Monitors liquid chromatographic separation methods

An example for the separation for flavonoids with HP-RPC is the screening method employed for the systematic identification of glycosylated flavonoids and other phenolic compounds in plant food materials by Lin et al20 These authors used an analytical 4.6 mm x 250 mm 5 pm C18 silica column at 25 °C with linear gradient elution (eluent A (0.1% FA in water and eluent B 0.1% FA in ACN) at 1.0 ml min-1. DAD was performed at 270, 310, 350, and 520 nm to monitor the UV/VIS absorption. The LC system was directly coupled to an ESI mass spectrometer without flow splitting and the mass spectra acquired in the positive and negative ionization mode. The same analytical scheme (aqueous MeOH extraction, reversed-phase liquid chromatographic separation, and diode array and mass spectrometric detection) can be applied to a wide variety of samples and standards and therefore allows the cross-comparison of newly detected compounds in samples with standards and plant materials previously identified in the published literature. 

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

Most of the methods described for spirolides have been developed for rapid monitoring of these toxins in phytoplankton or shellfish matrices. Due to mass selectivity, a baseline separation of the different spirolides is not achieved in most cases. For research and toxin profiling purposes, a comprehensive separation method for a vast suite of spirolides may be of interest. Recently, several isobaric spirolides, which coelute and thus remain unidentified under standard chromatographic conditions, were detected (Krock et al., unpublished data). Only the attempt at a baseline-separation of all compounds revealed these variants. This was achieved by the following liquid chromatographic conditions for fractionation of spirolides ... 

A column liquid chromatographic method for the simultaneous determination of chloroquine, amodiaquine and their monodesethyl metabolites in human plasma, red blood cells, whole blood and urine has been developed (41). The drugs and internal standards are extracted as bases with dichloromethane and then re-extracted into an acidic aqueous phase. Separation is achieved using a reversed-phase column and a mobile phase of phosphate buffer (pH 3.0) methyl cyanide (88 12). The absorbance of the drugs is monitored at 340 nm with a sensitivity limit of 10 pmol/ml. The mean overall recovery from each biological fluid is more than 75%. This method can be applied to therapeutic, pharmacokinetic, and epidemological studies. 

Liquid chromatographic methods Separation and quantitative analysis of theaflavins and thearubigens has also been achieved by gel permeation chromatography on Sephadex LH-20, monitoring the eluting peaks at 380 nm. Reversed-phase LC separation has also been conducted using a Cig column, with a mobile phase consisting of 29% aqueous acetone and 1% acetic acid. 

Investigations may be carried out on the tracer level, where solutions are handled in ordinary-sized laboratory equipment, but where the substance studied is present in extremely low concentrations. Concentrations of the radioactive species of the order of 10 m or much less are not unusual in tracer work with radioactive nuclides. A much larger amount of a suitably chosen non-radioactive host or carrier is subjected to chemical manipulation, and the behavior of the radioactive species (as monitored by its radioactivity) is determined relative to the carrier. Thus the solubility of an actinide compound can be judged by whether the radioactive ion is carried by a precipitate formed by the non-radioactive carrier. Interpretation of such studies is made difficult by the formation of radiocolloids, and by adsorption on glass surfaces or precipitates. Tracer studies provide information on the oxidation states of ions and complex-ion formation, and are used in the development of liquid-liquid solvent extraction and chromatographic separation procedures. Tracer techniques are not applicable to solid-state and spectroscopic studies. Despite the difficulties inherent in tracer experiments, these methods continue to be used with the heaviest actinide and transactinide elements, where only a few to a few score atoms may be available [11]. 

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