Pure reference compound

FTICR-MS is capable of powerful mixture analysis, due to its high mass range and ultrahigh mass resolving power. However, in many cases it is still desirable to couple a chromatographic interface to the mass spectrometer for sample purification, preconcentration, and mixture separation. In the example given above, DTMS under HRMS conditions provides the elementary composition. Apart from DTMS, PyGC-MS can be performed to preseparate the mixture of molecules and to obtain the MS spectrum of a purified unknown. Direct comparison with the pure reference compound remains the best approach to obtain final proof. 

Finally, consideration must be given to the availability of pure reference compounds from which to construct analytical calibration curves. Some compounds (such as phenolic acids) may be purchased commercially, but for others (such as benzoxazinoids) it will be necessary to first isolate and purify them from recognized natural sources described in the literature12 or to synthesise them.11... 

Alkyl nitrates are also formed by the reaction of AgN03 with alkyl bromides in an acetonitrile solvent. The drawback of this exchange reaction is that in most cases the yield is only about 60 to 80%. Dichloromethane extraction with solvent removal under reduced pressure has been employed to isolate the alkyl nitrates as pure reference compounds, as well as to synthesize the hydroxyalkyl nitrates from the hydroxyhalides. Direct nitration of the alkanes is achieved with 12% HNO3 in the presence of solid copper. This method is especially useful in preparing mixtures of alkyl nitrates from mixtures of the starting alkanes. 

In the case of the polychlorinated biphenyls (PCBs), one of the major improvements in analysis has resulted from the availabihty of pure reference compounds, so that concentrations need not be expressed as equivalents of some commercially available mixture of PCBs. While the techniques required to run these analyses are not simple, modern machine methods should put them within the reach of any laboratory which has the proper equipment and is wilhng to put in the time and effort. 

A standard reference material may therefore be either a highly pure reference compound or a well-characterized substance or a calibration standard. 

Such a separation of diethylenetriamine and triethylenetetramine, which were available as relatively pure reference compounds, is illustrated in Figure 4.78. 

We defined an ideal solution from relation [3.20], i.e. stating that the coefficient of activity in convention (I) (pure reference compound) was equal to 1 at all temperatures, all pressures and all compositions. We will show that this causes all coefficients of activity, regardless of the convention chosen, to be equal to 1 for an ideal solution. 

By introducing the fugacity of the gas / in the mixture, analogous to the expression of the chemical potential of a perfect pure gas, we can write that of a gas i of a real mixture in convention (I), pure reference compound, in the form ... 

Pure reference compounds were not available for components mariced with asterisks. Tentative identities have been ascribed from boiling points... 

Figure 29.2 a Paper chromatography, b The chromatogram produced. Components of the mixture can be identified by comparison with pure reference compounds or by calculating Revalues (see Figure 29.3) and comparing these values with those in tables of data. 

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