Chromatographic procedures

Nevertheless, within the same work group, once the chromatographic procedures are established, SARA analyses are very often performed to characterize heavy feedstocks or to follow their conversion. 

In the research described in the last problem, the authorst determined the following distribution of molecular weights by a chromatographic procedure ... 

Potency of hGH preparations is quantitatively deterrnined, in terms of mass per vial, by one or more chromatographic procedures (50). Biopotency is calculated from the mass-based potency using a conversion factor, typically 3 lU/mg. Traditionally a bioactivity assay using hypophysectomized rats has been used to determine potency however, the imprecision of this assay has resulted in its use only as a semiquantitative indicator of bioactivity (1), sometimes referred to as a bioidentity test. 

Several gas-Hquid chromatographic procedures, using electron-capture detectors after suitable derivatization of the aminophenol isomers, have been cited for the deterrnination of impurities within products and their detection within environmental and wastewater samples (110,111). Modem high pressure Hquid chromatographic separation techniques employing fluorescence (112) and electrochemical (113) detectors in the 0.01 pg range have been described and should meet the needs of most analytical problems (114,115). 

The measurement of VLE can be carried out in several ways. A common procedure is to use a recycle stiU which is designed to ensure equiHbrium between the phases. Samples are then taken and analy2ed by suitable methods. It is possible in some cases to extract equiHbrium data from chromatographic procedures. Discussions of experimental methods are available (5,11). Eor the more challenging measurements, eg, conditions where one or more components in the mixture can decompose or polymeri2e, commercial laboratories can be used. 

Mounting electrodes in a bioreactor is costly, and there is an additional contamination risk for sensitive cell cultures. Some other sensors of prac ticai importance are those for dissolved oxygen and for dissolved carbon dioxide. The analysis of gas exiting from a bioreactor with an infrared unit that detects carbon dioxide or a paramagnetic unit that detects oxygen (after carbon dioxide removal) has been replaced by mass spec trophotometry. Gas chromatographic procedures coupled with a mass spectrophotometer will detect 1 the volatile components. 

Results found by the NIR method compared well with those obtained by the reference chromatographic procedures. The developed PLS/NIR method does not consume any solvent as no sample preparation is necessary, improving the laboratory efficiency without sacrifice the accuracy. 

Repeated chromatography on neutral alumina yields minor quantities of solid samples of C76, Cg4, C90 and C94 believed to be higher fullerenes. A stable oxide C70O has been identified. Chromatographic procedures for the separation of these compounds are reported. [Science 2S2 548 7997.]... 

The volume of ether solution must be reduced to approach the solubility limit of the triphenylene in ether before the chromatographic procedure. 

Although the traditional method of separating the diastereomeric compounds generated in a resolution procedure is fractional crystallization, chromatographic procedures are now common and convenient. Diastereomeric compounds exhibit different adsorption... 

Indeed, great emphasis was placed on the presentation of compounds in crystalline form for many years, early chromatographic procedures for the separation of natural substances were criticized because the products were not crystalline. None the less, the invention by Tswett (3) of chromatographic separation by continuous adsorption/desorption on open columns as applied to plant extracts was taken up by a number of natural product researchers in the 1930s, notably by Karrer (4) and by Swab and lockers (5). An early example (6) of hyphenation was the use of fluorescence spectroscopy to identify benzo[a]pyrene separated from shale oil by adsorption chromatography on alumina. 

The very extensive changes that have taken place over recent years and the broad application to organic separations necessitated a major revision of Part C covering solvent extraction and chromatographic procedures. These particular... 

The percentages of amino acids in silk fibroin which Poison et al. (224) found by direct visual and indirect photometric analysis of ninhydrin paper-partition chromatograms are shown in Table VII. The percentages obtained for alanine, glycine, and serine appear to be reasonably accurate, inasmuch as they agree closely with those found by other methods. It would be of interest to determine alanine by the microbiological method reported recently by Sauberlich and Baumann (238), in view of the widely different values found for this amino acid by the described ninhydrin-chromatographic procedure and the selec-... 

The development and adaptation of procedures for the separation, isolation, purification, identification, and analysis of the components of the pyrethrum mixture have been studied and evaluated. Results of studies to determine the molar extinction coefficient of pyrethrin I as well as a gas chromatographic procedure for the determination of pyrethrins are reported. The use of chromatographic separation procedures (including partition, adsorption, gas, and thin-layer chromatography), colorimetry, and infrared spectrophotometry are discussed. 

One purpose of this work was to develop a gas chromatographic procedure based on separation and quantitation of each of the com-... 

Table II presents some data using the gas chromatographic procedure and comparing the results to the standard AOAC procedure. The samples of pyrethrum concentrate and AOAC analyses were supplied by several of the principal pyrethrum producers from the United States and abroad.

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

Affinity chromatographic procedures have been widely accepted for purification of biological macromolecules48). This technique is also one of the most convenient... 

HPLC has proved to be fast and sensitive for the analyses of phenolic plant constit-nents, and is especially useful for the analysis of anthocyanins. The first application of HPLC to anthocyanin analyses was in 1975 by Manley and Shubiak and it has now become the method of choice for the separation of mixtures of anthocyanins and anthocyanidins. HPLC is now used for anthocyanin qualitative, quantitative, and preparative work, offering improved resolution compared to chromatographic procedures previously employed. It also allows for simultaneous rapid monitoring of the eluting anthocyanins. ... 

Because of their polymeric forms, alkylenebis(dithiocarbamates) are insoluble in water and most organic solvents. Additionally, they form strong complexes with different metal ions No extraction and chromatographic procedure has been reported for the parent compound of this chemical class. These compounds decompose readily under acidic conditions, for example by contact with the fruit or plant juice generated during sample preparation. 

The analytical chemist working on chromatographic procedures should consider... 

Isolation of Sesquiterpene Lactones. The ether extract was evaporated and dissolved in 952 ethanol. Then an equal volume of 42 aqueous lead acetate was added. After 1 hour the mixture was filtered to remove precipitated chlorophyll and phenolic products and the ethanol removed under vacuum. The aqueous layer was extracted with chloroform giving a dark colored oil from which the sesquiterpenes were isolated by a combination of chromatographic procedures, i.e., LH-20 gel permeation, silica gel using both packed columns and thin layer plates. A variety of solvents were also used to purify the individual sesquiterpene lactones, e.g., benzene-acetone (1 1), ethyl acetate, chloroform-methanol (9 1). On thin layer chromatographic plates, spots were visualized by spraying with 22 aqueous KMn04 solution. 

Extracts which demonstrate sufficient activity in the bloassay are next fractionated by a simple partitioning procedure (Figure 1) which separates the components into gross chemical classes. The various fractions are re-assayed and those showing activity are then further fractionated and purified by appropriate chromatographic procedures. 

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