manufacturer:       Finnigan

model:                   AQA

annotation:           Dokumente engl.

The Finnigan AQA ^TM MS detector has been specifically designed and engineered for liquid chromatographic detection using Atmospheric Pressure Ionization (API) and Mass Spectrometry (MS) technology. These technologies can provide sensitive and selective detection of organic molecules.

Interfacing High Performance Liquid Chromatography (HPLC er LC) and MS provides the separation scientist with one of the most powerful analytical tools available. Both LC and MS have developed to a point whereby they represent two of the most important techniques in characterizing and detecting organic compounds. Although the potential benefits of interfacing LC to MS have been clearly recognized for mang years, producing a truly automated `connect and use" Interface has proven to be a challenging task.

Atmospheric Pressure Ionization (API) techniques now provide highly sensitive detection using conventional to capillary LC flow rates on bench­top MS detector systems. LC/MS works with typical solvent compositions, whether the separation is achieved by isocratic or by gradient elution.

Historically, LC/MS has been compatible only with volatile buffer systems using modifiers such as trifluoroacetic acid, formic acid and acetic acid. Phosphate buffers, although extensively used in LC Separations, were not suited to LC/MS due to rapid blocking of the ion sampling region caused by the deposition of involatile phosphate salis. The self-cleaning AQA API source allows for extended periods of Operation in LC/MS with chromatographic buffers such as phosphates er ion pairing agents and Samples in dirty matrices.

API using Electrospray (ESI) or Atmospheric Pressure Chemical Ionization (APCI) Interfaces has proved to be invaluable in meeting sensitivity requirements in quantitative methods. lt can also provide structural Information, which is complementary to techniques such as NMR and infra red spectroscopy.

This introduction focuses on the principal components of the System.

System Overview

The Finnigan AQA MS detector is an integral part of the LC detection system. Key points of the system are:

•        The sample is introduced into the ion source using an LC system, possibly through a column.

•        In an API MS detector, the part of the source where ionization takes place is held at atmospheric pressure, giving rise to the term Atmospheric Pressure Ionization (API).

•        In ESI, the sample is ionized in the liquid phase, whilst in APCI, ionization occurs in the gas phase. In both Gases, efficient desolvation is needed to remove the solvents from the sample.

•        Ions, now in the gas phase, are passed through the mass analyzer and are collected at the detector.

•        The detected Signal is sent to the data system and stored ready for processing.

The main features of the Finnigan AQA MS detector are:

•            Dual ESPAPCI orthogonal probe

•            Self-cleaning API-LC/MS Interface

•            Flow-focused source, eliminating the need for electrostatic focusing

Schematic diagram of the Finnigan AQA API inlet, analyzer and detector system.

The LC eluent is ionized at the API probe wich the resulting ions flow­focused into a hexapole RF lens. The quadrupole mass analyzer filters the ions before detection.