Qualitative analysis techniques

Another qualitative analysis technique is a flame test. A dissolved ionic compound is placed in a flame. Table 9.4 lists the flame colours associated with several ions. Notice that all the ions are metallic. The flame test is only useful for identifying metallic ions in aqueous solution. 

Any of the qualitative analysis techniques can be applied with the selection based on the change being considered. Again, following the risk analysis protocol, issues that cannot be resolved using qualitative techniques should be escalated for a more detailed risk analysis starting with the semi-quantitative analysis technique described in Section 4.3. 

Before providing some examples of qualitative analysis techniques, the basis for discrimination should be considered. Given a limited set of samples, all of which display significantly different spectra, it is possible that individual bands could be used to identify each species. In practice, such simple approaches are not practical nor accurate. For example, the mere observation of a band near 1700 cm does not unambiguously indicate the presence of acetone, as many species exhibit a band in that region. Certainly, a more certain identification can be made by searching for the presence of multiple bands. Add to the determination a requirement that the observed bands have specific intensities relative to one another, and the determination improves greatly. The obvious extension is to utilize all bands present to discriminate the species. 

There are several forms of electrophoresis. In slab gel electrophoresis the conducting buffer is retained within a porous gel of agarose or polyacrylamide. Slabs are formed by pouring the gel between two glass plates separated by spacers. Typical thicknesses are 0.25-1 mm. Gel electrophoresis is an important technique in biochemistry, in which it is frequently used for DNA sequencing. Although it is a powerful tool for the qualitative analysis of complex mixtures, it is less useful for quantitative work. 

In addition to qualitative analysis of nearly all the elements of the periodic table, EEL spectra also enable determination of the concentration of a single element which is part of the transmitted volume and hence gives rise to a corresponding ionization edge. As in all comparable spectroscopic techniques, for quantification the net edge signal, which is related to the number N of excited atoms, must be extracted from the raw data measured. The net intensity 4 of the feth ionization shell of an individual element is directly connected to this number, N, multiplied by the partial cross-section of ionization ) and the intensity Iq of the incident electron beam, i.e. ... 

Filtering cells and cell fractions from fluid media. These particles, after concentration by filtration, may be examined through subsequent quantitative or qualitative analysis. The filtration techniques also have applications in fields related to immunology and implantation of tissues as well as in cytological evaluation of cerebrospinal, fluid. 

Qualitative human error prediction is the most important aspect of assessing and reducing the human contribution to risk. For this reason, it will be described in some detail in this section. The qualitative analysis performed in SPEAR involves the following techniques ... 

If the results of the qualitative analysis are to be used as a starting-point for quantification, they need to be represented in an appropriate form. The form of representation can be a fault tree, as shown in Figure 5.2, or an event tree (see Bellamy et al., 1986). The event tree has traditionally been used to model simple tasks at the level of individual task steps, for example in the THERP (Technique for Human Error Rate Prediction) method for human reliability... 

Because most research effort in the human reliability domain has focused on the quantification of error probabilities, a large number of techniques exist. However, a relatively small number of these techniques have actually been applied in practical risk assessments, and even fewer have been used in the CPI. For this reason, in this section only three techniques will be described in detail. More extensive reviews are available from other sources (e.g., Kirwan et al., 1988 Kirwan, 1990 Meister, 1984). Following a brief description of each technique, a case study will be provided to illustrate the application of the technique in practice. As emphasized in the early part of this chapter, quantification has to be preceded by a rigorous qualitative analysis in order to ensure that all errors with significant consequences are identified. If the qualitative analysis is incomplete, then quanhfication will be inaccurate. It is also important to be aware of the limitations of the accuracy of the data generally available... 

The purpose of this chapter is to show that improvements in safety, quality, and productivity are possible by applying some of the ideas and techniques described in this book. The fact that error reduction approaches have not yet been widely adopted in the CPI, together with questions of confidentiality, has meant that it has not been possible to provide examples of all the techniques described in the book. However, the examples provided in this chapter illustrate some of the most generally useful qualitative techniques. Case studies of quantitative techniques are provided separately in the quantification section (Chapter 5). The first two case studies illustrate the use of incident analysis techniques (Chapter 6). 

Multidimensional gas chromatography has also been used in the qualitative analysis of contaminated environmental extracts by using spectral detection techniques Such as infrared (IR) spectroscopy and mass spectrometry (MS) (20). These techniques produce the most reliable identification only when they are dealing with pure substances this means that the chromatographic process should avoid overlapping of the peaks. 

Most organic substances can be dissolved readily in a suitable organic solvent and some are directly soluble in water or can be dissolved in aqueous solutions of acids (basic materials) or of alkalis (acidic materials). Many inorganic substances can be dissolved directly in water or in dilute acids, but materials such as minerals, refractories, and alloys must usually be treated with a variety of reagents in order to discover a suitable solvent in such cases the preliminary qualitative analysis will have revealed the best procedure to adopt. Each case must be considered on its merits no attempt at generalisation will therefore be made. It is however of value to discuss the experimental technique of the simple process of solution of a sample in water or in acids, and also the method of treatment of insoluble substances. 

We will explore the two major families of chemometric quantitative calibration techniques that are most commonly employed the Multiple Linear Regression (MLR) techniques, and the Factor-Based Techniques. Within each family, we will review the various methods commonly employed, learn how to develop and test calibrations, and how to use the calibrations to estimate, or predict, the properties of unknown samples. We will consider the advantages and limitations of each method as well as some of the tricks and pitfalls associated with their use. While our emphasis will be on quantitative analysis, we will also touch on how these techniques are used for qualitative analysis, classification, and discriminative analysis. 

A primary goal of this chapter is to learn how to achieve control over the pH of solutions of acids, bases, and their salts. The control of pH is crucial for the ability of organisms—including ourselves—to survive, because even minor drifts from the optimum value of the pH can cause enzymes to change their shape and cease to function. The information in this chapter is used in industry to control the pH of reaction mixtures and to purify water. In agriculture it is used to maintain the soil at an optimal pH. In the laboratory it is used to interpret the change in pH of a solution during a titration, one of the most common quantitative analytical technique. It also helps us appreciate the basis of qualitative analysis, the identification of the substances and ions present in a sample. 

Cyclodextrin-modified solvent extraction has been used to extract several PAHs from ether to an aqueous phase. Data evaluation shows that the degree of extraction is related to the size of the potential guest molecule and that the method successfully separates simple binary mixtures in which one component does not complex strongly with CDx. The most useful application of cyclodextrin-modified solvent extraction is for the simplification of complex mixtures. The combined use of CDx modifier and data-analysis techniques may simplify the qualitative analysis of PAH mixtures. 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

To overcome the problems of relatively low sample capacity associated with SPME, a technique known as stir-bar sorptive extraction has been reported by Baltussen etal. A glass-coated magnetic stir bar was coated with 50-100 iL of PDMS. Sample extraction was performed by placing the stir bar in the sample with subsequent stirring for 30-120 min. After extraction, the stir bar was removed and analytes were thermally desorbed at 150-300 °C for 5 min for GC, or liquid desorbed for LC. Qualitative analysis of organochlorine residues in wine has been reported using a commercially available product known as Twister. ... 

Howard [772] has been amongst the first to show the usefulness of conventional SEC for polymer/additive systems. Coupek el al. [773] have also reported results with this technique in an early stage their work was limited to synthetic mixtures of additives. The use of open-column SEC in the analysis of plastics additives has been reported [774], Qualitative analysis of additives has been performed by stopped-flow SEC with IR detection [775]. Polypropylene oligomers were isolated from a PP/(Irganox 1010, Irgafos 168, DBS) matrix by dissolution (toluene)/precipitation (methanol) and Soxhlet... 

The amount of information, which can be extracted from a spectrum, depends essentially on the attainable spectral or time resolution and on the detection sensitivity that can be achieved. Derivative spectra can be used to enhance differences among spectra, to resolve overlapping bands in qualitative analysis and, most importantly, to reduce the effects of interference from scattering, matrix, or other absorbing compounds in quantitative analysis. Chemometric techniques make powerful tools for processing the vast amounts of information produced by spectroscopic techniques, as a result of which the performance is significantly... 

Trace analysis is particularly attractive for SFE-HPLC since quantitative transfer of all analytes extracted to the chromatographic system becomes possible. At present, on-line SFE-HPLC appears to be feasible for qualitative analysis only quantitation is difficult due to possible pump and detector precision problems. Sample size restrictions also appear to be another significant barrier to using on-line SFE-HPLC for quantitative analysis of real samples. On-line SFE-HPLC has therefore not proven to be a very popular hyphenated sample preparatory/separation technique. Although online SFE-HPLC has not been quantitatively feasible, SFE is quite useful for quantitative determination of those analytes that must be analysed by off-line HPLC, and should not be ruled out when considering sample preparatory techniques. In most cases, all of the disadvantages mentioned with the on-line technique (Table 7.15) are eliminated. On- and off-line SFE-HPLC were reviewed [24,128]. 

Table 10.32 is a shortlist of the characteristics of the ideal polymer/additive analysis technique. It is hoped that the ideal method of the future will be a reliable, cost-effective, qualitative and quantitative, in-polymer additive analysis technique. It may be useful to briefly compare the two general approaches to additive analysis, namely conventional and in-polymer methods. The classical methods range from inexpensive to expensive in terms of equipment they are well established and subject to continuous evolution and their strengths and deficiencies are well documented. We stressed the hyphenated methods for qualitative analysis and the dissolution methods for quantitative analysis. Lattimer and Harris [130] concluded in 1989 that there was no clear advantage for direct analysis (of rubbers) over extract analysis. Despite many instrumental advances in the last decade, this conclusion still largely holds true today. Direct analysis is experimentally somewhat faster and easier, but tends to require greater interpretative difficulties. Direct analysis avoids such common extraction difficulties as ... 

The use of vibrational spectroscopy for the qualitative analysis of absorbed surface species is first considered, and a Table is then included which summarises a number of the key features of the various quantitative techniques. We then proceed to summarize these in groups depending not upon the probe used (as in the preceding chapters), but in terms of the signal emitted by the specimen which is used in each identification process. 

These techniques are generally able to provide quantitative as well as qualitative analysis of the specimen surface, and a number of them may be used in combination to maximize the amount of information obtained. 

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