Peak quantitation

Antunes, M.C., Simao, J.E.J., Duarte, A.C., and Tauler, R., Multivariate curve resolution of overlapping voltammetric peaks quantitative analysis of binary and quaternary metal mixtures, Analyst, 127, 809-817, 2002. 

The QMS platform combines the identification of proteins with their quantitative detection in one procedure. While protein identification can be deduced from peptide mass fingerprinting (PMF) or MS/MS spectra (see section Mass Spectrometry (MS)), protein quantitation is based on analysing either peak areas or signal intensities, or a combination of both. Several computer programs, in most cases reagent specific ones, are available. For each peak, quantitation values are calculated before differentially expressed proteins are identified by the comparison of control and treated samples. 

In general. As values between 0.9 and 1.2 are acceptable. If Ts > 1 peak tailing is in evidence if As < 1 peak fronting is evident. The practical impact of peak tailing or fronting is that adjacent peaks are not as well separated as they would be if they were symmetrical, leading to difficulties in peak quantitation. 

The perpendicular drop method produces accurate peak areas for symmetrical overlapped peaks of similar height and width. In this case, the portion of the second peak attributed to the first peak is offset by the portion of the first peak attributed to the second peak and vice versa. For overlapped peaks of significantly different size, the perpendicular drop method always overestimates the peak area of the smaller peak as the smaller peak gains more area from the larger peak than it loses to the larger peak. Quantitation errors are further exacerbated in the case of a smaller peak imposed on the tail of a much larger tailing peak. This method tends to show little injection-to-injection variability because of its simplicity. 

Two problems of peak quantitation need special attention the influence of external parameters on area and height and the errors coming from peak overlap. 

Spot analysis software of choice examples are ImageQuant (Amersham Biosciences), MicroVigene (Vigene Tech, Billerica, MA, USA) or P-SCAN [Peak quantitation with Statistical Comparative Analysis (http //abs.cit.nih.gov)]. 

Calcium Silicate Hydrates. XRD patterns of cement pastes with and without SBR dispersion or powder at 26 range of 17°-19° are displayed in Fig. 3. The diffraction peak at about 18° is ascribed to the diffraction of (001) crystal plane of Ca(OH)2. Software MDI Jade 6.5 is also used to integrate the diffraction peak quantitatively. The results show that the content of Ca(OH)2 increases gradually with the prolongation of hydration time. The addition of SBR dispersion and powder decreases the content of Ca(OH)2 significantly before 3 days, and the effect of the dispersion is more evident. The content of Ca(OH)2 in the pastes with SBR dispersion and powder is 0.1 and 0.2 times that in the control paste after 6 hours, 0.6 and 0.8 times after 1 days, 0.7 and 1.0 times after 3 days. It indicates that the addition of SBR dispersion and powder delays the cement hydration before 3 days. But after 3 days, the effect of the SBR dispersion and powder on the cement hydration is not... 

The findings clearly indicate that the oxonolysis-GPC method can also be applied to the analysis of the sequence distribution of 1,2 units in polybutadiene by successive derivation of polyols to trifluoroacetates. It is remarkable that the peak corresponding to the 1,4-1,4 sequence is clearly observed in this measurement in addition to 1,4-(l,2)n-l,4 sequences. On the basis of the relative intensity of each peak, quantitative measurement of the sequence distribution can be made by compensation with an appropriate correction factor for the refractive index or UV absorptivity of each fraction. 

A continuous or transient signal The temporal length of the sampling event Volume of sample available Number of samples being analyzed Number of replicates per sample Number of elements being determined Detection limits required Precision/accuracy expected Dynamic range needed Integration time used Peak quantitation routines... 

Before we go on to discuss these in greater detail and how these parameters affect the data, it is important to remind ourselves how a scanning device like a quadrupole mass analyzer works. Although we wiU focus on quadrupole technology, the fundamental principles of measurement protocol wiU be very similar for all types of mass spectrometers that use a sequential approach for multielement peak quantitation. 

FIGURE 12.6 Signal-to-background noise degrades when more than one point, spread over the same integration time, is used for peak quantitation. 

FIGURE 21.2 There are typically two approaches to peak quantitation— peak hopping (usually at peak maximum) and multichannel scanning (across the full width of the peak). 

So, when evaluating isotopic ratio precision, it is important that the measurement protocol and peak quantitation procedure are optimized. Isotope precision specifications are a good indication regarding what the instrument is capable of, but once again, these will be defined in aqueous-type standards, using relatively short total measurement times (typically 5 min). For that reason, if the test is to be meaningful, it should be optimized to reflect your real-world analytical situation. 

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