RF spark

Due to the relative uniformity of ion formation by the RF spark (although its timing is erratic), the most widely used method of quantitation in SSMS is to assume equal sensitivity for all elements and to compare the signal for an individual element with that of the total number of ions recorded on the beam monitor. By empirically calibratii the number of ions necessary to produce a certain blackness on the plate detector, one can estimate the concentration. The signal detected must be corrected for isotopic abundance and the known mass response of the ion-sensitive plate. By this procedure to accuracies within a factor of 3 of the true value can be obtained without standards. 

Ionization and fragmentation of materials by a variety of means, principally by electron bombardment, or the softer techniques of chemical ionization, field ionization or fast atom bombardment. Analysis of the range of mass fragments produced. Elemental composition of non-volatile materials by application of an RF spark. 

Spark source mass spectrometry is used for the examination of non-volatile inorganic samples and residues to determine elemental composition. An RF spark of about 30 kV is passed between two electrodes, one of which may be the sample itself, causing vaporization and ionization. Powdered samples or residues from ashed organic materials can be formed into an electrode after mixing with pure graphite powder. 

Instrumentation. The instrument used in this investigation was a commercial Mattauch-Herzog mass spectrometer equipped with photographic and electrical detection systems and an RF spark source. The resolution of the instrument was 1 part in 5,000. All trace elements were determined from mass spectra recorded on Ilford Q-2 photographic... 

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. 

The spectra produced by the rf spark are quite simple. Ions produced by the spark are accelerated into the analyser region, are mass separated, and fall on the photoplate where a latent image is generated and later developed. Figure 4 shows a series of mass spectra generated from a silicon sample and is chosen to illustrate most of the common ion types. Singly and multiply charged species can be seen as well as compound ions and molecular ions. The... 

D. L. Malm, RF Spark Source Mass Spectrometer for the Analysis of Surface Films. 

Fig. 6. Rf spark mass spectrum of a high duty steel sample. It shows eleven spectra with graded sensitivities caused by different exposure times -...

In this method, a pulsed RF spark is used to produce an ion beam, which is resolved into the individual masses (elm) in a double focussing mass spectrometer, with the masses being recorded either photographically or electrically. 

Fig. 15.6. RF spark source. Reproduced from Ref. [7] with permission. John Wiley Sons Ltd, 2008.

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