Programmed-temperature splitless injection

For routine analysis of liquid samples, four injection techniques are available split, splitless, on-column and programmed temperature vaporising injection [90]. 

There are several types of sample introduction systems available for GC analysis. These include gas sampling valves, split and splitless injectors, on-column injection systems, programmed-temperature injectors, and concentrating devices. The sample introduction device used depends on the application. 

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. 

Gas chromatographic analysis starts with introduction of the sample on the column, with or without sample preparation steps. The choice of inlet system will be dictated primarily by the characteristics of the sample after any preparation steps outside the inlet. Clearly, sample preparation has a profound influence on the choice of injection technique. For example, analysts may skip the solvent evaporation step after extraction by eliminating solvent in the inlet with splitless transfer into the column. Sample introduction techniques are essentially of two types conventional and programmed temperature sample introduction. Vogt et al. [89] first described the latter in 1979. Injection of samples, which... 

Solvent venting, without splitting Liquid sample from syringe into cold inlet. Solvent is vented at low temperature, condensing nonvolatiles. Heat programming subsequently vaporises the residues, which enter column as in splitless injection Dilute samples thermally labile Broad, some focusing required 1-1000 80-95... 

Figure 5.19 Formation of amino acids on ice surfaces irradiated in the laboratory (Nature Nature 416, 403-406 (28 March 2002) doi 10.1038/416403a-permission granted). Data were obtained from analysis of the room temperature residue of photoprocessed interstellar medium ice analogue taken after 6 M HCl hydrolysis and derivatization (ECEE derivatives, Varian-Chrompack Chirasil-L-Val capillary column 12 m x 0.25 mm inner diameter, layer thickness 0.12 pirn splitless injection, 1.5 ml min-1 constant flow of He carrier gas oven temperature programmed for 3 min at 70°C, 5°C min-1, and 17.5 min at 180°C detection of total ion current with GC-MSD system Agilent 6890/5973). The inset shows the determination of alanine enantiomers in the above sample (Chirasil-L-Val 25 m, single ion monitoring for Ala-ECEE base peak at 116 a.m.u.). DAP, diaminopentanoic acid DAH, diaminohexanoic acid a.m.u., atomic mass units.

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. 

Gas chromatograph systems are composed of an inlet, carrier gas, a column within an oven, and a detector (O Figure 1-1). The inlet should assure that a representative sample reproducibly, and frequently automatically, reaches the column. This chapter will cover injection techniques appropriate for capillary columns. These include direct, split/splitless, programmed temperature vaporization, and cool on-column injection (Dybowski and Kaiser, 2002). 

Two microliters of the sample are injected by splitless injection (290°) and separated with a constant helium flow of 1.5 ml/min while programming the oven temperature from 80-290°C in approximately 10 min. 

Figure 3. Total ion chromatogram of extractable organics in a typical lot of Ambersorb XE-340 resin (SP-2100,10-m capillary column, temperature program 50(2)-250 at 5 °C/min, 1.0-pL splitless injection). 1, naphthalene 2,1- or 2-methylnaphthalene 3, biphenyl 4, 1,V-biphenyl, 2- or 3-methyl 5, fluorene 6, anthracene-phenanthrene 7tl- or 2-phenylnaphthalene 8, pyrene 9, fluoranthene 10, terphenyl isomer 11, benzo[b]naphthothiophene isomer 12, binaphthalene isomer 13, benzofluoranthene isomer. (Reproduced from...

Typically splitless injection is used for trace analysis by capillary GC. Splitless injections can exhibit problems with carryover, poor repeatability, and labile analytes. Penton (1991) reports improved results with the temperature-programmable injector. With a temperature-programmable injector, samples are injected into a glass insert at an injector temperature below the boiling point of the analysis solvent the injector temperature is then rapidly programmed to a higher value. Penton reported this technique offered greater ease of optimization and improved precision. 

When the extracted analytes are to be retained directly on the chromatographic column or at the retention interface, their insertion can be accomplished in various ways, namely (a) by injection into the column, whether directly (SFC, GC) or with the aid of a cooling system (GC, HPLC) (b) by split-splitless injection (SFC, GC) (c) by using a programmed temperature vaporizer (GC) or (d) by injection into a cold trap and subsequent thermal desorption (GC) or elution (HPLC). 

GC-MS (70 eV) analysis is possibly performed with a modern sensitive instrument equipped with a PEG-type bound-phase fused-silica (30 m x 0.32 mm i.d. 0.25 pm film thickness) capillary column, working with helium as carrier gas at flow-rate of 1.2mL/min, transfer line temperature 220 °C and MS source temperature 150 °C. Analysis is carried out in single ion recording (SIR) mode. In the optimized chromatographic conditions proposed by Fedrizzi et al. (2007a), the GC injector is set at a temperature of 250 °C and operates in splitless injection mode for 1 min the oven temperature is programmed to start at 35 °C (5 min), then increased by 1 °C/min to 40 °C, and finally increased by 10°C/min to 250 °C. 

Instruments IR-85 Fourier Transform infrared spectrometer, through an IBM GC-IR interface. The interface consisted of a gold-coated Pyrex light-pipe with potassium bromide windows. A scan rate of 6 scans/sec and a spectral resolution of 8 cm- - were used for data acquisition. Samples were introduced into the system via splitless injections. A fused silica capillary column, 30 m x 0.32 mm i d DB-WAX (dj 1.0 pm), was employed with the outlet end connected directly to the GC-IR light-pipe entrance. Helium was used as the carrier gas at an average linear velocity of 41.4 cm/sec (35°C). No make-up gas was employed in the system. The column temperature was programmed from 35°C to 180°C at 2°C/min. The GC-IR light-pipe assembly was maintained at 170°C. 

Sample extracts were analysed by capillary gas chromatography with electron capture detection using either Perkin-Elmer series 8310 or 8510 instruments. One microlitre aliquots were injected via a split/splitless injection system operated in the splitless mode. The components were separated on a 25 m WCOT fused silica capillary column (CP-Sil-5, internal diameter 0.22 pm, Chrompack, UK). The stationary phase was non-polar 100% dimethylpolysiloxane. The temperature program for the separation of chlorobenzenes was based upon the work of Lee et al (1986). Quantification was based on the method of internal or external standard. 

Separation and identification of the BTEX mixture was carried out on a Carlo Erba HRGC 5300 Mega Series gas chromatograph, with split/splitless injection and flame ionization detection. A 30 m x 0.25 mm id x 0.1 im film thickness DB-5 capillary column was used, with temperature programming from an initial temperature held at 50°C for 3 min before commencing a 16°Cmin 1 rise to 120°C, with a final hold time of 7 min. The detector temperature was set at 250°C. 

This injector, named PTV programmed temperature vaporizer), is conceptually similar to the split/splitless model. The temperature of the injection chamber can be programmed to effect a gradient, e.g. from 20 up to 300 °C, in a few tens of seconds (Figure 2.6). So, the advantages of the split/splitless injection are combined with those of the cold injection onto the column. 

Figure 4. Glass capillary gas chromatograms of aromatic hydrocarbons in New York Bight surface sediments. Analysis conditions 20 m X 0.32-mm i.d. Jaeggi SE-54 column installed in a Carlo Erba Model 2150 gas chromatograph equipped with split/splitless injection helium carrier gas at 0.55 kg/cm2 injection at room temperature, program 80°-240°C at 3°/minute injector and detector at 250°C. Numbered peaks are identified in Table V.

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