Apparatus for analytically determining organic substances

p0001The invention relates to a device for the analytical determination of organic substances which are present in concentrations up to the ppm and ppt range, by means of mass analysis, the materials are to be transferred from a reservoir into a mass analyzer, the reservoir via a metering device directly to the mass analyzer connected and the mass analyzer, a quadrupole mass spectrometer with a channeltron electro-multiple and mass correction diaphragm (see Patent application Federal Republic of Germany P 35 10 378.7-52).

p0002The analytical determination of organic chemicals in the gas phase is accompanied from well-known reasons of great difficulties, exert a direct influence on the concentration limits of the measured chemicals. The conventional methods put in many cases requires an enrichment step. During this complicated procedures but can lead to significant errors, since both the sampling and compression are not standardized. For sample transport occur great losses of substance when used for this purpose gas mice or spraying. It should be remembered also that in case of a gas phase reaction naturally continue the reactions during transport, which is directly coupled to the distortion of the final results. In rare cases, the detection and identification methods are satisfactory combined directly with the sample chamber or recipient, the known systems operate on the basis of special spectroscopic methods.

p0003There are currently not even systems for direct determination of the chemical composition of the gas phase mixtures without enrichment in the ppb range. The direct use of mass analyzers is also unsuitable for such detection ranges, since their operating parameters, such as the operating pressure range from 1.3332 · 10⁻² - 1.3332 · 10⁻⁴ Pa (10⁻⁴ - 10⁻⁶ Torr), such a high noise / signal gives a ratio that the or less present in the ppb range substances can not be detected. A reduction of the operating pressure to values ​​below 13332 · 10⁻⁴ Pa (10⁻⁶ Torr), which would come close to the desired measuring range, would only cause that both the noise and the measurement signal are eliminated.

p0004The the object underlying the invention is to design the ec means such that even substances that are present in the ppm to ppt range, can be directly detected by mass analysis.

p0005The solution is described in the present invention in the characterizing feature of claim 1.

p0006The further claims disclose advantageous embodiments of the invention.

p0007The invention is particularly useful for determining the photostability of volatile organic compounds (eg, environmental chemicals, concentration-/ time graphs half-lives, reaction rate constants.), The photostability difficult vaporizable compounds (environmental chemicals that are counted among the 1,2-diketones; with the resulting CO a detection limit of 200 ppt), the airborne concentration of organic chemicals in a manufacturing plant (benzene and 1,2-trans-dichloroethylene concentration; detection limit 100 ppt - 5 ppb), the concentration of organic chemicals in enclosed spaces (pentachlorophenol detection in offices; 40 ug / m - 55 g / m³), ​​analysis of aqueous and solid samples (benzene detection from the river Goldach / Kreis Erding; detection limit 10 ppb; and CO₂ proof from the carrier material (silica, alumina neutral, Montmorillonid, sands from Tulorosa, Egypt, Libya and Saudi Arabia to the Mineralisierungsexerpimenten under standardized conditions; Detection limit for CO₂ least 100 ppt)) as well as the concentration of toxic substances in inhalation chambers (biacetyl, benzene, carbon tetrachloride, Freon 11 and 12, benzaldehyde, chlorobenzene and 1,2-trans-dichloroethylene; detection limit of at least 100 - 500 ppt)...

p0008Areas of application, the blood alcohol determination, determination of volatile compounds in the urine (eg ketones), determination of chlorinated hydrocarbons in fat tissue, determination of volatile products from the sewage sludge, waste slag and fly ash, monitoring of road and urban air are (all pollutants, including nitrogen oxides, sulfur dioxide and organic environmental chemicals in the air), control of exhaust gases from combustion engines and their proper identification and quantification, verification of the completeness of the gas phase reaction in the chemical industry (eg ammonia synthesis), thermal decomposability of market products from the semiconductor industry, the determination of hydrogen, helium, nitrogen and other gases in different areas of the industry and the control of the thermal decomposition of organic environmental chemicals in waste incineration and pyrolysis processes.

p0009The invention will be explained in the following 1 and 2 using an exemplary embodiment by means of Figs. More detail.

p0010Apparent from Fig. 1 system essentially consists of 3 parts, namely a vacuum controllable recipient part 1, an optimized Massenanalysatorsystem 2 and a special separator system 3.

p0011The recipient Part 1 consists of a spherical glass reactor 4 with variable recipients sizes range 1 - 400 liters, additional inserts, eg irradiator 5, for various purposes. The recipient is surrounded by a heating jacket 6, the temperature ranges allows up to 200 ° C. The entire system 1 can 7 (here Galileo PT-60) down to 1.3332 · 10⁻⁶ Pa (10⁻⁸ Torr) to be evacuated using a turbo molecular pump. By using a viton sealed gate valve of the reaction chamber 8 can be separated from the pump stand (backing pump 9: Edwards E2 M8). After reaching the desired pressure can be brought into the gas phase with the substances from the intake system 10, the samples or sample components and their concentration can be determined by means of the pressure measurements. The intake system 10 is composed of a noble metal housing 4 Vakuumabdichtbaren openings. From the upper side it is provided with a spring-loaded metal rod 11, by means of which the volatile samples that are in standardizable capillaries, may be mechanically released. For solid samples porcelain are available. Below the inlet system 10 a variable gas valve combination 12 (CJT vacuum technology, Ramelsbach) is housed, which has the task of gaseous samples monitored in the reactor 4 involved.

p0012The recipient Part 1 provides job opportunities in the printing areas 133.32 - 1.3332 · 10⁻⁶ Pa (1 - 10⁻⁸ Torr) and in different pressure ranges with different recipients volume using gas or gas mixtures.

p0013When optimized Massenanalysatorsystem 2 with the special separator element 3, a quadrupole mass spectrometer 13 (UTI, 10-02) is used, by installing a chan eltron-electro-multipliers 14 with a mass correction diaphragm 15, and by incorporating an ion pump 16 (Varian Vacion 8 l / s is modified), wherein the ion pump 16 is mounted perpendicular to the Massenanalysatorturbomolekularpumpeneinheit 17th The optimal operation of the plant was evaluated by the following points:<ul><li>a) sealing of the entire system by means of the pressure rise measurements against time, with the maximum allowable leak rate of 1 x 10⁻³ Pa · 1.3332 l / s (1 x 10⁻⁵ Torr l / s) and</li><li>b) Sensitivity measurements on the quadrupole 13 using the reference compounds, benzene, chloroform and diacetyl, wherein a detection limit of at least 100 ppb is achieved.</li></ul>

p0014The mass analyzer 13 is usually in the pressure range between 1.3332 · 10⁻² - operated 1.3332 · 10⁻⁴ Pa (10⁻⁴ and 10⁻⁶ Torr). The detection of the ions, both those of the substances to be tested as well as the other gas components (impurities) is effected by means of a secondary electron multiplier. If concentrations of the substances in the ppb and ppt range are detected, it is not enough simply to increase the vacuum range in mass 13 accordingly, since the signal / noise ratio makes it impossible in this case the measurement. On the other hand, although a mere reduction in pressure in turn would ensure clean measurement conditions, in the present case but would prevent the detection of substances since their concentration would be lowered accordingly in the ion source. In the invention, even the pressure range of the mass analyzer 13 in areas of 1.3332 · 10⁻⁷ Pa (10⁻⁹ Torr) is depressed so that the noise disappears, but by using the chan eltron-electromultipliers 14 with mass correction diaphragm 15 the sensitivity of detection considerably improves the fabrics. It created virtually pure spectra of the substances.

p0015The mass correction diaphragm 15 is not located directly at Canneltron 14 but is inserted between the input to the turbo molecular pump 17 and the access to the ion pump 16, ie below the ion pump 16. This location is particularly convenient, as a placement above the ion pump could delay the cleaning process unnecessarily.

p0016The mass correction diaphragm 15 serves to regulate and increase the relative probabilities and concentrations of the individual molecules in the analyzer 13. To this end, its passage opening 31 is variable in diameter, either manually or automatically adjustable. It has a structure which may correspond to an iris diaphragm of an optical camera. The regulator 32 for the mass correction diaphragm 15/31 can either manually (switch position 43 to position 33) or automatically (position 34) are operated.

p0017In automatic operation, it is connected via a control unit 35 and an interface 36 to a processor unit 37 in conjunction. This processor unit monitored or controlled by a further control unit 38 to the regulator 39 for the channeltron 14 when the switch 40 is switched to the position 41 (automatic) 37th The position 42 is again intended for manual operation.

p0018The variable mass correction diaphragm 15 is controlled in cooperation with the channeltron 14 of the processor unit. This action (open or close the passage opening 31) leads to the change in intensity of the fragment ions of the respective, compounds to be measured. substance-specific settings of the passage opening 31 in order to optimize the detection limit required for each pressure range. Unlike all previous devices in which the passage opening is constant at a value z. B. for nitrogen, can be found therefore for each compound to be detected automatically, the optimum setting of the mass correction diaphragm 15.

p0019This is illustrated in FIG. 2 It shows the pattern of intensity in% relative to the surface of the passage opening 31 of the mass correction diaphragm 15 mm² / 100 for the compounds benzene (curve 44) and trichlorethylene (curve 45). The pressure is (2.2 x 10⁻⁶ Torr) set at 2.933 · 10⁻⁴ Pa. Both curves 44 and 45 illustrate that in each case an optimal passage area (maximum), z. B. approximately 54 mm² / 100 and about 42 mm² / 100, for the measurement is automatically adjustable. The outer diameter of the mass correction diaphragm 15 is 48 mm, its thickness 2 mm.

p0020After the optimum setting of the mass correction diaphragm 15 by means of the processor unit 37 and increases the control unit 38 on the output voltages of the channeltron 14 the intensities of the mole and fragment ions. Here all the belonging to a fragment peaks are registered cumulatively through targeted reduction in the resolution.

p0021The separator element 3 between the reactor 4 and the Massenanalysatorsystem 2 is composed of three needle valves 28-20, which can be combined both in series and parallel. The needle valve 18 is closed under normal conditions, ie, the pressures are in the reactor 4 through 1.3332 · 10⁻⁴ Pa (10⁻⁶ Torr) and the concentration of the test substances is correspondingly high. Then, the dosage via the two Reduziernadelventile 19 must be 20 carried out continuously, so that both the pressure and the concentration of the substances in suitable for the mass analyzer 13 value ranges are. In the event that this value ranges already prevail in the reactor 4, can be connected directly via the needle valve 18th

p0022To carry out the experiments spherical reactors 4 can be used Pyrex glass, wherein the light source 5 different lamp types can be used. When using the gas-phase Massenanalysatorsystems 2 the following test scheme is adhered to:<ul><li>1. inclusions of air-free substances in capillary tubes.</li><li>2nd generation of vacuums in the chamber 1 down to 1.3332 · 10⁻⁵ - 1.3332 · 10⁻⁶ Pa (10⁻⁷ - 10⁻⁸ Torr).</li><li>3. dosage of the chemicals from the intake system 10 into the reactor 4 to the initial concentrations (1-25 ppm).</li><li>4. stabilization of the mass analyzer 13 to the specified concentration. </li><li>5. actuating the light source 5 to the burn-in of the lamp.</li><li>6. measuring the decrease of the starting compounds and detecting the formation of photoproducts using the optimized Massenanalysatorsystems. 2</li></ul>