Supersonic GC-MS

SuperMass was established in order to bring the benefits of GC-MS with supersonic molecular beams to its potential users in a compact and reliable bench top system termed Supersonic GC-MS. This document describes the various aspects and features of the Supersonic GC-MS so that you can evaluate its benefits for your research and applications.

1. Introduction - What is a Supersonic Molecular Beam (SMB)

A Supersonic molecular beam (SMB) is formed by the expansion of a gas through a ~0.1 mm pinhole into a vacuum chamber. In this expansion the carrier gas and heavier sample molecules obtain the same final velocity so that the sample compounds are accelerated to the carrier gas velocity, since it is the major gas component. Furthermore, the uniform velocity ensures a slow intra-beam relative motion, resulting in the cooling of the internal vibrational degrees of freedom.
SMB’s are characterized by the following features that are of importance for GC-MS:

We have explored over the coarse of last 15 years the use of these unique properties of SMB for improving mass spectrometry and GC-MS [1-20]. We found that the SMB results in important implications to both GC sampling and molecular ionization processes. The intra-molecular vibrational cooling conditions prevailing in SMB substantially improve the level of information available through electron impact ionization (EI). Hyperthermal surface ionization, which is unique to the use of SMB, provides an ultra sensitive and selective ionization method, that is ideal for use with drugs and aromatic compounds. The use of SMB for interfacing and ionization improves all aspects of GC-MS and enables a truly optimized fast GC-MS analysis of a wide range of samples.

The basic GC-MS instrument modifications for conversion into a Supersonic GC-MS include:

In addition to these modifications, the basic apparatus includes the Hewlett Packard 5972 or 5973 MSD quadrupole mass analyzer and ion detector in its original unmodified vacuum system, pumped by a 60L/sec diffusion pump. An additional such air cooled 60L/sec diffusion pump and 520 L/min rotary pump are added for the small supersonic nozzle vacuum chamber and its differential pumping chamber.

In a book "Supersonic Molecular Beam Mass Spectrometry - The Quest for Ultimate Performance GC-MS and Fast GC-MS" the Supersonic GC-MS technology is described and demonstrated through 51 figures and many applications.
This book is available free on request.
You may ask for it at:  amirav@supermass.co.il.
Please add a brief description of your application and range of GC-MS interests. 

We would be delighted to try your samples and meet your requirements so that you could closely evaluate the suitability of Supersonic GC-MS to solve your tough applications.  Please challenge us at: amirav@supermass.co.il.
 

2. Summary of Supersonic GC-MS Advantages and Unique Features

We consider our Supersonic GC-MS technology to be a major breakthrough, with improvements of all the major aspects of GC-MS, including the level of MS information obtained, speed of analysis, sensitivity, selectivity, scope of use, flexibility and ease of use. Supersonic GC-MS contains the broadest range of features and capabilities ("Super Enhancement Package") to provide you with the cutting edge technology and competitive advantage.

  1. Information
The vibrational cooling effect in EI, provides the highest level of mass spectral information. The unique capabilities of the EI-SMB ion source truly make it the "Ideal Ion Source".

  2. Speed
SMB enables the highest capability fast GC-MS, from the reduction or elimination of sample preparation to the final fast analysis results. This fast GC-MS approach is based mostly on the high flow rate capability of the SMB inlet and on the improved separation power of the MS with EI or HSI of the SMB compounds, as well as on several other SMB features. Fast GC-MS (a few minutes down to a few seconds) is achieved, characterized by unrestricted column type, length and flow rate, very high temperature operation capability, thermally labile compound analysis capability, higher sensitivity, selective ionization with HSI and enhanced molecular ion peak in EI. SMB uniquely enables ultra fast ion source response time, simple syringe based large size fast splitless injections and compatibility with the scanning speed of quadrupole mass analyzers through the use of high flow megabore (or widebore) columns. The unique capabilities of "Extract-Free Dirty Sample Introduction" with the optional ChromatoProbe sample introduction device and Laser Desorption sampling method are also very important to the issue of fast analysis due to reduced sample preparation requirements.

  3. Sensitivity

  4. Scope of use
SMB enables the ultimate scope of use and range of GC-MS applications.

  5. Selectivity

This feature of enhanced molecular ion simplifies the deconvolution of overlapping GC peaks using the AMDIS deconvolution software of the NIST library and is thus very important for achieving fast GC-MS. The enhanced selectivity simplifies target and complex mixtures fast GC-MS analyses.

  6. Flexibility  (and ease of use)

     The "Super Enhancement Package"   

Supersonic GC-MS contains the broadest range of features and capabilities ("Super Enhancement Package") to provide you with cutting edge technology and a competitive advantage. These features are either inherent/standard or optional as marked.

3. The Supersonic GC-MS Instrument

In the Supersonic GC-MS the sample is introduced through the Hewlett Packard GC injector as usual. The analytical column output is mixed with about 160 ml/min helium or hydrogen make-up gas and flow through a 20 cm long megabore transfer line to the supersonic nozzle. The make up gas identity, flow rate and transfer line and nozzle temperature are controlled by the ChemStation software. The nozzle is made of alumina ceramic, with a length of ~0.4 mm and a 80 micron diameter. 

The mixture of carrier gas and sample molecules expand through the supersonic nozzle into the first vacuum chamber, which is pumped by a 520 L/min rotary pump. The emerging supersonic free jet is skimmed, differentially pumped by a 60L/sec air cooled diffusion pump, and enters the electron ionization (EI) ion source in the high vacuum MS chamber (60 L/sec air-cooled original HP diffusion pumps). The sample molecules in the beam are ionized by the molecular-fly-through cylindrical EI ion source that allows free passage of the SMB. The ions are extracted by an ion optics lens system attached to the EI ion source and are guided by a 90 degrees ion deflector into a the Hewlett Packard quadrupole mass analyzer (MSD). The 90 degrees ion deflector unit also serves as the hyperthermal surface ionization (HSI) surface with a heated rhenium foil under a high transmission mesh. Computer controlled low flow rate of oxygen keeps the rhenium surface clean. The quadrupole mass analyzer is located 90 degrees relative to the SMB axis and no modification is performed to the HP MSD except in the removal of its ion source. An "exit lens" is added at the exit of the quadrupole, which is a plate with a 5 mm hole, positioned between the quadrupole and the channeltron ion detector. It is used for background ion filtration, by external voltage biasing at the ion energy plus 1-2 eV.

Fast GC is achieved with the 6890 GC without any modification, using split or splitless standard syringe based injections. Alternatively (option), the sample could be loaded in a micro vial with the ChromatoProbe direct/dirty sample introduction device for intra injector thermal desorption. Short columns (3-6 meters long, 0.53 or 0.25 mm ID) with high flow rates (4-200 mL/min) can be used for fast GC and even the Alltech Multicapillary high column flow rate is acceptable without splitting. 

Supersonic GC-MS is designed specifically to bring the supersonic molecular beam GC-MS technology to the public as a commercially available bench-top GC-MS product. This new system design is based on the several basic concepts listed as follows.

This new Supersonic GC-MS system brings the SMB technology to a user friendly bench top system in a design that targets reliability as a prime consideration.

4. Electron Ionization of Molecules in the SMB

Supersonic expansion of a gas into a vacuum system results in a uniform velocity to all the expanding species. Accordingly, the supersonic expansion leads to low relative velocity collisions of the sample compounds and the carrier gas atoms, resulting in substantial supercooling of the sample compound vibrational temperature to well below 70K. This is like having the ion source at an ultra-low temperature but without condensing the sample compounds. As a result, the level of information contained in the EI mass spectra is greatly increased. We consider EI with SMB to be the ideal ionization method, having an enhanced molecular ion peak and superior detailed molecular and structural information with the following features and advantages: [6, 11, 19]

1.		The exact molecular ion peak practically always exists in 70 eV electron ionization (EI) MS with SMB. The relative height of the molecular ion peak is increased by up to several orders of magnitude due to the vibrational supercooling. On the other hand, the conventional EI fragmentation pattern is retained. Actually, the EI-MS of small molecules is relatively unchanged while for large molecules, due to their large vibrational heat capacity, a substantial increase in M+ can be observed.
2.		The level of information achieved in a single EI-SMB-MS scan, is greater than that provided by standard EI and CI combined, without the CI problems, and with the uniform high sensitivity of EI to all molecules. This is one of the reasons for our consideration of EI-SMB as the ideal ionization method.
3.		Total fragmentation tunability and fragment order of appearance information is achieved through the control of the electron energy. Due to the molecular vibrational supercooling, the electron energy is the only parameter that governs the degree of ion fragmentation. Thus, this control over the degree of fragmentation is achieved with a minimal loss of sensitivity since the reduced electron ionization cross section at low electron energy is compensated for by the reduced degree of fragmentation so that the molecular ion intensity is relatively unchanged.
4.		Unique structural and isomeric information is provided due to the vibrational supercooling. Any small isomer mass spectral difference is amplified (sometimes considerably amplified) with EI-SMB.
5.		Improved library search and confirmation is achieved due to the molecular weight information by confining the search to library molecules having this molecular weight only. Note that about 30% of the NIST library compounds have no molecular ion (below 2% normalized intensity). This value grows to 50% for compounds with molecular weight over 300 amu.
6.		Elemental analysis is possible by accurate isotopic abundance analysis of the relative intensity of the molecular ion group of mass spectral peaks. The features of enhanced molecular ion abundance combined with total lack of residual intra-ion source chemical ionization and reduced vacuum background enable an accurate measurement of the intensity ratios of the molecular ion peaks, resulting in elemental analysis with a unit resolution mass analyzer. If the elemental content is known, then geo-chemical and isotope abundance information is available through the analysis of these molecular ion peak ratios.
7.		Deuterium exchange at the supersonic nozzle can be employed (option) for NH and OH labeling. The on-line mixing of the carrier gas with deuterated methanol or heavy water enables effective and fast deuterium exchange before the supersonic expansion. It provides unique structural and isomeric information.

5. Hyperthermal Surface Ionization

The uniform velocity of all species in the supersonic molecular beam means that the velocities of the carrier gas (hydrogen or helium) and that of the sample molecules are equal. Since the sample compounds are a minor component of the SMB, the velocity of the sample compounds is increased to that of the carrier gas while the carrier gas is only marginally decelerated. Accordingly, the sample compounds are accelerated and their kinetic energy is increased, by about the mass ratio of the sample compound and the carrier gas, to the hyperthermal kinetic energy range of 1-30 eV. Thus, the kinetic energy of the sample molecule increases with its molecular weight and the nozzle temperature and it is reduced by increasing the carrier gas atomic or molecular weight.
We have found that the surface ionization yield of organic molecules acquired with hyperthermal kinetic energy is increased by many orders of magnitude relative to thermal surface ionization and it can be up to three orders of magnitude higher than EI. This phenomenon of hyperthermal surface ionization (HSI) was discovered by Amirav and Danon [1, 2, 6] and studied in detail from its various mechanisms through its analytical applications [4, 7-10, 12, 16, 19, 20].

HSI is based on a molecule-surface electron transfer process which is promoted by the image potential formed between the ion and the surface. This image potential facilitates the molecule-surface electron transfer and ionization process. The molecular ionization requires the energy difference between the molecular ionization energy and the surface work function (surface ionization energy). When an ion approaches the surface, an image potential is formed between the ion and surface. This image potential reduces its potential energy that can be lower than that of the scattered neutral compound at a given distance from the surface. This critical distance is called the curve crossing distance (Rc). Below this distance a spontaneous electron transfer from the molecule to the surface may occur and can be calculated using a modified Landau Zenner curve crossing equation. If the sample compound has hyperthermal kinetic energy above the thermodynamic energy requirement, it can be scattered as an ion from the surface. Since a portion of the molecular kinetic energy is lost, either to the surface or to internal vibrational degrees of freedom, most of the ionized compounds are reneutralized. As a result, the ionization efficiency is dramatically increased with the molecular kinetic energy, since an increased portion of the scattered ions have sufficient kinetic energy to overcome the image potential in their exit trajectories. Other HSI mechanisms, including negative ion HSI, are described in references 2 and 6 but the mechanism briefly described above is analytically the most significant.

The degree of ionization also depends on the surface work function and molecular ionization energy. Rhenium oxide has proven to be an ideal surface for HSI as it combines a high work function with excellent long term stability that is essential for analytical applications. This is achieved by the direct current heating of a rhenium foil to about 1000K while bleeding oxygen on it at a partial pressure of 2-3x10-5 milliBar. As a result, the oxygen catalyticaly combusts all the organic surface impurities and maintains a steady state of surface cleanliness.
We found that HSI can serve as a universal, ultra sensitive ion source with tunable selectivity that is ideal for compounds with low ionization energies such as drugs and aromatic compounds. This tunable selectivity was demonstrated combined with the very high HSI yield that is estimated to be over 10% at the surface, and about 2% for the ratio of ions at the surface to nozzle flux (assuming 20% jet separation efficiency).

While HSI provides molecular ions only for polycyclic aromatic hydrocarbons, the HSI mass spectra are usually characterized by a rich and informative fragmentation pattern. The degree of HSI fragmentation naturally depends on the compound but it also depends on the molecular kinetic energy. The HSI fragments usually correspond to those which appear in EI mass spectra albeit with different relative peak intensities. In some cases, such as with cocaine, the HSI MS can be identified by the NIST EI library. In other cases a HSI library must be built and can be effective.

In summary, HSI is characterized by the following two major features and advantages:

A) Increased Sensitivity.
Hyperthermal surface ionization is the most sensitive ion source for  positive ion formation due to:

Minimum detected amount of 400 attograms was demonstrated in an experimental system.

B) Tunable Ionization Selectivity.
The hyperthermal surface ionization yield depends on the surface  work-function, sample molecule and molecular kinetic energy. These parameters can be easily controlled through the choice of the carrier gas such as helium, hydrogen or their mixture (on-line prepared with the ChemStation), the nozzle temperature and/or the choice of surface such as rhenium oxide or molybdenum oxide. Over 1E+5 anthracene/dodecane selective ionization was achieved. The high selectivity may involve only a minor ionization yield reduction of the selected molecules. Selective ionization can help to simplify complex mixture analysis and opens the door for a much faster GC-MS analysis, such as of cocaine in a single hair [20].

6. Fast and Ultra-Fast GC-MS

The unique features of SMB-MS enable a fast GC-MS which provides a complete solution for all the requirements of an optimized, high performance, fast, high temperature and thermolabile compatible GC-MS. The HP 6890 GC serves for fast GC-MS, connected to the SMB nozzle with two columns simultaneously, having no limitations on the column ID, length or flow rate. In this way the conventional GC becomes a fast GC-MS inlet that comprises a new approach for fast GC-MS. The subject of fast GC-MS with SMB is discussed in detail in a recent paper and review [17, 19] (available upon request).
In contrast to the microbore column based fast GC-MS, our approach offers a much better solution to all the requirements of fast GC-MS, from sample preparation to data analysis in that:

1.		Fast injection is achieved with a conventional syringe, even for relatively nonvolatile compounds, due to the very high injector flow rate (up to 240 ml/min).
2.		High repetition rate fast injection can be achieved with laser desorption injection (option) in an atmospheric or helium purged compartment provides the ultimate automated high repetition rate sample injection method.
3.		A unique extract free dirty sample introduction method and device (ChromatoProbe, option), enables a true fast analysis including the step of sample preparation.
4.		Fast analysis is achieved with samples having a very wide boiling point range, due to simple and fast column flow programming up to 2000 cm/sec carrier gas velocity. This unique column flow programming enables the widest column flow programming dynamic range.
5.		A wide temperature range fast GC-MS is achieved with appropriate columns heated up to 460 C and without any ion source related peak tailing.
6.		GC-MS of thermally labile compounds is achieved with the very fast and ultra fast GC-MS for molecules that are usually probed by particle beam or APCI LC-MS (ultra fast injection, on-column injection, short column, high carrier gas linear velocity and no ion source dissociation).
7.		Compatible mass scanning rate is enabled, even with the quadrupole mass analyzer. The reduced number of separation plates associated with the use of a high flow rate short megabore column results in a normal peak width of ~ 1 sec after ~5-10 seconds which does not require TOF-MS. Thus, the quadrupole mass analyzer can be used.
8.		Sufficient overall GC-MS resolving power is provided, even for complex mixture fast analysis. The GC column time separation and MS resolving power are supplemented by a tunable selective hyperthermal surface ionization, or low electron energy EI-SMB which produces a dominant or only M+ (orthogonal MS separation). Thus, many target compounds can be  analyzed in a few seconds in real world complex mixtures.
9.		Ultra fast ion source response time exists with SMB, which allows the monitoring of tail free fast GC peaks originating even from relatively nonvolatile molecules.
10.		Very high sensitivity is achieved with hyperthermal surface ionization. This sensitivity can be translated into simpler sample preparation for faster analysis.
11.		Superior low concentration sensitivity is achieved with more than 1 microLiter fast splitless injections due to the high column flow rate. This is in marked contrast to microbore column fast GC-MS. Fast splitless injections also enable significantly faster temperature programming and GC cooling down time since the initial GC temperature can be much higher!.
12.		Resolution, time and sensitivity trade-off choice is enabled for optimal results. The coupling with a conventional GC is allowed without any constraints on the column diameter, length and carrier gas flow rate. Thus, critical parameters such as chromatographic time and resolution can be optimized, with regards to and in consideration of the desired injected sample amount. This is easily achieved due to the practically unlimited column flow allowable. The recently introduced multi-capillary fast GC column from Alltech, with its very high column flow rate requirement, is ideally coupled with the SMB-MS.

Improved Conventional GC-MS Flexibility and Capabilities
While fast GC-MS is ideally suited for the fast screening of a large number of samples, confirmation is also needed, preferably with the same GC-MS instrument. Supersonic GC-MS provides this highly desirable feature, supplementary to fast GC-MS, and can be configured with both a standard analytical and a short column which are simultaneously connected to the SMB interface. In addition, Supersonic GC-MS provides several advantages over standard GC-MS that make it a higher capability GC-MS. It provides increased available level of MS information, enhanced molecular ion peak, HSI, higher temperature operation and the many unique features mentioned above. Further contributions include:

1.		Any column diameter and length can be used for optimized trade-off of chromatography parameters such as injection volume, speed of analysis and chromatographic resolution. (faster GC-MS instead of fast GC-MS)
2.		Flow programming of the GC can be used without any flow limitations. Thus, the injection and analysis time of the standard chromatography can be considerably reduced. (Faster GC-MS instead of fast GC-MS)
3.		A very large amount of solvent can be injected  (i.e. 100 microLiter splitless) with an injection time of 4 microLiter/sec. Large volume injections directly improve the achievable minimum detected concentration which is actually the required parameter in most analyses. Moreover, unlike with standard PTV, the high flow rate amenable with SMB enables direct injections into the column, without the split related compound discrimination that occurs with standard PTV. Note, that while the large column flow reduces the injection time, the differential pumping protects the MS from the solvent.
4.		All of the available GC injectors can be used with different columns (type, ID and length) that can be simultaneously connected to the nozzle for higher analysis flexibility.
5.		Column replacement does not require opening of the vacuum chamber.
6.		(Option) One injector can be converted into a direct sample introduction device (ChromatoProbe) combined with a high flow short column as a transfer line.
7.		An effective coupling with an external purge and trap or thermal desorption system can be achieved due to the high flow allowed.
8.		The two ion sources EI-SMB  and HSI are interchangeable without breaking vacuum.

7. Sensitivity Considerations and Evaluation

At this time sensitivity specifications are available only upon request and the general discussion pertains to the experimental apparatus at Tel Aviv University. It can serve as an initial guideline.

Hyperthermal surface ionization is the most sensitive ion source for positive ion mass spectrometry due to:

Minimum detected amount of 400 attograms was demonstrated with the experimental apparatus.

Electron Impact ionization in SMB is about as sensitive as the conventional EI. The reduced ionization probability of the faster molecules in the SMB and the inherent jet separation losses are compensated for by:

Minimum detected amount of 60 femtograms was demonstrated with single ion monitoring of the molecular ion peak of eicosane with the experimental apparatus.

Unique Supersonic GC-MS and Fast Supersonic GC-MS further contributes to enhanced sensitivity through:

8. The Analysis of Thermally Labile and Relatively Non Volatile Compounds

The use of SMB for sampling and ionization considerably increases the scope of use of GC-MS and broadens the range of compounds amenable for such analysis in two areas:

A)  Thermolabile GC-MS
The analysis of thermally labile molecules is considerably improved in comparison with conventional GC-MS owing to the following reasons:

When these three elements are combined, fast GC-MS with the Supersonic GC-MS can be considered equivalent to, or in some cases even softer than particle beam LC-MS which involves high temperature thermal vaporization from reactive metal surfaces in the EI ion source [14].

B)  The Highest Temperature Tailing-Free GC-MS
Tailing-Free GC-MS is achieved without any mass spectrometric ion source related limitations. The vacuum background elimination processes ensures tailing-free GC at any temperature, and the fly-through EI ion source provides an enhanced M+ due to the vibrational supercooling. Currently, the limitation is 460 C with the SGE-HT-5 column. Note that the combination of short column and 2000 cm/sec potential column flow velocity, further extends the range of non volatile molecules amenable for GC-MS analysis.

9. Applications of Supersonic GC-MS and Fast GC-MS

Supersonic GC-MS and fast GC-MS excel in a wide range of applications due to the broad range of advantages and unique features available as listed in section 2. Accordingly, in any non-standard applications it can replace the available standard instrumentation and provide a competitive advantage. A list of a few major such applications include:

1. Petroleum-MS.
Petrochemical analysis should benefit from many of the unique features of SMB-MS including molecular ion information in alkanes, molecular ion only MS at low electron energies EI, unique isomer information, aromatic selective detection and higher temperature GC-MS.
The added information can quickly be translated into saved money.

2. Forensic Analysis
The system flexibility and broad range of new capabilities are all important for a variety of forensic applications including fast GC-MS of thermally labile explosives, molecular ion information for arson investigations, trace level of drug detection with HSI and including the optional ChromatoProbe serving as a probe for dirty samples.

3. Clinical Toxicology - Screening of Drugs in Urine.
The sensitivity and selectivity of HSI combined with fast GC-MS enables the injection of small samples of untreated urine for drug screening in a few minutes from the sample to the results. This can turn Supersonic GC-MS into a potential competitor for the multi-billion Dollar market of drug screening in urine that is currently dominated by immunoassay techniques. The same GC-MS with a second longer column can serve for confirmation, featuring enhanced M+ in EI. In some cases the exceptional sensitivity of HSI will enable the detection of ultra trace levels of drugs in plasma and urine extracts. A unique capability of fast drug detection in a single, untreated human hair opens up many new possibilities.

4. Process Control.
The very fast analysis capability and selectivity enable simple and effective process control.

5. GC-MS research and General Organic and Inorganic Mass Spectrometry.
The easy to use ChromatoProbe direct sample introduction (Option), fast GC-MS capability, extended temperature range, enhanced molecular ion peak, isotope and elemental information, tunable fragmentation, possible choice between two columns without any hardware change and many other features are all important to this application.

6. Environmental Analysis.
The analysis of thermally labile pesticides (carbamates) is important application. Environmental analysis can further benefit from improved sensitivity with HSI in the analysis of PAH's, large splitless injection capability, fast GC-MS screening ability and enhanced M+. The optional DSI device (ChromatoProbe) enables extract free pesticide analysis in fruit, vegetables, spices and other food items.

10. Direct/Dirty Sample Introduction Device (ChromatoProbe)

A unique (US patent) Direct Sample Introduction (DSI) device was developed by us which is especially suitable for use with Supersonic-GC-MS. This "ChromatoProbe" serves for three major applications, each with many advantages. A dedicated booklet is available upon request with detailed description of ChromatoProbe, SnifProbe and its applications.

1.		Direct Sample Introduction for Mass Spectrometry Studies.   The ChromatoProbe, effectively transforms a conventional GC injector, (second GC injector in the GC-MS) followed by a short column, into a cost-effective alternative to the standard direct probe. It possesses the advantages of faster and easier operation, faster ChromatoProbe/GC-MS interchange, capability of sampling solutions, possible use as a micro-chemical (derivatization) reactor and easy conversion into a fast GC-MS channel.
2.		Extract-Free Dirty Sample Introduction For GC-MS Analysis.   This new method is based on sampling in a micro vial that retains the harmful and non-volatile matrix residue of real world samples. Thus, it eliminates the need for further sample clean-up, while the test tube is a disposable item. Each analysis begins with gentle solvent vaporization, preferably at a relatively low injector temperature such as 120 C for water/urine (20 C above the solvent boiling temperature), followed by brief injector heating to the temperature required for achieving effective intra injector thermal extraction and sample compound vaporization. The sample semi-volatile compounds are focused on the early portion of the column and are analyzed by the chromatography as usual. This method brings the many known advantages of thermal extraction in an easy to use low cost fashion, combined with the many advantages of SMB-MS. It facilitates extract free analysis of drugs in urine or hair, or pesticides in blended fruit and vegetable items, or in milk, juice and slurries. The DSI also uniquely allows large size sample injections of conventional extracts without the associated residues that usually restrict the sample size, and thus lower detected concentration limits can be achieved. The containment of the non-volatile compounds in the disposable test tube also results in faster analysis that can end at a lower column temperature.
3.		SnifProbe Gas Analysis   SnifProbe (option) is based on the use of 15 mm short pieces of standard 0.53 mm ID capillary or PLOT column for sampling air born, head space, aroma or air pollution samples. Thus, SnifProbe extends the ChromatoProbe range of samples that now also includes gas phase samples. The short (15 mm) column is inserted into the SnifProbe easy-insertion-port and the SnifProbe is located or aimed at the sample environment. A miniature pump is operated for pumping 6-60 ml/min of air sample through the sample collection short piece of column. After a few seconds of pumping, the short column is removed from the SnifProbe with tweezers and placed inside a ChromatoProbe glass vial having a 0.5 mm hole at its bottom. The ChromatoProbe sample holder with its glass vial and sample in the short column are introduced into the GC injector as usual. The sample is then quickly and efficiently vaporized from the short sample column and is transferred to the analytical column for conventional GC and or GC-MS analysis.   SnifProbe enables many of the manual SPME, air bags and Tenax tube applications, with a few advantages. SnifProbe is ideal for field or process operation, it is small, enables fast sampling, compatible with the full range of semi volatile compounds and enables low cost sensitive analysis.

Note that the combination of Supersonic GC-MS with the ChromatoProbe (DSI) is especially effective since:

11. Laser Desorption Fast GC-MS

An important additional aspect of fast GC-MS pertains to the issue of high repetition rate automated sample injection method. The quest for such a method is further complicated by the need to achieve it for a large variety of samples, on/in a variety of complex matrices, and without sample preparation. Today, automated sample injection is performed with an autosampler that is capable of performing about one injection per minute. It is also limited to relatively clean samples, in the form of liquid solutions (or gases) introduced in crimped vials that are located on a sample tray. As a result, the standard autosampler is practically incompatible with the majority of ultra-fast GC-MS analyses, and a new and much faster injection method is desirable for ultra-fast GC-MS.
The use of focused or slightly defocused laser light for sample desorption and volatilization seems to be the ideal injection method for ultra-fast GC-MS, comprising several inherent desirable features [18] including:

The subject of laser desorption for analytical purposes is not new, and matrix assisted laser desorption ionization is a major subject of research today. However, most of the laser desorption schemes are based on laser desorption of samples that are placed inside the mass spectrometer vacuum chamber. Our recently developed novel method of laser desorption is based on the “injection” of samples placed at ambient atmospheric pressure, either under helium purging conditions or in the open air [18]. The laser desorption unit was mounted on a home made ultra-fast GC-MS injector inlet, with a thermally insulated clamp and mounting rod. The sample was placed on the sample holder, located inside the sample compartment. The laser used was a pulsed XeCl Excimer laser with 30-50 mJ 308 nm laser pulses of about 12 nsec duration. The laser pulse energy at the sample was only 3-5 mJ due to its energy reduction through the light transfer optics. The laser pulses were controlled by a pulser and either a single laser pulse or a train of typically 20 pulses at a repetition rate of 50 Hz was employed for 0.4 sec injection time. The laser light was softly focused on the sample with about a 0.1 mm desorption point diameter. After laser desorption, the sample vapor or particles were swept by a helium carrier gas that was provided by a tube above the sample. This sweeping helium gas also served as both a purge gas and fast GC carrier gas. A very high carrier gas flow rate of over 300 ml/min was essential for achieving effective and fast laser desorption injection, since, depending on the laser pulse energy, the desorbed sample volume could be over 1 ml. The thermal insulation of the sample from the separately heated injector enabled the analysis of relatively volatile compounds. The laser desorbed vapor and particles were further transferred through a glass frit filter that prevented nozzle clogging and also acted as a thermal vaporizer for the sample particles. After the glass frit, the sample passed through a 50 cm long megabore column that enables ultra-fast GC separation, followed by supersonic expansion, ionization and mass analysis as described throughout this document.
The application of laser desorption fast GC-MS analysis was employed and studied by us using a variety of samples and matrices, including: a) The analysis of dioctylphthalate oil (and its cleaning procedure) on a stainless steel surface; b) The analysis of methylparathion and aldicarb pesticides on an orange leaf; c) The analysis of methylparathion pesticide on the surface of liquid water. d) The analysis of paracetamol and codeine in a tablet; e) The analysis of lidocaine at one ppm level in coagulated blood.

The Laser desorption inlet is proposed only as an optional inlet system that requires some further R&D for its coupling with the HP 6890 GC and with a new laser system.

12. Links

Enclosed are a few links for some of the technologies and components that are used in the Supersonic GC-MS and/or   that could be used in its current or future options.

13. References *(recommended for reading as a review)

In a book "Supersonic Molecular Beam Mass Spectrometry - The Quest for Ultimate Performance GC-MS and Fast GC-MS" the Supersonic GC-MS technology is described and demonstrated through 51 figures and many applications.
This book is available free on request.
You may ask for it at:  amirav@supermass.co.il.
Please add a brief description of your application and range of GC-MS interests.

We shall be delighted to try your samples and meet your requirements so that you could closely evaluate the suitability of Supersonic GC-MS to solve your needs.  Please challenge us at: amirav@supermass.co.il.