Hardware manual

Technical Information 6
Agilent 7500 Series ICP-MS Hardware Manual 6-19
Gas Flow Tuning
Flow rates of the reaction gases are set in the tuning window of Agilent’s
MassHunter Workstation (or ChemStation) Software. Due to the ‘MultiTune’
capability of MassHunter Workstation (or ChemStation), reaction gases can
also be automatically switched during the analysis.
Q-pole
The Q- pole of the Agilent 7500 consists of a pre- filter and a main filter. The
inner surface of the Q- pole rods is hyperbolic giving an ideal electrical field
inside the Q- pole.
Only RF voltage is supplied to the Q- pole pre- filter, while RF and DC voltage
is supplied to the main Q- pole filter. The purpose of the pre- filter is to direct
ions from the Omega lens along the right path into the Q- pole main filter. To
the Q- pole main filter, both about 3 MHz of RF voltage (V) and DC voltage (U)
are supplied (Figure 134). When the highest mass 260 is analyzed, 559 V of DC
voltage and 3,338 V of RF voltage are supplied. The maximum voltage is ±
3,897 V.
In addition, the pole bias (PB) is supplied to the Q- pole. When the pole bias is
at 0 V, this is the ground level, if the pole bias is used at + 2 V, the average
voltage shifts +2V. A positive pole bias voltage reduces the ion speed, which
gives a better peak shape. Therefore, the pole bias can be used when the peak
shape becomes poor. Pole bias values up to + 5 V may be used. Excessively high
pole bias reduces sensitivity for lighter masses drastically, so if the peak shape
is still poor at higher than a +5 V pole bias, the Q- pole should be cleaned.
When the ShieldTorch system is used, the ion energy is lower than the normal
system, therefore, the pole bias can be used at negative voltage as low as - 10 V
is acceptable.