Programmed-temperature split injection

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

Rgure 5 Programmed temperature vaporizer injector. (From Hinshaw JV and Seferovic W (1986) Programmed-temperature split-splitless injection of triglycerides comparison to cold on-column injection. Journal of High Resolution Chromatography 9 69-77.)... 

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. 

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). 

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.

Analyses of the starting material and products were carried out by GC and GC-MS analyses. For GC analyses, a Shimadzu gas chromatograph, GC-17A, was used. A 60-m-long narrow bore (0.25-mm) DB5 with 0.25-gm phase thickness supplied by J W Scientific was used. The GC parameters were as follows split injection (split ratio of 50 1), carrier gas of hydrogen at 1 cm3/min at 30°C. The heating program was as follows initial temperature of 30°C, initial time of 2 min, rate of 30-250°C at 3°C/min, final time... 

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. 

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). 

Actually, same articles show the possibility of use split injection [8] in HT-HRGC analyses of substances up to C78. However, volatile materials from the septum accumulate at the head of the column during the cooldown portion of the temperature program. When the columns are reheated to analyze the next sample, these accumulated volatiles are eluted, producing peaks, a baseline rise, or both. This difficulty can be solved using commercial septa already available for HT-HRGC, which exhibit very low bleed levels. 

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...

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. 

Identincation. The components in the fractionated oils mentioned above were analyzed by GC and GC/MS resulting in the identification of 12 hydrocarbon terpenes and 72 oxygenated compounds. Gas chromatographic conditions were OV-101 column, 50 m X 0.25 mm i.d., 80 C to 200 C at 2 C/min. GC/MS was conducted with a JEOL JMS-SX102AQQ (El mode, 70 eV) equipped with a JEOL MP-7010 data processor unit. The analytical conditions were almost the same as the GC conditions OV-101, 50 m X 0.25 mm i.d. temperature program, 80-200 C at 2 °C/min He, 0.64 mL/min split injection (1 50). NIST public data library of MS spectra (data number 49,496) which was supplied from JEOL LTD was used for matching of mass spectral pattern. 

CP 9002, 50 m length, 0.32 mm ID CP-SIL 5 CB column with pre-column 1 m, 0.32 mm ID, carrier gas He split injection temperature program 45-300 °C, 4°C/min FID detector. Heptane correlation ratios (ratios Cj to C5) were calculated according to the method developed by Halpern (1995). 

Figure 3. SFC-MS response vs. probe tip temperature for Triton X-100. Conditions 10 m X 50 urn i.d. X 0.1 um film DB-17 column, column temperature = 90 C, probe stem temperature = 90 C, 0.1 uL of a 25 mg/ml Triton X-100 in methylene chloride solution split injected, split ratio 1 2, pressure program = 100 atm for 3 min, ramp to lAO atm in 3 min, ramp to 325 atm in 23 min, methane Cl, MS source temperature = 200 C.

Capillary GLC columns are excellent for the analysis of TAGs. It is essential that a precolumn (retention gap) of uncoated, silanized silica tube (1.0 m x 0.53 mm ID) be attached to the analytical column. The injection technique of choice for both EAME and TAGs should be on-column. Split injection almost always leads to quantitative errors in these analyses. Both helium and hydrogen are adequate carrier gasses. A 7-10 m bonded phase (OVl, film thickness 0.1 pm) 0.53 mm ID column is used with a temperature stability of at least 350°C, but aluminum-clad columns are avoided. A temperature program is used, starting at 100°C rising to 350°C at 10°Cmin . While the carrier gas velocity for... 

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