Chromatographic analysis efficiency

A reliable chromatographic method has been developed for the quantitative aneilysis of hydrophobic impurities in water-soluble polymeric dyes. The method utilizes both the molecular sieve effect of normal gel permeation chromatography and solute-column packing interaction, modified by solvent composition. This method eliminates the need to extract the impurities from the polymeric dye with 100 extraction efficiency, as would be required for an ordinary liquid chromatographic analysis. 

Probably the most common distillation method used as a form of sample preparation for chromatographic analysis is steam distillation [31,32]. Solvent extraction and gas phase stripping methods are generally inefficient procedures for isolating polar, acidic, or basic compounds in an aqueous matrix due to the low efficiency of water immiscible solvents for the extraction of these compounds and their low volatility and high water affinity which results in a very slow transfer to the gas phase using... 

Another method to detect energy transfer directly is to measure the concentration or amount of acceptor that has undergone an excited state reaction by means other than detecting its fluorescence. For instance, by chemical analysis or chromatographic analysis of the product of a reaction involving excited A [117, 118]. An early application of this determined the photolyzed A molecules by absorption spectroscopic analysis. [119-121], This can be a powerful method, because it does not depend on expensive instrumentation however, it lacks real-time observation, and requires subsequent manipulation. For this reason, fluorescence is the usual method of detection of the sensitized excitation of the acceptor. If it is possible to excite the donor without exciting the acceptor, then the rate of photolysis of the acceptor (which is an excited state reaction) can be used to calculate the FRET efficiency [122],... 

Additional advances have been made in the use of leaving groups other than halide for the nonphosphorus component of the Michaelis-Arbuzov reaction. The sensitive species 3,5-d i-t-b u ty I -4-hydroxybenzyl acetate has been noted to undergo efficient reaction (75-85% isolated yields) with a series of trialkyl phosphites upon heating at relatively low temperature (95°C) without the use of excess phosphite or additional catalyst.138 Chromatographic analysis of the reaction mixture indicates virtually quantitative conversion in the process. 

An essential step in the analysis of trace pollutants in environmental matrices is the pretreatment procedure. Methods that are more efficient have been developed in the last few years, facilitating subsequent chromatographic analysis. Because of the complexity of the matrices, the sample pretreatment procedure includes both extraction and purification of the target analytes. 

Gas chromatographic analysis of samples taken from the waste tank showed a steady decline in all three pesticides from the water. The results of the GC analysis of the water as a function of time are shown in Table V and graphed in Figure 9. The efficiency factors were calculated and are presented in Table VI. 

Reductive alkylation is an efficient method to synthesize secondary amines from primary amines. The aim of this study is to optimize sulfur-promoted platinum catalysts for the reductive alkylation of p-aminodiphenylamine (ADPA) with methyl isobutyl ketone (MIBK) to improve the productivity of N-(l,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (6-PPD). In this study, we focus on Pt loading, the amount of sulfur, and the pH as the variables. The reaction was conducted in the liquid phase under kinetically limited conditions in a continuously stirred tank reactor at a constant hydrogen pressure. Use of the two-factorial design minimized the number of experiments needed to arrive at the optimal solution. The activity and selectivity of the reaction was followed using the hydrogen-uptake and chromatographic analysis of products. The most optimal catalyst was identified to be l%Pt-0.1%S/C prepared at a pH of 6. 

Chromatography is a separation technique and, consequently, a satisfactory chromatographic analysis demands, a prion, that an adequate separation of the constituents of the sample is obtained. The separation must be such that an accurate quantitative measurement of each component is possible. In order to achieve this separation, an appropriate phase system must be chosen so that the individual components can be moved apart from one another in the column. The column must, therefore, be designed to have sufficient efficiency to separate all the components of the mixture. To do this, the concept of the Reduced Chromatogram must be introduced. 

It has been recently reported (109) that use of both Penase and lactamase II hydrolysis and screening assays prior to chromatographic analysis can tentatively classify -lactams into three subgroups the first group includes a ceftiofur metabolite represented by desfuroyl-ceftiofur-cysteine the second, cephapirin and the third, penicillin G, ampicillin, amoxicillin, and cloxacillin. In this approach, portions of aqueous extracts of tissues are treated separately with Penase and lactamase II, and results are compared with those of untreated samples and positive controls. Bioactive ceftiofur metabolites are present, provided that the extracts retain inhibitory activity after Penase treatment but lose activity after lactamase II treatment and are positive in response to the immunochemical Lac-Tek-Cef test but negative to the Lac-Tek-Bl test (113). This approach can eliminate a large number of negative samples and, therefore, increases the efficiency of the assay. 

Capillary columns are composed of fused silica which has shown remarkable properties of inertness and efficiency in chromatographic analysis. Glass capillaries and stainless steel are sometimes used too but their applications are nowadays limited. 

Harrison et al. [33] studied the factors governing the extraction and gas chromatographic analysis of PAHs in water. Factors such as initial concentration, presence of suspended solids and prolonged storage of the samples affected considerably extraction efficiencies. It is recommended that water samples should be collected directly into the extraction vessel and that analysis should be carried out as soon as possible after extraction. 

The main method applied in analysis of fire debris is GC. The analysis of fire debris has three stages. The first stage is isolation of accelerants from the matrix and their concentration, followed by separation of particular components and their chromatographic analysis and, last, identification of potential accelerants. The efficiency of the first stage strongly determines the possibility of identification of the isolated and adsorbed organic compounds. An improperly performed first stage could make it impossible to identify the questioned substances. 

SBSE can be successfully used in the analysis of environmental samples [93-97] and for food analysis [98, 99]. PDMS is the most commonly used polymer, primarily because of its thermal stability and durability. SBSE has been modified by application of derivatization with different reagents (acetic anhydride, BSTFA, etc) [100-104]. This approach is suitable for the extraction of compounds requiring derivatization. The use of multistep derivatization with several extraction elements (each reaction is performed on a different stir bar) allows efficient extraction, desorption, and chromatographic analysis of compounds with different functional groups (e.g., phenols, steroids, amines, thiazoles, ketones). Acetic anhydride (ester formation), ethyl chloroformate (reaction of acids and amines), tetraethyloborane, and sodium bis-trimethylotrifluoroacetamide have been used for extraction and simultaneous derivatization [105]. 

The success of the chromatographic analysis depends on the quality of separation of the peaks in the chromatogram. The quality of separation of two adjacent peaks 1 and 2 can be measured by resolution, which is defined as the ratio of the distances between the peak maxima to the average peak width (or to the width of the second peak as the widths of the zones of compounds 1 and 2 are approximately equal for closely adjacent peaks on an efficient chromatographic column) ... 

In an ideal chromatographic analysis the sample molecules will be completely separated, and detection of components will result in a series of discrete individual peaks corresponding to each type of molecule. However, to minimize the possibility of overlapping peaks, or of peaks composed of more than one substance, it is important to maximize the separation efficiency of the technique, which depends on ... 

Ferreira, V., Sharman, M., Cacho, J.F. and Dennis, J. (1996) New and efficient microextraction/solid-phase extraction method for the gas chromatographic analysis of wine volatiles,/. Chromatogr. A, 731, 247-259. 

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