1
Introduction
Ion Polarity Modes
Thermo Scientific
TSQ Quantum XLS and TSQ Quantum GC User Guide
5
In isobutane positive ion mode CI, the main peak observed is MH
+
.
In ammonia positive ion mode CI, the main peaks observed are MH
+
and [M+NH
4
]
+
.
Negative sample ions are most commonly formed by one of the following:
• Sample molecules capture the secondary thermal electrons present in the ion source
• Electron transfer from ionized reagent gas (e.g. NH
2
-
)
• Proton abstraction
Molecular ions observed in negative ion chemical ionization mass spectra are usually M
-
or
[M-H]
-
.
Ion Polarity Modes
You can operate the TSQ Quantum XLS and TSQ Quantum GC mass spectrometers in
either of two ion polarity modes: positive or negative. Both positively charged and negatively
charged ions form in the ion source of the mass spectrometer. The mass spectrometer controls
whether positive ions or negative ions are transmitted to the mass analyzer for mass analysis by
changing the polarity of the potentials applied to the ion source and ion optics. The ion optics
deliver the ions produced in the ion source, in a collimated beam, to the mass analyzer. The
mass spectrometer can switch between positive and negative polarity modes in under 95 ms.
The information obtained from a positive-ion mass spectrum is different from and
complementary to the information from a negative-ion spectrum. Thus, the ability to obtain
both positive-ion and negative-ion mass spectra aids you in the qualitative analysis of your
sample. You can choose the ion polarity mode and ionization mode to obtain maximum
sensitivity for the particular analyte of interest.
Scan Modes
You can operate the TSQ Quantum XLS and TSQ Quantum GC mass spectrometers in a
variety of scan modes. The most commonly used scan modes can be divided into two
categories: single mass spectrometry (MS) scan modes and MS/MS scan modes. The scan
modes in each category are as follows:
• MS scan modes: Q1MS and Q3MS scan modes
• MS/MS scan modes: Product scan mode, Parent scan mode, Neutral Loss scan mode
• Data-dependent scan mode
The scan modes that can be employed depend on the number and type of rod assemblies and
the voltages applied to the rod assemblies.
