Inlet system direct insertion probe

There are different types of instruments that can be attached to the El source for MS analysis. The most commonly used technique consists of the analysis of a gaseous sample obtained from the gas chromatograph. However, other introduction systems, such as reservoir inlets and direct insertion probes, are also frequently used. 

Note The below-mentioned sample introduction systems (reservoir inlets, various direct insertion probes, and chromatographs) are of equal importance to other ionization methods. 

Direct-inlet probe. A shaft or tube having a sample holder at one end that is inserted into the vacuum system of a mass spectrometer through a vacuum lock to place the sample near to, at the entrance of, or within the ion source. The sample is vaporized by heat from the ion source, by heat applied from an external source, or by exposure to ion or atom bombardment. Direct-inlet probe, direct-introduction probe, and direct-insertion probe are synonymous terms. The use of DIP as an abbreviation for these terms is not recommended. 

Section 6.4 deals with other EI-MS analyses of samples, i.e. analyses using direct introduction methods (reservoir or reference inlet system and direct insertion probe). Applications of hyphenated electron impact mass-spectrometric techniques for poly-mer/additive analysis are described elsewhere GC-MS (Section 7.3.1.2), LC-PB-MS (Section 7.3.3.2), SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

Highly volatile samples cannot be introduced into the ion source by means of a direct insertion probe even when cooling is applied. A reference inlet system or reservoir inlet system is better suited for that purpose. [59] The name of this type of... 

The mass spectrum of dicofol (a diphenylmethanol derivative) depends on the type of inlet system used on the mass spectrometer. The spectrum obtained by GC-MS (Fig. 3A) is identical with that of pp -dichlorobenzophenone, presumably formed by elimination of chloroform from the parent compound in the heated injection port. On the other hand, the direct insertion probe spectrum (Fig. 3B)... 

Vaporize compounds of varying volatility. This is accomplished in the inlet system. Introduction of the sample is done by direct insertion probe, reservoir inlet, or following a chromatographic separation (GC, HPLC, and CE). As mentioned earlier, to introduce the LC flow to the mass spectrometer on-line, we need an appropriate interface. Development of appropriate interfaces was the utmost for evolution of the LC-MS coupling. 

Bombick et al. [3] presented a simple, low cost method for producing thermal potassium metal ions for use as Cl reagents. All studies were performed on a commercial gas chromatography-mass spectrometiy (GC-MS) system. Thermionic emitters of a mixture of silica gel and potassium salts were mounted on a fabricated probe assembly and inserted into the Cl volume of the ion source through the direct insertion probe inlet. Since adduct ions (also referred to as cationized molecular ions or pseudomolecular ion ) of the type (M + K)+ have been observed, molecular weight information is easily obtained. The method is adaptable to any mass spectrometer with a Cl source and direct inlet probe (DIP). In addition, the technique is compatible with chromatographic inlet systems, i.e., GC-MS modes, which will provide additional dimensions of mass spectral information. 

An alternative direct introduction interface was reported by Covey and Henion (20) which they termed the thermospray interface. It differed from those previously described in that it had a dual probe interface which is introduced into the mass spectrometer via the standard direct insertion probe inlet. The dual purpose LC/MS interface could provide the conventional direct liquid inlet system or, alternatively, a copper vaporizer situated at the end of the probe could be heated electrically to produce thermospray ionization. A diagram of the probe system is shown in Figure 15. 

The most straightforward tool for the introduction of a sample into a mass spectrometer is called the direct inlet system. It consists of a metal probe (sample rod) with a heater on its tip. The sample is inserted into a cmcible made of glass, metal, or silica, which is secured at the heated tip. The probe is introduced into the ion source through a vacuum lock. Since the pressure in the ion source is 10-5 to 10-6 torr, while the sample may be heated up to 400°C, quite a lot of organic compounds may be vaporized and analyzed. Very often there is no need to heat the sample, as the vapor pressure of an analyte in a vacuum is sufficient to record a reasonable mass spectrum. If an analyte is too volatile the cmcible may be cooled rather than heated. There are two main disadvantages of this system. If a sample contains more than one compound with close volatilities, the recorded spectrum will be a superposition of spectra of individual compounds. This phenomenon may significantly complicate the identification (both manual and computerized). Another drawback deals with the possibility of introducing too much sample. This may lead to a drop in pressure, ion-molecule reactions, poor quality of spectra, and source contamination. 

C. Basic Inlet Systems 1. Direct Insertion or Solids Probe... 

Sample Inlet System. Volatile or volatilizable compounds may be introduced into the spectrometer via a pinhole aperture or molecular leak which allows a steady stream of sample molecules into the ionization area. Non-volatile or thermally labile samples are introduced directly by means of an electrically heated probe inserted through a vacuum lock. Numerous methods of sample ionization are available of which the most important are electron impact (El) chemical ionization (Cl), field ionization (FI), field desorption (FD),fast atom bombardment (FAB), and rf spark discharge. 

With nonvolatile samples, other sample inlet systems must be used. A common one is the direct probe method. The sample is placed on a thin wire loop or pin on the tip of the probe, which is then inserted throngh a vacnnm lock into the ionization chamber. The sample probe is positioned close to the ion sonrce. The probe can be heated, thus causing vapor from the sample to be evolved in proximity to the ionizing beam of electrons. A system such as this can be used to study samples of molecules with vapor pressures lower than 10" mmHg at room temperature. 

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