Subject eluent

To this solution was added at one time the above-obtained ethyl acetate solution at -15°C, and the resulting mixture was stirred for 1 hour at -10°C to -15°C. The reaction mixture was cooied to -30°C, and water (80 ml) was added thereto. The aqueous layer was separated, adjusted to pH 4.5 with sodium bicarbonate and subjected to column chromatography on Diaion HP-20 resin (Mitsubishi Chemical Industries Ltd.) using 25% aqueous solution of isopropyl alcohol as an eluent. The eluate was lyophilized to give 7-[2-methoxyimino-2-(2-amino-1,3-thiazol-4-yl)acetamido] cephalosporanic acid (syn isomer) (1.8 g), MP 227°C (decomp.). 

Under argon, a mixture of 145 (0.046 mmol), 132 (0.046 mmol), Pd(PPli3)4 (0.2 (junol), Cul (0.2 [miol), and diisopropylamine (0.015 mmol) in THF (4 mL) was stirred in the dark at 50°C for 2 days. Ethynylbenzene (0.92 mmol) was then added and stirred at 50°C overnight. After concentration, die residue was dissolved in CHCI3 and filtered. The filtrate was subjected to preparative SEC with CHCI3 as eluent in order to remove catalyst residues and unreacted starting materials. Polymer 42 was obtained as a yellow solid in 85% yield. SEC analysis (THF, polystyrene standards) Mw = 280,000 (PDI = 6.5). 

The amount of residual sulfonate ester remaining after hydrolysis can be determined by a procedure proposed by Martinsson and Nilsson [129], similar to that used to determine total residual saponifiables in neutral oils. Neutrals, including alkanes, alkenes, secondary alcohols, and sultones, as well as the sulfonate esters in the AOS, are isolated by extraction from an aqueous alcoholic solution with petroleum ether. The sulfonate esters are separated from the sultones by chromatography on a silica gel column. Each eluent fraction is subjected to saponification and measured as active matter by MBAS determination measuring the extinction of the trichloromethane solution at 642 nra. (a) Sultones. Connor et al. [130] first reported, in 1975, a very small amount of skin sensitizer, l-unsaturated-l,3-sultone, and 2-chloroalkane-l,3-sultone in the anionic surfactant produced by the sulfation of ethoxylated fatty alcohol. These compounds can also be found in some AOS products consequently, methods of detection are essential. 

Methyl acrylate (94.7 mg, 1.1 mmol) is added dropwise at room temperature to a suspension of morphinolone 132 (253 mg, 1 mmol), CsF (132 mg, 1 mmol), and Si(OMe)4 58 (150 pL) under argon. After stirring for 1 h the reaction mixture is subjected to flash chromatography on silica gel (eluent petroleum ether-ethyl acetate, 8 2) to afford a 1 1 mixture of isomers 133 (82% yield) as a colorless oil [68] (Scheme 3.18). 

It is sometimes possible to improve detection by changing the pH of the eluent, or by the use of photochemical reactions. The common barbiturates used in therapy are weak acids that are easily separated in their acid (unionised) forms. Because the conjugate bases are much stronger chromophores than the acids, barbiturates have been detected by post-column mixing with a pH 10 borate buffer followed by uv absorption at 254 nm. An example of the second approach is the detection of cannabis derivatives in body fluids involving the conversion of cannabis alcohols to fluorescent derivatives on subjecting the column effluent to intense uv radiation. 

Donnan exclusion causes strong acids to elute in the void volumes of the column. Weak acids which are partially ionized in the eluent are not subject... 

Figure 4.11 Direct injection analysis of haemoglobin in red blood cells. Column, Asahipak ES-502C eluent, 32 min linear gradient from 25% 30 mM sodium phosphate buffer to 65% 30 mM sodium phosphate containing 300 mM sodium chloride pH 5.5 flow rate, 1.0 ml min-1 detection, 425 nm. Samples. A, normal subject and B, diabetic patient.

One fact to keep in mind with such phases is that weak acid cation-exchange materials based on carboxylic acid functional groups are subject to esterification in the presence of alcohol containing eluents. Even thongh typical eluent conditions (i.e., weakly acidic aqneous eluents containing alcohol) do not favor ester formation, such stationary phases typically exhibit slowly declining capacity when operated in the presence of alcohol-containing eluents. Consequently, such columns are normally operated with acetonitrile, tetrahydrofuran or acetone rather than with methanol, in order to avoid this problem. 

Unless subjected to a drastic drying procedure and stored under special conditions, each eluent contains water at a concentration level that can significantly affect retention behavior. Even commercial pure solvents" have significant but variable amounts of moisture. To maintain an eluent with a definite water concentration is almost impossible because the dry or wet container surface alone may alter the concentration appreciably. Furthermore, changes in the water content on opening the flask or pouring the eluent into another container are virtually inevitable. 

System (8) has been described for quantitation of corticosteroids as common adulterants in local drugs [156]. The sample is extracted from its matrix by methanol, and the resulting supernatant layer subjected to the HPLC analysis. The column used was an ODS-Zorbax column (25 cm x 4.6 mm), and the mobile phase 7 2 11 acetonitrile-methanol-aqueous 1% phosphoric acid. An eluent flow rate of 0.8 mL/min was used, and the analyte detection was performed using the UV absorbance at 240 nm. The calibration graph was found to be linear in the ranges of 1-15 pg/mL for betamethasone, 0.5-20 pg/mL for prednisolone, and 1-30 pg/mL for cortisone acetate. 

Plumericin, isoplumericin, plumieride, 13-O-coumaroylplumieride and protoplumericine A were isolated from the ethyl acetate extract of P. rubra heartwood [85]. The extract (44 g) obtained by percolation was submitted to column chromatography on silica gel with light petroleum ether/ethyl acetate (1 1) and methanol as eluent to furnish four fractions (A-D). Fraction C directly afforded plumericin (1.22 g) after recrystalUzation from toluene/ethyl acetate. Fraction B was rechromatographed on a silica gel with toluene/ethyl acetate (9 1), and isoplumericin (140 mg) was isolated from fraction 2. Fraction D was also rechromatographed on a silica gel column, but with chloroform/methanol/water (90 10 0.5 to 70 30 10) as solvent system. Fraction 3 was 13-O-coumaroylplumieride (2.0 g) and fraction 7 was protoplumericine (1.6 g). Fraction 5 was subjected to Sephadex LFI20 column eluted with methanol, followed by silica gel column eluted with chloroform/ methanol/water (85 15 0.7) to furnish plumieride (120 mg). 

Two ion chromatographic techniques were utilized to quantify formic acid in both diesel engine exhaust and mine air subjected to diesel emissions. A commonly used anion separation system utilizing a weak borate eluent adequately separated the acids of interest in diesel exhaust. It was, however, affected by the presence of strong acids during subsequent consecutive analyses. 

In order to preclude this problem and the necessary frequent regeneration of the anion system s suppressor column, an ion chromatography exclusion scheme was utilized. Samples collected in a mine environment were reliably concentrated by freeze-drying and then analyzed on an ICE system with dilute hydrochloric acid eluent. The precision of the ICE method was experimentally determined to be 2.5% in a concentration range of 1 to 10 yg/mL. The accuracy was not independently determined but good precision and recovery yield confidence that measured values are within 5% of the true value. No interferences were observed in the ICE system due to strong acids, carbonic acid or other water soluble species present in mine air subject to diesel emissions. 

Some time s(especi ally when only a few compds are in a mixt), it is more convenient not to extrude the column, but instead to subject it to a more prolonged washing directly in the tube. This treatment, called elution, will usually separate the components more efficiently into wider bands and these may then be removed(together with solvents) and collected separately in clean receivers as the percolation thru the column continues. Solvents used in washing the column are called eluents or elution agents and they may be ales, eth, acet, dichloroethane, dichloro-methane, chlf, et acetate or petr ether(Refs 58 78)... 

Separation is dependent on three different mechanims Donnan exclusion, steric exclusion, and adsorption/partitioning. Donnan exclusion causes strong acids to elute in the void volume of the column. Weak acids that are partially ionized in the eluent are not subject to the Donnan exclusion and can penetrate into the pores of the packing. Separation is achieved through differences in acid strength, size, and hydrophobicity. The major advantage of ion exclusion is the ability to handle samples that contain both strong and weak acids. 

---