Analysis, wet chemical

Analysis of Trace or Minor Components. Minor or trace components may have a significant impact on quaHty of fats and oils (94). Metals, for example, can cataly2e the oxidative degradation of unsaturated oils which results in off-flavors, odors, and polymeri2ation. A large number of techniques such as wet chemical analysis, atomic absorption, atomic emission, and polarography are available for analysis of metals. Heavy metals, iron, copper, nickel, and chromium are elements that have received the most attention. Phosphoms may also be detectable and is a measure of phosphoHpids and phosphoms-containing acids or salts. 

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

Volatile impurities, eg, F2, HF, CIF, and CI2, in halogen fluoride compounds are most easily deterrnined by gas chromatography (109—111). The use of Ftoroplast adsorbents to determine certain volatile impurities to a detection limit of 0.01% has been described (112—114). Free halogen and haHde concentrations can be deterrnined by wet chemical analysis of hydrolyzed halogen fluoride compounds. 

Until the last War, variants of optical emission spectroscopy ( spectrometry when the technique became quantitative) were the principal supplement to wet chemical analysis. In fact, university metallurgy departments routinely employed resident analytical chemists who were primarily experts in wet methods, qualitative and quantitative, and undergraduates received an elementary grounding in these techniques. This has completely vanished now. 

Trace element analysis has become sufficiently important, especially to industrial users, that commercial laboratories specialising in trace and ultratrace elemental analysis are springing up. One such company specialises in high-resolution glow-discharge mass spectromety , which can often go, it is claimed, to better than parts per billion. This company s advertisements also offer a service, domiciled in India, to provide various forms of wet chemical analysis which, it is claimed, is now nearly impossible to find in the United States . 

During production and characterization of various internal animal tissue reference materials for a number of metals, a comparative study was performed for Pb in six bovine teeth and two bovine bone materials using calibration with a solid RM and two versions of wet chemical analysis with GF-AAS and electrochemical (DPASV) detection. There was good agreement in the range of approx. 1.3-3 tng/kg dry weight for all techniques used (Liicker et al. 1992). 

Sophisticated instrumental techniques are continually being developed and gradually replace the classical wet chemistry analytical methods. Wet chemical analysis is destructive the sample is dissolved or altered. Nowadays the analyst is highly focused on instrumental methods and chemometrics. Yet, chemical work-up methods (e.g. hydrolysis with alcoholic alkali, alkali fusion, aminolysis, and transesterification, etc.) and other wet laboratory skills should not be forgotten. 

The objective of this monograph is to include all major studies of metal ions in their aqueous solutions as well as some other important studies in their zerovalent metallic state or in alloys, since the nanoparticles of many of these metals have become too important. Besides, the study of the precipitation of metal ions in aqueous solutions, upon sonication, which has been carried out in our laboratory, would also be discussed. Some of such data include unpublished work. The sequence of metallic ions in this chapter are as they come in the sequence of wet chemical analysis of basic radicals, besides the cationic charge has been kept in mind to make groups and sequences that follow the detailed description. 

Four samples of faujasite were synthesized at Si/Al ratios of 2.61, 2.80, 2.97 and 3.03 using published methods from seeded slurries (8-9) and using proprietary methods. One additional sample of Si/Al ratio 2.58 was purchased from Union Carbide. The samples were characterized by X-ray powder diffraction, by surface area measurements, and by wet chemical analysis. The results of these measurements are contained in Table I. 

Analysis procedures can be additionally classified into procedures that involve physical properties, wet chemical analysis procedures, and instrumental chemical analysis procedures. Analysis using physical properties involves no chemical reactions and at times relatively simple devices (although possibly computerized) to facilitate the measurement. Physical properties are especially useful for identification, but may also be useful for quantitative analysis in cases where the value of a property, such as specific gravity or refractive index (Chapter 15), varies with the quantity of an analyte in a mixture. 

Wet chemical analysis usually involves chemical reactions or classical reaction stoichiometry, but no electronic instrumentation beyond a weighing device. Wet chemical analysis techniques are classical techniques, meaning they have been in use in the analytical laboratory for many years, before electronic devices came on the scene. If executed properly, they have a high degree of inherent accuracy and precision, but they take more time to execute. 

Distinguish between wet chemical analysis, instrumental analysis, and analysis using physical properties. 

When would you choose a wet chemical analysis procedure over an instrumental analysis procedure When would you choose an instrumental analysis procedure over a wet chemical analysis procedure ... 

What is different about the analytical strategy for instrumental analysis, compared to wet chemical analysis ... 

The activities carried out in a wet lab would probably include sample preparation and wet chemical analysis procedures (for example, extractions, solution preparations, and titrations)—activities that do not utilize sophisticated electronic instrumentation. 

A wet chemical analysis would likely be chosen when a more precise result is needed or when the analyte is a major, rather than a minor, constituent. An instrumental analysis procedure would likely be chosen when a minor constituent present at a low level is to be determined and when a faster method with a greater scope or practicality is needed. 

Several investigators have utilized thermal techniques for the separation of sulfate species collected on filter media with subsequent analysis by electron impact mass spectrometry, wet chemical analysis or sulfur flame photometry. In most instances the separation between sulfuric acid and its ammonium salts was incomplete or problems were encountered in recovering the species of interest from filters heavily laden with particulate (29-34). 

Potassium oxalate, along with calcium oxalate, is found in leaves and roots of certain plants. It is used for cleaning and bleaching straw and for removing stains. It also is used in photography, in clinical tests, as a secondary pH standard, and in wet chemical analysis. The analytical apphcation involves standardization of many oxidizing agents in titrimetric analysis. 

Wet chemical analysis, Luvak, Inc., Boylston, MA. b Neutron activation analysis. Union Carbide. Tuxedo, NY. 

Electron beam techniques have aided electrical measurements greatly, but these methods often lack sensitivity (X-ray and Auger spectroscopy and ESCA [electron spectroscopy for chemical analysis]) and accuracy (SIMS [secondary-ion mass spectrometry], etc.), two attributes that are of prime importance in IC process technology. Fortunately, materials can be analyzed with both accuracy and sensitivity by wet chemical analysis. 

Wet chemical analysis is especially useful to semiconductor IC manufacturers in the following five areas ... 

The determination of specific phosphorus compounds in thin films is important. Only through wet chemical analysis was it possible to first discover the presence and then to accurately measure the quantities of P2Os, P203, and phosphine found in plasma, plasma-enhanced, LPO-LTO (low-pressure oxide-low-temperature oxide), and CVD (chemical vapor deposition) processes (3). Methods such as X-ray or FTIR spectroscopy would have seen all phosphorus atoms and would have characterized them as totally useful phosphorus. In plasma and plasma-enhanced CVD films, phosphine is totally useless in doping processes. 

When aluminum-silicon (Al-Si) metallization was deposited on wafers by evaporation, wet chemical analysis was used to study the changes in concentrations of Al to Si in the single evaporating cup. Wet chemical analysis was also used to determine the uniformity of silicon in aluminum and the evaporation patterns on the wafers in a rotating evaporator. The results revealed an accumulation of silicon in the cup and clearly showed the total lack of uniformity within a wafer and from wafer to wafer. The study showed why metallization problems were occurring and how to stop them. 

Natural ceramic raw materials have the disadvantage that they are not soluble in water and consequently unsuitable for wet chemical analysis. That is why they are first destructed in the laboratory. Destruction means that a substance or a mixture of substances is heated together with a substance or a mixture of substances and as a result the component to be destructed is largely separated into ions and consequently dissolves in water. The destruction method and the substances are specific for the substance undergoing the destruction. Different methods applied to the same substance lead to different results. 

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