Practical Protein Chemistry - A. Darbre 1989

Application of electron impact mass spectrometry for determining the amino acid sequence of peptides and proteins
Sample preparation methods
Recording mass spectra

The permethylated acetyl peptide is dissolved in a drop of chloroform, and the solution is carefully transferred to an evaporator mounted on a metal rod used for introducing the sample into the ion source of a mass spectrometer. Chloroform is evaporated from the evaporator by blowing air through the solution via the drawn-out tip of a Pasteur pipette. After the evaporation of chloroform, the evaporator is inserted via the rod into the ion source, where the test substance is vaporized. The best results are achieved when the evaporator lacks a special heating element and is instead heated by the thermal radiation from the heated walls of the ionization chamber. The Use of an independently heated evaporator is ineffective when analyzing mixtures. Maintaining the Temperature of the ionization chamber at ~100 °C, easily volatile impurities such as dimethyl sulfoxide or Hydrocarbons are evaporated from the sample under analysis. If the pressure in the ionization chamber region increases during this process, the rod is temporarily withdrawn, the system is left until the pressure drops to the required level, and the sample is reintroduced. After the evaporation of all volatile impurities, vaporization of the test substance is initiated as follows. Having withdrawn the evaporator from the ionization chamber, the device for increasing its temperature is turned on, and the temperature of the ionization chamber is raised at a steady rate up to 350 °C. Following each 30 °C increment in the temperature of the ionization chamber, the evaporator is inserted, and the mass spectrum is recorded several times over the mass-to-charge range from m/z 1000 to m/z 90.