Product scans, mass spectrometry

Data-dependent software programs allow real-time decisions to be made during an analysis. This approach features a preestablished threshold for the detection of a peak during full-scan mass spectrometry and MS/MS scan modes. If a peak of interest is detected in real-time, then the mass spectrometer is switched from full-scan mode to another scan mode to obtain more information from the same analysis. For example, the system may be automatically switched to the production mode during the analysis of a chromatographic peak to obtain substructural information. Thus, more detailed information is obtained in fewer analyses. This powerful... 

Montaudo, G., Puglisi, C., Scamporrino, E., and Vitalini, D. Identification of Pyrolysis Products of Polysulfides by CAD-Linked Scanning Mass Spectrometry, /. Anal Appl Pyrolysis, 10, 283,1987. 

Tandem mass spectrometry (MS/MS) is a method for obtaining sequence and structural information by measurement of the mass-to-charge ratios of ionized molecules before and after dissociation reactions within a mass spectrometer which consists essentially of two mass spectrometers in tandem. In the first step, precursor ions are selected for further fragmentation by energy impact and interaction with a collision gas. The generated product ions can be analyzed by a second scan step. MS/MS measurements of peptides can be performed using electrospray or matrix-assisted laser desorption/ionization in combination with triple quadruple, ion trap, quadrupole-TOF (time-of-flight), TOF-TOF or ion cyclotron resonance MS. Tandem... 

MS-MS is a term that covers a number of techniques in which two stages of mass spectrometry are used to investigate the relationship between ions found in a mass spectrum. In particular, the product-ion scan is used to derive structural information from a molecular ion generated by a soft ionization technique such as electrospray and, as such, is an alternative to CVF. The advantage of the product-ion scan over CVF is that it allows a specific ion to be selected and its fragmentation to be studied in isolation, while CVF bring about the fragmentation of all species in the ion source and this may hinder interpretation of the data obtained. 

Figure 5.42 Structures of three monhydroxylated metabolites of Indinavir proposed on the basis of the product-ion scans of their (M - - H)+ ions. Reprinted by permission of Elsevier Science from Identification of in vitro metabolites of Indinavir by Intelligent Automated LC-MS/MS (INTAMS) utilizing triple-quadrupole tandem mass spectrometry , by Yu, X., Cui, D. and Davis, M. R., Journal of the American Society for Mass Spectrometry, Vol. 10, pp. 175-183, Copyright 1999 by the American Society for Mass Spectrometry.

The mass spectrometry employed electrospray ionization and each metabolite gave an [M + H]+ ion which was then used as a precursor ion for a product-ion MS-MS scan. For subsequent MS" experiments, the base peak of the previous MS-MS experiment was chosen under computer control and this allowed all analytes to be studied in a single chromatographic separation. 

Selected-decomposition monitoring An MS-MS scan in which the first stage of mass spectrometry is set to transmit a selected ion and the second to transmit only a selected product ion. This technique increases the selectivity of the analysis. 

Polymer/additive analysis greatly benefits from high-resolution mass data, which often leads to unambiguous identification of (known) additives. However, the investment and operating costs of this instrument do not easily justify its (exclusive) use for the purpose of routine polymer/additive analysis. Analysis of organic polymer additives by means of mass spectrometry is aided by the utilisation of precursor ion and second-generation product ion (MS3) scanning experiments [169], A four-sector... 

Figure 2.14 Tandem mass spectrometry product ion scan experiments in space (a) and in time (b)...

Fig. 11.16. Representation of three tandem mass spectrometry (MS/MS) scan modes illustrated for a triple quadrupole instrument configuration. The top panel shows the attributes of the popular and prevalent product ion CID experiment. The first mass filter is held at a constant m/z value transmitting only ions of a single mlz value into the collision region. Conversion of a portion of translational energy into internal energy in the collision event results in excitation of the mass-selected ions, followed by unimolecular dissociation. The spectrum of product ions is recorded by scanning the second mass filter (commonly referred to as Q3 ). The center panel illustrates the precursor ion CID experiment. Ions of all mlz values are transmitted sequentially into the collision region as the first analyzer (Ql) is scanned. Only dissociation processes that generate product ions of a specific mlz ratio are transmitted by Q3 to the detector. The lower panel shows the constant neutral loss CID experiment. Both mass analyzers are scanned simultaneously, at the same rate, and at a constant mlz offset. The mlz offset is selected on the basis of known neutral elimination products (e.g., H20, NH3, CH3COOH, etc.) that may be particularly diagnostic of one or more compound classes that may be present in a sample mixture. The utility of the two compound class-specific scans (precursor ion and neutral loss) is illustrated in Fig. 11.17.

What are the three most common tandem mass spectrometry (MS/MS) scan modes (product ion scan, precursor ion scan, constant neutral loss scan). 

Tandem mass spectrometry (MS-MS) is a term which covers a number of techniques in which one stage of mass spectrometry, not necessarily the first, is used to isolate an ion of interest and a second stage is then used to probe the relationship of this ion with others from which it may have been generated or which it may generate on decomposition. The two stages of mass spectrometry are related in specific ways in order to provide the desired analytical information. There are a large number of different MS-MS experiments that can be carried out [9, 10] but the four most widely used are (i) the product-ion scan, (ii) the precursor-ion scan, (iii) the constant-neutral-loss scan, and (iv) selected decomposition monitoring. 

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