Chromatography eluants

Recent work describing the use of subcritical water as a chromatographic mobile phase has been reported. Water heated to 100-200°C, pressurized to 20-50 bar, can be used as a reversed-phase chromatography eluant. This application exists somewhere in the boundary region between pSFC and HPLC. Stationary phases that have been used successfully for subcritical... 

The solvents used for liquid chromatography are the commoner ones such as water, acetonitrile, and methanol. For the reasons just stated, it is not possible to put them straight into the ion source without problems arising. On the other hand, the very viscous solvents that qualify as matrix material are of no use in liquid chromatography. Before the low-boiling-point eluant from the LC column is introduced into the ion source, it must be admixed with a high-boiling-point matrix... 

In dynamic FAB, this solution is not stationary but flows steadily over the target area. Usually, the liquid flow is the eluant from a liquid chromatography column, but it need not be. 

At such a rate of scanning, it is even possible to examine eluants from capillary GC (gas chromatography) columns during GC/MS operations. 

Three general methods exist for the resolution of enantiomers by Hquid chromatography (qv) (47,48). Conversion of the enantiomers to diastereomers and subsequent column chromatography on an achiral stationary phase with an achiral eluant represents a classical method of resolution (49). Diastereomeric derivatization is problematic in that conversion back to the desired enantiomers can result in partial racemization. For example, (lR,23, 5R)-menthol (R)-mandelate (31) is readily separated from its diastereomer but ester hydrolysis under numerous reaction conditions produces (R)-(-)-mandehc acid (32) which is contaminated with (3)-(+)-mandehc acid (33). 

Isolation procedures for many biochemicals are based on chromatography. Practically any substance can be selected from a crude mixture and eluted at relatively high purity from a chromatographic column with the right combination of adsorbent, conditions, and eluant. For bench scale or for a small pilot plant, such chromatography has rendered alternate procedures such as electrophoresis nearly obsolete. Unfortunately, as size increases, dispersion in the column ruins resolution. To produce small amounts or up to tens of kilograms per year, chromatography is an excellent choice. When the scale-up problem is solved, these procedures should displace some of the conventional steps in the chemical process industries. 

Conventional elution chromatography has the serious disadvantage of dilution, and usually a concentration step must follow. The technique of displacement chromatography circumvents dilution and may even result in an eluant more concentrated than the feed. A displacer compound breaks the desired product from the chromatographic material sharply, and a column heavily loaded with several biochemicals will release them one at a time depending on their adsorption equilibria. However, the displacers tena to be expensive and can be troublesome to remove from the product. 

The product may also be purified by flash chromatography using 19/1 (v/v) petroleum ether, (bp 3Q-60 C)/ethyl acetate as eluant. A column of 2-cm diameter was packed to a height of 25 cm with Kieselgel 60 (230-400 mesh) supplied by BOH Chemicals Ltd. In one run chromatography of 4.19 g of crude product afforded 3.70 g (88%) of the a.g-unsaturated ester which was... 

A-(9-Acridinyl)maleiinide (NAM) [49759-20-8] M 274.3, m 248 , 255-258 . Purified by chromatography on silica gel using CH2CI2 as eluant. Evaporation of pooled fractions that gave the correct NMR spectra gave a solid which was recrystd from Me2CO as pale yellow prisms. IR v (nujol) 1710 (imide) UV (MeOH) (nm), (e M- cm ) 251 (159 500), 343 shoulder (7 700), 360 (12 400) and 382shoulder (47... 

When the reaction of S2CI2 with ammonia is carried out in a polar solvent, e.g., DMF, the hydrolysis of the reaction mixture with aqueous HCl produces a mixture of the cyclic sulfur imides S7NH, 1,3-, 1,4- and 1,5-S6(NH)2 and 1,3,5- and 1,3,6-S5(NH)3, which can be separated by chromatography on silica gel using CS2 as eluant (Section 6.2.1). °... 

A feature of ion exchange chromatography is, of course, that ionic solutions are used as eluants, so that the eluted species are present in an electrolyte background. The problem which now arises in the application of electrical... 

It is appropriate to refer here to the development of non-suppressed ion chromatography. A simple chromatographic system for anions which uses a conductivity detector but requires no suppressor column has been described by Fritz and co-workers.28 The anions are separated on a column of macroporous anion exchange resin which has a very low capacity, so that only a very dilute solution (ca 10 4M) of an aromatic organic acid salt (e.g. sodium phthalate) is required as the eluant. The low conductance of the eluant eliminates the need for a suppressor column and the separated anions can be detected by electrical conductance. In general, however, non-suppressed ion chromatography is an order of magnitude less sensitive than the suppressed mode. 

A solution of 3.7I g (0.013 mol) of tributyltin hydride in 10 mL benzene is added dropwise to a solution of 3.09 g (0.011 mol) of S-[(S)-4-(benzyloxy)-3-pentenyl] 5-methyl carbonodithioate in 25 mL of degassed, anhyd benzene under an atmosphere of argon, followed by 5 mg of AIBN. The mixture is heated under reflux for 2.5 h and then is concentrated under reduced pressure. Flash chromatography of the residue using ht,0/petroIeum ether 1 50 containing 1 % triethylamine as eluant gives a colorless oil yield 3.87 g (78%) [a] - 26 (e = 1. CHCl3). 

A solution containing 447 mg (1.38 mmol) of 3-(4-mcthylphenylsulfonyl)-1-nonene, 928 mg (3.19 mmol) of tributyltin hydride, and 10 mg of AIBN. in dry benzene is heated under reflux under an atmosphere of nitrogen for 2 h. Concentration under reduced pressure and chromatography on neutral alumina using benzene as eluant gives the product yield 443 mg (65%) further purification by distillation, bp 136-142X/0.003 Torr. 

A mixture of 40 mmol or the a-nitro alcohol 1, 48 mmol of (terf-butyldimethyl)chlorosilane or chlorotri-mcthylsilanc, 6.8 g (100 mmol) of I /(-imidazole and 10 mL of DMF is stirred at 20 C for 12 h. Water is added and the mixtnre is extracted with hexane. The combined extract is washed wilh water and sat. aq NaCl and dried over MgS04. Exaporation gives the O-silyl nitro alcohol as an oil which is distilled (bulb-to-bulb) yield 45 - 97%. If unreacled starting material is present in the distillate, it can be removed by chromatography over silica gel (30 g/ l g of product) with l,t,0/pcntanc 1 9 as eluant. 

A solution of 1-trimethylsilyloxycyclohex-l-ene (5.12 mmol) and benzaldehyde dimethyl acetal (5.47 mmol) in dichloromethane (15 ml) was cooled to —78°C, and to this was added TMSOTf (0.05 mmol) in dichloromethane (0.5 ml). The mixture was stirred at -78°C for 8h, and then quenched by the addition of water at —78 °C. Dichloromethane (50 ml) was added, and the mixture was washed with saturated sodium hydrogen carbonate solution and brine, and dried. Concentration provided a crude oil consisting of a 93 7 mixture of erythro- and r/jreo-2-(methoxyphenyl-methyl)cyclohexanone. Chromatography on silica gel (20g, eluant petroleum ether ether 10 1) gave the pure erythro (82%) and threo (6.7%) isomers as oils. 

Hie hydrolytic depolymerization of nylon-6 was followed by gel permeation chromatography (GPC), viscometry, and gravimetry. GPC determinations were performed on a Waters 150C chromatography system using benzyl alcohol as die eluant, two Plgel 10-p.m crosslinked polystyrene columns, and a differential refractometer detector. The flow rate was 1 mL/min. The concentration of the polymer solutions was 0.5 wt% and dissolution was accomplished at 130°C. 

Figure 4-1. Components of a simple liquid chromatography apparatus. R Reservoir of mobile phase liquid, delivered either by gravity or using a pump. C Glass or plastic column containing stationary phase. F Fraction collector for collecting portions, called fractions, of the eluant liquid in separate test tubes.

In a preliminary report, Ross et al. [40] used affinity chromatography to identify a putative bovine renal brush border Na /H exchanger. Brush border membranes were solubilized with Triton X-100 and chromatographed sequentially over lentil lectin Sepharose 4B and 5-(A-benzyl-iV-ethyl)amiloride coupled to epoxy-activated Sepharose 6B. The eluant contained 178- and 146-kDa proteins that were susceptible to Endo-F. Moreover, the eluants reacted on dot blot immunoassays with antisera to a 20-amino acid peptide of a human Na /H exchanger vide infra). The relationship between these proteins and the 66-kDa protein previously identified by the same investigators using amiloride photolabeling is presently unclear. 

---