Temperature programming conditions

S. J. Marin, B. A. Jones, W. D. Felix, and J. Clark, Effect of high-temperature on high-temperature liquid chromatography column stability and performance under temperature-programmed conditions,/. Chromatogr. A 1030 (2004), 255-262. 

Fig. 32.7 Influence of column length on analysis time. Analysis of bacterial acid methyl esters under temperature-programmed conditions.

The various triacylglycerol (TAG) components of coconut oil may be separated and quantified by gas chromatography with the use of stable silicon gum stationary phase under temperature-programed conditions and identified by reference to standard TAG solutions. The carbon number of a TAG component is the sum of carbon atoms of the fatty acids attached to the glycerol moiety. For example, the carbon numbers of trilaurin and oleodistearin are 36 and 54, respectively. The relative amounts of each TAG in a sample of fat serves to establish its identity. For coconut oil, this test may also serve to distinguish it from other lauric oils (see Table 4 and Figure 5). 

Fig. 20.7. Separation of C9 to C17 hydrocarbons by fast chromatography, with rapid temperature programming. Conditions 5 m X 0.32 mm, 0.25 tm d/, 60°C, 19.2°C/s. [From G. L. Reed, K. Clark-Baker, and H. M. McNair. J. Chromatogr. ScL, 37 (1999) 300. Reproduced from the Journal of Chromatographic Science by permission of Preston Publications, A Division of Preston Industries, Inc.]...

LC-GC is usually limited to sample preconcentration and clean-up or to heart-cut analysis. Comprehensive LC-GC is difficult to accomplish because the solvent evaporation process is slow. Besides, the analytes contained in a single LC fraction can differ vastly with respect to their volatilities, which often requires the GC part of the separation to be carried out under temperature programmed conditions. Consequently, the time required for a single second dimension GC separation is measured in the best case in minutes rather than seconds, as in GC X GC. Thus, the... 

The extreme sensitivity of the electron capture detector is considerably more utilized with highly inert glass or fused silica columns, where minimum sample loss occurs and the separated electron-absorbing molecules can easily be detected and quantified. As capillary columns generate considerably less bleeding than the packed columns, the electron capture detector can be easily used under temperature programming conditions. 

However, the pre-exponential factor, k and niAlmAm parameters present significant differences. These differences may be related to the different progression of the gasification process in the two different cases. Gasification through isothermal or temperature programmed conditions will certainly differ in the way they use-up the various sites that are available. 

Yamamoto et al. (1982) developed a quantitative method for the determination of putrescine, cadaverine, spermidine, and spermine in foods. Separation of the amines from foods was achieved by eluting through a cation-exchange resin column and then converted to their (ethyloxy) carbonyl derivatives by the reaction with ethyl chloroformate in aqueous medium before application to the gas chromatograph with a flame ionization detector. They used 1,8-diaminooctane as an internal standard and performed the separation and determination of the resulting derivatives on a 1.5% SE-30/0.3% SP-1000 on Uniport HP column (0.5 m) under the temperature-programmed condition. Staruszkiewicz and Bond (1981) developed a GLC procedure for the quantitative determination of the diamines putrescine... 

The development of new catalysts for the storage and reduction of NO, from lean-burn engines is a challenge to meet the demands of the Euro IV norm in 2005. The new catalyst systems should also be able to adsorb NO, already at comparable low temperature and desorb it at high temperature. Cu and Ba exchanged zeolites of various types (Y, MOR, MFI, L, CHA) and their ability to adsorb NOx isothermally from a dry feed and to desorb it under temperature-programmed conditions (55-600°C) are described. Their NOx adsorption /desorption properties under wet conditions are compared. Furthermore, a zeolite material modified by manganese oxide is developed which is able to adsorb NOx from a wet feed already at temperatures as low as 120 °C and desorb it above 350°C. 

The reduced catalysts were carburized under either isothermal or temperature-programmed conditions at 1 atm. Unless otherwise stated, the carburizing gas was a mixture of H2 and CO (H2/CO = 3 by volume). 

The standard procedure in gas chromatography is to perform 1 D GC on a 30-to 60-m-long capillary column, under temperature-programming conditions, thereby achieving a peak capacity of some 100-150. If more resolution is desired, the higher potential of 2D GC is invoked (Figure 1). 

Low resolution mass spectrometry was performed by the Penn State Chemistry Department on a Kratos MS 9/50. Capillary gas chromatography was performed on a Hewlett-Packard 5880A Series GC. The capillary column used was a 12 m crosslinked methylsilicone fast analysis column utilizing a flame ionization detector. Helium was used as the carrier gas at a flow rate of 2.2 mL/min under various temperature programming conditions. 

The N calculation above cannot be used for temperature programmed conditions. It is only relevant to isothermal operation. For temperature program analysis, it is more relevant to describe the quality of the chromatography column by resolution or Trennzahl (Tz). The latter is related to the separation number SN, which is calculated for the separation of successive pairs of a homologous series, such as... 

Figure 11 (A) Isothermal temperature conditions iead to an exponential increase in retention times for successive members of a series of homologous compounds. Peaks get broader, and for approximately equal amounts injected, their peaks will get smaller (assuming similar response factors). (B) Linder temperature programmed conditions, peak widths are now similar over the elution range for the sample, and total analysis time can be reduced significantly compared with isothermal operation. Peaks should be approximately similar heights if the same amounts are injected. Here, it would be suspected that more of the later eluting compounds are present.

Since much analysis is conducted under temperature programmed conditions, eqn [21] is modified by recognizing that absolute elution times are now... 

Fig. 2 Separation of chemical warfare agents and the C and M standard series mixture hy GC with temperature programing. Conditions 30 m X 0.33 mm I.D. fused-silica capillary column with 0.25 p,m film of DB-5 carrier gas, helium at a flow rate of 2 ml/min detection, flame-ionization detector (FID).

Gmb Test Mix for use under temperature programming conditions (Restek) similar mixture available from Supelco... 

To study details of the activity and selectivity behavior of a catalyst, or to get a reaction engineering fingerprint of different catalysts a microprocessor controlled pulse reactor combined with a gaschromatograph or mass-spectrometer is a very powerful tool, especially if it is operated under temperature programmed conditions. Fig. 26 shows the flow diagram of such a unit developed in our laboratory /46/. 

A gas chromatograph with flame ionization detector was used to obtain chromatographic data using a 6 foot 1/8 inch o.d. stainless steel column packed with 10% w/w SE-30 on 80/300 mesh Chromport S. The injection port temperature is maintained at about 150 C. A temperature programming rate of ca 6 /min and a helium carrier gas flow rate of ca 30 cm min are employed. Products can also be separated, either isothermally or under temperature programmed conditions, on a 6 foot 1/4 inch o.d. stainless steel column containing 15% w/w Carbowax 20M on silane-treated 60/80 mesh Chromosorb P. Retention data are reported as Kovats retention indices. Peak area measurements are made with a planimeter and are reproducible to 0.1 cm. ... 

Hydroconversion of heptane (H2/ -C7 = 16) was carried out under temperature-programmed conditions over pillared beidellite, pillared montmorillonite, a ultrastable Y-zeolite, H-ZSM-5 and silica-alumina, all containing 1 wt% of Pt. The conversions of heptane over five catalysts are shown as a function of the reaction temperature. As shown in Fig. 3.59, pillared beidellite is more active than pillared montmorillonite, and the former is almost as active as the zeolites. Silica — alumina is the least active. 

A program written in BASIC was used to calculate the RI values for each peak on two columns and to identify the terpenes using our RI library data and peak areas [37], For the creation of a RI data bank on two stationary phases in temperature-programming conditions, some standard terpene compounds and some well-characterized mixtures as well as RI literature data on the same columns in the same operating conditions as in our laboratory were used. 

The main problem is to create the data bank of RI values for terpenes on two columns sufficient for the identification of these compounds in complex mixtures. This work is very time consuming because we have only a few standard com pounds and the reproducibility of literature RI data is often low, especially for the polar column. During the last five years, we have created a RI database con taining RI values of over 100 terpenes in OV-101 and PEG 20M stationary phases in temperature-programming conditions. Mainly, we use natural extracts with known composition and GC-MS data together with literature RI values on two columns in the same analysis conditions as in our laboratory. 

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