Basic Eluents

Distyrylpyrazine [14990-02-4] M 284.3, m 219 . Recrystd from xylene chromatographed on basic silica gel (60-80 mesh) using CH2CI2 as eluent, then vac sublimed on to a cold surface at 10 torr [Ebied J Chem Soc, Faraday Trans / 78 3213 1982], Operations should be carried out in the dark. 

The well-dried chromatogram (1 h at 105°C if acidic or basic eluents have been employed) is immersed in the dipping solution for 1 s or homogeneously sprayed with the spray solution and then dried in a stream of cold air. Acids yield blue zones on a colorless or pale blue background [1] which gradually darkens. 

Resin-based TSK-GEL PW columns are durable to alkaline conditions, which cannot be used with silica-based columns. Such durability facilitates separations with basic eluents and allows the use of alkaline cleaning reagents. 

A solution of 3.5 g 4-(2,3-epoxypropoxy)carbazole in 50 ml absolute alcohol is mixed with 30 ml isopropylamine and heated for 3 hours under reflux. When the reaction is finished, the reaction mixture is evaporated to dryness. The residue obtained is taken up in methylene chloride and chromatographed over an aluminum oxide column (300 g basic aluminum oxide, activity stage IV eluent methylene chloride). The eluted fractions are evaporated and the residue is dissolved in methanol and acidified with 2N ethereal hydrochloric acid. 

Modifier additives also play a role in method optimization and are typically added to the modifier at concentrations less than 1 % (v/v). Additives can provide increased efficiency by minimizing undesirable interactions between the analyte and the CSP, and may be necessary to elute certain types of compounds. The type of additive (acidic or basic) that will produce the best results depends upon the functionality of the analyte [72]. Certain additives are strongly retained on the stationary phase, and their effect may persist even after they are removed from the eluent [22]. The impact of both modifiers and additives can also be affected by the proximity of the operating conditions to the critical point of the eluent [73]. 

Proton magnetic resonance (CDC13) 8, number of protons, multiplicity, coupling constant J in Hz. 1.5-2.2 (2, multiple ), 2.7-3.0 (4, multiplct), 7.0 (1, doublet, J = 2.5), 7.1-7.5 (6, multiplet), 7.7-8.2 (4, multiplet). A sample recrystallized from methanol-chloroform melted at 183-185°. The submitters also obtained pure product, m.p. 181-183°, after chromatography on basic alumina with 20% petroleum ether in dichloromethane as eluent. 

A polyethylene-coated (PEE) silica column was used with water-methanol eluents to achieve the separation and retention of 27 pesticides.40 The retention times of 33 commercial pesticides were determined on an octadecyl (ODS)-derivatized alumina column using water-methanol eluents and compared with retention properties on an ODS-silica column packing.41 More recently, RP-HPLC was used in combination with diode array detection for the identification and quantification of 77 pesticides (acidic, basic, and neutral) in groundwater samples.42... 

When mentioned, deactivated silica gel means that it was treated with 5% triethy-lamine in pentane and the column was eluted with the same solvent mixture until the outflowing eluent was basic according to pH paper. 

In column chromatography, the adsorbant is usually alumina but can be silica gel. Except that alumina tends to be basic and silica gel, acidic, I don t know why the former is used more often. Remember, if you try out an eluent (solvent) on silica gel plates, the results on an alumina column may be different. 

Fig. 19.17. Schematic showing the most basic elements that should be a part of an LC-NMR system. The dotted arrows represent electronic controls and the solid lines represent the flow path of chromatographic eluent.

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