PTV injection

Certainly, the precision and accuracy of the PTV techniques are generally superior to those of the classical hot split and splitless techniques and approach those obtained by cold on-column Injection [ 34,36,37, -54-57,62,64]. However, less is known concerning optimization of PTV injection and probably more parameters have to be considered than for cold on-column injection. The latter is, consequently, the preferred injection technique for most samples, except those contaminated by larg< amounts of involatile Impurities and for headspace vapors. 

Principles and Characteristics As mentioned already (Section 3.5.2) solid-phase microextraction involves the use of a micro-fibre which is exposed to the analyte(s) for a prespecified time. GC-MS is an ideal detector after SPME extraction/injection for both qualitative and quantitative analysis. For SPME-GC analysis, the fibre is forced into the chromatography capillary injector, where the entire extraction is desorbed. A high linear flow-rate of the carrier gas along the fibre is essential to ensure complete desorption of the analytes. Because no solvent is injected, and the analytes are rapidly desorbed on to the column, minimum detection limits are improved and resolution is maintained. Online coupling of conventional fibre-based SPME coupled with GC is now becoming routine. Automated SPME takes the sample directly from bottle to gas chromatograph. Split/splitless, on-column and PTV injection are compatible with SPME. SPME can also be used very effectively for sample introduction to fast GC systems, provided that a dedicated injector is used for this purpose [69,70],... 

David, F., C. Devos, D. Joulain, et al. 2006. Determination of suspected allergens in non-volatile matrices using PTV injection with automated liner exchange and GC-MS. J. Sep. Sci. 29 1587-1594. 

Forcada, M., J. Beltran, F.J. Lopez, et al. 2000. Multiresidue procedures for determination of triazine and organophosphorus pesticides in water by use of large-volume PTV injection in gas chromatography. 

PTV injection Produces better quantitative results than classi-... 

An alternative for achieving a lower column load and enough analyte in the detector is to perform an additional separation before the analytes reach the analytical column. In this separation, part of the sample that is not of interest can be eliminated, and at the same time the important analytes can be kept. This preliminary separation can be done using bidimensional chromatography (see further), but simpler techniques are also reported, such as programmed temperature vaporization (PTV) injection, etc. 

It has been shown that the PTV injector is a very useful technique for large-volume injection, especially for the analysis of a dirty sample. Because the vaporization of the solvent is carried out at a low temperature, nonvolatile matrix constituents remaining in the liner will not contaminate the GC column. However, the PTV injection technique is less suited when analyzing volatile compounds because only components with volatility significantly below that of the solvent are trapped in the cold liner, unless liners packed with a selective adsorbent is used [4]. 

HRGC-FTIR analysis was carried out with a Nicolet 20 SXB system interfaced to a Dani 6500 gas chromatograph. A J W fused silica DB-5 colujnn, 30 m x 0.32 mm id, df = 0.25 pm, was used. PTV injection (4(T -200°C) was performed. The temperature program was 60° to 250°C at 5°/min. Light pipe and transfer line were held at 200°C He (2 ml/min) was employed as carrier gas. Vapor phase spectra were recorded from 4000 - 700 cm- with a resolution of 8 cm-. ... 

Splitless injection is generally the preferred choice for the analysis of pesticides by virtue of its robustness. However, oncolumn and programmed temperature vaporizer (PTV) injection have also been used for this purpose. One important, interesting approach here is the direct injection of large sample volumes using a PTV injector or an Autoloop. These interfaces have been used for the determination of pesticides in water samples. ... 

All heated injector systems are well-known sources of error, due to the possibility of artifact formation, and in many cases, split, splitless, or PTV injection provides discrimination of high-boiling compounds by thermal degradation. Only cold on-column injection ensures quantitative sample transfer from the injection port into the capillary column without thermal stress of the samples or discrimination of high-boiling compounds. 

The methods for transferring LC fractions to GC were developed hand in hand with large-volume GC injection. They mostly involved on-column techniques, since these show best performance and follow rather simple rules. The main drawback, the sensitivity to nonevaporating by-products, is not important, since efficient preseparation by LC is also efficient in removing the contaminants . The principal alternative, programmed temperature vaporizing (PTV) injection in solvent split mode, has rarely been applied. 

The low concentration levels of the compounds in environmental samples impose specific requirements in terms of sample injection for GC analysis. In addition to the common injection techniques of capillary GC (split, splitless, on-column, and programmed temperature vaporized (PTV) injection), some other sample introduction methods coupled to GC such as solid-phase microextraction (SPME), headspace, etc., have favored the versatility of GC and reduced the time required for sample preparation. These techniques have an advantage over the conventional injection methods, which is that a preconcentration step prior to GC... 

Teske, J., J. Efer, and W. Engewald, Large-Volume PTV Injection New Results on Direct Injection of Water Samples in GC Analyis, Chromatographia 1997 46(11/12) 580-586. 

Grob, K. (1986) Glassical Split and Splitless Injection in Gapillary Gas Ghro-matography with Some Remarks on PTV Injection, Huethig, Heidelberg. 

Teske, J., Efer, J., and Engewald, W., Large volume PTV injection Comparison of direct water injection and in-vial extraction for GC analysis of triazines, Chromatographia, 47, 35,1998. 

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