Mass spectrometric response

C. E. Heine, J. F. Holland, and J. T. Watson. Influence of the Ratio of Matrix to Analyte on the Fast Atom Bombardment Mass Spectrometric Response of Peptides Sampled from Aqueous Glycerol. Anal. Chem., 61(1989) 2674-2682. 

The stream from a gas chromatograph is split, with one segment directed to a commercial electron capture detector and the other to this source. Three responses can be observed (I) an electron capture response from the usual gas chromatograph-electron capture detector combination (2) an electron capture response from the API source, which should duplicate the normal response and (3) a mass spectrometric response based on ions generated under API conditions. 

The most important advantage of such an IDMS procedure is that it compensates in an ideal way both for losses during sample workup and for variations in mass spectrometric response. As demonstrated by Claeys et al. (1977), the use of a stable isotope-labeled internal standard, as opposed to the use of homologs, produces the lowest variance factors due to instrumental stability and sample manipulating errors. Moreover, IDMS can be used both with and without prior chromatographic separation, as for instance in... 

Stable isotope-labeled derivatives (De Leenheer and Cruyl, 1980) are much easier to prepare (incorporation of the isotope via a labeled derivatiz-ing agent), but do not fulfill all the purposes of the stable isotope-labeled analog, as they only account for losses after the derivatization process, such as variations in ionization efficiency and mass spectrometric response. 

E. Leize, A. Jaffrezic, and A. Van Dorsselaer, Correlation between solvation energies and electrospray mass spectrometric response factors. Study by electrospray mass spectrometry of supramolecular complexes in thermodynamic equilibrium in solution, J. Mass Spectrom. 31 (1996), 537-544. 

To quantitatively determine the absolute amounts of certain esters present in the oxidation products, the mass spectrometer responses to these compounds were compared with the response to the internal reference, octadecane. Using authentic samples of the esters of interest, relative mass spectrometric response factors were determined. From these response factors, listed in Table I, the amounts of esters present in the oxidative degradation products were calculated using an INCOS subroutine. 

There has recently been some interest in nanoflow LC as a mean of normalizing the mass spectrometric response [55-58], Nanospray is more than simply a reduction of ESI flow rate. ESI is an electrohydrodynamic process, with daughter droplets generated when Columb repulsion in a charged liquid (the parent droplet) overcomes... 

Scamporrino, E., Maravigna, R, Vitalini, D., and Mineo, R, A New Rrocedure for Quantitative Correction of Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometric Response, Rapid Comm. Mass. Spectrom., 12, 646, 1998. 

As an approximation to a universal response detector, an ultraviolet (UV) detection with a high concentration of in vivo sample or in vitro incubation can be used to calibrate the mass spectrometric response of the metabolites. Josephs et al. (2009) recently reported the use of high-performance liquid chromatography (HPLC)-UV detection to get area responses of a 30-tiM in vitro microsome or hepatocyte incubation. The incubated sample was then diluted in matrix to create a single point calibration for mass spectrometric quantitation of the metabolites. The results from this method were successfully verified using buspirone and proprietary compounds for which the synthetic standards for their metabolites were available. 

FIGURE 17.1 Mass spectrometric response ratio of turanose over n-octyl-glucopyranoside as a function of flow rates in nanospray. Turanose (10 mol/L) and w-octyl-glucopyr-anoside (10 mol/L) were prepared in neat solvent as a 10 1 (molar ratio) mixture. The curves represent the surface-to-volume ratio of initial droplets at different flow rates predicated using different theoretical models. [Reprinted from Schmidt et al. (2003) with permission.]... 

Schneider, K. and Chait, B.T. (1993) Matrix-assisted laser desorption mass spectrometry of homopolymer oligodeoxynucleotides. Influence of base composition on the mass spectrometric response. Org. Mass Spectrom., 28 (11), 1353-1361. 

However, methods have been developed to test for the presence of ionization suppression or enhancement of an analyte extracted from a complex matrix, to take its effects into account and thus hopefully alleviate the problem or even eliminate it altogether. An early systematic approach (Buhrman 1996), directed at detection and quantification of ionization suppression and other parameters, was later modified (Matuszewski 2003) to take account of the possibihty of ionization enhancement, and this modification is adopted here. The approach compares the results obtained for the mass spectrometric responses (peak areas) in three different LC/MS experiments for a target analyte, using the same known amount of analytical standard at the same final concentration in each case ... 

The several possibihties described in Section 8.3 may seem confnsing bnt in practice the problem is not usually too comphcated for analytical methods based on mass spectrometric detection, as a resnlt of the excellent degree of linearity observed for mass spectrometric response over ranges of several orders of magnitnde in the concentration (amonnt) of anal5d e introdnced. The best way to proceed will vary with the details of the reqnired analysis and the... 

The ionisation and fragmentation behaviour (mass spectrometric response) should be comparable. 

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