Exact mass filtering

Figure 7.13 illustrates the utility of mass defect filtering (also known as exact mass filtering) and UPLC. It shows results of UPLC/MS assay of a bile sample containing buspirone and its metabolites.184 The top trace shows the (unfiltered) TIC for the sample the middle trace is the result of an exact mass filter the bottom trace is an extracted ion chromatogram for the M+16 or hydroxylated metabolites based on their exact masses. It is readily apparent that this new software tool may be very helpful for metabolite identification studies. 

Exact mass filter exclusion based on the decimal places of a parent dmg, is a post processing filter which allows complete removal of unexpected entities (ions) which do not agree with the criteria preset by the user. Such a filter is fully adjustable once the samples have been processed. This process can dramatically reduce the number of ions in the analyte sample by filtering out the vast majority of matrix-related ions. This will also allow use of very low threshold values to detect low-level metabolites without having to go through the very tedious and long task of manual exclusion of false positives. Typically, extracted ion chromatogram windows of 0.1 mDa allow the... 

To assure consistency and speed in multidisciplinary structure analysis of low-MW compounds involving various techniques (IR, NMR, MS, etc.) most industrial laboratories use a Standard Operating Procedure (SOP). In such schemes IR analysis is frequently used as a cheap filter for a quick starting control and as a means for verification. As IR detects only structural units identification of an unknown compound on the basis of IR is difficult. Mass spectrometry is used as the prime identification tool and is especially important in the determination of the exact mass and gross formulae. While structural prognostication on the basis of MS is difficult for the non-expert, a posteriori interpretation is quite feasible. H NMR is both easy and cheap, however requires greater sample quantities than either... 

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. 

Alkali refined oil should always be tested to ensure it is completely free from break (solid residue). This is done by shaking a few drops of concentrated HCl with 25 mL of oil, then heating it at around 280-300°C. The presence of break is indicated by a cloudy appearance at a high temperature. It is then cooled and stirred with CCL, and 1% filter aid (inert powder or granules such as diatomaceous earth, fly ash or sand). The solid residue is then separated and dried to a constant weight to obtain the exact mass, which is the breaking content of the oil. 

The model consists of a two dimensional harmonic oscillator with mass 1 and force constants of 1 and 25. In Fig. 1 we show trajectories of the two oscillators computed with two time steps. When the time step is sufficiently small compared to the period of the fast oscillator an essentially exact result is obtained. If the time step is large then only the slow vibration persists, and is quite accurate. The filtering effect is consistent (of course) with our analytical analysis. Similar effects were demonstrated for more complex systems [7]. 

The water had the pec aliar fish-1 ike smell of the masses otflab—uha iniestinalis—floating on the surface.. The stones on the sides of the canals, the hurdles placed to keep up the banks, floating pieces of stick, and indeed every solid body with which the water came in contact, were coated with a reddish-brown deposit, similar to that which was found to separate from the filtered water In Amsterdam. This deposit was observed to be particularly abundant near the iron sluice gates. A pipe from one of the mains in the city was examined at the same time, and found to be coatad on the inside with a thick slimy deposit of vegetal remains, which presented under the miorcscopo an appearance exactly similar to that of the deposits above alluded to. 

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