Oven temperature ramp rates

The example in Figure 2.120 displays the separation of a phenol mix with different GC oven heating rates. The speed of analysis increases with increasing oven temperature ramp rate at the expense of separation power and an increased analyte elution temperature. Each Ib C/min increase in temperature ramp rate reduces the retention factor by 50%, but at reduced peak resolution. With a ramp rate of 20 C/min pentachlorophenol (compound 11) elutes at 238 °C, while a ramp of lO C/min leads to a 30 °C less elution temperature of 208 °C, but with the trade-off of a 50% increased analysis time. However, if resolution is sufficient then temperature ramp rates should be optimized for increased productivity. In splitless injection for trace analysis, a quick jump from the low oven temperature below the solvent boiling point to a moderately high oven... 

Figure 2.120 Effect of oven temperature ramp rate on analysis time, resolution and elution temperature (Khan, 2013). Experimental conditions Column type TG-5MS,...

Figure 2.121 Effect of adjusting the iinear velocity combined with increased oven temperature ramp rates (Khan, 2013). Experimental conditions and analytes as of Figure 2.120, Rs...

Oven program Initial temperature Initial hold time Ramp rate Final temperature Final hold time Detector Temperature Auxiliary gas Hydrogen Air... 

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. 

Set the oven temperature to ramp 140° to 350° at a rate of 10°/min (total run time of 21.0 min). Set the track mode to on (injector temperature follows the oven temperature conditions). Set the injection mode to on-column injection. Set the FID at 375°. Set the hydrogen carrier gas constant flow mode to on with a pressure of 5.5 psi (140°). 

Reverse phase HPLC analysis was performed using a Zorbax C3 analytical column. The oven temperature was maintained at 40°C. Solvent A = H20/0.1 % TFA and Solvent B = 100% acetonitrile/0.1% TFA. Flow rate = ImVmin. The column was equilibrated in 35% solvent B. Following sample injection the column was maintained for 5 minutes with 35% solvent B then ramped to 49% solvent B over 45 minutes. Samples were prepared by precipitation with ice-cold acid/acetone (Witkowska et al., 1993) and solubilization of the pellet in 0.1% TFA/20% acetonitrile. 

Obtain a piece of paper and write down these conditions for later reference. The column is 1.8 m stainless steel, 3 mm o.d., packed with 10% SE-30 on 60 to 80 mesh Chromosorb-W. The helium flow rate is 25 mL/min., the gas flow rates for the detector are 30 mL/min for Hj) and 60 mL/min of air. The initial oven temperature is 35 C with a 4 minute hold. The ramp rate is 12 C/min to 250 °C, with a final hold of 1 min. Both the inlet port and detector block temperatures are 270 "C. The "input" attenuation is initially at 10, and the "output" attenuation is initially at 2048. After 10 minutes, the output attenuation will be changed to 256 for 5 minutes, then changed to 8 and left there until the programmer reaches the cool cycle. 

A. Ramping During the first stage, termed ramping, the diaphragm is cured in three steps, by increasing the oven temperature to 90-95 C, then to 330°C, and finally to 365°C, at a rate of about 2°C min. ... 

To further characterize the products released upon thermochemolysis, comprehensive GC x GC-TOFMS was utilized. Thermochemolysis was performed at 280°C under conditions as described above. GC x GC-TOFMS analysis was performed using an Agilent 6890 GC with a GC X GC modulator (Leco) coupled to a Pegasus IV TOF mass spectrometer (Leco). The GC injector was operated in split mode (20 1) with a column flow rate of 1 mL/min and held at 250°C. GC x GC separation utilized a nonpolar column and a polar column a BPX5 (30 m X 0.25 mm x 0.25 pm SGE) and a BPX50 (1.8 m X 0.1 mm x 0.1 pm SGE), respectively. The GC oven temperature was held for 10 min at 35°C and ramped to 300°C at a rate of 5°C/min and then held for 5 min the second column was ramped at +15°C relative to the first column with a modulation time was 4 s. Mass spectra were acquired in electron ionization mode from 33 to 500 amu with an acquisition rate of 135 Hz. 

Thermal cycle experiments are t5tpicaUy performed in single-chamber ovens. Dual-chamber systems are sometimes employed, but single-chamber equipment tends to dominate the test space. The main drawback of a dual-chamber oven is the lack of control over the thermal loading profile when transferring from one chamber (or thermal zone) to the other. Regardless of whether a single or dual chamber is used, temperature is cycled from a maximum to a minimum (T in) value. Temperature is ramped from one temperature extreme to another at a controlled rate, referred to as the ramp rate. Temperature is also held at the maximum and minimum values for a predetermined time known as the dwell time. Table 59.1 lists typical... 

In addition, changing the heating rate also will affect the position of Tg on the temperature scale. If a ramp heatup is used, an increase of heating rate generally will cause an elevation of Tg. When the heating rate exceeds 2 °C/min (for most samples), the sample temperature may lag the DMA oven temperature so that a time lag in the apparent Tg will be observed and the transition will appear to occur at a higher temperature. This is also discussed more fully in a later section of this chapter. 

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