RU2308117C2 - Analyzing method using hyperboloid mass spectrometer of three-dimensional ion trap type - Google Patents

Abstract

FIELD: hyperboloid mass spectrometry; development of high-definition and high-sensitivity instruments.

SUBSTANCE: proposed method for analyzing using hyperboloid mass spectrometer of three-dimensional ion trap type includes introduction of ions into trap space while varying electric field parameters (amplitude and frequency) In the process amplitude and frequency of high-frequency voltage applied across analyzer electrodes so that operating point of ion being analyzed will not change its position

where U(t) is peak-to-peak amplitude and ω(t) is HF voltage frequency.

EFFECT: enhanced efficiency of ion entrapping without reducing range of masses recorded in taking one scan.

1 cl, 1 dwg

Description

The invention relates to the field of mass spectrometry and can be used to create hyperboloid mass spectrometers with high resolution and sensitivity.

A known method of analysis in a hyperboloid mass spectrometer of the type "three-dimensional ion trap", by which by selecting the parameters of the electric field limit the possible range of captured masses. Due to this, the necessary resolution of the device is realized. According to this method, the ions form in the working volume of the analyzer by ionization by an electron beam, after which the ions are sorted for some time necessary to achieve the desired degree of sorting, and then output to the measuring device [1].

The known method has several disadvantages, the main of which is the low efficiency of the use of the sample and the electron stream introduced into the analyzer. This leads to a significant decrease in the scanning speed of the mass range and exorbitant electronic load on the electrodes of the device, leading to a quick contamination of the latter and a limited service life of the analyzer.

A known method of analysis of ions in a hyperboloid mass spectrometer such as a three-dimensional ion trap, according to which ions are introduced from outside into the working volume of the analyzer and capture in a wide range of masses due to collisions of ions with molecules of a buffer gas [2]. In the known method, the above disadvantages are eliminated.

However, the known method also has several disadvantages, the main of which is the need for the presence of a buffer gas at a relatively high pressure (approximately 1 mTorr) in the working volume of the analyzer. The main function of the buffer gas in the known method is to reduce the kinetic energy of ions through collisions, resulting in a decrease in the amplitude of ion vibrations and compression of the ions to the center of the trap. Disadvantages: low efficiency of ion capture (at a pressure of 1 mTorr - about 0.2%) and discrimination of ions by mass.

There is a method of analyzing ions in a hyperboloid mass spectrometer such as a three-dimensional ion trap, according to which ions are introduced from the outside into the trap volume simultaneously with a change in the amplitude of the RF voltage applied to the analyzer electrodes [3]. The known method allows to reduce the required pressure of the buffer gas, to increase the efficiency of ion capture by more than an order of magnitude and to compensate for the discrimination of ions by mass.

However, the known method has a significant drawback. Changing the parameters of the electric field leads to a significant change in the position of the working points of the ions on the stability diagram. Thus, by the known method, an increase in the sensitivity of hyperboloid mass spectrometers is accompanied by a significant decrease in the range of captured masses within a single scan.

The aim of the present invention is to eliminate the disadvantage of this method, increasing the sensitivity of hyperboloid mass spectrometers of the type "three-dimensional ion trap" without reducing the range of captured masses within a single scan.

This goal is achieved by the fact that ions are introduced into the working volume of a three-dimensional ion trap, to the electrodes of which an RF voltage is applied, they are accumulated there, while the working points of the analyzed ions are placed in a stable region of the overall stability diagram, and the accumulated ions are removed from the volume of the trap into the detector system by transferring their operating points to an unstable region by changing the parameters of the electric field: the amplitude or frequency of the RF voltage. In this case, the introduction of ions into the volume of the trap is carried out simultaneously with a change in time of the amplitude and frequency of the RF voltage applied to the analyzer electrodes. The change in the amplitude and frequency of the RF voltage is carried out in such a way that the working point of the analyzed ion on the stability diagram does not change its position. Such a change is possible subject to the following ratio:

- частота ВЧ напряжения, прикладываемого к электродам анализатора, соответственно.where U (t) is the amplitude and

- the frequency of the RF voltage applied to the electrodes of the analyzer, respectively.

In this case, according to the proposed method, the amplitude of ion vibrations introduced into the volume of the analyzer of a hyperboloid mass spectrometer while increasing the amplitude and the square of the frequency of the RF voltage, is constantly reduced for all ions whose operating points lie inside a stable region. Moreover, as shown by the results of the analysis, the capture efficiency of ions by this method is equivalent to the capture efficiency by a known method, however, the range of captured masses per scan covers the entire stable region. Thus, the proposed method of analysis allows the capture of ions with high efficiency without reducing the range of captured masses.

The drawing shows the dependences of the amplitudes of the oscillations of ions in the r- and z-coordinates when changing the parameters of the electric field inside the analyzer by the proposed method. It can be seen that the oscillation amplitudes along the r and z coordinates are continuously decreasing (data obtained for a pulsed signal of the meander type).

The proposed analysis method allows significantly (more than an order of magnitude) to increase the sensitivity of devices without reducing the range of captured masses. The implementation of the proposed method does not cause difficulties.

LITERATURE

1. Sheretov E.P., Zenkin V.A., Boligatov O.I. Three-dimensional quadrupole mass spectrometer with accumulation / Instruments and experimental equipment, 1971, No. 1.

2. G. C. Stafford, P. E. Kelly, J. E. P. Syka, W. Reynolds, J. E. J. Todd, Int. J. Mass Spectrom. Ion Proces. 60 (1984) 85.

3. V.M. Doroshenko, R.J. Cotter. Method and apparatus for trapping ions by increasing trapping voltage during ion introduction. United States Patent No. 5399857, 1995.

Claims (1)

The method of analysis in a hyperboloid mass spectrometer of the type "three-dimensional ion trap", in which ions are introduced into the working volume of the trap to the electrodes of which an RF voltage is applied, accumulate there, while the working points of the analyzed ions are placed in a stable region of the general stability diagram, and output accumulated ions from the trap volume into the detector system by transferring their operating points to the unstable region by changing the electric field parameters, characterized in that the ions are introduced into the trap volume by one temporarily with a change in time of the amplitude and frequency of the RF voltage, the amplitude and frequency of the RF voltage changing in time so that the operating point of the analyzed ion in the stability diagram does not change its position

where U (t) is the amplitude,

- frequency of the RF voltage.

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