Mass spectrometry quantitative 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. 

Mass spectrometry has become an essential analytical tool for a wide variety of biomedical applications such as food chemistry and food analysis. Mass spectrometry is highly sensitive, fast, and selective. By combining mass spectrometry with HPLC, GC, or an additional stage of mass spectrometry (MS/MS), the selectivity increases considerably. As a result, mass spectrometry may be used for quantitative as well as qualitative analyses. In this manual, mass spectrometry is mentioned frequendy, and extensive discussions of mass spectrometry appear, for example, in units describing the analyses of carotenoids (unitfia) and chlorophylls (unit F4.5). In particular, these units include examples of LC/MS and MS/MS and the use of various ionization methods. 

Process solvents SRC s, and liquefaction products also were examined by column chromatography (11). The sample was dissolved in chloroform or THF, pre-adsorbed on neutral alumina (12), and eluted from neutral alumina to give saturates, aromatics, and three polar fractions. The saturate fraction was analyzed quantitatively by mass spectrometry, and compound identification in distillates and solvents was confirmed by combined GC-MS or high-resolution MS analysis of column chromatography fractions. 

Mass spectrometry is sensitive, rugged, and has the ability to provide extensive qualitative and quantitative information. Mass spectrometry also provides a large dynamic range, can be automated, and has a fast analysis time. These characteristics have made mass spectrometry a very powerful and attractive analysis tool for medicinal chemistry and combinatorial chemistry. However, not all synthetic organic compounds are readily detected by mass spectrometry, and the sensitivity can vary with the mode of ionization. As a result, sensitivity is dependent on the physical characteristics of the compound. 

Mass Spectrometric Identification of Interacting Proteins. The preparation of proteins obtained after TAP is introduced into a spectrometer, and the different proteins are identified. In such an analysis, a sample of protein affinity purified using the epitope tag and the one without the epitope tag is labeled with stable isotopes and then compared for the relative abundance of different peaks in the two samples to determine the interacting proteins in a particular preparation. Thus, this is essentially a quantitative ICAT mass spectrometry described in Chapter 4. In case the proteins are purified over a DNA column without the use of an epitope tag, it is compared with a sample that cannot bind with DNA in the matrix. The samples are labeled with stable isotopes. The interacting proteins are identified by their relative abundance. 

Various types of analytical information about the analyzed molecule can be obtained using mass spectrometry. The determination of the molecular weight is one of the most common goals. The observation of molecular species (molecular ions, molecular adducts, or ions formed by a loss of specific neutrals from the analyzed and ionized molecule) are often sufficient proof for the presence of the desired molecule. Accurate mass measurements of molecular species provide information about the elemental composition of ions and their precursor molecules consequently, mass spectrometry has largely replaced traditional elemental analysis. Mass spectrometry is a powerful technique for both qualitative and quantitative analyses. GC, HPLC, TEC, and CE are separation techniques compatible with mass spectrometry. When combined with such chromatographic methods, mass spectrometry becomes a unique method for the identification of submicromolar quantities of analytes. 

Mass spectrometry allows analysis by hydrocarbon family for a variety of petroleum cuts as deep as vacuum distillates since we have seen that the molecules must be vaporized. The study of vacuum residues can be conducted by a method of direct introduction which we will address only briefly because the quantitative aspects are ek r metiy difficult to master. Table 3.6 gives some examples the matrices used differ according to the distillation cut and the chemical content such as the presence or absence of olefins or sulfur. 

The conventional method for quantitative analysis of galHum in aqueous media is atomic absorption spectroscopy (qv). High purity metallic galHum is characteri2ed by trace impurity analysis using spark source (15) or glow discharge mass spectrometry (qv) (16). 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

Spark Source Mass Spectrometry (SSMS) is a method of trace level analysis—less than 1 part per million atomic (ppma)—in which a solid material, in the form of two conducting electrodes, is vaporized and ionized by a high-voltage radio frequency spark in vacuum. The ions produced from the sample electrodes are accelerated into a mass spectrometer, separated according to their mass-to-charge ratio, and collected for qualitative identification and quantitative analysis. 

In other articles in this section, a method of analysis is described called Secondary Ion Mass Spectrometry (SIMS), in which material is sputtered from a surface using an ion beam and the minor components that are ejected as positive or negative ions are analyzed by a mass spectrometer. Over the past few years, methods that post-ion-ize the major neutral components ejected from surfaces under ion-beam or laser bombardment have been introduced because of the improved quantitative aspects obtainable by analyzing the major ejected channel. These techniques include SALI, Sputter-Initiated Resonance Ionization Spectroscopy (SIRIS), and Sputtered Neutral Mass Spectrometry (SNMS) or electron-gas post-ionization. Post-ionization techniques for surface analysis have received widespread interest because of their increased sensitivity, compared to more traditional surface analysis techniques, such as X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES), and their more reliable quantitation, compared to SIMS. 

ICPMS is uniquely able to borrow a quantitation technique from molecular mass spectrometry. Use of the isotope dilution technique involves the addition of a spike having a different isotope ratio to the sample, which has a known isotope ratio. This is usefiil for determining the concentration of an element in a sample that must undergo some preparation before analysis, or for measuring an element with high precision and accuracy. ... 

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