Qualitative analysis mass determination

Precipitation reactions have many applications. One is to make compounds. The strategy is to choose starting solutions that form a precipitate of the desired insoluble compound when they are mixed. Then we can separate the insoluble compound from the reaction mixture by filtration. Another application is in chemical analysis. In qualitative analysis—the determination of the substances present in a sample—the formation of a precipitate is used to confirm the identity of certain ions. In quantitative analysis, the aim is to determine the amount of each substance or element present. In particular, in gravimetric analysis, the amount of substance present is determined by measurements of mass. In this application, an insoluble compound is precipitated, the precipitate is filtered off and weighed, and from its mass the amount of a substance in one of the original solutions is calculated (Fig. 1.6). Gravimetric analysis can be used in environmental monitoring to find out how much of a heavy metal ion, such as lead or mercury, is in a sample of water. 

Qualitative Analysis involves determining the nature of a pure unknown compound or the compounds present in a mixture. Quantitative Analysis involves measuring the proportions of known components in a mixture, and the chemical techniques include volumetric analysis and gravimetric analysis. Instrumental Analysis include several physical techniques including spectroscopic techniques, mass spectrometry, polarography, nuclear magnetic resonance, etc. 

Without specific references to mass analyzer design, explain how a mass spectrometer can determine that the different molecular fragments created have different charges and masses (or mass-to-charge ratios) Why is this fact important in its use in qualitative analysis ... 

Coupling chromatographic procedures with immunochemical techniques can also provide a very sensitive and specific analytical system for either determinative or confirmatory analysis. If the antibody used is very specific for the analyte of interest and the antibody reactivity is known to be sensitive to small variations in the structure of the analyte tested, positive reactions with the method are strongly indicative that an analyte of defined structural characteristics is present in the sample. Full rigorous confirmation, however, would depend on further analysis by mass spectrometry, which is the method of choice in confirmatory analysis. Mass spectrometry gives specific information on the identity and structure of the compound of interest. Coupled with chromatographic techniques it becomes a very powerful confirmatory tool for both quantitative and qualitative assessment of drug residues in foods. 

An unknown substance, X, was isolated from rabbit muscle. Its structure was determined from the following observations and experiments. Qualitative analysis showed that X was composed entirely of C, H, and 0. A weighed sample of X was completely oxidized, and the H20 and C02 produced were measured this quantitative analysis revealed that X contained 40.00% C, 6.71% H, and 53.29% O by weight. The molecular mass of X, determined by mass spectrometry, was 90.00 u (atomic mass units see Box 1-1). Infrared spectroscopy showed that X contained one double bond. X dissolved readily in water to give an acidic solution the solution demonstrated optical activity when tested in a polarimeter. 

Walker et al. [114] examined several methods and solvents for use in the extraction of petroleum hydrocarbons from estuarine water and sediments, during an in situ study of petroleum degradation in sea water. The use of hexane, benzene and chloroform as solvents is discussed and compared, and quantitative and qualitative differences were determined by analysis using low-resolution computerised mass spectrometry. Using these data, and data obtained following the total recovery of petroleum hydrocarbons, it is concluded that benzene or benzene-methanol azeotrope are the most effective solvents. 

Most applications of DLI LC-MS deal with qualitative analysis, where in most cases only molecular-mass information is obtained. DLI LC-MS found extensive apphcation in the analysis of pesticides and related compounds [35], in the quahtative and quantitative determination of corticosteroids and metabolites in equine urine [36]. Highly labile compounds such as vitamin B12 (molecular weight 1354) and erythromycin A (molecular weight 733) were analysed by DLI negative-ion Cl LC-MS [33]. As an example, the negative-ion Cl spectram of 92 ng vitamin B12 is shown in Figure 4.7. 

Mass spectrometry (MS) is a widely used detection technique that provides quantitative and qualitative information about the components in a mixture. In qualitative analysis it is very important to determine the molecular weight... 

Mass spectrometry is a powerful qualitative and quantitative analytical tool that is used to assess the molecular mass and primary amino acid sequence of peptides and proteins. Technical advancements in mass spectrometry have resulted in the development of matrix-assisted laser desorption/ion-ization (MALDI) and electrospray ionization techniques that allow sequencing and mass determination of picomole quantities of proteins with masses greater than 100kDa (see Chapter 7). A time-of flight mass spectrometer is used to detect the small quantities of ions that are produced by MALDI. In this type of spectrometer, ions are accelerated in an electrical field and allowed to drift to a detector. The mass of the ion is calculated from the time it takes to reach the detector. To measure the masses of proteins in a mixture or to produce a peptide map of a proteolytic digest, from 0.5 to 2.0 p.L of sample is dried on the tip of tlie sample probe, which is then introduced into tire spectrometer for analysis. With this technique, proteins located on the surfaces of cells are selectively ionized and analyzed. 

Precursor (parent) ion scan Scanning analyzer Selective mass filter Yes Qualitative analysis Determine possible precursor ions of a given ion frag ment Triple-quadrupole only... 

Qualitative analysis may be extended to provide semi-quantitative determination of concentrations. This may be carried out by addition of internal standards at known concentrations. Quantitation for each analyte detected is achieved by ratio of the total ion current for the analyte to that of the closest eluting internal standard. However, as the response of different compounds to mass selective detectors can vary considerably, this approach can lead to significant errors. A complementary approach that has found favour and can reduce the uncertainty involves the analysis of standards of tentatively identified compounds, in order to calculate response factors to the nearest internal standard. Standards are usually analysed several times over a period of time to calculate a mean response factor. This enables a semi-quantitative analysis of reasonable accuracy to be performed by reference to an in-house database of response factors. This eliminates the need for extensive calibrations for every batch and also reduces the errors from widely varying response factors. 

Surface Characterization. Most modem techniques for the characterization of surfaces have been developed since 1970 (74,75). Surface techniques allow for both qualitative and quantitative characterization of trace levels of molecular species (see Surface AND INTERFACE ANALYSIS). Most recently an extension of surface analysis utilizing laser ionization has been introduced (76). In surface analysis by laser ionization (sah), a probe beam, composed of ions, electrons, or laser light, is directed to the surface under examination to remove a sample of material. An untuned, high intensity laser passes dose to, but paralld and above the surface. The laser has sufficient intensity to induce a high degree of nonresonant, and hence nonselective, photoionization of the vaporized sample of material within the laser beam. The nonselectively ionized sample is then subjected to mass spectral analysis to determine the nature of the unknown species. A highlight of this technique is the use of efficient, nonresonant, and therefore nonselective photoionization by pulsed imtuned laser radiation. The commercial availabiUty of intense laser radiation makes this technique viable. The mass spectrometer, not the laser, performs the chemical differentiation. 

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