Neutral elution

FIGURE 9.52 Mass concentrations of acidic and neutral elutable organics in fine particles ( 2.1 (im) at Hopi Point (Grand Canyon region), at San Nicholas Island in the Pacific Ocean upwind of Los Angeles, in West Los Angeles, and downwind at Rubidoux. The bare represent all of the organics that elute between the n-alkanes C and C , where n is shown under each bar. Note the different scales for concentrations (adapted from Mazurek et al., 1997). 

Comparisons between this technique and neutral elution (see below) for detecting DSBs in irradiated DNA show good agreement, which is satisfying. Probably the TAFE system will become the method of choice. 

Neutral elution techniques To detect DSBs it is possible to make use... 

Wash nonspecifically bound BH-RNase and its fragments by passing through five column volumes of washing buffer at 1 mL/min, and elute bound Ad-C with 0.1 M citric acid. Neutralize eluted protein immediately by mixing with 1 /10th volume of 1 M NaPi pH 7.2. 

A solution of l,3-dimethyl-5-methoxyindole (4.5 g, 0.026 mol) in DMSO (27 ml) was maintained at as cone. HCl (23 ml, 0.77 mol) was added dropwise over 15 min. Stirring was continued for 3 h at room temperature and the reaction mixture was then poured into ice-watcr (100 ml). The mixture was neutralized vvith NaHCOj to pH 7 and extracted with EtOAc (100 ml x 2). The EtOAc was removed in vacuo and the residue purified by chromatography on silica using hexane-EtOAc (7 3) for elution. The yield was 4.35 g (88%). 

Capillary zone electrophoresis also can be accomplished without an electroosmotic flow by coating the capillary s walls with a nonionic reagent. In the absence of electroosmotic flow only cations migrate from the anode to the cathode. Anions elute into the source reservoir while neutral species remain stationary. 

The elution order for neutral species in MEKC depends on the extent to which they partition into the micelles. Hydrophilic neutrals are insoluble in the micelle s hydrophobic inner environment and elute as a single band as they would in CZE. Neutral solutes that are extremely hydrophobic are completely soluble in the micelle, eluting with the micelles as a single band. Those neutral species that exist in a partition equilibrium between the buffer solution and the micelles elute between the completely hydrophilic and completely hydrophobic neutrals. Those neutral species favoring the buffer solution elute before those favoring the micelles. Micellar electrokinetic chromatography has been used to separate a wide variety of samples, including mixtures of pharmaceutical compounds, vitamins, and explosives. 

Methanol, which elutes at 4.69 min, is included as a neutral species to indicate the electroosmotic flow. When using standard solutions of each vitamin, CZE peaks are found at 3.41 min, 4.69 min, 6.31 min, and 8.31 min. Examine the structures and p/Ca information in Figure 12.47, and determine the order in which the four B vitamins elute. 

Vitamin Bi is a cation and must, therefore, elute before the neutral species methanol thus it elutes first at 3.41 min. Vitamin B3 is a neutral species and should elute with methanol at 4.69 min. The remaining two B vitamins are weak acids that partially ionize in the pH 9 buffer. Of the two, vitamin Be is the stronger acid and is ionized (as the anion) to a greater extent. Vitamin Be, therefore, is the last of the vitamins to elute. 

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S0 3, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach Hquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH NO, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and cosdy ore particle/leach hquor separation step. 

The residue is leached to give cesium sulfate solution, which can be converted to cesium chloride by ion exchange on Dowex 50 resin and elution with 10% HCl, treatment using ammonia or lime, to precipitate the alurninum, or by solvent extraction, followed by purification at neutral pH using hydrogen peroxide or ammonia. 

Endo 3a,4,S,6,7,7a-Hexahydro-4,7-methano-2-lndene-l-one (2). A solution ol octacaibonyidcobalt (1.0 g, 3 mmol) and bicycio [2 2.1) hepi-2-ene 1 (3.0 g, 32 mmol) in Isooctane (100 mL) was stirred first with acetylene and then under a mixture of 1.1 of acetylene and carbon monoxyde at 60-70°C until gas absorption ceased (total 1550 mL). The mixture was concentrated and the residue chromatographed on neutral alumina. Petroleum ether PhH (1 1) eluted acetylene hexacaibonyl dicobalt 70 mg, PhH CHCla (1.1) eluted a yellow oil which after distillation afforded 3 54 g of 2 (74%), bp 101-102°C (15 mm) Colorless crystals from pentane, mp32°C. 

Benzeneazodiphenylamine (4-phenylazodiphenylamine) [28110-26-1] M 273.3, m 82, pK 1.52. Purified by chromatography on neutral alumina using anhydrous C6H6 with 1% anhydrous MeOH. The major component, which gave a stationary band, was cut out and eluted with EtOH or MeOH. [Hogfeldt and Bigeleisen J Am Chem Soc 82 15 I960.] Crystd from pet ether or EtOH. See Sudan I. 

M 644.9, m 156-158". Purified by chromatography on a Kieselgel column and eluted with CH2Cl2-EtOAc (5 1), and recryst from EtOH-Me2CO as colourless crystals. It is an electrically neutral ionophore with high selectivity for Ba " ions and with high lipophilicity. [Chem Ber 118 1071 1985.]... 

Calcium ionophore I (ETH 1001) [58801-34-6] M 685.0. This is a neutral Ca selectophore. It can be purified by thick layer (2mm) chromatography (Kieselgel F245) and eluted with Me2CO-CHCl3 (2 1). [Helv Chim Acta 56 1780 1 973.]... 

Carbonate ionophore I [ETH 6010] (heptyl 4-trifluoroacetylbenzoate) [129476-47-7] M 316.3, b 170°/0.02 Torr, d 0.909. Purified by flash chromatography (2g of reagent with 30g of Silica Gel 60) and eluted with EtOAc/hexane (1 19). The fractions that absorbed at 260nm were pooled, evapd and dried at room temp (10.3 Torr). The oily residue was distd in a bubbled-tube apparatus (170°/0.02 Torr). Its IR (CHCI3) had peaks at 1720, 1280, 940cm and its sol in tetrahydrofuran is 50mg/0.5mL. It is a lipophilic neutral ionophore selective for carbonate as well as being an optical humidity sensor. [Anal Chim Acta 233 41 1990.]... 

A solution of 5 g (14 mmoles) of 5a-cholest-2-ene in 100 ml ethyl acetate and 8 ml of 2.8 M (22 mmoles) cyanogen azide (CAUTION See Chapter 15 and ref. 139b) in ethyl acetate is heated at 50-53° for 24 hr, during which time about 22 mmoles of nitrogen is evolved. Solvent is removed by evaporation and the residue is applied in benzene to a column of 160 g of neutral alumina (activity grade III). Elution with petroleum ether-benzene (1 1) gives 1.6 g of... 

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