Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

The overall goal of this procedure is to acquire electron impact ionization, mass spectra of volatile inorganic compounds susceptible to oxidation or hydrolysis. This is accomplished by first transferring the sample into a custom made lockable test tube with flange under inert conditions using a slink line. The second step is to attach the cold inlet system to the mass spectrometer and fix the lock test tube filled with sample to this inlet system.

Next, the cold inlet system is evacuated and the connection to the iron source of the mass spectrometer is opened in the final step. The sample is carefully leaked into the mass spectrometer by opening the needle valve of the cold inlet system and a mass spectrum is recorded. Ultimately, mass spectrometry is used to determine the molecular ion of a substance and to confirm its structure using the fragment ions.

The main advantage of this technique versus the existing methods, such as easy and Maori under innu conditions, cold spray and lefty, is that you can analyze very volatile and sensitive compounds by mass spectrometry. Demonstrating the sample preparation procedure will be Marcus Mann, a graduate student from the inorganic Chemistry Department of Professor Hogan. First, evacuate a lockable test tube previously attached to a multiple manifold schlink line, and remove residual water by heating with a heat gun.

Once the test tube is called, bent it with dry argonne, then evacuate again while heating after evacuating the test tube, immerse it into a cold trap filled with liquid nitrogen. Condense a small amount of the sample into the test tube from a sample container previously attached to a manifold of the schleck line. Following this, close the lock on top of the test tube as well as the manifold, and remove the lock test tube from the nitrogen bath prior to sample measurement.

Tune and calibrate the mass spectrometer according to the instructions provided by the manufacturer of your mass spectrometer. Next, remove the push rod of the direct inlet from the iron source and install the outer interface for the test tube to prevent heating of the push rod tip, set the inlet method to septum in the control software of the mass spectrometer. Connect the flange of the lockable test tube filled with the sample to the outer interface.

Then open the needle valve of the outer interface and evacuate the inlet after evacuation. Carefully open the ball valve to the ion source to complete the evacuation Step close the needle valve of the outer interface. Start a mass measurement in the software of the mass spectrometer with the needle valve closed.

Open the Teflon tap of the test tube very briefly, allowing gas phase molecules of the analyte to enter the outer part of the interface. After closing the Teflon tap, carefully open the needle valve while observing the vacuum gauge of the ion source, allowing the analyte molecules to enter the ion source of the mass spectrometer. Once the needle valve of the outer interface has been closed, close the ball valve to the ion source.

Then stop the acquisition of mass spectra in the software. Evacuate the inlet system while the needle valve is opened. Completely vent the interface while the ball valve and needle valve are closed.

Once the interface has been evacuated, again, open the needle valve in order to remove residual sample vapor in the interface. After repeating the previous step at least three times, remove the lockable test tube from the interface. If not performing additional analysis with other samples, remove the outer interface from the flange of the ion source and replace it with the push rod.

An electron impact ionization mass spectrum of tris, trior methyl phosphate is presented here. The signal of the molecular ion can be observed and the fragment ions can also be assigned to the analyzed phosphate. The presented interface allows for the straightforward measurement of mass spectra for compounds such as tris, trior, methyl phosphate, which decomposes rapidly when in contact with air.

The operation of the novel interface is easy and fast and presents no obstacle when operating the mass spectrometer with the routinely applied direct inlet. Using the push rod Once mastered mass spectra of very volatile and sensitive compounds can be acquired in a few minutes if the procedure is performed properly.