Specifications, in analytical

Danzer K (2001) Selectivity and specificity in analytical chemistry. General considerations and attempt of a definition and quantification. Fresenius J Anal Chem 369 397... 

There are no analytical proofs for the exact structure of polycyclic naphthenic compounds with number of rings over five. However, based on the results of mass spectral analysis of heavy oil fractions, it can be said that there are polycyclic naphthens with seven or eight rings in their structure. At the moment, it is very difficult to be specific in analytical terms of the exact chemical structure of such molecules. 

A prerequisite for any meaningful Py—GC analysis is to define optimal experimental conditions with a view to obtaining specific and reproducible results. According to Levy [100], specificity in analytical pyrolysis is defined as a measure of the relationship of the composition and structure of the initial material to the characteristic pyrolysis products, whereby such materials can be differentiated. 

It is proposed to hold similar discussions on a regular basis at national meetings of the ACS, and possibly to organize a subdivision of the Pesticide Division for those interested specifically in analytical aspects of pesticide chemistry research. 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

Traditionally, chiral separations have been considered among the most difficult of all separations. Conventional separation techniques, such as distillation, Hquid—Hquid extraction, or even some forms of chromatography, are usually based on differences in analyte solubiUties or vapor pressures. However, in an achiral environment, enantiomers or optical isomers have identical physical and chemical properties. The general approach, then, is to create a "chiral environment" to achieve the desired chiral separation and requires chiral analyte—chiral selector interactions with more specificity than is obtainable with conventional techniques. 

Specifications and Analytical Methods. Vinyl ethers are usually specified as 98% minimum purity, as determined by gas chromatography. The principal impurities are the parent alcohols, limited to 1.0% maximum for methyl vinyl ether and 0.5% maximum for ethyl vinyl ether. Water (by Kad-Fischer titration) ranges from 0.1% maximum for methyl vinyl ether to 0.5% maximum for ethyl vinyl ether. Acetaldehyde ranges from 0.1% maximum in ethyl vinyl ether to 0.5% maximum in butyl vinyl ether. 

The objective of the FCC is to define food-grade chemicals in terms of the characteristics that estabUsh identity, strength, and quahty. It provides specifications in monograph form for some 900 food additives, together with analytical test procedures by which compliance with the specifications can be determined. The third edition was pubUshed in 1981 supplements followed in 1983, 1986, 1991, and 1993. The fourth edition is in preparation as of this writing and is to include monographs for almost 1000 food chemicals, including flavors. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

Both arsonic and arsinic acids give precipitates with many metal ions, a property which has found considerable use in analytical chemistry. Of particular importance are certain a2o dyes (qv) containing both arsonic and sulfonic acid groups which give specific color reactions with a wide variety of transition, lanthanide, and actinide metal ions. One of the best known of these dyes is... 

Simple analytical methods are available for determining minimum stages and minimum reflux ratio. Although developed for binary mixtures, they can often be applied to multicomponent mixtures if the two key components are used. These are the components between which the specification separation must be made frequendy the heavy key is the component with a maximum allowable composition in the distillate and the light key is the component with a maximum allowable specification in the bottoms. On this basis, minimum stages may be calculated by means of the Fenske relationship (34) ... 

In addition to this drive to look beyond manufacturing to specifications, new analytical methods such as molecular weight distribution, Mooney relaxation, and other measures of polymer processibiHty are being explored. 

Entrainment ratio is another jet characteristic commonly used in air distribution design practice. Specifically, it is used in analytical multizone models (see Chapter 8) when one needs to evaluate the total airflow rate transported by the jet to some distance from a diffuser face. Airflow rate in the jet, Q,., can be derived by integrating the air velocity profile within the jet boundaries ... 

Spot tests may prove ultimately to be the most, important example of determinations in which traces are major constituents. The technique is well known15 apd has proved very valuable in analytical chemistry. As often carried out, a reagent (specific if possible) is made to react in or on filter paper with the element sought, usually present as a trace. The results are normally qualitative or semiquantitative, it often being difficult to make them quantitative by methods other than x-ray emission spectrography.16 With this technique, however, not only is it possible... 

It is interesting to note that there have been very few specific analytical applications reported, which demonstrate that super-critical chromatography gives results superior to either gas chromatography or liquid chromatography alone. As a consequence, considering the added complexity of the super-critical chromatograph, its value in analytical chemistry must be considered questionable. 

The set of possible dependent properties and independent predictor variables, i.e. the number of possible applications of predictive modelling, is virtually boundless. A major application is in analytical chemistry, specifically the development and application of quantitative predictive calibration models, e.g. for the simultaneous determination of the concentrations of various analytes in a multi-component mixture where one may choose from a large arsenal of spectroscopic methods (e.g. UV, IR, NIR, XRF, NMR). The emerging field of process analysis,... 

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