AB Sciex QTRAP 4500 LC/MS/MS system, System User'S Manual, Page: 26 / 138

Principles of Operation
4500 Series of Instruments System User Guide
26 of 138 RUO-IDV-05-0264-A
Theory of Operation
Mass spectrometry measures the mass-to-charge ratio of ions to identify unknown compounds,
to quantify known compounds, and to provide information about the structural and chemical
properties of molecules.
The 4500 series of instruments has a series of quadrupole filters that transmit ions according to
their mass-to-charge (m/z) ratio. The first quadrupole in this series is the QJet
®
ion guide, which
is located between the orifice plate and the Q0 region. The QJet ion guide does not filter ions, but
focuses them before they enter the Q0 region. By prefocusing the larger ion flux created by the
wider orifice, the QJet ion guide increases system sensitivity and improves the signal-to-noise
ratio. In the Q0 region, the ions are again focused before passing into the Q1 quadrupole.
The Q1 quadrupole is a filtering quadrupole that sorts the ions before they enter the Q2 collision
cell. The Q2 collision cell is where the internal energy of an ion is increased through collisions
with gas molecules to the point that molecular bonds break creating product ions. This technique
allows users to design experiments that measure the m/z of product ions to determine the
composition of the parent ions.
After passing through the Q2 collision cell, the ions enter the Q3 quadrupole for additional
filtering, and then enter the detector. In the detector, the ions create a current that is converted
into a voltage pulse. The voltage pulses leaving the detector are directly proportional to the
quantity of ions entering the detector. The system monitors these voltage pulses and converts
the information into a signal. The signal represents the ion intensity for a particular m/z value and
the system displays this information as a mass spectrum.
Data Handling
The Analyst software requires a computer running the Windows operating system. The computer
with the associated system software works with the system controller and associated firmware to
control the system and data acquisition. During system operation, the acquired data is sent to the
Analyst software where it can be displayed as either full mass spectra, intensity of single or
multiple ions versus time, or total ion current versus time.