Methods chromatographic separation

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

However, tandem mass spectrometry, as a separation technique, does have limitations. It cannot easily differentiate between isomeric and isobaric species, and, in complex matrices, the presence of components with a high surface activity can suppress the ionization of components with a lower surface activity, leading to the nondetection of analytes (66). Therefore, the combination of MS-MS with a readily available chromatographic separation method such as TLC affords analysts real benefits. 

For isohexide nitrates gas-liquid chromatographic separation methods using OF-1 (Ref. 52), OV-101 (Refs. 53-59), OV-17 (Ref 60), or OV-210 (Ref 61) columns have been reported. Most of the methods described are used to detect traces of nitrates, as well as of their metabolites, in urine and plasma probes.62-69 All known isohexide nitrates can be measured in mixtures by using a DB-5 capillary column.70-71 Electron-capture detection was applied for the g.l.c. determination of isosorbide dinitrate71 and its metabo-lites.7,b... 

In the third section, a gel chromatographic separation method will be set up in order to enable the evaluation of the changes of molecular weight distribution of the HEC substrate due to a slow cellulolysis. In... 

Today the situation is the reverse. Multiple measurements are often made on each subject. By taking as many measurements as possible, it is hoped that the complete picture of each subject will be less error-prone than each individual measurement considered separately. As an illustration, the development of chromatographic separation methods and detection techniques like spectrophotometry has made it possible to identify many substances in one blood sample from a patient. At the same time, the cost of each experiment has increased. Consequently, new methods for data analysis are needed, methods that can utilize the information in the data also when the subjects are few and the measurements are many. 

Kutter, J.P., Current developments in electrophoretic and chromatographic separation methods on microfabricated devices. Trends. Anal. Chem. 2000, 19, 352-363. 

Y4. Yamamoto, R., Hattori, S., Inukai, T., Matsuura, A., Yamashita, K., Kosaka, A., and Kato, K., Enzyme immunoassay for thyroxine and triiodothyronine in human serum, with use of a covalent chromatographic separation method. Clin. Chem. 27, 1721-1723 (1981). 

A Dual-Beam Photodiode Array Spectrometer System for Liquid Chromatographic Separation Methods Development... 

TABLE 14 Summary of Chromatographic Separation Methods for Antibodies and Related Molecules... 

In this context, enantioselective analysis and in particular chromatographic separation methods have gained a vital interest and central importance for the following reasons. 

This book covers some of the significant advances in hyphenated chromatographic separation methods for polymer characterization. Chromatographic separation techniques in this volume include size-exclusion chromatography, liquid chromatography, and field flow fractionation methods that are used in conjunction with information-rich detectors such as molecular size-sensitive or compositional-sensitive detectors or coupled in cross-fractionation modes. 

We hope this book will encourage and catalyze additional activity and method development in hyphenated chromatographic separation methods for polymer characterization. 

In both concentration mechanisms described above, there is little diffusion process observed as in usual elution procedures with ion exchange or other chromatographic separation method, such as conventional HSCCC and HPLC. If there is no basic compound such as ammonia in the stationary phase, ions move to the tail with a different flow rate as a function of distribution ratio between the stationary phase and the mobile phase. Many ions can be separated from each other in that case, but because there is no pH border in the column, concentration is not effected, but only separation with diffusion. 

As with most other chromatographic separation methods, gel permeation chromatography-size-exclusion chromatography (GPC-SEC) is based on partitioning of analyte polymer molecules between the stationary phase (which, in the case of GPC-SEC, is contained within the pores of a porous stationary-phase support) and the mobile phase. Ideally, the mobile phase establishes a concentration equilibrium with the stationary phase at each plate in the column before being transferred to the next plate. The concentration equihb-rium is dictated by an equal chemical potential of the polymer chain between the two phases [1,2]. In normal conditions of GPC-SEC, the polymer concentration Cm in the mobile phase is sufficiently low, and the solution behaves ideally dilute. Its chemical potential per molecule in the mobile phase is then given as... 

The size-selective precipitation (SPP) was predominantly developed by Pileni [50c]. One example (SPP) is monodisperse silver particles (2.3 nm, 0= 15%), which are precipitated from a polydisperse silver colloid solution in hexane by the addition of pyridine in three iterative steps. Recently, Schmid [52a] has reported the two-dimensional crystallization of truly monodisperse AU55 clusters. Chromatographic separation methods have thus far proven unsuccessful because the colloid decomposed after the colloidal protecting shell had been stripped off [42a]. The size-selective ultracentrifuge separation of Pt colloids has been developed by Colfen [52b]. Although this elegant separation method gives truly monodisperse metal... 

R. Udisti, E. Barbolani, G. Piccardi. Ion Chromatographic separation method of some species and their determination at ppb level in Antarctic snow and ice, Ann. Chim. (Rome), 81 (1991), 325-341. 

High Performance Liquid Chromatographic Separation Methods... 

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