Qualitative Tools

Application of mass spectrometry to analysis of additives in polymers is mainly used as a qualitative tool and relates to three main areas ... 

The SOM is mainly used as a qualitative tool, to identify groups rather than to provide some numerical estimate of similarity. Nevertheless, these methods also show promise as quantitative tools. Recent unpublished work by Leung and Cartwright4 on the fluorescence of dyes has shown that the SOM can be used as a sensitive way to determine quantitatively the composition of mixtures containing several fluorescent species. When a sample of unknown composition is fed into the trained map, the node to which the sample points indicates the concentration of each species by the value of each of the different weights (Figure 3.31). 

The genesis of in silico oral bioavailability predictions can be traced back to Lip-inski s Rule of Five and others qualitative attempts to describe drug-like molecules [13-15]. These processes are useful primarily as a qualitative tool in the early stage library design and in the candidate selection. Despite its large number of falsepositive results, Lipinski s Rule of Five has come into wide use as a qualitative tool to help the chemist design bioavailable compounds. It was concluded that compounds are most likely to have poor absorption when the molecular weight is >500, the calculated octan-l-ol/water partition coefficient (c log P) is >5, the number of H-bond donors is >5, and the number of H-bond acceptors is >10. Computation of these properties is now available as an ADME (absorption, distribution, metabolism, excretion) screen in commercial software such as Tsar (from Accelrys). The rule-of-5 should be seen as a qualitative, rather than quantitative, predictor of absorption and permeability [16, 17]. 

Nevertheless, Equation (6.17) can serve as a qualitative tool for explaining membrane swelling upon water uptake. Under equilibrium conditions, the elastic pressure in Equation (6.15) increases with increasing vapor pressure due to Equation (6.14). Overall, by invoking Equations (6.14)-(6.17), we obtain a relation between external conditions (Ps and P ") and X ... 

Overall sampling quality — heuristic analysis. If the system of interest can be thought of as fluctuating about one primary structure (e.g., a native protein), use qualitative tools, such as projections onto a small number of PCA modes or all-to-all RMSD plots to simplify visualization of trajectory quality. Such... 

A chromatographic peak provides valuable information, namely, the elapsed time from the injection point or the difference in elution times of two peaks (qualitative information), the peak shape (qualitative or quantitative information), and the peak size(quantitative information). The simplest qualitative tool is simply the comparison of retention data from known and unknown samples. A chromatogram illustrating the commonly used retention nomenclature is given in Figure 4.1. The retention time (tp>) is the time elapsed from injection of the sample component to the recording of the peak maximum. The retention volume (VR) is the product of the retention time and the flow rate of the carrier gas. Generally, the adjusted retention time (t ) or adjusted retention volume (V >) and the relative retention (rA/B) are used for qualitative analysis. Adjusted retention time (volume) is the difference between the retention time (volume) of the sample and an inert component (usually air). The relative retention is the ratio of the adjusted retention time (or volume) of a standard to the adjusted retention time (or volume) of the unknown, (see Chapter 2). 

As a qualitative tool, gas chromatography has been limited to retention data and a variety of ancillary techniques. Despite the limitation, retention data are widely used, and various tabulations of such information are available (2). Because mass chromatography provides both molecular weight and retention time for each peak, the technique represents a powerful means of identifying compounds as is illustrated in Figure 3 and Table I. 

Without authentic standards or a spectroscopic detection scheme, compound identification is difficult. Our choice of a desorption/ionization method is potassium ionization of desorbed species (K+IDS) with mass spectrometric detection (n. 12) which provides a rapid qualitative tool for compound identification. Using K+IDS, molecular weight data is available and fragmentation is minimal. Ions appear as M[K], the mass of the analyte plus 39 Da, the mass of potassium. Hence, structure identification is possible based on a knowledge of starting materials and the molecular weight data afforded by K+IDS. 

As shown in Figure 13-7, the pH of the mobile phase influences the retention of the various compounds in the sample. What does this imply about the qualitative nature of retention time in HPLC Is HPLC a quantitative or qualitative tool ... 

Symbolic dynamics is a powerful, but qualitative, tool. We can easily imagine a system trajectory that is close to the trajectory shown in Fig. 2.11(a), but not quite identical. Both trajectories axe then characterized by the same word, ABC AC. Thus, symbol sequences do not specify system trajectories uniquely. In other words, there is no one-to-one correspondence between the impact parameters b and the words constructed from the alphabet A, B, C. ... 

Perhaps the simplest test method for the evaluation of antistatic finishes is the ash test. A piece of the fabric to be evalnated is mbbed briskly on a piece of plastic or rubber (the vinyl covered arms of a chair, for example). The fabric is then placed over an ashtray containing cigarette ash. The amount of ash transferred to the fabric is an indication of the amount of static charge imparted to the fabric. Owing to the difficulty in quantifying the results, this test is mainly nsed as a qualitative tool to distinguish between antistatic-treated and untreated fabrics. 

We conclude this section by noting that linear potential sweep and cyclic voltammetry are excellent qualitative tools in the study of electrode reactions. However, their value for obtaining quantitative information is rather limited. The best advice to the novice in the field is that cyclic voltammetry should always be the first experiment performed in a new system, but never the last. 

Generally ion exchange techniques are considered as qualitative tools. If they are applied with appropriate care, however, they yield quantitative results as depicted in Figure 4-11. Each of the malate and succinate points in this figure was obtained by summing the amount of radioactivity... 

Lahti, Rossi and Berson have r ently developed a useful qualitative tool for predicting the energy levels of non-Kekule ffiplepules by using a semiempirical INDO/S-CI calculation. They obtained very similar results on pxyallyl as that of Morokuma. P. M. Lahti, A. R. Rossi and J. A. Berson, Am. Chem. Sof.. 107, 2273 (1985). 

IPG-DALT can be used for the separation of up to 5000 components in a protein mixture, and has now been incorporated as a qualitative tool for diagnostic analysis. It is not generally used for quantitation of proteins in a mixture, however, because loss of low molecular weight components often occurs during the SDS equilibration and transfer steps. An excellent overview of the capabilities and technical protocols of IPG-DALT is available in a review article.14... 

TLC methods were first developed in 1966 for analytical separation of the kavalactones (Young etal., 1966). TLC in combination with the colorimetric method allowed for the quantitative determination of the amount of individual kavalactones (kavain, methysticin and yangonin) present in the kava rootstock (Csupor, 1970a,b). However, when TLC proved to be inadequate, GLC methods were developed for quantitative analysis of the constituents from P. methysticum plant (Duve, 1981 Smith, 1983). GLC was first used in 1971 as a qualitative tool to identify kavalactones from the root (Achenbach etal., 1971). GLC, however, is a destructive method that has major drawbacks since it causes decomposition of components particularly when high injection port temperatures are used. This problem of heat decomposition was overcome by the development of HPLC methods for quantitative analyses of kavalactones, first by Gracza and Ruff (1980) and then by Smith and co-workers (Smith etal., 1984), who in particular successfully developed a HPLC method for quantitative analyses of kavalactones in different parts of the P. methysticum plant. These analytical methods all relied on the availability of analytical standards for accurate identification of the major constituents from ka-ra resin and as such none of these methods alone provided simultaneous qualitative and quantitative analysis. 

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