Quantitative analysis using mass spectrometry

The degree of specificity of a quantitative analysis using mass spectrometry depends on how the spectrometer is used, and even more on the signal that is used during the correlation. For example, we can use the ion current as a signal to determine the concentration of the compound that is studied as long as there is no interference with other substances (in... 

Many methods exist that improve the specificity of quantitative analysis using mass spectrometry. These methods can be classified into either of two categories those that act upon the sample and those that act on the spectrometer. 

The goal of quantitative analysis in mass spectrometry is to correlate the intensity of the signals with the quantity of the compound present in the sample. Several quantitative analysis methods using mass spectrometry have been developed and many applications using these methods have been described [19]. 

NMR) [24], and Fourier transform-infrared (FT-IR) spectroscopy [25] are commonly applied methods. Analysis using mass spectrometric (MS) techniques has been achieved with gas chromatography-mass spectrometry (GC-MS), with chemical ionisation (Cl) often more informative than conventional electron impact (El) ionisation [26]. For the qualitative and quantitative characterisation of silicone polyether copolymers in particular, SEC, NMR, and FT-IR have also been demonstrated as useful and informative methods [22] and the application of high-temperature GC and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is also described [5]. 

Sun, T., and R.E. Lovins, Quantitative protein sequencing using mass spectrometry use of low ionizing voltages in mass spectral analysis of methyl- and phenylthiohydantoin amino acid derivatives. Anal Biochem, 1972. 45(1) 176-91. 

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. 

Selected ion monitoring mass chromatogram showing caffeine and caffeine-D3 eluted from a capillary gas chromatography column. [From D. W. Hill, B. T. McSharry, and L. S. Trzupek, Quantitative Analysis by Isotopic Dilution Using Mass Spectrometry." J. Chem. Ed. 1988, 65, 907.]... 

Liu, Y. M., Akervik, K., and Maljers, L. (2006). Optimized high resolution SRM quantitative analysis using a calibration correction method on triple quadmpole system. In Proceedings of the 54th ASMS Conference on Mass Spectrometry and Allied Topics. ASMS, Seattle, WA. 

Yu, C., Penn, L. D., Hollembaek, J., Li, W., and Cohen, L. H. (2004). Enzymatic tissue digestion as an alternative sample preparation approach for quantitative analysis using liquid chromatography-tandem mass spectrometry. Anal. Chem. 76 1761-1767. 

Quantitative analysis of compounds by measurement of specific fragments using mass spectrometry. Analysis of the chemical structure of a compound by measurement of the molecular weight of fragments formed by bombardment of the molecule by ions. 

Since light and heavy amino acids are chemically identical, the labeling process will not affect the chemical properties of the peptides and therefore differentially labeled peptides will co-elute from the HPLC column. However, these peptides are isotopically distinct from each other the peaks from light and heavy labeled peptides can be accurately distinguished and quantified by using mass spectrometry. An example of a study using SILAC includes the quantitative proteomic analysis of 495 proteins in renal cells towards the exploration of molecular mechanisms of calcineurin-inhibitors induced nephrotoxicity [82], In a second study, a... 

Perkins, D.N., Pappin, D.J.C., Creasy, D.M., Cottrell, J.S. (1999) ProbabUity-based protein identification by searching sequence databases using mass spectrometry data. Electrophoresis, 20 (18), 3551-3567. Silva, J.C., Denny, R., Dorschel, C., et al. (2006) Simultaneous qualitative and quantitative analysis of the Escherichia coli proteome-A sweet tale. Molecular and Cellular Proteomics, 5 (4), 589-607. 

Traditionally, analytical atomic spectroscopy implied the use of electromagnetic radiation in the ultraviolet ( 200-350nm) and visible ( 350-800nm) region of the spectra for qualitative and quantitative analysis. With the use of some of the same sources to produce ions for detection using mass spectrometry, the term often encompasses the area of elemental mass spectroscopy. In this section the focus will remain on optical techniques. 

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. 

As mentioned in Section 3.7, CE and CEC are not used on a routine basis when ultimate performance (accuracy and precision etc.) is required for tme trace level quantitative analysis of small molecules using mass spectrometry. Direct coupling of bench scale CEC (and CE to some extent) to MS is not straightforward. However, both CE and CEC are key technologies for development of integrated lab-on-a-chip devices (Section 4.4.7) and this is the reason for the following discussion. 

Kongo, C., Tomita, M., Suzuki, M. (1999) Quantitative secondary ion mass spectrometry analysis of impurities in GaN and Al Gai. N films using molecular ions MCs and MCs2 - Applied Surface Science, 144—145,306-309. 

Rushnir MM et al (2005) Assessing analytical specificity in quantitative analysis using tandem mass spectrometry. Clin Biochem 38 319-327... 

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