Column elution method

C, generator column/elution method, average values of 6-7 laboratories, OECD 1981) 0.200 (20°C, quoted, Schmidt-Bleek et al. 1982)... 

Table 2. Comparison of the extraction behavior of tracer einsteinium, fermium, and mendelevium after treatment with various reducing agents. The column-elution method of extraction chromatography was used with the extractant HDEHP adsorbed on a column bed of a fluoroplastic powder (20)...

Ogawa T (1990) Fractionation and characterization of polyacetal copolymers by column elution method. J Appl Polym Sci 40 1519 1527... 

A high performance Hquid chromotography (hplc) method to determine citric acid and other organic acids has been developed (46). The method is an isocratic system using sulfuric acid to elute organic acids onto a specific hplc column. The method is sensitive for citric acid down to ppm levels and is capable of quantifying citric acid in clear aqueous systems. 

Elution with salt pulses A multiple step elution is performed by the introduction of, for example, 5%, 10%, 25%, 50%, and 100% of 1.5 M sodium chloride in 19 mM phosphate buffer (pH 2.5) containing 5% methanol. Each step is for 10 min and run at 0.5 mL/min. This elution method compromises analytical system dimensionality, as the peak capacity of the ion-exchange chromatography (IEX) step is equal at most to the number of salt steps. However, in the second dimension only one or two columns are needed and there is no particular limitation in the second dimension separation time as peptides are eluted in portions in a controlled manner. However, the number of salt steps is limited by the total analysis time. In this case the multidimensional system is relatively simple. 

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

In some cases, so called direct plasma injection techniques may be used23 83 104 108 instead of protein precipitation for loading plasma samples onto an HPLC/MS/MS system. Some direct plasma injection systems use a column switching technique in which the plasma is loaded onto an extraction column that retains the small molecules. The other plasma components are sent to waste and the flow is switched so that the small molecules are eluted onto an analytical column that connects to the MS/MS.23 83 108 One variation of the column switching method is turbulent flow chromatography commercialized by Cohesive Technologies (now part of Thermo, San Jose, CA).23... 

A method has been described [55] for separating polychlorinated biphenyls from chlorinated insecticides. This procedure involves adsorption chromatography on alumina and charcoal columns, elution with increasing fractional amounts of hexane on alumina columns, and with acetone-diethyl ether on charcoal columns. The polychlorinated biphenyls and chlorinated pesticides are then determined by gas chromatography-mass spectrometry on the separate eluates without interference. 

Glutamic acid and its salts (especially the sodium salt) enhance the flavour of many convenience foods. Bejaars et al. (1996) described the determination of free glutamic acid in soups, meat products and Chinese food. The method involves hot water extraction of test portions followed by filtration and dilution. The extracts were treated with N,N-dimethyl-2-mercapto-ethyl-ammonium chloride and o-phtaldialdehyde to convert glutamic acid into a stable fluorescent, l-alkylthio-2-alkyhsoindole. Homocysteic acid was used as the internal standard. Separation was made on a Ci8 column, eluted with... 

Another isocratic elution method was applied for the determination of flavonols in green and black tea leaves and green tea infusions by RP-HPLC. The chemical structures of the flavonols studied are shown in Fig. 2.66. Infusions of teas were prepared by mixing lg of tea leaves with 100 ml of boiling water for 5min, then they have filtered and used for HPLC analysis. The infusion step was repeated three times. Flavonoids were hydrolysed by mixing lg of tea leaves with 40 ml of 60 per cent aqueous ethanol and 5 ml of 6 M HC1. The suspension was heated at 95°C for 2 h, then filtered and the volume was adjusted to 50 ml with 60 per cent aqueous ethanol. Separation was performed in an ODS column (150 X 4.6mm i.d.) operated at 30°C. The isocratic mobile phase consisted of 30 per cent aqueous ACN in 0.025 M KH2P04, and the pH was adjusted to 2.5 with 6 M HC1. The... 

The recycle elution method can be applied to mixtures of very similar compounds that cannot be fully separated by a single pass through the column. This method makes more effective use of a column. The effluent from the column is repeatedly re-passed through the same column. The number of cycles multiplies the total theoretical plate number of the column if the system is... 

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