Mass Spectrometry: Sample introduction

 Sample introduction is the very first step in the analysis of mass spectrum of the sample compound. In this step, the sample to be analyzed is introduced from the sample inlet to the ion source where the ionization of the sample molecules takes place.

 

Must read: Mass spectrometry- Basics first

The sample can be a solid, liquid or in gaseous form. But the sample must get converted into its vapour molecules before entering the ionization chamber.

The sample inlet is partially evacuated while the ionization chamber operates at much lower pressure than sample inlet. A small pinhole called molecular leak is present at the opening on ionization chamber to ensure a steady and continuous stream supply of molecules from sample inlet. This simple system can be used for the volatile liquids and gaseous samples. Direct probe is another method used commonly for the non volatile or relatively less volatile samples.

In direct probe method, a small amount of sample placed on the tip of wire loop on the probe is inserted through a vacuum lock into ionization chamber. The probe is kept near to the opening of ionization chamber so that the vapour molecules produced on heating the probe can enter easily to the ionization chamber.

 

The more versatile variant of this is if chromatograph is connected with sample inlet system. As in Gas chromatography – mass spectrometry (GC-MS), the gas exiting from the chromatograph is directly passed through mass spectrometry. The enhanced efficiency mass spectrometers with those capable of making at least one scan per second in the range of 10-300 m/z are required for this purpose.