in Figure 20. (A) Data collected during the oxidation of the Pt/C electrode and (B) during the reduction long dashes, first shell O coordination number (no. of O atoms) short dashes, first shell Pt coordination number (no. of Pt atoms) solid line, absorption peak intensity (effectively white line intensity).(Reproduced with permission from ref 43. Copyright 1995 Elsevier Sequoia S.A., Lausanne.)...

Figure 12.11—Comparison of UV andfluorescence detection after chromatographic separation. Aflatoxins, which are carcinogenic contaminants present in certain batches of grain cereals, are controlled by HPLC analysis. It can be seen that the peak intensities in UV detection vary with concentration whereas fluorescence detection is much more sensitive to aflatoxin G2 and B2. (Reproduced by permission of SUPELCO.)...

Fig. 3.48. Enhancement of the absorption in the fundamental band in a hydrogen-argon mixture at low and high densities at 152 K the profiles are normalized to give Si(l) the same peak intensity. The argon density was 8 ama-gat (solid line) and 820 amagat (dashed line), respectively. The density splitting of the (overlap-induced) Q branch and the density narrowing of the S lines are apparent. A new (quadrupole-induced) Q line appears inthe wide absorption dip (between Qp and Qr) observed at high density. Reproduced with permission from the National Research Council of Canada from [137].

The theoretical spectra considering the lattice relaxation effects are shown in fig. 12. The separation between peaks decreases upon expansion of the bond lengths. For example, the separation between peaks A and B is 1.03 eV, 0.87 eV, 0.75 eV for 0%, +2%, +4% relaxed models, respectively. Comparing with the experimental spectrum, the multiplet energy splitting is reproduced best of all for the +2% relaxed model. Contrary to the peak positions, the peak intensities are not significantly influenced by the bonds lengthening. 

The portion of the spectrum in the range 1200-1500 cm 1 is poorly reproduced (both frequencies and peak intensities) by the calculations on the two most stable conformers (A and B), either in the absence or in the presence of the continuum dielectric (Figure 2.11, top), thus showing that in this case the reduction of the effects of the aqueous environment to an average dielectric effect is not sufficient to explain the experimental behaviour (the treatment is even worse if the isolated conformers are considered). 

The SIMS spectra are all obtained in the same way a molecular peak (high mass >100 amu peaks were preferred) characteristic of the investigated polymer sample is selected and the signal intensity is optimized by adjusting the first lens (extraction) potential. The time required for this procedure and the acquisition of one spectrum (160-10 amu) corresponds to a total ion dose less than 2.1013 ions/cm2. The relative peak intensities for the same polymer are perfectly reproducible from one analysis to another, indicating that a good control of the... 

Figure 5.3. Effect of the concentration of nitric acid on the peak intensities of severai metals in sediment slurry using Ru as permanent modifier. (Reproduced with permission of Elsevier, Ref [10].)...

Fig. 3.9 Washing and target incubation cycles of NSTBA with 10 nM thrombin. Graph shows intensities of dominant peaks. Peak intensities are highly reproducibly at every incubation cycle. A further incubation in which 10 nM thrombin was dissolved in a 1% solution of human serum produced similar peak intensities. Control experiments incubating only with bovine serum albumin, insulin, and human serum do not show any increased signals compared to the washed sensor [49]... 

Assuming the true absorptions to have Lorentzian form and assuming a triangular slit function, Ramsay 121, 122) investigated the effect of finite resolving power upon these band shapes for the vibrations of a variety of compounds. This approach reproduced satisfactorily the observed band profiles. However, he did not obtain a simple relationship between true and apparent integrated intensities. Ramsay found that bands are best characterized by their apparent peak intensities [loge(J o/r) J and their apparent half-intensity band widths These quantities are related to... 

To assess the suitability of the nanocrystals as optically active centers for their incorporation into optoelectronic devices, a monolayer of particles was deposited onto mercaptopropionic acid derivatized ITO substrates. Their photoelectrochemical response was assessed under conditions of illumination using LED whose peak intensity (A.pk = 470 nm) is greater than the calculated bandgap. As can be seen from the inset of Fig. 2, upon illumination of the SnS-derivatized electrode the current is observed to quickly increase and remain relatively constant during the illumination time, here 20 s, and upon switching off of the LED the current returns to its preillumination value. This photocurrent response profile is reproducible over many cycles (in a number of trials for periods in excess of an hour). An average photocurrent (current under illumination minus background current) for a number of similarly prepared electrodes has yielded values of between 6 and 8 nA cm . ... 

Collections of Py-MS spectra were published [47], and also specific interpretation techniques were adapted to process Py-MS data, mainly developed for providing pertinent comparisons. Most techniques are oriented toward comparing multi-component fingerprint information. Therefore, the stability of the results (reproducibility) is an important quality that must be maintained when performing Py-MS work. It was shown [47] that variability of 1-3% in peak intensities can be noticed for replicates within 1 day of work and up to 10-11% in long term (one month). 

Several applications of univariate statistical analysis for data evaluation in Py-MS are known [73]. One such application is the evaluation of reproducibility of a replicate of an analysis for the peak intensity at a given m/z value. If a series of measurements are made on identical specimens, this will provide a sample xi, X2...Xn. This sample will allow the calculation of parameters such as the mean m and the standard deviation s. By comparing the value s for different m/z values it is possible to select those m/z that are more reproducible (smaller s). 

Although less important than peak frequencies, peak intensities obviously play a role in quantitative analysis and, in many cases, qualitative identification. Multivariate calibration techniques and their transferability depend on reproducible relative peak heights. A possibly lengthy method development procedure may fail when a different spectrometer is used, if the observed intensities vary. Reproducibility of absolute signal is difficult to achieve between labs or even between instruments of the same design, but it is important for a particular instrument. Absolute intensities can at least be used to evaluate day-to-day instrument performance and to detect hardware or alignment problems. 

Recalibration of the instrument response function reduces or eliminates most of the instrumental factors that lead to relative intensity variations over time. For example, a luminescent standard could be used at the beginning of each session as described in Section 10.3.3. Use of the same standard and correction procedure during qualification could establish the true value of one or more peak ratios for future reference. Table 10.9 shows results for this approach applied to the example of calcium ascorbate. The ratio of the 767- and 1587 cm" peak intensities was monitored after calibration of the response function with a luminescent standard. The standard deviations listed in Table 10.9 for the 767/1582 peak height ratio provide indications of the reproducibility of the response correction and sample spectra. 

Figure 6-30. Peak intensities calculated for a hypothetical NOESY experiment involving four nuclei, D—A-B-C, with D 4 A from A and B 2 A from A and C. The curve labeled AA is for the diagonal peak, and the remaining curves are for the various cross peaks. (Reproduced from F. J. M. van de Ven, Multidimensional NMR in Liquids, VCH, New York, 1995, p. 188.)...

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