Standardizing methods

Because of their diversity and complexity as well as the gradual internationalization of the different standards, it has proven necessary to standardize the methods of sample preservation, handling, fractionation, and analysis throughout the chain of separation and treatment. All these stages are the object of precise protocols established by official national and international organizations. They describe in as minute detail as possible the procedures employed not only for each analysis but very often giving different procedures for the same analysis in different matrices. These are the standards or standardized methods discussed in Chapter 7. 

The criterion retained up to now in the specifications is not the true vapor pressure, but an associated value called the Reid vapor pressure, RVP. The procedure is to measure the relative pressure developed by the vapors from a sample of motor fuel put in a metallic cylinder at a temperature of 37.8°C. The variations characteristic of the standard method are around 15 millibar in repeatability and 25 millibar in reproducibility. 

In the standard method, the metal enclosure (called the air chamber) used to hold the hydrocarbon vapors is immersed in water before the test, then drained but not dried. This mode of operation, often designated as the wet bomb" is stipulated for all materials that are exclusively petroleum. But if the fuels contain alcohols or other organic products soluble in water, the apparatus must be dried in order that the vapors are not absorbed by the water on the walls. This technique is called the dry bomb" it results in RVP values higher by about 100 mbar for some oxygenated motor fuels. When examining the numerical results, it is thus important to know the technique employed. In any case, the dry bomb method is preferred. 

There is no reliable standard method to characterize odor and specifications often indicate merely a not-unpleasant odor . 

The water content of crude oils is determined by a standardized method whose procedure is to cause the water to form an azeotrope with an aromatic (generally industrial xylene). Brought to ambient temperature, this azeotrope separates into two phases water and xylene. The volume of water is then measured and compared with the total volume of treated crude. 

The water and sediment contents of crude oils is measured according to the standard methods NF M 07-020, ASTM D 96 and D 1796, which determine the volume of water and sediments separated from the crude by centrifuging in the presence of a solvent (toluene) and of a demulsifylng agent Table 8.13 gives the bottom sediment and water content of a few crude oils. 

Figure I represents a two-dimensional damage distribution of an impact in a 0/90° CFRP laminate of 3 mm thickness. Unlike in ultrasonic testing, which is usually the standard method for this problem, there is no shadowing effect on the successive layers by delamination echos. With the method of X-ray refraction the exact concentration of debonded fibers can be calculated for each position averaged over the wall thickness. Additionally the refraction allows the selection of the fiber orientation. The presented X-ray refraction topograph detects selectively debonded fibers of the 90° direction.

The usual practical situation is that in which two solids are bonded by means of some kind of glue or cement. A relatively complex joint is illustrated in Fig. XII-14. The strength of a joint may be measured in various ways. A common standard method is the peel test in which the normal force to separate the joint... 

By the standard methods of statistical thermodynamics it is possible to derive for certain entropy changes general formulas that cannot be derived from the zeroth, first, and second laws of classical thermodynamics. In particular one can obtain formulae for entropy changes in highly di.sperse systems, for those in very cold systems, and for those associated, with the mixing ofvery similar substances. 

Sohaefer H F III, Thomas J R, Yamaguohi Y, DeLeeuw B J and Vaoek G 1995 The ohemioal applioability of standard methods in ah initio moleoular quantum meohanios Modern Electronic Structure Theory vo 2, ed D R Yarkony (Singapore World Soientifio) pp 3-54... 

The anhydrous chloride is prepared by standard methods. It is readily soluble in water to give a blue-green solution from which the blue hydrated salt CuClj. 2H2O can be crystallised here, two water molecules replace two of the planar chlorine ligands in the structure given above. Addition of dilute hydrochloric acid to copper(II) hydroxide or carbonate also gives a blue-green solution of the chloride CuClj but addition of concentrated hydrochloric acid (or any source of chloride ion) produces a yellow solution due to formation of chloro-copper(ll) complexes (see below). 

Zincill) chloride. ZnCl2, is the only important halide—it is prepared by standard methods, but cannot be obtained directly by heating the hydrated salt. It has a crystal lattice in which each zinc is surrounded tetrahedrally by four chloride ions, but the low melting point and solubility in organic solvents indicate some covalent... 

These are not essential if the acid and amine obtained on hydrolysis are crystalline but crystalline derivatives of the acid and amine can be prepared by the standard methods for acids (p. 349) and amines (pp. 374, 376) respectively. 

The method is general for all organic halogen compounds and is the standard method for almost all such compounds, except of course... 

Method, There are two standard methods for the estimation of urea, (i) the hypobromite method, (ii) the urease method (p. 519). The chief merit of the hypobromite method is the rapidity of the analysis the results obtained are considered sufficiently accurate for most medical requirements, e.g., for the estimation of urea in urine. For accurate metabolic work, however, the urease method should be employed. 

Provided that the balance is functioning correctly, the main source of error is in the weights themselves these should be calibrated by one of the standard methods so that their relative values are known, and they should be carefully cleaned with tissue paper and checked from time to time. To make the best use of the balance, weighing should be carried out by the method of swings, but for this purpose it is necessary first to determine the sensitivity of the balance. 

As you are about to see, the standard methods for using the NaBH(OAc)3 catalyst call for it to be in a dried, powder form. Strike supposes the benzene in the above reaction can be distilled off to leave dry catalyst. But don t quote Strike on that Maybe it could be made in situ in the DCE solvent of the reaction to come (don t ask). Aw hell Just go and buy the shit ... 

The resulting oligonucleotide is often of surprising purity as judged by analytic HPLC or electrophoresis, and up to 30 mg of a deoxyeicosanucleotide (20-base DNA) can be routinely obtained. Nevertheless small amounts of short sequences, resulting from capping and from base-catalysed hydrolysis, must always be removed by quick gel filtration, repeated ethanol precipitation from water (desalting), reverse-phase HPLC, gel electrophoresis, and other standard methods. 

Iminothiobutyramide (30), containing four nucleophilic centers (only two of which might react with two electrophilic sites in phenacylbromide), undergoes the Hantzsch reaction preferentially, yielding the enamine (31) in dry dioxane or (4-phenylthiazol-2-yl)acetone (32) in isopropanol. Other enamines are obtainable from the ketone (32) by standard methods (626) (Scheme 15). 

In general ketones are more stable than their enol precursors and are the products actually isolated when alkynes undergo acid catalyzed hydration The standard method for alkyne hydration employs aqueous sulfuric acid as the reaction medium and mer cury(II) sulfate or mercury(II) oxide as a catalyst... 

A standard method for prepanng sodium cyclopentadienide (CsHsNa) is by the reaction of cyclopentadiene with a solution of NaNH2 in liquid ammonia Write a net ionic equation for this reaction identify the acid and the base and use curved arrows to track the flow of electrons... 

It IS often necessary to prepare ketones by processes involving carbon-carbon bond formation In such cases the standard method combines addition of a Gngnard reagent to an aldehyde with oxidation of the resulting secondary alcohol... 

A standard method for the preparation of an a ammo acid uses a bromo carboxylic acids as the substrate and aqueous ammonia as the nucleophile... 

Acyl transfer from an acid an hydride to an alcohol is a standard method for the prep aration of esters The reaction IS subject to catalysis by either acids (H2SO4) or bases (pyri dine)... 

Nucleophilic substitution by ammonia on a halo acids (Section 19 16) The a halo acids obtained by halogenation of car boxylic acids under conditions of the Hell-Volhard-Zelinsky reaction are reac tive substrates in nucleophilic substitu tion processes A standard method for the preparation of a ammo acids is dis placement of halide from a halo acids by nucleophilic substitution using excess aqueous ammonia... 

The reaction of an aryl diazonium salt with potassium iodide is the standard method for the preparation of aryl iodides The diazonium salt is prepared from a primary aro matic amine m the usual way a solution of potassium iodide is then added and the reac tion mixture is brought to room temperature or heated to accelerate the reaction... 

Reduction of aryl nitro compounds (Sec tion 22 9) The standard method for the preparation of an arylamine is by nitra tion of an aromatic ring followed by reduction of the nitro group Typical re ducing agents include iron or tin in hydro chloric acid or catalytic hydro genation... 

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