Oven Temperature Programming

The capillary column is placed in an oven because the interactions between compounds and the stationary phase depend on the tanperature. Increasing the stationary phase speeds the elution of the compounds and therefore decreases the time of analysis. Most users work with temperature programming. Certain screening methods aim to detect a large number of compounds in a single analysis and frequently use temperature programming ranges from 40 to 350°C. 

In practice, when performing an analysis on matrix extracts, one must keep in mind that temperature progranuning must take into account the volatilities of analytes and also those of the interfering compounds from the matrix that must be eluted to prevent pollution of the capillary column. Since the precise boiling points of interfering compounds are generally unknown, the final programmed temperature of an oven frequently corresponds to the maximal temperature that the column can stand in order to evacuate as many pollutants as possible. 

The analysis of very volatile compounds, of certain solvents, for example, can lead to maintaining an oven at a temperature below ambient. In order to do this, a cryogenic liquid, generally carbon dioxide, is sequentially injected into the oven to cool it. The COj is compressed in a cylinder at a pressure around 200 bars. The 

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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.

Chromatographic Conditions. GC/MS-MS analyses were performed on a Varian 3800 gas chromatograph (Varian Chromatography Systems, Walnut Creek, CA) equipped with a 1079 split/splitless injector and a ion trap spectrometer (Varian Saturn 2000, Varian Chromatography Systems) with a waveboard for MS-MS analysis. The system was operated by Saturn GC/MS Workstation v5.4 software. The MS-MS detection method was adapted from reference. PCBs were separated on a 25 m length x 0.32 mm i.d., CPSil-8 column coated with a 0.25-pm film. The GC oven temperature program was as follows 90 °C hold 2 min, ramp 30 °C/min to 170 °C, hold for 10 min, rate 3 °C/ min to 250 °C, rate 20 °C/min to a final temperature of 280 °C, and hold for 5 min. Helium was employed as the carrier gas, with a constant column flow of 1.0 mL/min. 

Gas Chromatography-Mass Spectrometry. A Finnigan 4500/Incos instrument with a 30-m X 0.32-mm i.d. capillary column coated with SP-B-5 was used. The GC parameters were as follows injector, 270 °C column oven temperature programmed, 50 °C (0.1 min, hold) 15 °C/min to 100 °C, 5 °C/min to 270 °C internal standard, anthracene-djo helium flow, 3.0 mL/min sample size, 3.0 /xL. MS conditions were as follows El, 70 eV scan (m/z), 35-650 daltons source temperature, 250 °C filament current, 0.5 A sensitivity, 10-8 A/V. (NOTE When the name of a compound is followed by (confirmed) , it means that the standard material was analyzed for confirmation under conditions identical to those of the sample when the name is followed by (tentative) , it means that the mass fragmentography showed the best fit (>80 ) based on the National Bureau of Standards [NBS] library computer search.)... 

Figure D1.2.2 Sample GC chromatogram of the FAME from butter fat (Sweet Cream Butter, Wisconsin Grade AA, Roundy s, Milwaukee, Wise.) prepared using the sodium methoxide method (see Basic Protocol 2). Equipment DB-23 fused silica capillary column, 30 m x 0.32 mm i.d., 0.25 pm film thickness, FID detector. Temperature, injector 225°C detector 250°C. Column (oven) temperature program 100°C initial, hold 4 min, ramp to 198°C at 1.5°C/min, hold 10 min. Total run time was 80 min. Split injection.

Fig. 12.3 Fast cocaine determination in coca leaves by GC according to Ilias et al. (adapted from [37]). (a) Schematic of the total analysis time, (b) Fast GC-FID chromatogram using a short 100 p,m i.d. column and a fast oven temperature programming.

Gas Chromatographic Conditions. All analyses were performed on a Hewlett Packard 5890 GC equipped with a 5970 Mass Selective Detector or a Hewlett Packard 6890 GC equipped with a Nitrogen Phosphorous Detector (Hewlett Packard, Inc., Avondale, PA). A DB 35 (35% phenyldimethylpolysiloxane), 30 m x 0.25 mm ID X 0.25 [im column (J W Scientific, Inc., Folsom, CA) was used for all analyses. Carrier gas was helium at a linear velocity of 30 cm/sec. Samples were analyzed using split injections (split ratio = 30 1) with injector and detector (NPD) temperatures of 260°C and 250°C, respectively. Oven temperature programming was as follows initial temperature of 80°C for 1 min increase temperature at 3.5°C/min to 115°C increase at 15°C/min to 180°C increase at 60 C/min to 190°C hold at 190°C for 6 min. 

Sample preparation and derivatization methods for GC analysis of BAs have been also proposed. In a method developed by Daudt and Ough (1980), amines are distilled from the alkalized grape juice or wine sample and trapped in an acidified solution. After concentration under vacuum, methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, isobutylamine, a-amylamine, isoamylamine, pyrrolidine, and 2-phenethylamine in their salt form are derivatized with triflu-oroacetic (TFA) anhydride. TFA derivatives are extracted with ethyl ether and analyzed by GC-MS with a capillary fused silica poly( ethylene) glycol (PEG) column and the following oven temperature program 8 min at 70 °C, l°C/min to 160 °C, isotherm for 90 min. 

Figure 4.19 GC/MS chromatogram of total ions recorded in SIM mode in the TCA and TCP analysis of a wine extract. Chromatographic conditions Injector and detector temperatures 200 and 240 °C, respectively oven temperature program 50°C for 5min, 1.5°C/min until 100°C, isotherm for 3min, 30°C/min until 250 °C, isotherm for 5 min. Carrier gas He column head pressure 8 psi. (Reproduced from J. Agric. Food Chem., 2002, 50, 1032-1039, Soleas et al., with permission of the American Chemical Society)...

Figure 4.21 GC-FID analysis of the four VPs in a wine (analytes in exploded window). Analytical conditions DBWax (PEG, 30m x 0.32mm i.d. 0.25(im coating thickness) capillary fused column (J W) split injection oven temperature program 4min at 40°C, 2.5°C/min until 185°C, isotherm for 15min, 10°C/min until 220 °C, isotherm for 10 min injector and detector temperature 250 °C carrier gas He at flow rate 1.93mL/min...

Differences in retention times in the chromatograms are due to the different oven temperature program used. Some remarkable differences in the profiles evidence the different enrichment obtained by the two methods. Data reported in Table 5.2 and Figure 5.3 show evidence of generally good linear correlations between XAD-2 extraction and HS-SPME enrichment methods. In the conditions used for SPME/GC-FID analysis, some compounds such as octanoic and decanoic acids partially overlap ethyl myristate and ethyl palmitate, respectively. 

Chemical Analysis. Gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) techniques were used to analyze 4-chlorophenol and its oxidation intermediates. For GC-MS analysis, the samples were acetylated in pyridine. The samples were first evaporated to dryness. Then 200 xL of pyridine and 200 (xL of acetic anhydride were added to the dry residue. The samples were heated at 65 °C for 2-3 h to ensure the complete acetylation reaction, and then gently evaporated to dryness in a nitrogen stream. Finally, the residue was redissolved in 0.1 mL of hexane for GC analysis. A GC (HP model 5890) equipped with mass selective detector (HP model 5971) and SPB-5 capillary column (Supelco Co., PA., 25- X 0.2-mm i.d. X 0.33-p.m film thickness) was used. To separate different intermediate products, various oven-temperature programs were performed. The GC-MS interface line was maintained at 300 °C. The mass-... 

For GC/MS analysis of 3-MH and 3-MHA, a fused-silica apolar column (10m x 0.32mm i.d. 0.25-gm film thickness) connected to the PEG-like polar column can be used with the following operative conditions carrier gas He (flow rate 1.2mL/min), transfer line temperature 220 °C, MS source temperature 150 °C, GC injector temperature 250 °C, injection in splitless mode, oven temperature program from a 35°C isotherm for 5 min, l°C/min to 40 °C, 10°C/min to 250°C. 

Figure 8.12. The El mass spectrum (70eV) of 2-methoxy-3,5-dimethylpyrazine. GC/ MS conditions PEG fused silica capillary column (30m x 0.25 mm 0.25- xm film thickness) carrier gas He at flow rate 1.2mL/min oven temperature program 50°C for lmin, increased to 220 °C at 10°C/min, isotherm for 10 min injector temperature 200 °C transfer line temperature 250 °C. (Reproduced from Journal of Agricultural and Food Chemistry, 2004,52 p. 5426, Simpson et al., with permission of American Chemical Society.)...

Figure 8.14. GC/MS analysis of amine-pentafluorobenzyl derivatives in a Cabernet Sauvignon wine. Analytical conditions 5% phenyl-95 % dimethlypolysiloxane capillary column (30 m x 0.25 mm, 0.25 pm) oven temperature program 45 °C for 4 min, 15°C/min to 280 °C, isotherm for 15 min. (1) methyl- -amine and methylamine (coeluted), (2) ethylamine, (3) n-propylaminc, (4) w-hexylamine, (5) 2-phenylethylamine, (6) 1,4-diaminobutane, and (7) 1,5-diaminopentane. (Reproduced from Journal of Agricultural and Food Chemistry, 2000, 48, p. 3314, Ngim et al., with permission of American Chemical Society.)...

Figure 8.15. The El (70 eV) mass spectrum of ethyl carbamate. Conditions for GC/MS analysis PEG fused silica capillary column (30m x 0.25mm, 0.25pm) oven temperature program 40 °C for 0.75 min, increased to 60 °C at 10°C/min, then to 150 °C at...

The wine sample is extracted by ethyl acetate and the organic solution is dried with magnesium sulfate. The GC/MS analysis of the extract can be performed using a fused silica methyl silicone column and the following oven temperature program 60 °C isotherm for 2 min, then raised to 250 °C at 6°C/min. Identification of analyte is based on the library mass spectrum shown in Fig. 8.16 (Chisholm and Samuels, 1992). 

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