Analytical Fractionation

The application from van der Hoeven et al. (1997) used an ADS cartridge online SPE to measure cortisol and prednisolone in plasma and arachidonic acid in urine. A precolumn packed with a C18 alkyl-diol support (LiChrosphere RP-18 ADS, 25 /an, Merck) was used. To reduce run time, column switching was programmed as heart-cut , diverting only the analyte fraction into the analytical column. Another LiChrosphere column (125 x 4 mm inner diameter, Merck) handled separation. After the injection of 100 fiL plasma, the lower limit of detection for prednisolone was 1 ng/mL while cortisol was readily quantitated at its endogenous level of 100 ng/mL. The run time was 5 min. For arachidonic acid, a Hypersil ODS column (200 x 3.0 mm inner diameter, 5 /.an) was used. The injection volume was 200 //I. and run time was 9.5 min. The detection limit was 1 ng/mL and recovery was 77%. 

Another approach is to consider petroleum constituents in terms of transportable materials, the character of which is determined by several chemical and physical properties (i.e., solubility, vapor pressure, and propensity to bind with soil and organic particles). These properties are the basis of measures of teachability and volatility of individual hydrocarbons. Thus, petroleum transport fractions can be considered by equivalent carbon number to be grouped into 13 different fractions. The analytical fractions are then set to match these transport... 

Coupling a screening system with an analytical fraction collector can be helpful when very small amounts (submilligrams to single-digit milligrams) are required. It often also provides the first opportunity to isolate enriched samples for further use in the method development, for example, as retention time markers. The choice of stationary phases in the method development system can be based on... 

Figure 1. Schematic of the strategy for the coupled bioassay-analytical fractionation of residue organics isolated from aqueous environmental samples.

Analytical Fractionation of the Phenolic Substances of Grapes and Wine and Some Practical Uses of Such Analyses... 

Singleton, V.L. 1974, Analytical fractionation of the phenolic substances of grapes and wine and some practical uses of such analyses. In Chemistry of Winemaking (A.D. Webb, ed.) pp. 184-211. American Chemical Society, Washington, D.C. 

Hasle, 3.R. and Abdullah, M.I., 1981. Analytical fractionation of dissolved copper, lead and cadmium in coastal seawater. Mar. Chem., 10 487-503. 

Burba, R, Aster, B.,Nifant eva,T.,Shkinev, V., and Spivakov, B. Y. (1998). Membrane filtration studies of aquatic humic substances and their metal species A concise overview. Part 1. Analytical fractionation by means of sequential-stage ultrafiltration. Talanta 45, 977-988. 

Aster, B., Burba, E and Broekaert, J.A.C. (1996) Analytical fractionation of aquatic humic substances and their metal species by means of multistage ultrafiltration. Fresenius J. Anal. Chem., 354, 722-728. 

Plasma is the main biological sample used in clinical and toxicological analysis, as concentrations found in this matrix are correlated to the pharmacological effect, as well as to the side and toxic effects. However, oral fluid has also been employed in some specific applications because of the advantages associated to this alternative specimen easy, painless, and noninvasive collection, which does not require qualified personnel, it represents the free analyte fraction, and it has a window of detection similar to that in plasma. Within the possible applications of oral fluid analysis, two are of special relevance ... 

Gomez-Ariza, J. L., Giraldez, I., Sanchez-Rodas, D., and Morales, E. (1999). Metal readsorption and redistribution during the analytical fractionation of trace elements in oxic estuarine sediments. Anal. 

Extensive use of column chromatography has been necessary to separate the Rauwolfia alkaloids, and in this connection attention is drawn to a publication which concerned itself with the more refined technique of gradient elution chromatography (123). Paper chromatography has been used extensively for analytical, fractionation, and identification purposes (124, 15). This tool is not particularly useful for the assay of crude extracts, since certain alkaloids show up clearly whereas others cannot be resolved. More information as to specific alkaloidal composition is better obtained from more highly purified fractions. 

Enzymatic extraction carried out using in vitro models of the gastrointestinal tract is cheaper, faster, more reproducible, and ethically easier than the alternative of studies involving people and animals. Estimation of nutrient bioavailability (including trace elements, both essential and toxic) is particularly important for nutritionists, pharmacists, and toxicologists. Application of sequential procedures allows analyte fractionation (metals usually), but enzyme selectivity allows leaching of certain speciation forms of the determined elements. Table 6.9 gives examples of application of enzymatic extraction procedures for trace element analysis and speciation analysis [71, 72]. 

This can be done, for example, by multiple detection, where the absolute comonomer concentration, Wk, is measured for each analytical fraction after concentration detector calibration according to... 

Fairly wide use has been made of preparative gel electrophoresis in protein chemistry, and in principle there is no reason why the same procedures should not be adopted for use with nucleic acids which have the advantage that much may be accomplished with very small quantities of purified material. Thus, it is relatively easy in many situations to introduce radioactive label at very high levels and specific activity, and the use of for this purpose offers a degree of sensitivity that cannot be matched in work on proteins. The extinction coefficients of nucleic acids are also very high in the ultraviolet, so that with say 20 pg in 1 ml or less it is possible to measure optical properties, thermal melting profiles, sedimentation coefficients, and even molecular weights by sedimentation equilibrium in an instrument equipped with scanner optics. Consequently, the sacrifice of resolution that, by a malign law of nature, always accompanies any attempt to scale up an analytical fractionation method is often at least partly avoided. 

Representative Physical Parameters for TPH Analytical Fractions Based on Correlation to Relative Boiling Point Index... 

The preparative fractionation scheme will apply the chromatography developed for the analytical scheme to larger samples. From 10 to 20 mg of the pure compound isolated from aquatic humic substances needs to be the objective of the preparative fractionation. The preparative fractionation might have to begin with as much as a kilogram of initial material. After structural determination of a number of aquatic humic substance components, the analytical fractionation, combined with spectral determinations. 

To minimize total number of steps while achieving cleanest analyte fractions... 

The technique has many variations, which Koenigbauer and Majors (34) classified into four types direct transfer, indirect transfer, reversed transfer, and loop transfer. The analyte fraction of the first column eluate can be diverted directly to a second HPLC column (direct transfer), or eluted from column 1 to column 2 with a step gradient to a stronger mobile phase (indirect transfer), or eluted into a loop injector prior to the second column (loop transfer). The combination of the two columns provides sufficient clean-up for a specific analysis. With reversed transfer, the analyte is concentrated on the head of the first column and, after the sample interferences are passed through the first column, the analyte is transferred to the second column by reversing the flow through the first column. 

---