High-performance liquid chromatography solvent preparation

We isolated C7g, Cg2 and Cg4 by high-performance liquid chromatography (the preparation is described in detail elsewhere ). Laser-desorption time-of-flight mass spectra were obtained to confirm the purity of the isolated samples. We used an ArF (193 nm) laser as the desorption light source . Mass spectra for the samples of C78, Cg2 and Cg4 are shown as inserts to Fig. la-c. We measured C NMR spectra of the higher fuiierenes using CS2 as the solvent with Cr(C5H702)3 as a relaxant. 

Sample preparation for analysis by hyphenated methods requires some additional planning when compared to nonhyphenated methods. All steps, extraction, concentration, and final solvent selection must take into consideration and be compatible with all the components of the hyphenated instrumentation. For gas chromatographic methods, all the components in the mixture must be in the gaseous state. For liquid chromatography (LC) or high-performance liquid chromatography (HPLC), the samples of the analytes of interest can be solids or liquids, neutral or charged molecules, or ions, but they must be in solution. If the follow-on analysis is by MS, then each of the analytes may require a different method of introduction into the MS. Metals and metal ions may be introduced by HPLC if they are in solution but commonly are introduced via AAS or inductively coupled plasma (ICP). Other analytes may be directly introduced from HPLC to MS [2],... 

Raman often is evaluated as an alternative to an existing high performance liquid chromatography (HPLC) method because of its potential to be noninvasive, fast, simple to perform, and solvent-free. Raman was compared to HPLC for the determination of ticlopidine-hydrochloride (TCL) [43], risperidone [44] in film-coated tablets, and medroxyprogesterone acetate (MPA) in 150-mg/mL suspensions (DepoProvera, Pfizer) [45] it was found to have numerous advantages and performance suitable to replace HPLC. In an off-line laboratory study, the relative standard deviation of the measurement of the composition of powder mixtures of two sulfonamides, sulfathiazole and sulfanilamide, was reduced from 10-20% to less than 4% by employing a reusable, easily prepared rotating sample cell [46]. 

In the separation of biomolecules, sample preparation almost always involves the use of one or more pretreatment techniques. With high-performance liquid chromatography (HPLC), no one sample preparation technique can be appHed to all biological samples. Several techiques may be used to prepare the sample for injection. For example, complex samples require some form of preffactionation before analysis, samples that are too dilute for detection require concentration before analysis, samples in an inappropriate or incompatible solvent require buffer exchange before analysis, and samples that contain particulates require filtration before injection into the analytical instrument. 

High-performance liquid chromatography (HPLC), followed by GC/MS, has been used to fractionate and then quantitate the aliphatic and aromatic hydrocarbons present in liquid fuel precursors in order to determine the fuel potential of the compounds. Kerosene had the advantage of not requiring any sample preparation. Other light fuel oils may require the use of methylene chloride as a solvent prior to HPLC analysis (Lamey et al. 1991). The sensitivity, precision, and recovery of this method were not reported. 

The method of complete electrolysis is also important in elucidating the mechanism of an electrode reaction. Usually, the substance under study is completely electrolyzed at a controlled potential and the products are identified and determined by appropriate methods, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), and capillary electrophoresis. In the GC method, the products are often identified and determined by the standard addition method. If the standard addition method is not applicable, however, other identification/determination techniques such as GC-MS should be used. The HPLC method is convenient when the product is thermally unstable or difficult to vaporize. HPLC instruments equipped with a high-sensitivity UV detector are the most popular, but a more sophisticated system like LC-MS may also be employed. In some cases, the products are separated from the solvent-supporting electrolyte system by such processes as vaporization, extraction and precipitation. If the products need to be collected separately, a preparative chromatographic method is use-... 

High-performance liquid chromatography does similar things with more sophisticated instrumentation. It can separate closely related chemical compounds on a research scale or on a preparative scale liquid solvents, or mixtures of several solvents under positive pressure, replace the "carrier gas" of Fig. 11.3. The solid support must have small particle sizes (3- to 10-pm diameter), so that relatively high pressures can be sustained throughout the column, and it is at the interface between the liquid eluant and the solid particles that the chromatographic separation is accomplished. 

Sample preparation also includes certain matrix separation steps (e.g., by ion exchange, extraction chromatography and others), analyte enrichment (by co-precipitation and also ion exchange, e.g., Pu separation is performed using TEVA resin ) and preconcentration steps (e.g., by evaporation of solvent) off line or on line by high performance liquid chromatography (HPLC) or capillary electrophoresis (CE) in order to improve the detection limits and avoid disturbing interference problems in ICP-MS. 

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