Peak-to-total ratio

The ratio by which the total detector efficiency is multiplied in Eq. 12.3 is called the peak-to-total ratio (P). Figure 12.13 shows how P is measured. 

Figure 12.13 The peak-to-total ratio is equal to the number of counts under the peak (Afp) divided by the total number of counts (A ,).

Figure 12.16 Peak-to-total ratio as a function of energy for Nal(Tl) scintillators of different sizes. The source-to-detector distance is 0.10 m (from Ref. 3).

PEAK TO TOTAL RATIO Not to be confused with the above. This is the ratio of the number of counts in a full-energy peak to the total number of counts in the whole spectrum. 

Measurements were taken on 158Er at a total of 14 target-stopper distances. A portion of the total-projected spectra taken at four of the target-stopper separations is shown in Fig. 1. These spectra are of excellent statistical quality and reveal a favorable peak-to-background ratio in the 0° detector as a result of using the Compton suppression shield. 

COLLECTION OF DATA. It should be emphasized that the correct choice and preparation of the sample combined with careful collection of data will greatly aid in the total process. It is extremely important that the sample is pure, or if not, that all the impurity phases are known. Figure 1 shows a comparison of data collected from a typical 1970 s diffractometer, a modern computer controlled diffractometer and a high resolution diffractometer using synchrotron radiation at the National Synchrotron Light Source. The excellent resolution and high peak to background ratio (typically 1000 1) obtained from the synchrotron data enable very weak peaks to be easily observed. 

Thus, as the peak-to-background ratio (Ip/Ib) increases, a greater percentage of the total analysis time should be spent counting at the peak. Figure 9.1 shows a graphical representation of the distribution of the total analysis time for different peaJc-to-background ratios. 

Detection limits. The detection limits mainly depend on the amount of SPM or sediment used for the element determination. For the elements which are influenced by blanks as mentioned before, the detection limits may be calculated from the standard deviation of the blank values. The total blank is constant for a given mixture of acids and filter stock but affects different amounts of SPM and sediments, depending on the amount of SPM on the filter or the employed sediment mass. Therefore, the detection limits may be normalized for each 1 mg of SPM loaded on the filter. The detection limits are a factor of 2 better for 2 mg of SPM on a filter than for 1 mg. For other elements, detection limits are derived from the peak to background ratio taken from TXRF spectra of SPM or sediments, respectively. For SPM and sediments the detection limits vary between 3 pglg (e.g., for Cu, Ni or Zn) and and 25 pglg (e.g.. for V). 

The mercury film electrode has a higher surface-to-volume ratio than the hanging mercury drop electrode and consequently offers a more efficient preconcentration and higher sensitivity (equations 3-22 through 3-25). hi addition, the total exhaustion of thin mercury films results in sharper peaks and hence unproved peak resolution in multicomponent analysis (Figure 3-14). 

Figure 4. Improvement in sensitivity with the CAT. PFA and a reference peak at m/e 315. The observed improvement in signal-to-noise ratio results from the longer total scanning time and also the fact that many sweeps are made during this time. The overall improvement in signal-to-noise ratio depends on the detailed power spectrum of the noise (9). Resolution 12,000 here and for all following time averaged spectra...

For solution nebulization MC-ICPMS and MC-TIMS, typical runs consist of up to 100 ratios collected over 30 minutes to 1 hour. This includes time for background measurement (typically monitored at half mass on either side of the peak) and peak centering, but excludes filament warm-up time for TIMS and nebulizer cleaning for MC-ICPMS. Sample sizes of-1000-10 ng of total U for TIMS and MC-ICPMS are required to attain 2a measurement uncertainties of a permil or better on (e.g., Stirling et... 

In the graphic form the abscissa represents the mass of ions (to be more precise, the mass-to-charge ratio, m/z), while the ordinate represents the relative intensity of these ions peaks. Atomic mass units (unified atomic mass unit) or daltons are used as units to measure masses of ions, while intensity is represented in percent relative to the base peak in the spectmm or to the total abundance of all the ions in the spectra. The atomic mass unit (dalton) is equal to the mass of one-twelvth of the mass of a 12C atom (1,661 x 10-27 g) (see Chapter 1). 

To calculate the total amount of volatiles included in the hair samples from different body regions the area beneath all peaks was calculated using the GCM-SPostrunAnalysis software including all peaks above a signal-to-noise ratio of 3 1 (exceeding an area of 200.000 units). From those, 20 distinct peaks were selected for peak comparison and the area beneath the peak was used to evaluate the differences between sex and season. 

Results are presented in the percentage. Percentage of single chromatographic peak areas was measured on the basis of area of the single peaks to the total peak area ratio. Selected results were statistically evaluated using a t-test at the 0.05 level. The intervals of significance are presented in tables. 

Fig. 9 Series of electropherograms obtained on-chip from mixtures of 361 nM anti-BSA antibody with different concentrations of labeled BSA (BSA ). The ratio of total concentration of BSA to total concentration of antibody (Ag/Ab) is given at the top of each electropherogram. Two main complex peaks are identified. Essentially no BSA is seen in A, while BSA dominates in F. (Reprinted with permission from Ref. 33. Copyright 1998 Wiley-VCH.)...

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