Axis BTA 2100D Manual do Operador descarregar pdf (Página 221)

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NOTE: This value is not used if the nonresonant CID method is selected. A

value of 0 gives a fixed rf storage field, i.e., no modulation

Modulation Rate:

The number of microseconds that will be spent at each step. The range is 29

usec to 5600 usec, with the default value of 3000 usec/step. The default value is

adequate for nearly all applications.

Number of Frequencies: Enter an odd integer in the range of 1 to 121 for the

number of frequencies. A frequency number of one generates a single

supplementary frequency applied to the end caps. An integer of 3, generates

three frequencies: the resonance frequency and frequencies 500 Hz above and

below that frequency

CID Frequency Offset : For certain applications it maybe desirable to offset the

dissociation frequency. The CID frequency can be adjusted between  3000 Hz

Tandem Mass Spectrometry (MS/MS)

How to Customize Parent Ion Isolation

If you wish to further optimize parent ion isolation by reducing the isolation

window, first build a method with a mass isolation window of 3 m/z, an excitation

time of 0 msec, and a CID (excitation) amplitude of 0 volts. This permits you to

observe only the isolation of the parent ion without the influence of CID. The

exact fractional mass of the ion should be used for the parent ion mass.

Use a fixed sample source, such as perfluorotributylamine (PFTBA) calibration

gas, or the column bleed obtained by raising the gas chromatograph oven

temperature to 300C. Adjust the isolation parameters to isolate a single ion.

How to Select an Excitation Technique

The compound and matrix you are using determine which excitation technique

you should use. Nonresonant excitation works well with most compounds, but

resonant excitation has been found to work better with some. You are advised to

begin your analysis with nonresonant excitation because it requires optimization

of fewer parameters. If the results desired cannot be obtained using nonresonant

excitation, switch to resonant excitation.

How to Optimize the Nonresonant CID Parameters

Follow these steps to optimize the nonresonant or resonant excitation CID

parameters. Determine whether the CID (excitation) amplitude used was too

large or too small.

NOTE: If the CID (excitation) amplitude used was too large, the parent ion and

product ion spectra will be absent because both ions will have been ejected from

the trap. If the value was too small, the parent ion spectrum will be dominant and

the product ion spectrum will be weak or missing.

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