Chromatographic analysis mechanisms

The compound 2-amino-2, 6 -propionoxylidide was synthesized by saturating with gaseous ammonia at room temperature a suspension of 50 g (0.195 mol) of 2-bromo-2, 6 -propion-oxylidide in a mixture of 500 ml of 95% alcohol and 400 ml of concentrated aqueous ammonia. The saturation was carried out under mechanical stirring. After 25 hours the mixture was resaturated with ammonia gas. The stirring at room temperature was continued for a total period of 116 hours, and a sample was taken at that time. Gas chromatographic analysis indicated that about 95% of the bromo compound had been converted to the desired product. 

Formation of an intimate ion pair of OH " and aminium radical cation was also proposed for the intermediate step before deprotonation. The presence of the above radical was verified through UV analysis of the polymer formed with the characteristic band on the end group. Through chromatographic analysis of the TBH-DMT reaction products, H2O was detected as the above mechanism proposes after deprotonation. 

Our previous work showed that alachlor, a compound that is structurally similar to metolachlor, could be separated from its acidic metabolites using a C-18 SPE cartridge (12). However, this procedure does not allow the separation of the OXA and the ESA. Thus, different adsorption mechanisms and solvent systems will be explored to separate the analytes into three fractions metolachlor, OXA, and ESA. This procedure is depicted in Figure 4 [not included in excerpt]. The SPE procedure will be necessary to avoid overlapping of the eight isomers of each compound in the chiral chromatographic analysis. 

The reaction mechanism including the formation and decomposition of quaternary cations may be a general pathway in amine alkylation processes on acidic zeolites. Pouilloux et al. (247), for example, synthesized dimethylethylamine from ethylamine and methanol on an acidic catalyst. At the reaction temperature of 503 K, trimethylamine was determined by gas chromatographic analysis, which can be explained by the formation and decomposition of trimethylethylammonium ions, (CIl3)3N CH2CH3. 

Deans, D. R., Huckle, M. T., Peterson, R, M. New combination of columns for gas chromatographic analysis of gases by using a non mechanic switching technique. Chromatographia4, 279(1971). 

A 4-L, three-necked, round-bottomed flask equipped with mechanical stirrer, bubble counter, and a stopper is charged with 1.6 L tap water, 300 g of sucrose (Note 1), and 200 g baker s yeast (Note 2), which are added with stirring in this order. The mixture is stirred for 1 hr at about 30°C, 20.0 g (0.154 mol) of ethyl acetoacetate (Note 3) are added, and the fermenting suspension (Note 4) is stirred for another 24 hr at room temperature. A warm (ca. 40°C) solution of 200 g sucrose (Note 1) in 1 L of tap water is then added, followed 1 hr later by an additional 20.0 g (0.154 mol) of ethyl acetoacetate (Note 3). Stirring is continued for 50-60 hr at room temperature. When the reaction is complete by gas chromatographic analysis... 

The retention behavior of nucleic acid constituents in the presence of increasing concentrations of an organic modifier is typical of that expected based upon solvophobic mechanisms with increasing concentrations of organic modifier, the capacity for solute retention is decreased. As expected, the use of a stronger eluent under reversed-phase conditions (e.g., acetonitrile vis-a-vis methanol) results in a subsequent decrease in the capacity ratios of all compounds in the chromatographic analysis. 

Scheme 2. Proposed mechanism for the electrocatalytic oxidation of ethanol on smooth platinum in acidic medium during the positive potential sweep (all the species with colored filling were detected either by IR reflectance spectroscopy or by chromatographic analysis).

To be amenable to gas chromatographic analysis, a compound must volatilize without thermal decomposition and not interact with the analytical system in such a manner so as to cause irreversible surface adsorption or surface catalyzed decomposition. In addition, the polarities of the various chemical entities to be analyzed must be considered so that an appropriate GC separation mechanism (i.e., partitioning, adsorption, etc.) can be chosen. Although these factors might seem to suggest that GC is a very selective analytical technique, in fact a wide variety of chemical entities which can appear as extractables and leachables are amenable to GC separation and analysis. ... 

Evidence for a radical coupling mechanism (as opposed to a carbanionic carbonyl addition mechanism) in the intramolecular Smh-promoted Barbier reactions has come from studies on appropriately functionalized substrates in the 3-keto ester series. It is well known that heterosubstituents are rapidly eliminated when they are adjacent to a carbanionic center. Indeed, treatment of a 3-methoxy organic halide (suitably functionalized for cyclization ) with an organolithium reagent leads only to alkene (equation 48). No cyclized material can be detected. On the other hand, treatment of the same substrate with Sml2 provides cyclized product and a small amount of reduced alcohol, with none of the alkene detected by gas chromatographic analysis (equation 49). ... 

In modern automated clinical chemistry instruments, the relation between analyte concentration and signal is often very stable so that calibration is necessary infrequently (e.g., at intervals of several months). Built-in process control mechanisms may help ensure that the relationship remains stable and indicate when recalibration is necessary. In traditional chromatographic analysis (e.g., high-performance liquid chromatography [HPLC]), on the other hand, it is customary to calibrate each analytical series (run), which means that calibration is carried out daily. Aronson et aft established a detailed simulation model of the various factors influencing method performance with focus on the calibration function. 

This study was undertaken to develop techniques for direct monitoring of organic hydrothermal synthesis reactions in DACs combined with direct microscopic and spectroscopic observations. Such direct observation provided additional insight into the mechanism, kinetics and phase behavior (miscibility characteristics) of the fluid-rich system. Described below are some results on the direct monitoring of citric acid-HaO system at high P and T with DAC Raman spectroscopy combined with quench product gas chromatographic analysis. 

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