Firma:              Finnigan

Modell:            SSQ 710

Kommentar:   Dokumente engl.

The Finnigan MAT 700 Series system is a high-sensitivity analytical instrument comprising one or more inlet systems, a mass spectrometer, and a data system. The mass spectrometer consists of an ion source, one or more mass analyzers (two in a TSQ 700, one in an SSQ 700), and an electron multiplier all enclosed in an vacuum manifold. Each mass analyzer contains four metal rods held in a square array. This arrangement is called a quadrupole rod assembly or a quad.

A sample is introduced into the ion source where it is ionized. The ions are then focused into the analyzer assembly where they are separated by mass-to-charge ratio. The ions are then converted into an electrical signal when they are detected by the electron multiplier. The signal is amplified and then passed on for further processing and for display.

All instrument control functions for 700 series instruments, from tuning the instrument to acquiring data, and all data analysis tasks are controlled from a DECstation 2100.

The 700 Series can be operated in a wide variety of scan modes, ionization modes, ion polarity modes, and mass range modes.

Quads can be operated in one of two capacities:

• as ion transmission devices or
• as mass analyzers

lonization Modes

Initial ionization of sample molecules occurs in the ion source. In the EI/CI/FAB configuration, the 700 Series offers three ionization modes:

•     EI (electron ionization)

•     CI (chemical ionization)

•     optional FAB (fast atom bombardment) ionization.

In the optional thermospray configuration, three types of ionization are available:

•     thermospray buffer ionization

•     thermospray filament ionization

•     thermospray discharge ionization

The best method of ionization depends upon the application and type of sample to be analyzed.

Mass Range Modes

Two mass ranges are available on the 700 series: the low mass range (10 to 2 000 u) and the high mass range (20 to 4 000 u). In the low mass range mode, unit resolution is obtained throughout the entire mass range. In the high mass range mode, somewhat less than unit resolution is obtained.

In the operation of the system, the ranges scanned by the mass analyzers can be set independently. Thus, both mass analyzers can be set to the low mass range; both can be set to the high mass range; or the first can be set high and the second low.

When the instrument is analyzing compounds with molecular weights of 2 000 u or less, both mass analyzers are set to the low mass range. In this way, unit resolution is obtained for all parent and daughter ions in each of the scan modes.

The SSQ 700 has a single quadrupole rod assembly and two lenses. The rod assemblies and lenses (and the electron multiplier) are mounted on a rail. Ions from the ion source enter the analyzer assembly, are separated by mass-to-charge ratio, and then are passed on to the electron multiplier. For a block diagram of the analyzer assembly, see Figure 7-1.

Figure 7-1. Block diagram of the analyzer assembly (b) SSQ 700

5 kV Dynodes

The SSQ 700 is equipped with a positive ion / negative ion electron multiplier that consists of two conversion dynodes and a continuous dynode electron multiplier (Fig. 8-2) The conversion dynodes are metal surfaces, one maintained at +5 kV and the other at -5 kV.

Figure 8-2. Schematic representation of the SSQ 700 electron multiplier and conversion dynodes

Positive and negative high voltages exist an the respective conversion dynodes continuously when the electron multiplier is on. The nature of the ions being detected is determined by switching the ion-source and analyzer-assembly lens voltages and the quadrupole offset voltages to allow positive or negative ions to be injected successively into the analyzer assembly and mass analyzed. When the positive or negative ions strike their respective conversion dynode surfaces, several secondary particles are produced. These particles then enter the cathode of the electron multiplier and are processed as in the TSQ 700.

SAMPLE INTRODUCTION: GC / TRANSFER LINE

The standard configuration of the 700 Series GC/MS/MS or GC/MS system includes a Varian 3400 Gas Chromatograph (GC) and GC accessory cabinet. The Varian 3400 GC is described in detail in the documentation provided with the GC.

The GC interfaces to the ion source region of the mass spectrometer via a simple transfer line and interface flange. The GC is placed on the GC accessory cabinet. Adjustment of the GC cabinet's four feet allows precise alignment of the transfer line to the EI/CI/FAB ion source within the vacuum manifold.