Ethylacetate elution solvent

The elution solvents used were benzene-ethylacetate-acetone (100 5 2) for antioxidants and chloroform-hexane (2 1) for UV absorbers and butanol-glacial acetic acid (97 3) for organotin compounds. An ethanolic solution of 2,6-dichloro-p-benzoquinone-4-chlorimine was used as spray reagent for antioxidants and UV stabilisers. 

Bromocriptine 2 (0.65 g, 1 mmol) was dissolved in 100 ml of dry ethanol and 60 ml of tetrafluoroboric acid / diethylether complex (85 %) was added while stirring. After standing overnight at RT the solvent was evaporated and the raw product isolated by extraction in the system dichloromethane 12% ammonia in water and evaporated to the dry residue. This residue was applied to the chromatographic column (I.D. = 2 cm, lenght = 20 cm) packed with silicagel and eluted with dichloromethane / ethylacetate =1 1. The fractions containing 2 were evaporated to the dry residue and crystallized from alcohol. 

The column extraction is based on the following principle the water sample is distributed as a film at the contact with the adsorbent. Afterwards, the elution with immiscible water solvents is performed (e.g. diethylether, ethylacetate or chlorinated solvents). All the lyphophyle pollutants are extracted from the aqueous into the organic phase. During the process the aqueous phase remains on the stationary phase and emulsion formation is no longer possible. The extract can be vaporized and the pollutants will be analyzed. 

Elution of the sorbent is carried out using organic solvents such as ethylacetate, methanol, acetonitrile, or mixtures of solvents. Frequently, the eluent is concentrated to achieve higher sensitivity and the final extract is analysed without any additional treatment. Nevertheless, when analysing heavily contaminated samples, some authors have included a extract cleanup step using activated alumina. ° The recoveries obtained were satisfactory in several applications, as can be seen in Table 28.6. 

In contrast to reversed-phase, the stationary phase in normal-phase chromatography is polar, usually silica or alumina, and uses nonpolar solvents, e.g., hexane and ethylacetate, that are not compatible with the API processes nsed in LC-MS. In normal-phase chromatography compounds elute progressively from the least to the most polar. The technique is not applicable to the highly polar compounds encountered... 

A widely employed chromatographic system is the one based on polyamide plates eluted with water-formic acid (200 3 v/v) in the first direction and benzene-acetic acid (9 1 v/v) in the second direction. A third run with 1 M ammonia-ethanol (1 1 v/v) or ethylacetate-acetic acid-methanol (20 1 1 v/v/v) in the direction of solvent 2 resolves especially basic Dns-amino acids or Glu/Asp and Thr/Ser pairs. 

Thin-layer chromatography (TLC) is mainly applied in micropreparative taxoid separation.Silica gel 6OF254 preparative plates are usually employed for this purpose. The problem of taxoid separation involves not only their similar chemical structure (e.g., paclitaxel vs. cephalomannine) but also the different coextracted compounds usually encountered in crude yew extracts (polar compounds such as phenolics and non-polar ones such as chlorophylls and biflavones) the separation is therefore very difficult. The common band of paclitaxel and cephalomannine was satisfactorily resolved from the extraneous fraction in isocratic elution with ethylacetate as polar modifier " and n-heptane-dichloromethane as solvent mixture, and was of suitable purity for high-performance liquid chromatography (HPLC) quantitative determination. The combination of micropreparative... 

Systematic studies on selection of the best mobile phases to ensure the best micropreparative separation of analyzed taxoids—especially of 10-DAB 111 as well as its less polar derivatives, baccatin III, paclitaxel, and cephalomannine, obtained from the extracts of fresh and dried needles and stems of T. baccata— have been undertaken by Mroczek and Glowniak.The TLC investigation on silica gel included solvent systems with one and two polar modifiers and multicomponent mobile phases, as well as some multiple development techniques and gradient elutions. As polar modifiers, methanol, acetone, dioxane, ethylacetate and ethylmethylketone as well as their mixtures were reinvestigated dichloromethane, chloroform, benzene, toluene, heptane, and their mixtures were used as solvents. 

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