.DescriptionInjection flaws allow attackers to relay malicious code through an application to another system. These attacks include calls to the operating system via system calls, the use of external programs via shell commands, as well as calls to backend databases via SQL (i.e., SQL injection). Whole scripts written in Perl, Python, and other languages can be injected into poorly designed applications and executed. Any time an application uses an interpreter of any type there is a danger of introducing an injection vulnerability.Many web applications use operating system features and external programs to perform their functions. Sendmail is probably the most frequently invoked external program, but many other programs are used as well.
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When a web application passes information from an HTTP request through as part of an external request, it must be carefully scrubbed. Otherwise, the attacker can inject special (meta) characters, malicious commands, or command modifiers into the information and the web application will blindly pass these on to the external system for execution.SQL injection is a particularly widespread and dangerous form of injection. To exploit a SQL injection flaw, the attacker must find a parameter that the web application passes through to a database. By carefully embedding malicious SQL commands into the content of the parameter, the attacker can trick the web application into forwarding a malicious query to the database. These attacks are not difficult to attempt and more tools are emerging that scan for these flaws.
The consequences are particularly damaging, as an attacker can obtain, corrupt, or destroy database contents.Injection vulnerabilities can be very easy to discover and exploit, but they can also be extremely obscure. The consequences of a successful injection attack can also run the entire range of severity, from trivial to complete system compromise or destruction. In any case, the use of external calls is quite widespread, so the likelihood of an application having an injection flaw should be considered high.Environments AffectedEvery web application environment allows the execution of external commands such as system calls, shell commands, and SQL requests. The susceptibility of an external call to command injection depends on how the call is made and the specific component that is being called, but almost all external calls can be attacked if the web application is not properly coded.Examples. A malicious parameter could modify the actions taken by a system call that normally retrieves the current user's file to access another user's file (e.g., by including path traversal './' characters as part of a filename request).
Example of a GC-MS instrumentGas chromatography–mass spectrometry ( GC-MS) is an method that combines the features of and to identify different substances within a test sample. Applications of GC-MS include detection, investigation, environmental analysis, investigation, and identification of unknown samples, including that of material samples obtained from planet Mars during probe missions as early as the 1970s. GC-MS can also be used in airport security to detect substances in luggage or on human beings. Additionally, it can identify in materials that were previously thought to have disintegrated beyond identification. Like, it allows analysis and detection even of tiny amounts of a substance.GC-MS has been regarded as a ' for substance identification because it is used to perform a 100% test, which positively identifies the presence of a particular substance. A nonspecific test merely indicates that any of several in a category of substances is present.
Although a nonspecific test could statistically suggest the identity of the substance, this could lead to identification. Contents.History The first on-line coupling of gas chromatography to a mass spectrometer was reported in 1959.The development of affordable and has helped in the simplification of the use of this instrument, as well as allowed great improvements in the amount of time it takes to analyze a sample. In 1964, a leading U.S. Supplier of analog computers, began development of a computer controlled under the direction of.
By 1966 Finnigan and collaborator Mike Uthe's EAI division had sold over 500 quadrupole residual gas-analyzer instruments. In 1967, Finnigan left EAI to form the Finnigan Instrument Corporation along with Roger Sant, T. Chou, Michael Story, and William Fies. In early 1968, they delivered the first prototype quadrupole GC/MS instruments to Stanford and Purdue University. When Finnigan Instrument Corporation was acquired by Thermo Instrument Systems (later ) in 1990, it was considered 'the world's leading manufacturer of mass spectrometers'. Instrumentation. The insides of the GC-MS, with the column of the gas chromatograph in the oven on the right.The GC-MS is composed of two major building blocks: the and the.
The gas chromatograph utilizes a capillary column which depends on the column's dimensions (length, diameter, film thickness) as well as the phase properties (e.g. 5% phenyl polysiloxane).
The difference in the chemical properties between different in a mixture and their relative affinity for the stationary phase of the column will promote separation of the molecules as the sample travels the length of the column. The molecules are retained by the column and then elute (come off) from the column at different times (called the retention time), and this allows the mass spectrometer downstream to capture, ionize, accelerate, deflect, and detect the ionized molecules separately. The mass spectrometer does this by breaking each molecule into fragments and detecting these fragments using their mass-to-charge ratio. GC-MS schematicThese two components, used together, allow a much finer degree of substance identification than either unit used separately. It is not possible to make an accurate identification of a particular molecule by gas chromatography or mass spectrometry alone. The mass spectrometry process normally requires a very pure sample while gas chromatography using a traditional detector (e.g.
) cannot differentiate between multiple molecules that happen to take the same amount of time to travel through the column ( i.e. Have the same retention time), which results in two or more molecules that co-elute. Sometimes two different molecules can also have a similar pattern of ionized fragments in a mass spectrometer (mass spectrum).
Combining the two processes reduces the possibility of error, as it is extremely unlikely that two different molecules will behave in the same way in both a gas chromatograph and a mass spectrometer. Therefore, when an identifying mass spectrum appears at a characteristic retention time in a GC-MS analysis, it typically increases certainty that the analyte of interest is in the sample.Purge and trap GC-MS For the analysis of compounds, a (P&T) concentrator system may be used to introduce samples. The target analytes are extracted by mixing the sample with water and purge with inert gas (e.g.
) into an airtight chamber, this is known as purging. The volatile compounds move into the headspace above the water and are drawn along a (caused by the introduction of the purge gas) out of the chamber. The volatile compounds are drawn along a heated line onto a 'trap'. The trap is a column of material at ambient temperature that holds the compounds by returning them to the liquid phase. The trap is then heated and the sample compounds are introduced to the GC-MS column via a volatiles interface, which is a split inlet system. P&T GC-MS is particularly suited to (VOCs) and compounds (aromatic compounds associated with petroleum).A faster alternative is the 'purge-closed loop' system. In this system the inert gas is bubbled through the water until the concentrations of organic compounds in the vapor phase are at equilibrium with concentrations in the aqueous phase.
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The gas phase is then analysed directly. Types of mass spectrometer detectors The most common type of mass spectrometer (MS) associated with a gas chromatograph (GC) is the quadrupole mass spectrometer, sometimes referred to by the (now ) trade name 'Mass Selective Detector' (MSD). Another relatively common detector is the ion trap mass spectrometer. Additionally one may find a magnetic sector mass spectrometer, however these particular instruments are expensive and bulky and not typically found in high-throughput service laboratories. Other detectors may be encountered such as time of flight (TOF), tandem quadrupoles (MS-MS) (see below), or in the case of an ion trap MS n where n indicates the number mass spectrometry stages.GC-tandem MS When a second phase of mass fragmentation is added, for example using a second quadrupole in a quadrupole instrument, it is called tandem MS (MS/MS). MS/MS can sometimes be used to quantitate low levels of target compounds in the presence of a high sample matrix background.The first quadrupole (Q1) is connected with a collision cell (Q2) and another quadrupole (Q3). Both quadrupoles can be used in scanning or static mode, depending on the type of MS/MS analysis being performed.
Types of analysis include product ion scan, precursor ion scan, (sometimes referred to as multiple reaction monitoring (MRM)) and neutral loss scan. For example: When Q1 is in static mode (looking at one mass only as in SIM), and Q3 is in scanning mode, one obtains a so-called product ion spectrum (also called 'daughter spectrum'). From this spectrum, one can select a prominent product ion which can be the product ion for the chosen precursor ion.
The pair is called a 'transition' and forms the basis for SRM. SRM is highly specific and virtually eliminates matrix background.Ionization After the molecules travel the length of the column, pass through the transfer line and enter into the mass spectrometer they are ionized by various methods with typically only one method being used at any given time. Once the sample is fragmented it will then be detected, usually by an, which essentially turns the ionized mass fragment into an electrical signal that is then detected.The ionization technique chosen is independent of using full scan or SIM. Block diagram for gas chromatography using electron ionization for collecting mass spectrum. Electron ionization By far the most common and perhaps standard form of ionization is (EI). The molecules enter into the MS (the source is a quadrupole or the ion trap itself in an ion trap MS) where they are bombarded with free electrons emitted from a filament, not unlike the filament one would find in a standard light bulb.
The electrons bombard the molecules, causing the molecule to fragment in a characteristic and reproducible way. This 'hard ionization' technique results in the creation of more fragments of low mass-to-charge ratio (m/z) and few, if any, molecules approaching the molecular mass unit.
Hard ionization is considered by mass spectrometrists as the employ of molecular electron bombardment, whereas 'soft ionization' is charge by molecular collision with an introduced gas. The molecular fragmentation pattern is dependent upon the electron energy applied to the system, typically 70 eV (electron Volts). The use of 70 eV facilitates comparison of generated spectra with library spectra using manufacturer-supplied software or software developed by the National Institute of Standards (NIST-USA).
Spectral library searches employ matching algorithms such as Probability Based Matching and dot-product matching that are used with methods of analysis written by many method standardization agencies. Sources of libraries include NIST, Wiley, the AAFS, and instrument manufacturers.Cold electron ionization The 'hard ionization' process of can be softened by the cooling of the molecules before their ionization, resulting in mass spectra that are richer in information. In this method named cold electron ionization (cold-EI) the molecules exit the GC column, mixed with added helium make up gas and expand into vacuum through a specially designed supersonic nozzle, forming a supersonic molecular beam (SMB). Collisions with the make up gas at the expanding supersonic jet reduce the internal vibrational (and rotational) energy of the analyte molecules, hence reducing the degree of fragmentation caused by the electrons during the ionization process. Cold-EI mass spectra are characterized by an abundant molecular ion while the usual fragmentation pattern is retained, thus making cold-EI mass spectra compatible with library search identification techniques. The enhanced molecular ions increase the identification probabilities of both known and unknown compounds, amplify isomer mass spectral effects and enable the use of isotope abundance analysis for the elucidation of elemental formulae.
Chemical ionization. Main article:In a reagent gas, typically or is introduced into the mass spectrometer. Depending on the technique (positive CI or negative CI) chosen, this reagent gas will interact with the electrons and analyte and cause a 'soft' ionization of the molecule of interest. A softer ionization fragments the molecule to a lower degree than the hard ionization of EI. One of the main benefits of using chemical ionization is that a mass fragment closely corresponding to the molecular weight of the analyte of interest is produced.In positive chemical ionization (PCI) the reagent gas interacts with the target molecule, most often with a proton exchange. This produces the species in relatively high amounts.In negative chemical ionization (NCI) the reagent gas decreases the impact of the free electrons on the target analyte.
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This decreased energy typically leaves the fragment in great supply.Analysis A mass spectrometer is typically utilized in one of two ways: full scan or selective ion monitoring (SIM). The typical GC-MS instrument is capable of performing both functions either individually or concomitantly, depending on the setup of the particular instrument.The primary goal of instrument analysis is to quantify an amount of substance. This is done by comparing the relative concentrations among the atomic masses in the generated spectrum.
Two kinds of analysis are possible, comparative and original. Comparative analysis essentially compares the given spectrum to a spectrum library to see if its characteristics are present for some sample in the library. This is best performed by a because there are a myriad of visual distortions that can take place due to variations in scale. Computers can also simultaneously correlate more data (such as the retention times identified by GC), to more accurately relate certain data.
Deep learning was shown to lead to promising results in the identification of VOCs from raw GC-MS dataAnother method of analysis measures the peaks in relation to one another. In this method, the tallest peak is assigned 100% of the value, and the other peaks being assigned proportionate values. All values above 3% are assigned. The total mass of the unknown compound is normally indicated by the parent peak. The value of this parent peak can be used to fit with a chemical containing the various which are believed to be in the compound. The pattern in the spectrum, which is unique for elements that have many natural isotopes, can also be used to identify the various elements present. Once a chemical formula has been matched to the spectrum, the molecular structure and bonding can be identified, and must be consistent with the characteristics recorded by GC-MS.
Typically, this identification is done automatically by programs which come with the instrument, given a list of the elements which could be present in the sample.A 'full spectrum' analysis considers all the 'peaks' within a spectrum. Conversely, selective ion monitoring (SIM) only monitors selected ions associated with a specific substance. This is done on the assumption that at a given retention time, a set of is characteristic of a certain compound. This is a fast and efficient analysis, especially if the analyst has previous information about a sample or is only looking for a few specific substances. When the amount of information collected about the ions in a given gas chromatographic peak decreases, the sensitivity of the analysis increases. So, SIM analysis allows for a smaller quantity of a compound to be detected and measured, but the degree of certainty about the identity of that compound is reduced.Full scan MS When collecting data in the full scan mode, a target range of mass fragments is determined and put into the instrument's method.
An example of a typical broad range of mass fragments to monitor would be m/z 50 to m/z 400. The determination of what range to use is largely dictated by what one anticipates being in the sample while being cognizant of the solvent and other possible interferences. A MS should not be set to look for mass fragments too low or else one may detect air (found as m/z 28 due to nitrogen), carbon dioxide ( m/z 44) or other possible interference. Additionally if one is to use a large scan range then sensitivity of the instrument is decreased due to performing fewer scans per second since each scan will have to detect a wide range of mass fragments.Full scan is useful in determining unknown compounds in a sample. It provides more information than SIM when it comes to confirming or resolving compounds in a sample. During instrument method development it may be common to first analyze test solutions in full scan mode to determine the retention time and the mass fragment fingerprint before moving to a SIM instrument method.Selective ion monitoring In selective ion monitoring (SIM) certain ion fragments are entered into the instrument method and only those mass fragments are detected by the mass spectrometer.
The advantages of SIM are that the detection limit is lower since the instrument is only looking at a small number of fragments (e.g. Three fragments) during each scan. More scans can take place each second. Since only a few mass fragments of interest are being monitored, are typically lower. To additionally confirm the likelihood of a potentially positive result, it is relatively important to be sure that the ion ratios of the various mass fragments are comparable to a known reference standard.Applications Environmental monitoring and cleanup GC-MS is becoming the tool of choice for tracking organic pollutants in the environment. The cost of GC-MS equipment has decreased significantly, and the reliability has increased at the same time, which has contributed to its increased adoption in.Criminal forensics GC-MS can analyze the particles from a human body in order to help link a criminal to a. The analysis of debris using GC-MS is well established, and there is even an established American Society for Testing and Materials (ASTM) standard for fire debris analysis.
GCMS/MS is especially useful here as samples often contain very complex matrices and results, used in court, need to be highly accurate.Law enforcement GC-MS is increasingly used for detection of illegal narcotics, and may eventually supplant drug-sniffing dogs. 1 A simple and selective GC-MS method for detecting marijuana usage was recently developed by the Robert Koch-Institute in Germany. It involves identifying an acid metabolite of tetrahyhydrocannabinol (THC), the active ingredient in marijuana, in urine samples by employing derivatization in the sample preparation. GC-MS is also commonly used in forensic toxicology to find drugs and/or poisons in biological specimens of suspects, victims, or the deceased. In drug screening, GC-MS methods frequently utilize liquid-liquid extraction as a part of sample preparation, in which target compounds are extracted from blood plasma.
Sports anti-doping analysis GC-MS is the main tool used in sports anti-doping laboratories to test athletes' urine samples for prohibited performance-enhancing drugs, for example. Security A post–September 11 development, systems have become a part of all. These systems run on a host of technologies, many of them based on GC-MS. There are only three manufacturers certified by the to provide these systemsone of which is Thermo Detection (formerly Thermedics), which produces the, a GC-MS-based line of explosives detectors. Robert P., Adams (2007).
Identification of Essential Oil Components By Gas Chromatography/Mass Spectrometry. Allured Pub Corp. Adlard, E. R.; Handley, Alan J. Gas chromatographic techniques and applications. London: Sheffield Academic. Eugene F.
Barry; Grob, Robert Lee (2004). Modern practice of gas chromatography. New York: Wiley-Interscience. Eiceman, G.A. Gas Chromatography.
Meyers (Ed.), Encyclopedia of Analytical Chemistry: Applications, Theory, and Instrumentation, pp. 10627. Chichester: Wiley. Giannelli, Paul C.
And Imwinkelried, Edward J. Drug Identification: Gas Chromatography. In Scientific Evidence 2, pp. 362. Charlottesville: Lexis Law Publishing. McEwen, Charles N.; Kitson, Fulton G.; Larsen, Barbara Seliger (1996).
Gas chromatography and mass spectrometry: a practical guide. Boston: Academic Press. McMaster, Christopher; McMaster, Marvin C. GC/MS: a practical user's guide.
The gas chromatograph utilizes a capillary column which depends on the column's dimensions (length, diameter, film thickness) as well as the phase properties (e.g. 5% phenyl polysiloxane).
The difference in the chemical properties between different in a mixture and their relative affinity for the stationary phase of the column will promote separation of the molecules as the sample travels the length of the column. The molecules are retained by the column and then elute (come off) from the column at different times (called the retention time), and this allows the mass spectrometer downstream to capture, ionize, accelerate, deflect, and detect the ionized molecules separately. The mass spectrometer does this by breaking each molecule into fragments and detecting these fragments using their mass-to-charge ratio. GC-MS schematicThese two components, used together, allow a much finer degree of substance identification than either unit used separately. It is not possible to make an accurate identification of a particular molecule by gas chromatography or mass spectrometry alone. The mass spectrometry process normally requires a very pure sample while gas chromatography using a traditional detector (e.g.
) cannot differentiate between multiple molecules that happen to take the same amount of time to travel through the column ( i.e. Have the same retention time), which results in two or more molecules that co-elute. Sometimes two different molecules can also have a similar pattern of ionized fragments in a mass spectrometer (mass spectrum).
Combining the two processes reduces the possibility of error, as it is extremely unlikely that two different molecules will behave in the same way in both a gas chromatograph and a mass spectrometer. Therefore, when an identifying mass spectrum appears at a characteristic retention time in a GC-MS analysis, it typically increases certainty that the analyte of interest is in the sample.Purge and trap GC-MS For the analysis of compounds, a (P&T) concentrator system may be used to introduce samples. The target analytes are extracted by mixing the sample with water and purge with inert gas (e.g.
) into an airtight chamber, this is known as purging. The volatile compounds move into the headspace above the water and are drawn along a (caused by the introduction of the purge gas) out of the chamber. The volatile compounds are drawn along a heated line onto a 'trap'. The trap is a column of material at ambient temperature that holds the compounds by returning them to the liquid phase. The trap is then heated and the sample compounds are introduced to the GC-MS column via a volatiles interface, which is a split inlet system. P&T GC-MS is particularly suited to (VOCs) and compounds (aromatic compounds associated with petroleum).A faster alternative is the 'purge-closed loop' system. In this system the inert gas is bubbled through the water until the concentrations of organic compounds in the vapor phase are at equilibrium with concentrations in the aqueous phase.
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The gas phase is then analysed directly. Types of mass spectrometer detectors The most common type of mass spectrometer (MS) associated with a gas chromatograph (GC) is the quadrupole mass spectrometer, sometimes referred to by the (now ) trade name 'Mass Selective Detector' (MSD). Another relatively common detector is the ion trap mass spectrometer. Additionally one may find a magnetic sector mass spectrometer, however these particular instruments are expensive and bulky and not typically found in high-throughput service laboratories. Other detectors may be encountered such as time of flight (TOF), tandem quadrupoles (MS-MS) (see below), or in the case of an ion trap MS n where n indicates the number mass spectrometry stages.GC-tandem MS When a second phase of mass fragmentation is added, for example using a second quadrupole in a quadrupole instrument, it is called tandem MS (MS/MS). MS/MS can sometimes be used to quantitate low levels of target compounds in the presence of a high sample matrix background.The first quadrupole (Q1) is connected with a collision cell (Q2) and another quadrupole (Q3). Both quadrupoles can be used in scanning or static mode, depending on the type of MS/MS analysis being performed.
Types of analysis include product ion scan, precursor ion scan, (sometimes referred to as multiple reaction monitoring (MRM)) and neutral loss scan. For example: When Q1 is in static mode (looking at one mass only as in SIM), and Q3 is in scanning mode, one obtains a so-called product ion spectrum (also called 'daughter spectrum'). From this spectrum, one can select a prominent product ion which can be the product ion for the chosen precursor ion.
The pair is called a 'transition' and forms the basis for SRM. SRM is highly specific and virtually eliminates matrix background.Ionization After the molecules travel the length of the column, pass through the transfer line and enter into the mass spectrometer they are ionized by various methods with typically only one method being used at any given time. Once the sample is fragmented it will then be detected, usually by an, which essentially turns the ionized mass fragment into an electrical signal that is then detected.The ionization technique chosen is independent of using full scan or SIM. Block diagram for gas chromatography using electron ionization for collecting mass spectrum. Electron ionization By far the most common and perhaps standard form of ionization is (EI). The molecules enter into the MS (the source is a quadrupole or the ion trap itself in an ion trap MS) where they are bombarded with free electrons emitted from a filament, not unlike the filament one would find in a standard light bulb.
The electrons bombard the molecules, causing the molecule to fragment in a characteristic and reproducible way. This 'hard ionization' technique results in the creation of more fragments of low mass-to-charge ratio (m/z) and few, if any, molecules approaching the molecular mass unit.
Hard ionization is considered by mass spectrometrists as the employ of molecular electron bombardment, whereas 'soft ionization' is charge by molecular collision with an introduced gas. The molecular fragmentation pattern is dependent upon the electron energy applied to the system, typically 70 eV (electron Volts). The use of 70 eV facilitates comparison of generated spectra with library spectra using manufacturer-supplied software or software developed by the National Institute of Standards (NIST-USA).
Spectral library searches employ matching algorithms such as Probability Based Matching and dot-product matching that are used with methods of analysis written by many method standardization agencies. Sources of libraries include NIST, Wiley, the AAFS, and instrument manufacturers.Cold electron ionization The 'hard ionization' process of can be softened by the cooling of the molecules before their ionization, resulting in mass spectra that are richer in information. In this method named cold electron ionization (cold-EI) the molecules exit the GC column, mixed with added helium make up gas and expand into vacuum through a specially designed supersonic nozzle, forming a supersonic molecular beam (SMB). Collisions with the make up gas at the expanding supersonic jet reduce the internal vibrational (and rotational) energy of the analyte molecules, hence reducing the degree of fragmentation caused by the electrons during the ionization process. Cold-EI mass spectra are characterized by an abundant molecular ion while the usual fragmentation pattern is retained, thus making cold-EI mass spectra compatible with library search identification techniques. The enhanced molecular ions increase the identification probabilities of both known and unknown compounds, amplify isomer mass spectral effects and enable the use of isotope abundance analysis for the elucidation of elemental formulae.
Chemical ionization. Main article:In a reagent gas, typically or is introduced into the mass spectrometer. Depending on the technique (positive CI or negative CI) chosen, this reagent gas will interact with the electrons and analyte and cause a 'soft' ionization of the molecule of interest. A softer ionization fragments the molecule to a lower degree than the hard ionization of EI. One of the main benefits of using chemical ionization is that a mass fragment closely corresponding to the molecular weight of the analyte of interest is produced.In positive chemical ionization (PCI) the reagent gas interacts with the target molecule, most often with a proton exchange. This produces the species in relatively high amounts.In negative chemical ionization (NCI) the reagent gas decreases the impact of the free electrons on the target analyte.
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This decreased energy typically leaves the fragment in great supply.Analysis A mass spectrometer is typically utilized in one of two ways: full scan or selective ion monitoring (SIM). The typical GC-MS instrument is capable of performing both functions either individually or concomitantly, depending on the setup of the particular instrument.The primary goal of instrument analysis is to quantify an amount of substance. This is done by comparing the relative concentrations among the atomic masses in the generated spectrum.
Two kinds of analysis are possible, comparative and original. Comparative analysis essentially compares the given spectrum to a spectrum library to see if its characteristics are present for some sample in the library. This is best performed by a because there are a myriad of visual distortions that can take place due to variations in scale. Computers can also simultaneously correlate more data (such as the retention times identified by GC), to more accurately relate certain data.
Deep learning was shown to lead to promising results in the identification of VOCs from raw GC-MS dataAnother method of analysis measures the peaks in relation to one another. In this method, the tallest peak is assigned 100% of the value, and the other peaks being assigned proportionate values. All values above 3% are assigned. The total mass of the unknown compound is normally indicated by the parent peak. The value of this parent peak can be used to fit with a chemical containing the various which are believed to be in the compound. The pattern in the spectrum, which is unique for elements that have many natural isotopes, can also be used to identify the various elements present. Once a chemical formula has been matched to the spectrum, the molecular structure and bonding can be identified, and must be consistent with the characteristics recorded by GC-MS.
Typically, this identification is done automatically by programs which come with the instrument, given a list of the elements which could be present in the sample.A 'full spectrum' analysis considers all the 'peaks' within a spectrum. Conversely, selective ion monitoring (SIM) only monitors selected ions associated with a specific substance. This is done on the assumption that at a given retention time, a set of is characteristic of a certain compound. This is a fast and efficient analysis, especially if the analyst has previous information about a sample or is only looking for a few specific substances. When the amount of information collected about the ions in a given gas chromatographic peak decreases, the sensitivity of the analysis increases. So, SIM analysis allows for a smaller quantity of a compound to be detected and measured, but the degree of certainty about the identity of that compound is reduced.Full scan MS When collecting data in the full scan mode, a target range of mass fragments is determined and put into the instrument's method.
An example of a typical broad range of mass fragments to monitor would be m/z 50 to m/z 400. The determination of what range to use is largely dictated by what one anticipates being in the sample while being cognizant of the solvent and other possible interferences. A MS should not be set to look for mass fragments too low or else one may detect air (found as m/z 28 due to nitrogen), carbon dioxide ( m/z 44) or other possible interference. Additionally if one is to use a large scan range then sensitivity of the instrument is decreased due to performing fewer scans per second since each scan will have to detect a wide range of mass fragments.Full scan is useful in determining unknown compounds in a sample. It provides more information than SIM when it comes to confirming or resolving compounds in a sample. During instrument method development it may be common to first analyze test solutions in full scan mode to determine the retention time and the mass fragment fingerprint before moving to a SIM instrument method.Selective ion monitoring In selective ion monitoring (SIM) certain ion fragments are entered into the instrument method and only those mass fragments are detected by the mass spectrometer.
The advantages of SIM are that the detection limit is lower since the instrument is only looking at a small number of fragments (e.g. Three fragments) during each scan. More scans can take place each second. Since only a few mass fragments of interest are being monitored, are typically lower. To additionally confirm the likelihood of a potentially positive result, it is relatively important to be sure that the ion ratios of the various mass fragments are comparable to a known reference standard.Applications Environmental monitoring and cleanup GC-MS is becoming the tool of choice for tracking organic pollutants in the environment. The cost of GC-MS equipment has decreased significantly, and the reliability has increased at the same time, which has contributed to its increased adoption in.Criminal forensics GC-MS can analyze the particles from a human body in order to help link a criminal to a. The analysis of debris using GC-MS is well established, and there is even an established American Society for Testing and Materials (ASTM) standard for fire debris analysis.
GCMS/MS is especially useful here as samples often contain very complex matrices and results, used in court, need to be highly accurate.Law enforcement GC-MS is increasingly used for detection of illegal narcotics, and may eventually supplant drug-sniffing dogs. 1 A simple and selective GC-MS method for detecting marijuana usage was recently developed by the Robert Koch-Institute in Germany. It involves identifying an acid metabolite of tetrahyhydrocannabinol (THC), the active ingredient in marijuana, in urine samples by employing derivatization in the sample preparation. GC-MS is also commonly used in forensic toxicology to find drugs and/or poisons in biological specimens of suspects, victims, or the deceased. In drug screening, GC-MS methods frequently utilize liquid-liquid extraction as a part of sample preparation, in which target compounds are extracted from blood plasma.
Sports anti-doping analysis GC-MS is the main tool used in sports anti-doping laboratories to test athletes' urine samples for prohibited performance-enhancing drugs, for example. Security A post–September 11 development, systems have become a part of all. These systems run on a host of technologies, many of them based on GC-MS. There are only three manufacturers certified by the to provide these systemsone of which is Thermo Detection (formerly Thermedics), which produces the, a GC-MS-based line of explosives detectors. Robert P., Adams (2007).
Identification of Essential Oil Components By Gas Chromatography/Mass Spectrometry. Allured Pub Corp. Adlard, E. R.; Handley, Alan J. Gas chromatographic techniques and applications. London: Sheffield Academic. Eugene F.
Barry; Grob, Robert Lee (2004). Modern practice of gas chromatography. New York: Wiley-Interscience. Eiceman, G.A. Gas Chromatography.
Meyers (Ed.), Encyclopedia of Analytical Chemistry: Applications, Theory, and Instrumentation, pp. 10627. Chichester: Wiley. Giannelli, Paul C.
And Imwinkelried, Edward J. Drug Identification: Gas Chromatography. In Scientific Evidence 2, pp. 362. Charlottesville: Lexis Law Publishing. McEwen, Charles N.; Kitson, Fulton G.; Larsen, Barbara Seliger (1996).
Gas chromatography and mass spectrometry: a practical guide. Boston: Academic Press. McMaster, Christopher; McMaster, Marvin C. GC/MS: a practical user's guide.
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New York: Wiley. Message, Gordon M. Practical aspects of gas chromatography/mass spectrometry. New York: Wiley. Niessen, W. Current practice of gas chromatography–mass spectrometry.
New York, N.Y: Marcel Dekker. Weber, Armin; Maurer, Hans W.; Pfleger, Karl (2007). Mass Spectral and GC Data of Drugs, Poisons, Pesticides, Pollutants and Their Metabolites. Weinheim: Wiley-VCH.External links. at the US National Library of Medicine (MeSH)., a mass spectral reference database of plant metabolites.
VSI stands for 'Vapour Sequential Injection'. The VSI system is the most advanced vapour injection system on the market. It was originally developed by Prins and has now been completely redesigned to suit advanced modern engines. All components used in the VSI system satisfy the most demanding regulations and certification standards.
The VSI system is based on the principle of converting liquefied petroleum gas (LPG) or natural gas (CNG) to vapour form before sequentially injecting it into the engine. We also offer solutions for cars with a direct injection fuel system!
High-quality components- Unique diagnostic software
- Optimal performance
Reduced emissions
No noticeable difference compared to running your vehicle on petrol!
We can convert all cars with an MPI (multipoint injection) engine to LPG or CNG! The number of LPG and CNG systems for cars with a direct injection fuel system is also growing rapidly.
Thanks to our extensive range of products, we lead the market. We know from experience which system works best for a particular engine. Find out which system suits your car best by searching our database.
The following are the main components that are added to your car when an LPG conversion is installed.
The components that make up our VSI LPG-system are shown below. The main components meet the same standards as OEM-parts, and have been specifically developed for LPG and CNG systems. They satisfy the most demanding regulations and certification standards.
1. LPG-tank
2. ECU (Electronic Control Unit)
3. Switch
4. Evaporator (eVP-500)
5. Filter
6. Injectors
*Only a few layout modifications are required to make this Prins VSI LPG system suitable for CNG.
Would you like more information?
If you require more information, you can download our brochure or contact us.
