DE102011009503A1 - Method for detection environmental pollutants that are organophospherous compounds, particularly nerve agents, involves sucking gaseous environmental samples - Google Patents

Abstract

The method involves sucking gaseous environmental samples. The measurements are executed such that an environmental sample is analyzed with added ammonia in a measurement and in another measurement an environmental sample is analyzed without added ammonia. A proton transfer mass spectrometer (PTRMS)-analytical apparatus is used with a supply device for adding ammonia as auxiliary chemical product in the environmental sample. An independent claim is also included for a device for executing a method.

Description

The invention relates to a method and apparatus for detecting environmental toxins with a proton transfer mass spectrometer (PTRMS) analyzer. With a PTRMS, environmental samples can be analyzed almost online, or at least close to real-time.

• • Das IMS erbringt nur relative Signalarme und schlecht aufgelöste Spektren. Weil sich die geräteintern generierten IMS-Spektren von hochtoxischen Zielsubstanzen und potenziellen harmlosen Störstoffen häufig überlappen, kommt es zu einer relativ hohen Fehlalarmrate, die im Einsatz inakzeptabel ist. Durch Zusatz von Ammoniak werden jedoch beim Ionisationsprozess ganze Substanzgruppen ausgeblendet, wodurch diese als potenzielle Störstoffe entfallen und Fehlalarme reduziert werden.
• • Bei einem IMS wird ein interner Luftkreislauf geführt, in den die Probenluft eingespeist wird. Der Ammoniak, der in der Regel bei Kampfstoffdetektoren verwendet wird, entstammt einem Salz, in der Regel Ammoniumcarbamat. Dieses Salz zersetzt sich langsam und setzt dabei neben Kohlendioxid eben auch Ammoniak frei. Aufgrund des Luftkreislaufes reichen die Ammoniakspuren aus dem Salz aus, um die gewünschten Ammoniakkonzentrationen zu erzielen. Bei der Ionenmobilitätsspektrometrie stört die Luftfeuchtigkeit. Deshalb besitzen solche Geräte auch sogenannte Trockenfilter, in der Regel Molekularsiebe, über die der interne Kreislauf geführt wird.
• • Das Ammoniak setzt sich im IMS-Gerät fest, weil das Gerät mit Normaldruck arbeitet und der Ammoniak deshalb an den Wandungen anhaftet. Es dauert normalerweise viele Stunden, um ein IMS-Gerät vom Ammoniak freizuspülen.

In another analyzer, an ion mobility spectrometer (IMS), it is known to use ammonia as an auxiliary chemical.

• • The IMS provides only relative signal arms and poorly resolved spectra. Because the in-house generated IMS spectra of highly toxic target substances and potentially harmless contaminants often overlap, a relatively high false alarm rate is observed, which is unacceptable in use. By adding ammonia, however, entire groups of substances are hidden during the ionization process, eliminating them as potential contaminants and reducing false alarms.
• • In an IMS, an internal air circuit is fed into which the sample air is fed. The ammonia, which is typically used in warfare detectors, comes from a salt, usually ammonium carbamate. This salt decomposes slowly and releases ammonia as well as carbon dioxide. Due to the air cycle, the traces of ammonia from the salt are sufficient to achieve the desired ammonia concentrations. In ion mobility spectrometry disturbs the humidity. Therefore, such devices also have so-called dry filters, usually molecular sieves, over which the internal circuit is performed.
• • The ammonia gets stuck in the IMS unit because the unit operates at normal pressure and the ammonia sticks to the walls. It usually takes many hours to purge an IMS device of ammonia.

The invention has the object of providing a method and an apparatus for detecting environmental toxins using a PTRMS device in such a way that a secure, accurate evaluation can take place.

This object is achieved on the one hand by the features of method claim 1 and on the other by the features of the device claim 2.

The advantages of the invention therefore result that two measurements are carried out successively. One measurement refers to an aspirated environmental sample with added ammonia. Another measurement refers to an environmental sample without added ammonia. Measurements with and without ammonia provide additional information that increases detection reliability and reduces false alarms. The method and apparatus is suitable for the detection of organophosphorus compounds. These include nerve agents, but also very many insecticides and pesticides, eg. B. also the well-known E605. Highly toxic compounds can be identified real-time and with great certainty.

If the environmental sample ammonia has been added, a mass-selective measurement of the ammonia-containing environmental sample is carried out in the PTRMS device. The ammonia serves as an auxiliary chemical and interferes with the ionization processes that take place in the device for analysis. The spectra are much clearer and thus easier to evaluate. Above all, the ammonia prevents the fragmentation, ie a breakage of the chemical molecules in the ionization. Only then do the spectrometer generate signals that are highly specific for, for example, nerve agents and that allow a secure identification by the system. In this respect, the auxiliary chemical serves to reduce unwanted false alarms.

If the PTRMS is operated without ammonia and at high drift tensions, then the drug molecule breaks up, fragmenting it. The fragment is characteristic for the chemical substance class, but not for the warfare agent. The emergence of this fragment could thus also be a harmless member of the chemical class of substances or a completely different compound that happens to have this molecular weight. This would then lead to a false alarm in the facility. A clear identification based only on the detected fragment is therefore not possible.

Ammonia prevents fragmentation. Thus, the warfare agent is detected as a whole molecule, which significantly increases the detection security. Nevertheless, there remains a residual risk of false alarms. There are natural and environmental substances conceivable, which could again coincidentally have a molecular weight that is identical to that of a warfare agent. That too would lead to a false alarm. However, if one recognizes the molecular weight of, for example, a warfare agent with the auxiliary chemical ammonia and then shuts off the ammonia, then fragmentation sets in and the fragment of the molecule on the chemical substance class, here the methylphosphonate, indicates instead of the warfare agent. This additional information further increases the detection reliability. As a result, environmental toxins in the ambient air can be measured and identified with high quality.

It is preferable that in the sequential measurements, a measurement of an environmental sample with added ammonia takes place first, because a fragmentation is suppressed. After an alarm triggered by the device in the ammonia mode, the supply of ammonia is automatically interrupted and then carried out a verification measurement without ammonia.

In principle, the reverse procedure is also conceivable, namely to measure permanently without ammonia and only after the occurrence of special molecular fragments, which could originate from organophosphorus compounds, to begin with the ammonia dosage.

With a PTRMS humidity is needed. To enrich the air with moisture is a storage container in the device. This makes it possible in the context of training the supply of ammonia in a simple manner to pass air through aqueous ammonia solutions and this enriched gas stream simply add the circulating air sample.

A PTRMS device works internally with a negative pressure of less than 50 mbar, preferably less than 10 mbar. As a result, ammonia attachment effects are reduced and rapid switching back and forth between ammonia and non-ammonia operation is enabled.

For PTRMS devices, the resolution is very high. In this respect, hiding substance classes, as in an IMS, not required. However, organophosphorus compounds, such as nerve agents, tend to fragment in the PTRMS. Although this can be partially compensated by a reduction in the so-called drift voltage, this is disadvantageous for the ionization processes, in particular with regard to the substance quantification. The addition of ammonia suppresses fragmentation in the PTRMS ionization process, allowing even the high drift rates favorable for these processes to be maintained.

The operation of the device is described below by way of example: gaseous environmental samples are continuously drawn in via an air inlet of the proton transfer mass spectrometer (PTRMS). An ammonia feed device connected to the air inlet on the PTRMS supplies ammonia to the environmental samples to prevent fragmentation.

The supply device has a shut-off device. This is automatically activated when a suspicion of environmental toxins is measured. This will be followed by a measurement without ammonia. One obtains measurement results concerning the fragments and not with respect to the starting materials, as in the previous measurement. The subsequent measurement without ammonia increases the detection reliability.

The device for detecting comprises an evaluation and identification algorithm that automatically evaluates the spectrums measured internally according to predefined criteria and alerts accordingly when environmental toxins are analyzed. The means for detecting can be used by soldiers under field conditions of use.

Hereinafter, embodiments of the invention will be described.

The chemical warfare agents (CWA) sarin, soman, cyclosarin and tabun were characterized by proton transfer mass spectrometry (PTRMS). It has been found that PTRMS is a suitable technique for detecting nerve agents in a highly sensitive, highly selective and near real-time manner. Furthermore, methods have been found which can suppress the molecular fragmentation significantly occurring in the hollow cathode ionization in the PTRMS. For this purpose, the drift voltage was varied as one of the most important parameters in this context. In addition, ammonia was introduced as a reactant gas. Auxiliary chemicals such as ammonia, so-called "dopants", have an influence on the gas-phase ionization processes and are very common in connection with the realization of ion mobility spectrometry (IMS) warfare agent detectors, albeit for other reasons and not necessarily to suppress molecular fragmentation. By both, the variation in drift voltage and the use of ammonia as the reactant gas, molecule fragmentation can be effectively suppressed. The suppression of fragmentation is essential, especially for real-time detection and the implementation of a detection algorithm for automatic identification in field applications. Downside is, however, that In extreme cases, substance identification must take place via a single peak, the so-called "single-peak recognition", which also entails uncertainties. However, certain fragments provide additional information and indicate what chemical class the analyte detected is, although the fragmentation and rearrangement products of nerve agents considered as fragments are generally not characteristic of the subject warfare agent. The reference to the chemical class in turn can serve to confirm the identification on the basis of the single-peak recognition or the unfragmented analyte. It has been found that it is easily possible to switch between ammonia and water gas phase chemistry within a few seconds and thus to switch between fragment and molecular ion spectrum. In this respect, a controlled fragmentation is useful for the most reliable substance identification, possibly also from more complex mixtures possible. PTRMS proved to be a promising analytical technology for the realization of future warfare agent detectors. In terms of sensitivity, response time and selectivity or identification reliability, PTRMS is in many ways a bridging technology between IMS and classical and gas chromatograph mass spectrometry (GC-MS). The PTRMS technology as well as the special device hardware from IONICON Analytik GmbH are described in a number of publications. [3-5]. Normally, water in the internal system atmosphere is used as the reactant gas. From this, H ₃ O ⁺ reactants are formed by hollow cathode ionization. The water comes from a reservoir from which the headspace is controlled via a mass flow controller. Under the influence of a voltage gradient, the reactant ions pass through a small opening in the adjacent drift tube section, into which the analyte is also fed via a gas inlet system. The analyte gas flow is set between 50 and 1000 ml min ^-1 and the temperature of the inlet system between 40 and 150 ° C. The working pressure in the drift tube is maintained between 2.2-2.4 mbar, while the drift tube voltage is usually varied between 400 and 1000 V and the drift tube temperature between 40 and 120 ° C. Within the drift tube, proton transfer reactions occur between reactant ions and the gaseous analytes, provided that the proton affinities of the analyte are higher than those of the reactant gas. The drift voltage has a significant influence on the fragmentation of the analyte or the formation of productions that arise through dissociative and non-dissociative proton transfer processes in the drift tube. Furthermore, the drift voltage is crucial to prevent the formation of higher reactant gas adducts of the type (H ₂ O) _n H ₃ O ⁺ with n = 1-4. The productions (protonated analyte and optionally fragment ions) are passed through an opening at the end of the tube, focused by means of a special lens system and fed to the mass spectrometric detector. The device type PTRMS high sensitive is based on a classic quadrupole mass filter detector. In the case of the PTR-ToF 8000, however, the m / z mass ratios are determined by measured flight times [6-7]. To carry out the experiments, the PTR systems were exposed to test gases of defined concentration. The test gases of nerve agents were prepared by special test gas generators, which are suitable for handling such toxic substances. These are based on a permeation process in which the target substances are sealed in plastic tubes. The small absolute amounts of warfare agent which permeate through the tube walls per unit of time pass into the ambient atmosphere of the closed system and are diluted in a corresponding volume by a stream of air passing the tube. The permeation rate is temperature controlled. Accordingly, the concentration is determined by the permeation temperature on the one hand and the flow rate of the diluent gas flow on the other hand, of course, the characteristics of the tube material and the tube dimensions have an influence on the absolute concentration. Starting from an analyte gas volume flow of 1 l min ^-1 , the generator flow rates or dilution gas flow rates were varied between 1.5-2 l min ^-1 according to the desired concentrations.

The main objective of the investigations was not to determine the actual detection limits for nerve agents using PTRMS, as this technique is recognized for its high sensitivity and real-time capability. Instead, the investigations aimed to investigate the ionization mechanisms, gas phase reactions and molecular rearrangements under the PTR ionization conditions in detail and to explore possibilities of control. In this aspect, a mid-three ppb level of warfare agent concentration was chosen to ensure adequate signal intensities. The PTRMS high sensitive was loaded at a concentration of 200 ppb and the PTR-ToF 8000 at a concentration between 500 and 1000 ppb. The adjusted concentrations were checked by GC-FPD.

Tabun (NATO acronym: GA) belongs to the chemical class of organophosphates (organophosphoric acid esters), while sarin and cyclosarine (NATO acronyms: GB, GD and GF) belong to the organophosphates (organophosphonic acid esters). The latter differ from each other only in terms of their page group groups. These are an isopropyl group in the case of sarin, a pinacolyl group in the case of soman, and a cyclohexyl group in the case of cyclosarin. Notwithstanding the structural similarities, the esters of phosphoric and phosphonic acids differ substantially in their physical properties, chemical stability and toxicity.

Results

Proton transfer reactions between a reactant H ₃ O ⁺ to an analyte A (eg a warfare agent) follow the fundamental equation: H ₃ O ⁺ + A → [A · H] ⁺ + H ₂ O

However, depending on the physical and chemical properties of the analyte, reactant gas adducts of the analyte may also occur: H ₃ O ⁺ + A + nH ₂ O → [A · H · (H ₂ O) _n ] ⁺ + H ₂ O

Adducts up to n = 2 were observed in connection with nerve agent measurements. In addition to the analyte properties, however, the drift voltage also has a significant influence on the formation of the different product adducts or production clusters. Moreover, the proton affinity of the reactant gas used (in the simplest case, water) has effects on fragmentation behavior and cluster stabilities. In addition to water, ammonia was also used as the reactant gas in connection with the present investigations. Since the ammonia was not introduced into the system instead of the water and also not directly into the hollow cathode region, but into the system together with the analyte gas stream, water-based reactant ions were initially formed in the hollow cathode even when measured with ammonia. However, as soon as these reactant ions reach the analyte / ammonia mixture in the drift tube, proton transfer to ammonia molecules takes place in a very rapid process, since ammonia has a very high proton affinity. In a subsequent process, these ammonia-based reactant ions react with the analytes to form the actual productions or production clusters.

The 1a - 1e show the PTR mass spectra of sarin at different drift voltages. The spectra were recorded with an unmodified PTRMS high sensitive from the company IONICON Analytik GmbH and without additional reactant gas, ie with "normal" water chemistry. The accumulation time per mass point m / z was 100 ms. The drift tube pressure was 2.1 mbar, the drift tube temperature 60 ° C.

At a drift voltage of 600 V, no molecule peak can be recognized by the sarin ( 1a ). Such would be expected at m / z 141 (140 + 1). Instead, a peak at m / z 99 dominates in the spectrum, at m / z 97 a very weak peak is visible. The latter probably correlates with the protonated methylphosphonic acid, which can be considered as the hydrolysis product of sarin.

The peak at m / z 99 is known from classical electron impact ionization (EI) of organofluorophosphonates:

Accordingly, both peaks (m / z 97 and 99) correspond to organophosphonate fragments or their rearrangement products. If the drift voltage is lowered to 500 V, but the analyte concentration is kept constant, the absolute intensity of the m / z 99 increases ( 1b ). The intensity of the peak at m / z 97, on the other hand, decreases slightly.

If the drift voltage is further lowered to 400 V, the intensity of the peak m / z 99 continues to increase, while the peak at m / z 97 almost completely disappears ( 1c ). At the same time, a peak appears at m / z 117, which corresponds to the water adduct of the m / z 99 molecule fragment. At m / z 141, a weak peak appears, which is due to the protonated sarin [GB · H] ⁺ .

In the drift voltage range between 300 V and 400 V, a point is reached at which the m / z 99 fragment, its m / z 117 fragment-water adduct and the protonated sarin (m / z 141) appear with approximately the same intensity ( 1d ). A weak peak at m / z 159 can also be seen. This corresponds to the protonated sarin / water adduct [GB · H ₂ O · H] ⁺ .

If this point is exceeded and the drift voltage further reduced to 200 V, the peak at m / z 99 disappears almost completely. The most intense peak of the spectrum is then m / z 141 (protonated sarin), followed by its water adduct, which gives a peak at m / z 159 ( 1e ).

The ionization of the unfragmented sarin is less effective than that of the major fragment at m / z 99. This is evident from the fact that the peak intensity of the m / z 99 at 400 V is significantly higher than the sum of the intensities of all peaks associated with unfragmented sarin in 200 V (m / z 141 and 159). In total, and separated from the ion species, a drift voltage of 400 V gives the highest total ion yield, which is detected by the mass spectrometer. However, at this drift voltage, the fragment ion peak at m / z 99 and its water adduct peak at m / z 117 dominate in the mass spectrum. At least under the conditions of the so-called water chemistry, ie as long as water molecules are the basis for the intermediately formed Reaktantionen, drift voltages of well below 400 V are required to avoid fragmentation. Since higher water clusters are formed at lower drift voltages, which adversely affects the overall ionization ratios, the suppression of fragmentation (in terms of identification performance) and the optimization of ionization efficiency (in terms of total ion yield and thus sensitivity) for organophosphorus compounds therefore stand in the way. In the literature, results of PTRMS experiments with drug simulants such as diisopropyl methylphosphonate (DIMP) are published. The results obtained with real warfare agents are thus consistent with regard to the general fragmentation behavior [7]. However, in the literature spectra, the peak at m / z 97, which corresponds to the protonated methyl phosphonic acid, dominates instead of the m / z 99 in real warfare spectra. The m / z 99 corresponds with the fluoromethylphosphonic acid and accordingly can not occur in spectra of non-fluorinated simulants (see above). It is further known from the literature that fragmentation by lowering the drift voltage can be effectively suppressed in simulation substances for organophosphonate-based chemical warfare agents [7]. However, the disadvantage of a drift voltage decrease is that larger reactant ion clusters of the type [H (H ₂ O) _n ] ⁺ with n to 4 occur (see above).

The results achieved with the warfare agent sarin and with water chemistry were confirmed with chemically related warfare agents and gave rise to further possibilities to deliberately manipulate the gas phase ion chemistry of nerve agents in the PTRMS. The variation of the drift voltage is primarily aimed at influencing the kinetic energy that ions can reach between molecular collisions in the gas phase. A lower drift voltage means a lower acceleration in the drift, in that a lower kinetic energy between two collisions and thus a lower probability of molecular fragmentation. Another approach is to reduce the mean free path between two bursts in the gas phase. This can be done by increasing the drift tube internal pressure. Effectively, with a smaller mean free path, the duration in which ions are accelerated between two bursts in the electric field of the drift tube and thus also the kinetic energy that the ions can acquire, is reduced. It quickly became apparent that the variation of this parameter (at least in the range made possible by the device manufacturer) does not significantly affect the fragmentation behavior of the target substances. Finally, ammonia was considered as a reactant gas. Ammonia is often used as a reactant gas, so-called "dopant" in ion mobility spectrometry, although for other reasons and not primarily to suppress molecule fragmentation.

In the 2a - 2e The sarin PTR spectra are shown at different drift voltages. The spectra were recorded with the same instrument, the same system settings and the same analyte concentration. The only difference was that ammonia was added to the analyte gas stream. A first approach of ammonia dosing to replace the water reservoir of the PTRMS by a source of ammonia was soon rejected, as this would be technically very complicated. Furthermore, it was found that it is not absolutely necessary to meter dry, gaseous ammonia from a compressed gas cylinder. Instead, it has proven expedient and easily feasible to pass a relatively small volume of air through a concentrated aqueous solution of ammonia and add this ammonia-enriched gas stream to the analyte gas stream prior to entry into the PTRMS. A flow rate of 50 ml min ^-1 through the aqueous ammonia solution proved to be appropriate. In view of the comparability of ammonia and water spectra with respect to the (total) ion yield and to eliminate dilution effects by the addition of the ammonia gas stream, a corresponding volume gas stream of dry air had been added in the "Water Chemistry Experiments". In this respect, the comparability of water and Ammoniakexperimenten.

As expected, the ammonia considerably influences the ionization processes in the PTRMS. At a drift voltage of 600 V hardly a fragmentation is observed. Instead, almost exclusively ion species contain unfragmented sarin, with the protonated sarin / ammonia cluster dominating [GB · NH ₃ · H] ⁺ at m / z 158 in the spectrum. The merely protonated sarin [GB · H] ⁺ occurs with a far less intense peak at m / z 158 ( 2a ).

If the drift voltage is successively reduced to 400 V, this has hardly any influence on the fragmentation behavior (in contrast to pure "water chemistry"). ( 2 B - 2c ).

Furthermore, at 400 V, another ammonia cluster with two attached ammonia molecules [GB · (NH ₃ ) ₂ · H] ⁺ with a weak peak at m / z 175 occurs. It can also be observed in the case of "ammonia chemistry" that the total ion yield reaches a maximum at a drifting voltage of 400 V ( 2c ).

The further reduction of the drift voltage to 200 V is associated with a reduction in the peak intensities of m / z 141 and m / z 158, whereas the intensity of the m / z 175 increases slightly ( 2d - 2e ).

As a result, it should be noted that fragmentation in the case of ammonia chemistry does not play a significant role in any applied drift voltage. Thus, fragmentation by using ammonia as a reactant gas could be effectively suppressed.

Further experiments were carried out with a PTR ToF 8000 from Ionicon Analytik GmbH. The aim was to investigate the comparability of quadrupole and time-of-flight mass spectrometer measurements in connection with PTR ionization conditions.

The 3a - 3c show sarin PTR-ToF spectra. The experiments were carried out analogously to the experiments with the PTRMS high sensitive Fa. IONICON. Accordingly, the drift voltages were varied between 600 V and 200 V for water and ammonia chemistry. Here, however, only the most relevant spectra are shown. In all PTR ToF mass spectra a fragmentation behavior of the Sarin's, which is comparable in the PTR quadrupole MS at first glance. Depending on the drift voltage and the type of reactant gas, productions based on fluoromethyl phosphonic acid and unfragmented sarin are formed in changing intensity ratios. However, in PTR-ToF-MS, in general, the reactant gas adducts of all ionic species are more abundant relative to the single protonated species than in the case of PTR quadrupole MS.

While the protonated fluoro-methyl phosphonate at m / z 99 in PTR quadrupole MS represents the only significant peak at 600 V drift voltage and pure water chemistry ( 1a ), the equilibrium in the PTR-ToF-MS is shifted towards the single and even double-clustered adduct (m / z 117 and 135) ( 3a ).

When the drift voltage is successively lowered to 200 V, the fragments disappear almost completely, with the singly water-clustered species dominating in the spectrum and the corresponding peak gaining intensity at m / z 159 ( 3b ). This occurs to a greater extent than in PTR quadrupole MS (cf. 1e ).

As soon as ammonia is applied as a reactant gas, an almost complete suppression of the fragmentation occurs independently of the selected drift voltage (by way of example) 3c at 400 V). Protonated sarin can only be observed at high drift voltages (not shown here). A reduction in the drift voltage causes the peak of the protonated sarin to disappear at m / z 141, leaving only the peaks of the singly and doubly ammonia-clustered sarin at m / z 158 and 175 in the spectrum.

Summary

It has been found that organophosphorous nerve agents tend to fragment under the ionization conditions of the PTR, whereas in Atmospheric Pressure Ionization (API), as in IMS, they form very stable, unfragmented ionic species. The extent of fragmentation can be reduced by lowering the drift voltage. More effective, however, is the use of ammonia as a reactant gas ("dopant") to suppress fragmentation. In any case, and independent of the choice of reactant gas, drift voltages of around 400 V provide the highest ionization efficiency and therefore the highest total ion yield. At this drift voltage and "water chemistry" fragmented nerve agents, however, almost completely. However, a real-time, unambiguous identification of the analyte based solely on molecular fragments is not possible. In this respect, the suppression of fragmentation for a unique identification is essential, especially as only a time-consuming Vortrennstufe, especially for the identification of multi-component mixtures, can be avoided. The introduction of ammonia chemistry solves this problem. In the case of ammonia-based reactant chemistry, no fragmentation occurs to any significant extent. Accordingly, only those production clusters are formed which contain unfragmented nerve agent. Thus, the optimum drift voltage of 400 V can be chosen for the ionization efficiency. On the other hand, the identification is then based solely on the molecular ions, which can form quite different production clusters, but in the core always consist of unfragmentiertem warfare agent. However, the identification is not based on a characteristic signal pattern. Although fragmentation is fundamentally unfavorable at first, it should be noted that certain fragments can certainly provide additional information and thus contribute to increasing the reliability of identification. Although fragments such as fluorophosphonic acid do not allow a clear identification of nerve agents, they are an indication of the presence of a nerve agent. Viewed from this perspective, targeted fragmentation in "water chemistry" in the gas phase can provide additional structural information and thus be useful for confirming mass information found in gas-phase "ammonia chemistry" for unambiguous identification. Of course, it is of course possible to operate a PTR system permanently in water chemistry and to change to ammonia chemistry as soon as certain fragments such as the fluorophosphonic acid appear. In contrast to the IMS, it is easily possible under the PTR ionization conditions at 2 mbar to switch back and forth between water and ammonia chemistry within a few seconds. The variation of the drift voltage as the most important system parameter in this context takes even less time. It is advantageous to realize the ammonia dosage via the analyte gas stream instead of replacing the native water reservoir with an ammonia source. First of all, the simple technical feasibility counts, but it also has other advantages: the initial ionization processes in the hollow cathode are not influenced by the option to add ammonia. This means that in any case only H ₃ O ^{+ are produced} as reactant ions and therefore models for calculating the analyte concentration remain valid even if ammonia is added in the drift tube. Regardless, the quick change is between ammonia and water chemistry in the first place possible in that two corresponding sources are basically available in parallel and available. Furthermore, PTR quadrupole and PTR ToF MS spectra were found to differ in detail even though they were recorded under identical experimental conditions and although the PTR hardware should be identical according to the manufacturer's instructions. In both water and ammonia chemistry, differences in the distribution ratios of protonated ionic species and their specific reactant gas adducts (single, double, and mixed clustered) were observed. In general, proportionally more reactant gas adducts appear in the ToF spectra than in the quadrupole spectra. Assuming that the PTR hardware is identical in both systems, the ion clusters should in principle appear in comparable intensity ratios. However, the differences actually observed indicate that the differences in the interfaces to the mass spectrometers and possibly the mass spectrometers themselves must be justified. Cluster stability also plays a role here. If this is true, it should be noted that a ToF-MS is more suitable for the detection of nerve agents than a quadrupole, since the total ion yield is higher overall.

Furthermore, it can be observed especially in water chemistry that the relative proportions of fragmented and unfragmented warfare agent or associated ion clusters in ToF and quadrupole are different. In general, less fragmentation was observed in the ToF than in the quadrupole. Since fragmentation and production take place in the drift tube, the observation of such differences may be an indication that there are differences in the PTR hardware used in both systems. Since uncontrolled fragmentation in this context is fundamentally unfavorable in PTR, this phenomenon also leads to the finding that PTR-ToF-MS is particularly well suited for the detection of nerve agents.

In summary, both PTR variants, PTR quadrupole MS and PTR-ToF-MS, are suitable for the detection of nerve agents, the most toxic agents among chemical warfare agents. These are detected highly sensitive, highly selective and near real-time. Finally, the PTR-ToF-MS v. a. Due to its sensitivity and detection speed, it is best suited as the base technology for future warfare agents. Assuming that also reactivated gas-clustered productions are relevant for determining the total concentration of the active substance, it is important that these species do not appear to be lost in PTR-ToF-MS or that they can be transferred to the detector with special care and recorded accordingly. PTR-ToF-MS also represents a remarkable and promising technology for future field-capable warfare agents in that it closes the analytical-technological gap between ion mobility spectrometry and classical GC-MS.

literature sources

1. Eiceman GA, Karpas Z. Ion Mobility Spectrometry 2nd Edition, Taylor and Francis 2005 ,

Second Sun Y, Ong KY. Detection Technologies for Chemical Warfare Agents and Toxic Vapor, CRC Press 2005 ,

Third www.ptrms.com

4th Müller M, Gray M, Wisthaler A, Hansel A, in: Hansel A, Märk T (eds.). Proc. 3rd Int. Conf. PTRMS and its Application, Innsbruck University Press (IUP): Innsbruck 2007 ,

5th Jordan A, Haidacher S, Hanel G, Hartungen E, Märk L, Seehauser H, Schottkowsky R, Sulzer P, Märk T, Int. J. Mass Spectrom. 2009; 286: 122 ,

6th Mayhew CA, Sulzer P, Petersson F, Haidacher S, Jordan A, Märk L, Watts P, Mark TD, Int J Mass Spectrom 2010; 289: 58-63 ,

7th Petersson F, Sulzer P, Mayhew CA, Watts P, Jordan A, Mark L, Mark T, Rapid Commun Mass Spectrom. 2009; 23: 3875-3880 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Sun Y, Ong KY. Detection Technologies for Chemical Warfare Agents and Toxic Vapor, CRC Press 2005 [0048]
• www.ptrms.com [0049]
• Müller M, Gray M, Wisthaler A, Hansel A, in: Hansel A, Märk T (eds.). Proc. 3rd Int. Conf. PTRMS and its Application, Innsbruck University Press (IUP): Innsbruck 2007 [0050]
• Jordan A, Haidacher S, Hanel G, Hartungen E, Märk L, Seehauser H, Schottkowsky R, Sulzer P, Märk T, Int. J. Mass Spectrom. 2009; 286: 122 [0051]
• Mayhew CA, Sulzer P, Petersson F, Haidacher S, Jordan A, Märk L, Watts P, Mark TD, Int J Mass Spectrom 2010; 289: 58-63 [0052]
• Petersson F, Sulzer P, Mayhew CA, Watts P, Jordan A, Mark L, Mark T, Rapid Commun Mass Spectrom. 2009; 23: 3875-3880 [0053]

Claims (3)

Method for detecting environmental toxins which are organophosphorus compounds, in particular nerve agents, in which a proton transfer mass spectrometer (PTRMS) analyzer is used and the PTRMS analyzer has a feed device for metering in ammonia as an auxiliary chemical, with the steps: Aspiration of gaseous environmental samples, • Performing at least two consecutive measurements, such that one environmental sample with added ammonia is analyzed in one measurement and one environmental sample without added ammonia in another measurement. Device which is designed to carry out the method according to claim 1 and has the following elements: A proton transfer mass spectrometer (PTRMS) as an analyzer having an air inlet through which gaseous environmental samples can be drawn, An ammonia feed device connected to the air inlet on the PTRMS as auxiliary chemical, That the supply device has a shut-off device, such that at least two successive measurements can be carried out, such that one environmental sample with added ammonia and in another measurement an environmental sample without added ammonia can be analyzed in one measurement. Device according to claim 2, that the shut-off device is automatically actuated, depending on whether a previous measurement indicates environmental toxins.

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