Axis BTA 2100D Instrukcja Operatora Pobierz pdf (Strona 196)

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Mass Defect

Mass defect is defined as the difference between the nominal mass of an atom

(or ion) and its exact mass. Its importance arises from the fact that the Saturn

GC/MS reports molecular weights to the nearest integer mass unit only. The

software must decide which mass to assign the measured intensity to. If the

exact mass of an ion happens to fall close to the dividing line between integer

masses, it may be assigned to the wrong mass. This is more likely for molecules

with higher molecular weights, since the mass defects for several atoms may add

together to produce a sizable mass defect. The mass defect parameter may be

set to any value from -300 mu per 100u to +300 mu per 100u. The formula for

calculating the mass defect parameter is:

umux

MassInteger

MassIntegerMassActual

DefectMass 100/10





For example, hexachlorobenzene (C

) with an exact mass (for the base peak)

of:

8104.283)9659.361(9689.345()0000.126(





xxx

has a mass defect of:

umux 100/76.6610284/)2848104.283(



Similarly, dodecane (C

) has an exact mass of:

2028.170)0078.126()0000.1212(





and a mass defect of:

umux 100/29.11910170/)1702028.170(



Obviously, if a sample contains both of these compounds, the mass defect

parameter cannot be optimized for both in a single segment. For most analyses

the mass defect should be set to 0 in order to avoid mass misassignments, or

carefully program it with multiple segments.

Cal Gas

The calibration gas may be turned on during an acquisition by clicking on the Cal

Gas checkbox.

Ionization Mode - EI Auto

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