Programmed temperature vaporizing PTV

A programmed-temperature vaporizer (PTV) has also been used as an interface for introducing the LC fraction to the GC unit (84,96) and to desorb the analytes retained in the SPE sorbent contained in the PTV liner. Water samples can then be injected directly in to the PTV injector. 

Another interface for RPLC-GC is the programmed-temperature-vaporization (PTV) system, an interesting application of which is the determination of phthalates... 

Numerous types of GC injectors have been manufactured over the past four decades. The most commonly used injection techniques have been reviewed and described by Grob, who correctly states that analysts must fully understand the techniques before they can make the most appropriate choice for their particular application(s). For most GC capillary column applications, the split/splitless, programmed-temperature vaporization (PTV) and on-column injectors remain the most popular. However, over the last few years, technology has progressed rapidly to provide injectors that allow more of the sample extract on to the GC column without overloading it. 

Programmed temperature vaporization (PTV) Most versatile inlet Allows large volume injection Little-no sample degradation Effective trace (to sub-ppb) analysis Expensive Requires optimization of many parameters Not well-known... 

For capillary GC, the split/splitless inlet is by far the most common and provides an excellent injection device for most routine applications. For specialized applications, there are several additional inlets available. These include programmed temperature vaporization (PTV) cool on-column and, for packed columns, direct injection. PTV is essentially a split/splitless inlet that has low thermal mass and a heater allowing rapid heating and cooling. Cool injection, which can be performed in both split and splitless mode with the PTV inlet, reduces the possibility of sample degradation in the inlet. Capabilities of the commonly available inlets are summarized in Table 14.3. 

Modern GC instruments represent high resolution systems that are fully automated from sample injection to final data reduction. Utilization of new injection devices has provided the means to enhance the performance level significantly. Studies have shown, for example, that injection of the tranquilizer propio-nylpromazine and its sulfoxide into a hot injection port gave much poorer results than on-column injection at low temperature (44). In the latter case, however, nonvolatile sample components could enter the column. This disadvantage of classic sample injection can be eliminated through use of a programmed temperature vaporization (PTV) injector. 

A programmed temperature-vaporization (PTV) injector (with a sorbent-packed liner) was used to preconcentrate and inject the sample. Thermal desorption was performed and the analytes were passed to a primary column (16 m X 0.32 mm i.d., film thickness 5 p.m, 100% methyl polysiloxane) and separated according to analyte vapour pressure. Selected heart-cuts were transferred to a second column (15 m X 0.53 mm i.d., Al203/Na2S04 layer, open tubular column with 10 (im stationary phase) where final separation was performed according to chemical functionality. 

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. 

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. ... 

Brossa et al. developed an automated SPE-GC-MS method for the determination of endocrine disrupting compounds including six phthalate esters. The interface device was a programmed temperature vaporizer (PTV), whose liner was packed with Tenax. The samples were spiked with 50% of methanol and 15 ml of this mixture were preconcentrated. Before elution, the precolumn was dried with nitrogen. The analytes were desorbed in the backflush mode with three ethyl acetate fractions of 100 /rl and online transferred to the GC system. The performance of the method was tested with several environmental water samples. The recoveries achieved were satisfactory and the detection limits were between 1 to 36 ng/1. 

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... 

Stir bar has to be removed, introduced into a glass tube, and transferred to thermal desorption instrument. After desorption and cryofocusing within a cooled programmed temperature vaporization (PTV) injector, the volatiles were transferred onto the analytical GC column. Comparison of SPME and the above-mentioned stir bar sorptive extraction (SBSE) technique using identical phases for both techniques exhibited striking differences in the recoveries, which has been attributed to ca. 100 times higher phase ratio in SBSE than in SPME. A comprehensive treatment of SBSE, discussion of the principle, the extraction procedure, and numerous applications was recently been published by David and Sandra (2007). 

A programmed-temperature vaporization (PTV) inlet is a hybrid of the techniques described above. It is a spUt/spUtless inlet that has been modified to allow cold injection and rapid temperature programming. Similar to on-column injection, the injection occurs while the inlet is cold. In contrast, the injection is performed into a chamber, similar to the spUt and spUtless techniques. This chamber is then rapidly heated to desorb the sample into the capillary column. This inlet also allows for the injection of up to hundreds of microUters of sample. There are numerous modes in which a PTV inlet can be operated, making it perhaps the most versatile of all available inlets. 

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