Tests, spectrometer resolution

One of the more powerful techniques is a new software tool called mass defect filtering.176 185-188 A mass defect can be defined as the difference between the exact mass and nominal mass of a compound.189 Typically, drug-like molecules (and their metabolites) will have mass defects that differ from those of endogenous matrix materials. While a mass spectrometer that has unit mass resolution cannot differentiate a test compound from an isobaric matrix compound, a high mass resolution MS may be able to differentiate many isobaric matrix compounds from test compounds. 

The temporal widths of the IR pulses and the time resolution of this spectrometer are tested with the use of a Ge sample that, when exposed to the pump pulses, results in transient IR absorption at 2290 cm. Modeling the risetime of this absorption gives a cross-correlation width (full width at half-maximum, fwhm) of 1.8 ps. 

In this chapter we focus primarily on calibration of LC-MS where the mass spectrometer is operating at unit resolution, resolution that is sufficient to separate two peaks one mass unit apart. This kind of low-resolution mass filter covers almost 90 percent of the instruments commonly used for qualitative and/or quantitative analysis of small molecules. Batch-to-batch qualification testing of the instrument is also described. For the calibration of high-resolution mass spectrometers such as magnetic sector, TOF, or FTICR coupled with liquid chromatography, readers are referred to specific publications. 

Detail tests on nuclear models require not only a knowledge of energy, spin and parity of many levels, but also the determination of transition multipolarities and branching ratios. Precise intensities are thus needed. The well shielded anti-Compton spectrometer offers a rather simple solution especially for accurate angular distribution measurements. When the spectra are very complex, like in the case of final doubly odd nuclei, intensities cannot be determined without use of high resolution instruments. The curved crystal spectrometer provides a powerful solution at, unfortunately, non negligible cost. 

Specifications for a probe head/field strength (magnet) combination are given by the spectrometer manufacturer for line shape, sensitivity, resolution, and radio-frequency field strengths. A specific test is considered passed when the specification value is met. 

MS-based assays that are aimed to characterize the specificity of catalytic NRPS domains and tailoring enzymes for carrier protein substrates can be done on high-resolution mass spectrometers or, for small substrate T domains (<20 kDa),105 on low-resolution mass spectrometers. For investigation of T domain substrate tolerance, the native T domain substrates of a catalytic NRPS domain or tailoring enzyme are exchanged by different T domains, for example, from different NRPS systems. In addition, the tolerance of T domain order can be tested for C domains and aminoacyl transferases by reverse-ordered tethering of native biosynthetic substrates to the native T domains and MS detection of the reaction product on the assayed upstream active site.93... 

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