Analytical methods ethyl acetate production

For efficient extraction of macrolide and lincosamide residues from edible animal products, bound residues should be rendered soluble, most if not all of the proteins should be removed, and high recoveries for all analytes should be provided. Since tliese antibiotics do not strongly bind to proteins, many effective extraction methods have been reported. Sample extraction/deproteinization is usually accomplished by vortexing liquid samples or homogenizing semisolid samples with acetonitrile (136—139), acidified (136,140-142) orbasified acetonitrile (143), methanol (14, 144, 145), acidified (145-147) or basified methanol (148), chloroform (149-151), or dichloromethane under alkaline conditions (152). However, for extraction of sedecamycin, a neutral macrolide antibiotic, from swine tissues, use of ethyl acetate at acidic conditions has been suggested (153), while for lincomycin analysis in fish tissues, acidic buffer extraction followed by sodium tungstate deproteinization has been proposed (154). 

Concentration Determination of In-Process Samples. The concentration of the unisolated desired product in solution at a particular intermediate step may also need to be determined by HPLC. A data calculation sheet such as Excel with the response factors of the standards and the dilution factor of the sample could be incorporated in the data calculation sheet prior to injection of reaction sample to facilitate the results reporting for the concentration of the intermediate in solution. Hence, only the area of the desired intermediate in solution needs to be populated in the spreadsheet, and the concentration result then can be determined. The determined concentration of the intermediate in solution ensures adequate charging of the raw materials used in the further steps of the synthesis. Also, this intermediate in solution is sometimes further concentrated and the concentration is monitored until the desired concentration is obtained. A solvent switch step is sometimes performed, and the HPLC method must be able to selectively separate the reaction solvents (if they are UV active) from the desired intermediate and potential impurities that may be formed. These reaction solvents may include toluene, inhibited THF with cresol or BHT (if inhibited with BFIT, this is very hydrophobic, so proper elution of this additive may be necessary), ethyl acetate, and so on. Sample preparation here is also important, and the appropriate diluent must be determined to ensure solubility of all components and no reactivity with the sample analyte. 

General procedure for preparation of 2-amino-4-(phenylthio)-4//-chromene-3-carbonitrile 6 In an oven-dried screw cap test tube, a mixture of sahcyhc aldehyde 1 (1 mmol), malononitrile 2 (1 mmol), thiophenol 5 (1 mmol) and sodium formate (10 mol%) was stirred with 4 mL of ethanol at room temperature for 2-3 h. On completion of the reaction as monitored by TLC, the product was precipitated out and filtered the filtrate was preserved for reuse. The crude residue was subjected to column chromatography using silica gel (60-120 mesh) and petrol ether-ethyl acetate mixture to obtain pure product 6, characterized by analytical and conventional spectroscopic methods. 

Bitencourt-Mendes et al. [90] described a method for saccharin determination in liquid sweetener products. The method is based on the precipitation reaction of Ag(I) ions with saccharin in aqueous medium (pH 3.0), using a FIA system with merging zones, the suspension was stabilized with 5 g/L Triton X-100. Based on interference studies performed with the substances commonly found in liquid sweeteners, such as sodium cyclamate, methylparaben, sodium aspartame, and benzoic and citric acids, at the analyte-to-interferent mole ratio of up to 1 10 no interference with the saccharin determination was observed. The presence of chloride ions interferes with the method, but a preceding liquid-liquid saccharin extraction with ethyl acetate was successfully employed to overcome this drawback. 

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