Examination of Mixtures

Phthalocyanines and metal phthalocyanines which require high probe (and often high source) temperatures (>350°C) in conventional El mass spectrometry, readily give molecular ions as the base peak 65b) in FD spectra and minimal fragmentation occurs, providing a rapid method for the qualitative examination of mixtures of phthalocyanines. 

Although a considerable amount of work was done on the compatibility of various components of explosive mixtures no systematic study of this particular problem was made until in 1938 T. Urbanski [6] began a series of investigations which comprised examination of mixtures ... 

It is evident that if a mixture contains two or more constituents which are members of the same class of compounds or are soluble in the same reagents, separation can not be effected in the way outlined. In such cases fractional distillation or crystallization must be resorted to. A thorough knowledge of the properties of compounds is of great value in the examination of mixtures, and is of service in the purification of compounds. The purification of ethyl bromide prepared from potassium bromide, alcohol, and sulphuric acid, is an example. The bromide prepared in this way may contain ether, which is separated with difficulty from the halide by distillation. When the mixture is shaken with concentrated sulphuric acid, the ether dissolves and the bromide is unaffected. In effecting the separation of compounds it is often necessary to convert them into other substances. Thus, acetone can be separated from many other substances which are soluble in water by converting it into the difficultly soluble addition-product with sodium hydrogen sulphite. 

For example, the examination of mixtures of polyamides and polyolefins is relatively easy because the polyamide component can be degraded by acid hydrolysis, and the resulting low molecular weight fragments can then be identified according to the procedure described in Section 6.2.10. The Table 1.3 lists some of the most important polymer blends together with their trade names and suppliers. 

Pappas and Million have described a gas chromatographic technique for the examination of mixtures of corrosive fluorides such as boron-, tri- and pentafluoride, free chlorine, chloryl fluoride, dichlorotetrafluoroethane, hydrofluoric acid and uranium hexafluoride. These workers used columns constructed of Teflon packed with a Teflon support and using either Kel-F or fluorocarbon oil as liquid phase. The technique was applied to halocarbon coolant analysis and in uranium fuel recovery. 

In addition, additive effects that are difficult to assess must also be considered. Examinations of mixtures have provided preliminary information. They show that although the intensities of compounds with a similar aroma note add up, the intensity of the mixture is usually lower than the sum of the individual intensities (cf. 3.2.1.1). For substances which clearly differ in their aroma note, however, the odor profile of a mixture is composed of the odor profiles of the components added together, only when the odor intensities are approximately equal. If the concentration ratio is such that the odor intensity of one component predominates, this component then largely or completely determines the odor profile. 

The reactions of the amines discussed above, with the exception of the isonitrile test, are of importance not merely for the classification of compounds but also for the preparation of solid derivatives and in some instances for the examination of mixtures. Such reactions, which serve simultaneously as classification and as identification reactions, are ideal for the purposes of organic analysis. 

The laboratory work in this part of the course will include a study of two or three relatively simple mixtures, each consisting of from two to six components. The identification of these mixtures will require a thorough mastery of the preceding work, espe-ciallj - since it is impossible to outline a set of procedures that may be applied directly to the gi-eat vaiiety of combinations that may be met. More or less specific instructions may be given, however, concerning the preliminary examination of mixtures. 

The examination of mixtures, such as ointments, containing oils or fats is mostly for the estimation of the proportions of known constituents to ensure that the preparation has been made to the prescribed formula. If the usual constants are determined and average values for normal individual oils used in calculation, a reasonably accurate result can be obtained well within the limits of probable error in the compounding of the article. 

Low-temperature n.m.r. examination of mixtures of magnesium cyclo-pentadienide and magnesium chloride (and bromide) in THF (0.05—0.56 mol 1 ) indicate that CjHgMgX predominates in the equilibrium ... 

A water-soluble mixture may be in the form of a mixture of water-soluble solids or in the form of a liquid. The liquid mixtimes are frequently aqueous solutions. The prelirninary examination of a liquid mixture (see 1) will indicate whether a volatile solvent (i.e., removable on a boiling water bath) is present. If a volatile solvent is present, distil 20 g. of the mixtime from a water bath until no more hquid passes over set aside the volatile solvent for identification. Dissolve the residue (B) in water as detailed below for a mixture of solids. 

Vandoni and Viala examined the vapour pressures of mixtures of nitric acid in acetic anhydride, and concluded that from o to mole-fraction of nitric acid the solution consisted of acetyl nitrate, acetic acid and excess anhydride in equimolar proportions the solution consisted of acetyl nitrate and acetic acid, and on increasing the fraction of nitric acid, dinitrogen pentoxide is formed, with a concentration which increases with the concomitant decrease in the concentration of acetyl nitrate. 

Prior separation of mixtures into individual components may not be needed. If the mass spectrometer is capable of MS/MS operation, one of the mass spectrometers is used to isolate individual ions according to m/z value (mass-to-charge ratio), and the other is used to examine their fragmentation products to obtain structural information. 

A good LC/MS instrument routinely provides a means for obtaining the identities and amounts of mixture components rapidly and efficiently. It is not unusual to examine micrograms or less of materia). LC/MS is used in a wide range of applications, including environmental, archaeological, medical, forensic, and space sciences, chemistry, biochemistry, and control boards for athletics and horse racing. 

The first scheme for the separation of the six chief alkaloids of opium, VIZ., morphine, codeine, thebaine, papaverine, narcotine and narceine, is probably that of Plugge. Much later Kljatschkina investigated for each of these six bases the properties by means of which isolation and estimation could probably be effected and, on the basis of the results, devised a plan for such analyses. More recently Anneler has published a detailed account of a scheme with the same objective. l Attention had already been given to complex, systematic analyses of this kind, in connection with examination of the mixtures of opium alkaloids, which have long been in use in medicine in these at first only morphine and other alkaloids were determined, but in the more recent schemes provision is made for the estimation of each alkaloid. ... 

The g r) that results from the modified Verlet (MV) closure is very close to the simulation results in Figs. 2 and 3. The MV results for g d), or equivalently, y d), are plotted in Fig. 4(a). The resulting equation of state is similar to the CS expression. An even more demanding test is an examination of the MV results for y r) for r < d. As is seen in Fig. 4(b), the MV results for y(0) are quite good [25], and are better than the PY and HNC results. Some results have also indicated that the MV closure gives quite accurate results for a mixture of hard spheres [26]. 

The piperidine, pyrrolidine, and morpholine enamines of cyclohexanone substituted in the 3-position by methyl, phenyl, and l-butyl have been prepared (49). The complexity of the NMR spectra in the ethylenic hydrogen region indicated a mixture of isomeric enamines. Estimation of the per cent of each isomer by examination of the NMR spectra was not possible, nor were the isomeric enamines separable by vapor-phase chromatography. 

Most substituents (Q, Me, OMe) in the 2-position have only a small effect, if any, on the hydration of the quinazoline cation they are similar in this respect to substituents in the 5-, 6-, and 8-positions (see above). Although hydration in the 2-aminoquinazoline cation was at first considered absent,a closer examination of the entire spectra of both species indicated that the cation spectrum may be that of a mixture. Hydration in the cation has now been confirmed by the rapid-reaction technique (the stopped-flow method) which showed that the unstable hydrated neutral species had a half-life of 4.0 sec at 20° and pH 9.60. The 2-hydroxyquinazoline cation has not been studied, but... 

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