Temperature programmed analysis

The undoubtedly structure-sensitive reaction NO -r CO has a rate that varies with rhodium surface structure. A temperature-programmed analysis (Fig. 10.8) gives a good impression of the individual reaction steps CO and NO adsorbed in relatively similar amounts on Rh(lll) and Rh(lOO) give rise to the evolution of CO, CO2, and N2, whereas desorption of NO is not observed at these coverages. Hence, the TPRS experiment of Fig. 10.8 suggests the following elementary steps ... 

Temperature-programmed analysis of the same mixture shown in Fig. 10 is illustrated in Fig. 11. The program rate was 6.3 C/min starting from 23 C and a pressure drop of 30 bar. A temperature increase of 50 to 70 C leads to a r uction of the k values by a factor of around 100, i.e., samples that have k values in the range 100-200 at room temperature elute at the higher temperature with k < 5. 

Figure 4.16 a Schematic of a temperature-programmed analysis setup b TPR profile of CuO, CeOj, and a copper-doped ceria sample, Ceo.9Cuo.1O2, showing the effect of Cu doping on the reduction temperature. 

Bhatia S, Beitramin J, Do DD (1990) Temperature programmed analysis and its applications in catalytic systems. Catalysis Today 7.3, pp. 309-435. 

He or H2 exhibit relatively flat minima, so changes in hnear velocities will be not significant to coliunn efficiency dinhng temperature-programmed analysis. 

Temperature-programmed analysis. (Courtesy of Agilent Technologies.)... 

Figure 4 temperature programmed analysis of coked catalysts (A) Pd(0.9) (B) Pt(0.9) (1) temperature programmed hydrogenation (TPHy) (2) TPO after TPHy. 

The GCxGC resolution advantage is known to improve the efficiency of enantioselective essential oil analysis (in contrast to one-dimensional analysis). In a single temperature-programmed analysis, the individual antipodes of optically active components can be separated and are effectively free from matrix interferences. The enantiomeric compositions of a number of monoterpene hydrocarbons and oxygenated monoterpenes in Australian tea tree Melaleuca alternifolia), including sabinene, a-pinene, (3-phellandrene, limonene, trans-sabinene hydrate, ds-sabinene hydrate, linalool, terpinen-4-ol, and a-terpineol shown in Figure 7,... 

A gas chromatographic method may be employed for analysis for both benzoic acid and sorbic acid in food, as described in AOAC method 983.16. The acids are extracted from an acidified aqueous homogenized food sample into ether. The acids are then extracted from the ether solution into aqueous alkali, and after acidification they are re-extracted into dichloromethane. Treatment of the residue with N-methyl-N-trimethylsilyltrifluoroacetamide converts the benzoic and sorbic acids into trimethylsilyl esters. These esters are then analyzed with a glass column packed with a support coated with OV-1, in a temperature programmed analysis. Phenylacetic and caproic acids are used as internal standards for benzoic and sorbic acids, respectively. An LC method has also been described for analysis of benzoic acid with simultaneous determination of sorbic acid, and methyl, ethyl, propyl, and butyl p-hydroxybenzoates. The preservatives were extracted from meat or seasonings with 70% ethanol, and analyzed by reversed-phase LC using a Cig stationary phase with a linear gradient from 10 to 70% methanol in 1.5% aqueous ammonium acetate and 1.5% aqueous acetic acid. 

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... 

By decreasing the temperature to 40 °C it is possible to separate the air peak also into O2 and N2 (see Fig. 7-12). The CO2 peak will not elute at temperatures of 40 °C. If CO and CO2 have to be analyzed in the shortest possible time a temperature programmed analysis is necessary, as shown in Fig. 7-13. Total analysis time will be less than 4 minutes. With this type of adsorbent it is possible to separate air, CO, CH4 and CO2 on one column, without column switching. CO and CO2 can be analyzed down to about the 500 ppm level in air. 

In temperature-programmed analysis, a controlled change of the column temperature occurs... 

Figure 16. Predicled (A) and experimenlal (B) chromatograms for fatty acid methyl ester mixture with temperature-programmed analysis at 40°C/min...

Total retention time in temperature-programmed analysis... 

The products of the two types of reaction can be identified on almost any GC column or phase difunctional compounds are more rapidly eluted on silicone liquid phases, but are less likely to be confused with mono-functional compounds on polyester phases. With both types of liquid phase, temperature-programmed analysis is generally necessary if all the fragments must be determined. Dicarboxylic acid standards are readily available for comparison, but aldehydo-esters are not and it may be necessary to make up a suitable standard by ozonolysis of monoenoic esters of known stmcture that are commercially available, e.g. methyl petroselinate, methyl oleate and methyl vaccenate. A GC trace of the ozonolysis products of such a mixture on an EGS column is illustrated in Figure 6.13. 

In all of the above discussion, one must understand that the column temperature is fixed. The Kovats retention indices can be made applicable to temperature programmed analysis by use of... 

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