| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
FAQS
There are no parameters that need to be set. An instrument capable of obtaining a mass accuracy of 12 ppm is needed to use Rational Numbers Search. 2) Will the Rational Numbers search engines work for
every compound? No, the success of the program is compound
dependent. Compounds that give at least one fragment ion will
work, but the more fragment ions you have, the better the results. Paradoxically, having more heteroatoms in a molecule makes it easier to distinguish compounds, even though more heteroatoms in a molecular formula increases the number of possible compounds within the mass window of the experimentally determined molecular weight. Steroids with only one or two oxygen atoms are about the most difficult compounds to distinguish because of their combination of a high carbon/heteroatom ratio, large number of fragment ions, and the very large number of compounds in the indices with the same formula. Less polar compounds like these are still best handled with GCMS. 3) What do you mean by an index? The Rational Numbers Search engine works on an index. The index contains only the minimal information needed for comparing mass spectral data to chemical structures. For example, there is not sufficient information in the indexes to draw any of the structures. This means that the results are ID numbers and the user must have access to PubChem to view the chemical structures. 4) Will an EI version
be available later?
Right now MathSpec, Inc. is focusing on using accurate-mass CID-type
data because of the lack of libraries for LCMS. These search engines should work for EI with some modifications.
In the future we also plan to add silicon to the list of possible elements and "mathematically" silylate the indices. 5) Is the software suitable for
data from all types of high-resolution mass spectrometers?
Yes. Each spectrum is captured in WordPad or Notepad and saved as a text
file, using the vender's "Copy Spectrum List" utility. 6) Is it really necessary to acquire
accurate-mass fragmentation data? Why isn't the accurate mass of the whole compound sufficient to identify it?
This is a very common misconception about accurate-mass. For example,
the compound shown here on our website, xemilofiban, has the formula C18H22N4O4.
The PubChem database has about 700 compounds with that same formula
and exact mass and 938 compounds within 10 ppm of its exact
mass (PubChem on 11-21-07). 7) Can the program use data where a comma is used as the decimal separator (radix point)?
The search engines can handle data from both "comma countries" and "dot countries". 8) Is the program expensive? Do I need to purchase an expensive workstation to use the program?
The search engines and indices all reside on our computers. The processing is done there. Most searches take only a few seconds per unknown; up to ten unknown compounds can be analyzed per run. 9) The isotope ratio data from my instrument is sometimes way off. Can Rational Numbers Search work without isotope data? |