Temperature-programming rates

Figure 5. Graphs of Retention Time of (R) 4-Benzyl-2-oxazolidinone against Temperature Program Rate for Three Different Initial Temperatures...

Adjust the temperature program rate to the appr[Pg.87]

The possibility of readsorption and further reaction of desorbed products was examined by varying the residence time of the products in the reactor, which is achieved by varying the carrier gas flow rate and the size of the catalyst bed. A number of different temperature programming rates from... 

FIGURE 6.4 Gas chromatograms of a mixture containing C5-C15 normal alkanes using temperature-programming rates of (a) 10, (b) 20, and (c) 30°C/min. The silicon column was native non-polar, and the carrier gas was air. In all cases, the initial column temperature was 30°C, and the temperature program was initiated at the time of injection [598]. Reprinted with permission from the American Chemical Society. 

Figu re 17.2 Ar-TPD profiles of solid acids temperature programmed rate 2Kmin... 

The heat of adsorption of Ar was also measured for acidity evaluation. In the case of Ar-TPD, an effect of the probe molecule diffusion in micropores is observed with some samples, such as zeoUtes, at high temperature-programmed rates. The adsorption method is not influenced by diffusion of the adsorbed molecule because the Ar isotherm is measured at static equilibrium. It is also advantageous that the usual BET apparatus can be used to obtain the adsorption isotherm. In addition, the adsorption behavior of Ar is of the Henry type at temperatures around room temperature. 

Fig. 1 Fast GC analysis of aviation turbine engine fuel using a typical laboratory GC instrument. Conditions hydrogen carrier gas temperature programming rate, 70-170°C at 120°C/min (actual 75°C/min) microbore column 3 m x 0.10 mm ID.

The additive standards for the MS library were dissolved in a suitable solvent and a sample was injected into the GC/MS system, or a sample was transferred into an injection port liner as is done for real world samples. Additive standards were mn at temperature program rates of 10 °C or 15 °C due to the lack of the necessity for multi-component separation. The actual temperature program used is listed on each Total Ion Chromatogram (TIC). 

At first the chromatographic conditions of the chiral main column must be optimized carefully. Capillary columns coated with chiral stationary phases of suitable enantio-selectivities are used as main columns. Chiral resolutions are commonly achieved isothermally or by low temperature programming rates, starting at least 20°C below precolumn temperature. Precolumns are chosen with respect to (i) the versatility of application, to (ii) the direct injection of high sample volumes and (iii) with respect to the requisite time of analysis. 

In any chromatographic separation problem, a proper choice of operating conditions is essential. These include primarily the choice of carrier gas and its flow-rate, temperatures of the injection port and the detector, as well as the column itself. For difficult separations, a proper temperature programming rate must also be adjusted. 

The test is performed under optimized conditions of carrier gas flow and temperature program rates, which are adjusted for column length and carrier gas viscosity. Table 2.16. To obtain a correct value for the gas hold-up time for thick-film columns (df > 0.7 p,m) it should be measured at 100°C (methane is considerably retained at... 

Figure 8 shows the C-GCxGC of a jet juel. In this separation, the oven temperature program rate was reduced from 2°C/min to 1°C /min. As wifli gasoline, the hydrocarbon aromatic classes were readily resolved, and their carbon number distributions are readily distinguishable fiom C7 to C13. As expected, this sample did not contain benzene. Note that cleanly separated compounds at approximately X = 85 min, Y = 90 s (labeled phenolics ) were almost as retained as the di-aromatics (naphthalenes). The O-GCxGC separation (Fig. 9) revealed the presence of oxygen in these compounds, which were identified as phenolics. 

Temperature-programmed oxidation (TPO) measurements were performed in a CRY-1 DTA equipment connected with a gas chromatograph (GC) for effluent gas analysis. The amount of CO2 produced was measured at a temperature programmed rate of 20 °C/min. A 10 vol. % oxygen in N2 was introduced at a flow rate of 15ml/min. 

The range of the isovolatility curves can be extended by extrapolation through mathematical procedures, by injections at different temperature programming rates [12] or by use of the more polar homologous series (2-methylketones and fatty acids methyl esters [11], alcohols [12]) instead of the n-alkanes. 

Ong et al. [16] also consider some selective effects of conditions on retention, mainly of the temperature program rate, which can even cause changes in the elution order for some compounds. The researchers also present relationships between different parameters and retention, which will be of high interest to those trying to improve their GCxGC analytical procedures. Their conclusion, "optimisation of a GCxGC analysis will be a tedious exercise," is true for present GCxGC procedures that select by trial and error column sets and operation conditions. 

Flinshaw provides a useful comparison of experimental results arising from experiments where different isothermal temperatures are used, the temperature programming rate is altered, column length is altered, carrier gas flow rate is altered, and where column ID is altered to achieve equivalent resolution performance using a combination of a narrower and shorter column. 

It is important in all cases to specify the analysis conditions, such as the isothermal conditions and phase for eqn [21], and temperature program rate and phase for eqn [22],... 

GC An optimal temperature program rate for fast-GC will deliver the best separation in the shortest possible time. Method development and optimization can be achieved using a chemometric approach such as central composite design. This type of approach is suitable for the development of a method for the analysis of a sample of limited complexity, but optimization procedures for temperature programs become more complex, more time consuming, and may offer limited success for samples containing a greater number of components (e.g., >20). 

A recent study determined that a generally applicable optimum temperature program rate offered a suitable compromise between peak capacity, separation power, and analysis time. This concept uses /m as a fundamental time unit, and showed that a temperature... 

---