Target compounds characteristics

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

Aging studies, performed in the laboratory, are useful for confirming theoretical models describing the behavior of the object at short-, medium-, and long-term intervals. Formed alteration products, (e.g., by oxidation, reduction, polymerization, scission, hydration, dehydration, dehydrogenation, etc.) are the target compounds in such studies. Three-dimensional (3D) diagrams can be built from the spectra or other characteristic curves obtained at different times. 

On the other hand, the SIM analysis of a predefined set of analytes (Fig. 3.1.4a) require visual inspection, but only to exclude unexpected interferences in the signal of a target compound. For the purpose of detecting unexpected interferences, it is necessary, and is also a CAP accreditation requirement, to monitor at least two ion species per compound (Fig. 3.1.4b and c), so as to recognize artificial variations in the intensity ratios between two ion chromatograms. Figure 3.1.5 shows examples of characteristic organic acid profiles in patients with selected conditions [32]. 

In certain cases, the enantiomer of high purity is usually obtained by recrystallizing the enantiomer mixture which is recovered by decomposing the diastereomeric salt. In such a case, it is favorable to know the crystallizing characteristic of the target compound. For instance, the crystallizing characteristic of an enantiomer mixture can be outlined by its binary phase diagram. 

While many non-metallic, non-polar materials are transparent to THz radiation, many target compounds have characteristic THz spectra that can be used as a fingerprint for identification. While crystalline, high energy explosives have characteristic THz fingerprint spectra that can be used to identify these threats, home-made NH4N03 bombs could pose a change to THz security applications because these materials can have featureless THz spectra below 3 THz. 

---