GC-TOFMS

An advantage of the microbore gas chromatrography/time-of-flight mass spectrometry (GC/TOFMS) method over the other two approaches is that separation efficiency need not be compromised for speed of analysis. The rapid deconvolution of spectra ( scan rate ) with TOFMS makes it the only MS approach to achieve several data points across a narrow peak in full-scan operation. However, the injection of complex extracts deteriorates performance of microbore columns quickly, and an increased LOD and decreased ruggedness result. Microbore columns may be used in water analysis if the LOD is sufficiently low, but they can rarely be used in real-life applications to complicated extracts. 

GC-FTIR, GC-AED, GC-ICP-MS, cf. Chapter 7), fast GC separations (1996) and most recently the development of sophisticated injectors with temperatureprogramming capability and high-resolution systems (GC-ToFMS). As a result, modem GC systems are quite advanced (Scheme 4.3) and GC is one of the most widely applied instrumental techniques. 

The usefulness of ultrafast GC with separation of simple samples in a few seconds is limited. Extremely fast analysis in the ms range is only possible if the required number of theoretical plates is relatively low. GC-ToFMS allows ultrafast separations (within seconds). 

The mass spectrometer is a mass-flow sensitive device, which means that the signal is proportional to the mass flow dm/dl of the analyte, i.e. the concentration times the flow-rate. It is only now possible to realise the high (theoretically unlimited) mass range and the high-sensitivity multichannel recording capabilities that were anticipated many years ago. Of considerable interest to the problem of polymer/additive deformulation are some of the latest developments in mass spectrometry, namely atmospheric pressure ionisation (API), and the revival of time-of-flight spectrometers (allowing GC-ToFMS, MALDI-ToFMS, etc.). 

The use of GC-MS in polymer/additive analysis is now well established. Various GC-based polymer/additive protocols have been developed, embracing HTGC-MS, GC-HRMS and fast GC-MS with a wide variety of front-end devices (SHS, DHS, TD, DSI, LD, Py, SPE, SPME, PTV, etc.). Ionisation modes employed are mainly El, Cl (for gases) and ICPI (for liquid and solid samples). Useful instrumental developments are noticed for TD-GC-MS. GC-SMB-MS is a fast analytical tool as opposed to fast chromatography only [104]. GC-ToFMS is now about to take off. GC-REMPI-MS represents a 3D analytical technique based on compound-selective parameters of retention time, resonance ionisation wavelength and molecular mass [105]. 

Resolution HR-CGC, GC-ToFMS, HRMS, HR-ICP-MS, MS/MS, DI-HRMS, HRLEELS, HRTGA LR-NMR, LRRS... 

Various techniques have been introduced which still lack specific applications in polymer/additive analysis, but which may reasonably be expected to lead to significant contributions in the future. Examples are LC-QToFMS, LC-multi-API-MS, GC-ToFMS, Raman spectroscopy (to a minor extent), etc. Expectations for DIP-ToFMS [132], PTV-GC-ToFMS [133] and ASE are high. The advantages of SFC [134,135], on-line multidimensional chromatographic techniques [136,137] and laser-based methods for polymer/additive analysis appear to be more distant. Table 10.33 lists some innovative polymer/additive analysis protocols. As in all endeavours, the introduction of new technology needs a champion. 

Standards Agency [13,14]. The techniques of GC-MS, GC x GC-ToFMS [15] and LC-MS have been used. 

Leco Separation Science Application Note, Pegasus II GC/TOFMS, Form No. 203-821-091. 

ShelUe, R. Marriot, P. Morrison, P. Concepts and preliminary observations on the triple-dimensional analysis of complex volatile samples by using GC x GC-TOFMS. Anal. Chem. 2001, 73, 1336-1344. 

The mass range of commercial TOF instruments is up to 10,000 Da. Resolution depends on the type of TOF and ranges from 1000 for instruments designed as dedicated detectors for GC (GC-TOFMS) to 20,000 for reflectron instruments. One limitation to the use of a conventional reflectron instrument is a loss in sensitivity about 10% of the ions are lost with a conventional wire grid reflectron. 

The rapid collection of the entire mass spectrum made possible by the TOF makes it ideal for interfacing with a chromatograph. It is especially useful when combined with fast GC, which requires the rapid collection of hundreds of mass spectra. For example, the LECO Pegasus 4D GC-TOFMS collects the entire mass range from 1 to 1000 Da in 170 p.s and collects up to 500 mass spectra/s. (A detailed description of this instrument can be found at www.leco.com.)... 

Rapid Determination and (Juantification of Sensitizers and Skin Irritants in Fragrances by GC-TOFMS. LECO Separation Science Application Note, Form 203-821-191,3/03-REV2,1. 

Compound EADl subjected to GC>secondary column, matched well with 1k(eadi) = 1108 corifirining the same identity in both GC-EAD and GCxGC-TOFMS analysis. Spectrum, retention and GC-EAD behaviour of compound EADl was identical to that obtained for synthetic ipsenol (2-methyl-6-methylene-7-octen-4-ol, 1). 

LOD, defined here as the lowest quantity of analyte injected on-column to be detected with respect to peak identification criteria of S/B > 3, plus verification of the isotope abundance ratio for at least two isotopologs of the molecular ion and retention time consistency in both GC dimensions, was 0.5 pg for 2,3,7,8-TeCDD (Figure 11.24). This represents an improvement by a factor of 5-10 compared with conventional GC-TOFMS but is an order of magnitude higher than for GC-HRMS instruments (typically 0.04pg for 2,3,7,8-TeCDD). 

The sensitivity of the GC x GC-TOFMS instrument is acceptable for measurements of dioxin-like compounds... 

APPLICATION OF GC X GC-TOFMS TO THE CHARACTERIZATION OF EXTRATERRESTRIAL ORGANIC MATTER... 

The combination of GC x GC with TOFMS has considerable potential for the study of samples of astro-biological significance, for example in the study of complex hydrocarbon mixtures extracted from Late Archean sediments [31] or in characterizing the products of laboratory synthesis of Titan tholins [32]. Presented here is the general principles of two-dimensional gas chromatography-time-of-flight mass spectrometry (GC x GC-TOFMS) analysis for the... 

To further characterize the products released upon thermochemolysis, comprehensive GC x GC-TOFMS was utilized. Thermochemolysis was performed at 280°C under conditions as described above. GC x GC-TOFMS analysis was performed using an Agilent 6890 GC with a GC X GC modulator (Leco) coupled to a Pegasus IV TOF mass spectrometer (Leco). The GC injector was operated in split mode (20 1) with a column flow rate of 1 mL/min and held at 250°C. GC x GC separation utilized a nonpolar column and a polar column a BPX5 (30 m X 0.25 mm x 0.25 pm SGE) and a BPX50 (1.8 m X 0.1 mm x 0.1 pm SGE), respectively. The GC oven temperature was held for 10 min at 35°C and ramped to 300°C at a rate of 5°C/min and then held for 5 min the second column was ramped at +15°C relative to the first column with a modulation time was 4 s. Mass spectra were acquired in electron ionization mode from 33 to 500 amu with an acquisition rate of 135 Hz. 

When the Py-GC x GC-TOFMS is used, many more species can be resolved in a chromatogram. The increase in resolving power can be observed across the whole chromatogram when compared to one-dimensional separation. The pyrolyzate is dominated by one- to four-ring aromatic compounds however, with the increased separation it is also possible to identify a number of aliphatic hydrocarbons which are retained less on the second column than the aromatic components. Aliphatic hydrocarbons include branched alkanes, alkenes, and cyclic compounds in the range of C8-C17. The more polar moieties such as phenols and benzonitriles are also separated from the hydrocarbons. 

FIGURE 18.1 Total ion chromatograms from GC-MS and GC X GC-TOFMS (contour and surface plots) of products released upon pyrolysis of Murchison. T, toluene MT, methyl-thiophene BN, benzonitrile N, naphthalene BT, benzothio-phene TT, thenothiophenes. 

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