Functional Description
MS Detector
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______________________ Finnigan LTQ Hardware Manual _______________________
during ionization optimization. View ports are placed at the front and side of
the ion source housing, which allows visual aid in positioning the probe
during ESI operation, and enables easy addition of accessories.
Ion source lifetime is excellent due to several special features. The drain size
and angle prevents ion source corrosion by allowing eluants to flow directly
from the probe into the drain when auxiliary gases are off. For liquids that do
not enter the drain directly, the floor of the ion source interior is specially
sloped to enable maximum drainage of collected eluants. Additionally, the
zero dead volume LC grounding union that connects the LC flow to the ESI
sample inlet is offset from the ion source to prevent LC leaks from dripping
directly on the ion source housing.
The Ion Max ion source incorporates a universal mounting platform and
interface for use with ESI, APCI, NSI, and APPI ionization sources. For more
information on the analysis of ions produced by the Ion Max ion source,
please refer to Finnigan Ion Max API Source Manual.
Ion Source Interface
The ion source interface consists of the components of the API source that
are held under vacuum (except for the atmospheric pressure side of the ion
sweep cone). The ion source interface includes an ion transfer capillary, two
cartridge heaters, heater block, platinum probe sensor, vent prevent ball, ion
sweep cone, tube lens, and skimmer. See Figure 2-8 and Figure 2-9.
The ion transfer capillary assists in desolvating ions that are produced by
ESI, APCI, NSI, or APPI. The capillary is an elongated, 2.5-in. cylindrical
tube made of metal that has a hole bored through the center of its long axis.
Two heater cartridges are embedded in the heater block. The heater block
surrounds the ion transfer capillary and heats it to temperatures up to 400 °C.
A platinum probe sensor measures the temperature of the heater block.
Typical temperatures of the ion transfer capillary are 270 °C for ESI and
250 °C for APCI. Ions are drawn into the ion transfer capillary in the
atmospheric pressure region and transported to the capillary-skimmer region
of the vacuum manifold by a decreasing pressure gradient. A potential of
typically 0 to
±
10 V (positive for positive ions and negative for negative ions)
assists in repelling ions from the ion transfer capillary to the skimmer. The
vent prevent ball falls into the space occupied by the ion transfer capillary
when the capillary is removed, thus preventing air from entering the vacuum
manifold. The vent prevent ball allows you to remove the ion transfer
capillary for cleaning without venting the system.
The ion sweep cone is a metallic cone over the capillary. The ion sweep cone
acts as a physical barrier that protects the entrance of the capillary.
The system electronics include a voltage monitor circuit and an
overtemperature/undertemperature circuit to protect the heaters. The voltage
monitoring circuit detects shorting failures. The overtemperature portion of
the circuit is intended to function as a thermal limit switch to prevent the
