RU2105299C1 - Method of analysis of microimpurities in atmospheric air - Google Patents

Abstract

FIELD: analytical chemistry. SUBSTANCE: method of analysis of microimpurities in atmospheric air includes ionization of analyzed gas, separation of formed ions in periodic, variable electric field asymmetric in polarity, selection and registration of ions. Value of intensity of electric field is chosen within range from 0.8 kV/mm up to value of intensity corresponding to break-down of analyzed gas. EFFECT: increased reliability of method. 2 cl, 3 dwg

Description

 The invention relates to the field of analytical chemistry, in particular to methods for analyzing impurities in a gas based on ionic mobility. Specifically, the proposed method can be used to create, on its basis, portable operational means for detecting explosives, drugs, carcinogens by their gas emissions.

 A known method for the analysis of impurities in gases, including ionization of the analyzed gas flow, separation of the ions obtained by a system of intersecting and perpendicular electric fields and gas flow velocity fields and registration of ions, (see, USSR AS N 528503, class N 31/08).

 The separation of ions in the known method is based on the difference in the mobility of ions of different grades when they move under the influence of an electric field and a velocity field of a gas stream, an ion with less mobility is carried away by the gas stream and more likely to overcome the effect of the gas stream velocity perpendicular to the vector.

 The disadvantage of this method is the low selectivity of separation, due to the threshold nature of the cutoff of ions by their mobility. This leads to the fact that, along with target ions with a certain mobility, ions with a similar and lower mobility are recorded.

 Closest to the proposed method is the analysis of trace gases in gases, including ionization of the test gas, separation of the formed ions in an alternating, periodic, asymmetric in polarity field, selection and registration of ions (see AS USSR N 966583, class G 01 N 27/62) .

 The selectivity of the known method is based on the effect on the ions of an alternating, periodic, asymmetric in polarity electric field.

 The disadvantage of this method is its relatively low analysis selectivity.

 The aim of the present invention is to eliminate this drawback, namely increasing the selectivity of the analysis.

 The specified goal in the method of analysis of microimpurities in atmospheric air, including ionization of the test gas, separation of the formed ions in an alternating, periodic, asymmetric in polarity electric field, selection and registration of ions, is achieved by the fact that the amplitude of the alternating, periodic, asymmetrical in polarity of the electric field E choose in the range from 0.8 kV / mm to the field value corresponding to the electrical breakdown of the test gas.

 The separation of ions in an alternating, periodic, asymmetric in polarity, high-intensity electric field in the specified range can significantly increase the selectivity of the analysis of trace elements in atmospheric air.

 To simplify the implementation of the method, an alternating, periodic, asymmetric in polarity electric field is created by a superposition of periodic alternating and constant electric fields.

 To simplify the implementation of the method, the separation of ions is carried out in crossed alternating, periodic and constant electric fields.

 The inventive method can significantly increase the selectivity of the method, based on the separation of ions by mobility, and has no analogues in the technique of gas analysis, which confirms the "inventive step" of the proposed method.

 In an atmosphere of air with the presence of water molecules and other polar molecules, a molecular “fur coat” is formed around the ions of the test gas in a finite time — an ionic cluster from this medium that changes the mobility of the ions. When exposed to an ionized gas, for example, ions in atmospheric air, which is under normal conditions (pressure and humidity), by an alternating electric field, the movement of positive and negative ions occurs in two opposite directions. During this movement, the spherical symmetry of polar molecules such as water is broken. due to the viscous forces arising from the motion of an ion coated with a molecular "coat", the atmosphere surrounding the ion is deformed and breaks down.

 To eliminate this molecular "coat" significant efforts are required on the part of an alternating electric field acting on ions. Under this condition, ions move in a dense medium so fast that the formation of an ionic atmosphere substantially decreases on its path and, as a result, additional electrical inhibitory forces do not appear, and the ion freed from screening exhibits its specific properties, which underlie gas analysis in separation of ions by mobility under normal conditions.

 Thus, in order to free the ion from the shielding sticking of polar molecules and to analyze microimpurities in a gas under normal conditions, it is necessary to influence the ions with an alternating, periodic, asymmetric in polarity high-intensity electric field.

 The upper boundary of the amplitude amplitude of an alternating, periodic, asymmetric in polarity electric field is limited by electric breakdown in air and depends on many parameters (shape of electrodes, frequency of electric field, gas pressure, impurity content in gas, etc.). For dry air, it does not exceed 3 kV / mm. For example, a breakdown in dry air between plane-parallel electrodes, to which an alternating voltage from 50 Hz to 300 MHz was applied, was experimentally studied, measurements were carried out at an air pressure of 50 to 1000 mm Hg. (see J. Mick, J. Kregs Electric breakdown in gases. - M .: Foreign literature, 1960, 605 p.). It was found that when using an alternating electric field, the magnitude of the electric field at which breakdown occurs has a complex dependence that decreases with increasing field frequency.

 The lower limit of the amplitude of the intensity of an alternating, periodic, asymmetric in polarity electric field is limited by the selectivity of the method.

In FIG. Figure 1 shows the ionograms of dried atmospheric air in the presence of vapors of 2,4,6-trinitrotoluene (TNT) with a concentration of 10 ** (- 13) g / cm ³ . The a - ionogram is recorded at E = 0.8 kV / mm, b - at E = 1 kV / mm, c - at E = 1.2 kV / mm, d - at E = 1.4 kV / mm. From FIG. 1 it follows that with increasing amplitude of the alternating, periodic, asymmetric in polarity of the electric field selectivity of the analysis increases. If, for case a, TNT pairs (marked with an asterisk in Fig. 1) resolve poorly against atmospheric air, then for cases c and d the resolution of the method is quite high.

 Very close in position to the response to TNT pairs is the response to iodine (J) pairs. In FIG. Figure 2 shows how air ionograms with an admixture of iodine and TNT vapor change when the amplitude of an alternating, periodic, asymmetric in polarity electric field changes from 1.8 kV / mm (ionogram a) to 2.0 kV / mm (ionogram d) through 0 , 05 kV / mm. If the responses merge at E = 1.8 kV / mm, then peaks are well resolved even at E = 2 kV / mm.

 Thus, the selectivity of the analysis increases with increasing amplitude of an alternating, periodic, asymmetric in polarity electric field. The lower limit of the amplitude amplitude of an alternating, periodic, asymmetric in polarity electric field is limited to 0.8 kV / mm, less than which the improvement in the resolution of the selectivity of the method does not occur in comparison with the known method. The upper limit of the amplitude of an alternating, periodic, asymmetric in electric field strength is limited by the electrical breakdown of the test gas.

 In FIG. 3 presents a block diagram of a device that implements the proposed method for the analysis of trace elements in atmospheric air.

 The device (Fig. 3) that implements the method includes a flow channel 1, containing sequentially arranged ionization chamber 2, ion-separating device 3, made, for example, in the form of two parallel electrodes 4 and two parallel electrodes 5 located perpendicular to the electrodes 4, and registration system 6. Electrodes 4, 5 form a drift gap. In principle, the electrodes 4 and 5 can be combined with each other. The device also contains a source of alternating, periodic, asymmetric in polarity voltage 9, connected to the electrodes 4, formed in parallel connected source of alternating, periodic voltage 6 and a constant voltage source 7. A source of constant compensating voltage 8, is simultaneously connected to the electrodes 5 and the registration system 6.

 The analysis is carried out as follows. The analyzed mixture of microimpurities passes through the ionizer 2, where it is ionized and after separation in the drift gap enters the registration system. By changing the value of the compensating voltage from the source 8, applied simultaneously to the parallel electrodes 5 and the recording system 6, the conditions for the selection of ions in the drift gap are successively changed and at the same time the current of ions that have not deviated under these conditions is measured, recording the entire spectrum of the ions formed from the mixture in the form of ionograms or dependencies ion current from the value of the compensating voltage. The magnitude of the amplitude of an alternating, periodic, asymmetric in polarity electric field is selected in the range from 0.8 to 3 kV / mm.

 The implementation of the source of alternating, periodic, asymmetrical in polarity voltage in the form of two parallel-connected sources of alternating, periodic voltage and constant voltage allows you to most easily implement the device 9, choosing different ratios of amplitudes of alternating, periodic voltage and constant voltage to change the degree of asymmetry of alternating, periodic, asymmetric in voltage polarity, the most simple and quick change the frequency of the periodic voltage.

 To simplify the implementation of the separation of ions produced in crossed alternating, periodic, symmetrical in polarity electric field and constant electric fields.

 The developed device layout fully confirmed the advantage of the proposed method. Thus, the inventive method, allows you to create gas analyzers with high resolution.

Claims (3)

 1. The method of analysis of microimpurities of substances in atmospheric air, including ionization of the test gas, separation of the formed ions in an alternating, periodic, asymmetric in polarity electric field, selection and registration of ions, characterized in that the amplitude of the alternating, periodic, asymmetric in polarity of the electric field E choose in the range from 0.8 kV / mm to the field value corresponding to the electrical breakdown of the test gas.  2. The method according to claim 1, characterized in that the alternating, periodic, asymmetric in polarity electric field is created by a superposition of periodic, alternating and constant electric fields.  3. The method according to claim 1, characterized in that the separation of ions is carried out in crossed alternating, periodic, symmetric and constant electric fields.

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