Mass spectroscopy definition

Although a number of assays and technologies are available to characterize and test protein molecules, such as peptide mapping, protein sequencing, carbohydrate analysis, electrophoresis, ELISA, and mass spectroscopy, they are not as definitive as the methods used for small molecule drugs. Hence, the test for similarity is not as well defined in the case of proteins. However, as... 

Indeed, there is almost no book using the term mass spectroscopy and all scientific journals in the field bear mass spectrometry in their titles. You will find such highlighted rules, notes and definitions throughout the book. This more amusing one - we might call it the zeroth law of mass spectrometry - has been... 

Single-crystal X-ray crystallography remains the only definitive technique for the structural characterization of heteronuclear gold cluster compounds, although other techniques, in particular Mossbauer, NMR, IR, and fast atom bombardment mass spectroscopies (FABMS), have yielded valuable information, especially concerning the nature of these species in solution. Electron spectroscopy, which has proved to be of great value in the identification of homonuclear gold cluster compounds (210) has received little attention by workers in this area,... 

Why does mass spectroscopy allow the definitive identification of analytes ... 

A more general approach that can be employed for all mass analyzers [as time-of-flight (TOF), ion cyclotron resonance (Fourier trans-form-mass spectroscopy, FT-MS), Q-TOF] is based upon measuring the full width half-maximum, as shown in Fig. 2.2. In the same figure, the definition of mass accuracy is also reported. This parameter reflects on the specificity of mass measurements. In fact, on one hand it allows to determine the accurate mass of a selected ion (and, consequently, its elemental composition). On the other hand it allows to operate in accurate mass mode in order to identify species of interest present in complex matrices on the basis of their elemental composition. 

The ultraviolet-visible spectra of most compounds are of limited value for qualitative analysis and have been largely superseded by the more definitive infrared and mass spectroscopies. Qualitative analytical use of ultraviolet-visible spectra has largely involved describing compounds in terms of the positions and molar absorptivities of their absorption maxima, occasionally including their absorption minima. Indeed, some organic compounds are still characterized in terms of the number of peaks in the UV-visible spectrum and their absorbance ratios. This is usually the case in phytochemistry and photodiode array chromatography and when the analyst has a limited range of compounds to work with whose spectra are known to differ. In the pharmacopeias, however, absorbance ratios have found use in identity tests, and are referred to as Q-values in the U.S. Pharmacopia (USP). 

The absolute configuration of the epoxide group of insect JHs was determined by spectroscopy and circular dichroism [29], In the first method, perchloric acid was used to catalyze the hydrolysis of the epoxide in the presence of H2180. The resulting v/c-diol was analyzed by mass spectroscopy and definitively demonstrated the 10/ , 115 chirality of the epoxide [30]. The chirality was confirmed by circular dichroism. The epoxide was hydrolyzed by sulfuric acid and tetrahydrofuran and the circular dichroism cotton effect of the resulting acyclic glycol was measured in the presence of tris(dipivaloylmethanato)praseodymium [31]. 

A variety of 3-D superlattices formed from metal nanopartides has been reported [1-8]. For instance, gold nanopartides, when stabilized by alkylthiolates RS (R = n-Ci2H2s) and rather narrowly distributed in size, could be obtained by the repeated fractional crystallization of a mixture of 1.5-3.5 nm particles from unpolar solvents. The success of fractionation was controlled by mass spectroscopy [6j. Based on these data, definite numbers of atoms could be assigned to the particles of distinct fractions (e.g., 140, 225, 314, and 459), all of which consisted of fee-structured octahedra. Solutions of these remarkably well-defined particles can be used to... 

Although the term was originated to describe the failure of organic coatings, it is clear that cathodic disbondment can lead to the accelerated failure of adhesive joints as well. The work of Davis and Watts illustrates this phenomenon for steel substrates bonded with an epoxy adhesive and shows how a combination of XPS and Secondary Ion mass spectroscopy (SIMS) are able to provide a definitive picture of the locus of failure. Such a combined approach enables a detailed mechanism of failure to be postulated. 

Definite Method. The definitive method for total calcium measurement is isotope dilution mass spectroscopy [9]. It has strict performance guidelines and is the accuracy standard against which all methods should be compared. 

A recent approach to the study of fuel cell oxidations has used mass spectroscopy directly coupled to the cell [29], since the mass spectrum allows a clear definition of whether an observed current is due to the formation of CO2 or merely the oxidation of hydrogen. In situ IR spectroscopy is another promising method these experiments clearly show that adsorbed carbon monoxide is formed during the pulsed oxidation of all small molecules containing carbon. Unfortunately, the time taken to record a spectrum, typically 10 minutes, and the pulse modulation essential to obtain the sensitivity, make uncertain the interpretation of these observations in the context of data obtained on clean surfaces after only a few milliseconds. 

Under normal circumstances, retention time is a good tool to identify components by GC. Often, however, retention time alone is not definitive because many compounds have similar retention times. Structural information can be obtained independently from several spectroscopic techniques. This has led to hyphenated techniques, such as gas chromatography-mass spectroscopy, gas chromatography-infrared spectroscopy and others. If spectroscopic, reference spectra are available, confirmation of analyte identity is very likely. 

The selective detectors discussed in the previous sections often do not provide enough information to elucidate with 100% probability the nature of the eluting solutes. For this reason, data with selective detectors can be erratic. The future in this respect definitely belongs to the spectroscopic detectors that allow. selective recognition of the separated compounds. Today, the hyphenated techniques CGC-mass spectroscopy (CGC-MS), CGC-Fourier transform infrared spectroscopy (CGC-FTIR), and CGC-atomic emission detection (CGC - AED) are the most powerful analytical techniques available. They provide sensitive and selective quantitation of target compounds and structural elucidation or identification of unknowns. The applicability and ease of use of the hyphenated techniques were greatly increased by the introduction of fused silica wall coaled open tubular columns. The main reason for this is that because of the low flows of capillary columns, no special interfaces are required and columns are connected directly to the different spectrometers. The introduction of relatively inexpensive benchtop hyphenated systems has enabled many laboratories to acquire such instrumentation, which in turn has expanded their applicability ever further. 

A different definition uses the peak width at half height as Am (50 % definition) for the calculation (see Fig. 1). This approach is used often for Fourier transform mass spectroscopy (FTMS) and time-of-flight (TOF) instruments. In modem mass spectrometers, the resolution is calculated directly by the computer from the peak width. 

Scheme 7.37. The results of E2 elimination of HCl and HCI fromf/ire<7-5-chloro-6-deuterio-decane with f-butoxide (2-methyl-2-propoxide [(CH3)3C0 ]) in methylsuUmyhnethane (dimethyl sulfoxide, DMSO [(CH3)2SO]) solvent. Note that syn-elimination provides ( )-alkene that has lost deuterium ( H) and (Z)-alkene that has lost protium ( H).Thus,examination of the separated alkenes by mass spectroscopy provides definitive information about the path, and the results must be complementary to those in Scheme 7.36. (See Scheme 7.36 for reference information).

---