Performance Characteristics Of Mass Spectra

The most important performance characteristics for a MALDI-TOF spectrum are resolution and signal-to-noise (S/N) ratio. The resolving power of a mass spectrometer is its ability to distinguish between ions with slightly different m/z ratios. Usually, the resolution of a particular peak in the mass spectrum is expressed as the peak width measured at half of its maximum height (full width at half maximum, or FWHM). Numerically, resolution is expressed as R=m/Am, or the ratio of the mass of one ion to the difference of a closely neighbored second ion. The intensity is given in arbitrary units or in relative units, where the most abundant signal is assigned the 100% value. The S/N ratio is an additional factor to characterize the quality of a mass spectrum. It is expressed as the ratio of a particular signal intensity to the average noise intensity. To increase sensitivity and/or S/N ratios, spectra can be summed up, which simply means that spectra from multiple laser shots are averaged. Typically, sensitivities are in the low femtomole to attomole range.

The quantitative abilities of MALDI-TOF MS are limited. Absolute quantitation of isolated signals cannot

Fig. 1 Depicted is a schematic overview of the MALDI-TOF process. The text provides a detailed description.

be achieved. However, relative quantitation employing a reference standard with a known concentration is possible. Relative quantitation with MALDI-TOF is, for example, routinely used to analyze the allele frequency of single nucleotide polymorphisms (SNPs) in equimolar mixtures of genomic DNA (DNA pools). For more details, the reader is referred to the respective chapter in this encyclopedia.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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