Analysis of High Molecular Weight Compound by Direct Sample Inlet DI – Electron Ionization (EI) MS

This video will show you the analysis of high molecular weight compounds by direct sample inlet or DI in mass spectrometer or MS.
As the name implies, in direct sample inlet analysis, sample will be introduced directly into the mass spectrometer without the need to pass through a gas chromatography or GC for separation. This make it very useful for samples that are incompatible with GC. For example, high molecular weight compounds or non-volatile compounds. DI can be very useful as a complementary technique for synthetic compounds identification during a drug development process.
Here is the principle of DI. Sample is placed in a sample cup and introduced using the DI probe which will be heated once it is inserted into the mass spectrometer. The heated probe will vaporize the sample which will enter the ion source box. In the ion source box, high energy electrons produced by filament will ionized the compounds in the sample which generate fragment and molecular ions. This ionization technique is called the electron ionization.
Electron ionization in MS produces a mass fingerprint which we call a mass spectrum. This fingerprint is unique to the compound. For example, the mass spectrum shown here is unique to Adenosine using electron ionization. Different compounds will have different mass spectra that can be used for compounds identifications by comparing with the mass spectrum in some databases. In electron ionization, molecular ion peak is usually low, while the fragments ions are higher depending on the compound structure.
To perform DI analysis, sample must be introduced by DI probe. Samples for DI is usually solid. Position the probe standing vertically, remove the sample cap and put the sample cup containing the sample into the probe. Then, put the sample cap back onto the probe. Once sample is placed in the DI probe, we may insert the DI probe into the MS to begin the analysis. When the analysis ends, gently pull out the DI probe.
We may proceed to perform qualitative data processing by using GCMSsolution. Data acquired contains the mass spectrum of the analysed sample. With the acquired mass spectrum, it is possible to perform a preliminary identification by comparing against the mass spectrum in some commercial databases.
This video introduced direct sample injection into MS using DI probe. It is a simple and straightforward technique to identify synthetic compounds with high boiling point such as Adenosine.

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